Decomposing the causes for niche differentiation between species using hypervolumes

Abstract

1. Hutchinsons n-dimensional hypervolume concept holds a central role across different fields of ecology and evolution. The question of the amount of hyper-volume overlap and differentiation between species is of great interest to understand the processes that drive niche dynamics, competitive interactions and, ultimately, community assembly.\n\n2. A novel framework is proposed to decompose overall differentiation among hypervolumes into two distinct components: niche shifts and niche contraction / expansion processes. Niche shift corresponds to the replacement of space between the hypervolumes occupied by two species, whereas niche contraction / expansion processes correspond to net differences between the amount of space enclosed by each hypervolume.\n\n3. Hypervolumes were constructed for two Darwin finches, Geospiza conirostris and Geospiza magnirostris, using intraspecific trait data from Genovesa Island, where they live in sympatry. Results showed that significant niche shifts, not niche contraction, occurred between these species. This means that Geospiza conirostris occupied a different niche space and not a reduced space on Genovesa.\n\n4. The proposed framework allows disentangling different processes and understand the drivers of niche partitioning between coexisting species. Niche displacement due to competition can this way be separated from niche contraction due to specialization or expansion due to lower pressure on newly occupied ecological settings.