Long–term variation of demographic parameters in four small game species in Europe: opportunities and limits to test for a global pattern
Résumé
Long-term variation of demographic parameters in four small game species in Europe: opportunities and limits to test for a global pattern. For decades, decreases in several populations of some small sedentary game species have been reported in Europe. From the literature, we extracted mortality and reproductive rates that were available for European populations in four iconic species, the grey partridge (Perdix perdix), the black grouse (Tetrao tetrix), the capercaillie (T. urogallus) and the brown hare (Lepus europaeus), to examine how demographic parameters vary with time. Our study revealed the need to consider many confounding factors (age, sex, origin of studied individuals, season, country and methods) and the scarcity of recent demographic studies. Statistical analyses showed contrasted patterns of demographic traits with time within and between species. Our results highlighted that there may be consistency with a population decrease in grey partridge and black grouse that has been reported in the literature. However, analyses in capercaillie and brown hare showed less support for a population decrease at the European scale. The significant effects of interactions between time and age (in grey partridge, capercaillie and brown hare), method or origin of individuals on demographic traits and the emergence of contrasted patterns between short, intermediate and long monitoring periods (in grey partridge and black grouse) suggested that further studies should pay particular attention to potential confounding factors. Finally, the lack of recent data and doubts about the relative importance of reported causal factors indicate the need for further studies on the links between demographic traits, densities and environmental changes in the long term, and particularly on the role of predation and habitat change.