Phase- and season-dependent changes in social behaviour in cyclic vole populations

Abstract

Background: Social behaviour has been linked to hypotheses explaining multiannual population cycles of small rodents. In this paper we aimed to test empirically that the degree of space sharing among adult breeding female voles is higher during the increase phase than in the crash phase, and that the degree of sociality is positively related to population growth rate as suggested by Lambin and Krebs (Oikos 61:126-132, 1991) and Andreassen et al. (Oikos 122:507-515, 2013). We followed 24 natural bank vole Myodes glareolus populations over an area of 113 km² by monthly live trapping throughout a complete population cycle of three summers and two winters.

Results: Using spatially explicit capture-recapture models, we modelled the overlap in adult female home ranges and total population growth rate per season. We identified an increase phase before and during the peak density observation and a crash phase following the peak. Female home range overlap were seasonal- and phase-dependent, while population growth rate was associated with season and female home range overlap. High female home range overlap in the increase phase corresponded to a high population growth rate.

Conclusions: We suggest that intrinsic social behaviour plays a key role in the increase phase of vole population cycles, as social behaviour leads to an increased growth rate, whereas extrinsic factors (predation and/or food) initiate the crash phase. Our results are consistent with those of other studies in a variety of small rodent species.

Keywords: Extrinsic; Intrinsic; Myodes; Population cycles; Territoriality.

Fig. 1

Trapping grid design. a Shows the main, cross-shaped design with 16 traps, and b the alternative design used when the main design did not encompass any suitable vole habitat, with 12 traps

Fig. 2

Top: a simulation with three peak years illustrating the cycle phase in the present paper in blue. Bottom: minimum number known to be alive (MNKA) per trap per month from June 2013 to August 2015 (missing trapping in September 2014 denoted with NA). We used these estimates to define the increase and decrease phases of the cycle for further analyses. Seasons are shown with colours: blue = summer, orange = fall, white = winter, red = spring

Fig. 3

Female density per hectar (mean ± 2SE) (a), residual female home range overlap (mean ± 2SE) (b), and population growth rate (mean ± 2SE) (c) across seasons from summer 2013 (June–August) to Winter 2014–2015 (December–February). Due to too few captures, we were not able to estimate female density and consequently home range overlap after November 2014

Fig. 4

Correlation between population growth rate (mean ± 2SE) and residual female home range overlap (mean ± 2SE). Summer 13 = June–August 13, Fall 13 = September–November 13, Winter 13/14 = December–February 13/14, Spring 14 = March–May 14, Summer 14 = June–August 14, Fall 14 = October–November 14. Grey represent the increase phase of the cycle and blue represents the peak crash of the cycle