Phylogeny and extinction risk in mammals

Abstract

Detailed knowledge of the evolutionary relationships between species can inform studies in ecology and conservation. This phylogenetic information is becoming a recognized basis for evaluating conservation priorities. However, associations between species risk of extinction and the properties of a phylogeny such as diversification rates and phylogenetic lineage ages remain unclear. Limited taxon-specific analyses suggest that species in older lineages are at greater risk. Extinction due to chance events is more likely over time, or groups may become more specialized over time, reducing their potential to adapt to new conditions. This thesis has four main parts. The first aims to identify evolutionary characteristics that predict the fates of species, by testing for associations between lineage age, clade size, diversification rates, evolutionary distinctiveness and extinction risk for terrestrial mammals. There were no significant global or regional associations, and three significant results within two taxonomic groups. Extinction risk increases for evolutionarily unique primates and decreases with lineage age when lemurs are excluded. Lagomorph species (rabbits, hares and pikas) that have more close relatives are less threatened. The second part of this thesis investigates why primate species in both younger and evolutionarily distinct lineages are more likely to be threatened. This section aims to identify the immediate causes of extinction risk (e.g. factors such as hunting and habitat loss and their variation in space) and how they relate to evolutionary history and species biology. The relationships between phylogeny and extinction risk are mediated by the evolutionary trend of increasing body size through time. Evolutionarily distinct primate species are smaller- bodied and thus more susceptible to the effects of habitat fragmentation. Species in younger lineages generally have larger body sizes. Larger species are preferentially hunted and reproductively less resilient. The third section of the thesis examines why lagomorph species with fewer close relatives are more likely to be threatened. The non-random extinction of small clades disproportionately threatens genetic diversity and phylogenetic history. This section explores the lagomorph phylogeny to test if differences in lagomorph evolution, biogeography and ecology explain current patterns of diversity and threat. Diversification was unrelated to climate, topography, geographic range size or geographic isolation. For lagomorphs in general, extinction risk was positively correlated with increasing human population density and negatively correlated with occurrence in anthropogenically modified habitat. Habitat generalists were less likely to be threatened, and paleoendemic species with few close relatives tend to be habitat specialists. The fourth and final section of the thesis expands on the use of phylogenies in ecology and conservation. This chapter aims to quantify ecological similarity between rodent species in order to compare it with phylogenetic relatedness. Results are related to ecological theory on ecological character displacement, and to conservation in the context of competition between introduced and native species. Morphological data can identify species with high probabilities of competing with invasive rats and house mice. The findings of this thesis contribute to our understanding of the patterns of threat to evolutionary history. The results in each section incorporate spatially explicit data on threats to mammals, and a process-based approach to interpreting the patterns of diversity. The inclusion of paleobiogeographic data provides more information on the origins of diversity and how to best preserve it. These research outputs can assist in planning and implementing actions to mitigate threats and conserve multiple measures of diversity.