Population dynamics of the Italian roe deer (Capreolus capreolus italicus): analysis of a 109 years-long time series of density indexes

Previous research has shown effects of competitive interactions between roe deer and other species of ungulates which can affect population growth, conservation and resource use. In this paper we add further information on the impact of interspecific interactions, with specific emphasis on the effects of climate and habitat. Time series analysis plays an important role in the detection of mechanism leading populations fluctuations. We studied the population dynamics of the Italian roe deer (Capreolus capreolus italicus) in a Mediterranean area (Castelporziano Preserve near Rome, Italy) using a time-series of annual population density indexes obtained by bag records available from 1878 to 1986. Four other species of ungulates were present in the Preserve (at least during a part of the study period): the Maremma wild boar (Sus scrofa majori), the native red deer (Cervus elaphus), and two alien species, the fallow deer (Dama dama) and the nilgai (Boselaphus tragocamelus). The time series were splitted in two sub-periods characterised by a different composition of the herbivore community: the first one (1878-1940), characterized by higher complexity, with the presence of all five ungulate species; and the second one (1945-1986) with three species. The results of the analysis indicate that direct density dependence was present in both periods, but was stronger during the second one. We found a negative effect of red deer population size on roe deer growth rate during the first period. Significant inter-specific interactions were detected using a density threshold. More specifically, roe deer suffered the competition with fallow deer when at high density, and benefited from facilitation by nilgai when at low density. In the multivariate analysis, we found a negative effect of the amount of pine plantations. Apart a slightly negative effect of spring drought on roe deer growth rate of the following year, in this population climatic effects have played a minor role. This latter result indicates that the dynamics of roe deer populations in Mediterranean areas can be different from that one taking place at northern latitudes or in alpine regions, where climatic effects are much more relevant.