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 distinct 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 smallerbodied and thus more susceptible to the effects of habitat fragmentation. Species in younger v Publications during candidature Peer-reviewed papers Verde Arregoitia, L.D., Blomberg, S.P. & Fisher, D.O. (2013) Phylogenetic correlates of extinction risk in mammals: species in older lineages are not at greater risk.

The role of evolutionary modes for trait-based cascades in mutualistic networks

“…Here we evaluated trait-based cascades using minimal model systems of phylogenetically structured mutualistic networks. Although species’ traits can drive organismal and organism-environment interactions in a myriad of complex manners, we explored two specific dimensions of functional diversity expected to have strong consequences to ecological dynamics: body size, a dimension of functional diversity with ubiquitous effect on ecological systems (Purvis et al 2000; Cardillo et al 2005; Reynolds et al 2005; Seguin et al 2014; Terzopoulou et al, 2015; Verde Arregoitia, 2016; Chichorro et al 2019) and trait distinctiveness, a facet of functional diversity that warrants unique and/or rare biological interactions and ecosystem functions (Violle et al 2017). Our results show that extinction cascades based on trait distinctiveness have a more detrimental effect on network robustness, especially when traits evolve under strong phylogenetic signal.…”

“…Although body size has been found to be a fundamental trait capable of predicting species response to environmental gradients (Seguin et al 2014; Fritschie & Olden 2016) and their extinction risk (Purvis et al 2000; Cardillo et al 2005; Reynolds et al 2005; Terzopoulou et al, 2015; Verde Arregoitia, 2016; Chichorro et al 2019), its effects depend on the threat and responses and can be fairly inconsistent, as size is represented by different aspects among taxonomic groups (Chichorro et al 2019). As our simulations are independent of taxonomic identity (and therefore generalist), our finding that trait distinctiveness was more important for robustness further supports the inclusion of other traits, or other facets of functional diversity, rather than size-related traits alone.…”