Phylogenetic approaches for studying competition in mammals

Abstract

Interspecific competition is often proposed to shape mammalian evolution. Many studies use trait and distribution data on extant species, but this ignores temporal aspects of competition. Phylogeny provides a framework for integrating present-day data with clade histories. Here, I use phylogenetic comparative methods and present-day data to investigate the role of competition in the evolution of four mammalian clades: New World leaf-nosed bats (Phyllostomidae), New World monkeys (Platyrrhini), Australasian possums (Phalangeriformes), and ground squirrels (Marmotini). I ask four specific questions: (1) Do community phylogenies, and/or the traits of community members, show patterns expected under competition? (2) Is there evidence of competition in the relationship among species’ trait differences, phylogenetic differences and patterns of coexistence? (3) Does the intensity of competition affect rates of morphological evolution? (4) Are the tempo and/or mode of mammalian body size evolution influenced by competition? I found evidence for competition in monkeys and squirrels, but not bats or possums. Competition did not influence rates of morphological evolution; instead body mass was the most important correlate across the groups. Across all mammals, the best-supported model of body size evolution corresponded to a scenario in which mammals experienced a relatively early burst of morphological evolution, followed by a slowdown in rate as competition for niches increased. In addition, around 60% of the variation in the tempo of body-mass evolution was explained by just a few predictors. In conclusion, I find some support for competition shaping mammalian evolution. However, there is evidence that the importance of other processes may outweigh the effects of competition in some groups. Further study and methodological improvements are required to fully understand the relative role of competition in evolution. The methods developed in this thesis provide a useful starting point for such studies.