Seasonal variation in diet composition and similarity of sympatric red and roe deer

David Storms, Philippe Aubry, Jean-Luc Hamann, Sonia Saïd, Hervé Fritz, Christine Saint-Andrieux & François Klein

Use of food resources by herbivores depends on intrinsic constraints, essentially body size and morpho-physiological characteristics, which determine the range of foods they tolerate and environmental constraints, such as seasonality and interspecific interactions, which determine the availability of resources. We analysed a collection of rumen contents samples from sympatric populations of red (Cervus elaphus) and roe (Capreolus capreolus) deer and tested several theoretical predictions relating to the impact of intrinsic and environmental constraints on diet composition, diversity and similarity. Red deer consumed more slowly digestible, fibrous forage than roe deer and had a more diverse diet throughout the year, which supports predictions deriving from specific body size and morpho-physiological characteristics. In conformity with the optimal foraging theory, both species consumed more slowly digestible forage in times of low food availability (i.e. winter) than during the rest of the year. An increase in diet similarity in winter, along with predictions from the theory on competitive interaction processes, led us to assume that food resources were not limiting and that exploitative competition between red and roe deer was unlikely in our study area. We underline the importance of studies of food resources use by sympatric herbivores in answering applied ecological questions at the local scale and suggest that the Euclidean geometrical approach we used is particularly well suited to the analysis of resource matrices, a common end-product of long-term field data gathering on the feeding habits of animals.

Key words: Capreolus capreolus, Cervus elaphus, diet overlap, diet similarity, Principal Component Analysis, resource partitioning, seasonal variation