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Population size is a crucial parameter for both ecological research and conservation planning. When individuals are aggregated, estimating the size of a population through sampling raises methodological challenges, as the high variance between sampling units leads to imprecise estimates. Choosing the right sample design depending on the population aggregation level could improve the precision of estimates; however, this is difficult because studies comparing sample designs for aggregated populations have been limited to a few populations and sampling designs, so their results cannot be generalised.To address this gap, we combined simulations of spatial point populations and field counts of three plant species to compare the relative precision of estimates between three sampling methods: simple random sampling (SRS), systematic sampling (SYS) and spatially balanced sampling (SBS). Comparisons were performed on density and aggregation gradients for a range of sample sizes.Our simulations showed that SYS and SBS were always more precise than SRS when individuals were aggregated, reducing sampling variance up to 80% and 60%. The highest precision for estimating population size was always obtained when the average distance between sampling units equalled the diameter of the clusters (i.e. the groups of individuals). The difference in precision was similar for the natural populations, with sampling variance lowered by up to 75% (SYS) and 60% (SBS) compared to SRS.These findings lead us to recommend using SYS or SBS rather than SRS to estimate population size when individuals are spatially aggregated, as these consistently provide more precise estimates. Assessing cluster diameters in the field enables a quick assessment of the potential gain in precision to expect, and thus the best choice of sampling method depending on the trade‐off between precision and field constraints. [ABSTRACT FROM AUTHOR]

In this paper, a mathematical model is applied to investigate the effect of density of allelochemicals on plant population involving delay. The model is constructed using a system of nonlinear delay differential equations. In the model, there are three state variables: plant populations (P1 & P2) and density of allelochemical (T). It is assumed that in the presence of density of allelochemicals, plant populations are affected. It further delays the conversion of resource into the density of allelochemicals and hence affects the plant population adversely. This effect is observed by using delay in the competition model. Equilibrium points are calculated. Using the Routh–Hurwitz theorem, certain explicit formulations defining the stability and path of the Hopf‐bifurcation periodic solutions at the positive equilibrium are obtained. Further, the direction of these bifurcating periodic solutions is also studied. Numerical simulation and graphical support are provided for analytical findings using MATLAB. [ABSTRACT FROM AUTHOR]

Occupancy models have been underused in multispecies plant studies. We evaluated the effectiveness of occupancy models to document impacts of management on grassland plant species populations in a pilot study. The study was designed to answer three questions: (1) From a list of 44 plant species, how many will have sufficient frequency to be analyzed? (2) Within a single site, which factor (sampling year or unit) influences occupancy and detection of each plant species? (3) How does the number of plots and visits affect the number of species with sufficient frequency for analysis? In 2012 and 2013, occupancy and detection probabilities of 44 plant species were assessed using permanently marked plots on two different grassland sites. Within each site, a fire and grazing managed unit and a burn‐only control unit were used to test the efficacy of occupancy modeling for multiple plant species and study design. Four of the 44 species had sufficiently high known presence (π) on both sites and years to be analyzed. There was little evidence to support that occupancy was different between years, despite very different weather patterns. There was support that occupancy was different in the burned and grazed unit compared with the control for Rhus copallinum L. Detection was highest (≥0.8) for R. copallinum, while the other species analyzed varied. In 2012, eight species had sufficient π for analysis. In 2013, 12 species had sufficient π for analysis. Occupancy models can be useful for investigating multiple plant species; however, a priori investigation of species' distribution is necessary to ensure species can be analyzed. Detection of plants was never 1, and therefore, detection should continue to be incorporated in plant population models, regardless of modeling technique. [ABSTRACT FROM AUTHOR]

In‐row plant densities have not been studied for common beans with type II growth habit and contrasting reactions to white mould. Advanced breeding lines with partial resistance or susceptibility to white mould were combined with 4, 7, 10 or 13 plants m−1 and with or without fungicide at a constant between‐row spacing of 0.5 m in five sprinkler‐irrigated field trials conducted during the autumn–winter season in Brazil. White mould pressures in the trials covered the whole range from zero to moderate/high (46–60% of white mould severity index). In all trials, means of white mould incidence, severity and yield did not vary significantly between 7 and 13 plants m−1 for the partially resistant line, regardless of the fungicide levels. For the susceptible line, 13 plants m−1 increased white mould incidence and severity under moderate disease, regardless of the fungicide levels, and decreased yield compared with 10 plants m−1 when fungicide was applied twice under moderate/high disease pressure. For the susceptible line, 7 or 10 plants m−1 maximized yield in all trials, with or without fungicide applications. The results suggest that the current recommendation of 11–13 plants m−1 could be used for type II beans with partial resistance to white mould in either a conventional or organic system. For susceptible genotypes, 7–10 plants m−1 seems to be the most appropriate in‐row plant density. This study may improve the recommendation of in‐row plant density for type II beans cultivated under white mould pressure. [ABSTRACT FROM AUTHOR]

Large animal species, which provide important ecological functions such as dispersal of seeds or top–down control of seed predators, are very vulnerable in fragmented forests, being unable to survive in small fragments, and facing increasing hunting pressure. The loss of large animals affects two main ecological processes crucial for the tree reproductive cycle: seed dispersal of large seeds (e.g. provided by tapirs) and control of seed predator population (e.g. provided by large cats). The changes in both processes are expected to increase seed mortality since seeds are not dispersed away from conspecifics (causing increased pre‐dispersal mortality due to negative density dependent effects) and/or face increased predation after a dispersal event (post‐dispersal mortality). Although an extensive body of empirical knowledge exists on seed predation, the link between seed loss and adult tree community composition and structure is not well established, as well as the temporal scale seed changes affect adults. Using an individual‐based forest model (FORMIND), we evaluate the long‐term consequences of increased pre and post‐dispersal seed mortality on the future forest biomass retention of a Brazilian northeastern Atlantic forest. Our results show that forest biomass is significantly affected after 80–93% pre‐dispersal loss of large seeds, or post‐dispersal predation densities of 20–25 predators per parent tree. Large‐seeded tree species are at increased risk of local extinction causing up to 26.2% loss of forest biomass when both pre and post‐dispersal processes are combined. However, these changes can last up to 100 years after the occurrence of defaunation. In summary we conclude that large animal loss has the potential to reduce future forest biomass and tree species‐richness by impacting seed survival, and should be considered in the planning of biodiversity friendly landscapes as well as in calculations of the global carbon budget. [ABSTRACT FROM AUTHOR]

In plant–arthropod associations, the first herbivores to colonise a plant may directly or indirectly affect community assembly on that particular plant. Whether the order of arrival of different arthropod species further modulates community assembly and affects plant fitness remains unclear. Using wild Brassica oleracea plants in the field, we manipulated the order of arrival of early‐season herbivores that belong to different feeding guilds, namely the aphid Brevicoryne brassicae and caterpillars of Plutella xylostella. We investigated the effect of herbivore identity and order of arrival on community assembly on two B. oleracea plant populations during two growth seasons. For this perennial plant, we evaluated whether foliar herbivory also affected herbivore communities on the flowers and if these interactions affected plant seed production. Aphid infestation caused an increase in parasitoid abundance, but caterpillars modulated these effects, depending on the order of herbivore infestation and plant population. In the second growth season, when plants flowered, the order of infestation of leaves with aphids and caterpillars more strongly affected abundance of herbivores feeding on the flowers than those feeding on leaves. Infestation with caterpillars followed by aphids caused an increase in flower‐feeding herbivores compared to the reversed order of infestation in one plant population, whereas the opposite effects were observed for the other plant population. The impact on plant seed set in the first reproductive year was limited. Our work shows that the identity and arrival order of early season herbivores may have long‐term consequences for community composition on individual plants and that these patterns may vary among plant populations. We discuss how these community processes may affect plant fitness and speculate on the implications for evolution of plant defences. [ABSTRACT FROM AUTHOR]

Questions The order of plant species arrival can affect recruitment and subsequent plant community development via priority effects, but is often overlooked. Priority effects occur when early-colonizing plant species affect the establishment of later-arriving species, and are hypothesized to depend on species identity and habitat conditions. In riparian ecosystems on the banks of rivers, a strong moisture gradient induces a zonation of plant species with different degrees of adaptation to soil moisture. Further, riparian zones receive seeds during floods and later in the season via wind dispersal. As such, we questioned if recruitment in riparian zones is primarily affected by (1) environmental conditions (i.e. soil moisture), (2) arrival order, and (3) species identity, or an interaction between these factors. Location Riparian zones of tributaries in the Vindel River catchment, northern Sweden. Method We designed a controlled greenhouse experiment and a large-scale field experiment where we sowed five plant species representing different dispersal events and habitat moisture preferences. We sowed seeds in three arrival order treatments (all species simultaneously, species group A phased 3 wk before group B, and vice versa) and under different soil moisture treatments in the greenhouse (dry, dry-after-wet and wet) and under a range of moisture conditions in the field. Results We found strong priority effects as early-arriving species grew bigger and often produced higher seedling densities compared to later-arriving species, both in the greenhouse and after two growing seasons in the field. Priority effects in the greenhouse were strongest in the dry and dry-after-wet treatments and weaker under wet conditions. Consistent but weaker patterns were observed in the field after the first growing season. The relative abundance of species in plant communities assembled without phased arrival interacted with soil moisture and species identity. Priority effects were strongest for species with a low relative abundance (i.e. less competitive species). Conclusions Our findings that priority effects influenced recruitment and interacted with soil moisture suggest that priority effects should be considered when addressing riparian vegetation changes after shifts in flooding regimes. This is especially important because floods will not only affect habitat conditions, but also the phasing of seed arrival. [ABSTRACT FROM AUTHOR]

Accelerating rates of biodiversity loss may result in a rapid decline in important ecosystem processes such as carbon capture. Whether extirpation-resistant species compensate for the decline in ecosystem processes associated with the loss of extirpation-prone species is poorly understood., We apply a novel approach to answer this question using an assemblage of salt marsh plants. First, manipulations were performed to simulate a realistic sequence of species loss, based on observed sensitivity to disturbance. Then, changes in biomass and primary production of extirpation-resistant species were monitored over three consecutive growing seasons., Extirpation-resistant species did not compensate for the loss of either biomass or primary production associated with the removal of extirpation-prone species., Factors that determine the potential for compensation within ecosystems are discussed. These include resource-regulated compensation rates, the level of functional redundancy within an assemblage and the extirpation resistance of species which possess good compensation traits., Synthesis. These results suggest that we cannot assume extirpation-resistant species will compensate for the decline in ecosystem processes associated with biodiversity loss across all ecosystems. Understanding those factors that influence the ability of ecosystems to compensate for declines in ecosystem processes associated with biodiversity loss constitutes a significant challenge. [ABSTRACT FROM AUTHOR]

In humid savannas, the transition from juvenile to mature tree sizes is thought to be a major demographic bottleneck because smaller plants are topkilled by frequent fires. Species with the highest net rates of sapling growth should dominate the tree component of savannas by reaching fire-proof sizes, 'escape size', more rapidly than competitors. However, tests of this prediction have failed to explain eucalypt dominance in Australian savannas as eucalypt mean growth rates are low. We tested the escape hypothesis directly by recording the number and identity of tagged individuals reaching escape size in a long-term study. Results were consistent with the escape hypothesis with greater than six times more eucalypts reaching escape height than non-eucalypts in frequently burnt savannas. The pattern was reversed where fires were excluded for 5 years, with more non-eucalypts emerging than eucalypts. We conclude that mean growth rates alone are a poor predictor of the rates at which juvenile savanna trees transition to mature tree size. Only the fastest growing individuals make the transition to mature trees whereas mean values include many suppressed individuals. Measures of maximum growth rates will provide more robust estimators of demographically important effects on mature tree cover. The mechanistic basis for the remarkable ability of juvenile eucalypts to escape frequent fires is not yet understood. [ABSTRACT FROM AUTHOR]

Plant-plant interactions are known to vary with changing environmental conditions; however, we have little empirical knowledge of the impact of abrupt environmental changes on millennial scale plant-plant interaction outcomes for long-lived plant species. Here, we used palaeoecological data (13-7.6 k years ) and a novel statistical modelling approach to determine the impact of multiple environmental drivers on predicted tree-grass population interaction outcomes from our study site in eastern England. Changes from high to low herbivore density shortly preceded changes to low fire levels and a shift to warmer summers. These transitions occurred during a period of increasing nitrogen (N) availability. Shortly thereafter, there was a shift in landscape dominance from grasses to oaks and then a change to decreasing N availability. Model predictions of tree-grass interaction outcomes varied over time with respect to all environmental changes. During the time of high disturbances and cool summers, grasses were predicted to out-compete oaks. After climate warming and the loss of regular disturbances, the predicted outcome was stable coexistence. However, changes in the N cycle corresponded with different predicted outcomes: unstable competition under increasing N availability and facilitation of oaks by grasses when N availability was declining. Akaike Information Criterion weights indicate that climate warming and fewer fires were consistent with the best-fitting model of oak-grass interactions for the entire time series (i.e. competitive exclusion to stable coexistence). However, reconciling the conflicting model predictions with the observed population dynamics suggests that a temporary period of unstable competition preceded the predicted shift to stable coexistence. This dynamic behaviour is consistent with known patterns of shifts between alternative stable states. Synthesis. We show that abrupt changes in environmental conditions over time lead to similarly abrupt changes in tree-grass interaction outcomes, which were shown to vary in contrasting directions with respect to resource versus non-resource variables. The approach described here allows plant ecologists to test hypotheses of plant-plant interactions over successional time scales for long-lived species and thus can lead to new knowledge about the structural role of these interactions in community dynamics. [ABSTRACT FROM AUTHOR]

Insect infestation, soil moisture, and yield were examined in populations of ≈ 33 140 plants/ha (low) and ≈ 40 340 plants/ha (high) of an oilseed sunflower, Helianthus annuus L, cv.‘Triumph 660CL’with two levels of weediness. Less weedy plots resulted from the application of herbicide combination of S-metolachlor and sulfentrazone, whereas more weedy plots resulted from application of sulfentrazone alone. Among the 12 weed species recorded, neither plant numbers nor biomass differed between crop plant densities. Larvae of the stalk-boring insects Cylindrocopturus adspersus (Coleoptera: Curculionidae) and Mordellistena sp. (Coleoptera: Mordellidae) were less abundant in high density sunflowers, ostensibly due to reduced plant size. However, the same effect was not observed for Dectes texanus (Coleoptera: Cerambycidae) or Pelochrista womanana (Lepidoptera: Tortricidae), two other stalk-boring insects. Soil moisture was highest in low density and lowest in the high density sunflowers that were less weedy. Stalk circumference, head diameter, and seed weight were reduced for sunflower plants with short interplant distances (mean = 20 cm apart) compared to plants with long interplant distances (mean = 46 cm apart). These three variables were greater in less weedy plots compared with more weedy plots and positively correlated with interplant distance. Yields on a per-hectare basis paralleled those on a per-plant basis but were not different among treatments. The agronomic implications of planting density are discussed in the context of weed and insect management. [ABSTRACT FROM AUTHOR]

Subapical ears are largely responsible for grain yield variations in prolific maize ( Zea mays L.) grown under conditions favourable for the expression of prolificacy trait, but limited information exists on yield components contributing to yield responses. A field experiment was conducted to determine the yield components of apical and subapical ear in prolific maize after various pollination treatments at two plant populations. Hybrid Pioneer 3733 was grown in the perfect stands of 71 428 and 35 714 plants ha−1. Three pollination treatments were carried out: (i) free pollination; (ii) subapical earshoots were covered to prevent pollination; and (iii) apical earshoots were covered to prevent pollination. Grain yields of free pollinated plants were by 50.1 % larger at low plant population (265 g per plant) than at high plant population (177 g per plant) due to a 45.3 % increase in kernels per plant, whereas 1000-kernel weight slightly increased by 3.3 %. These increased kernels per plant at low plant population were, in part, the result of kernel increments on apical ear (10.1 %), and mainly associated with kernels from subapical ears that did not occur at high plant population. At low plant population, the total grain yield per plant was reduced by 94 g (35.5 %) after the apical ear was bagged to prevent pollination, but only 52 g (19.6 %) when the subapical ear was bagged. When subapical ear development was stopped at low plant population, grain yield on apical ears increased by only 3.9 % as a result of heavier 1000-kernel weights, clearly demonstrating limitations in kernel set and size. After grain development on apical ear was prevented, subapical ear enlarged to 80.3 % of maximum apical ear yield because the former had, on average, 2.5 % lighter 1000-kernel weight and 17.5 % fewer kernels than the latter. Ears did not differ in row number when only apical or subapical ear was developed on plant, whereas subapical ears tended to have fewer rows than apical ears when both were present on the same plant. Our results showed that: (i) plant population affected all yield components on both apical and subapical ear except row number; (ii) the occurrence of subapical ear is triggered by achieving maximum potential kernel set on apical ear; and (iii) subapical ear is inferior in potential grain yield to apical one even when the latter was prevented from pollination. [ABSTRACT FROM AUTHOR]

In alpine environments, flowering phenology can differ within local populations even at the same elevation. We assessed the effects of differences in flowering phenology due to snowmelt timing caused by local geographic heterogeneity on the genetic structure of a population of an alpine plant,Erythronium grandiflorumPursh. We established a study plot of 250×70 m at 3,340 m above sea level in the Front Range of the Rocky Mountains, CO, USA. The flowering phenology was considerably influenced by snowmelt timing due to local geographic heterogeneity. Twenty-two patches ofE. grandiflorumwere recognized in the study plot and were classified into three phenological groups: early, middle, and late. To express the differentiation of flowering phenology among the patches, we defined phenological distance and analyzed the relationship between genetic and phenological distances. Additionally, since genetic distance is expected to co-vary with geographic distance, we also analyzed the relationship between genetic distance and geographic distance among patches. The results revealed not only that isolation by distance was present among patches, but also that the differences in snowmelt timing gave rise to phenologically distant patches ofE. grandiflorum, which in turn determine the genetic structure caused by the limited pollen flow between patches. [ABSTRACT FROM AUTHOR]

To study the effect of global warming concomitant with rising CO2 on plant growth under field-like conditions, a CO2–temperature gradient chamber (CTGC) was created from a standard temperature gradient chamber (TGC). Despite great daily and seasonal changes in ambient air temperature, the gradient of air temperatures was simulated by 5°C warmed conditions at the air outlet, rising at a rate of 1°C at 5 m intervals. Also, CO2 concentrations were linearly increased from the air inlet to the outlet; those at the air inlet and 25 m distance from the air inlet were 372 p.p.m and 756 p.p.m. (doubled), respectively. The CTGC proved successful in biological experiments conducted through a full growth season in 1998. This apparatus will be useful for understanding plant response to simultaneous changes in CO2 and temperature. Being a combination of a TGC and a CO2 gradient chamber, the improved CTGC allows parameters and validation data sets to both be obtained for models contributing to plant growth, species composition, and global carbon flux analysis. [ABSTRACT FROM AUTHOR]

Intercropping of chilli (Capsicum annuum) and dwarf bean (Phaseolus vulgaris) is a recently adopted practice by farmers in Sri Lanka. As chilli fetches a higher market price, the bean population which could be incorporated into a 100% population of chilli has to be found. In the present experiment, effects of three bean populations (100, 75 and 50% of sole crop population 250000 pi ha-1) and four row arrangements (1:1, 1:2, 2:1 and 2:2) were tested at Kundasale, Sri Lanka. The land equivalent ratio (LER) of all intercrops were significantly greater than one, indicating a greater productivity per unit land area in intercropping than sole cropping. At 100% and 75% bean populations, LER and intercrop yields of bean were significantly greater than at 50%. Row arrangement did not have a significant effect on either LER or bean yield in intercrops. Intercrop bean yields were lower than sole bean yields indicating significant competition from chilli. Chilli yields were not affected by either bean population or row arrangement. Intercrop chilli yields were greater than the sole chilli yield indicating significant positive effects from bean. Greater radiation interception and lower weed growth and the absence of overlap between yield formation periods of the two component crops were probably responsible for the greater productivity (LER) of intercrops. [ABSTRACT FROM AUTHOR]

Introduction of genetic monogerm seed and the advancement of agricultural techniques raised the possibility of eliminating costly thinning operations in sugar beet farming. However, this requires high and uniform seedling emergence to provide prerequisite plant populations in the field. This work investigated the minimum levels of seedling emergence for non-thinned sugar beet farming. The experiment was carried out in a loamy soil to investigate the effects of three levels of emergence (60, 50 and 35%) and two intra-row spacings (8 and 15cm) with or without thinning using seed source of graded viability of cv Eva in 1992 and 1993 under field conditions in Eastern Anatolia. Plant population throughout the growing period was monitored and data were taken of yield and quality parameters. On average, 60, 50 and 35% emergence levels were achieved using seed source of 90, 72 and 54% viability range, which resulted in different levels of plant stands depending on intra-row spacing and thinning, Plant density at harvest ranged between 49 500 and 124 500 ha-1 on average depending on initial establishment, intra-row spacing and thinning. Root yield and sugar yield were the highest at plant stands between 90000 and 100000 ha-1, below or above of which declined. Impurity contents (e.g. Na, K and a-amino N contents) and extractable sugar content decreased but sugar content and clear juice purity enhanced as plant stands at harvest increased. [ABSTRACT FROM AUTHOR]

Fodder sorghum (M. P. Chari) was grown at varying populations to examine its influence on light interception, leaf area index and biomass production. DMY, CGR and IPAR depending on LAI reached maximum at LAI 5 of 150 000 plants ha-1 stand and thus yielded higher biomass. Therefore, physiological potential of fodder sorghum crop was found to be maximum at a population density of 150 000 plants ha-1. Further increases in population developed mutual shading and adversely affected the crop growth rate and dry matter accumulation. Significant linear relationships of dry matter yield with IPAR, plant population densities, LAI and CGR clearly indicate the interdependence of these characters. [ABSTRACT FROM AUTHOR]

This historical data set consists of 44 permanent 1-m2 quadrats located on northern mixed prairie in Miles City, Montana, USA. Individual plants in these quadrats were identified and mapped annually from 1932 through 1945. Quadrats were located in six pastures assigned to cattle grazing treatments with light, moderate, and heavy stocking rates of 1.24, 0.92, and 0.76 ha/animal-unit-month (two pastures in each). These data provide unique opportunities to test the interactive effects of grazing and climate variables on demographic rates, plant-plant interactions, and population and community dynamics. We provide the following data and data formats: (1) the digitized maps in shapefile format; (2) a tabular version of the entire data set [a table that replaces the full spatial data with one (x, y) coordinate for each individual perennial plant record]; (3) grazing treatment information; (4) an inventory of the years each quadrat was sampled; (5) a species list, containing information on plant growth forms and shapefile geometry type (e.g., points or polygons); (6) a record of changes in species names; (7) daily precipitation and temperature records; and (8) counts of annual plants in the quadrats (annuals were counted, not mapped, by the original mappers). [ABSTRACT FROM AUTHOR]

An abstract of the article "Mapped quadrats in sagebrush steppe: long-term data for analyzing demographic rates and plant-plant interactions," by Luke Zachmann, Corey Moffet, and Peter Adler is presented.