Ecomorphological pattern in Bermuda birds: The influence of competition and implications for nature preserves

Summary Previous ecomorphological studies of introduced land birds on oceanic islands have revealed several patterns consistent with the hypothesis that interspecific competition influenced the assembly process of that community. We extend one of these analyses to Bermuda, which differs from the previous islands in its size, latitude and isolation from the mainland. We tested for the presence of morphological overdispersion in surviving introduced passeriforms. Despite a possible predominance of random events in the assembly process due to Bermuda's small size and the presence of migrant species, the surviving passeriforms were morphologically overdispersed. The presence of this pattern supports the hypothesis that the assembly of the Bermuda passeriform community has been influenced by interspecific competition. This marks the third distinct community of island land birds in which this competitive pattern has been identified. This is particularly interesting because certain attributes of Bermuda and its avifauna make it more equivalent to communities in mainland refuges than avian assemblages on islands studied previously. This suggests that interspecific competition may have important effects on the structure of refuge communities.     

Patterns in the assembly of an island plant community

Aim  To test for patterns in the assembly of an island plant community.
Location  Islands off the west coast of Vancouver Island, British Columbia, Canada.
Methods  Twenty-seven islands were visited by boat, and the abundance of six woody angiosperm species was quantified. Null models were then used to test whether: (1) some species co-occur less than expected by chance (i.e. co-occurrence assembly rule), (2) the incidence and abundance of some species are inversely related to the abundance of other species (i.e. incidence assembly rule), and (3) support for assembly rules precludes evidence for nestedness, which refers to a pattern in species composition in which the species present on depauperate islands form regular subsets of those occurring on progressively more diverse islands.
Results  Most species co-occurred with other species at frequencies expected by chance. However, one species ( Sambucus racemosa ) co-occurred with other species less frequently than randomized expectations. The observed incidence and abundance patterns of most species were also consistent with randomized patterns. However, the incidence and abundance of S. racemosa declined with the abundance of other plant species. Weak, variable support was found for nestedness of the total plant community. However, stronger, consistent support was found after removing S. racemosa from the matrix prior to analyses.
Main conclusions  Most species were assembled on islands in a manner consistent with randomized expectations. However, non-random distributional patterns were observed in one species whose distribution was consistent with the hypothesis that competition limits the assembly of island communities.     

Testing multiple assembly rule models in avian communities on islands of an inundated lake,Zhejiang Province,China

Aim A fundamental question in community ecology is whether general assembly rules determine the structure of natural communities. Although many types of assembly rules have been described, including Diamond’s assembly rules, constant body‐size ratios, favoured states, and nestedness, few studies have tested multiple assembly rule models simultaneously. Therefore, little is known about the relative importance of potential underlying factors such as interspecific competition, inter‐guild competition, selective extinction and habitat nestedness in structuring community composition. Here, we test the above four assembly rule models and examine the causal basis for the observed patterns using bird data collected on islands of an inundated lake. Location Thousand Island Lake, China. Methods  We collected data on presence–absence matrices, body size and functional groups for bird assemblages on 42 islands from 2007 to 2009. To test the above four assembly rule models, we used null model analyses to compare observed species co‐occurrence patterns, body‐size distributions and functional group distributions with randomly generated assemblages. To ensure that the results were not biased by the inclusion of species with extremely different ecologies, we conducted separate analyses for the entire assemblage and for various subset matrices classified according to foraging guilds. Results The bird assemblages did not support predictions by several competitively structured assembly rule models, including Diamond’s assembly rules, constant body‐size ratios, and favoured states. In contrast, bird assemblages were highly significantly nested and were apparently shaped by extinction processes mediated through area effects and habitat nestedness. The nestedness of bird assemblages was not a result of passive sampling or selective colonization. These results were very consistent, regardless of whether the entire assemblage or the subset matrices were analysed. Main conclusions Our results suggest that bird assemblages were shaped by extinction processes mediated through area effects and habitat nestedness, rather than by interspecific or inter‐guild competition. From a conservation point of view, our results indicate that we should protect both the largest islands with the most species‐rich communities and habitat‐rich islands in order to maximize the number of species preserved.     

Tree diversity on islands: assembly rules,passive sampling and the theory of island biogeography

Aim Species diversity is distributed heterogeneously through space, for reasons that are poorly understood. We tested three hypotheses to account for spatial variation in coniferous tree species diversity in a temperate island archipelago. The theory of island biogeography (ToIB) predicts that island area affects species diversity both directly (by increasing habitat diversity) and indirectly (by increasing abundances, which in turn reduce extinction rates). The ToIB also predicts that island isolation directly affects species diversity by reducing immigration rates. The passive sampling hypothesis predicts that island area and isolation both affect species diversity indirectly, by increasing and decreasing abundances, respectively. Community assembly rules (i.e. even partitioning of conifer abundances among islands) might also reduce tree species diversity beyond the core predictions of ToIB and the passive sampling hypothesis. Location Barkley Sound, British Columbia, Canada. Methods The abundances of eight coniferous tree species were quantified on 34 islands and two (1 ha) mainland plots. The predictions of the ToIB and the passive sampling hypothesis were tested using path analysis, and null models were used to test for abundance‐based assembly rules and to further test the passive sampling hypothesis. Results Path analysis showed that island area and isolation did not have direct, statistical effects on tree species diversity. Instead, both geographic variables had direct statistical effects on total tree abundances, which in turn predicted tree diversity. Results from several passive sampling null models were correlated with observed patterns in species diversity, but they consistently overestimated the number of tree species inhabiting most islands. A different suite of null models showed support for community assembly rules, or that tree species often reached higher abundances on islands that housed fewer heterospecific trees. Main conclusions Results were inconsistent with the ToIB. Instead, patterns in tree diversity were best explained by a combination of stochastic (passive sampling) and deterministic (assembly rules) processes. Stochastic and deterministic processes are commonly considered to be exclusive explanations for island community structure, but results from this study suggest that they can work synergistically to structure island tree communities.     

Phylogenetic diversity and community assembly in a naturally fragmented system

We sought to assess effects of fragmentation and quantify the contribution of ecological processes to community assembly by measuring species richness, phylogenetic, and phenotypic diversity of species found in local and regional plant communities. Specifically, our fragmented system is Craters of the Moon National Monument and Preserve, Idaho, USA. CRMO is characterized by vegetated islands, kipukas, that are isolated in a matrix of lava. We used floristic surveys of vascular plants in 19 kipukas to create a local species list to compare traditional dispersion metrics, mean pairwise distance, and mean nearest taxon distance (MPD and MNTD), to a regional species list with phenotypic and phylogenetic data. We combined phylogenetic and functional trait data in a novel machine‐learning model selection approach, Community Assembly Model Inference (CAMI), to infer probability associated with different models of community assembly given the data. Finally, we used linear regression to explore whether the geography of kipukas explained estimated support for community assembly models. Using traditional metrics of MPD and MNTD neutral processes received the most support when comparing kipuka species to regional species. Individually no kipukas showed significant support for overdispersion. Rather, five kipukas showed significant support for phylogenetic clustering using MPD and two kipukas using MNTD. Using CAMI, we inferred neutral and filtering models structured the kipuka plant community for our trait of interest. Finally, we found as species richness in kipukas increases, model support for competition decreases and lower elevation kipukas show more support for habitat filtering models. While traditional phylogenetic community approaches suggest neutral assembly dynamics, recently developed approaches utilizing machine learning and model choice revealed joint influences of assembly processes to form the kipuka plant communities. Understanding ecological processes at play in naturally fragmented systems will aid in guiding our understanding of how fragmentation impacts future changes in landscapes.     

放牧干扰梯度下川西亚高山植物群落的组合机理

为了阐明放牧干扰对川西亚高山区域植物群落的组合过程以及群落结构的影响, 研究了放牧干扰梯度下的功能群均匀度和群落谱系结构的变化趋势。结果显示: 在干扰较轻的阔叶林与针叶林样地, 部分样方的功能群均匀度显著高于无效模型, 随着干扰梯度的增强, 功能群均匀度呈线性下降, 样方平均值从0.930降至0.840, 其高于无效模型的次数也逐渐降低, 干扰程度较大的草甸中出现部分样方的功能群均匀度显著低于无效模型。随着干扰程度的增强, 群落的谱系结构指数也呈逐渐上升趋势, 净关联指数平均值由-0.634逐渐增加至2.360, 邻近类群指数由-0.158上升至2.179。草甸与低矮灌丛受干扰较为严重, 其大部分样方的谱系结构指数显著高于随机群落, 表明干扰群落的谱系结构呈聚集分布。功能群均匀度与谱系结构的变化趋势一致, 表明生境筛滤效应与种间竞争作用的平衡决定着群落的组合过程。干扰降低了竞争作用, 促进了少数耐干扰功能群的优势地位, 造成功能群均匀度下降, 同时通过生境筛滤作用, 使群落的谱系结构呈现出聚集分布; 而未干扰的群落中由于竞争作用的效应, 功能群均匀度较高, 谱系结构也更加分散。研究区域植物群落的功能群均匀度与物种丰富度呈负相关, 表明物种间特别是相似物种间的竞争限制了群落的物种多样性。研究结果说明, 生态位分化和物种间的相互竞争在物种共存与群落组合中具有重要作用。     

The importance of species pool size for community composition

We investigated if an increase in species pool size leads to more pronounced turnover in local communities and assessed if this increase relates to stronger competition for environmental niches or to more random placement of species. We compared compositional turnover of pteridophytes (ferns and lycophytes) at 15 sites in mountain ecosystems on 13 islands in southeast Asia and Melanesia that mainly differed in the size of their species pool. Each site was sampled with 16 plots of 20 × 20 m². Using multiple regression on distance matrices, we investigated the relationship between environmental distance and compositional turnover at different spatial extents within sites with different species pool sizes. Additionally, we tested the hypothesis that the intensity of competition increases with increasing species pool size. This was done by assessing how realized niche overlap and unevenness of communities relate to environmental distance and species pool size. With increasing species pool size, there was an increase in: a) proportional turnover in community composition, b) the importance of environmental distance for explaining turnover in community composition and c) a decrease in environmental niche overlap between species indicating an increasing importance of competition for community composition. Our results support the idea that increasing species pool size increases the competition for available environmental niches, and thereby leads to a tighter connection between environmental factors and community composition.     

Species richness and structure of ant communities in a dynamic archipelago: effects of island area and age

Aim To assess how ant species richness and structure of ant communities are influenced by island age (disturbance history) in a dynamic archipelago. Location Cabra Corral dam, Salta Province, north‐west Argentina (25°08′ S, 65°20′ W). Methods Ant species richness on remaining fragments (islands) of a flooded forest was determined, as well as island area, isolation and age. Simple linear regressions were performed to assess relationships between ant species richness and those insular variables. Furthermore, a stepwise multiple linear regression analysis was conducted in order to determine the relative influence of each insular variable on ant species richness. Islands were categorized in two age classes (old and young) and co‐occurrence analyses were applied within each class to evaluate changes in community structure because of interspecific competition. Results Simple regression analyses indicated a moderate, positive effect of island area on ant species richness. Weak, marginally non‐significant relationships were found between ant species richness and both island isolation and island age, showing the tendency for there to be a decrease in ant species richness with island isolation and that ant species richness might be higher in old islands. The multiple regression analysis indicated that island isolation and age had no significant effects on the number of ant species, island area being the only independent variable retained in the analysis. On the contrary, whereas a random pattern of species co‐occurrence was found on young islands, ant communities in old islands showed a significantly negative pattern of species co‐occurrence, suggesting that the effect of competition on community structure was stronger on older islands than on younger islands. Main conclusions Island area was the most important variable explaining ant species richness on the islands of Cabra Corral dam. However, both island isolation and island age (or disturbance history) might also contribute to shape the observed community patterns. The present study also shows that island age significantly affects the strength with which interspecific interactions structure ant communities on islands.     

What is the role of predation on stability of natural communities? A theoretical investigation.

A basic question in ecology concerns the role of species interaction on dynamics of natural communities. In this framework, ecologists have considered predation, competition, mutualism, the three most important interactions, highlighting their specific effects on distribution and abundance of species, providing knowledge about phenomena like coexistence and extinction. This paper seeks to identify the effects of predation on stability of natural communities by mathematical models. Simple multispecies community models, organized in trophic levels, are analyzed by means of a qualitative technique, loop analysis, combined with a computer calculation procedure. Results do not support the hypothesis of predation as a stabilizing factor. Rather, the outcomes of the analysis suggest that predation may or may not stabilize a community. This depends on the predator's behaviour and on the network of the community.     

Isolation‐driven functional assembly of plant communities on islands

The physical and biotic environment is often considered the primary driver of functional variation in plant communities. Here, we examine the hypothesis that spatial isolation may also be an important driver of functional variation in plant communities where disturbance and dispersal limitation may prevent species from occupying all suitable habitats. To test this hypothesis, we surveyed the vascular plant composition of 30 islands in the Gulf of Maine, USA, and used available functional trait and growth form data to quantify the functional composition of these islands. We categorized species based on dispersal mode and used a landscape metric of isolation to assess the potential role of dispersal limitation as a mechanism of isolation‐driven assembly. We tested for island and species level effects on functional composition using a hierarchical Bayesian framework to better assess the causal link between isolation and functional variation. Growth form composition and the community mean value of functional traits related to growth rate, stress tolerance, and nutrient use varied significantly with island isolation. Functional traits and growth forms were significantly associated with dispersal mode, and spatial isolation was the strongest driver of primary trait variation, while island properties associated with environmental drivers in our system were not strong predictors of trait variation. Despite the species‐level association of dispersal mode and functional traits, dispersal mode only accounted for a small proportion of the overall isolation effect on community‐level trait variation. Our study suggests that spatial isolation can be a key driver of functional assembly in plant communities on islands, though the role of particular dispersal processes remains unclear.     

Fungal-Fungal Associations Affect the Assembly of Endophyte Communities in Maize (Zea mays)

Many factors can affect the assembly of communities, ranging from species pools to habitat effects to interspecific interactions. In microbial communities, the predominant focus has been on the well-touted ability of microbes to disperse and the environment acting as a selective filter to determine which species are present. In this study, we investigated the role of biotic interactions (e.g., competition, facilitation) in fungal endophyte community assembly by examining endophyte species co-occurrences within communities using null models. We used recombinant inbred lines (genotypes) of maize (Zea mays) to examine community assembly at multiple habitat levels, at the individual plant and host genotype levels. Both culture-dependent and culture-independent approaches were used to assess endophyte communities. Communities were analyzed using the complete fungal operational taxonomic unit (OTU) dataset or only the dominant (most abundant) OTUs in order to ascertain whether species co-occurrences were different for dominant members compared to when all members were included. In the culture-dependent approach, we found that for both datasets, OTUs co-occurred on maize genotypes more frequently than expected under the null model of random species co-occurrences. In the culture-independent approach, we found that OTUs negatively co-occurred at the individual plant level but were not significantly different from random at the genotype level for either the dominant or complete datasets. Our results showed that interspecific interactions can affect endophyte community assembly, but the effects can be complex and depend on host habitat level. To our knowledge, this is the first study to examine endophyte community assembly in the same host species at multiple habitat levels. Understanding the processes and mechanisms that shape microbial communities will provide important insights into microbial community structure and the maintenance of microbial biodiversity.     

Competition and introduction regime shape exotic bird communities in Hawaii

Complex combinations of historical and local-regional processes determine the assembly of ecological communities. We investigated such processes in the Hawaiian introduced avifauna, comprising 140 years of historical records of invasions and extinctions of birds. Here the particular introduction regime (i.e., colonization attempts and number of introduced species) and priority effects constitute the historical (and regional) component, and competition is the local component. These processes are theoretically supported by means of a Lotka–Volterra model of species competition, finding that changes in the specific introduction regime might result in different extinction dynamics. Both field data and model outcomes support the biotic resistance hypothesis, so that the invasibility of new incomers decrease with species richness. Finally, we found that the resistance to new invaders depends on the particular introduction regime. Thus, community assembly models built to predict the success of exotic species should consider more scenarios than random introduction regimes.     

Interspecific Interactions between Primates,Birds, Bats,and Squirrels May Affect Community Composition on Borneo

For several decades, primatologists have been interested in understanding how sympatric primate species are able to coexist. Most of our understanding of primate community ecology derives from the assumption that these animals interact predominantly with other primates. In this study, we investigate to what extent multiple community assembly hypotheses consistent with this assumption are supported when tested with communities of primates in isolation versus with communities of primates, birds, bats, and squirrels together. We focus on vertebrate communities on the island of Borneo, where we examine the determinants of presence or absence of species, and how these communities are structured. We test for checkerboard distributions, guild proportionality, and Fox's assembly rule for favored states, and predict that statistical signals reflecting interactions between ecologically similar species will be stronger when nonprimate taxa are included in analyses. We found strong support for checkerboard distributions in several communities, particularly when taxonomic groups were combined, and after controlling for habitat effects. We found evidence of guild proportionality in some communities, but did not find significant support for Fox's assembly rule in any of the communities examined. These results demonstrate the presence of vertebrate community structure that is ecologically determined rather than randomly generated, which is a finding consistent with the interpretation that interactions within and between these taxonomic groups may have shaped species composition in these communities. This research highlights the importance of considering the broader vertebrate communities with which primates co‐occur, and so we urge primatologists to explicitly consider nonprimate taxa in the study of primate ecology. Am. J. Primatol. 75:170‐185, 2013. © 2012 Wiley Periodicals, Inc.     

Phylogeny and co‐occurrence of mammal species on Southeast Asian islands

Aim Islands have often been used as model systems in community ecology. The incorporation of information on phylogenetic relatedness of species in studies of island assemblage structure is still uncommon, but could provide valuable insights into the processes of island community assembly. We propose six models of island community assembly that make different predictions about the associations between co‐occurrences of species pairs on islands, phylogenetic relatedness and ecological similarity. We then test these models using data on mammals of Southeast Asian islands. Location Two hundred and forty islands of the Sundaland region of Southeast Asia. Methods We quantified the co‐occurrence of species pairs on islands, and identified pairs that co‐occur more frequently (positive co‐occurrence) or less frequently (negative co‐occurrence) than expected under null models. We then examined the distributions of these significantly deviating pairs with respect to phylogenetic relatedness and ecological differentiation, and compared these patterns with those predicted by the six community assembly models. We used permutation regression to test whether co‐occurrence patterns are predicted by relatedness, body size difference or difference in diet quality. Separate co‐occurrence matrices were analysed in this way for seven mammal families and four smaller subsets of the islands of Sundaland. Results In many matrices, average numbers of negative co‐occurrences were higher than expected under null models. This is consistent with assemblage structuring by competition, but may also result from low geographic overlap of species pairs, which contributes to negative co‐occurrences at the archipelago‐wide level. Distributions of species pairs within plots of phylogenetic distance × ecological differentiation were consistent with competition, habitat filtering or within‐island speciation models, depending on the taxon. Regressions indicated that co‐occurrence was more likely among closely related species pairs within the Viverridae and Sciuridae, but in most matrices phylogenetic distance was unrelated to co‐occurrence. Main conclusions Simple deterministic models linking co‐occurrence with phylogeny and ecology are a useful framework for interpreting distributions and assemblage structure of island species. However, island assemblages in Sundaland have probably been shaped by a complex idiosyncratic set of interacting ecological and evolutionary processes, limiting the predictive power of such models.     

Functional trait assembly through ecological and evolutionary time

A classic community assembly hypothesis is that all guilds must be represented before additional species from any given guild enter the community. We conceptually extend this hypothesis to continuous functional traits, refine the hypothesis with an eco-evolutionary model of interaction network community assembly, and compare the resultant continuous trait assembly rule to empirical data. Our extension of the “guild assembly rule” to continuous functional traits was rejected, in part, because the eco-evolutionary model predicted trait assembly to be characterized by the expansion of trait space and trait/species sorting within trait space. Hence, the guild rule may not be broadly applicable. A “revised” assembly rule did, however, emerge from the eco-evolutionary model: as communities assemble, the range in trait values will increase to a maximum and then remain relatively constant irrespective of further changes in species richness. This rule makes the corollary prediction that the trait range will, on average, be a saturating function of species richness. To determine if the assembly rule is at work in natural communities, we compared this corollary prediction to empirical data. Consistent with our assembly rule, trait “space” (broadly defined) commonly saturates with species richness. Our assembly rule may thus represent a general constraint placed on community assembly. In addition, taxonomic scale similarly influences the predicted and empirically observed relationship between trait “space” and richness. Empirical support for the model’s predictions suggests that studying continuous functional traits in the context of eco-evolutionary models is a powerful approach for elucidating general processes of community assembly.     

Patterns of bird invasion are consistent with environmental filtering

Predicting invasion potential has global significance for managing ecosystems as well as important theoretical implications for understanding community assembly. Phylogenetic relationships of introduced species to the extant community may be predictive of establishment success because of the opposing forces of competition/shared enemies (which should limit invasions by close relatives) versus environmental filtering (which should allow invasions by close relatives). We examine here the association between establishment success of introduced birds and their phylogenetic relatedness to the extant avifauna within three highly invaded regions (Florida, New Zealand, and Hawaii). Published information on both successful and failed introductions, as well as native species, was compiled for all three regions. We created a phylogeny for each avifauna including all native and introduced bird species. From the estimated branch lengths on these phylogenies, we calculated multiple measurements of relatedness between each introduced species and the extant avifauna. We used generalized linear models to test for an association between relatedness and establishment success. We found that close relatedness to the extant avifauna was significantly associated with increased establishment success for exotic birds both at the regional (Florida, Hawaii, New Zealand) and sub‐regional (islands within Hawaii) levels. Our results suggest that habitat filtering may be more important than interspecific competition in avian communities assembled under high rates of anthropogenic species introductions. This work also supports the utility of community phylogenetic methods in the study of vertebrate invasions.     

Overdispersion of body size in Australian desert lizard communities at local scales only: no evidence for the Narcissus effect

Both local and regional processes may contribute to community diversity and structure at local scales. Although many studies have investigated patterns of local or regional community structure, few have addressed the extent to which local community structure influences patterns within regional species pools. Here we investigate the role of body size in community assembly at local and regional scales in Ctenotus lizards from arid Australia. Ctenotus has long been noted for its exceptional species diversity in the Australian arid-zone, and previous studies have attempted to elucidate the processes underlying species coexistence within communities of these lizards. However, no consensus has emerged on the role of interspecific competition in the assembly and maintenance of Ctenotus communities. We studied Ctenotus communities at several hundred sites in the arid interior of Australia to test the hypothesis that body sizes within local and regional Ctenotus assemblages should be overdispersed relative to null models of community assembly, and we explored the relationship between body size dispersion at local and regional scales. Results indicate a striking pattern of community-wide overdispersion of body size at local scales, as measured by the variance in size ratios among co-occurring species. However, we find no evidence for body size overdispersion within regional species pools, suggesting a lack of correspondence between processes influencing the distribution of species phenotypes at local and regional scales. We suggest that size ratio constancy in Ctenotus communities may have resulted from contemporary ecological interactions among species or ecological character displacement, and we discuss alternative explanations for the observed patterns. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Plant radiation history affects community assembly: evidence from the New Zealand alpine

The hypothesis that early plant radiations on islands dampen diversification and reduce habitat occupancy of later radiations via niche pre-emption has never, to our knowledge, been tested. We investigated clade-level dynamics in plant radiations in the alpine zone, New Zealand. Our aim was to determine whether radiations from older colonizations influenced diversification and community dominance of species from later colonizations within a common bioclimatic zone over the past ca 10 Myr. We used stem ages derived from the phylogenies of 17 genera represented in alpine plant communities in the Murchison Mountains, Fiordland, and assessed their presence and cover in 262 (5 × 5 m) vegetation plots. Our results show clear age-related community assembly effects, whereby congenerics from older colonizing genera co-occur more frequently and with greater cover per unit area than those from younger colonizing genera. However, we find no evidence of increased species richness with age of colonization in the alpine zone. The data support priority effects via niche pre-emption among plant radiations influencing community assembly.     

Phylogenetic relatedness of co‐occurring waterbird communities: a test of Darwin's competition‐relatedness hypothesis

The competition–relatedness hypothesis of Darwin states that competition is greater among species that are phylogenetically closely‐related, and such species will tend to appear in separate communities (i.e. the species within communities will be phylogenetically overdispersed). Many studies have tested (and mainly refuted) this hypothesis for plant and bacterial communities. Results for the few studies with avian species are not conclusive. We tested Darwin's hypothesis for waterbirds using a set of open, artificial fish ponds in Doñana, south‐western Spain, that provide relatively homogeneous habitat where competition is likely to be intense. Monthly counts of 38 ponds (for 11 months, i.e. 418 censuses) recorded 76 bird species. Darwin's hypothesis predicted that species appearing in the same pond would be less related phylogenetically than expected if species occurred randomly across ponds and months according to the structure of the overall community across the entire pond complex. However, the waterbird community did not show a predominantly overdispersed pattern, suggesting that interspecific competition among phylogenetically related species was not the main force structuring communities. In contrast, the proportion of clustered communities was higher than expected throughout the annual cycle, indicating that related waterbirds tend to co‐occur on the same site, probably because they have similar microhabitat preferences. Clustering patterns were mainly driven by abundant and closely related duck species, and also by shorebirds. However, few individual pond communities remained significantly different from random after correction for multiple testing. Furthermore, the probability of co‐occurrence of a given species pair was negatively related to the phylogenetic distance between them. In conclusion, our study shows waterbird communities are mainly phylogenetically clustered or random, and do not support the competition‐relatedness hypothesis.     

Native versus exotic community patterns across three scales: Roles of competition,environment and incomplete invasion

Three fundamental, interrelated questions in invasion ecology are: (1) to what extent do exotic species outcompete natives; (2) are native and exotic communities functionally similar or different; and (3) are differences in biogeographic patterns in native and exotic communities due to incomplete invasions among exotics? These questions are analogous to general questions in community ecology regarding the relative roles of competition, environmental response and dispersal limitation in community assembly. We addressed each of these questions for plant communities in discrete meadow patches, using analyses at three scales ranging from the landscape to microsites. A weak positive relationship between native and exotic species richness in microsites, and a predominance of positive correlations in abundance among native and exotic species pairs suggest that competition has been less important than other factors in determining native versus exotic abundance and community composition. In contrast, models of species richness and community compositional change across scales suggest native versus exotic community patterns are largely determined by a mix of scale-dependent concordant (shared positive or negative) and discordant relationships with environmental variables. In addition, detailed analyses of species-area and species-abundance relationships suggest ongoing expansion of exotic species populations, indicating that the assembly of the exotic community is in its early stages. Thus, while competition does not appear to strongly affect native versus exotic abundances and compositions at present, it may intensify in the future. Our results indicate that synoptic patterns in native versus exotic richness that have been previously attributed to a single cause may in fact be due to a complex mix of concordant and discordant responses to environmental factors across scales. They also suggest that conservation efforts aimed at promoting natives and reducing exotics should focus on the factors and scales for which such a response (i.e., promotion of high native and low exotic richness) can be expected.