Food availability as a major driver in the evolution of life-history strategies of sibling species

Abstract

Life-history theory predicts trade-offs between reproductive and survival traits such that different strategies or environmental constraints may yield comparable lifetime reproductive success among conspecifics. Food availability is one of the most important environmental factors shaping developmental processes. It notably affects key life-history components such as reproduction and survival prospect. We investigated whether food resource availability could also operate as an ultimate driver of life-history strategy variation between species. During 13 years, we marked and recaptured young and adult sibling mouse-eared bats (Myotis myotis and Myotis blythii) at sympatric colonial sites. We tested whether distinct, species-specific trophic niches and food availability patterns may drive interspecific differences in key life-history components such as age at first reproduction and survival. We took advantage of a quasi-experimental setting in which prey availability for the two species varies between years (pulse vs. nonpulse resource years), modeling mark-recapture data for demographic comparisons. Prey availability dictated both adult survival and age at first reproduction. The bat species facing a more abundant and predictable food supply early in the season started its reproductive life earlier and showed a lower adult survival probability than the species subjected to more limited and less predictable food supply, while lifetime reproductive success was comparable in both species. The observed life-history trade-off indicates that temporal patterns in food availability can drive evolutionary divergence in life-history strategies among sympatric sibling species.

Keywords: age at first reproduction; bats; demography; life‐history trade‐off; multistate capture–recapture model; survival.

Figure 1

Mean model‐averaged (across all models of Table 1 with Akaike weight > 0.02) demographic rates of Myotis myotis and Myotis blythii. Given are mean values and unconditional standard errors. Note that for juvenile survival, we provide the geometric mean because this rate was year‐specific in the best models. For reproduction, the probability shown is that of a given female that has not yet reproduced to start reproducing in a given year (1st, 2nd, or 3rd year)

Figure 2

Model‐averaged (across models from Table 3 with Akaike weight > 0.02) annual survival probabilities of lesser (Myotis blythii) and greater (Myotis myotis) mouse‐eared bats. Open green symbols refer to lesser mouse‐eared bats, closed orange symbols to greater mouse‐eared bats, squares refer to adults (at least 1 year old) and circles refer to first‐year individuals (from weaning until age 1 year). The vertical bars show the limit of the 95% confidence intervals. The shaded areas indicate years with mass occurrence of cockchafers (pulse resource years), with their local spatial occurrence (N: surroundings of Naters nursery roost; R: surroundings of Raron nursery roost; note the occurrence around the two nursery roosts in 1998)