Abstract
Author SummaryThe changing distribution of species over the surface of the Earth, likened by Darwin to “a grand game of chess with the World for a board”, is a central theme in the evolution of life. Studies of the fossil record and molecular estimates of species ages appear to show that species follow a predictable trend of expansion and contraction of their geographic range over evolutionary time. However, using computer simulations we show that the observed correlation between the age of a species and the extent of its range is expected even if changes in range area have occurred randomly through time. Our results cast doubt on the evidence for directional trends in the long-term evolution of species ranges and suggest that the general rules governing this grand game may need to be re-evaluated.
Highlights
The geographic area occupied by a species is known to vary through time [1,2], but whether these dynamics follow any regular trends or are instead largely idiosyncratic remains controversial [3,4,5,6]
To examine the extent to which these processes could account for the patterns observed between range size and species age, we developed a stochastic model of range evolution that incorporates the effects of speciation and extinction on geographic range size [27,31,32,33]
Range size is positively correlated with evolutionary age across much of the parameter space, and it is evident that high rates of range evolution give rise to stronger positive correlations (Figure 1, unfilled circles), resulting from increased extinction of smallranged species
Summary
The geographic area occupied by a species is known to vary through time [1,2], but whether these dynamics follow any regular trends or are instead largely idiosyncratic remains controversial [3,4,5,6]. In the fossil record, where the trajectories of individual lineages can be traced through time, the predominant trend appears to be for newly formed species to gradually expand their ranges, only to later undergo a gradual decline to extinction This pattern of ‘‘rise and fall’’ has been reported from a taxonomically broad set of groups including mammals [10,20], plankton [8,9], and marine mollusks [7]. A pattern emerging from these studies is that no single model of range evolution appears to apply across groups [3]: while in some cases range size is independent of species age, in others there is evidence for increasing, decreasing, or cyclical range size trends
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