Seasonal variation in the range areas of the diurnal rodentOctodon degus

Abstract

Both breeding activity and abundance and quality of available food are expected to influence daily movements of animals. Animals are predicted to range over large areas to meet high energy demands associated with reproduction (females) or to increase mating success (males). However, animals should expand their range areas whenever food conditions deteriorate. To examine the extent to which breeding activity versus food availability influence space use, we compared the size and location of range areas (home ranges) of the degu (Octodon degus), a diurnal rodent from semiarid environments of north-central Chile, during the austral winter and summer seasons. Degus produce young during the austral spring (September–October) when high-quality food is readily available. In contrast, degus do not breed during the austral summer (January–March) when food is scarce and of low quality. We predicted that degus would range over smaller areas in winter if the availability of food has a greater influence on space than breeding activity. Individuals were radiotracked in winter and the following summer over a 3-year period. Surveys of herbaceous cover were conducted during winter and summer to determine seasonal changes in the abundance and quality of primary food. In summer degus expanded and moved the location of their range areas to locations with available food. Given that preferred food was less abundant in summer than winter, we suggest that degu range areas are strongly influenced by food conditions.

Ecological drivers of group living in two populations of the communally rearing rodent, Octodon degus

“…To track changes in the abundance of primary food (Quirici et al 2010), we collected samples of green herbs at 3 and 9 m from the center of each burrow system. In particular, we randomly chose one location at 3 m and 1 at 9 m in the north, east, south, or west directions.…”

“…Degus are diurnal, medium-sized rodents (ca. 180 g) that feed mostly on the green leaves of grasses and forbs and breed generally once per year (Ebensperger and Hurtado 2005b; Quirici et al 2010). Degus are plural breeders with communal care of offspring (Brown 1987; Solomon and Getz 1997; Silk 2007), i.e., 1–5 males and 1–8 multiple lactating females share underground nests and rear their litters communally (Ebensperger et al 2002, 2004, 2007; Hayes et al 2009).…”

Intraspecific variation in space use, group size, and mating systems of caviomorph rodents

“…Finally, food availability correlated with home-range size of degus in one year but not another (Quirici et al 2010), probably due to differences between years in sample size ( n = 7 and 19), although ecological factors also might have changed between years. During the austral summer food abundance and quality, measured as amount of insoluble fiber, decline.…”

“…During the austral summer food abundance and quality, measured as amount of insoluble fiber, decline. Home-range sizes then increase compared to winter, despite an increase in population density related to the influx of juveniles born into the population (Quirici et al 2010). The authors suggest that lower abundance of food resources and higher density increase competition, forcing animals to expand ranges to obtain adequate food (Quirici et al 2010).…”

“…However, ecological conditions often vary spatially and temporally, thus providing opportunities to examine shifts in spacing patterns of individuals seasonally and across geographic distances that exhibit variable resource availability. Although authors report changes in home-range characteristics, many of them do not describe spatial organization as such; that is, positions of these populations along the continuum between undefended home ranges and territoriality (Asher et al 2004; Endries and Adler 2005; Quirici et al 2010). Such characterization requires longer-term studies of neighboring animals to record amounts of home-range overlap and, ideally, to observe behavioral interactions.…”