Assessing survival in a multi-population system: a case study on bat populations

Abstract

In long-lived animals, adult survival is among the most important determinants of population dynamics. Although it may show considerable variation both in time and among populations and sites, a single survival estimate per species is often used in comparative evolutionary studies or in conservation management to identify threatened populations. We estimated adult survival of the isabelline serotine bat Eptesicus isabellinus using capture-recapture data collected on six maternity colonies scattered over a large area (distance 8-103 km) during periods varying from 8 to 26 years. We modelled temporal and inter-colony variations as random effects in a Bayesian framework and estimated mean annual adult survival of females on two scales and a single survival value across all colonies. On a coarse scale, we grouped colonies according to two different habitat types and investigated the effect on survival. A difference in adult survival was detected between the two habitat types [posterior mean of annual survival probability 0.71; 95% credible interval (CI) 0.51-0.86 vs. 0.60; 0.28-0.89], but it was not statistically supported. On a fine scale, survival of the six colonies ranged between 0.58 (95% CI 0.23-0.92) and 0.81 (0.73-0.88), with variation between only two colonies being statistically supported. Overall survival was 0.72 (95% CI 0.57-0.93) with important inter-colony variability (on a logit scale 0.98; 95% CI 0.00-8.16). Survival varied temporally in a random fashion across colonies. Our results show that inference based solely on single colonies should be treated with caution and that a representative unbiased estimate of survival for any species should ideally be based on multiple populations.

Comparing survival among species with imperfect detection using multilevel analysis of mark—recapture data: a case study on bats

“…We only used a single colony of both Nyctalus species, and therefore colony and species characteristics are confounded. More species and sites per species ideally from a variety of geographical areas (Papadatou et al 2011) would help clarify our finding in future analyses. Further, closely related species may show similarities in life history traits because of recent common ancestry, and not independent responses to evolutionary and ecological processes (Bennett and Owens 2002).…”

“…a single population may be particularly exposed to high risks of mortality), and the large 95% CI including ‘0’ for colony variances may be due to the fact that these were estimated based on only 2 and 4 sample sites for P. auritus and M. bechsteinii respectively. Hence the use of more sites per species or other level of interest is strongly recommended, although the exact number will depend on species, the degree of spatial heterogeneity, the size of the targeted populations, and accumulated experience from many species and geographical areas in future (Papadatou et al 2011).…”

“…However, model specification is not straightforward for users without programming skills. Solutions may be provided by making BUGS codes publicly available (Supplementary material Appendix 1, Kéry and Schaub 2011, Papadatou et al 2011), collaborations between statisticians and ecologists, and training on hierarchical Bayesian modelling (Gimenez 2008, Ogle et al 2009).…”

Ecology of Zoonotic Infectious Diseases in Bats: Current Knowledge and Future Directions

“…Longitudinal infection and demographic data are required to understand how birth, survival, coloniality, migration and torpor affect infection dynamics within bat populations. Frequently, researchers monitor one part of the process, such as survival (Papadatou et al., 2011), infection (Drexler et al., 2011; Field et al., 2011) or seroprevalence (Breed et al., 2011). However, some studies captured long‐term longitudinal data.…”

Do Bat Gantries and Underpasses Help Bats Cross Roads Safely?

“…Roadkill is hard to quantify due to the difficulty of finding carcasses [10], but low reproductive rates make bats particularly vulnerable to elevated adult mortality e.g. [11].…”