Jens-Christian Svenning | bioRxiv Science

bioRxiv2015

Resurrection of the island rule – human-driven extinctions have obscured a basic evolutionary pattern

Islands are or have been occupied by unusual species, such as dwarf proboscideans and giant rodents. The discussion of the classical but controversial \"island rule,\" which states that mammalian body sizes converge on intermediate sizes on islands, has been stimulated by these unusual species. In this paper, we use an unprecedented global data set of the distributions and the body sizes of mammals and a novel analytical method to analyze body size evolution on islands; the analyses produced strong support for the island rule. Islands have suffered massive human-driven losses of species, and we found that the support for the island rule was substantially stronger when the many late-Quaternary extinct species were also considered (particularly, the tendency for dwarfing in large taxa). In this study, the decisive support generated for the island rule confirmed that evolution is markedly different on islands and that human impact may obscure even fundamental evolutionary patterns.

Ecology↗

bioRxiv2015

Historic and prehistoric human-driven extinctions have reshaped global mammal diversity patterns

AimTo assess the extent to which humans have reshaped Earths biodiversity, by estimating natural ranges of all late Quaternary mammalian species, and to compare diversity patterns based on these with diversity patterns based on current distributions.\n\nLocationGlobally\n\nMethodsWe estimated species, functional and phylogenetic diversity patterns based on natural ranges of all mammalian species (n=5747 species) as they could have been today in the complete absence of human influence through time. Following this we compared macroecological analyses of current and natural diversity patterns to assess if human-induced range changes bias for evolutionary and ecological analyses based on current diversity patterns.\n\nResultsWe find that current diversity patterns have been drastically modified by humans, mostly due to global extinctions and regional to local extirpations. Current and natural diversities exhibit marked deviations virtually everywhere outside sub-Saharan Africa. These differences are strongest for terrestrial megafauna, but also important for all mammals combined. The human-induced changes led to biases in estimates of environmental diversity drivers, especially for terrestrial megafauna, but also for all mammals combined.\n\nMain conclusionsOur results show that fundamental diversity patterns have been reshaped by human-driven extinctions and extirpations, highlighting humans as a major force in the Earth system. We thereby emphasize that estimating natural distributions and diversities is important to improve our understanding of the evolutionary and ecologically drivers of diversity as well as for providing a benchmark for conservation.

Ecology↗