Seasonal variation of abundance and survival of the red ? bellied tree squirrel (Callosciurus erythraeus) introduced in Argentina

BENITEZ, V; ALMADA CHAVEZ, S; MESSETTA, L; GOZZI, C; LAZCOZ, M; DAGNINO, G; DONCASTER, C. P; GUICHÓN, ML

Mendoza, Argentina

Congreso; International Mammalogical Congress; 2009

Biodiversity Research Group (GIB), Institute for Aridlands Research (IADIZA), Center for Science & Technology Mendoza (CCT), National Council of Science and Technology (CONICET), International Federation of Mammalogists(IFM) and SAREM

Following a biological invasion, introduced populations are expected to show marked differences in demographic parameters from their native ancestors. A wild population of the Asiatic red-bellied tree squirrel has established in the Argentine Pampas from a few individuals introduced in 1970. We present results from the first study to estimate population parameters for this exotic squirrel in Argentina. Our objective is to estimate abundance and survival by fitting statistical models to capture-recapture data. Mark-recapture methodology was used at two study sites between October 2007 and November 2008. Squirrels were live-trapped seasonally in a 40x40 m grid over a total of 1370 and 1600 trap days per site. Each individual was tagged with a permanent internal transponder allowing individual recognition on recapture. A record was kept of its sex, weight, and reproductive status. Capture histories of individuals are being used to estimate population size, capturability, and survival rates, using open and robust design methods in MARK software. The best-fitting model in each design is selected on the basis of its AIC. The number of squirrels per hectare is estimated to average 13.3±9.8 s.d. for the open model and 14.9±12.3 s.d. for the robust model. Since capturability estimates are low in both models, minimum number alive (8.3±2.3 ind./ha) may underestimate true abundance. However, extremely low values in some seasons (2-15%) seem to inflate estimations. Survival rates were relatively high throughout the year (open model: 0.82±0.13, robust model: 0.85±0.11). We discuss how the ranging and dispersal behaviour of this invading squirrel is likely to influence capturability and the estimation of density and survival in these populations. Overall density and survival rates estimated in this study are higher than those previously reported for C. erythraeus in its native range. Biological traits favouring invasion success of this squirrel are further analysed.