Browsing by Author "Hsieh, Chia"

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    Evolutionary history and environmental variability structure contemporary tropical vertebrate communities
    (Wiley, 2024) Hsieh, Chia; Gorczynski, Daniel; Bitariho, Robert; Espinosa, Santiago; Johnson, Steig; Lima, Marcela Guimarães Moreira; Rovero, Francesco; Salvador, Julia; Santos, Fernanda; Sheil, Douglas; Beaudrot, Lydia; Program in Ecology and Evolutionary Biology
    Aim Tropical regions harbour over half of the world's mammals and birds, but how their communities have assembled over evolutionary timescales remains unclear. To compare eco-evolutionary assembly processes between tropical mammals and birds, we tested how hypotheses concerning niche conservatism, environmental stability, environmental heterogeneity and time-for-speciation relate to tropical vertebrate community phylogenetic and functional structure. Location Tropical rainforests worldwide. Time period Present. Major taxa studied Ground-dwelling and ground-visiting mammals and birds. Methods We used in situ observations of species identified from systematic camera trap sampling as realized communities from 15 protected tropical rainforests in four tropical regions worldwide. We quantified standardized phylogenetic and functional structure for each community and estimated the multi-trait phylogenetic signal (PS) in ecological strategies for the four regional species pools of mammals and birds. Using linear regression models, we test three non-mutually exclusive hypotheses by comparing the relative importance of colonization time, palaeo-environmental changes in temperature and land cover since 3.3 Mya, contemporary seasonality in temperature and productivity and environmental heterogeneity for predicting community phylogenetic and functional structure. Results Phylogenetic and functional structure showed non-significant yet varying tendencies towards clustering or dispersion in all communities. Mammals had stronger multi-trait PS in ecological strategies than birds (mean PS: mammal = 0.62, bird = 0.43). Distinct dominant processes were identified for mammal and bird communities. For mammals, colonization time and elevation range significantly predicted phylogenetic clustering and functional dispersion tendencies respectively. For birds, elevation range and contemporary temperature seasonality significantly predicted phylogenetic and functional clustering tendencies, respectively, while habitat diversity significantly predicted functional dispersion tendencies. Main conclusions Our results reveal different eco-evolutionary assembly processes structuring contemporary tropical mammal and bird communities over evolutionary timescales that have shaped tropical diversity. Our study identified marked differences among taxonomic groups in the relative importance of historical colonization and sensitivity to environmental change.
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    Evolutionary History, Extinction, and Environmental Variability Shape the Tropical and Subtropical Diversity Disparity of Terrestrial Mammals
    (2024-08-01) Hsieh, Chia; Beaudrot, Lydia
    Tropical and subtropical moist forests are home to over half of all extant vertebrate species worldwide, yet they face increasing anthropogenic pressures that are degrading multiple facets of their diversity. High tropical species diversity has been hypothesized to have resulted from an evolutionary history of high species diversification in stable environments relative to temperate regions. However, recent studies have found that varying degrees of environmental variability and historical extinction of large-bodied vertebrates likely lead to the uneven distribution of species richness and body sizes among tropical regions (i.e., tropical diversity disparity) on different continents. However, little is known about how evolutionary history, historical extinction, and environmental variability have shaped the geographic differences among tropical regions in other facets of their diversity. This limited knowledge not only hinders our ability to unravel fundamental questions about drivers of biodiversity distributions but also to assess biodiversity changes that have implications for conservation given ongoing anthropogenetic pressure and environmental change. Hence, to address this research gap, I tested the relative effects of evolutionary and macroecological drivers on 1) community structure, 2) predator-prey interactions, and 3) functional diversity of vertebrate assemblages in tropical and subtropical moist forests globally. I focused on mammals because this well-studied vertebrate class has species-level functional trait data, a well-resolved phylogeny, and community composition data available from both in-situ observations and the reconstructed ranges of extinct species. First, using in-situ observations from 15 protected tropical forests worldwide, I found that the coupled phylogenetic and functional community structure of ground-dwelling mammals has been shaped by slow niche evolution, and phylogenetic clustering tendencies were predicted by colonization time. Second, I found geographic differences in the dietary breadth of carnivoran predators among 380 large mammal communities in the Neotropical, Afrotropical, and Indomalayan realms, for which speciation rates and present temperature seasonality supported dietary niche generalization while historical extinction led to dietary niche specialization. Thirdly, I found geographic differences in the vulnerability to functional diversity loss of tropical and subtropical moist forest mammals from historical and predicted future extinctions. Functional vulnerability to loss increased in mammal assemblages with slower niche evolution but decreased under greater present environmental variability. By integrating evolutionary and macroecological approaches, this dissertation has unraveled the essential roles of evolutionary history, extinction, and present environmental variability in shaping multiple facets of the diversity of extant forest mammals in the global tropics and subtropics.