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Extreme homogenization: The past, present and future of mammal assemblages on islands
Author(s) -
Longman Emily K.,
Rosenblad Kyle,
Sax Dov F.
Publication year - 2018
Publication title -
global ecology and biogeography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.164
H-Index - 152
eISSN - 1466-8238
pISSN - 1466-822X
DOI - 10.1111/geb.12677
Subject(s) - jaccard index , homogenization (climate) , mammal , geography , ecology , colonization , biology , biodiversity , artificial intelligence , pattern recognition (psychology) , computer science
Abstract Aim We documented how the similarity of mammal assemblages on continental and oceanic islands has changed since initial human colonization, since European arrival and overall. We investigated how levels of similarity might change in the future. Location Continental and oceanic islands worldwide. Time period Human settlement of islands to the present, as well as projections for the future. Major taxa studied Mammals. Methods We used mammal occurrence data on islands to calculate the change in similarity using a pairwise approach based on Jaccard's index and a multisite approach based on Jaccard's and Sørensen's measures. We divided the mammal assemblages into two time periods, before and after island colonization or trade began with Europeans. We unpacked the mechanisms driving changes in similarity, exploring how initial similarity interacts with seven types of species turnover events to determine overall change. Finally, we calculated how future similarity levels will change if past trends in introductions and extinctions continue. Results Mammals, on both continental and oceanic islands, show one of the most pronounced cases of homogenization ever observed, and on oceanic islands mammals show the largest increase in homogenization ever observed for a terrestrial group. Most of the homogenization observed to date has been driven by recent historical changes, not by changes that occurred before European arrival. If current patterns of species introductions and extinctions continue, then oceanic islands will experience little additional homogenization, whereas continental islands will homogenize greatly beyond current levels. Main conclusions Mammal assemblages on oceanic islands show nearly an order of magnitude greater change in similarity than plant and bird assemblages. Projections of future similarity indicate that continental and oceanic islands are on different trajectories of change. These trajectories could be altered by management actions, but in some cases those actions that would be impactful run counter to current conservation norms.