Interdependent phenotypic and biogeographic evolution driven by biotic interactions

Biotic interactions are hypothesized to be one of the main processes
shaping trait and biogeographic evolution during lineage diversification.
Theoretical and empirical evidence suggests that species with similar
ecological requirements either spatially exclude each other, by preventing
the colonization of competitors or by driving coexisting populations to
extinction, or show niche divergence when in sympatry. However, the extent
and generality of the effect of interspecific competition in trait and
biogeographic evolution has been limited by a dearth of appropriate
process-generating models to directly test the effect of biotic
interactions. Here, we formulate a phylogenetic parametric model that
allows interdependence between trait and biogeographic evolution, thus
enabling a direct test of central hypotheses on how biotic interactions
shape these evolutionary processes. We adopt a Bayesian data augmentation
approach to estimate the joint posterior distribution of trait histories,
range histories, and co-evolutionary process parameters under this
analytically intractable model. Through simulations, we show that our
model is capable of distinguishing alternative scenarios of biotic
interactions. We apply our model to the radiation of Darwin’s finches—a
classic example of adaptive divergence—and find limited support for in
situ trait divergence in beak size, but stronger evidence for convergence
in traits such as beak shape and tarsus length and for competitive
exclusion throughout their evolutionary history. These findings are more
consistent with pre-sympatric, rather than post-sympatric, niche
divergence. Our modeling framework opens new possibilities for testing
more complex hypotheses about the processes underlying lineage
diversification. More generally, it provides a robust probabilistic
methodology to model correlated evolution of continuous and discrete
characters.