The scale-dependent importance of habitat factors and dispersal limitation in structuring Great Lakes shoreline plant communities

Niche-based and neutral models of community structure posit distinct mechanisms underlying patterns in community structure; correlation between species’ distributions and habitat factors points to niche assembly while spatial pattern independent of habitat suggests neutral assembly via dispersal limitation. The challenge is to disentangle the relative contributions when both processes are operating, and to determine the scales at which each is important. We sampled shoreline plant communities on an island in Lake Michigan, varying the extent and the grain of sampling, and used both distance-based correlation methods and variance partitioning to quantify the proportion of the variation in plant species composition that was attributable to habitat factors and to spatial configuration independent of habitat. Our results were highly scale dependent. We found no distance decay of plant community similarity at the island scale (1−33 km). All of the explained variation (32%) in species composition among samples at this scale was attributed to habitat factors. However, at a site intensively sampled at a smaller scale (5−1,200 m), similarity of species composition did decay with distance. Using a coarse sampling grain (transects), habitat factors explained 40% of the variation, but the purely spatial component explained a comparable 22%. Analyzing plots within transects revealed variation in species composition that was still jointly determined by habitat and spatial factors (18 and 11% of the variance, respectively). For both grain sizes, most of the habitat component was spatially structured, reflecting an abrupt alongshore transition from sandy dunes to cobble beach. Space per se explained more variation in species composition at a second site where the habitat transition was more gradual; here, habitat acted as a less selective filter, allowing the signal of dispersal limitation to be detected more readily. We conclude that both adaptation to specific habitat factors and habitat-independent spatial position indicative of dispersal limitation determine plant species composition in this system. Our results support the prediction that dispersal limitation—a potentially, but not necessarily, neutral driver—is relatively more important at smaller scales.     

Contrasting patterns and mechanisms of spatial turnover for native and exotic freshwater fish in Europe

Aim We compare the distribution patterns of native and exotic freshwater fish in Europe, and test whether the same mechanisms (environmental filtering and/or dispersal limitation) govern patterns of decrease in similarity of native and exotic species composition over geographical distance (spatial species turnover). Locations Major river basins of Europe. Methods Data related to geography, habitat diversity, regional climate and species composition of native and exotic freshwater fish were collated for 26 major European river basins. We explored the degree of nestedness in native and exotic species composition, and quantified compositional similarity between river basins according to the beta‐sim (independent of richness gradient) and Jaccard (dependent of richness gradient) indices of similarity. Multiple regression on distance matrices and variation‐partitioning approaches were used to quantify the relative roles of environmental filtering and dispersal limitation in shaping patterns of decreasing compositional similarity over geographical distance. Results Native and exotic species exhibited significant nested patterns of species composition, indicating that differences in fish species composition between river basins are primarily the result of species loss, rather than species replacement. Both native and exotic compositional similarity decreased significantly with increasing geographical distance between river basins. However, gradual changes in species composition with geographical distance were found only for exotic species. In addition, exotic species displayed a higher rate of similarity decay (higher species turnover rate) with geographical distance, compared with native species. Lastly, the majority of explained variation in exotic compositional similarity was uniquely related to geography, whereas native compositional similarity was either uniquely explained by geography or jointly explained by environment and geography. Main conclusions Our study suggests that large‐scale patterns of spatial turnover for exotic freshwater fish in Europe are generated by human‐mediated dispersal limitation, whereas patterns of spatial turnover for native fish result from both dispersal limitation relative to historical events (isolation by mountain ranges, glacial history) and environmental filtering.     

Geography,environment, and spatial turnover of species in China's grasslands

Environment and spatial processes are key factors in shaping species composition in a community. These two factors make competing predictions concerning the decay of species composition similarity with environmental divergence and geographic distance. Unfortunately, these can be difficult to test independently because changes in environment are commonly well correlated with geographic distance. However, an opportunity is provided by exploiting marked regional differences in the spatial structure of the environment. In this study, we test the predictions of environment filtering and dispersal in explaining species turnover using > 300 study sites spanning ?4000 km, across three major grasslands in China in which the environment is spatially structured to different degrees. We find that species composition similarity decayed with environmental divergence in the same way in all three regions, and even across biogeographic regions between which dispersal barriers are evident; in contrast, the decay of species composition similarity with geographic distance depended largely on the spatial structure of the environment. We conclude that, at the scale of study, environmental filtering rather than spatial processes best explains patterns of species turnover in China's grasslands.     

Soil and bark biodiversity forms discrete islands between vineyards that are not affected by distance or management regime

Within geographic regions, the existing data suggest that physical habitat (bark, soil, etc.) is the strongest factor determining agroecosystem microbial community assemblage, followed by geographic location (site), and then management regime (organic, conventional, etc.). The data also suggest community similarities decay with increasing geographic distance. However, integrated hypotheses for these observations have not been developed. We formalized and tested such hypotheses by sequencing 3.8 million bacterial 16S, fungal ITS2 and non-fungal eukaryotic COI barcodes deriving from 108 samples across two habitats (soil and bark) from six vineyards sites under conventional or conservation management. We found both habitat and site significantly affected community assemblage, with habitat the stronger for bacteria only, but there was no effect of management. There was no evidence for community similarity distance–decay within sites within each habitat. While communities significantly differed between vineyard sites, there was no evidence for between site community similarity distance–decay apart from bark bacterial communities, and no correlations with soil and bark pH apart from soil bacterial communities. Thus, within habitats, vineyard sites represent discrete biodiversity islands, and while bacterial, fungal and non-fungal eukaryotic biodiversity mostly differs between sites, the distance by which they are separated does not define how different they are.     

Wind dispersal of alpine plant species: A comparison with lowland species

Question: The prominent role of wind dispersal in alpine habitats has been recognized early but has rarely been quantified. The aim of this study is to compare wind dispersal under alpine and lowland conditions and to analyse whether differences are caused by species traits, e.g. terminal velocity of seeds (V_term) or weather conditions. Location and Methods: We characterized wind dispersal potential of > 1100 Central European species using measured V_term To quantify the habitat effect on wind dispersal, we measured meteorological key‐parameters and simulated dispersal distance spectra of nine selected species under typical alpine conditions (foreland of the Scaletta‐glacier, Switzerland) and typical lowland conditions (grassland in Bad Lippspringe, Germany). Results: Lowland species had higher V_term compared to alpine species. However, this difference is absent when only species of species of open habitats are concerned. The meteorological measurements showed that the alpine habitat was mainly characterized by higher frequency and strength of updrafts. The simulations showed that under alpine conditions long distance dispersal occurred much more frequent. Conclusions: More than 50 % of the alpine species have a fair chance to be dispersed by wind over long distances, while this proportion is less than 25 % for species from open habitats in the lowland. The more prominent role of wind dispersal in alpine habitats is mainly a result of differences in environmental conditions, namely more intense vertical turbulence in the alpine habitat, and does not result from prominent differences in plant traits, namely V_term, between alpine and lowland species.     

Species abundance distributions as a proxy for the niche-neutrality continuum

Aims Species abundance distributions (SADs) are often used to verify mechanistic theories underlying community assembly. However, it is now accepted that SADs alone are not sufficient to reveal biological mechanisms. Recent attention focuses on the relative importance of stochastic dispersal processes versus deterministic processes such as interspecific competition and environmental filtering. Here, we combine a study of the commonness and rarity of species (i.e. the SAD) with mechanistic processes underlying community composition. By comparing the occurrence frequencies of each and every species with its abundance, we quantify the relative contributions of common and rare species to the maintenance of community structure. Essentially, we relate the continuum between commonness and rarity with that of niches and neutrality.Methods An individual-based, spatially explicit model was used to simulate local communities in niche spaces with the same parameters. We generated sets of assemblages from which species were eliminated in opposing sequences: from common to rare and from rare to common, and investigated the relationship between the abundance and frequency of species. We tested the predictions of our model with empirical data from a field experiment in the environmentally homogeneous alpine meadows of the Qinghai–Tibetan plateau.Important findings Our simulations support the widespread notion that common species maintain community structure, while rare species maintain species diversity, in both local and regional communities. Our results, both from theoretical simulations and from empirical observations, revealed positive correlations between the abundance of a particular species and its occurrence frequency. SAD curves describe a continuum between commonness and rarity. Removing species from the 'rare' end of this continuum has little effect on the similarity of communities, but removing species from the 'common' end of the continuum causes significant increases in beta diversity, or species turnover, between communities. In local communities distributed in a homogenous habitat, species located at the 'common' end of the continuum should be selected by environmental filtering, with niche space partitioning governed by interspecific competition. Conversely, species located at the 'rare' end of the continuum are most likely subject to stochastic dispersal processes. Species situated at intermediate locations on this continuum are therefore determined by niche and neutral processes acting together. Our results suggest that, in homogeneous habitats, SAD curves describing the common-rare continuum may also be used to describe the continuum between niches and neutrality.     

Patch dynamics and temporal dispersal partly shape annual plant communities in ephemeral habitat patches

Most organisms in ephemeral habitat patches have resting stages which form a local species pool in response to temporal variations in the patch's availability and suitability. Temporal dispersal from the local species pool may, therefore, be an important process shaping the community assembly, particularly soon after patch creation, and possibly interacting with environmental filtering. As the temporal variation of the environmental conditions has a major effect on the composition of the local species pool, we investigated how well contemporary conditions (both patch availability and patch suitability) and temporal dispersal (approximated by environmental temporal variation and temporal distance) explain the changes in community composition in a given locality through successive ephemeral habitat cycles. We used arable weeds in annual crops as models. We calculated temporal weed community dissimilarity indices between weed communities surveyed in cropping seasons at intervals of two to eight years within a given field. The weeds were surveyed twice each cropping season to account for any changes in the relative contributions of temporal dispersal and contemporary conditions during the season. Patch availability explained most of the temporal weed dissimilarity, suggesting that patch dynamics have the greatest effect on weed community assembly. Temporal distance and temporal variation of the environmental conditions had more effect at the start of the cropping season than later, while patch suitability had more effect in the middle of the season. These results suggest that temporal dispersal drives the weed community assembly when ephemeral habitat patches are created. These assemblies are further shaped by environmental filtering. This is consistent with a temporal source sink dynamic mechanism where the seed bank acts as the main weed source. However, a large part of temporal weed dissimilarity remains unexplained, suggesting that other ecological processes such as spatial dispersal and founder effect may also shape the weed community.     

Metacommunities of spiders in grassland habitat fragments of an agricultural landscape

Arthropod communities in fragmented agricultural landscapes depend on local processes and the interactions between communities in the habitat islands. We aimed to study metacommunity structure of spiders, a group that is known for high dispersal power, local niche partitioning and for engaging in species interactions. While living in fragmented habitats could lead to nestedness, other ecological traits of spiders might equally lead to patterns dominated either by species interactions or habitat filtering. We asked, which community pattern will prevail in a typical agricultural landscape with isolated patches of semi-natural habitats. Such a situation was studied by sampling spiders in 28 grassland locations in a Hungarian agricultural landscape. We used the elements of metacommunity structure (EMS) framework to distinguish between alternative patterns that reveal community organization. The EMS analysis indicated coherent species ranges, high turnover and boundary clumping, suggesting Clementsian community organization. The greatest variation in species composition was explained by local habitat characteristics, indicating habitat filtering. The influence of dispersal could be detected by the significant effect of landscape composition, which was strongest at 500 m. We conclude that dispersal allows spiders to respond coherently to the environment, creating similar communities in similar habitats. Consistent habitat differences, such as species rich versus species poor vegetation, lead to recognisably different, recurrent communities. These characteristics make spiders a predictable and diverse source of natural enemies in agricultural landscapes. Sensitivity to habitat composition at medium distances warns us that landscape homogenization may alter these metacommunity processes.     

Dispersal and genetic structure in the American marten, Martes americana

Natal dispersal in a vagile carnivore, the American marten (Martes americana), was studied by comparing radio-tracking data and microsatellite genetic structure in two populations occupying contrasting habitats. The genetic differentiation determined among groups of individuals using F(ST) indices appeared to be weak in both landscapes, and showed no increase with geographical distance. Genetic structure investigated using pairwise genetic distances between individuals conversely showed a pattern of isolation by distance (IBD), but only in the population occurring in a homogeneous high-quality habitat, therefore showing the advantage of individual-based analyses in detecting within-population processes and local landscape effects. The telemetry study of juveniles revealed a leptokurtic distribution of dispersal distances in both populations, and estimates of the mean squared parent-offspring axial distance (sigma2) inferred both from the genetic pattern of IBD and from the radio-tracking survey showed that most juveniles make little contribution to gene flow.     

Effect of landscape context on fish metacommunity structuring in stream networks

相似文献   

北京不同类型人工林中蛾类群落特征

近年来,绿化造林工程在北京市大规模展开,涉及林地生境类型多样.林地昆虫群落组成和多样性特征受林分树种组成、立地条件、管护方式的影响.通过对北京市5种人工林样地中蛾类群落结构、多样性和相似性及其时空动态特征的调查,探讨了蛾类多样性变化对生境类型的生态响应.结果 表明:共获得标本7046头,隶属于25科269种,以夜蛾科(...     

Decay of similarity of gamasid mite assemblages parasitic on Palaearctic small mammals: geographic distance, host-species composition or environment

Aim The similarity between parasite assemblages should decrease with increasing geographic distance between them, increasing dissimilarity in environmental conditions, and/or increasing dissimilarity of the local host fauna, depending on the dispersal abilities of the parasites and the intimacy of their associations with the host. We tested for a decay in the similarity of gamasid mite assemblages parasitic on small mammals with increasing geographic, ‘environmental’ and ‘host faunal’ (= ‘host’) distances. Location We used data on assemblages of haematophagous gamasid mites (superfamily Dermanyssoidea) parasitic on small mammals (Insectivora, Lagomorpha and Rodentia) from 26 different regions of the northern Palaearctic. Methods Similarity in mite assemblages was investigated at the compound community level across all regions, and at the component community level, across populations of the same host species for each of 11 common host species. Similarity between pairs of mite communities was estimated using both the Jaccard and the Sorensen indices. Environmental distance was estimated as the dissimilarity between locations in a composite measure of climatic variables, and host faunal distance was simply taken as the reciprocal of indices of similarity between the composition of host faunas in different locations. Generalized Linear Models (GLM) and Akaike's Information Criterion were used to select the best model of decay in similarity as a function of geographic, ‘environmental’ and ‘host faunal’ distances. Results Overall, despite slight differences among host species, the similarity in mite assemblages decreased with both increasing ‘environmental’ distance and increasing ‘host faunal’ distance, but was generally unaffected by geographic distance between regions. The similarity of component communities of gamasid mites among host populations was determined mainly by similarity in the physical environment, whereas that of compound communities varied mainly with host‐species composition. Main conclusions Our results indicate that the general decay in community similarity with increasing geographic distances does not apply to assemblages of gamasid mites; it is possible that they can overcome great distances by means of passive dispersal (either by phoresy or wind‐borne), or more likely they occur wherever their hosts are found as a result of tight cospeciation in the past. Mite assemblages on small mammalian hosts seem to be affected mainly by local environmental conditions, and, to a much lesser extent, by the species composition of local host communities.     

Host habitat patchiness and the distance decay of similarity among gastro-intestinal nematode communities in two species of <Emphasis Type="Italic">Mastomys</Emphasis> (southeastern Senegal)

Beta-diversity, or how species composition changes with geographical distance, has seldom been studied for different habitats. We present here quantitative estimates of the relationship between geographic distance and similarity of parasitic nematode communities in two closely related rodent host species that live in habitats with very different spatial configurations. In southeastern Senegal Mastomys natalensis lives exclusively inside human villages whereas M. erythroleucus is continuously distributed outside villages. Both host species and their gastro-intestinal nematodes were sampled on the same spatial scale. Beta-diversity was found to be higher in parasite communities of M. erythroleucus than in those of M. natalensis, and significantly related to geographic distance in this first species. Even on the local spatial scale studied, host dispersal limitation, and stochastic events, may affect species turnover in nematode communities of M. erythroleucus. In M. natalensis, no relationship was found between geographic distance and nematode community similarity, however, suggesting low host dispersal rates between habitat patches. Together with previous population genetic results, this study illustrates the need for different approaches with regard to dispersal in natural populations and its effect on biodiversity.     

Environment, dispersal and patterns of species similarity

Aim The aim of this paper is to evaluate the combined effects of geographical distance and environmental distance on patterns of species similarity (similarity in species composition between sites), and to identify factors affecting the rate of decay in species similarity with each type of distance. Location Israel. Methods Data on species composition of land snails and land birds were recorded in 27 sites of 1 × 1 km scattered across a rainfall gradient in Israel. Matrices of similarity in species composition between all pairs of sites were computed and analysed with respect to corresponding matrices of geographical distance and rainfall distance (defined as the difference in mean annual rainfall between sites, and used as a measure of environmental distance). Mantel tests were applied to determine the correlation between species similarity and each type of distance. Factors affecting the decay in species similarity were investigated by comparing different subsets of the data using randomization tests. Results Both rainfall distance and geographical distance had negative effects on species similarity. The effect of rainfall distance was statistically significant even after controlling for differences in geographical distance, and vice versa. The per‐unit effect of rainfall distance on species similarity decreased with increasing geographical distance, indicating that the two types of distances interacted in determining the similarity in species composition. Snails showed a higher rate of decay in species similarity with geographical distance than birds, and large snails showed a higher rate of decay than small snails, which are better passive dispersers. The per‐unit effects of both rainfall distance and geographical distance on species similarity were higher in the desert region than in the Mediterranean region. Analyses focusing on a grain size of 10 × 10 m showed a lower similarity in species composition and a lower rate of decay in species similarity with rainfall distance than analyses carried out at a grain size of 1 × 1 km. Main conclusions Patterns of similarity in species composition are influenced by the combined effects of environmental variation, the position of the area along environmental gradients, the dispersal properties of the component species, and the scale (both spatial extent and grain size) at which the patterns are examined.     

History,rather than contemporary processes,determines variation in macroinvertebrate diversity in artesian springs: the expansion hypothesis

1. The relative importance of contemporary and historical processes is a fundamental question in understanding patterns of biodiversity. We tested the hypothesis that species‐sorting into different habitats (limnocrenes, rheocrenes, helocrenes), rather than history, would account for the greatest variation in macroinvertebrate diversity in desert artesian springs of The Bonneville Basin, U.S.A. These springs were isolated at the valley scale c. 9000 years ago by aridity and high salinity. Thus, the valley scale will account for the greatest variation in community composition if history and dispersal limitation are important, whereas niche‐based sorting processes will be most important if habitat accounts for the greatest variation in community composition. 2. We identified 302 taxa from 280 sites and used a partial redundancy analysis, additive partitioning and classification strength (CS) to partition the variability in diversity among the springs. The valley scale accounted for more variation in community composition in limnocrene habitats (32.5%) than all other spatial and environmental variables combined. Valleys also accounted for 58% (additive partitioning) and 83% (CS) of the regional variation in diversity in analyses that included all three habitat types. That is, the average community similarity was 25% across the region, but increased to 41% within valleys. By contrast, habitat filtering did not account for significant variation in community composition in any of the analyses. Our study is one of the few suggesting the over‐riding importance of neutral processes in determining patterns of diversity (history and dispersal limitation). 3. The ‘expansion’ hypothesis suggests that the youthful age of a region, combined with slow dispersal by a fauna dominated by generalists, will maximise the imprint of history. These communities appear to exist in a pre‐equilibrial state, where the maximum carrying capacity has not been reached and niche space is plentiful. With time, we predict that local richness will increase while β‐diversity decreases as species expand their distribution across the region. Consequently, the importance of niche‐based processes may increase with time as the imprint of history fades.     

Both traits and phylogenetic history influence community structure in snakes over steep environmental gradients

Assemblages of closely related organisms are generated on axes of deep time diversification, biogeographic processes related to dispersal and habitat filtering, and competition. Using models that account for phylogeny, ecology, and traits, we examine how the interaction among biogeography, habitat filtering, and trait convergence influences community assemblage in Nearctic snakes. With 122 community surveys, environmental niche, trait data including size, diet, parity and habitat preference, and a nearly complete phylogeny of snakes from the United States, we ask 1) do phylogenetic species variability (PSV) and traits change in predictable and correlated ways given ecology and geographic distance, 2) are the measured traits variable within and across communities and how is this related to PSV at local scales, and 3) is there evidence of habitat filtering or trait divergence? Following a general trend of western to eastern North American origin and dispersal of major groups, we similarly show a significant decrease in PSV in this direction but unexpectedly with stable trait variance, showing that traits and phylogenetic variability are disconnected at the community level. We also demonstrate that trait variability and not PSV dominates local communities. Finally, regardless of phylogeny, we show that certain traits, such as reproductive mode (parity) frequency, change within communities in response to steep ecological gradients.     

Univariate Community Assembly Analysis (UniCAA): Combining hierarchical models with null models to test the influence of spatially restricted dispersal,environmental filtering,and stochasticity on community assembly

Identifying the influence of stochastic processes and of deterministic processes, such as dispersal of individuals of different species and trait‐based environmental filtering, has long been a challenge in studies of community assembly. Here, we present the Univariate Community Assembly Analysis (UniCAA) and test its ability to address three hypotheses: species occurrences within communities are (a) limited by spatially restricted dispersal; (b) environmentally filtered; or (c) the outcome of stochasticity—so that as community size decreases—species that are common outside a local community have a disproportionately higher probability of occurrence than rare species. The comparison with a null model allows assessing if the influence of each of the three processes differs from what one would expect under a purely stochastic distribution of species. We tested the framework by simulating “empirical” metacommunities under 15 scenarios that differed with respect to the strengths of spatially restricted dispersal (restricted vs. not restricted); habitat isolation (low, intermediate, and high immigration rates); and environmental filtering (strong, intermediate, and no filtering). Through these tests, we found that UniCAA rarely produced false positives for the influence of the three processes, yielding a type‐I error rate ≤5%. The type‐II error rate, that is, production of false negatives, was also acceptable and within the typical cutoff (20%). We demonstrate that the UniCAA provides a flexible framework for retrieving the processes behind community assembly and propose avenues for future developments of the framework.     

Avian host composition,local speciation and dispersal drive the regional assembly of avian malaria parasites in South American birds

Identifying the ecological factors that shape parasite distributions remains a central goal in disease ecology. These factors include dispersal capability, environmental filters and geographic distance. Using 520 haemosporidian parasite genetic lineages recovered from 7,534 birds sampled across tropical and temperate South America, we tested (a) the latitudinal diversity gradient hypothesis and (b) the distance–decay relationship (decreasing proportion of shared species between communities with increasing geographic distance) for this host–parasite system. We then inferred the biogeographic processes influencing the diversity and distributions of this cosmopolitan group of parasites across South America. We found support for a latitudinal gradient in diversity for avian haemosporidian parasites, potentially mediated through higher avian host diversity towards the equator. Parasite similarity was correlated with climate similarity, geographic distance and host composition. Local diversification in Amazonian lineages followed by dispersal was the most frequent biogeographic events reconstructed for haemosporidian parasites. Combining macroecological patterns and biogeographic processes, our study reveals that haemosporidian parasites are capable of circumventing geographic barriers and dispersing across biomes, although constrained by environmental filtering. The contemporary diversity and distributions of haemosporidian parasites are mainly driven by historical (speciation) and ecological (dispersal) processes, whereas the parasite community assembly is largely governed by host composition and to a lesser extent by environmental conditions.     

Floristic patterns and plant traits of Mediterranean communities in fragmented habitats

Aim To contrast floristic spatial patterns and the importance of habitat fragmentation in two plant communities (grassland and scrubland) in the context of ecological succession. We ask whether plant assemblages are affected by habitat fragmentation and, if so, at what spatial scale? Does the relative importance of the niche differentiation and dispersal‐limitation mechanisms change throughout secondary succession? Is the dispersal‐limitation mechanism related to plant functional traits? Location A Mediterranean region, the massif of Albera (Spain). Methods Using a SPOT satellite image to describe the landscape, we tested the effect of habitat fragmentation on species composition, determining the spatial scale of the assemblage response. We then assessed the relative importance of dispersal‐related factors (habitat fragmentation and geographical distance) and environmental constraints (climate‐related variables) influencing species similarity. We tested the association between dispersal‐related factors and plant traits (dispersal mode and life form). Results In both community types, plant composition was partially affected by the surrounding vegetation. In scrublands, animal‐dispersed and woody plants were abundant in landscapes dominated by closed forests, whereas wind‐dispersed annual herbs were poorly represented in those landscapes. Scrubby assemblages were more dependent on geographical distance, habitat fragmentation and climate conditions (temperature, rainfall and solar radiation); grasslands were described only by habitat fragmentation and rainfall. Plant traits did not explain variation in spatial structuring of assemblages. Main conclusions Plant establishment in early Mediterranean communities may be driven primarily by migration from neighbouring established communities, whereas the importance of habitat specialization and community drift increases over time. Plant life forms and dispersal modes did not explain the spatial variation of species distribution, but species richness within the community with differing plant traits was affected by habitat patchiness.     

Phylogenetic and functional diversity area relationships in two temperate forests

Phylogenetic diversity (PD, the diversity of lineages) and functional diversity (FD, the diversity of functional traits or groups in a biological community) reflect important yet poorly understood attributes of species assemblages. Until recently, few studies have examined the spatial variation of PD and FD in natural communities. Yet the relationships between PD and FD and area (termed PDAR and FDAR), like the analogous species–area relationship (SAR), have received less attention and may provide insights into the mechanisms that shape the composition and dynamics of ecological communities. In this study, we used four spatial point process models to evaluate the likely roles of the random placement of species, habitat filtering, dispersal limitation, and the combined effects of habitat filtering and dispersal limitation in producing observed PDARs and FDARs in two large, fully mapped temperate forest research plots in northeast China and in north‐central USA. We found that the dispersal limitation hypothesis provided a good approximation of the accumulation of PD and FD with increasing area, as it did for the species area curves. PDAR and FDAR patterns were highly correlated with the SAR. We interpret this as evidence that species interactions, which are often influenced by phylogenetic and functional similarity, may be relatively unimportant in structuring temperate forest tree assemblages at this scale. However, the scale‐dependent departures of the PDAR and FDAR that emerged for the dispersal limitation hypothesis agree with operation of competitive exclusion at small scales and habitat filtering at larger scales. Our analysis illustrates how emergent community patterns in fully mapped temperate forest plots can be influenced by multiple underlying processes at different spatial scales.