Phylogenetic structure of mammal assemblages at large geographical scales: linking phylogenetic community ecology with macroecology

Abstract

Phylogenetic community ecology seeks to explain the processes involved in the formation of species assemblages by analysing their phylogenetic structure, and to date has focused primarily on local-scale communities. Macroecology, on the other hand, is concerned with the structure of assemblages at large geographical scales, but has remained largely non-phylogenetic. Analysing the phylogenetic structure of large-scale assemblages provides a link between these two research programmes. In this paper, I ask whether we should expect large-scale assemblages to show significant phylogenetic structure, by outlining some of the ecological and macroevolutionary processes that may play a role in assemblage formation. As a case study, I then explore the phylogenetic structure of carnivore assemblages within the terrestrial ecoregions of Africa. Many assemblages at these scales are indeed phylogenetically non-random (either clustered or overdispersed). One interpretation of the observed patterns of phylogenetic structure is that many clades underwent rapid biome-filling radiations, followed by diversification slowdown and competitive sorting as niche space became saturated.

Figure 1.

Numbers of African ecoregions showing significant phylogenetic structure in carnivore assemblages, using two metrics, NRI and NTI. (a) Null models constructed from biome source pools, (b) null models constructed from continental source pools. Light grey bars, clustered; unfilled bars, random; dark grey bars, overdispersed.

Figure 2.

Box and whisker plots showing the distributions of p-values (on the x-axis) for phylogenetic structure metrics ((a,c) NRI and (b,d) NTI) among ecoregions. Null models are constructed from (a,b) biome and (c,d) continental source pools. p-values at the left extreme of the distributions (p < 0.025) indicate phylogenetic clustering; p-values at the right extreme of the distributions (p > 0.975) indicate phylogenetic overdispersion. Ecoregions are grouped into biomes, as follows: TSMBF, tropical and subtropical moist broadleaf forests; TSGSS, tropical and subtropical grasslands, savannahs and shrublands; MGS, montane grasslands and shrublands; MFWS, Mediterranean forests, woodlands and scrub; FGS, flooded grasslands and savannahs; DXS, deserts and xeric shrublands. Width of the boxes is proportional to the number of ecoregions in each biome.

Figure 3.

Associations between ecoregion area and phylogenetic structure ((a,c) NRI and (b,d) NTI) of ecoregion carnivore assemblages, using null models constructed from (a,b) biome and (c,d) continental source pools. Open circles represent ecoregions in which assemblage structure is consistent with the null model; triangles represent ecoregions in which assemblages are significantly overdispersed (positive NRI or NTI value) or significantly clustered (negative NRI or NTI value).