Evolutionary dynamics of the elevational diversity gradient in passerine birds

Abstract Low elevation regions harbor the majority of the world’s species diversity compared to high elevation areas. This global elevational diversity gradient, suggests that lowland species have had more time to diversify, or that net diversification rates have been higher in the lowlands (either due to higher ecological limits or intrinsically higher diversification rates). However, highlands seem to be cradles of diversity as they contain many young endemics, suggesting that their rates of speciation are exceptionally fast. Here, we use a phylogenetic diversification model that accounts for the dispersal of species between different elevations to examine the evolutionary dynamics of the elevational diversity gradient in passerine birds, a group that has radiated globally to occupy almost all elevations and latitudes. We find strong support for a model where passerines diversify at the same rate in the highlands and the lowlands but where the rate of dispersal from high to low elevations is more than twice as fast as in the reverse direction. This suggests that while there is no consistent trend in diversification across elevations, highland regions act as species pumps because the diversity they generate migrates into the lowlands, thus setting up the observed gradient in passerine diversity. This species pump is particularly strong in the tropics, where the inferred rate of speciation is 1.4 times faster than in the temperate zone. We conclude that despite their lower diversity, highland regions are disproportionally important for maintaining diversity in the adjacent lowlands. The extinction of species in the tropical highlands due to rapid climate change this century could thus have major and long-lasting impacts on global passerine diversity.

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From plant populations to communities: using hierarchical trait environment relationships to reveal within ecosystem filtering

10.1101/825471 ◽

2019 ◽

Author(s):

Lucas Deschamps ◽

Raphaël Proulx ◽

Nicolas Gross ◽

Guillaume Rheault ◽

Vincent Maire

Keyword(s):

Evolutionary Dynamics ◽

Functional Trait ◽

Population Characteristics ◽

Diversity Gradient ◽

Species Specific ◽

Turn Over ◽

Favorable Conditions ◽

Nutrient Conservation ◽

Space Occupation ◽

Demographic Responses

AbstractExplaining the existence of highly diverse plant communities under strong abiotic filtering is a long-standing challenge in ecology. Hierarchical aspects of abiotic and biotic filters are rarely taken into account and studies focus mainly on community-level aggregated patterns. Because variations in biotic conditions might take place in short abiotic gradient and within the tolerance of species in regional pool, it is likely that biotic filtering will select individuals within species and adjust population characteristics. To challenge this idea, we replicated a diversity gradient in four highly contrasted wetlands with an almost complete species turn-over, sampling individuals in communities irrespective of their taxonomic identities or status. Using hierarchical distributional modelling, we analyzed the variation of the mean and dispersion of functional trait space at the ecosystem, community and species level. We found that the abiotic differences between ecosystems filtered species contrasted in their growth/nutrient conservation trade-off, while within ecosystems community variation were mainly due to the partitioning of canopy and leaf adaptations to light conditions. We found strong species-specific functional and demographic responses of dominant species along the diversity gradient, especially for traits linked to biomass and space occupation. Two contrasted strategies emerged, with species using plasticity to maintain equally dense populations, while others used plasticity to become overwhelmingly abundant when in favorable conditions. Our results demonstrate that within ecosystems, variation in biotic conditions selects individuals within populations, revealing the importance of phenotypic variation for a species to be maintained in more or less diverse communities. Because phenotypic variations are related to demographic responses, it offers a way to link the study of species diversity and eco-evolutionary dynamics.

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