Is there direct and delayed density dependent variation in population structure in a temperate European cyclic vole population?

Abstract

Population structure, in terms of the body mass, condition, sex and reproductive status of individuals, has been found to vary in phase with population density in cyclic populations of microtine rodents. Because sustained population cycles involve delayed density dependent changes in the population growth rate, we would expect at least some life history traits also to depend on past densities. Detailed, long‐term studies of changes in vole life history traits are however few, and are largely restricted to northern Europe. In view of the uncertainty as to whether the cyclic microtine populations of western Europe represent the same phenomenon as those of northern Europe, we studied temporal variation in the structure of a clearly cyclic population of the common vole Microtus arvalis Pallas, in the cereal plains of mid‐western France. Our data set contains seasonal, individual‐level data from long‐term, large‐scale trapping covering four entire population cycles. We found considerable cyclic variation in population structure in spring (April), but less so in summer (June). In spring of post‐peak years, animals were of low body weight and body condition (particularly females), litter sizes were smaller and there was a reduction in the proportion of breeders. All of these could be proximal drivers of increased mortality rates, or decreased birth rates, contributing to the population declines. Few life history traits, however, showed direct density dependent variation, and none of the traits studied here showed delayed density dependence. We have shown declines in the fecundity and body condition of voles from a western European population that coincides with, and may be a proximal cause of, cyclic declines in population density. Closer attention to proximal causes, by which ecological processes drive cycles, could clarify the extent to which microtine cycles across Europe represent a single phenomenon.

Common vole (Microtus arvalis) ecology and management: implications for risk assessment of plant protection products

“…Lemmus spec. ), because they are considered to be associated with the same suite of demographic characteristics, including summer population decline and density‐dependent variation in body mass (the Chitty effect) . The occurrence of multiannual cycles in population density increases from Southern to Northern Europe and with increasing altitude moving from marine to continental conditions .…”

“…), 29,30 because they are considered to be associated with the same suite of demographic characteristics, including summer population decline and density-dependent variation in body mass (the Chitty effect 33 ). 31,34 The occurrence of multiannual cycles in population density increases from Southern to Northern Europe and with increasing altitude moving from marine to continental conditions. 31,32,35 Some of the European common vole population outbreaks are cyclical, 31,32 while in other regions the populations seem to fluctuate irregularly.…”

The interplay between seasonality and density: consequences for female breeding decisions in a small cyclic herbivore

“…However, density does not appear to have a strong impact on the proportion of breeding females or on litter size during the core breeding season (see also [26]) but we found evidence that the proportion of breeders is reduced during the high density phase (Figure 5c). Due to the relation between body size and reproduction, during autumn and winter, only the bigger common voles are able to reproduce, but they reproduce less.…”

“…This reduction of reproduction rate in autumn and winter becomes stronger at high population density, up to a complete halt in breeding at the highest local densities (Figure 5c). Additionally, individuals are smaller after a population crash [26] and smaller individuals produce smaller litters [35]. An additive negative effect of past June abundance was found on litter size, resulting in a litter size reduction of 28% in springs following crashes.…”

Sheep grazing causes shift in sex ratio and cohort structure of Brandt's vole: Implication of their adaptation to food shortage

“…They are important criteria in explaining the population fluctuation of small rodents (Redfield et al 1978;Oli & Dobson 1999;Norrdahl & Korpimaki 2002;Janova et al 2003;Inchausti et al 2009). They are important criteria in explaining the population fluctuation of small rodents (Redfield et al 1978;Oli & Dobson 1999;Norrdahl & Korpimaki 2002;Janova et al 2003;Inchausti et al 2009).…”