Interspecific and intraspecific competition as causes of direct and delayed density dependence in a fluctuating vole population

Abstract

A 3-to 5-year cycle of vole abundances is a characteristic phenomenon in the ecology of northern regions, and their explanation stands as a central theoretical challenge in population ecology. Although many species of voles usually coexist and are in severe competition for food and breeding space, the role of interspecific competition in vole cycles has never been evaluated statistically. After studying community effects on the population dynamics of the gray-sided vole (Clethrionomys rufocanus) in the subarctic birch forest at Kilpisjärvi, Finland, we report statistical results showing that both interspecific and intraspecific effects are important in the direct year-to-year density dependence. However, interspecific effects are not detectable in the 2-year delayed density dependence that is crucial for generating the characteristic cycles. Furthermore, we show that most of the competition takes place during the winter. The results are evaluated against two models of community dynamics. One assumes that the delayed effects are caused by an interaction with a specialist predator, and the other assumes that they are caused by overgrazing food plants. These statistical results show that vole cycles may be generated by a species-specific trophic interaction. The results also suggest that the graysided vole may be the focal species in the birch-forest community, as field voles may be in the taiga and as lemmings may be on the tundra.Ever since the 3-to 5-year vole cycles were first described by Elton (1), their mechanism has been hotly debated (2). The most popular current hypothesis is that the cycles are caused by an interaction with specialist predators (3-5), but overgrazing (6) and various intrinsic factors (7, 8) have also been suggested. The dynamics of cyclic voles usually are described well by simple second-order autoregressive models (9,10,47). In these models, density dependence is distributed about equally between a direct effect acting within 1 year and a 2-year delayed effect. Current research aimed at understanding the vole cycle has focused on developing models that can explain this pattern of density dependence or other associated aspects of the second-order autoregressive dynamics (10)(11)(12)47). Almost all of this work has focused on predation by weasels as the mechanism generating the delayed density dependence. This focus is not surprising, because predator-prey interaction is a simple and ecologically plausible mechanism that generates cyclic dynamics, which tend to show up as second-order autoregressive dynamics in time-series analyses (13).

Determinants of lemming outbreaks

“…Population increase during winter in lemmings results from winter reproduction (4, 16)-a demographic trait virtually absent in the gray-sided vole (14). The recruitment com- ponent of lemming winter growth can also explain why only lemmings exhibited density-dependent growth rate in winter, as recruitment in northern rodents appears to be more sensitive to density than adult survival (17).…”

“…and because direct density dependence (i.e., β dd < 1 implies negative density dependence) is notoriously a strong predictor of lemming and gray-sided vole population dynamics (11,14). Delayed density dependence (i.e., dependence on X t−2 ) was not considered as we analyzed growth rates only during the lemming outbreak period (fall 2006 to fall 2007).…”

“…One assumes that lemmings are more sensitive than voles to climate variation (10,12). The other emphasizes community processes and predicts that lemming outbreaks are limited by indirect interaction with voles mediated by shared predators (13)(14)(15). To our knowledge, no previous study has evaluated the relative merits of these (not necessarily mutually exclusive) hypotheses.…”

Long-term transients and complex dynamics of a stage-structured population with time delay and the Allee effect

“…In this paper our goal is to show that long-living transients mimicking complex dynamics are likely to be a common property of a conceptual, baseline single species population dynamics model. Time delays are widely recognized as an inherent feature of population dynamics (Beretta and Kuang, 1998;Hansen et al, 1998;May, 2001;Murdoch et al, 2003;Ruan, 2006). Triggered by Hutchinson seminal work (Hutchinson, 1948), there have been a large number of theoretical studies concerned with the implications of time delays for populations and communities (Hastings, 1984;Aiello and Freedman, 1990;Murdoch et al, 2003;Ruan, 2009).…”

Delay driven spatiotemporal chaos in single species population dynamics models

“…Delayed density dependence is thought to be one of the main factors causing population uctuations (Berryman and Turchin 1997). The most commonly considered causal mechanisms are resource competition (Hansen et al 1998), cannibalism (Briggs et al 2000), and maternal e ects (Ginzburg and Taneyhill 1994) where the nutritional environment of the parental generation can in uence the growth and reproductive potential of the next generation. Delays may also occur as a consequence of developmental time and/or interaction between individuals of di erent stages (Royama 1981, Hastings 1984.…”