On the expansion threshold of a species' range

June 19, 2018, University of Vienna
Species’ range margins arise due to intrinsic interplay between ecological and evolutionary dynamics. The collapse of adaptation can be explained by just two dimensionless parameters - these are depicted on the axes. Adaptation fails when genetic drift reduces genetic diversity below that required for adaptation to heterogeneous environment. Credit: Polechova

What stops a species adapting to an ever-wider range of conditions, continuously expanding its geographic range? The biomathematician Jitka Polechová, an Elise Richter Fellow at the University of Vienna, has published a paper in PLoS Biology which 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.

All species have restricted distributions. Yet a joint coherent 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 reduces 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 . Furthermore, the theory explains that the benefits of into marginal populations are likely to outweigh the costs, offering a theoretical base for management strategies of threatened populations.

Explore further: Hitting the borders of expansion

More information: Jitka Polechová et al. Is the sky the limit? On the expansion threshold of a species' range, PLOS Biology (2018). DOI: 10.1371/journal.pbio.2005372

Related Stories

Hitting the borders of expansion

May 5, 2015

Why does a species not adapt to an ever-wider range of conditions, gradually expanding its geographical range? In their paper published on May 5 in PNAS (Proceedings of the National Academy of Sciences), Jitka Polechova and ...

Genetic diversity helps protect against disease

May 23, 2018

So much for survival of the fittest – diversity is the key: a team of researchers from the Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB) has succeeded in demonstrating experimentally that genetic diversity ...

Dispersal key for understanding marine biodiversity

October 28, 2016

Dispersal plays a key role to connect populations, and contrastingly, its moderate limitation is one of the main processes to maintain species coexistence and promote regional biodiversity. A study recently published in Scientific ...

Species' evolutionary choice—disperse or adapt?

April 28, 2015

Dispersal and adaptation are two fundamental evolutionary strategies available to species given an environment. Generalists, like dandelions, send their offspring far and wide. Specialists, like alpine flowers, adapt to the ...

Recommended for you

Some female termites can reproduce without males

September 24, 2018

Populations of the termite species Glyptotermes nakajimai can form successful, reproducing colonies in absence of males, according to a study published in the open access journal BMC Biology.

Photosynthesis discovery could help next-gen biotechnologies

September 24, 2018

Researchers from The University of Queensland (UQ) and the University of Münster (WWU) have purified and visualized the 'Cyclic Electron Flow' (CEF) supercomplex, a critical part of the photosynthetic machinery in all plants, ...

How fruits got their eye-catching colors

September 24, 2018

Red plums. Green melons. Purple figs. Ripe fruits come in an array of greens, yellows, oranges, browns, reds and purples. Scientists say they have new evidence that plants owe their rainbow of fruit colors to the different ...

Custom circuits for living cells

September 24, 2018

A team of Caltech researchers has developed a biological toolkit of proteins that can be assembled together in different ways, like Legos, to program new behaviors in cells. As a proof-of-concept, they designed and constructed ...

Birds' voiceboxes are odd ducks

September 24, 2018

Birds sing from the heart. While other four-limbed animals like mammals and reptiles make sounds with voiceboxes in their throats, birds' chirps originate in a unique vocal organ called the syrinx, located in their chests. ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.