Breeding state and season affect interspecific interaction types: indirect resource competition and direct interference

Abstract

Indirect resource competition and interference are widely occurring mechanisms of interspecific interactions. We have studied the seasonal expression of these two interaction types within a two-species, boreal small mammal system. Seasons differ by resource availability, individual breeding state and intraspecific social system. Live-trapping methods were used to monitor space use and reproduction in 14 experimental populations of bank voles Myodes glareolus in large outdoor enclosures with and without a dominant competitor, the field vole Microtus agrestis. We further compared vole behaviour using staged dyadic encounters in neutral arenas in both seasons. Survival of the non-breeding overwintering bank voles was not affected by competition. In the spring, the numbers of male bank voles, but not of females, were reduced significantly in the competition populations. Bank vole home ranges expanded with vole density in the presence of competitors, indicating food limitation. A comparison of behaviour between seasons based on an analysis of similarity revealed an avoidance of costly aggression against opponents, independent of species. Interactions were more aggressive during the summer than during the winter, and heterospecific encounters were more aggressive than conspecific encounters. Based on these results, we suggest that interaction types and their respective mechanisms are not either–or categories and may change over the seasons. During the winter, energy constraints and thermoregulatory needs decrease direct aggression, but food constraints increase indirect resource competition. Direct interference appears in the summer, probably triggered by each individual’s reproductive and hormonal state and the defence of offspring against conspecific and heterospecific intruders. Both interaction forms overlap in the spring, possibly contributing to spring declines in the numbers of subordinate species.

Secondhand horror: effects of direct and indirect predator cues on behavior and reproduction of the bank vole

“…Breeding bank vole females require a breeding territory and if the breeding habitat is occupied, the surplus females cannot breed. As the density of females became far too high and no opportunities for an individual's own breeding territory existed anymore, all females started to breed regardless of costs (Eccard et al 2011). As the density of females became far too high and no opportunities for an individual's own breeding territory existed anymore, all females started to breed regardless of costs (Eccard et al 2011).…”

Excretion and measurement of corticosterone and testosterone metabolites in bank voles (Myodes glareolus)

“…Few studies have been exploiting fecal samples for glucocorticoid measurements in bank voles, but to our knowledge, a proper analytical and physiological validation of a method to measure fecal steroid metabolites (FCM or FTM) is still lacking. Harper and Austad (2000) performed a validation experiment for measuring FCM in red-backed voles (Myodes gapperi) with a corticosterone radioimmunoassay (RIA), which has been used as a reference for experiments using fecal samples for monitoring stress in bank voles (Ylönen et al 2006, Eccard et al 2011a). However, the RIA used in Harper and Austad (2000) was designed to detect the actual hormone rather than its metabolites.…”

Turning Shy on a Winter's Day: Effects of Season on Personality and Stress Response in Microtus arvalis

“…) and a decrease (Andrews & Belknap ; Eccard et al. ) in aggression have been reported to occur in different rodents species during short days. In addition, short days can impair spatial learning and memory (Walton et al.…”

“…Animals have evolved seasonally induced changes in physiology and behaviour to cope with these recurrent and predictable fluctuations in photoperiod, food abundance and temperature (Scherbarth & Steinlechner ; Eccard et al. ). Typically, in temperate environments, the winter is the adverse season as the temperature decreases together with the availability of food resources as the photoperiod shortens.…”