Phylogenetic community structure in Minnesota oak savanna is influenced by spatial extent and environmental variation

The relative importance of environmental filtering, biotic interactions and neutral processes in community assembly remains an openly debated question and one that is increasingly addressed using phylogenetic approaches. Closely related species may occur together more frequently than expected (phylogenetic clustering) if environmental filtering operates on traits with significant phylogenetic signal. Recent studies show that phylogenetic clustering tends to increase with spatial scale, presumably because greater environmental variation is encompassed at larger spatial scales, providing opportunities for species to sort across environmental gradients. However, if environmental filtering is the cause of species sorting along environmental gradients, then environmental variation rather than spatial scale per se should drive the processes governing community assembly. Using species abundance and light availability data from a long‐term experiment in Minnesota oak savanna understory communities, we explicitly test the hypothesis that greater environmental variation results in greater phylogenetic clustering when spatial scale is held constant. Concordant with previous studies, we found that phylogenetic community structure varied with spatial extent. At the landscape scale (~1000 ha), communities were phylogenetically clustered. At the local scale (0.375ha), phylogenetic community structure varied among plots. As hypothesized, plots encompassing the greatest environmental variation in light availability exhibited the strongest phylogenetic clustering. We also found strong correlations between species functional traits, particularly specific leaf area (SLA) and perimeter per area (PA), and species light availability niche. There was also a phylogenetic signal in both functional traits and species light availability niche, providing a mechanistic explanation for phylogenetic clustering in relation to light availability. We conclude that the pattern of increased phylogenetic clustering with increased environmental variation is a consequence of environmental filtering acting on phylogenetically conserved functional traits. These results indicate that the importance of environmental filtering in community assembly depends not on spatial scale per se, but on the steepness of the environmental gradient.     

Phylogenetic and morphological relationships between nonvolant small mammals reveal assembly processes at different spatial scales

The relative roles of historical processes, environmental filtering, and ecological interactions in the organization of species assemblages vary depending on the spatial scale. We evaluated the phylogenetic and morphological relationships between species and individuals (i.e., inter‐ and intraspecific variability) of Neotropical nonvolant small mammals coexisting in grassland‐forest ecotones, in landscapes and in regions, that is, three different scales. We used a phylogenetic tree to infer evolutionary relationships, and morphological traits as indicators of performance and niche similarities between species and individuals. Subsequently, we applied phylogenetic and morphologic indexes of diversity and distance between species to evaluate small mammal assemblage structures on the three scales. The results indicated a repulsion pattern near forest edges, showing that phylogenetically similar species coexisted less often than expected by chance. The strategies for niche differentiation might explain the phylogenetic repulsion observed at the edge. Phylogenetic and morphological clustering in the grassland and at the forest interior indicated the coexistence of closely related and ecologically similar species and individuals. Coexistence patterns were similar whether species‐trait values or individual values were used. At the landscape and regional scales, assemblages showed a predominant pattern of phylogenetic and morphological clustering. Environmental filters influenced the coexistence patterns at three scales, showing the importance of phylogenetically conserved ecological tolerances in enabling taxa co‐occurrence. Evidence of phylogenetic repulsion in one region indicated that other processes beyond environmental filtering are important for community assembly at broad scales. Finally, ecological interactions and environmental filtering seemed important at the local scale, while environmental filtering and historical colonization seemed important for community assembly at broader scales.     

Filtering across Spatial Scales: Phylogeny,Biogeography and Community Structure in Bumble Bees

Despite the expansion of phylogenetic community analysis to understand community assembly, few studies have used these methods on mobile organisms and it has been suggested the local scales that are typically considered may be too small to represent the community as perceived by organisms with high mobility. Mobility is believed to allow species to mediate competitive interactions quickly and thus highly mobile species may appear randomly assembled in local communities. At larger scales, however, biogeographical processes could cause communities to be either phylogenetically clustered or even. Using phylogenetic community analysis we examined patterns of relatedness and trait similarity in communities of bumble bees (Bombus) across spatial scales comparing: local communities to regional pools, regional communities to continental pools and the continental community to a global species pool. Species composition and data on tongue lengths, a key foraging trait, were used to test patterns of relatedness and trait similarity across scales. Although expected to exhibit limiting similarity, local communities were clustered both phenotypically and phylogenetically. Larger spatial scales were also found to have more phylogenetic clustering but less trait clustering. While patterns of relatedness in mobile species have previously been suggested to exhibit less structure in local communities and to be less clustered than immobile species, we suggest that mobility may actually allow communities to have more similar species that can simply limit direct competition through mobility.     

Functional and phylogenetic structure of forest and savanna bird assemblages across spatial scales

Ecological and evolutionary mechanisms that drive community assembly vary in space and time. However, little is known about how such mechanisms act in contrasting habitats. Here, we estimated the functional and phylogenetic structure of forest and savanna bird assemblages across different spatial scales to understand: 1) the mechanisms that govern the structure of assemblages in these habitats; 2) the relationship between phylogenetic and functional structure; and 3) the influence of species richness on the functional and phylogenetic structure of assemblages. We used a null model where forest and savanna bird species were allowed to occur in the same null assemblages and other where species were separated based on their habitats. According to the first null model, forest bird assemblages were functionally and phylogenetically clustered at all spatial scales, whereas savanna bird assemblages generally showed random functional and phylogenetic structure. These results can be explained by the low dispersal rate of forest species across of the patchy habitats and the widespread distribution of savanna species. However, in the second null model, both forest and savanna bird assemblages showed random functional and phylogenetic structure at regional and local scales. This suggests that trait‐based assembly might not play an important role in both habitats and across different spatial scales. In addition, the phylogenetic and functional structure of assemblages were not correlated, evidencing that caution is necessary when using phylogenetic relationships as a surrogate to functional distances among species. Finally, the relationships between species richness and functional and phylogenetic structure indicated that an increase in the number of species can promote both clustering and overdispersion, depending on the studied habitat and scale. Our study shows that integrating different types of habitat, spatial scales and biodiversity components in a single framework can shed light on the mechanisms that determine the community assembly.     

Dissecting spatiotemporal patterns of functional diversity through the lens of Darwin's naturalization conundrum

Darwin's naturalization conundrum describes the paradigm that community assembly is regulated by two opposing processes, environmental filtering and competitive interactions, which predict both similarity and distinctiveness of species to be important for establishment. Our goal is to use long‐term, large‐scale, and high‐resolution temporal data to examine diversity patterns over time and assess whether environmental filtering or competition plays a larger role in regulating community assembly processes. We evaluated Darwin's naturalization conundrum and how functional diversity has changed in the Laurentian Great Lakes fish community from 1870 to 2010, which has experienced frequent introductions of non‐native species and extirpations of native species. We analyzed how functional diversity has changed over time by decade from 1870 to 2010 at three spatial scales (regional, lake, and habitat) to account for potential noninteractions between species at the regional and lake level. We also determined which process, environmental filtering or competitive interactions, is more important in regulating community assembly and maintenance by comparing observed patterns to what we would expect in the absence of an ecological mechanism. With the exception of one community, all analyses show that functional diversity and species richness has increased over time and that environmental filtering regulates community assembly at the regional level. When examining functional diversity at the lake and habitat level, the regulating processes become more context dependent. This study is the first to examine diversity patterns and Darwin's conundrum by integrating long‐term, large‐scale, and high‐resolution temporal data at multiple spatial scales. Our results confirm that Darwin's conundrum is highly context dependent.     

Using Plant Functional Traits and Phylogenies to Understand Patterns of Plant Community Assembly in a Seasonal Tropical Forest in Lao PDR

Plant functional traits reflect different evolutionary responses to environmental variation, and among extant species determine the outcomes of interactions between plants and their environment, including other plant species. Thus, combining phylogenetic and trait-based information can be a powerful approach for understanding community assembly processes across a range of spatial scales. We used this approach to investigate tree community composition at Phou Khao Khouay National Park (18°14’-18°32’N; 102°38’- 102°59’E), Laos, where several distinct forest types occur in close proximity. The aim of our study was to examine patterns of plant community assembly across the strong environmental gradients evident at our site. We hypothesized that differences in tree community composition were being driven by an underlying gradient in soil conditions. Thus, we predicted that environmental filtering would predominate at the site and that the filtering would be strongest on sandier soil with low pH, as these are the conditions least favorable to plant growth. We surveyed eleven 0.25 ha (50x50 m) plots for all trees above 10 cm dbh (1221 individual trees, including 47 families, 70 genera and 123 species) and sampled soils in each plot. For each species in the community, we measured 11 commonly studied plant functional traits covering both the leaf and wood economic spectrum traits and we reconstructed a phylogenetic tree for 115 of the species in the community using rbcL and matK sequences downloaded from Genebank (other species were not available). Finally we compared the distribution of trait values and species at two scales (among plots and 10x10m subplots) to examine trait and phylogenetic community structures. Although there was strong evidence that an underlying soil gradient was determining patterns of species composition at the site, our results did not support the hypothesis that the environmental filtering dominated community assembly processes. For the measured plant functional traits there was no consistent pattern of trait dispersion across the site, either when traits were considered individually or when combined in a multivariate analysis. However, there was a significant correlation between the degree of phylogenetic dispersion and the first principle component axis (PCA1) for the soil parameters. Moreover, the more phylogenetically clustered plots were on sandier soils with lower pH. Hence, we suggest that the community assembly processes across our site may reflect the influence of more conserved traits that we did not measure. Nevertheless, our results are equivocal and other interpretations are possible. Our study illustrates some difficulties in combining trait and phylogenetic approaches that may result from the complexities of integrating spatial and evolutionary processes that vary at different scales.     

A phylogenetic and trait‐based analysis of community assembly in a subtropical forest in central China

Despite several decades of study in community ecology, the relative importance of the ecological processes that determine species co‐occurrence across spatial scales remains uncertain. Some of this uncertainty may be reduced by studying the scale dependency of community assembly in the light of environmental variation. Phylogenetic information and functional trait information are often used to provide potentially valuable insights into the drivers of community assembly. Here, we combined phylogenetic and trait‐based tests to gain insights into community processes at four spatial scales in a large stem‐mapped subtropical forest dynamics plot in central China. We found that all of the six leaf economic traits measured in this study had weak, but significant, phylogenetic signal. Nonrandom phylogenetic and trait‐based patterns associated with topographic variables indicate that deterministic processes tend to dominate community assembly in this plot. Specifically, we found that, on average, co‐occurring species were more phylogenetically and functionally similar than expected throughout the plot at most spatial scales and assemblages of less similar than expected species could only be found on finer spatial scales. In sum, our results suggest that the trait‐based effects on community assembly change with spatial scale in a predictable manner and the association of these patterns with topographic variables, indicates the importance of deterministic processes in community assembly relatively to random processes.     

Phylogenetic relatedness and plant invader success across two spatial scales

Aim  Successful invaders often possess similar ecological traits that contribute to success in new regions, and thus under niche conservatism, invader success should be phylogenetically clustered. We asked if the degree to which non-native plant species are phylogenetically related is a predictor of invasion success at two spatial scales.
Location  Australia – the whole continent and Royal National Park (south-eastern Australia).
Methods  We used non-native plant species occupancy in Royal National Park, as well as estimated continental occupancy of these species from herbarium records. We then estimated phylogenetic relationships using molecular data from three gene sequences available on GenBank ( matK , rbcL and ITS1 ). We tested for phylogenetic signals in occupancy using Blomberg's K .
Results  Whereas most non-native plants were relatively scarce, there was a strong phylogenetic signal for continental occupancy, driven by the clustering of successful species in Asteraceae, Caryophyllaceae, Poaceae and Solanaceae. However, we failed to detect a phylogenetic signal at the park scale.
Main Conclusions  Our results reveal that at a large spatial scale, invader success is phylogenetically clustered where ecological traits promoting success appear to be shared among close relatives, indicating that phylogenetic relationships can be useful predictors of invasion success at large spatial scales. At a smaller, landscape scale, there was no evidence of phylogenetic clustering of invasion success, and thus, relatedness plays a much reduced role in determining the relative success of invaders.     

Intercontinental trends in functional and phylogenetic structure of stream fish assemblages

Understanding of community assembly has been improved by phylogenetic and trait‐based approaches, yet there is little consensus regarding the relative importance of alternative mechanisms and few studies have been done at large geographic and phylogenetic scales. Here, we use phylogenetic and trait dispersion approaches to determine the relative contribution of limiting similarity and environmental filtering to community assembly of stream fishes at an intercontinental scale. We sampled stream fishes from five zoogeographic regions. Analysis of traits associated with habitat use, feeding, or both resulted in more occurrences of trait underdispersion than overdispersion regardless of spatial scale or species pool. Our results suggest that environmental filtering and, to a lesser extent, species interactions were important mechanisms of community assembly for fishes inhabiting small, low‐gradient streams in all five regions. However, a large proportion of the trait dispersion values were no different from random. This suggests that stochastic factors or opposing assembly mechanisms also influenced stream fish assemblages and their trait dispersion patterns. Local assemblages tended to have lower functional diversity in microhabitats with high water velocity, shallow water depth, and homogeneous substrates lacking structural complexity, lending support for the stress‐dominance hypothesis. A high prevalence of functional underdispersion coupled with phylogenetic underdispersion could reflect phylogenetic niche conservatism and/or stabilizing selection. These findings imply that environmental filtering of stream fish assemblages is not only deterministic, but also influences assemblage structure in a fairly consistent manner worldwide.     

Non-Native Plants Disrupt Dual Promotion of Native Alpha and Beta Diversity

Non-native species can alter patterns of species diversity at multiple spatial scales, but the processes that underlie multi-scale effects remain unclear. Here we show that non-native species reduce native diversity at multiple scales through simultaneous disruption of two processes of native community assembly: species immigration, which enhances alpha diversity, and community divergence, which enhances beta diversity. Community divergence refers to the process in which local communities diverge over time in species composition because the history of species immigration and, consequently, the way species affect one another within communities are variable among communities. Continuous experimental removal of species over four years of floodplain succession revealed that, when non-native species were excluded, stochastic variation in the timing of a dominant native species’ arrival allowed local communities to diverge, thereby enhancing beta diversity, without compromising promotion of alpha diversity by species immigration. In contrast, when non-native species were allowed to enter experimental plots, they not only reduced native alpha diversity by limiting immigration, but also diminished the dominant native species’ role in enhancing native beta diversity. Our results highlight the importance of community assembly and succession for understanding multi-scale effects of non-native species.     

长江中游干流鱼类群落构建机制分析

研究选取长江中游5个采样点(宜昌、枝江、荆州、汉南、湖口)为代表, 采用系统发育群落结构方法分析了不同空间尺度下长江中游鱼类群落的构建机制。结果表明: (1)空间聚类分析显示, 在65%的相似性水平上, 所有样点可以划分为3个Group: GroupⅠ(宜昌)、GroupⅡ(枝江+荆州)和Group Ⅲ(汉南+湖口);在55%的相似性水平上, 所有样点可以划分为2个Group: Group A(宜昌)和Group B(枝江+荆州+汉南+湖口), 且聚类分析结果与采样点的空间分布相符合。(2)在不同空间尺度下, 鱼类群落构建机制存在差异: 从地区采样点尺度来看, 荆州江段鱼类群落表现为竞争作用主导群落构建, 其余采样点鱼类群落均为环境过滤作用;从区域尺度来看, 宜昌江段鱼类群落表现为环境过滤作用的建群机制, 其余4个采样点在扩大空间尺度后, 即分为Group A和Group B的情况下, 其鱼类群落构建机制转变为物种间竞争作用。因此, 长江中游干流鱼类群落构建机制表现了地区环境和空间尺度的共同作用。由于水流湍急, 宜昌始终表现为环境过滤作用。其他江段在采样点尺度多数表现了环境过滤作用, 但是在宏观的空间尺度上, 却由于空间异质性的增加, 容纳了远缘的物种, 群落构建机制转换为竞争作用。这样的转变有别于陆生植物中由小尺度竞争作用转为大尺度环境过滤作用的情况。     

Integrating trait and phylogenetic distances to assess scale‐dependent community assembly processes

Biodiversity is structured by multiple mechanisms that are dependent, at least in part, on ecological similarities and differences among species. Integrating traits and phylogenies in diversity metrics may provide deeper insight into community assembly processes across spatial scales. However, different traits are influenced by processes at different spatial scales, and it is not clear how trait‐spatial scale mismatches skew our ability to detect assembly patterns. An additional complexity is how phylogenetic distances, which might capture unmeasured traits, reflect spatially dependent processes. Here we analyze a freshwater zooplankton dataset from 91 ponds and show that different traits are associated with processes at different spatial scales. We first assessed the response of individual traits to processes at both α‐ and β‐scales, and then quantified the power of different combinations of traits and phylogenetic distances to reveal environmental and spatial drivers of α‐ and β‐diversity. We found that explanatory power was maximised when we accounted for environmental and spatial drivers with single, but different traits for α‐ and β‐diversity. Using the most appropriate trait for each spatial scale outperformed phylogenetic information, but phylogenetic information outperformed the same traits when these were used at the wrong spatial scale, and all outperformed taxonomic analyses that ignore trait and phylogenetic information. We demonstrate that accounting for species’ similarities and differences provides important information about dominant assembly mechanisms at different spatial scales, and that phylogeny is especially useful when measured traits are uninformative at a given spatial scale or when there is lack of trait data. Our study also indicates, however, that trait‐scale mismatches among phylogenetically conserved traits may affect the performance of phylogenetic indices compared to indices that account only for the best single trait at each spatial scale.     

Phylogenetic patterns differ for native and exotic plant communities across a richness gradient in Northern California

Aim Increasingly, ecologists are using evolutionary relationships to infer the mechanisms of community assembly. However, modern communities are being invaded by non‐indigenous species. Since natives have been associated with one another through evolutionary time, the forces promoting character and niche divergence should be high. On the other hand, exotics have evolved elsewhere, meaning that conserved traits may be more important in their new ranges. Thus, co‐occurrence over sufficient time‐scales for reciprocal evolution may alter how phylogenetic relationships influence assembly. Here, we examined the phylogenetic structure of native and exotic plant communities across a large‐scale gradient in species richness and asked whether local assemblages are composed of more or less closely related natives and exotics and whether phylogenetic turnover among plots and among sites across this gradient is driven by turnover in close or distant relatives differentially for natives and exotics. Location Central and northern California, USA. Methods We used data from 30 to 50 replicate plots at four sites and constructed a maximum likelihood molecular phylogeny using the genes: matK, rbcl, ITS1 and 5.8s. We compared community‐level measures of native and exotic phylogenetic diversity and among‐plot phylobetadiversity. Results There were few exotic clades, but they tended to be widespread. Exotic species were phylogenetically clustered within communities and showed low phylogenetic turnover among communities. In contrast, the more species‐rich native communities showed higher phylogenetic dispersion and turnover among sites. Main conclusions The assembly of native and exotic subcommunities appears to reflect the evolutionary histories of these species and suggests that shared traits drive exotic patterns while evolutionary differentiation drives native assembly. Current invasions appear to be causing phylogenetic homogenization at regional scales.     

Multi-scale phylogenetic structure in coastal dune plant communities across the globe

Aims Studies integrating phylogenetic history and large-scale community assembly are few, and many questions remain unanswered. Here, we use a global coastal dune plant data set to uncover the important factors in community assembly across scales from the local filtering processes to the global long-term diversification and dispersal dynamics. Coastal dune plant communities occur worldwide under a wide range of climatic and geologic conditions as well as in all biogeographic regions. However, global patterns in the phylogenetic composition of coastal dune plant communities have not previously been studied.Methods The data set comprised vegetation data from 18463 plots in New Zealand, South Africa, South America, North America and Europe. The phylogenetic tree comprised 2241 plant species from 149 families. We calculated phylogenetic clustering (Net Relatedness Index, NRI, and Nearest Taxon Index, NTI) of regional dune floras to estimate the amount of in situ diversification relative to the global dune species pool and evaluated the relative importance of land and climate barriers for these diversification patterns by geographic analyses of phylogenetic similarity. We then tested whether dune plant communities exhibit similar patterns of phylogenetic structure within regions. Finally, we calculated NRI for local communities relative to the regional species pool and tested for an association with functional traits (plant height and seed mass) thought to vary along sea–inland gradients.Important findings Regional species pools were phylogenetically clustered relative to the global pool, indicating regional diversification. NTI showed stronger clustering than NRI pointing to the importance of especially recent diversifications within regions. The species pools grouped phylogenetically into two clusters on either side of the tropics suggesting greater dispersal rates within hemispheres than between hemispheres. Local NRI plot values confirmed that most communities were also phylogenetically clustered within regions. NRI values decreased with increasing plant height and seed mass, indicating greater phylogenetic clustering in communities with short maximum height and good dispersers prone to wind and tidal disturbance as well as salt spray, consistent with environmental filtering along sea–inland gradients. Height and seed mass both showed significant phylogenetic signal, and NRI tended to correlate negatively with both at the plot level. Low NRI plots tended to represent coastal scrub and forest, whereas high NRI plots tended to represent herb-dominated vegetation. We conclude that regional diversification processes play a role in dune plant community assembly, with convergence in local phylogenetic community structure and local variation in community structure probably reflecting consistent coastal-inland gradients. Our study contributes to a better understanding of the globally distributed dynamic coastal ecosystems and the structuring factors working on dune plant communities across spatial scales and regions.     

Environmental filtering mediates grassland community assembly following restoration with soil carbon additions

The application of carbon (C) substrates has been viewed as a promising tool for lowering soil nitrogen (N) availability in grassland restoration. However, experimental evidence shows that C additions can enhance, suppress, or have no effect on native species productivity, making it difficult to predict the effects of C‐additions on plant communities. We used a community assembly approach to test the roles of environmental filtering and competition on community structure after C‐additions. We applied 3 recalcitrant C‐additions (wood chips, shavings, mixed chips + shavings), monitored temporal changes in soil N and P availability and species' abundances, and used phylogenetic tools to examine changes in community structure. All 3 soil C‐additions produced significant reductions in soil N and P fertility that, in turn, were correlated with increases in taxonomic species richness, diversity, and evenness, as well as shifts in community structure. In control and C‐amended plots, however, communities were composed of taxa that were more closely related than expected by chance (phylogenetically clustered); this pattern occurred across all C‐additions and years, and in both plot level and species pair‐wise metrics. In nonamended plots, phylogenetic clustering was correlated with soil N availability, consistent with environmental filtering. In C‐addition plots, biotic (clade specialization in different C additions) and abiotic factors (soil P variability) were important in structuring the community. These findings suggest that C‐additions create a different set of environmental filters and that variations in ecological traits among phylogenetically close species may be important in understanding and predicting the effects of C‐additions.     

Phylogenetic community structure and phylogenetic turnover across space and edaphic gradients in western Amazonian tree communities

Ecological and evolutionary processes influence community assembly at both local and regional scales. Adding a phylogenetic dimension to studies of species turnover allows tests of the extent to which environmental gradients, geographic distance and the historical biogeography of lineages have influenced speciation and dispersal of species throughout a region. We compare measures of beta diversity, phylogenetic community structure and phylobetadiversity (phylogenetic distance among communities) in 34 plots of Amazonian trees across white‐sand and clay terra firme forests in a 60 000 square kilometer area in Loreto, Peru. Dominant taxa in white‐sand forests were phylogenetically clustered, consistent with environmental filtering of conserved traits. Phylobetadiversity measures found significant phylogenetic clustering between terra firme communities separated by geographic distances of <200–300 km, consistent within recent local speciation at the watershed scale in the Miocene‐aged clay‐soil forests near the foothills of the Andes. Although both distance and habitat type yielded statistically significant effects on both species and phylogenetic turnover, the patterns we observed were more consistent with an effect of habitat specialization than dispersal limitation. Our results suggest a role for both broad‐scale biogeographic and evolutionary processes, as well as habitat specialization, influencing community structure in Amazonian forests.     

Integrating phylogenetic community structure with species distribution models: an example with plants of rock barrens

Approaches using phylogenetic pattern in ecological communities to deduce processes of community assembly have been criticised as disconnected from foundations in ecological mechanism, especially with respect to lack of data about abiotic and biotic niches. These criticisms can be addressed with analyses of organismal traits that underlie environmental filtering, competitive exclusion, and other candidate processes; however, the difficulty of assembling large trait databases means that such studies remain uncommon. We suggest a synthesis of phylogenetic community structure analysis and species distribution modeling that we believe can allow inference about community processes without prohibitive data requirements. We illustrate this method for angiosperm communities of rock barrens in eastern Canada. First, we analyzed phylogenetic community structure of four rock‐barren sites at three nested spatial scales (quadrat to region). For the nine most common species in our barrens, we used regional occurrence records to build species distribution models identifying environmental drivers of the nine species’ distributions. Coefficients of these models represent implicit trait data that summarize each species’ response to the environmental drivers in the model. We then tested for phylogenetic signal in these traits, to ask whether ecological forces acting on them could be generating phylogenetic community structure. We found strong phylogenetic clustering at the quadrat level, while patterns at larger scales were complex. Our distribution model suggested drought stress as the dominant driver for distributions of all the species, consistent with local correlations with soil depth, and the species’ responses to drought showed strong phylogenetic signal. The convergence of results from phylogenetic community structure and species distribution modeling suggests that barren communities are structured at the quadrat level by environmental filtering effects of moisture stress, to which species have phylogenetically patterned responses.     

不同空间尺度西藏色季拉山急尖长苞冷杉群落谱系结构特征

基于西藏色季拉山4 hm²亚高山暗针叶林固定样地调查数据,分析了急尖长苞冷杉群落内6个径级(1～2、2～4、4～7、7～11、11～16、>16 cm)的植物在5个空间尺度(5 m×5 m、10 m×10 m、20 m×20 m、50 m×50 m、100 m×100 m)上的谱系结构。结果表明: 不同空间尺度上,该群落的净谱系亲缘关系指数(NRI)和净最近种间亲缘关系指数(NTI)值均大于零,整体上表现为谱系聚集。在小空间尺度(5 m×5 m)上,谱系结构聚集强度最大。在所有空间尺度上,群落内小径级个体表现为谱系聚集,随着径级的增大(DBH>7 cm),逐渐表现为谱系发散,且发散程度随径级增加而增大。小径级个体的谱系聚集强度随空间尺度而增大;而大径级个体(DBH>7 cm)的谱系发散程度随空间尺度增加而增大。小径级群落的生境过滤和大径级群落的竞争排斥作用可能是驱动该区域急尖长苞冷杉群落构建的主要生态学过程。     

Scale dependence in the phylogenetic relatedness of alien and native taxa

达尔文的归化假说提出,由于生态位的不同,成功建群的外来物种与本地物种的关系不太密切。先前的研究对这一假设有支持也有反对,其中一个原因是外来物种和本地物种在大的空间尺度上有系统发育聚类的倾向,而在细微尺度上存在过度分散的倾向。然而,对于外来物种的系统发育关系如何改变其入侵群落的系统发育结构,以及在何种空间尺度上可能表现出这种影响,人们知之甚少。在本研究中,我们调查被入侵的森林下层植物群落在系统发育上是聚集的还是或过度分散的,亲缘关系如何随空间尺度变化,以及外来物种如何影响下层群落的系统发育模式。在澳大利亚东南部干旱森林的下层群落进行了5个空间尺度(1, 20, 500, 1500和4500 m²)的实地调查。使用两个指标的标准化效应量[(i)平均成对距离和(ii)平均最近分类单元距离]来量化群落与其外来和本地亚群落之间的系统发育关系,并研究系统发育模 式如何随空间尺度变化。研究结果表明,外来物种之间的亲缘关系非常密切,而且这种亲缘关系会随着尺度的增加而增加。在中等空间尺 度下(20–500 m²), 整个群落呈随机分布趋势,而本地物种高度分散,外来亚群落高度聚集。这说明亲缘关系密切的外来物种入侵使群落系统发育结构由过度分散向随机分布转变。外来物种和本地物种在空间尺度上是远亲,这支持了达尔文的归化假说,但只是在系统发育距离被量化为平均最近分类单元距离时成立。外来物种和本地物种的系统发育差异随着空间尺度的增加而增加,这与预期的模式相反。我们的研究结果表明,外来物种强大的系统发育聚类是由人类干预的引入驱动的,牵涉能够成功建群和传播的密切相关的类群。系统发育相关性的尺度依赖模式可能是由火灾和散布等随机过程引起的,这表明竞争和生境过滤并不是分别在小和大尺度上控制系统发育关系的唯一因素。区分不同进化深度的指标很重要,因为不同的指标可以显示不同的尺度依赖模式。     

植物群落构建机制研究进展

群落构建研究对于解释物种共存和物种多样性的维持是至关重要的,因此一直是生态学研究的中心论题。尽管近年来关于生态位和中性理论的验证研究已经取得了显著的成果,但对于局域群落构建机制的认识仍存在很大争议。随着统计和理论上的进步使得用功能性状和群落谱系结构解释群落构建机制变为可能,主要是通过验证共存物种的性状和谱系距离分布模式来实现。然而,谱系和功能性状不能相互替代,多种生物和非生物因子同时控制着群落构建,基于中性理论的扩散限制、基于生态位的环境过滤和竞争排斥等多个过程可能同时影响着群落的构建。所以,综合考虑多种方法和影响因素探讨植物群落的构建机制,对于预测和解释植被对干扰的响应,理解生物多样性维持机制有重要意义。试图在简要回顾群落构建理论及研究方法发展的基础上,梳理其最新研究进展,并探讨整合功能性状及群落谱系结构的研究方法,解释群落构建和物种多样性维持机制的可能途径。在结合功能性状和谱系结构研究群落构建时,除了考虑空间尺度、环境因子、植被类型外,还应该关注时间尺度、选择性状的种类和数量、性状的种内变异、以及人为干扰等因素对群落构建的影响。