The response of fawn survival to changes in habitat quality varies according to cohort quality and spatial scale
Résumé
1. Temporal and spatial variation can strongly affect life-history traits, but few studies to date have quantified the importance of the interplay between temporal and spatial components of population dynamics. 2. We analysed spatiotemporal variation in early survival of roe deer fawns over 15 years (1985–99) in an intensively monitored population in western France at two spatial scales: the maternal home range (a few tens of hectares) and the forest stand (a few hundreds of hectares). 3. Spatial variation in resource availability interacted with temporal variation to shape fawn survival. In good years, survival was not influenced by habitat quality (being 0·68 in the rich oak stand with hornbeam coppices vs. 0·64 in the poorer part of the reserve). At the home range scale, early survival of fawns during good years decreased with increasing occurrence of preferred plant species in the rich habitat; there was no effect in the poor habitat. 4. During bad years, however, there was a positive relationship between the occurrence of preferred plant species and survival of fawns in the poor habitat, whereas no relationship occurred in the rich habitat. Spatial variation in early survival during bad years was significant at the plot scale (from 0·19 to 0·40 in the poor habitat and from 0·49 to 0·61 in the rich habitat) even after accounting for the forest stand variations (from 0·27 to 0·51). The occurrence of key plant species therefore limits female reproductive success only in the poor habitat under harsh conditions. 5. Our findings highlight the crucial role of spatiotemporal interactions in shaping individual fitness in mammalian populations, and underline the importance of the scale of analysis when characterizing ecological processes.