A five-year cycle of coypu abundance in a remnant wetland: A case of sink population collapse?

In this work, we report a five-year study (2008–2013) of a coypu sub-population in a Mediterranean remnant wetland. Using a standardized transect, irregular inter-annual and seasonal patterns in mean abundance were observed over the five year period. A first phase of demographic explosion in autumn-winter 2008 was followed from 2009 to 2011 by a yearly-based hump-shaped pattern, with a progressive increase from winter to summer and a decline in abundance from late summer to winter. In 2013, a population crash was observed, with individuals being detected only occasionally. In 2010–2011, pattern in mean abundance was significantly correlated to pattern in minimum daily temperatures. Finally, in February 2012 a single event of snow with low temperatures probably contribute to the local population collapse. The correspondence between a strong isolated meteorological event (snow and sleet) and the disappearance of clear seasonal hump-shaped patterns followed by a population collapse suggests that this single climatic phenomenon played a role in strongly reducing coypu numbers. Our data may corroborate the hypothesis that extrinsic environmental stochasticity and intrinsic physiological sensitivity to cold weather may be important factors affecting coypu population dynamics. We hypothesize that this peripheral population may be a sink of a larger meta-population at regional scale. Our data may also have implications for wildlife management. In fact, at least for peripheral sub-populations, control/eradication plans should also take into consideration uncertainty deriving from stochastic events, which, disrupting local demography, may affect control success. In this regard, knowledge of spatial structure of coypu sub-populations may be important to devise appropriate strategies of population control.