Patterns of phylogenetic beta diversity in China's grasslands in relation to geographical and environmental distance

Patterns and determinants of beta (β-) diversity can be used to explore the underlying mechanisms regulating community assembly. Despite being the most commonly used measure of β-diversity, species turnover does not consider the evolutionary differences among species, treating all species equally. Incorporating information on phylogenetic non-independence or relatedness among species in the calculation of β-diversity may substantially advance our understanding of the ecological and evolutionary mechanisms structuring communities. Here, we investigate the relative influence of geographical distance and differences in environmental conditions (environmental distance) on the phylogenetic β-diversity between grassland communities expanding 4000 km across the Tibetan Plateau, the Inner Mongolia Plateau and the Xinjiang Autonomous Region in China. Both observed and standardized effect size of phylogenetic β-diversity were significantly correlated with geographical and environmental distance across all regions. However, the effect of geographical distance on the standardized effect size of phylogenetic β-diversity disappeared when environmental distance was controlled. We also found that within different regions, the effect of environmental distance on both observed and standardized effect size of phylogenetic β-diversity was more significant than geographical distance. Among environmental variables, climate played a more important role in shaping observed phylogenetic β-diversity across and within regions, and standardized effect size of phylogenetic β-diversity across regions. Soil properties played a more important role in shaping standardized effect size of phylogenetic β-diversity within regions. The phylogenetic β-diversity of species from dicot and monocot clades exhibited similar patterns along environmental and geographical distance. The results suggest that at the study scale, phylogeny of grassland communities in China is predominantly structured by environmental filtering, and the dominant environmental factors may be scale-dependent.     

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.     

Phylogenetic analysis suggests that habitat filtering is structuring marine bacterial communities across the globe

The phylogenetic structure and community composition were analysed in an existing data set of marine bacterioplankton communities to elucidate the evolutionary and ecological processes dictating the assembly. The communities were sampled from coastal waters at nine locations distributed worldwide and were examined through the use of comprehensive clone libraries of 16S ribosomal RNA genes. The analyses show that the local communities are phylogenetically different from each other and that a majority of them are phylogenetically clustered, i.e. the species (operational taxonomic units) were more related to each other than expected by chance. Accordingly, the local communities were assembled non-randomly from the global pool of available bacterioplankton. Further, the phylogenetic structures of the communities were related to the water temperature at the locations. In agreement with similar studies, including both macroorganisms and bacteria, these results suggest that marine bacterial communities are structured by “habitat filtering”, i.e. through non-random colonization and invasion determined by environmental characteristics. Different bacterial types seem to have different ecological niches that dictate their survival in different habitats. Other eco-evolutionary processes that may contribute to the observed phylogenetic patterns are discussed. The results also imply a mapping between phenotype and phylogenetic relatedness which facilitates the use of community phylogenetic structure analysis to infer ecological and evolutionary assembly processes.     

The Interplay between Environmental Filtering and Spatial Processes in Structuring Communities: The Case of Neotropical Snake Communities

Both habitat filters and spatial processes can influence community structure. Space alone affects species immigration from the regional species pool, whereas habitat filters affect species distribution and inter-specific interactions. This study aimed to understand how the interplay between environmental and geographical processes influenced the structure of Neotropical snake communities in different habitat types. We selected six studies that sampled snakes in forests, four conducted in savannas and two in grasslands (the latter two are grouped in a non-forest category). We used the net relatedness and nearest taxon indices to assess phylogenetic structure within forest and non-forest areas. We also used the phylogenetic fuzzy-weighting algorithm to characterize phylogenetic structure across communities and the relation of phylogenetic composition patterns to habitat type, structure, and latitude. Finally, we tested for morphological trait convergence and phylogenetic niche conservatism using four forest and four non-forest areas for which morphological data were available. Community phylogenetic composition changed across forest and non-forest areas suggesting that environmental filtering influences community structure. Species traits were affected by habitat type, indicating convergence at the metacommunity level. Tail length, robustness, and number of ventral scales maximized community convergence among forest and non-forest areas. The observed patterns suggested environmental filtering, indicating that less vertically structured habitats represent a strong filter. Despite the fact that phylogenetic structure was not detected individually for each community, we observed a trend towards communities composed by more closely related species in higher latitudes and more overdispersed compositions in lower latitudes. Such pattern suggests that the limited distribution of major snake lineages constrained species distributions. Structure indices for each community were also related to habitat type, showing that communities from non-forest areas tend to be more clustered. Our study showed that both environmental filtering and spatial gradients play important roles in shaping the composition of Neotropical snake communities.     

Co‐occurrence and phylogenetic distance in communities of mammalian ectoparasites: limiting similarity versus environmental filtering

Similarity between species plays a key role in the processes governing community assembly. The co‐occurrence of highly similar species may be unlikely if their similar needs lead to intense competition (limiting similarity). On the other hand, persistence in a particular habitat may require certain traits, such that communities end up consisting of species sharing the same traits (environmental filtering). Relatively little information exists on the relative importance of these processes in structuring parasite communities. Assuming that phylogenetic relatedness reflects ecological similarity, we tested whether the co‐occurrence of pairs of flea species (Siphonaptera) on the same host individuals was explained by the phylogenetic distance between them, among 40 different samples of mammalian hosts (rodents and shrews) from different species, areas or seasons. Our results indicate that frequency of co‐occurrence between flea species increased with decreasing phylogenetic distance between them in 37 out of 40 community samples, with 14 of these correlations being statistically significant. A meta‐analysis across all samples confirmed the overall trend for closely related species to co‐occur more frequently on the same individual hosts than expected by chance, independently of the identity of the host species or of environmental conditions. These findings suggest that competition between closely related, and therefore presumably ecologically similar, species is not important in shaping flea communities. Instead, if only fleas with certain behavioural, ecological and physiological properties can encounter and exploit a given host, and if phylogenetic relationships determine trait similarity among flea species, then a process akin to environmental filtering, or host filtering, could favour the co‐occurrence of related species on the same host.     

The effects of water pollution on the phylogenetic community structure of aquatic plants in the East Tiaoxi River,China

1. Water pollution is one of the most serious aquatic environmental problems worldwide. In China, recent agricultural and industrial development has resulted in rapid changes in aquatic ecosystems. Here, we reveal the effects of water pollution on the phylogenetic community structure of aquatic macrophytes in the Tiaoxi River, China.
2. We placed a rectangular plot at 47 sites within the Tiaoxi River from the mouth of the river to 88.5 km upstream, in which we recorded species abundance and measured 22 physico-chemical variables. Bayesian phylogeny using the rbcL and matK gene sequences was employed to quantify phylogenetic α- and β-diversity, and test the phylogenetic signal in four growth forms: emergent, floating-leaved, free-floating, and submerged.
3. Within communities, water contamination and phytoplankton abundance decreased species richness and phylogenetic diversity, which resulted in phylogenetic clustering; species within communities were more closely related to each other than expected. Between communities, differences in geographical distance and phytoplankton abundance resulted in phylogenetic dissimilarity among plots. Aquatic macrophytes showed phylogenetic signals in which related species responded more similarly to disturbance.
4. Thus, the observed patterns could be explained by environmental filtering and suggested that water pollution by human activity has added more filters to the existing environmental filters that drive the species assembly of macrophyte communities.

     

T4-like myovirus community shaped by dispersal and deterministic processes in the South China Sea

As the most abundant and genetically diverse biological entities, viruses significantly influence ecological, biogeographical and evolutionary processes in the ocean. However, the biogeography of marine viruses and the drivers shaping viral community are unclear. Here, the biogeographic patterns of T4-like viruses and the relative impacts of deterministic (environmental selection) and dispersal (spatial distance) processes were investigated in the northern South China Sea. The dominant viral operational taxonomic units were affiliated with previously defined Marine, Estuary, Lake and Paddy Groups. A clear viral biogeographic pattern was observed along the environmental gradient from the estuary to open sea. Marine Groups I and IV had a wide geographical distribution, whereas Marine Groups II, III and V were abundant in lower-salinity continental or eutrophic environments. A significant distance-decay pattern was noted for the T4-like viral community, especially for those infecting cyanobacteria. Both deterministic and dispersal processes influenced viral community assembly, although environmental selection (e.g. temperature, salinity, bacterial abundance and community, etc.) had a greater impact than spatial distance. Network analysis confirmed the strong association between viral and bacterial community composition, and suggested a diverse ecological relationship (e.g. lysis, co-infection or mutualistic) between and within viruses and their potential bacterial hosts.     

Altitude acts as an environmental filter on phylogenetic composition,traits and diversity in bee communities

Knowledge about the phylogeny and ecology of communities along environmental gradients helps to disentangle the role of competition-driven processes and environmental filtering for community assembly. In this study, we evaluated patterns in species richness, phylogenetic structure and life-history traits of bee communities along altitudinal gradients in the Alps, Germany. We found a linear decline in species richness and abundance but increasing phylogenetic clustering in communities with increasing altitude. The proportion of social- and ground-nesting species, as well as mean body size and altitudinal range of bee communities, increased with increasing altitude, whereas the mean geographical distribution decreased. Our results suggest that community assembly at high altitudes is dominated by environmental filtering effects, whereas the relative importance of competition increases at low altitudes. We conclude that inherent phylogenetic and ecological species attributes at high altitudes pose a threat for less competitive alpine specialists with ongoing climate change.     

Dispersal, environmental niches and oceanic-scale turnover in deep-sea bivalves

Patterns of beta-diversity or distance decay at oceanic scales are completely unknown for deep-sea communities. Even when appropriate data exist, methodological problems have made it difficult to discern the relative roles of environmental filtering and dispersal limitation for generating faunal turnover patterns. Here, we combine a spatially extensive dataset on deep-sea bivalves with a model incorporating ecological dynamics and shared evolutionary history to quantify the effects of environmental filtering and dispersal limitation. Both the model and empirical data are used to relate functional, taxonomic and phylogenetic similarity between communities to environmental and spatial distances separating them for 270 sites across the Atlantic Ocean. This study represents the first ocean-wide analysis examining distance decay as a function of a broad suite of explanatory variables. We find that both strong environmental filtering and dispersal limitation drive turnover in taxonomic, functional and phylogenetic composition in deep-sea bivalves, explaining 26 per cent, 34 per cent and 9 per cent of the variation, respectively. This contrasts with previous suggestions that dispersal is not limiting in broad-scale biogeographic and biodiversity patterning in marine systems. However, rates of decay in similarity with environmental distance were eightfold to 44-fold steeper than with spatial distance. Energy availability is the most influential environmental variable evaluated, accounting for 3.9 per cent, 9.4 per cent and 22.3 per cent of the variation in functional, phylogenetic and taxonomic similarity, respectively. Comparing empirical patterns with process-based theoretical predictions provided quantitative estimates of dispersal limitation and niche breadth, indicating that 95 per cent of deep-sea bivalve propagules will be able to persist in environments that deviate from their optimum by up to 2.1 g m(-2) yr(-1) and typically disperse 749 km from their natal site.     

Amphibian Beta Diversity in the Brazilian Atlantic Forest: Contrasting the Roles of Historical Events and Contemporary Conditions at Different Spatial Scales

Current patterns of biodiversity distribution result from a combination of historical and contemporary processes. Here, we compiled checklists of amphibian species to assess the roles of long-term climate stability (Quaternary oscillations), contemporary environmental gradients and geographical distance as determinants of change in amphibian taxonomic and phylogenetic composition in the Brazilian Atlantic Forest. We calculated beta diversity as both variation in species composition (CBD) and phylogenetic differentiation (PBD) among the assemblages. In both cases, overall beta diversity was partitioned into two basic components: species replacement and difference in species richness. Our results suggest that the CBD and PBD of amphibians are determined by spatial turnover. Geographical distance, current environmental gradients and long-term climatic conditions were complementary predictors of the variation in CBD and PBD of amphibian species. Furthermore, the turnover components between sites from different regions and between sites within the stable region were greater than between sites within the unstable region. On the other hand, the proportion of beta-diversity due to species richness difference for both CBD and PBD was higher between sites in the unstable region than between sites in the stable region. The high turnover components from CBD and PBD between sites in unstable vs stable regions suggest that these distinct regions have different biogeographic histories. Sites in the stable region shared distinct clades that might have led to greater diversity, whereas sites in the unstable region shared close relatives. Taken together, these results indicate that speciation, environmental filtering and limited dispersal are complementary drivers of beta-diversity of amphibian assemblages in the Brazilian Atlantic Forest.     

Incorporating phylogenetic metrics to microbial co‐occurrence networks based on amplicon sequences to discern community assembly processes

Co‐occurrence network analysis based on amplicon sequences is increasingly used to study microbial communities. Patterns of co‐existence or mutual exclusion between pairs of taxa are often interpreted as reflecting positive or negative biological interactions. However, other assembly processes can underlie these patterns, including species failure to reach distant areas (dispersal limitation) and tolerate local environmental conditions (habitat filtering). We provide a tool to quantify the relative contribution of community assembly processes to microbial co‐occurrence patterns, which we applied to explore soil bacterial communities in two dry ecosystems. First, we sequenced a bacterial phylogenetic marker in soils collected across multiple plots. Second, we inferred co‐occurrence networks to identify pairs of significantly associated taxa, either co‐existing more (aggregated) or less often (segregated) than expected at random. Third, we assigned assembly processes to each pair: patterns explained based on spatial or environmental distance were ascribed to dispersal limitation (2%–4%) or habitat filtering (55%–77%), and the remaining to biological interactions. Finally, we calculated the phylogenetic distance between taxon pairs to test theoretical expectations on the linkages between phylogenetic patterns and assembly processes. Aggregated pairs were more closely related than segregated pairs. Furthermore, habitat‐filtered aggregated pairs were closer relatives than those assigned to positive interactions, consistent with phylogenetic niche conservatism and cooperativism among distantly related taxa. Negative interactions resulted in equivocal phylogenetic signatures, probably because different competitive processes leave opposing signals. We show that microbial co‐occurrence networks mainly reflect environmental tolerances and propose that incorporating measures of phylogenetic relatedness to networks might help elucidate ecologically meaningful patterns.     

UniFrac: a new phylogenetic method for comparing microbial communities

We introduce here a new method for computing differences between microbial communities based on phylogenetic information. This method, UniFrac, measures the phylogenetic distance between sets of taxa in a phylogenetic tree as the fraction of the branch length of the tree that leads to descendants from either one environment or the other, but not both. UniFrac can be used to determine whether communities are significantly different, to compare many communities simultaneously using clustering and ordination techniques, and to measure the relative contributions of different factors, such as chemistry and geography, to similarities between samples. We demonstrate the utility of UniFrac by applying it to published 16S rRNA gene libraries from cultured isolates and environmental clones of bacteria in marine sediment, water, and ice. Our results reveal that (i) cultured isolates from ice, water, and sediment resemble each other and environmental clone sequences from sea ice, but not environmental clone sequences from sediment and water; (ii) the geographical location does not correlate strongly with bacterial community differences in ice and sediment from the Arctic and Antarctic; and (iii) bacterial communities differ between terrestrially impacted seawater (whether polar or temperate) and warm oligotrophic seawater, whereas those in individual seawater samples are not more similar to each other than to those in sediment or ice samples. These results illustrate that UniFrac provides a new way of characterizing microbial communities, using the wealth of environmental rRNA sequences, and allows quantitative insight into the factors that underlie the distribution of lineages among environments.     

UniFrac: a New Phylogenetic Method for Comparing Microbial Communities

We introduce here a new method for computing differences between microbial communities based on phylogenetic information. This method, UniFrac, measures the phylogenetic distance between sets of taxa in a phylogenetic tree as the fraction of the branch length of the tree that leads to descendants from either one environment or the other, but not both. UniFrac can be used to determine whether communities are significantly different, to compare many communities simultaneously using clustering and ordination techniques, and to measure the relative contributions of different factors, such as chemistry and geography, to similarities between samples. We demonstrate the utility of UniFrac by applying it to published 16S rRNA gene libraries from cultured isolates and environmental clones of bacteria in marine sediment, water, and ice. Our results reveal that (i) cultured isolates from ice, water, and sediment resemble each other and environmental clone sequences from sea ice, but not environmental clone sequences from sediment and water; (ii) the geographical location does not correlate strongly with bacterial community differences in ice and sediment from the Arctic and Antarctic; and (iii) bacterial communities differ between terrestrially impacted seawater (whether polar or temperate) and warm oligotrophic seawater, whereas those in individual seawater samples are not more similar to each other than to those in sediment or ice samples. These results illustrate that UniFrac provides a new way of characterizing microbial communities, using the wealth of environmental rRNA sequences, and allows quantitative insight into the factors that underlie the distribution of lineages among environments.     

Phylogenetic diversity of macromycetes and woody plants along an elevational gradient in Eastern Mexico

Phylogenetic information provides insight into the ecological and evolutionary processes that organize species assemblages. We compared patterns of phylogenetic diversity among macromycete and woody plant communities along a steep elevational gradient in eastern Mexico to better understand the evolutionary processes that structure their communities. Macrofungi and trees were counted and identified in eight sites from 100 to 3500 m asl, and sequence data retrieved from GenBank for the same or closely related species were used to reconstruct their phylogenies. Patterns of species richness and phylogenetic diversity were similar for both macrofungi and trees, but macromycete richness and diversity peaked at mid‐elevations, whereas woody plant richness and diversity did not show significant trends with elevation. Phylogenetic similarity among sites was low for both groups and decreased as elevational distance between sites increased. Macromycete communities displayed phylogenetic overdispersion at low elevations and phylogenetic clustering at high elevations; the latter is consistent with environmental filtering at high elevation sites. Woody plants generally exhibited phylogenetic clustering, consistent with the potential importance of environmental filtering throughout the elevational gradient.     

Macroecological patterns of archaeal ammonia oxidizers in the Atlantic Ocean

Macroecological patterns are found in animals and plants, but also in micro‐organisms. Macroecological and biogeographic distribution patterns in marine Archaea, however, have not been studied yet. Ammonia‐oxidizing Archaea (AOA) show a bipolar distribution (i.e. similar communities in the northernmost and the southernmost locations, separated by distinct communities in the tropical and gyral regions) throughout the Atlantic, detectable from epipelagic to upper bathypelagic layers (<2000 m depth). This tentatively suggests an influence of the epipelagic conditions of organic matter production on bathypelagic AOA communities. The AOA communities below 2000 m depth showed a less pronounced biogeographic distribution pattern than the upper 2000 m water column. Overall, AOA in the surface and deep Atlantic waters exhibit distance–decay relationships and follow the Rapoport rule in a similar way as bacterial communities and macroorganisms. This indicates a major role of environmental conditions in shaping the community composition and assembly (species sorting) and no, or only weak limits for dispersal in the oceanic thaumarchaeal communities. However, there is indication of a different strength of these relationships between AOA and Bacteria, linked to the intrinsic differences between these two domains.     

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.     

Metazoan parasites of freshwater cyprinid fish ( Leuciscus cephalus): testing biogeographical hypotheses of species diversity

The diversity and similarity of parasite communities is a result of many determinants widely considered in parasite ecology. In this study, the metazoan parasite communities of 15 chub populations (Leuciscus cephalus) were sampled across a wide geographical range. Three hypotheses of biogeographical gradients in species diversity were tested: (1) latitudinal gradient, (2) a 'favourable centre' versus 'local oasis' model, and (3) decay of similarity with distance. We found that the localities in marginal zones of chub distribution showed lower parasite species richness and diversity. A latitudinal gradient, with increasing abundance of larvae of Diplostomum species, was observed. There was a general trend for a negative relationship between relative prevalence or abundance and the distance from the locality with maximum prevalence or abundance for the majority of parasite species. However, statistical support for a 'favourable centre' model was found only for total abundance of Monogenea and for larvae of Diplostomum species. The phylogenetic relatedness of host populations inferred an important role when the 'favourable centre' model was tested. Testing of the hypothesis of 'decay of similarity with geographical distance' showed that phylogenetic distance was more important as a determinant of similarity in parasite communities than geographical distance between host populations.     

A phylogenetic perspective on species diversity, β‐diversity and biogeography for the microbial world

There is an increasing interest to combine phylogenetic data with distributional and ecological records to assess how natural communities arrange under an evolutionary perspective. In the microbial world, there is also a need to go beyond the problematic species definition to deeply explore ecological patterns using genetic data. We explored links between evolution/phylogeny and community ecology using bacterial 16S rRNA gene information from a high‐altitude lakes district data set. We described phylogenetic community composition, spatial distribution, and β‐diversity and biogeographical patterns applying evolutionary relatedness without relying on any particular operational taxonomic unit definition. High‐altitude lakes districts usually contain a large mosaic of highly diverse small water bodies and conform a fine biogeographical model of spatially close but environmentally heterogeneous ecosystems. We sampled 18 lakes in the Pyrenees with a selection criteria focused on capturing the maximum environmental variation within the smallest geographical area. The results showed highly diverse communities nonrandomly distributed with phylogenetic β‐diversity patterns mainly shaped by the environment and not by the spatial distance. Community similarity based on both bacterial taxonomic composition and phylogenetic β‐diversity shared similar patterns and was primarily structured by similar environmental drivers. We observed a positive relationship between lake area and phylogenetic diversity with a slope consistent with highly dispersive planktonic organisms. The phylogenetic approach incorporated patterns of common ancestry into bacterial community analysis and emerged as a very convenient analytical tool for direct inter‐ and intrabiome biodiversity comparisons and sorting out microbial habitats with potential application in conservation studies.     

Climate and geographic distance are more influential than rivers on the beta diversity of passerine birds in Amazonia

Variation in the spatial structure of communities in terms of species composition (beta diversity) is affected by different ecological processes, such as environmental filtering and dispersal limitation. Large rivers are known as barriers for species dispersal (riverine hypothesis) in tropical regions. However, when organisms are not dispersal limited by geographic barriers, other factors, such as climatic conditions and geographic distance per se, may affect species distribution. In order to investigate the relative contribution of major rivers, climate and geographic distance on Passeriformes beta diversity, we divided Amazonia into 549 grid cells (1° of latitude and longitude) and obtained data of species occurrence, climate and geographic position for each cell. Beta diversity was measured using taxonomic, phylogenetic and functional metrics of composition. The influence of climatic variables, geographic distance and rivers on these metrics was tested using regression analyses. Passerine beta diversity is characterized mainly by the change in species taxonomic identity and in phylogenetic lineages across climatic gradients and over geographic distance. However, species with similar traits are found throughout the entire Amazonia. The size of rivers was proportional to their effect on species composition. However, climate and geographic distance are relatively more important than rivers for Amazonian taxonomic and phylogenetic species composition.     

Arthropod communities on hybrid and parental cottonwoods are phylogenetically structured by tree type: Implications for conservation of biodiversity in plant hybrid zones

Although hybridization in plants has been recognized as an important pathway in plant speciation, it may also affect the ecology and evolution of associated communities. Cottonwood species (Populus angustifolia and P. fremontii) and their naturally occurring hybrids are known to support different plant, animal, and microbial communities, but no studies have examined community structure within the context of phylogenetic history. Using a community composed of 199 arthropod species, we tested for differences in arthropod phylogenetic patterns within and among hybrid and parental tree types in a common garden. Three major patterns emerged. (1) Phylogenetic diversity (PD) was significantly different between arthropod communities on hybrids and Fremont cottonwood when pooled by tree type. (2) Mean phylogenetic distance (MPD) and net relatedness index (NRI) indicated that communities on hybrid trees were significantly more phylogenetically overdispersed than communities on either parental tree type. (3) Community distance (D_pw) indicated that communities on hybrids were significantly different than parental species. Our results show that arthropod communities on parental and hybrid cottonwoods exhibit significantly different patterns of phylogenetic structure. This suggests that arthropod community assembly is driven, in part, by plant–arthropod interactions at the level of cottonwood tree type. We discuss potential hypotheses to explain the effect of plant genetic dissimilarity on arthropod phylogenetic community structure, including the role of competition and environmental filtering. Our findings suggest that cottonwood species and their hybrids function as evolutionarily significant units (ESUs) that affect the assembly and composition of associated arthropod communities and deserve high priority for conservation.