Estimating offspring production using capture‐mark‐recapture and genetic methods in red squirrels

Abstract

Reproductive rate is a key demographic parameter of life history and population ecology. In traditional population-ecology studies of small mammals, this and other vital rates are inferred from capture-mark-recapture (CMR) data. However, CMR assumes that immigrants at first capture can be distinguished from unmarked locally born offspring, an assumption not always met. We verified CMR estimates of locally born red squirrel (Sciurus vulgaris) offspring as a measure of reproductive rate, with candidate offspring (CO)-candidate parent (mothers, CPs) assignment by CERVUS, using ten DNA microsatellite loci. Seventytwo of 122 candidate offspring (59%) were assigned to 52 of 125 CPs in six populations. Estimates of mean litter size were 1.5 young (range 1-3). The 50 CO (41%) not assigned to a reproducing female in the study site were considered immigrants. Parentage assignment also provided evidence of dispersal between two of our sites. Overall, CMR and CERVUS agreed in 77% of cases. Considering only the 55 juveniles determined as locally born by CMR, 50 (91%) were also assigned as local offspring with CERVUS. The main discrepancy between the two methods was that 22 subadult squirrels classified immigrants by CMR, were assigned by CERVUS to females which had reproduced in our sites. It is concluded that although in our study system agreement between CMR and CERVUS in determining local offspring was high, using genetic parentage assignment helped to correctly classify some subadults, considered immigrants by CMR, as locally born. Hence, in largescale demographic studies, combining CMR with parentage assignment will allow more precise estimates of reproduction and dispersal.

No sex bias in natal dispersal of Eurasian red squirrels

“…In continuous subalpine conifer forests, average dispersal distances of Eurasian red squirrels were larger than in the fragmented habitats in this study. Animals of both sexes emigrated over 2132 ± 483 m (n = 10) after a Norway spruce seed-crop failure , while genetic parentage assignment revealed dispersal distances from 1.7 to 2.7 km between different conifer forest types (Di Pierro et al, 2010). Siberian flying squirrels (Pteromys volans), only one-third the mass of our red squirrels (100 against 300 g), dispersed much further (data of emigrants: mean ± SD, males 1130 ± 1550 m, maximum 5940 m, females 2400 ± 2270 m, maximum 8720 m, Hanski and Selonen, 2009).…”

Living on the edge: morphological and behavioral adaptations to a marginal high‐elevation habitat in an arboreal mammal

“…There is genetic evidence that dispersal occurs between 2 of our study sites (Di Pierro et al. 2010) and that also in the marginal site most of the newly caught animals are immigrants (our unpublished data). Hence, the animals monitored here arrived in a given study site coming from several directions and distances, guaranteeing differences in the early experiences of animals settling in that area.…”

“…However, the majority of red squirrels disperse when between 4 and 10 months old, while some disperse as adults (>1-year old), over 1 up to 5-10 km, and philopatry is rare Wauters et al 1994Wauters et al , 2011Di Pierro et al 2010). There is genetic evidence that dispersal occurs between 2 of our study sites (Di Pierro et al 2010) and that also in the marginal site most of the newly caught animals are immigrants (our unpublished data). Hence, the animals monitored here arrived in a given study site coming from several directions and distances, guaranteeing differences in the early experiences of animals settling in that area.…”

“…1994, 2011; Di Pierro et al. 2010). There is genetic evidence that dispersal occurs between 2 of our study sites (Di Pierro et al.…”

“…Moreover, it is reported that an animal's experience during early development could have an effect on its personality as adult (Stamps & Groothuis 2010). However, the majority of red squirrels disperse when between 4 and 10 months old, while some disperse as adults (>1-year old), over 1 up to 5-10 km, and philopatry is rare Wauters et al 1994Wauters et al , 2011Di Pierro et al 2010). There is genetic evidence that dispersal occurs between 2 of our study sites (Di Pierro et al 2010) and that also in the marginal site most of the newly caught animals are immigrants (our unpublished data).…”