On the Evolution of Reproductive Rates in Microtine Rodents

Abstract

The purpose of this study was to evaluate the effects of various patterns of population dynamics on the evolution of reproductive rates of voles. Population sizes of both field voles (Microtus agrestis) and bank voles (Clethrionomys glareolus) show different degrees of fluctuation in different regions; the degree of cyclicity increases northwards. Animals caught in both optimal and suboptimal habitats in three regions of Sweden were examined regarding litter size and length of reproductive season. The litter size was greater in optimal than in suboptimal habitats during the increase phase of cyclic populations. The breeding season was shorter during the peak than during the increase phase. In both species, during low—density phase, the reproductive rate of overwintered females increased northwards. Young—of—the—year females of the field vole, but not of the bank vole, showed a decrease in the reproductive rate with distance northwards. These results were compared with predictions based on three hypotheses on the evolution of reproductive rates, emphasizing, respectively, (1) food supply, (2) the pattern of density fluctuations, and (3) a combination of both food supply and the pattern of fluctuation. Observed between—habitat differences in reproductive patterns could be explained by hypothesis. 1. However, hypothesis 2 could explain part of the remaining variation among regions. In addition, when data from optimal habitats in the present study were combined with similar data from the literature, a high correlation was found between litter size and degree of cyclicity, confirming the predictions of hypothesis 2.

Moving forward in circles: challenges and opportunities in modelling population cycles

“…Many features that promote population cycles are evolvable traits, which suggests that evolution can play a key role in cyclicity; for example, litter size is correlated to cyclic propensity in rodents (Stenseth et al . ) and continuous prey adaptation has been shown to facilitate the emergence of consumer–resource cycles (Abrams & Matsuda ). Evolutionary processes can occur on fast timescales: during epizootics, disease transmission rates can change rapidly due to selection for disease resistance at high pathogen abundance and selection for relaxation at low pathogen abundance, promoting oscillatory eco‐evolutionary dynamics (Elderd et al .…”

“…Many features that promote population cycles are evolvable traits, which suggests that evolution can play a key role in cyclicity; for example, litter size is correlated to cyclic propensity in rodents (Stenseth et al 1985) and continuous prey Box 2 Cohort or consumer-resource cycles?…”

Specialist and generalist natural enemies as an explanation for geographical gradients in population cycles of northern herbivores

“…In particular, the funnel‐shaped southern Sweden surrounded by seas (Fig. 1), seems to accumulate large numbers of migrating and over‐wintering birds of prey from northern parts of the Fennoscandia, leading to the most stable vole dynamics observed within Fennoscandia (Erlinge et al 1983, 1984, Hansson and Henttonen 1985, 1988, Stenseth et al 1985, Hanski et al 1991, Agrell et al 1992, Oksanen et al 2001). In years with low numbers of voles, birds of prey may switch habitat further and change their diet to rabbits ( Oryctolagus cuniculus Linnaeus), which are only available there within Fennoscandia in dry habitats, or migrate further to continental Europe.…”

Reproductive behaviour of female Siberian lemmings during the increase and peak phase of the lemming cycle

“…In cyclic Microtus agrestis L. and Clethrionomys glareolus Schreb. populations in Sweden, the breeding season was shorter during the peak phase than during the increase phase (Stenseth et al 1985), and there are reports of curtailed reproduction at high densities in lemmings (Krebs 1993). There are conflicting reports regarding the relationships of litter size and proportion of pregnant females to the phase of the cycle (Krebs and Myers 1974).…”