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1. The biotic interactions hypothesis partially explains bird species turnover along a lowland Neotropical precipitation gradient

   https://doi.org/10.1111/geb.13047  

   Gomez, Juan Pablo ; Ponciano, José Miguel ; Londoño, Gustavo A. ; Robinson, Scott K. ; Fleishman, ed., Erica ( December 2019 , Global Ecology and Biogeography)

   We evaluated the influence of climate on the structure of bird communities along precipitation gradients. We hypothesize that mechanisms responsible for community turnover along precipitation gradients are similar to mechanisms operating along temperature and latitudinal gradients. We tested the hypothesis that environmental conditions affect community composition in dry forests, whereas biotic interactions affect community composition in wet forests.

   Low‐elevation forests along a precipitation gradient in Colombia where precipitation ranges from 700–4,000 mm annually but elevation and temperature remain constant.

   Present day.

   Neotropical forest birds.

   We sampled at 291 points in nine study areas (localities) across thec. 3,000‐mm precipitation range. In each locality, we obtained climatic characteristics and phylogenetic, morphological and physiological proxy data to test predictions about the evolutionary relationships and distribution of traits.

   Bird communities changed abruptly along the precipitation gradient and differed between dry and wet forests. Analyses of phylogenetic relationships, trait space, and observations at nests suggested that environmental filtering is more important in dry than in wet forests, especially for breeding. In contrast, we found little evidence that competition was more important in wet than in dry forests. Nest predation or competition for nest space, however, may be more critical in wetter forests.

   The two distinct bird communities we documented suggest that lowland precipitation gradients, across which temperature is constant, can be as important as temperature gradients in generating high beta diversity. We conclude that breeding in bird communities might be crucial for determining community assembly along environmental gradients. Given that recent population declines in tropical birds have been attributed to changes in precipitation, by understanding the mechanisms underlying community assembly along precipitation gradients our study may improve our ability to understand those declines and predict the effects of climate change on Neotropical avifauna.

    

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2. Deep biogeographic barriers explain divergent global vertebrate communities

   https://doi.org/10.1038/s41467-024-46757-z  

   Williams, Peter J. ; Zipkin, Elise F. ; Brodie, Jedediah F. ( March 2024 , Nature Communications)

   Biogeographic history can lead to variation in biodiversity across regions, but it remains unclear how the degree of biogeographic isolation among communities may lead to differences in biodiversity. Biogeographic analyses generally treat regions as discrete units, but species assemblages differ in how much biogeographic history they share, just as species differ in how much evolutionary history they share. Here, we use a continuous measure of biogeographic distance, phylobetadiversity, to analyze the influence of biogeographic isolation on the taxonomic and functional diversity of global mammal and bird assemblages. On average, biodiversity is better predicted by environment than by isolation, especially for birds. However, mammals in deeply isolated regions are strongly influenced by isolation; mammal assemblages in Australia and Madagascar, for example, are much less diverse than predicted by environment alone and contain unique combinations of functional traits compared to other regions. Neotropical bat assemblages are far more functionally diverse than Paleotropical assemblages, reflecting the different trajectories of bat communities that have developed in isolation over tens of millions of years. Our results elucidate how long-lasting biogeographic barriers can lead to divergent diversity patterns, against the backdrop of environmental determinism that predominantly structures diversity across most of the world.

    

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3. Phylogenetic uniqueness, not latitude, explains the diversity of avian blood parasite communities worldwide

   https://doi.org/10.1111/geb.12741  

   Clark, Nicholas J. ( April 2018 , Global Ecology and Biogeography)

   Characterizing macroecological patterns in biodiversity is key to improve our understanding of community assembly. Global biodiversity for many taxa follows a latitudinal gradient, with increased diversity in tropical latitudes. Less is known about global parasite biodiversity, inhibiting our ability to predict how global change will impact parasitic disease emergence. Using distribution and phylogenetic data for 2,386 avian haemosporidian blood parasites (generaPlasmodium,HaemoproteusandLeucocytozoon), I assessed how contemporary and historical drivers influence the composition of parasite communities worldwide.

   Global.

   Current.

   Haemosporidian blood parasites.

   Parasite distribution and cytochrome bsequence data were accessed from an open‐source database. Bayesian phylogenetic tree distributions were constructed for each parasite genus using two substitution models to capture uncertainty. Hierarchical regressions assessed effects of environmental variation, latitude and phylogenetic β‐diversity (β_div; a proxy for phylogenetic uniqueness) on the diversity and asymmetry of parasite communities around the globe.

   I uncovered biodiversity hotspots and identified broad variation in global diversity patterns among parasite genera. Community diversity increased with increasing phylogenetic uniqueness for all three parasite genera; however, these diverse and unique regions did not consistently occur in the tropics. I found no evidence of a latitudinal diversity gradient, and support for a latitudinal gradient in community phylogenetic asymmetry was weak.

   Global variation in avian haemosporidian phylogenetic diversity does not reflect a latitudinal gradient. Instead, parasite biogeography may reflect fundamental differences in host‐switching tendencies or the timing of avian evolutionary radiations. Examining the interplay between shared evolutionary history and phylogenetic diversity can provide important insights into the drivers of parasite biodiversity at global scales.

    

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4. The distribution of plants and seed dispersers in response to habitat fragmentation in an artificial island archipelago

   https://doi.org/10.1111/jbi.13568  

   Liu, Jiajia ; Slik, Ferry ; Coomes, David A. ; Corlett, Richard T. ; Wang, Yanping ; Wilson, Maxwell ; Hu, Guang ; Ding, Ping ; Yu, Mingjian ( April 2019 , Journal of Biogeography)

   Small, old‐growth forest fragments generally have more small‐seeded plants than large patches, due to the disappearance of large seed dispersing vertebrates. This pattern may differ for secondary forest fragments where differential migration ability rather than persistence of seed dispersers may be driving plant community assembly. In this study, we investigated the effect of habitat fragmentation on seed dispersers and plant community structure in regenerating forests.

   The Thousand Island Lake, China.

   Plants, birds and mammals.

   We compiled diversity and abundance data for birds and mammals on islands in the Thousand Island Lake, China. We also surveyed the secondary plant communities and measured seed dispersal traits.

   Community‐weighted mean seed size of woody plants decreased with island size. This pattern was related to compositional difference of the dispersers. We found that mammal diversity and abundance was only weakly or not related to island size; whereas bird diversity and abundance increased strongly with island size. Density of bird‐dispersed plants was significantly positively related with island size. Since birds tend to disperse smaller seeds than mammals, the trend in seed size may have been a consequence of the shift in relative abundance of the two disperser guilds.

   Differential responses of seed dispersers to habitat fragmentation may lead to pervasive shifts in the plant community structure of regenerating forest fragments. Our study highlights the importance of keeping large continuous forests in order to retain mammals and their dispersal capabilities.

    

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5. Dispersal syndromes drive the formation of biogeographical regions, illustrated by the case of Wallace’s Line

   https://doi.org/10.1111/geb.13250  

   White, Alexander E. ; Dey, Kushal K. ; Stephens, Matthew ; Price, Trevor D. ; Nogué, ed., Sandra ( January 2021 , Global Ecology and Biogeography)

   Biogeographical regions (realms) reflect patterns of co‐distributed species (biotas) across space. Their boundaries are set by dispersal barriers and difficulties of establishment in new locations. We extend new methods to assess these two contributions by quantifying the degree to which realms intergrade across geographical space and the contributions of individual species to the delineation of those realms. As our example, we focus on Wallace’s Line, the most enigmatic partitioning of the world’s faunas, where climate is thought to have little effect and the majority of dispersal barriers are short water gaps.

   Indo‐Pacific.

   Present day.

   Birds and mammals.

   Terrestrial bird and mammal assemblages were established in 1‐degree map cells using range maps. Assemblage structure was modelled using latent Dirichlet allocation, a continuous clustering method that simultaneously establishes the likely partitioning of species into biotas and the contribution of biotas to each map cell. Phylogenetic trees were used to assess the contribution of deep historical processes. Spatial segregation between biotas was evaluated across time and space in comparison with numerous hard realm boundaries drawn by various workers.

   We demonstrate that the strong turnover between biotas coincides with the north‐western extent of the region not connected to the mainland during the Pleistocene, although the Philippines contains mixed contributions. At deeper taxonomic levels, Sulawesi and the Philippines shift to primarily Asian affinities, resulting from transgressions of a few Asian‐derived lineages across the line. The partitioning of biotas sometimes produces fragmented regions that reflect habitat. Differences in partitions between birds and mammals reflect differences in dispersal ability.

   Permanent water barriers have selected for a dispersive archipelago fauna, excluded by an incumbent continental fauna on the Sunda shelf. Deep history, such as plate movements, is relatively unimportant in setting boundaries. The analysis implies a temporally dynamic interaction between a species’ intrinsic dispersal ability, physiographic barriers, and recent climate change in the genesis of Earth’s biotas.

    

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