Intra-specific competition, land-use and climate effects in the dynamics of two rodent species in Argentina

VERÓNICA ANDREO; MAURICIO LIMA; CECILIA PROVENSAL; JOSÉ PRIOTTO; JAIME POLOP

Mendoza

Congreso; 10th International Mammalogical Congress; 2009

Center for Science and Technology - CCT CONICET Mendoza, CONICET, International Federation of Mammalogists (IFM), Sociedad Argentina para el estudio de los Mamíferos (SAREM), entre otras instituciones

The objective of this work was to explain the numerical fluctuations of two sympatric rodent species in agro-ecosystems of central Argentina. We used mark–recapture data from small-mammal live-trapping conducted monthly from January 1990 to June 2007 in a 6 x 10 grid (0.30 ha). Peak annual MNKA (minimum number of animals known to be alive) obtained after the reproductive season of each year was used as an estimate of population abundance. Data series of temperature and rainfall were provided by the National University of Río Cuarto (Argentina). Normalized difference vegetation index (NDVI) data series was obtained from the global inventory modeling and mapping studies (GIMMS) AVHRR 8km (1981–2006) data set. We estimated the order of the feedback structure for each species by means of the partial rate correlation function (PRCF). We fitted the non-linear logistic population model of discrete time proposed by Royama (including extra terms to account for exogenous effects) using non-linear regression analyses. Models with the lowest AICc (Akaike information criterion corrected for small-sample bias) values were selected to draw inferences and run deterministic predictions to simulate the dynamic behavior of the fitted models. We found that both rodent species show a first-order negative feedback structure suggesting that these populations are regulated by intra-specific competition (limited by food, space or enemy free space). In Akodon azarae endogenous structure seems to be strongly influenced by human land-use represented by annual minimum NDVI, with spring and summer rainfall having little influence upon carrying capacity. Calomys venustus’ population dynamics, on the other hand, appears to be more affected by local climate, also with spring and summer rainfall influencing the carrying capacity of the environment, but combined with spring mean temperature.