Evolutionary history and environmental variability structure contemporary tropical vertebrate communities

Tropical regions harbor 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. 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, paleo-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. The phylogenetic and functional structure showed
non-significant yet varying tendencies toward 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. 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.