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Is the sky the limit? On the expansion threshold of a species' range

Date:
June 19, 2018
Source:
University of Vienna
Summary:
What stops a species adapting to an ever-wider range of conditions, continuously expanding its geographic range? A biomathematician now explains the formation of species' range margins. The theory shows that just two compound parameters, important for both ecology and evolution of species, are fundamental to the stability of their range: the environmental heterogeneity and the size of the local population.
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All species have restricted distributions. Yet a joint coherent theory explaining the span and borders of species' ranges has been missing both due to the complexity of the problem and the disparate traditions in ecology and evolution. Jitka Polechová provides a general, testable prediction for formation of species' range margins. The theory includes both population and evolutionary dynamics, and elucidates the role of dispersal for adaptation across a species' range. Dispersal has conflicting effects: on the beneficial side, it increases the genetic variation that is necessary for adaptation and counters the loss of genetic diversity due to genetic drift. However, dispersal also carries a cost: it may swamp adaptation to local conditions. This interplay is crucial for the evolution of a species' range.

The novel theory demonstrates that adaptation across a species' range depends on two dimensionless parameters: i) the fitness cost of dispersal -- a measure of environmental heterogeneity, and ii) the strength of genetic drift -- a measure of the reduction of genetic diversity. The more heterogeneous is an environment, the more challenging it is to expand into, and the lower the genetic diversity, the more limited is the scope for potential adaptation. Together, these two parameters define an expansion threshold: adaptation fails when the number of individuals accessible by dispersal within one generation is so small that genetic drift reduces genetic diversity below that required for adaptation to a heterogeneous environment. This threshold provides a testable prediction for the formation of a range margin and for the collapse of a species' range.

Interestingly, the parameters are independent of the genetic architecture, offering a wide scope for empirical tests of the theory across many species. Furthermore, the theory explains that the benefits of dispersal into marginal populations are likely to outweigh the costs, offering a theoretical base for management strategies of threatened populations.


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Materials provided by University of Vienna. Note: Content may be edited for style and length.


Journal Reference:

  1. Jitka Polechov�. Is the sky the limit? On the expansion threshold of a species’ range. PLOS Biology, 2018; 16 (6): e2005372 DOI: 10.1371/journal.pbio.2005372

Cite This Page:

University of Vienna. "Is the sky the limit? On the expansion threshold of a species' range." ScienceDaily. ScienceDaily, 19 June 2018. <www.sciencedaily.com/releases/2018/06/180619122522.htm>.
University of Vienna. (2018, June 19). Is the sky the limit? On the expansion threshold of a species' range. ScienceDaily. Retrieved December 13, 2024 from www.sciencedaily.com/releases/2018/06/180619122522.htm
University of Vienna. "Is the sky the limit? On the expansion threshold of a species' range." ScienceDaily. www.sciencedaily.com/releases/2018/06/180619122522.htm (accessed December 13, 2024).

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