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Many ecological phenomena are characterized by context dependency, and the relationship between diversity and productivity is no exception. We examined the relationship between macroalgal diversity,and nutrient availability by evaluating the effects of reduced nutrients and their subsequent replacement via local-scale nutrient loading in tide pools. Macroalgae in Oregon coast high-intertidal pools have evolved in a nitrate-rich upwelling ecosystem, but instead of settling on low-intertidal reefs (where algae are often immersed in nutrient-rich nearshore waters) these individuals have colonized high-zone pools, where they are isolated from the ocean for extended periods of time and are subjected to extended periods, of nitrate depletion. In some pools, this nutrient stress was ameliorated by a positive interaction: the excretion of ammonium by invertebrates. We conducted experimental manipulations to quantify invertebrate-mediated ammonium loading and macroalgal ammonium uptake in high-intertidal pools. Variation in tide pool volume and invertebrate biomass created a gradient of local-scale nutrient inputs, allowing us to address the relationship between nitrogen loading and algal diversity. Slow-growing species tolerant of low nitrogen availability were joined by fast-growing species with higher nitrogen requirements in pools with higher ammonium loading rates. A fourfold increase in the ammonium loading rate was associated with a doubling in the number of macroalgal species, and macroalgal assemblages in more species-rich pools were characterized by higher rates of biomass-specific ammonium uptake. These patterns contrast with productivity-diversity relationships in terrestrial systems, where local-scale nutrient enrichments generally result in reduced producer diversity due to displacement of subordinate species by aggressive competitors. Our data suggest that the effect of enrichment on diversity is context-dependent. Each ecosystem has a critical level of nutrient availability, determined by the level of nutrients typically available in that system. Below this critical level, local-scale nutrient additions increase diversity, but above it, diversity declines with enrichment.

Abstract Deserts are increasing in extent globally, but existing deserts are decreasing in health. The basic biology and ecology of foundation plant species in deserts are limited. This is a direct study that provides an estimate of the capacity for a locally dominant foundation shrub species in California to recover from damage. Desert shrubs are cleared and damaged by humans for many purposes including agriculture, oil and gas production, and sustainable energy developments; we need to know whether foundation species consistently facilitate the abundance and diversity of other plants in high‐stress ecosystems and whether they can recover. A total of 20 Ephedra californica shrubs were clipped to the ground at a single site and systematically resampled for regrowth 2 years later. These shrubs were damaged once and regrew rapidly, and relatively, larger shrubs were not more resilient. This study provides evidence for what we termed the “Groot Effect” because smaller individuals of this shrub species can recover from significant aboveground damage and continue to have positive effects on other plant species (similar to the popular culture reference to a benefactor tree species). The density of other plant species was consistently facilitated while effects on diversity varied with season. These findings confirm that E. californica is a foundation species that can be an important restoration tool within the deserts of California in spite of extreme cycles of drought and physical damage to its canopy.

Coastal wetlands are among the most productive ecosystems in the world. They generate critical services for humans including shoreline protection, carbon storage, pollution mitigation, and fisheries production. Restoration of coastal wetlands has historically been viewed as a secondary conservation strategy, but recently—given the continued loss of wetlands worldwide—many non-governmental and governmental organizations have elevated habitat restoration to be a primary method for wetland conservation. The long-held paradigm in coastal wetland restoration has been to restore target habitats by reducing physical stressors and avoiding competition among outplants, such as mangrove saplings or Spartina plugs. Recent ecological research, however, reveals that positive species interactions, such as facilitation, are critical to wetland recovery after disturbance. Here, we review the scientific evidence for the importance of positive species interactions in the recovery of salt-marsh and mangrove ecosystems and assess the extent to which they have been integrated into restoration studies. We found that only a small proportion of studies of marsh and mangrove restoration examined the effects of positive species interactions, despite the important role they play in the regrowth of coastal wetlands. We outline how positive species interactions can be systematically incorporated into future restoration work and discuss how this incorporation can help the reestablishment of coastal wetland biota through: (1) trophic facilitation, (2) stress reduction, and (3) associational defenses. The absence of positive interactions in restoration designs may partially explain the significant disparities between the functioning of natural and restored coastal plant ecosystems.

Summary: Few studies have explored how – within the same system – clonality and positive plant–plant interactions might interact to regulate plant community composition. Canopy‐dwelling epiphytes in species‐rich forests provide an ideal system for studying this because many epiphytic vascular plants undertake clonal growth and because vascular epiphytes colonize canopy habitats after the formation of nonvascular epiphyte (i.e. bryophyte and lichen) mats.We investigated how clonal integration of seven dominant vascular epiphytes influenced inter‐specific interactions between vascular epiphytes and nonvascular epiphytes in a subtropical montane moist forest in southwest China.Both clonal integration and environmental buffering from nonvascular epiphytes increased survival and growth of vascular epiphytes. The benefits of clonal integration for vascular epiphytes were higher when nonvascular epiphytes were removed. Similarly, facilitation from nonvascular epiphytes played a more important role when clonal integration of vascular epiphytes was eliminated. Overall, clonal integration had greater benefits than inter‐specific facilitation.This study provides novel evidence for interactive effects of clonality and facilitation between vascular and nonvascular species, and has implications for our understanding of a wide range of ecosystems where both high levels of clonality and facilitation are expected to occur. [ABSTRACT FROM AUTHOR]

Positive interactions between birds and mammals are a fascinating aspect of animal behaviour. Feeding associations may consist of local enhancement or facilitation, and in the latter case, of commensalism or mutualism depending on the benefits received by the facilitator. We report here on a previously undescribed feeding association between piscivorous birds and Eurasian otters Lutra lutra. In Spain, common kingfisher Alcedo atthis and grey heron Ardea cinerea were observed closely following foraging otters and benefited from feeding opportunities provided by these. Behavioural observations of otters in central Spain (28.4 hr; 19 days) revealed that an association with kingfishers occurred in 33% of otter foraging events (n = 92). Simultaneous observations in northern Spain (14.2 hr; 16 days) showed an association between otters and kingfishers or grey herons in 41.6% and 11.7% of otter foraging events (n = 77), respectively. The association probability between kingfishers and otters increased significantly when otters foraged closer to the shore and on small fish rather than other prey (crayfish or large fish). Birds fed on prey remain left by the feeding otters, on small fish captured by otters when these were satiated and playing, or on prey displaced by otters. Our observations are consistent with facilitation and commensalism: piscivorous birds gained feeding opportunities provided by the otters, with no apparent costs or benefits to the latter. Similar feeding associations have been described between other species of otters and piscivorous birds (kingfishers, herons, egrets, storks) in Asia, South America and Southern Africa, but had not yet been described in Europe. The occurrence of piscivorous bird–otter associations in different species and regions suggests that this commensalism may be often overlooked but widespread. We have shown that the association can be frequent and is context‐dependent, with benefits for associating birds depending on otters´ behaviour and targeted prey. [ABSTRACT FROM AUTHOR]

In an article published in 2000, Flora indicated that 5:1 is the "magic" ratio of positive-to-negative interactions. Flora's position is characteristic of the pervasive idea that there is a "magic" ratio of positive-to-negative interactions for improving interpersonal relationships. In the field of education, teachers are often recommended to maintain a specific ratio of positive-to-negative interactions with students (e.g., 5:1). Although this rule has good face validity, there is a lack of empirical support for any specific ratio. The authors support the idea of maintaining a high positive to negative ratio but argue against the use of any specific ratio. They include a discussion of the history of positive-to-negative interaction ratio recommendations, a summary of relevant research on students with emotional or behavioral disorder (EBD), an exploration of how teachers might adhere to these recommendations, and how each approach might affect students. The authors provide recommendations for teachers, researchers, and instructors in teacher preparation programs: considering how teachers might use the concepts behind the positive-to-negative interaction ratio to improve teaching, how instructors in teacher preparation programs might better teach preservice teachers, and advising how researchers might work to better understand the high positive to negative ratio. [ABSTRACT FROM AUTHOR]

• Solution properties of a transport system with complex interactions are investigated. • The transport system consists of two alternatives and two user groups. • Any possible model of the transport system is classified into nine cases. • Solution properties are analytically revealed in each case. • No / multiple stable equilibria exist in many cases. It is well known that uniqueness and stability are guaranteed properties of traffic equilibria in static user-equilibrium traffic assignment problems, if the link travel utilities are assumed to be strictly monotonically decreasing with respect to the link traffic volumes. However, these preferable properties may not necessarily hold in a wide range of transport problems with complex interactions, e.g. asymmetric interactions (including dynamic traffic assignment), social interactions, or with economies of scale. This study aims to investigate such solution properties of transport models with complex interactions between users. Generic formulations of models are considered in this study, both for utility functions and for the evolutionary dynamics relevant to the stability analysis. Such an analysis for a generic formulation is mathematically challenging due to the potential non-differentiability of the dynamical system, precluding the application of standard analyses for smooth systems. To address this issue, this study proposes a transport system with two alternatives and two user groups. While it is a simple model whose dynamics can be depicted on a plane, it also includes the core components of transport models, i.e. multiple choices and user-classes. This study classifies all possible formulations into nine cases with respect to the signs (i.e. positive or negative) of interactions between users. Then, the evolutionary dynamics of each case is mathematically analysed to examine stability of equilibria. Finally, the solution properties of each case is revealed. Multiple equilibria exist in many cases. In addition, cases with no stable equilibrium are also found, yet even in such cases we are able to characterise the circumstances in which the different kinds of unstable behaviour may arise. [ABSTRACT FROM AUTHOR]

• A high ratio of M. aquatica stimulated L. hexapetala' s flowering. • The total biomass and branching of L. hexapetala were lowest in the monoculture. • M. aquatica root/above-ground biomass was reduced by a high ratio of L. hexapetala. The invasion of aquatic ecosystems by non-native species often leads to competitive interactions with native species. However, non-native and native species can co-occur. This study presents a comparison between two wetlands species differing in origin: the invasive plant Ludwigia hexapetala (Lh) and the native plant Mentha aquatica (Ma). Both species were grown for three months in monocultures and in mixtures at different planting ratios (6Ma/0Lh, 5Ma/1Lh, 3Ma/3Lh, 1Ma/5Lh; 0Ma/6Lh). We assessed species performance in an experimental, outdoor garden. The shoot length, and flower production were measured weekly. At the end of the experiment, root and shoot biomasses were determined, the number of lateral branches was counted, and shoot lengths were measured. Based on biomass, two competition indices were calculated: the Relative Yield Total (RYT ab) index, and the Relative Competition Intensity (RCI) index. The RCI index suggested a facilitation effect for Mentha and for Ludwigia at the ratio of 1Ma/5Lh, whereas competition was established for both species at the ratio of 3Ma/3Lh. Both the total biomass of L. hexapetala and its production of lateral branches were significantly reduced when grown as a monoculture, suggesting intra-specific competition within L. hexapetala populations. The number of flowers produced by L. hexapetala was highest in the presence of a high ratio of M. aquatica individuals. However, when L. hexapetala outnumbered M. aquatica , its ratio of below/above-ground biomass decreased, indicating an inter-specific competition effect. The intra-specific competition for L. hexapetala was much stronger than interspecific competition. [ABSTRACT FROM AUTHOR]

Arid and semiarid ecosystems display several environmental filters naturally restricting plant community composition. Such filters become more severe after some disturbance and may thus hamper the survival of young plants. The role of remnant trees in succession needs to be better understood to identify patterns and functional traits that might facilitate natural regeneration in drylands. This study evaluated the role of remnant trees in the succession process in the caatinga vegetation (Brazilian seasonally dry tropical forest), testing the effect of a typical tree, the juazeiro (Ziziphus joazeiro Mart.) in richness and abundance of seedlings in areas of abandoned pasture, in Northeastern Brazil. A perimeter was outlined around each plant (n = 20) with a diameter equivalent to each tree crown; all seedlings of woody species up to 0.5 m in height, within that perimeter, were collected and identified. Control areas with the same dimensions were delimited in adjacent locations (n = 20) without the influence of remnant trees, followed by the same data surveys. Mean species richness was of 7.8 ± 4.8 under the juazeiro canopies, compared to 2.3 ± 1.9 in the control areas. Species abundance was also greater under the presence of Z. joazeiro , with an average of 16.9 ± 4.8, against 4.1 ± 4.2 individuals in the controls. Among the abiotic factors evaluated, it is suggested that soil and air temperatures may show a greater influence on the recruitment of seedlings, benefiting natural regeneration under Z. joazeiro. Z. joazeiro ramnant trees appear to facilitate the natural regeneration of tropical drylands. We suggest considering the use of these plants as catalysts for the nucleation process in the restoration of the caatinga. [Display omitted] • Facilitation plays an important role in dryland succession. • Remnant trees catalyse the natural regeneration process, creating regeneration nuclei. • Remnant trees can increase the diversity and density of seedlings in areas undergoing natural regeneration. • Remnant plants possibly alleviate water deficit and heat stress in drylands. [ABSTRACT FROM AUTHOR]

Plant facilitation has a pivotal role in regulating species coexistence, particularly under arid environments. The present study aimed to evaluate the facilitative effect of Calligonum polygonoides L. on its understory plants in coastal habitat. Forty Calligonum shrubs were investigated and the environmental data (soil temperature, moisture, pH, salinity, carbon and nitrogen content, and light intensity), vegetation composition, and diversity of associated species were recorded under- and outside canopies. Eight of the most frequent understory species were selected for evaluating their response to the facilitative effect of C. polygonoides. Bioactive ingredients of Calligonum roots were analyzed using gas chromatography-mass spectrometry (GC-MS), and mycorrhizal biodiversity in their rhizosphere soil was also assessed. The effect of Calligonum on understory plants ranged between facilitation and inhibition in an age-dependent manner. Old shrubs facilitated 18 and inhibited 18 associated species, while young shrubs facilitated 13 and inhibited 9 species. Calligonum ameliorated solar radiation and high-temperature stresses for the under canopy plants. Moreover, soil moisture was increased by 509.52% and 85.71%, while salinity was reduced by 47.62% and 23.81% under old and young shrubs, respectively. Soil contents of C and N were increased under canopy. This change in the microenvironment led to photosynthetic pigments induction in the majority of understory species. However, anthocyanin, proline contents, and antioxidant enzyme activities were reduced in plants under canopy. Thirteen mycorrhizal fungal species were identified in the rhizospheric soil of Calligonum with the predominance of Funneliformis mosseae. Thirty-one compounds were identified in Calligonum root extract in which pyrogallol and palmitic acid, which have antimicrobial and allelopathic activities, were the major components. The obtained results demonstrated that facilitation provided by Calligonum is mediated with multiple mechanisms and included a set of interrelated scenarios that took place in a species-specific manner.

Researchers now recognize the importance of the coral microbiome, but they often overlook other species that live on corals and influence coral–microbe interactions. These 'interstitial associates' should be incorporated into the metaorganism concept for insights into how facilitations between associates, corals, and their microbiomes can be leveraged in ecology and restoration. [ABSTRACT FROM AUTHOR]

Autogenic ecosystem engineers often provide cool microhabitats which are used by associated organisms to reduce thermal extremes. The value of such habitats is, however, dependent on key structural traits of the ecosystem engineer, and the intensity and duration of thermal exposure.Using an experimental mesocosm that mimicked the rocky intertidal environment, we assessed how the spatial configuration of the habitat formed by an autogenic ecosystem engineer, the oyster, influences its capacity to mitigate heat stress experienced by invertebrates during simulated emersion periods on tropical, Hong Kong rocky shores.At the average temperature experienced during summer low tides, oyster habitat ameliorated environmental and organismal temperatures, irrespective of the structural configuration of the oyster bed. As temperatures increased, however, vertically orientated oysters provided microclimates that facilitated cooler invertebrate body temperatures than horizontal beds, which no longer conferred any associational benefit as compared to bare rock surfaces.In the absence of oysters, physiological indicators of stress to associated organisms (i.e., heart rate and osmolality) increased with the intensity and duration of exposure to high temperatures. Such effects were, however, mitigated by association with vertical but not horizontal oyster configurations. In contrast, the osmolality of the oysters was not related to temperature, suggesting they remained in a state of metabolic quiescence throughout emersion.Structural traits such as the spatial configuration of ecosystem engineers are therefore critical to their effectiveness in environmental amelioration. As such, variations in the morphological traits of ecosystem engineers, which have important implications for their ecological role, need to be incorporated into conservation and restoration projects aimed at climate change adaptation. A plain language summary is available for this article. Plain Language Summary [ABSTRACT FROM AUTHOR]

Ecosystem engineering by burrowers is one of the most important determinants of spatio-temporal community patterns in marine soft-sediments. Current understanding of broad mechanisms by which this occurs is based on research on free-living assemblages, while equivalent knowledge for burrow-dwelling symbiotic assemblages is scarce. In this paper, we aim to differentiate the relative strength of density-versus trait-mediated responses of a symbiont ( Betaeus jucundus ; Crustacea: Alpheidae) to burrows created by a southern African axiidean sandprawn ( Callichirus kraussi ; Crustacea: Axiidea) in a marine dominated lagoon on the west coast of South Africa. Results of multiple linear regression analyses indicate that spatio-temporal variability in B. jucundus abundance was not related to densities of burrows produced by C. kraussi , but was better predicted by burrow traits, particularly the concentrations of potential trophic resources and fine sediment fractions along burrow walls. Chl- a and carbohydrate concentrations on burrow walls as well as abundance of B. jucundus peaked during spring upwelling, particularly at sites with greater sediment mud content. Quantities of fine sediment fractions along burrow walls were positively linked to concentrations of chl- a and carbohydrates and to abundances of B. jucundus . Our findings suggest that extrinsic processes (seasonal pulses of nutrients) and intrinsic burrow features (mud content) may be important in determining concentrations of trophic resources in burrows potentially available to symbionts. Our results also indicate that accurate prediction of spatio-temporal abundance patterns of certain symbionts may require knowledge of these intrinsic and extrinsic processes that influence the amount of potential trophic resources available in burrows to symbionts. [ABSTRACT FROM AUTHOR]

Background and Aims Dioecious plants are of particular concern in view of global environmental changes because reproductive females are more sensitive to abiotic stresses, thus compromising population viability. Positive interactions with other plants may counteract the direct effects of any abiotic environmental stress, allowing them to thrive and maintain a viable population in suboptimal habitats, although this process has not been tested for dioecious species. Furthermore, almost no data are available on the outcome of such species interactions and their link with local spatial patterns and sex ratios. Methods We set up a field experiment with Poa ligularis, a dioecious native grass from the arid grasslands of South America. We studied the interaction of male and female plants with cushion shrubs of contrasting ecological strategies. We experimentally limited direct shrub–grass competition for soil moisture and transplanted plants to evaluate the amelioration of abiotic stress by shrub canopies (i.e. sun and wind) on grasses. We also studied the distribution of naturally established female and male plants to infer process–pattern relationships. Key Results Positive canopy effects as well as negative below-ground effects were more intense for females than for males. Deep-rooted Mulinum spinosum shrubs strongly facilitated survival, growth and reproduction of P. ligularis females. Naturally established female plants tended to distribute more closely to Mulinum than co-occurring males. Female growth suffered intensive negative root competition from the shallow-rooted Senecio filaginoides shrub. Conclusions Interactions with other plants may reduce or enhance the effect of abiotic stresses on the seemingly maladapted sex to arid environments. We found that these biased interactions are evident in the current organization of sexes in the field, confirming our experimental findings. Therefore, indirect effects of climate change on population sex ratios may be expected if benefactor species abundances are differentially affected. [ABSTRACT FROM AUTHOR]

Under intensive environmental stress, reported that plants have complementary and positive interactions instead of competition among species. In order to examine whether there as a possible correlation between the performance of Halenia corniculata and the coverage/height of other plants with the same distribution, a total of 30 plots were established at two representative distributional areas. The height, total number of chasmogamous flowers and cleistogamous flowers, their overall plots coverage, and observed plants species on each plot were determined. Our results revealed that the number of chasmogamous and cleistogamous flowers of Halenia corniculata was increased when its height was increased. The performance of Halenia corniculata was found to have a significant correlation with the overall coverage of observed plants species in the plot as well as the height of observed plants in established plots. Our results suggest that the biennial plant Halenia corniculata might be able to choose a site inhabited by other perennial plants in the high-altitude region under environmental stress for appropriate growth and reproduction. One main reason that Halenia corniculata seedlings could be established in regions where other plants are inhabited might be due to the degree of light requirement by the seedling stage is different from that at the adult stage. The size of Halenia corniculata population in South Korea was found to be proportional to that of available sites that could support its life cycle, suggesting that available sites need to be secure in order to maintain its life cycle. [ABSTRACT FROM AUTHOR]

Recruitment is a bottleneck for forest regeneration especially in semi-arid Mediterranean environments. Ensuring natural forest regeneration is vital for preserving ecosystem function under climate warming and increased frequency and intensity of extreme droughts. Interspecific positive interactions are of paramount importance in these ecosystems. The net outcome of conspecific plant interactions in semiarid forests, however, has been less explored, particularly the range of environmental conditions for which juveniles benefit from nursing effects. We evaluated the direction and magnitude of intraspecific relationships between adults and juveniles of Pinus pinaster in a dry continental Mediterranean forest in the Iberian Peninsula. We measured the longitudinal shoot elongation of the last 15 yr and foliar functional traits in pine saplings growing under the canopy of adult pines and in open habitats. We examined the growth response to precipitation and the resilience and resistance of growth to two extreme drought events in 2005 and 2012. Our results show likely facilitation of saplings by adult conspecifics. Nursed saplings had a greater size relative to age, longer needles, and faster shoot elongation than saplings in open habitats. In addition, saplings under the canopy were more resistant and resilient to the first severe drought event. However, saplings grown in open habitats were more resilient to the second drought event, which might suggest a shift in the net balance of conspecific interactions with increased drought frequency and with tree ontogeny. These results have a direct application for the adaptation and restoration of semi-arid forest ecosystems under climate change. Currently, adults are used as nurse plants to enhance survival and growth of juveniles. However, this positive effect on sapling performance might shift to negative under scenarios of increasing frequency and intensity of drought events. [ABSTRACT FROM AUTHOR]

Abstract: Plant establishment is a challenge in semiarid environments due to intense and frequent drought periods. The presence of neighboring trees (nurses) can increase the establishment of seedlings (targets) by improving resource availability and microclimate. The nurse effect, however, might vary depending on nurse‐target species combinations but factors that predict this specificity are poorly known. We used a multispecies experiment to investigate the facilitation potential of trees from a range of successional stages, focusing on how nurse functional traits can predict species‐specific interaction outcomes. We conducted a factorial field experiment in a Brazilian semiarid tropical forest during a severe drought period. Sixty pairs of interacting tree species, 20 potential nurses, and three targets were used. Seedlings of all targets were planted both under and far from the nurse canopy, in a randomized block design replicated five times. Target growth and survival were monitored for 275 days from the beginning of the dry season, and interaction outcomes were calculated using the Relative Interaction Intensity (RII) index. Nurse functional traits such as successional stage, height, wood density, and canopy diameter were used as explanatory variables to predict RII values. The average effect of nurse species on target plants was in general positive, that is, seedling survival and growth increased under the nurse canopy. However, for growth pairwise interactions were significantly species specific. Successional stage was the only functional trait explaining RII values, with pioneer tree species being stronger facilitators than later successional trees. However, the explanation power of this variable was low, and positive, negative, or neutral interactions were found among nurse trees of all successional stages. Because seedling mortality during drought in semiarid systems is high, future studies should investigate how nurse traits related to water use could influence nurse facilitation skills. [ABSTRACT FROM AUTHOR]

Abstract: Spatial heterogeneity plays a crucial role in the coexistence of species. Despite recognition of the importance of self‐organization in creating environmental heterogeneity in otherwise uniform landscapes, the effects of such self‐organized pattern formation in promoting coexistence through facilitation are still unknown. In this study, we investigated the effects of pattern formation on species interactions and community spatial structure in ecosystems with limited underlying environmental heterogeneity, using self‐organized patchiness of the aquatic macrophyte Callitriche platycarpa in streams as a model system. Our theoretical model predicted that pattern formation in aquatic vegetation – due to feedback interactions between plant growth, water flow and sedimentation processes – could promote species coexistence, by creating heterogeneous flow conditions inside and around the plant patches. The spatial plant patterns predicted by our model agreed with field observations at the reach scale in naturally vegetated rivers, where we found a significant spatial aggregation of two macrophyte species around C. platycarpa. Field transplantation experiments showed that C. platycarpa had a positive effect on the growth of both beneficiary species, and the intensity of this facilitative effect was correlated with the heterogeneous hydrodynamic conditions created within and around C. platycarpa patches. Our results emphasize the importance of self‐organized patchiness in promoting species coexistence by creating a landscape of facilitation, where new niches and facilitative effects arise in different locations. Understanding the interplay between competition and facilitation is therefore essential for successful management of biodiversity in many ecosystems. [ABSTRACT FROM AUTHOR]

Top-down grazer control of cyanobacteria is a controversial topic due to conflicting reports of success and failure as well as a bias toward studies in temperate climates with large generalist grazers like Daphnia. In the tropical lowland lakes of Brazil, calanoid copepods of the Notodiaptomus complex dominate zooplankton and co-exist in high abundance with permanent blooms of toxic cyanobacteria, raising questions for grazer effects on bloom dynamics (i.e., top-down control vs. facilitation of cyanobacterial dominance). Accordingly, the effect of copepod grazing on the relative abundance of Microcystis co-cultured with a eukaryotic phytoplankton (Cryptomonas) was evaluated in a series of 6-day laboratory experiments. Grazer effects were tested in incubations where the growth of each phytoplankton in the presence or absence of the copepod Notodiaptomus iheringi was monitored in 1 L co-cultures, starting with a 6-fold initial dominance of Cryptomonas by biomass. Compared to the no grazer controls, N. iheringi reduced the growth of both phytoplankton, but Cryptomonas growth was reduced to negative values while Microcystis growth continued positively despite grazers. Hence, in a matter of 6 days selective grazing by N. iheringi increased the biomass of Microcystis relative to Cryptomonas by an order of magnitude compared to controls, and thus, facilitated the dominance of this cyanobacterium. To account for the potential effect of allelopathy, we performed a secondary experiment comparing the abundance and growth rate of Microcystis and Cryptomonas in single and mixed co-cultures in the absence of grazers. The growth rate of Microcystis was unaffected by the presence or relative abundance of Cryptomonas, and vice versa, indicating no allelopathic effects. Our results suggest that selectively grazing zooplankton may facilitate cyanobacteria blooms by grazing on their eukaryotic phytoplankton competitors in nature. Given that selective grazers predominate zooplankton biomass in warmer waters, grazer facilitation of blooms may be a common but poorly understood regulator of plankton dynamics in a warmer and more eutrophic world.

Abstract: Aims: The sign of interactions among plants in very harsh environments is under debate. The Antarctic tundra is one of the harshest environments on Earth and only two vascular plants (Deschampsia antarctica and Colobanthus quitensis) have successfully established natural populations. D. antarctica mostly establishes facilitative interactions with other species (mosses), but there is no information about the inter‐specific interactions established by C. quitensis. We assessed whether C. quitensis grows frequently associated with D. antarctica, and if D. antarctica neighbours have a positive effect on the survival, growth and photochemical efficiency of C. quitensis individuals. Location: King George Island, Antarctic Peninsula. Methods: To assess the spatial association among the two Antarctic vascular plants fifty 50 m × 50 cm quadrats were sampled on each of four different substrates: moss carpet areas; dead moss carpet areas dominated by D. antarctica; a transition zone between dead moss carpets and fellfields; and fellfields characterized by very poor vegetation cover. Infrared thermal images were taken to estimate whether growth associated with D. antarctica affected the foliar temperature of C. quitensis. The importance of D. antarctica neighbours on the growth, survival and photochemical efficiency of C. quitensis was evaluated with a neighbour removal experiment. Results: The number of C. quitensis individuals associated with D. antarctica was significantly higher than when growing alone in the moss carpet and the dead moss carpet, while in the transition zone there was a trend in that direction. C. quitensis individuals growing associated with D. antarctica were bigger than those growing alone in these three substrate types. In the fellfield site there were no significant differences, neither in the number nor the size of individuals when growing alone or associated with D. antarctica. Foliar temperature of C. quitensis individuals associated with D. antarctica was slightly (1.1°C) but significantly higher than in those growing alone. The growth, survival and photochemical efficiency of C. quitensis individuals with neighbours were higher than in individuals with neighbours removed. Conclusions: Our results indicate that D. antarctica has a facilitative effect on the growth, survival and photochemical efficiency of C. quitensis. Thus, facilitative interactions are present and are important in one of the harshest environments on Earth, although results from the fellfield site indicate that further research is needed. [ABSTRACT FROM AUTHOR]

Top-down grazer control of cyanobacteria is a controversial topic due to conflicting reports of success and failure as well as a bias toward studies in temperate climates with large generalist grazers like Daphnia. In the tropical lowland lakes of Brazil, calanoid copepods of the Notodiaptomus complex dominate zooplankton and co-exist in high abundance with permanent blooms of toxic cyanobacteria, raising questions for grazer effects on bloom dynamics (i.e., top-down control vs. facilitation of cyanobacterial dominance). Accordingly, the effect of copepod grazing on the relative abundance of Microcystis co-cultured with a eukaryotic phytoplankton (Cryptomonas) was evaluated in a series of 6-day laboratory experiments. Grazer effects were tested in incubations where the growth of each phytoplankton in the presence or absence of the copepod Notodiaptomus iheringi was monitored in 1 L co-cultures, starting with a 6-fold initial dominance of Cryptomonas by biomass. Compared to the no grazer controls, N. iheringi reduced the growth of both phytoplankton, but Cryptomonas growth was reduced to negative values while Microcystis growth continued positively despite grazers. Hence, in a matter of 6 days selective grazing by N. iheringi increased the biomass of Microcystis relative to Cryptomonas by an order of magnitude compared to controls, and thus, facilitated the dominance of this cyanobacterium. To account for the potential effect of allelopathy, we performed a secondary experiment comparing the abundance and growth rate of Microcystis and Cryptomonas in single and mixed co-cultures in the absence of grazers. The growth rate of Microcystis was unaffected by the presence or relative abundance of Cryptomonas, and vice versa, indicating no allelopathic effects. Our results suggest that selectively grazing zooplankton may facilitate cyanobacteria blooms by grazing on their eukaryotic phytoplankton competitors in nature. Given that selective grazers predominate zooplankton biomass in warmer waters, grazer facilitation of blooms may be a common but poorly understood regulator of plankton dynamics in a warmer and more eutrophic world. [ABSTRACT FROM AUTHOR]

Abstract: Latitudinal and elevational temperature gradients (LTG and ETG) play central roles in biogeographical theory, underpinning predictions of large‐scale patterns in organismal thermal stress, species' ranges and distributional responses to climate change. Yet an enormous fraction of Earth's taxa live exclusively in habitats where foundation species modify temperatures. We examine little‐explored implications of this widespread trend using a classic model system for understanding heat stresses – rocky intertidal shores. Through integrated field measurements and laboratory trials, we demonstrate that thermal buffering by centimetre‐thick mussel and seaweed beds eliminates differences in stress‐inducing high temperatures and associated mortality risk that would otherwise arise over 14° of latitude and ~ 1 m of shore elevation. These results reveal the extent to which physical effects of habitat‐formers can overwhelm broad‐scale thermal trends, suggesting a need to re‐evaluate climate change predictions for many species. Notably, inhabitant populations may exhibit deceptive resilience to warming until refuge‐forming taxa become imperiled. [ABSTRACT FROM AUTHOR]

Mounting evidence shows that the functioning and stability of coastal ecosystems often depends critically on habitat-forming foundation species such as seagrasses, mangroves and saltmarsh grasses that engage in facultative mutualistic interactions. However, although restoration science is now gradually expanding its long-standing paradigm of minimizing competition to including intraspecific, or within species, facilitation in its designs, the potential of harnessing mutualistic interactions between species for restoration purposes remains uninvestigated., Here, we experimentally tested whether a previously documented mutualism between marsh-forming Spartina alterniflora (cordgrass) and Geukensia demissa (mussels) can increase restoration success in degraded US saltmarshes., We found that co-transplanted mussels locally increased nutrients and reduced sulphide stress, thereby increasing cordgrass growth and clonal expansion by 50%. We then removed above-ground vegetation and mussels to simulate a disturbance event and discovered that cordgrass co-transplanted with mussels experienced three times greater survival than control transplants., Synthesis and applications. Our findings indicate that mussels amplify cordgrass re-colonization and resilience over spatial and temporal scales that exceed those of their actual mutualistic interaction. By experimentally demonstrating that mutualistic partners can enable foundation species to overcome stress barriers to establish and persist, we highlight that coastal restoration needs to evolve beyond the sole inclusion of intraspecific-positive interactions. In particular, we suggest that integrating mutualisms in restoration designs may powerfully enhance long-term restoration success and ecosystem resilience in the many coastal ecosystems where mutualisms involving foundation species are important ecosystem-structuring interactions. [ABSTRACT FROM AUTHOR]

In this study, the demography of the common demospongeIrcinia felixwas examined at Tamarindo, a coral reef located in the island municipality of Culebra, Puerto Rico. A preliminary study comparing the size structure of two subpopulations within the reef, Tamarindo Norte (TN) and Tamarindo Sur (TS), indicated that sponges at TN are significantly larger than sponges at TS. This result served as a baseline for the present comparative study in which we aimed to determine whether the spatial differences in population size structure can be explained either by a difference in rates of survival, growth, or recruitment, or a combination of these. To accomplish our goal, we followed the growth, survival and recruitment ofI. felixat the two localities for one year. Growth was the only demographic parameter that differed significantly between localities. Because the most obvious distinction between the study sites was the absence of the octocoralGorgonia ventalinaat TS, we hypothesized that the faster overall growth rate of sponges at TN was related to the presence of the octocoral. To test this hypothesis, we compared growth rates between sponges associated with the octocoral and those individuals not associated. We found that sponges growing nearG. ventalinagrew significantly faster than non-associated sponges. This result suggests that the octocoral facilitates the growth ofI. felixand therefore may account, at least in part, for the spatial differences in population size structure. [ABSTRACT FROM AUTHOR]

Deserts are increasing in extent globally, but existing deserts are decreasing in health. The basic biology and ecology of foundation plant species in deserts are limited. This is a direct study that provides an estimate of the capacity for a locally dominant foundation shrub species in California to recover from damage. Desert shrubs are cleared and damaged by humans for many purposes including agriculture, oil and gas production, and sustainable energy developments; we need to know whether foundation species consistently facilitate the abundance and diversity of other plants in high-stress ecosystems and whether they can recover. A total of 20 Ephedra californica shrubs were clipped to the ground at a single site and systematically resampled for regrowth 2 years later. These shrubs were damaged once and regrew rapidly, and relatively, larger shrubs were not more resilient. This study provides evidence for what we termed the 'Groot Effect' because smaller individuals of this shrub species can recover from significant aboveground damage and continue to have positive effects on other plant species (similar to the popular culture reference to a benefactor tree species). The density of other plant species was consistently facilitated while effects on diversity varied with season. These findings confirm that E. californica is a foundation species that can be an important restoration tool within the deserts of California in spite of extreme cycles of drought and physical damage to its canopy. [ABSTRACT FROM AUTHOR]

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Nurse plants reduce the environmental severity experienced by neighboring plants by providing shade, enabling nutrient accumulation or protection from herbivores within patches of vegetation. Nurse plants should preferentially promote the coexistence of ecologically dissimilar species with little niche overlap, and if ecological traits are conserved within evolutionary lineages, this should result in phylogenetic overdispersion. In contrast to competition, facilitation is expected to increase species richness. Therefore, to examine the role of facilitation as a driver of plant assemblages in Caatinga, we quantified the functional traits of nurse species and compared species richness, phylogenetic diversity, phylogenetic structure of the tree layer and of the herbaceous layer between patchy Caatinga and Caatinga with segregated plants. Results show that functional traits related to resilience and resistance against herbivory seem to be crucial for facilitation in Caatinga. Autochory occurs at a higher frequency in nurse plants than in Caatinga in general. The herbaceous layer of patchy Caatinga is richer in species than of Caatinga with segregated plants, and facilitation is the suggested cause. As the whole community of the 196 patches is phylogenetically overdispersed compared to the null expectations, facilitation seems to predominantly promote the coexistence of dissimilar species with little niche overlap. [ABSTRACT FROM AUTHOR]

Empirical evidence suggests that co-flowering species can facilitate each other through shared pollinators. However, the extent to which one co-flowering species can relieve pollination limitation of another while simultaneously competing for abiotic resource has rarely been examined. Using a deterministic model we explored the demographic outcome for one (“focal”) species of its co-occurrence with a species that shares pollinators and competes for both pollinator visitation and abiotic resources. In this paper we showed how the overall impact can be positive or negative, depending on the balance between enhanced fertilization versus increased competition. Our model could predict the density of co-flowering species that will maximize the pollination rate of the focal species by attracting pollinators. Because that density will also give rise to competitive effects, a lower density of co-flowering species is required for optimizing the trade-off between enhanced fertilization and competition so as to give the maximum possible facilitation of reproduction in the focal species. Results were qualitatively different when we considered attractiveness of the co-flowering species, as opposed to its density, because attractiveness, unlike density, had no effect on competition for abiotic resources. Whereas unattractive neighbours would not bring in pollinators, very attractive neighbours would captivate pollinators, not sharing them with the focal species. Thus optimal benefit to the focal species came at intermediate levels of attractiveness in the co-flowering species. This intermediate level of attractiveness in co-flowering species simultaneously maximized pollination and overall facilitation of reproduction for the focal species. The likelihood of facilitation was predicted to decline with the selfing rate of the focal species, revealing an indirect cost for an inbreeding mating system. Whether a co-flowering species can be facilitative depends on the way pollinators respond to the plant density: only a Type III functional response for visitation rate can result in facilitation. Our model provided both a conceptual framework and precise quantitative measures for determining the impacts of a neighbouring co-flowering species on reproduction. [ABSTRACT FROM AUTHOR]

As coastal population growth increases globally, effective waste management practices are required to protect biodiversity. Water authorities are under increasing pressure to reduce the impact of sewage effluent discharged into the coastal environment and restore disturbed ecosystems. We review the role of benthic macroalgae as ecosystem engineers and focus particularly on the temperate Australasian fucoid Hormosira banksii as a case study for rocky intertidal restoration efforts. Research focussing on the roles of ecosystem engineers is lagging behind restoration research of ecosystem engineers. As such, management decisions are being made without a sound understanding of the ecology of ecosystem engineers. For successful restoration of rocky intertidal shores it is important that we assess the thresholds of engineering traits (discussed herein) and the environmental conditions under which they are important. [ABSTRACT FROM AUTHOR]

Abstract The competitive exclusion principle states that species limited by the same factors cannot share the same environment. Challenging this paradigm, empirical studies often report competitors' coexistence in natural communities, which has long puzzled evolutionary ecologists. Theoretical studies on animal communities have conferred a prime role to the negative effects of interactions in explaining coexistence, but largely neglected the potential positive side of interactions. Here, we propose that living close to a competitor could have beneficial aspects because competitors may provide fitness‐enhancing social information, which under some circumstances may counter the negative effects of competition, thus promoting coexistence. We use conceptual models and discuss factors influencing social information use and their influence on the outcome of competitors' interaction in terms of coexistence probability. Finally, we discuss ecological and evolutionary implications of these processes and suggest exciting avenues for future research on animal communities.

The dynamic of plant communities is strongly influenced by biologicalinteractions. We studied the effects of Eichhornia azurea on the growth of the free-floating macrophytes Eichhornia crassipes, Salvinia minima, Salvinia auriculata and Limnobium laevigatum. The experiments were carried out in three lakes of the upper Paraná river floodplain. We used 0.5 m side squares where these species grew for 11 days (S. auriculata and L. laevigatum) and 17 days (E. crassipes and S. minima), in the presence and absence of E. azurea. There were no significant differences between the relative growth rates of macrophytes growing in the absence and presence of E. azurea. The relative interaction index showed the existence of competition between E. azurea and L. laevigatum, and neutrality with the other three species. There was no evidence of facilitation related to the improvement of physicochemistry characteristics that could enhance macrophytes growth. However, we do not discard a ‘mechanical’ facilitation between E. azurea, which offers protection against windand waves, and the other species of macrophytes.A dinâmica das comunidades vegetais é fortemente influenciada pelasinterações positivas e negativas que desempenham papel importante na manutenção e diversidade das espécies, coexistência e produtividade das comunidades vegetais. Foram estudados os efeitos da macrófita enraizada Eichhornia azurea sobre as espécies de macrófitas flutuantes Eichhornia crassipes, Salvinia minima, Salvinia auriculata e Limnobium laevigatum, em três ressacos da planície de inundação do alto rio Paraná, Brasil. Para os experimentos in situ foram utilizados quadrados de 0,5 m de lado, onde estas espécies cresceram durante 11 dias (S. auriculata e L. laevigatum) e 17 dias(E. crassipes e S. minima), em presença e ausência de E. azurea. Não houve diferenças significativas entre a taxa de crescimento relativo das macrófitas flutuantes crescendo na ausência e na presença de E. azurea. O índice de interação relativa demonstrou a existência de competição entre esta espécie e L. laevigatum e neutralidade na relação com as demais espécies. Não houve, porém, indícios da ocorrência de um mecanismo facilitador relacionado a mudanças nas características físicas e químicas, ocasionadas por E. azurea, que estimulasse o crescimento das espécies flutuantes. Porém, não descartamos a ocorrência de facilitação ‘mecânica’ entre E. azurea, a qual oferece proteção contra as ondas e o vento, e as espécies flutuantes livres.

Aims Facilitation by nurse plants is a common interaction in harsh environments and this positive plant-plant interaction may promote vegetation recovery in ecosystems affected by human activities. Determining the relevance of this process, however, requires assessing how nurse plants influence the establishment of other species, as well as the proportion of species in the regional species pool that would benefit from the presence of nurse plants in human-disturbed areas. Further, since vegetation recovery is a time-dependent process, the community-level consequences of facilitation are likely to vary among landscapes with different disturbance history. Thus, an integrative perspective of the relevance of nurse plants for vegetation recovery could be obtained by measuring their effects across different human-disturbed landscapes of the target region. This study focuses on these issues and uses a regional-scale approach to assess the community-level effects of a widespread nurse plant of American deserts, the creosotebush (Larrea tridentata). Methods This study was conducted in the southernmost portion of Chihuahuan Desert because most floodplain valleys of this region have been affected by human activities during the past centuries. For this study, we selected 10 floodplain valleys differing in their age (i.e. the time elapsed after human activities were ceased). At each landscape, we measured the cover of creosotebushes and the proportion of plant species positively associated with them, as well as the density of seeds in the soil beneath creosotebush canopies. All these data were regressed against the age of the landscapes. Further, to assess whether positive association patterns were due to facilitation or other processes, we conducted field experiments and measured the ecophysiological performance of plant species established beneath and outside creosotebush canopies. Important Findings Most plant species from the target region were positively associated to creosotebushes, and our field experiments and ecophysiological measures indicated that these distribution patterns can be attributed to facilitative interactions. In most landscapes, the density of seeds was higher beneath creosotebushes than in the surrounding habitats, suggesting that these shrubs may also act as seed traps. The community-level effects of creosotebushes increased with landscape age and creosotebush cover, indicating that magnitude of these effects depends on the disturbance history of each site. These results highlight the relevance of performing large-scale assessments for identifying the consequences of facilitation on vegetation recovery across space and time. We then propose that this kind of largescale approach should be taken into account in the development of conservation programs aimed at the recovery and preservation of plant biodiversity in harsh environments. [ABSTRACT FROM AUTHOR]

The majority of studies have demonstrated that the Barred Warbler Sylvia nisoria (BW) and the Red-backed Shrike Lanius collurio (RBS), where they occur sympatrically in central Europe, inhabit similar niches and are not averse to nesting in each other's vicinity. The present work compares the reproductive parameters, nest survival, and behavioural interactions between these two ecologically similar species. The study was carried out in eastern Poland in two types of habitat: a river valley and farmland. Inter-habitat analysis showed both species to have similar reproductive parameters, although nest survival of the RBS was greater in farmland than in the river valley. Interspecific comparison revealed that the BW built smaller nests, laid fewer and smaller eggs than the RBS, but the production of offspring was similar in both species. In comparison to the other populations from Europe, both the BW and RBS in eastern Poland experienced good breeding parameters, and this is likely to be related to the region's extensive agriculture management and abundant food resources. The main factor reducing breeding success in both species was the plundering of their broods by raptors. Analysis using the MARK program indicated that habitat parameters significantly affected brood survival in the RBS to a relatively constant extent throughout the season. While habitat factors were less decisive in BWs, the fate of this species' broods was strongly dependent on the phase of the reproductive cycle, and its nests were least likely to survive in the middle of the breeding season. The level of aggression between the BW and RBS was low, as demonstrated by experiments with stuffed models; this was a factor in favour of their nesting in close proximity to one another. [ABSTRACT FROM AUTHOR]

The competitive exclusion principle states that species limited by the same factors cannot share the same environment. Challenging this paradigm, empirical studies often report competitors' coexistence in natural communities, which has long puzzled evolutionary ecologists. Theoretical studies on animal communities have conferred a prime role to the negative effects of interactions in explaining coexistence, but largely neglected the potential positive side of interactions. Here, we propose that living close to a competitor could have beneficial aspects because competitors may provide fitness-enhancing social information, which under some circumstances may counter the negative effects of competition, thus promoting coexistence. We use conceptual models and discuss factors influencing social information use and their influence on the outcome of competitors' interaction in terms of coexistence probability. Finally, we discuss ecological and evolutionary implications of these processes and suggest exciting avenues for future research on animal communities. [ABSTRACT FROM AUTHOR]

Ecological theory predicts that positive interactions among organisms will increase across gradients of increasing abiotic stress or consumer pressure. This theory has been supported by empirical studies examining the magnitude of ecosystem engineering across environmental gradients and between habitat settings at local scale. Predictions that habitat setting, by modifying both biotic and abiotic factors, will determine large-scale gradients in ecosystem engineering have not been tested, however. A combination of manipulative experiments and field surveys assessed whether along the east Australian coastline: (1) facilitation of invertebrates by the oyster Saccostrea glomerata increased across a latitudinal gradient in temperature; and (2) the magnitude of this effect varied between intertidal rocky shores and mangrove forests. It was expected that on rocky shores, where oysters are the primary ecosystem engineer, they would play a greater role in ameliorating latitudinal gradients in temperature than in mangroves, where they are a secondary ecosystem engineer living under the mangrove canopy. On rocky shores, the enhancement of invertebrate abundance in oysters as compared to bare microhabitat decreased with latitude, as the maximum temperatures experienced by intertidal organisms diminished. By contrast, in mangrove forests, where the mangrove canopy resulted in maximum temperatures that were cooler and of greater humidity than on rocky shores, we found no evidence of latitudinal gradients of oyster effects on invertebrate abundance. Contrary to predictions, the magnitude by which oysters enhanced biodiversity was in many instances similar between mangroves and rocky shores. Whether habitat-context modifies patterns of spatial variation in the effects of ecosystem engineers on community structure will depend, in part, on the extent to which the environmental amelioration provided by an ecosystem engineer replicates that of other co-occurring ecosystem engineers. [ABSTRACT FROM AUTHOR]

Aims Positive interactions are defined as non-trophic interactions where at least one of the interacting species is benefited in terms of fitness and the other remains unaffected. Nevertheless, the bidirectional feedbacks between species may be positive, neutral or negative. Thus, if facilitated species induce negative effects on their 'nurses', the assumed definition of positive interactions could be reconsidered. Methods We assessed if ecological interactions between cushions of Azorella madreporica and their facilitated species are positive. Specifically, we tested if cover of facilitated species has any costs for cushion plants from an ecophysiological perspective, and if these costs increase with the amount of cover of facilitated species. In addition, through pathway analysis and correlations, we assessed if cover and richness of facilitated species have a direct and/or indirect effect on the fitness of cushion plants. Important Findings We found that facilitated plant species induced a significant cost for their nurses (cushion plants), and this cost increases with cover of the facilitated species. Additionally, the facilitated species exert a strong direct negative effect on the cushion's fitness and a moderate indirect negative cost evident through the nutrient status and physiological performance of cushion plants. We thus contribute evidence that positive interactions between high mountain cushion plants of central Chile and their 'facilitated' species may be an artifact more than a fact, especially when bidirectional effects are considered; contrasting with the majority of studies that document only one side of the interaction. [ABSTRACT FROM AUTHOR]

Empirical studies in salt marshes, arid, and alpine systems support the hypothesis that facilitation between plants is an important ecological process in severe or ‘stressful’ environments. Coastal dunes are both abiotically stressful and frequently disturbed systems. Facilitation has been documented, but the evidence to date has not been synthesized. We did a systematic review with meta-analysis to highlight general research gaps in the study of plant interactions in coastal dunes and examine if regional and local factors influence the magnitude of facilitation in these systems. The 32 studies included in the systematic review were done in coastal dunes located in 13 countries around the world but the majority was in the temperate zone (63%). Most of the studies adopt only an observational approach to make inferences about facilitative interactions, whereas only 28% of the studies used both observational and experimental approaches. Among the factors we tested, only geographic region mediates the occurrence of facilitation more broadly in coastal dune systems. The presence of a neighbor positively influenced growth and survival in the tropics, whereas in temperate and subartic regions the effect was neutral for both response variables. We found no evidence that climatic and local factors, such as life-form and life stage of interacting plants, affect the magnitude of facilitation in coastal dunes. Overall, conclusions about plant facilitation in coastal dunes depend on the response variable measured and, more broadly, on the geographic region examined. However, the high variability and the limited number of studies, especially in tropical region, indicate we need to be cautious in the generalization of the conclusions. Anyway, coastal dunes provide an important means to explore topical issues in facilitation research including context dependency, local versus regional drivers of community structure, and the importance of gradients in shaping the outcome of net interactions.

Las plantas en cojín que crecen en ambientes de alta montaña modifican microclimáticamente su entorno, generando microhábitats favorables para el establecimiento de otras especies, actuando como nodrizas. Varios estudios han demostrado que los cojines contienen una mayor riqueza de especies que los espacios abiertos. Sin embargo, hasta ahora, no se ha evaluado el efecto de los cojines sobre otros parámetros comunitarios como la abundancia de individuos, la diversidad y la equitatividad. En este trabajo se analiza el efecto que posee Oreopolus glacialis, una planta en cojín de la cordillera andina, sobre la riqueza, abundancia, diversidad y equitatividad de la comunidad vegetal en un ambiente de alta montaña ubicado a 1.900 m en Chile central. Se determino la riqueza y abundancia de especies que crecen tanto sobre cojines de O. glacialis como en los espacios abiertos entre cojines. Los resultados mostraron que la riqueza de especies y la abundancia de individuos por unidad de área es mayor dentro de los cojines que fuera de ellos. Sin embargo, los valores de diversidad y equitatividad sobre O. glacialis fueron menores que fuera de ellos debido a la presencia de algunas especies dominantes. Análisis particulares de la frecuencia y abundancia de cada especie mostraron que no todas las especies son afectadas de la misma manera por la presencia de este cojín, por lo que O. glacialis actuaría como nodriza sólo para una parte limitada de los componentes de la comunidadCushion plants growing in high mountain habitats can modify the microclimate within their canopy generating microhabitats more favorable for the recruitment of other plant species, acting as nurse plants. Although several studies have shown that species richness is higher within cushions than outside them, no attempts have been made in order to assess the effect of cushions on other community aspects such as total and individual abundance, diversity and evenness. In this study we analyzed the effect of Oreopolus glacialis -a cushion plant from the South American Andes- on the species richness, total and individual abundance, diversity and evenness of a plant community located in a high mountain environment at 1,900 m of altitude in central Chile. Species richness and abundance were determined both within and outside O. glacialis cushions. Results showed that, per area, species richness and individual abundance were higher within cushions. In contrast, diversity and evenness within O. glacialis cushions were lower than outside. This apparent incongruence was caused by some species being highly dominant within cushions. Analyses of the frequency and abundance of each species showed that not all the species were affected in the same way by the cushions, with only four species growing more frequently within cushions. This suggests that nurse effect of O. glacialis is a species-specific phenomenon

The effects of introduced species on native species have been widely studied, however, invader-invader interactions are still poorly explored. Two non-native invasive species, the bivalve Limnoperna fortunei and the submersed macrophyte Hydrilla verticillata, have infested many aquatic ecosystems worldwide, and they are rapidly becoming nuisances in several water bodies in Brazil. We tested the hypothesis that H. verticillata facilitates the establishment of L. fortunei more than do native macrophytes. We surveyed mussels attached to two native macrophytes and to this invasive macrophyte in three Brazilian reservoirs and compared the length, density and biomass of the attached mussels relative to the host macrophyte species. All of the values of these attributes in L. fortunei were higher in the mussels attached to H. verticillata than in those attached to the native macrophytes. These results supported our initial hypothesis because the settlement of L. fortunei appeared to be facilitated by the invasive macrophyte, allowing higher abundances of the mussels as well as the more effective establishment of the mussel population. Various mechanisms could interact to facilitate the superior performance of L. fortunei in the invasive plant. H. verticillata is more flexible and withstands more mussels without breaking. Furthermore, this plant has different attached algae, which may be more beneficial for mussels. Thus, as a response to the facilitation suggested by our work, the mussel has greater opportunities to succeed in habitats colonised by the non-native H. verticillata. Although we have not evaluated the effects of this facilitation on aquatic communities or the ecosystem, our results could represent the first step of an invasional meltdown.

Facilitation by the nurse effect can occur through an amelioration of environmental stress. Plant-microorganism interaction, however, is another key facilitation mechanism of the nurse effect, but is by far the least documented. Here we tested if microclimatic mitigation and soil microorganisms isolated from the root-zone of the nurse shrub Porlieria chilensis can increase the establishment of other native plants in a semiarid community. We conducted field and greenhouse experiments to evaluate the direct and indirect effects of the presence of P. chilensis on the survival and growth of three native plants. In the field experiment, we compared the survival and growth of transplanted individuals beneath nurses and outside of them in pots filled with soil from both microsites (beneath and outside nurses). Finally, in the greenhouse experiment we grew native plants in soil taken from both microsites (below and outside nurses) and with and without soil microorganisms (sterilization process). We found a clear and significant nurse effect of P. chilensis on the tested species through of amelioration of climatic (air temperature, soil moisture, and solar radiation) and edaphic (nitrogen availability) conditions, increasing the performance of these native species. Moreover, performance and establishment were enhanced when soil was kept with microorganisms. Thus, nurse effect mediated by microclimatic amelioration, edaphic improvement and presence of soil microorganisms could be key mechanisms to increase the establishment of native plant species in semiarid communities of central Chile. [ABSTRACT FROM AUTHOR]

1. Theoretical and empirical ecology has transitioned from a focus on the role of negative interactions in species coexistence to a more pluralistic view that acknowledges that coexistence in natural communities is more complex, and depends on species interactions that vary in strength, sign, and reciprocity, and such contexts as the environment and life-history stage. 2. We used a whole-community approach to examine how species interactions contribute to the maintenance of a rocky intertidal macroalgal canopy-understorey assemblage. We determined both the types of interactions in this network, and whether interactions were sensitive to environmental gradients. 3. Focusing on a structurally dominant canopy kelp Saccharina sessilis, and its diverse co-occurring understorey assemblage, we evaluated the role of the understorey in controlling S. sessilis recruitment and quantified the reciprocal effect of the S. sessilis canopy and understorey on one another using a removal experiment replicated across 600 km of coastline. We determined the sensitivity of interactions to natural variation in light and nutrient availability (replicated among four regions on the N.E. Pacific coast), and under different wave conditions (three wave regimes). 4. Surprisingly, species interactions were similar across sites and thus not context-dependent. Unexpectedly, the understorey community had a strong positive effect on the S. sessilis canopy, whereby the adult canopy decreased dramatically following understorey removal. Additionally, S. sessilis recruitment depended on the presence of understorey coralline algal turf. In turn, the canopy had a neutral effect on the coralline understorey, but a negative effect on non-calcifying algal turfs, likely eventually generating positive indirect canopy effects on the coralline understorey. Densitydependent intraspecific competition between S. sessilis adults and recruits may moderate this positive feedback between the S. sessilis canopy and coralline understorey. 5. Synthesis. Our research highlights the importance of positive interactions for coexistence in natural communities, and the necessity of studying multiple life-history stages and reciprocal species interactions in order to elucidate the mechanisms that maintain diversity. [ABSTRACT FROM AUTHOR]

Positive interactions have started to gain a place as important drivers of community structure and biological diversity. Defined as non-trophic interspecific interactions that increase the average individual fitness of one species, by definition, the presence of one plant species enhances the chances that another species co-occur in the same place, indicating that positive interactions may determine biological diversity. However, this has been poorly explored., The majority of the studies addressing community-level consequences of facilitation have compared the diversity of the plant assemblages growing within nurses vs. those growing outside them, reporting contrasting results among them. Nonetheless, nurses and their alternative microhabitats (open areas among nurses) are part of the same community. Thus, if nurses allow for the persistence of species that otherwise would be excluded from the community, a net increase in the species diversity at the entire community level will be generated even though nurse plants contained fewer species than open areas., Here, we conducted a bibliographic search using the ISI Web of Knowledge data base and reviewed the literature conducted on alpine plant communities where assessments of the diversity of plants growing within and outside a nurse species were available. In most cases nurse species substantially increased species richness at the community level, despite the fact that in some cases, they contained lower species numbers than open areas. Nurse species enhanced species richness more in systems with impoverished local diversity, suggesting that facilitative interactions in alpine habitats act as an insurance policy that sustains diversity under very harsh conditions. [ABSTRACT FROM AUTHOR]

Facilitation studies focus primarily on plants often neglecting the extended effects that cascade through ecological networks. Plants interact with other organisms through consumptive effects and a myriad of non-trophic effects such as habitat amelioration or pollination., Shrubs are a dominant benefactor species frequent in plant-facilitation studies but can also have direct and indirect interactions with animals. Herein, we use a systematic review to address the following two objectives: (i) to propose a conceptual framework that explores these interactions including the functional roles of the interacting species, and (ii) to quantitatively summarize the current state of this field examining effects beyond plant-plant interactions., To date, a relatively limited number of studies have examined the importance of coupled benefactor-subordinate plant positive interactions with animals (79 studies in total). From this set of studies, 36 studies documented positive plant interactions generating a total of 53 independent instances of either shrub-plant-animal or shrub-animal-plant interactions., These interaction pathways were evenly split between direct (49%) and indirect (51%) interactions of shrubs with animals. Hypotheses frequently tested included seed trapping, herbivore protection, magnet pollination and facilitation-mediated secondary seed dispersal. The most common functional role of shrubs was protection from herbivory, and the most common animal role associated with plant-facilitation complexes was that of a consumer., None of these studies explored bidirectional plant-animal interactions, used a network approach to describe the interaction sets, nor contrasted interaction strengths. Multitrophic, integrated sets of experiments incorporating plant facilitation into community dynamics are thus critical in advancing management of high-stress ecosystems wherein positive interactions are commonly reported. [ABSTRACT FROM AUTHOR]

Mutualisms are important structuring forces in ecological communities, influencing ecosystem functions, diversity, and evolutionary trajectories. New interactions, particularly between native and non-native species, are globally increasing in biotic communities as species introductions accelerate. Positive interactions such as novel mutualisms can affect the fitness of organisms in invaded communities. Non-natives can augment native mutualism networks, replace extinct native partners, or disrupt native mutualisms. Because they are actively forming or newly formed, novel mutualisms offer a unique opportunity to examine in real time the factors governing early mutualism formation and stability, including frequency-dependent processes and those relying on specific traits or functions. These central ecological questions have been inferred from long-formed mutualisms, but novel mutualisms may allow a glimpse of successes and failures in ecological time with insights into the relative importance of these factors as ecological systems shift. To this end, this commentary addresses how novel mutualisms inform our understanding of mutualism formation, stability, the importance of functional traits, and niche vs. neutral processes, using examples across multiple systems. Novel mutualism research thus far has been largely limited in both questions and ecosystems, but if more broadly applied could benefit both theoretical and applied ecology. [ABSTRACT FROM AUTHOR]

Facilitation is a major force shaping the structure and diversity of plant communities in terrestrial ecosystems. Detecting positive plant-plant interactions relies on the combination of field experimentation and the demonstration of spatial association between neighboring plants. This has often restricted the study of facilitation to particular sites, limiting the development of systematic assessments of facilitation over regional and global scales. Here we explore whether the frequency of plant spatial associations detected from high-resolution remotely sensed images can be used to infer plant facilitation at the community level in drylands around the globe. We correlated the information from remotely sensed images freely available through Google Earth with detailed field assessments, and used a simple individualbased model to generate patch-size distributions using different assumptions about the type and strength of plant-plant interactions. Most of the patterns found from the remotely sensed images were more right skewed than the patterns from the null model simulating a random distribution. This suggests that the plants in the studied drylands show stronger spatial clustering than expected by chance. We found that positive plant co-occurrence, as measured in the field, was significantly related to the skewness of vegetation patch-size distribution measured using Google Earth images. Our findings suggest that the relative frequency of facilitation may be inferred from spatial pattern signals measured from remotely sensed images, since facilitation often determines positive co-occurrence among neighboring plants. They pave the road for a systematic global assessment of the role of facilitation in terrestrial ecosystems. [ABSTRACT FROM AUTHOR]

Niche differences and average fitness differences jointly determine coexistence. However, little empirical information about the magnitude of these two mechanisms is available. Using multispecies population models fit to long-term demographic data for common, co-occurring species in five grassland and shrubland plant communities in western North America, we estimated the strength of stabilizing niche differences and average fitness differences. In all five communities, both pairwise and full community comparisons showed evidence for strong stabilizing mechanisms and relatively small average fitness differences. For a total of 17 species pairs, a measure of niche differences based on simulations of invasion growth rates ranged from 0.59 to 0.93 with a mean of 0.81, where 0 indicates complete niche overlap and 1 indicates zero niche overlap. A corresponding measure of average fitness differences ranged from 1.02 to 2.54 with a mean of 1.53, where 1 indicates identical fitness and a value of 2 indicates a fourfold difference in sensitivity to competition. Comparisons of full communities displayed similar patterns: niche differences ranged from 0.58 to 0.69 with a mean of 0.64, and the average fitness differences ranged from 1.42 to 1.63 with a mean of 1.47. In almost every case, the stabilizing mechanisms were much stronger than minimally necessary to prevent competitive exclusion. Considering that all but one of the species we studied are perennial grasses, which are often grouped in the same functional type, the magnitude of these niche differences is surprising. In all five communities, differences between intra- and interspecific effects at the recruitment stage contributed far more to stabilization than interactions affecting growth and survival. Our results indicate that for these abundant, cooccurring species (1) dynamics are far from neutral, with strong niche differences and weak fitness differences combining to stabilize coexistence, and (2) processes operating at early life stages account for a large proportion of the stabilizing effect. Given the limitations of our inductive approach, both these findings represent hypotheses in need of experimental testing. [ABSTRACT FROM AUTHOR]