Factoring history into threat assessments

Posted on December 13, 2016

Genetic variation allows populations to adapt to environmental changes, and it’s often the case that threatened species exhibit low genetic diversity. Human-produced habitat fragmentation is a well-recognised cause of genetic bottlenecks, but the additional effects of larger-scale biogeographic factors are rarely considered. As an example of such biogeographic impacts, populations that have managed to survive glacial extinction events in refuge areas tend to be more genetically diverse than those that were bottlenecked but later recolonised other areas. As a result, genetic diversity tends to be inversely related to the distance from glacial refuges. To see if threat status is related to biogeographic history, researchers at the University of Lausanne, Switzerland, compared the locations of glacial refuges and post-glacial colonization routes with regional and national conservation assessments for 18 widespread amphibian species. Because amphibians have been hard-hit by human-induced pressures (e.g., habitat loss, pesticides, invasive species), the analysis included human population density, pesticide use and fertilizer use as co-variables. Most species, especially the most vulnerable ones, had a higher threat status outside their glacial refuge areas, and their conservation status worsened as distances from these areas increased. Human population density was also a significant predictor of threat status and there was a significant interaction between refuge distance and pesticide use. In amphibians, genetic depression can be reflected in physical abnormalities and reduced survival, larval performance and competitive ability. These findings suggest that a population’s history (i.e., refugial versus post-glacial) should be considered when assessing its conservation status, alongside conventional criteria such as population size, distribution, migration patterns and potential threats.

Reference: Dufresnes, C. & Perrin, N. 2015. Effect of biogeographic history on population vulnerability in European amphibians. Conservation Biology, 29(4), 1235–1241. http://onlinelibrary.wiley.com/doi/10.1111/cobi.12490/pdf