Topic description / abstract:

What stops a species adapting to an ever-wider range of conditions, continuously expanding its geographic range?  All species have restricted distributions. Yet a theory explaining the span, continuity and borders of species’ ranges has been missing both due to the complexity of the problem and the disparate traditions in ecology and evolution. First, I will show that just two compound parameters are fundamental to the stability of a species’ range. The two parameters are 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 genetic diversity drops below that required for adaptation to a heterogeneous environment. The basic prediction is that a species will stop expanding as its parameters fall bellow the expansion threshold. Yet, there are other consequences: as conditions change over time, even the entire species’ range may find itself below the expansion threshold. This can lead to fragmentation of the species’ range — or even a collapse of the entire range and extinction of the species. In the second part of my talk, I will talk about the implications of the dynamic range fragmentation.

Biographical note:

Jitka Polechová is an evolutionary ecologist.  A biologist by training, she has been working on various aspects of speciation and species’ range dynamics. She has obtained her PhD in Zoology in 2005 from the Charles University in Prague, having spent about half of her time at the University of Edinburgh, developing theory of speciation. Then she moved to the University Tennessee, Knoxville, and started to work in species’ range problems. Next, when at the Center for Theoretical Study, Prague, she delved briefly into macroecological theory. Subsequently she moved back to Edinburgh for a couple of years, before arriving in Vienna in 2009 as a first postdoctoral research fellow of IST Austria. In 2015 she has been awarded Elise Richter Fellowship at the Department of Mathematics of the University of Vienna to work on evolutionary ecology of species’ ranges.