In the wild, small means death, whether the adjective describes the size or number. These life forms usually have secret weapons to defend themselves in the face of danger. However, what if a population that was large in number, with no exclusive “weapons” of their own, suddenly dwindled down to just a few individuals? The case of Iberian Lynx population represents such a dire case. Palomares and colleagues from Department of Conservation Biology in Estacion Biologica de Donana (CSIC) explored these two lynx populations as a model to determine whether demographic and genetic traits changed over time in vertebrates, which they discovered to be true. They also found that over time, female-biased sex ratio developed, age of territory acquisition decreased, mean litter size decreased, and rates of non-traumatic mortality increased, but there were no significant changes in overall mortality rates.
Twenty-five years ago, there were 10 Iberian lynx populations on the Iberian Peninsula. Now, only two remain. Located in Sierra Morena and Donana in Spain, the Iberian Lynx (Lynx Pardinus) populations are on the verge of extinction. They are going through what is known as extinction vortex – a positive feedback mechanism as a population size decreases. Small population, sex ratio bias, and inbreeding depression are some of the factors that contribute to extinction vortex and it becomes exceedingly difficult for any population to get out of it. These lynxes were not always small in number. Ever since the study was begun in 1983, the population size reduced little by little, and then eventually it plummeted due to a rabbit hemorrhagic disease outbreak (rabbits are lynxes’ primary prey).
The two lynx populations remaining in Sierra Morena and Donana were studied. In order to acquire and organize data, they used the methods of capture and radio-tracking, track surveys, and camera trapping. For genetic analyses, they obtained blood and tissue from captured or necropsied individuals. The study was started in 1983 and was extended to 2008 and the data were divided as early or late periods for this study in order to compare the relative decreases in population size. Only 2 to 10-year-old adults were considered because within this range, the animals breed and hold territories.
These results provided empirical evidence of how demographic and genetic traits may change concurrently and rapidly over time in a small, free-ranging vertebrate population at high risk of extinction. Even though the population remained small, several of these traits were associated with lowered individual fitness, which is counterintuitive according to theory of natural selection. Thus, the Iberian lynx population may be in extinction vortices. There were striking changes between the early and late periods of the study, which may be related to the abundance of the rabbits. The recovery of small vertebrate populations such as that of Iberian lynx subject to an extinction vortex may be particularly difficult. For the extant Iberian lynx to escape the extinction-vortex dynamic, restoration of habitat to increase carrying capacity and manipulation of demographic traits to increase genetic variability are absolutely necessary. Future studies would have to focus on other long-term projects of recovering populations in extinction vortex with these hypotheses, which would prevent further losses of essential species that maintain the natural systems on Earth.
Palomares, F., Godoy J. A., Rodriguez, A., Roques, S., Casasmarce, M., Revilla, E., Delibes, M. Aug 2012. Possible Extinction Vortex for a Population of Iberian Lynx on the Verge of Extirpation. Conservation Biology. “26 (4): 689–697.”