Does density-induced stress promote density-dependent reproduction in
root voles? Two field experiments
Abstract
Density dependence in reproduction plays an important role in
stabilising population dynamics via immediate negative feedback from
population density to reproductive output. Although previous studies
have shown that density dependence is associated with strong spacing
behaviour and social interaction between individuals, the proximal
mechanism for generating density-dependent reproduction remains unclear.
In this study, we investigated the effects of density-induced stress on
reproduction in root voles. Founder population enclosures were
established by introducing six (low density) and 30 (high density)
adults per sex into per enclosure (four enclosures per density in total)
during the breeding season from April to July 2012 and from May to
August 2015. Faecal corticosterone metabolite (FCM) levels, reproductive
traits (recruitment and the proportion of reproductive condition), and
founder population numbers were measured following repeated
live-trapping in both years. The number of founders was negatively
associated with recruitment rates and the proportion of reproductive
conditions, displaying a density-dependent reproduction. FCM level was
positively associated with the number of founders. The number of founder
females indirectly affected the proportion of reproductive females in
2012 and recruitment in 2015 through their FCM levels; the effect of the
number of male founders on the proportion of reproductive condition was
mediated by their FCM level in 2012, but the effect was not found in
2015. Our results showed that density-induced stress affected
density-dependent reproduction and that density-induced stress is one
ecological factor generating density-dependent reproduction.