Drivers of population growth variations for two Mediterranean sympatric Deer

Abstract

Detecting density-dependence (DD) in population fluctuations is essential for population control, herd management and harvest programs. However, little information has been obtained for deer in Mediterranean ecosystems. We assess the effects of density, climate and harvesting on population growth fluctuations of two sympatric red (Cervus elaphus hispanicus) and fallow deer (Dama dama), in two hunting reserves located in a protected area of south-east Spain. We use time series analysis of 16 consecutive years of abundance estimates and hunting extractions. We hypothesized a negative influence of density, deer hunting and drought on population growth rates. Through an integrative Bayesian state-space modeling making possible a unified population analysis we have been able to not only estimate the effects of DD, climate and harvest extractions but also to evaluate their relative impacts on deer population in each location. We found deer populations exhibiting a very strong potential to grow from low density. We detected DD having a stronger effect than hunting and climatic factors, especially for overabundant deer populations close to their carrying capacity. Density-dependent mechanisms compensate harvest extractions, reducing hunting effectiveness. Severe summer drought conditions had negative effects on growth rates and eventually led to delayed autumn deer deaths. The weather effect is more important the more abundant the deer are. In a climate change context, in Mediterranean environments the importance of weather factors could become much greater if both ungulates’ densities and aridity increase. Population size control here could modulate the negative effects of climatic constraints on deer and ecosystems conservation.