Small-scale altitudinal effects on reproduction in bank voles

Abstract

a b s t r a c tElevation gradients and corresponding changes in environment have the potential to affect seasonal reproduction and mortality and hence the seasonal age structure of animal populations. This has been frequently shown in mammals and birds on larger geographic scales, but evidence for small-scale gradient effects is scanty. We studied such small scale altitudinal effects on the proportions of juveniles in a population of bank voles (Myodes glareolus) in a forested habitat along an elevation gradient of 355 m. This was done by regular live trapping in different altitudes over a two-year period. We also measured altitudinal differences in ambient temperatures and vegetational parameters in order to shed light on the underlying mechanisms of such purported differences in age structure. As could be expected for a seasonal breeder, the proportion of juveniles showed an initial increase in spring, an optimum in summer and a subsequent regression in early autumn, reflecting the seasonal pattern of reproduction. In addition, there was evidence for altitudinal effects on the occurrence of juveniles, which was decreased in higher altitudes, assumingly driven by altitudinal differences in onset and/or intensity of annual breeding activity. This altitudinal gradient in juvenile occurrence was partly explained by corresponding differences in ambient temperatures. Furthermore, there was good support that the higher abundance of herbs in lower altitudes played an important role in explaining the altitudinal differences in the proportion of juveniles. In conclusion, our study strongly supports the existence of altitudinal small-scale gradient effects on reproductive parameters in a small rodent, most probably due to the action of altitude-related factors such as microclimate and vegetational parameters.

High nest failure but better nestling quality for early breeders in an alpine population of Northern Wheatear (Oenanthe oenanthe)

“…comm.) and late July (subalpine forest, Austria; Hille & Rödel 2014), when above‐ground food resources become more available. The increase in above‐ground activity and abundance of voles increases their detectability to predators (Yoccoz et al .…”

“…Indirect variation in predation risk across the season might also occur when alternative prey species, such as voles, become active above ground and more abundant in summer than in spring (Yoccoz et al . 1998, Hille & Rödel 2014). The timing of breeding at high elevations, where breeding conditions are particularly challenging, may therefore have severe consequences for the reproductive output and fitness of the individual (MacDonald et al .…”

What Causes Differences in the Age-Class Structure between Suburban and Forest Populations of Anolis homolechis?

“…Less is known, in contrast, of the variation in demographic success and population dynamics among urban and non-urban populations of native species (see [31][32][33]). Although a precise quantification of demographic parameters in different populations may require an important research effort, the estimation of the age-class distribution, such as the proportion of juvenile individuals, provides a suitable and frequently used proxy, integrating reproduction and early juvenile survival in the population [34][35][36]. Such a parameter is of high importance in demographic and population viability studies [37,38], as well as for species conservation and management [39][40][41].…”