Search

Niche theory is significant for understanding the function of community structure, interspecific relationships, and community dynamic succession. However, there are few studies on the soil animal niche in returning farmland to forest areas on the Loess Plateau, making it challenging to comprehend the utilization of soil animal resources, the stability of the local community, and the succession process in the areas. Therefore, this study collected soil animals in five typical vegetation types: Robinia pseudoacacia (R), Hippophae rhamnoides (H), Populus simonii (P), Pinus tabulaeformis (T), and Armeniaca sibirica x Hippophae rhamnoides (M), with abandoned grassland (G) used as a control group. Then, the number of soil animal taxa, individuals, diversity, and niche were sampled and examined in the study areas during the four seasons of spring, summer, autumn, and winter using the manual sorting method and the Tullgren method. The results revealed that 3872 soil animals from 3 Phyla, 8 Classes, 22 Orders, and 49 Families were captured in the study areas. The dominant groups of soil macrofauna were Diptera larvae, Julidae, and Formicidae, and the dominant groups of meso–micro soil fauna were Oribatida, Protospira, and Collembola juveniles. Soil animals have rich nutritional function groups, with the most saprophytic soil animal groups. The individual density and taxa number of soil animals in G were lower than other vegetation on the whole. H, M, and P had a higher Shannon–Winner index than the other vegetation. Seasonal changes had different effects on macro and meso–micro soil fauna. The diversity of soil macrofauna is higher in spring and summer, and that of meso–micro soil fauna is higher in autumn and winter. Oribatida, Diptera Larvae, and Formicidae had a large niche width in the main taxa of soil animals, with universal adaptability to the environment. Cicadellidae and Culicidae had narrow niche widths and were highly dependent on resources and the environment. There were 67 pairs of highly overlapped (Oik > 0.8) taxa of soil animals and 56 pairs of moderately overlapped (0.6 < Oik ≤ 0.8) taxa, accounting for 80.39% of the total number of taxa. Soil animals had high commonality in resource utilization, intense competition, and poor community stability. As a result, we can conclude that the soil animal community in the study areas was in the stage of succession.

Natural aquatic sites are disappearing worldwide, especially in the Mediterranean region where amphibians are frequently forced to move for reproduction to artificial sites designed for irrigation and cattle watering (i.e., wells, tanks and drinking troughs). In artificial aquatic sites, where resources (space and food) are usually limited, trophic niche information can be particularly useful to infer the suitability of habitats for amphibian conservation especially when more than one species co-occurs. In this paper, we focused on three newt species: The Italian newt (Lissotriton italicus), the Italian smooth newt (Lissotriton vulgaris meridionalis) and the Italian crested newt (Triturus carnifex) inhabiting man-made wells widespread in an area in Central Italy characterized by few available natural aquatic sites. Specifically, we analyzed the trophic spectrum of the species, their interactions and overlap, and discussed the potential role of wells in amphibian conservation. Overall, 550 newt individuals occurring in 16 distinct wells were sampled. The study species consumed similar resources, mainly of aquatic origin, with Diptera larvae and Cladocera representing the most important preys. The high degree of diet overlap observed may be due to site oligotrophy and high availability of small-sized prey, and it does not necessarily lead to competition. Newts had similar narrow niche width values and a generalist feeding pattern with high diversity among individuals. Lissotriton italicus and T. carnifex showed wider niche width in isolation than in syntopy condition, probably as a result of interspecific competition and/or intraguild predation. We showed that artificial aquatic sites are important for newt ecology and conservation since they allow up to three species to cohabit, thus representing a good surrogate of natural habitats. The study wells apparently provided suitable trophic conditions for newts in terms of prey availability and catchability. To date, just a few studies have contributed to a greater understanding of newts&rsquo, diet in artificial aquatic sites and this gap of knowledge has to be filled to clarify their role in amphibian ecology and conservation.

Producción Científica, The identification of the factors controlling the understory species distribution and abundance is essential to understand the ecology and dynamics of natural forests and their management response. We assess the relationships between environmental gradients and shrub functional groups distribution patterns and niche characteristics in a transitional area between the Eurosiberian and Mediterranean biogeographic regions in Northern Spain. Here, 772 plots from the 3rd Spanish National Forest Inventory were used. Shrub functional groups respond to the same complex environmental gradients as trees, i.e., the north-south climatic gradient and a slope gradient. Unimodal response curves of shrub functional groups and families dominate along both gradients, providing evidence of successful functional turnover. Similar to tree species, the niche location of functionally related shrubs is close. Functional groups occupying environments with sharp contrast or transitional environments have the broadest niches, whereas those specialized functional groups occupying localized habitats showed the narrowest niches. The knowledge of shrub species distributions and niche characteristics along complex environmental gradients will improve our ability to discuss potential conservation management goals or threats due to land-use changes and future climate change., Ministerio de Ciencia e Innovación - (RYC-2016-20528)

Made available in DSpace on 2021-06-25T11:52:41Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-03-04 European Regional Development Fund (Centre of Excellence EcolChange) University of Tartu (Estonian Research Council ) Moscow State University Natural Sciences and Engineering Research Council of Canada Discovery Grant Russian Science Foundation Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Swedish Research Council (Vetenskapsradet) The arbuscular mycorrhizal (AM) fungi are a globally distributed group of soil organisms that play critical roles in ecosystem function. However, the ecological niches of individual AM fungal taxa are poorly understood. We collected > 300 soil samples from natural ecosystems worldwide and modelled the realised niches of AM fungal virtual taxa (VT; approximately species-level phylogroups). We found that environmental and spatial variables jointly explained VT distribution worldwide, with temperature and pH being the most important abiotic drivers, and spatial effects generally occurring at local to regional scales. While dispersal limitation could explain some variation in VT distribution, VT relative abundance was almost exclusively driven by environmental variables. Several environmental and spatial effects on VT distribution and relative abundance were correlated with phylogeny, indicating that closely related VT exhibit similar niche optima and widths. Major clades within the Glomeraceae exhibited distinct niche optima, Acaulosporaceae generally had niche optima in low pH and low temperature conditions, and Gigasporaceae generally had niche optima in high precipitation conditions. Identification of the realised niche space occupied by individual and phylogenetic groups of soil microbial taxa provides a basis for building detailed hypotheses about how soil communities respond to gradients and manipulation in ecosystems worldwide. Univ Tartu, Inst Ecol & Earth Sci, EE-51005 Tartu, Estonia Univ Manchester, Sch Earth & Environm Sci, Manchester M13 9PL, Lancs, England Qatar Univ, Environm Sci Ctr, Doha 2713, Qatar Moscow Lomonsov State Univ, Dept Ecol & Plant Geog, Fac Biol, Moscow 119991, Russia King Saud Univ, Zool Dept, Coll Sci, Riyadh 11451, Saudi Arabia Russian Acad Sci, Inst Biol Problems, North Far East Branch, Magadan 685000, Russia Swedish Univ Agr Sci, Dept Ecol, S-75651 Uppsala, Sweden Univ Alberta, Dept Biol Sci, Edmonton, AB T6G 2E9, Canada Univ Nacl Cordoba, Inst Multidisciplinario Biol Vegetal, CONICET, X5000HUA, Cordoba, Argentina Univ Nacl Rio Cuarto, Fac Agron & Vet, Dept Biol Agr, X5804BYA, Cordoba, Argentina Univ Penn, Dept Biol, Philadelphia, PA 19104 USA Russian Acad Sci, Inst Biol Problems Cryolithozone, Siberian Branch, Yakutsk 677000, Russia Univ Djibouti, Dept Rech Sci Environm, Private Bag 1904, Djibouti, Djibouti Univ Aveiro, Dept Biol, P-3810193 Aveiro, Portugal Univ Aveiro, CESAM, P-3810193 Aveiro, Portugal Thompson Rivers Univ, Dept Nat Resource Sci, Kamloops, BC V2C 0C8, Canada Jules Verne Univ Picardie, Ecol & Dynam Syst Anthropises, F-80037 Amiens, France Univ Namibia, Dept Wildlife Management & Ecotourism, Private Bag 1096, Katima Mulilo, Namibia RAS, FEB, Bot Garden Inst, Vladivostok 690024, Russia Univ Calif Riverside, Dept Microbiol & Plant Pathol, Riverside, CA 92521 USA Univ Western Ontario, Dept Biol, London, ON N6A 5B7, Canada UPR Forets & Societes, CIRAD, Yamoussoukro, Cote Ivoire Univ Montpellier, Forets & Societes, CIRAD, F-34000 Montpellier, France INP HB, Inst Natl Polytech Felix Houphouet Boigny, Yamoussoukro, Cote Ivoire Beni Suef Univ, Bot & Microbiol Dept, Fac Sci, Bani Suwayf 62511, Egypt Czech Acad Sci, Inst Microbiol, Prague 14220, Czech Republic Charles Univ Prague, Dept Expt Plant Biol, Fac Sci, Prague 12843, Czech Republic Estonian Univ Life Sci, Chair Biodivers & Nat Tourism, EE-51006 Tartu, Estonia Murdoch Univ, Harry Butler Inst, Iluka Chair Vegetat Sci & Biogeog, Perth, WA 6150, Australia Stellenbosch Univ, Dept Geog & Environm Studies, ZA-7602 Stellenbosch, South Africa Univ Rwanda, Sch Sci, Coll Sci & Technol, Kigali 3900, Rwanda Univ Bern, Inst Plant Sci, CH-3013 Bern, Switzerland Estonian Univ Life Sci, Chair Crop Sci & Plant Biol, EE-51006 Tartu, Estonia Botswana Int Univ Sci & Technol, Dept Biol Sci & Biotechnol, Private Bag 16, Palapye, Botswana Nakhon Phanom Univ, Dept Biol, Nakhon Phanom 48000, Thailand Univ Tartu, Nat Hist Museum, EE-51014 Tartu, Estonia Univ Palermo, Dept Agr Food & Forest Sci, I-90128 Palermo, Italy Univ Bangui, Ctr Studies & Res Pharmacopoeia & Tradit African, Bangui, Cent Afr Republ Inst Amazon Invest Cient Sinchi, Leticia 910001, Amazonas, Colombia Univ Estadual Paulista, Dept Biodivers, BR-13506900 Sao Paulo, Brazil Radboud Univ Nijmegen, Inst Water & Wetland Res, Dept Aquat Ecol & Environm Biol, NL-6525 AJ Nijmegen, Netherlands Univ Tartu, Dept Bot, EE-51005 Tartu, Estonia Univ Estadual Paulista, Dept Biodivers, BR-13506900 Sao Paulo, Brazil University of Tartu: PLTOM20903 (Estonian Research Council ): MOBTP 105 (Estonian Research Council ): MOBERC20 (Estonian Research Council ): PRG352 (Estonian Research Council ): PRG609 (Estonian Research Council ): PRG 1065 (Estonian Research Council ): PRG 1170 (Estonian Research Council ): PRG 1409 Moscow State University: AAAA-A16-116021660039-1 Russian Science Foundation: 19-14-00038 FAPESP: 2016/25197-0 Swedish Research Council (Vetenskapsradet): 2017-05019 Swedish Research Council (Vetenskapsradet): QUEX-CAS-QP-RD-18/19

Saltmarsh‐mangrove ecotones occur at the boundary of the natural geographic distribution of mangroves and salt marshes. Climate warming and species invasion can also drive the formation of saltmarsh‐mangrove mixing communities. How these coastal species live together in a “new” mixed community is important in predicting the dynamic of saltmarsh‐mangrove ecosystems as affected by ongoing climate change or human activities. To date, the understanding of species interactions has been rare on adult species in these ecotones.Two typical coastal wetlands were selected as cases to understand how mangrove and saltmarsh species living together in the ecotones. The leaves of seven species were sampled from these coastal wetlands based on their distribution patterns (living alone or coexisting) in the high tidal zone, and seven commonly used functional traits of these species were analyzed.We found niche separation between saltmarsh and mangrove species, which is probably due to the different adaptive strategies they adopted to deal with intertidal environments.Weak interactions between coexisting species were dominated in the high tidal zone of the two saltmarsh‐mangrove communities, which could be driven by both niche differentiation and neutral theory.Synthesis. Our field study implies a potential opportunity to establish a multispecies community in the high tidal zone of saltmarsh‐mangrove ecotones, where the sediment was characterized by low salinity and high nitrogen., We found niche separation between saltmarsh and mangrove species and weak interaction between coexisting species in the high tidal zone of the saltmarsh‐mangrove mixing communities.

Intraspecific trait variation in generalist animals is widespread in nature, yet its effects on community ecology are not well understood. Newts are considered opportunistic feeders that may co-occur in different syntopic conditions and represent an excellent model for studying the role of individual feeding specialization in shaping the population dietary strategy. Here, we investigated the diet of three newt species from central Italy occurring in artificial habitats in different coexistence conditions to test the predictions of the niche width (NW) variation hypotheses. Population NW did not vary among species and between presence and absence of coexisting species. An overall positive relationship between individual specialization and population NW was observed. However, this pattern was disrupted by the condition of syntopy with newt populations showing an individual NW variation invariant with population NW in presence of coexisting species, whereas it was larger in populations occurring alone. The observed pattern of newt behavior was not consistent with any of the proposed scenarios. We found a consistent pattern with the degree of individual specialization being (1) size-dependent (specialized individuals increasing within larger sized species) and (2) assemblage-complexity-dependent (specialized individuals increasing in syntopic populations in comparison to singly populations).

6 pages, 4 figures, 2 tables, The squids Doryteuthis gahi and Illex argentinus coexist in the Patagonian shelf and other oceanic waters of the South Atlantic Ocean. Both species perform movements to and from shallow waters related to their ontogenetic growth. To examine changes in the trophic habitats in both species and across the ontogeny, we analyzed the stable isotopic values of δC and δN in their gladii. Based on sections of the gladii, we compared the trophic niche in three stages (adult [the newest section], juvenile [middle section], and a near-birth section [near the conus]). δC and δN values differed significantly between the two species and between gladius segments, revealing interspecific and ontogenetic differences in the trophic niche width. In particular, differences between segments of the gladius concurred with the ontogenetic and spawning migrations of these squids, in the Patagonian Shelf, JN was supported by the Andalucía Talent Hub Program (European Union)’s Seventh Framework Program, Marie Skłodowska-Curie actions and Andalusian Knowledge Agency, Spain. RRL thanks to CONACyT for the postdoctoral support

Small mammals are key components of forest ecosystems, playing vital roles for numerous groups of forest organisms: they exert bottom-up and top-down regulatory effects on vertebrate and invertebrate populations, respectively, they are fungus- and seed-dispersers and bioturbators. Therefore, preserving or restoring the diversity of small mammal communities may help maintain the functions of these ecosystems. In Romania, a country with low-intensity forest management and a high percentage of natural forests compared to other European countries, an overview of forest small mammal diversity and habitat type use is lacking, and our study aimed to fill this gap. We also aimed to partition the total small mammal diversity of Romanian forests into the alpha (plot-level), beta, and delta (among forest types) diversities, as well as further partition beta diversity into its spatial (among plots) and temporal (among years) components. We surveyed small mammals by live trapping in eight types of forest across Romania. We found that small mammal abundance was significantly higher in lowland than in mountain forests, but species richness was similar, being associated with the diversity of tree canopy, with the highest values in mixed forests. In contrast, small mammal heterogeneity was related to overall habitat heterogeneity. As predicted, community composition was most distinct in poplar plantations, where forest specialists coexist with open habitat species. Most of the diversity was represented by alpha diversity. Because of strong fluctuations in population density of dominant rodents, the temporal component of beta heterogeneity was larger than the spatial component, but species richness also presented an important temporal turnover. Our results show the importance of the time dimension in the design of the surveys aiming at estimating the diversity of small mammal communities, both at the local and regional scales.

Competitive diversification, that is, when increasing intraspecific competition promotes population niche expansion, is commonly invoked in evolutionary studies and currently plays a central role in how we conceptualize the process of adaptive diversification. Despite the frequency with which this idea is cited, the empirical evidence for the process is somewhat limited, and the findings of these studies have yet to be weighed objectively through synthesis. Here, we sought to fill this gap by reviewing the existing literature and collecting the data necessary to assess the evidence for competition as a diversifying force. Additionally, we sought to test a more recent hypothesis, which suggests that competition can act to both promote and inhibit dietary diversification depending on the degree to which a consumer depletes its resources. The surprising result of this synthesis was that increasing competition did not have a mean positive effect on population‐level diet breadth or the degree of individual specialization. Instead, we found that increasing intraspecific competition had a restricting effect on population‐level diet breadth in as many cases as it had a diversifying effect. This wide disparity in the effect of competition on consumer diet variation was negatively related to a metric for consumer resource depletion. Altogether, these findings call into question a long‐standing assumption of basic evolutionary models and lend some support to recent theoretical predictions. Specifically, these findings support the idea that competition is primarily diversifying for species with a small effect (per unit biomass) on their resources and that resource depletion limits the diversifying effect of competition for consumers with larger ecological effects.

In this paper, we determined diet composition, reproductive periodicity and fecundity of Astyanax intermedius in a headwater stream of a State Park of an Atlantic rainforest. We also evaluated the influence of rainfall, water temperature and fish size on niche width and niche overlap. Sampling was conducted monthly throughout one year in the Ribeirão Grande stream, southeastern Brazil. Diet consisted of 31 food items with equal contribution of allochthonous and autochthonous items. Females were larger than males, and the mean sizes at first maturation were 4.44 cm and 3.92 cm, respectively. Based on 212 pairs of mature ovaries, the number of oocytes per female ranged from 538 to 6,727 (mean = 2,688.7). Niche width and niche overlap were not related to rainfall nor water temperature and only niche width increased with fish size, suggesting that as fish grow, more items are included in diet. Our results suggested that A. intermedius fit as a typical opportunistic strategist which may explain the prevalence of this species in several isolated headwater basins of vegetated Atlantic forested streams where food resources are abundant and distributed throughout the year. RESUMO Neste trabalho nós determinamos a composição da dieta, periodicidade reprodutiva e fecundidade de Astyanax intermedius em um riacho de cabeceira de um Parque Estadual de Mata Atlântica. Avaliamos também a influência da chuva, temperatura da água e tamanho do peixe na amplitude e sobreposição de nicho. As amostragens foram realizadas mensalmente ao longo de um ano no riacho Ribeirão Grande, sudeste do Brasil. A dieta consistiu de 31 itens, com igual contribuição de itens alóctones e autóctones. As fêmeas foram maiores do que os machos e os comprimentos médios de primeira maturação foram de 4,44 cm e 3,92 cm, respectivamente. Com base nos 212 pares de ovários analisados, o número de ovócitos por fêmea variou de 538 a 6727 (média = 2688,7). A amplitude e a sobreposição de nicho não foram relacionadas à chuva e temperatura da água, e somente a amplitude de nicho aumentou com o tamanho do peixe, sugerindo que conforme o crescimento, mais itens são incluídos na dieta. Nossos resultados sugerem que A. intermedius apresenta um comportamento típico de espécie oportunista, o que pode explicar a prevalência desta espécie em diversos riachos de cabeceiras isolados de Mata Atlântica onde os recursos alimentares são abundantes e distribuídos ao longo do ano.

As movement is expensive in terms of energy required, mobile animals might have to utilize more energy rich resources than less mobile animals. As mobile animals are possibly more effective foragers we hypothesize a positive correlation between mobility and trophic niche width. We address this link using information on the trophic level of 35 winged, wingless and wing dimorphic species of ground beetles studied on 18 lake islands and at two mainland sites in northern Poland. Trophic analyses using stable isotope values (δ15 N, δ13C) revealed that winged individuals of wing dimorphic species are characterized by broader isotopic niches than wingless individuals. Macropterous species are characterized by depleted δ13C values, which can be interpreted in terms of lipid-rich prey selection. Wing dimorphic species are characterized by higher trophic levels, as inferred from δ15 N values, than winged species. Numbers of islands colonized by particular species were not correlated with δ15 N values, δ13C values or isotopic niche width. Our results point to a relationship between diet and wing morphology in ground beetles.

We examined spatial and environmental effects on the deconstructed assemblages of littoral macroinvertebrates within a large lake. We deconstructed assemblages by three biological trait groups: body size, dispersal mode and oviposition behaviour. We expected that spatial effects on assemblage structuring decrease and environmental effects increase with increasing body size. We also expected stronger environmental filtering and weaker spatial effect on the assemblages of flying species compared with assemblages of non-flying species. Stronger effect of environmental filtering was expected on the assemblages with species attaching eggs compared with assemblages of species with free eggs. We used redundancy analysis with variation partitioning to examine spatial and environmental effects on the deconstructed assemblages. As expected, the importance of environmental filtering increased and that of spatial effects decreased with increasing body size. Opposite to our expectations, assemblages of non-flying species were more affected by environmental conditions compared to assemblages of flying species. Concurring with our expectations, the importance of environmental filtering was higher in structuring assemblages of species attaching eggs than in structuring those with freely laid eggs. The amount of unexplained variation was higher for assemblages with small-sized to medium-sized species, flying species and species with free eggs than those with large-sized species, non-flying species and species with attached eggs. Our observations of decreasing spatial and increasing environmental effects with increasing body size of assemblages deviated from the results of previous studies. These results suggest differing metacommunity dynamics between within-lake and among-lake levels and between studies covering contrasting taxonomic groups and body size ranges. peerReviewed

Mycorrhizal symbiosis is a widespread association between plant roots and mycorrhizal fungi, which is thought to contribute to plant niche differentiation and expansion. However, this has so far not been explicitly tested. To address the effect of mycorrhizal symbiosis on plants’ realized niches, we addressed how mycorrhizal status (i.e. the frequency of occurrence of mycorrhizal symbiosis), flexibility (i.e. the ability to grow both with and without mycorrhizal symbiosis) and type of a plant species affect the realized niche optima, widths and volumes. For this, we used co-occurrence data from the flora of the Netherlands along soil fertility, moisture, pH, salinity, light and temperature gradients. Phylogenetic dependency of the species was taken into account using phylogenetic generalized least squares models. We show that facultatively and flexibly mycorrhizal plants have the widest niches compared to non-mycorrhizal and obligately mycorrhizal, and inflexible plants respectively. Among obligate plant symbionts, ecto- and ericoid mycorrhizal plants exhibited the widest niches compared to plants with other mycorrhizal types. Also, plants with different mycorrhizal statuses and types differed in their realized niche optima. Synthesis. Our results indicate that mycorrhizal symbiosis mediates plant niche differentiation and expansion, facilitating the understanding of current distribution patterns of plant species, as well as predicting shifts in plant distribution and dominance due to environmental changes.

Conditions experienced during the nonbreeding period have profound long‐term effects on individual fitness and survival. Therefore, knowledge of habitat use during the nonbreeding period can provide insights into processes that regulate populations. At the Falkland Islands, the habitat use of South American sea lions (Otaria flavescens) during the nonbreeding period is of particular interest because the population is yet to recover from a catastrophic decline between the mid‐1930s and 1965, and nonbreeding movements are poorly understood. Here, we assessed the habitat use of adult male (n = 13) and juvenile male (n = 6) South American sea lions at the Falkland Islands using satellite tags and stable isotope analysis of vibrissae. Male South American sea lions behaved like central place foragers. Foraging trips were restricted to the Patagonian Shelf and were typically short in distance and duration (127 ± 66 km and 4.1 ± 2.0 days, respectively). Individual male foraging trips were also typically characterized by a high degree of foraging site fidelity. However, the isotopic niche of adult males was smaller than juvenile males, which suggested that adult males were more consistent in their use of foraging habitats and prey over time. Our findings differ from male South American sea lions in Chile and Argentina, which undertake extended movements during the nonbreeding period. Hence, throughout their breeding range, male South American sea lions have diverse movement patterns during the nonbreeding period that intuitively reflects differences in the predictability or accessibility of preferred prey. Our findings challenge the long‐standing notion that South American sea lions undertake a winter migration away from the Falkland Islands. Therefore, impediments to South American sea lion population recovery likely originate locally and conservation measures at a national level are likely to be effective in addressing the decline and the failure of the population to recover.

The vast majority of plants obtain an important proportion of vital resources from soil through mycorrhizal fungi. Generally, this happens in exchange of photosynthetically fixed carbon, but occasionally the interaction is mycoheterotrophic, and plants obtain carbon from mycorrhizal fungi. This process results in an antagonistic interaction between mycoheterotrophic plants and their fungal hosts. Importantly, the fungal‐host diversity available for plants is restricted as mycoheterotrophic interactions often involve narrow lineages of fungal hosts. Unfortunately, little is known whether fungal‐host diversity may be additionally modulated by plant–plant interactions through shared hosts. Yet, this may have important implications for plant competition and coexistence. Here, we use DNA sequencing data to investigate the interaction patterns between mycoheterotrophic plants and arbuscular mycorrhizal fungi. We find no phylogenetic signal on the number of fungal hosts nor on the fungal hosts shared among mycoheterotrophic plants. However, we observe a potential trend toward increased phylogenetic diversity of fungal hosts among mycoheterotrophic plants with increasing overlap in their fungal hosts. While these patterns remain for groups of plants regardless of location, we do find higher levels of overlap and diversity among plants from the same location. These findings suggest that species coexistence cannot be fully understood without attention to the two sides of ecological interactions. Keywords: mycoheterotrophic interactions; mycorrhizal cheaters; niche overlap; niche width; plant coexistence; plant–belowground interactions

International audience; Background: Understanding the processes underlying diversification is a central question in evolutionary biology. For butterflies, access to new host plants provides opportunities for adaptive speciation. On the one hand, locally abundant host species can generate ecologically significant selection pressure. But a diversity of host plant species within the geographic range of each population and/or species might also eliminate any advantage conferred by specialization. This paper focuses on four Melinaea species, which are oligophagous on the family Solanaceae: M. menophilus, M. satevis, M. marsaeus, and finally, M. mothone. We examined both female preference and larval performance on two host plant species that commonly occur in this butterfly's native range, Juanulloa parasitica and Trianaea speciosa, to determine whether the different Melinaea species show evidence of local adaptation. Result: In choice experiments, M. mothone females used both host plants for oviposition, whereas all other species used J. parasitica almost exclusively. In no choice experiment, M. mothone was the only species that readily accepted T. speciosa as a larval host plant. Larval survival was highest on J. parasitica (82.0 % vs. 60.9 %) and development took longer on T. speciosa (14.12 days vs. 13.35 days), except for M. mothone, which did equally well on both host plants. For all species, average pupal weight was highest on J. parasitica (450.66 mg vs. 420.01 mg), although this difference was least apparent in M. mothone. Conclusion: We did not find that coexisting species of Melinaea partition host plant resources as expected if speciation is primarily driven by host plant divergence. Although M. mothone shows evidence of local adaptation to a novel host plant, T. speciosa, which co-occurs, it does not preferentially lay more eggs on or perform better on this host plant than on host plants used by other Melinaea species and not present in its distributional range. It is likely that diversification in this genus is driven by co-occurring Müllerian mimics and the resulting predation pressure, although this is also likely made possible by greater niche diversity as a consequence of plasticity for potential hosts.

P. 17-29 The effects of habitat fragmentation on species may change seasonally mainly due to variations in resource availability and biotic interactions. In critical periods, such as winter, when the importance of intraspecific competition diminish, species may relax their environmental requirements widening their ecological niche to exploit the scarcer trophic resources more efficiently in comparison with spring. Those variations in niche width may implicate seasonal expansions/retractions in species distribution. In this sense, an integrated knowledge on the spatial arrangement of breeding and wintering suitable patches is essential to infer seasonal movements (migratory connectivity). This paper shows that little bustard environmental preferences were more predictable and complex (controlled by a larger number of environmental factors) in spring than in winter, when potential distribution and ecological niche width were slightly larger. In spring, habitat variables (i.e. percentage of dry crops and pasturelands and altitude) ruled species’ distribution; while, winter pattern was driven by mixed criteria, based on both habitat and climate (i.e. percentage of dry crops and wastelands and winter rainfall). Suitable patches were more connected across spatial scales in winter than in spring, i.e. landscape was perceived as less fragmented. The overlap between potential breeding and wintering distribution areas was high. In fact, most of the predicted wintering areas coincided or showed high connectedness with predicted breeding patches. Conversely, there were significant breeding patches that were predicted with low suitability, showing little connectedness with potential winter areas. Spring habitat was a better predictor of little bustard’s wintering range than vice versa, which has clear management implications (preserving breeding sites closer to wintering areas ensures the conservation of a larger proportion of the total distribution range). This is an example of how predictive large-scale modeling procedures can contribute to the optimization of land management aimed at species conservation. SI

1. Food webs and trophic dynamics of coastal systems have been the focus of intense research throughout the world, as they prove to be critical in understanding ecosystem processes and functions. However, very few studies have undertaken a quantitative comparison of entire food webs from a key consumer perspective across a broad geographical area, limiting relevant comparisons among systems with distinct biotic and abiotic components.2. We investigate the structure and functioning of food webs in four tidal ecosystems of international importance for migratory shorebirds along the East Atlantic Flyway: Tejo estuary in Portugal, Sidi Moussa in Morocco, Banc d'Arguin in Mauritania and Bijagós archipelago in Guinea-Bissau. Basal food sources, shorebirds and their prey (benthic invertebrates) were sampled in all areas, and Bayesian stable isotope mixing models and community-wide metrics were used in a comparative analysis among areas.3. Significant differences among study areas were found in the structure of food webs, as well as in the relative importance of basal resource pools supporting each food web. Overall, the food web of Banc d'Arguin was characterized by lower trophic diversity and higher functional redundancy than the other sites. This result might be explained by the low number of trophic pathways of organic matter transfer in this seagrass-dominated system which, as a fossil estuary, lacks inputs from both freshwater and nutrient-rich offshore oceanic waters.4. Structure of shorebird communities was consistent with the main organizational patterns found for each food web, highlighting the less diverse character of the community of Banc d'Arguin. At Banc d'Arguin and Bijagós archipelago, which displayed the smallest and largest isotopic niche widths in bird assemblage, respectively, mean niche overlap among species was low, suggesting high interspecific partitioning in resource use. Tropical systems typically offer comparatively lower harvestable prey biomass for shorebirds and might thus strengthen interspecific competition, leading to low niche overlap among species.5. Our study reveals relevant differences in the structure of food webs and shorebird communities in coastal areas along an avian flyway. While differences in trophic redundancy of food webs point to distinct levels of ecosystem resilience, contrasts in the organization of shorebird communities highlight the plasticity in the foraging behaviour of species inhabiting areas with distinct environmental conditions.

Background Niche theory predicts that human disturbance should influence the assembly of communities, favouring functionally homogeneous communities dominated by few but widespread generalists. The decline and loss of specialists leaves communities with species that are functionally more similar. Evenness of species occupancy declines, such that species become either widespread of rare. These patterns have often been observed, but it is unclear if they are a general result of human disturbance or specific to communities that are rich in species, in complex, spatially heterogeneous environments where the problem has often been investigated. We therefore tested whether human disturbance impacts dominance/evenness of species occupancy in communities, specialism/generalism of species, and functional biotic homogenization in the spatially relatively homogeneous, species poor boreal forest region of Alberta, Canada. We investigated 371 boreal vascular plant communities varying 0 – 100% in proportion of human land use. Results Rank species occupancy curves revealed high species dominance regardless of disturbance: within any disturbance class a few species occupied nearly every site and most species were found in a low proportion of sites. However, species were more widespread and displayed more even occupancy in intermediately disturbed communities than among communities of either low or high disturbance. We defined specialists and generalists based on turnover in co-occupants and thereby assessed impacts of human disturbance on specialization of species and community homogenization. Generalists were not disproportionately found at higher disturbance sites, and did not occupy more sites. Communities with greater human disturbance were not more functionally homogeneous; they did not harbor communities with more generalists. Conclusions We unexpectedly did not observe strong linkages between species specialism/generalism and disturbance, nor between community homogenization and disturbance. These results contrast previous findings in more species rich, complex or spatially heterogeneous systems and ecological models. We suggest that broad occupancy-based intercommunity patterns are insensitive to human land use extent in boreal vascular plants, perhaps because of ubiquity of generalists, low species richness, and history of natural disturbance. The poor sensitivity of these metrics to disturbance presents challenges for monitoring and managing impacts to biodiversity in this region.

International audience; 1. The degree of individual specialization in resource use differs widely among wild populationswhere individuals range from fully generalized to highly specialized. This interindividualvariation has profound implications in many ecological and evolutionary processes. A recentreview proposed four main ecological causes of individual specialization: interspecific andintraspecific competition, ecological opportunity and predation.2. Using the isotopic signature of subsampled whiskers, we investigated to what degree threeof these factors (interspecific and intraspecific competition and ecological opportunity) affectthe population niche width and the level of individual foraging specialization in two fur sealspecies, the Antarctic and subantarctic fur seals (Arctocephalus gazella and Arctocephalustropicalis), over several years.3. Population niche width was greater when the two seal species bred in allopatry (low interspecificcompetition) than in sympatry or when seals bred in high-density stabilized colonies (highintraspecific competition). In agreement with the niche variation hypothesis (NVH), higherpopulation niche width was associated with higher interindividual niche variation. However, incontrast to the NVH, all Antarctic females increased their niche width during the interbreedingperiod when they had potential access to a wider diversity of foraging grounds and associatedprey (high ecological opportunities), suggesting they all dispersed to a similar productive area.4. The degree of individual specialization varied among populations and within the annualcycle. Highest levels of interindividual variation were found in a context of lower interspecificor higher intraspecific competition. Contrasted results were found concerning the effect ofecological opportunity. Depending on seal species, females exhibited either a greater or lowerdegree of individual specialization during the interbreeding period, reflecting species-specificbiological constraints during that period.5. These results suggest a significant impact of ecological interactions on the population nichewidth and degree of individual specialization. Such variation at the individual level may bean important factor in the species plasticity with significant consequences on how it mayrespond to environmental variability.

Resource-partitioning theory explains how, in heavily concentrated populations, specialist organizations arise and proliferate. The theory also addresses the process of market concentration itself, although far less attention has been devoted to the theoretical claims in this area. In this analysis, the theory is used to explain generalist concentration through the distribution of environmental (market) resources. It is argued that the higher the homogeneity and concentration of relevant environmental resources, the higher the concentration of large generalist organizations competing on the basis of scale. Using data on the Dutch daily newspaper industry from 1968 to 1994, statistical analyses show that concentration among generalist (national) newspapers occurs more fully in province-level markets where the readership base consists of relatively homogeneous sets of individuals in terms of age, religion, politics, and education. At the same time, these concentrated markets prove to be fertile areas for the operation of specialist papers, at least when resources are not fully homogenized. The analysis thus provides a more complete model of the resource-partitioning process among organizations in a population.

Specialists and generalists often coexist within a single population, but the biological drivers of individual strategies are not fully resolved. When sexes differ in their foraging strategy, this can lead them to different environmental conditions and stability across their habitat range. As such, sexual segregation, combined with dominance, may lead to varying levels of specialization between the sexes. Here, we examine spatial and temporal niche width (intraindividual variability in aspects of foraging behaviour) of male and female black-browed albatrosses ( Thalassarche melanophrys ), and its consequences for fitness. We show that females, where maximum foraging range is under fluctuating selection, exhibit more variable behaviours and appear more generalist than males, who are under directional selection to forage close to the colony. However within each sex, successful birds had a much narrower niche width across most behaviours, suggesting some specialization is adaptive in both sexes. These results demonstrate that while there are sex differences in niche width, the fitness benefit of specialization in spatial distribution is strong in this wide-ranging seabird.

International audience; Asexuals often occupy broad geographical and ecological ranges. Two models have been proposed to explain the ubiquity of asexuals: the General-Purpose Genotype (GPG) and the Frozen Niche Variation (FNV) model. According to these models, asexuals differ in their ecological niche width and may occupy narrow specialist niches or ubiquitous niches. A thousand water frogs from 37 different populations located in France in different habitats were studied, and two (hemi)clonal hybrid types were identified genetically, Rana esculenta and R. grafi. Altogether, 13 hemiclones were identified both in R. grafi and R. esculenta. Three of these were geographically and ecologically widely distributed, and usually very common in populations. In contrast, the remaining 10 hemiclones had small geographical ranges and were restricted to special habitat types, suggesting ecological niche specialization. The results suggest that in hybridogenetic water frogs GPG and FNV hemiclones coexist.; Les lignées asexuelles occupent souvent de vastes distributions géographiques et écologiques. Deux modèles ont été proposés pour expliquer l'ubiquité des lignées asexuelles: le ≪ General-Purpose Genotype ≫ (GPG) et le ≪ Frozen Niche Variation ≫ (FNV). Ces deux modèles diffèrent dans leur prédiction quant à la largeur de niche occupée par les asexués. Les asexués occuperaient des niches étroites, pour les asexués spécialistes ou bien, des niches larges pour les ubiquistes. Un millier de grenouilles vertes provenant de 37 populations localisées en France dans différents habitats ont été étudiées et 2 types d'hybrides (hémi)clonaux ont été identifiés génétiquement, R. esculenta et R. grafi. Treize hémiclones ont été identifiés parmi ces 2 hybrides dont trois présentaient une vaste distribution géographique et écologique, et étaient commun dans les populations. Au contraire, les 10 autres hémiclones avaient des distributions géographiques localisées, et étaient restreints à certains types d'habitats, occupant des niches plutôt spécialisées. Ces résultats suggèrent la coexistence d'hémiclones FNV et GPG chez les grenouilles vertes hybridogénétiques.

In this thesis I examine the dynamics of crayfish in streams and lakes. I have studied the influence of abiotic and biotic factors on abundance, growth, trophic position, niche breadth, and recruitment of crayfish, by conducting field studies, an outdoor channel experiment and timeseries analysis. Overall, the results show that abundance of crayfish is mostly affected by the abundance of predatory fish, in the absence of predators or at low densities the substrate size influenced crayfish abundance, both for native Koura (Paranephrops planifrons) in New Zealand and the introduced signal crayfish (Pacifastacus leniusculus) in Swedish streams. However, as the native noble crayfish (Astacus astacus) in Swedish streams was not influenced by substrate, this might be species specific due to differences in burrowing capacities. Crayfish abundances fluctuate from year to year and usually crayfish abundance is measured as catch per unit effort (CPUE), since baited traps are used to estimate how many crayfishes there are. By using CPUE data from Lake Bunn, that was inhabited by noble crayfish until 1974 and the introduced signal crayfish from 1982 and forward, I was able to model the population fluctuations observed against temperature data transformed into ecologically relevant parameters. The best model for both species revealed that the temperature during winter months explained most of the observed fluctuations in large adult crayfish. Further, I also found that the fluctuations were density dependent and at high density the CPUE of crayfish decreased in the lake. Crayfish are regarded cannibalistic and it is generally thought that the larger ones consume smaller ones, which may influence the recruitment success for crayfish. However, in the outdoor channel experiment I show that cannibalism was larger between juvenile crayfish and that the presence of large adults increased the survival of juveniles. But, the most important factor for survival and growth in juveniles were attributed to habitat complexity. A habitat of high complexity (i.e. high amount of cobbles) increases the shelter availability for the juveniles and, thus increases the survival- and growth rates of juveniles. In my thesis I also show that growth rate, trophic position, carbon signature and niche breadth are influenced mostly by the biomass of invertebrates. However, it was not all invertebrate groups that were responsible for this pattern. A high biomass of large, sedentary and less mobile invertebrate groups increased growth rate, trophic position and niche breadth of crayfish. These types of invertebrates are probably easier to catch than smaller, faster and free swimming invertebrates and are also commonly found in crayfish guts. The main conclusion from my results is that crayfish dynamics, such as abundance, growth rate, niche breadth and recruitment are affected by specific abiotic and biotic factors in a complex way. The knowledge this thesis has revealed may have great implications for conservation and management purposes. Det finns över 500 kräftarter i världen och vi hittar dem på alla kontinenter utom Antarktis och Arktis. I Sverige finns två arter, den inhemska flodkräftan och den introducerade signalkräftan. Signalkräftan introducerades till stor del för att ersätta förlusten av flodkräfta i många pestdrabbade vatten i södra Sverige. Att det just blev signalkräftan berodde främst på att den liknar vår inhemska flodkräfta, men också för att den ansågs växa fortare och kunde bilda tätare bestånd. I min avhandling har jag visat att detta inte stämmer i naturliga vattendrag. I en jämförelse mellan de båda arterna fann jag att de blev lika stora och bildade lika täta bestånd och att tätheten styrs framförallt av hur mycket rovfisk som finns. Detta gällde även för kräftor på Nya Zeeland där introducering av öring minskat förekomsten av kräftor i många vattendrag. I vattendrag där det fanns lite rovfisk var det andra faktorer som styrde tätheten. Den nyazeeländska kräftan och signalkräftan hade tätast bestånd i vattendrag med stenar runt 10 cm då det fanns lite rovfisk. Medan flodkräftan inte verkar bry sig om vilken storlek stenarna har. Andel sten, vilket påverkar ett habitats komplexitet, var också den mest betydande faktorn för överlevnad och tillväxt hos kräftyngel. Mycket stenar ger ett ökat skydd för de små kräftorna som kan undkomma kannibalism från vuxna men även från andra små kräftor. I mitt experiment visade det sig att kannibalismen mellan små kräftor var större än den mellan stora och små, vilket man inte tidigare trott. Detta berodde till stor del på att de små kräftorna minskade sin aktivitet i närvaro av stora kräftor och att de då stannade i gömslen mer än när de var ensamma. I gömslena fanns tillräckligt med föda för att de små kräftorna skulle kunna äta sig mätta utan att riskera kannibalism från vare sig de stora eller de andra små kräftorna. Detta ökade överlevnaden och tillväxten hos de små kräftorna som hade gott om gömslen trots att stora kräftor var närvarande. Tillväxten hos stora kräftor verkar enligt mina resultat bero på temperatur och tillgång på proteinrik föda som t.ex. mygglarver och andra småkryp som lever i vattendrag och sjöar. Detta stämmer väl med vad som visats i tidigare studier och det är framförallt mängden stora, långsamma och bottenlevande djur som är viktiga som föda för kräftor. Små, snabba och frilevande djur som t.ex. fiskyngel och sötvattensmärla, är svåra för kräftorna att fånga och de bidrar därför inte i någon större utsträckning till kräftornas proteinintag. Sammantaget betyder detta att kräftor försöker äta så mycket smådjur som möjligt eftersom dessa innehåller stor andel protein. Smådjur är dessutom jämförelsevis lättsmälta och innehåller inte några stora mängder kostfiber jämfört med växter. De kräftor som äter mycket småkryp (proteinrik föda) växer snabbare och kan därmed i slutänden få fler yngel. Jag upptäckte att kräftor i vattendrag med en större andel smådjur både växte snabbare och hade en högre position i näringskedjan än de kräftor som levde i vattendrag med lite smådjur. Detta innebär att skillnaderna i kräftors födoval mellan vattendrag, med låg respektive hög andel smådjur, bidrar till att kräftorna antar olika roller i olika vattendrag. I mina studier har jag även funnit att kräftor kan ta upp kol och kväve från olika sorters föda. Kol är en viktig beståndsdel i t.ex. fett och kväve är en viktig beståndsdel i t.ex. protein. Många djur, t.ex. rovfisk, äter bara en typ av föda och får därmed både kol och kväve, eller både fett och protein, från samma födokälla. De är därmed specialisterna som bara äter andra djur och det finns andra specialister, t.ex. sniglar som bara äter alger. I denna avhandling visar jag att detta inte passar in på allätare som kräftor. De äter i stort sett allt och tidigare studier har visat att kräftor verkar må bäst ifall de får en föda bestående av både djur och växter. Detta innebär att allätare som till exempel kräftor kan vara rovdjur om man tittar på proteinkällorna samtidigt som de är vegetarianer om man ser till fettkällorna. Det att kräftor kan vara vegetarianer i vattendrag med liten andel småkryp och rovdjur i vattendrag med stor andel småkryp påverkar de andra organismerna som lever i samma system. Sammantaget kan man säga att denna skillnad gör att det inte går att säga att kräftor har samma roll och påverkan på andra organismer i alla vattendrag. Vidare visar jag också att andel smådjur påverkar kräftornas nischbredd, d.v.s. den typ av miljö och den roll i födokedjan som kräftorna ockuperar i ett vattendrag. I vattendrag med mycket smådjur innehar kräftorna en större nisch än i vattendrag med låg andel småkryp. Även här är det främst andelen stora, långsamma och bottenlevande smådjur som är viktigast. Så man kan säga att om det finns många olika sorters smådjur och ett stort antal av stora, långsamma och bottenlevande smådjur kommer kräftor att växa bra, ha rollen som rovdjur och uppta en bredare nisch i vattendraget. Detta mönster gäller säkert även för sjöar då det tidigare har visat sig att kräftor i näringsrika sjöar växer bättre än i näringsfattiga sjöar och detta främst för att det finns en större mängd smådjur i näringsrika sjöar. I sjön Bunn undersöktes varför antalet kräftor varierar så mycket från år till år med hjälp av fångstdata och temperaturdata från 1946 fram till idag. Med hjälp av en matematisk modell kunde olika faktorer testas för att se om de påverkade skillnaden i fångst från år till år. Det var också möjligt att jämföra den inhemska flodkräftan och den introducerade signalkräftan, då flodkräftan fanns i sjön fram till 1974 och signalkräftan planterades in 1982 och finns där än idag. Det var samma faktorer som var viktigast för de två arterna och det var framförallt vintertemperaturen som var viktig. En varm vinter ökar troligen överlevnaden hos kräftor, vilket gör att fångsten ökar följande sommar. Då alla stora kräftor över 10 cm som fångas tas bort för mänsklig konsumtion varje år hade tätheten också en betydelse för hur många stora kräftor man fick följande år. Detta beror främst på att om man minskar antalet stora kräftor så gynnas tillväxten och överlevnaden hos de mindre kräftorna, eftersom konkurrensen från de stora försvinner. Detta frigör föda och gömslen, vilka jag visat i mina studier är de viktigaste faktorerna för tillväxt och överlevnad hos kräftor. Så, genom att studera kräftor i vattendrag och sjöar kan vi få en bättre förståelse för vad som påverkar kräftor. Detta kan vara av stor betydelse när vi planerar restaureringsåtgärder och gör upp bevarandeplaner inför framtiden. Speciellt om man betänker att under tiden 1946 till 2007 har vintertemperaturen ökat gradvis och fler år har en medeltemperatur över fryspunkten. Detta har säkert redan påverkat kräftorna i sjön Bunn och antagligen ser vi samma mönster på många andra håll i Sverige och i världen. Till en viss gräns kommer kräftorna troligtvis att gynnas av denna temperaturökning, men en vidare ökning kan komma att få negativa konsekvenser. Det är något vi behöver titta närmare på i vår fortsatta forskning om kräftornas liv och leverne.

We argue that combining the insights from both the industrial organization and organizational ecology perspectives is likely to produce value added. We develop a resource-based theory of market structure, where resources pertain to the environmental assets (together forming the resource space) without which a firm cannot operate viably. We propose that the distributive shape of the resource space, together with the presence or absence of exploitation economies, molds market structures in terms of density and concentration. Our theory unifies many unconnected strands of theory in the organization sciences domain.

At its core, this volume tackles the contradictory views of the performance-enhancing effects of organizational flexibility and inertia head on, and in doing so, contributes to the development of theory and empirical evidence at the interface of strategic management and organizational ecology. In addition to the inertia–flexibility nexus, the volume explores a wide range of additional connections between these two perspectives across nine topical areas that both ecological and strategic management researchers have examined: (1) Entrepreneurship, (2) Top Management Teams, (3) Organizational Change, (4) Organizational Learning, (5) Technology Strategy, (6) Competitive Strategy, (7) Cooperative Strategy, (8) Scale and Scope, and (9) Industry Evolution.

Resource-partitioning theory explains how, in heavily concentrated populations, specialist organizations arise and proliferate. The theory also addresses the process of market concentration itself, although far less attention has been devoted to the theoretical claims in this area. In this analysis, the theory is used to explain generalist concentration through the distribution of environmental (market) resources. It is argued that the higher the homogeneity and concentration of relevant environmental resources, the higher the concentration of large generalist organizations competing on the basis of scale. Using data on the Dutch daily newspaper industry from 1968 to 1994, statistical analyses show that concentration among generalist (national) newspapers occurs more fully in province-level markets where the readership base consists of relatively homogeneous sets of individuals in terms of age, religion, politics, and education. At the same time, these concentrated markets prove to be fertile areas for the operation of specialist papers, at least when resources are not fully homogenized. The analysis thus provides a more complete model of the resource-partitioning process among organizations in a population.