Patch use in a diurnal rodent: handling and searching under thermoregulatory costs

Abstract

1. The role of physiological complexity in animal foraging ecology was investigated through experiments to determine how animals manage time and energy during patch use under thermoregulatory costs. The Degu Octodon degus (Molina 1782), a diurnal rodent inhabiting the semiarid environments of central Chile, was studied. 2. Previous studies reported that Degus are constrained to specific foraging areas mainly by limits to thermal tolerance and food quality. Predation risk may also be important. Because new evidence shows that physiological processes are important in shaping foraging ecology, it was hypothesized that Degu foraging behaviour is influenced by the risk of hyperthermia as well as by the advantages of gathering food efficiently. 3. Feeding trials were conducted in an experimental arena with food offered in an experimental patch containing sand and placed under a heater. Using video cameras, the overall time budget was measured, including frequency and duration of patch visits, and events of food gathering. Besides ambient temperature (high or low), handling time was manipulated by using husked and unhusked sunflower seeds, and searching time by using two seed distributions. 4. Ambient temperature and husk state as well as ambient temperature and seed distribution interacted in their influence on both handling time and searching efficiency. These results imply that a thermally risky patch affects both parameters associated with patch use and diet selection and that this effect disappears when animals are not risking hyperthermia. 5. Degus decreased the frequency of patch visits under thermoregulatory costs. This behaviour resulted exclusively from the effect of ambient temperature. Data on time use suggest that direct exposure to higher environmental temperatures is avoided through changes in the duration of patch visits. Degus harvested food items in shorter foraging bouts when food was under a stressful thermal patch. 6. In conclusion, a time‐minimizing foraging behaviour, in face of Degus’ thermoregulatory physiology and related risks, was observed.

On the value of information: studying changes in patch assessment abilities through learning

“…During the annual cycle, degus experience significant changes in climate, food availability, and food quality. Accordingly, degus can modify their foraging physiology and behavior, and their daytime activity budget (Bozinovic 1995, Bozinovic and Vásquez 1999, Kenagy et al 2002, 2004, Bozinovic et al 2004). Under natural conditions, degus readily forage on experimental seed patches, and GUDs are reliable indicators of foraging success under different ecological scenarios (R. A. Vásquez, unpubl.).…”

Octodon degus (Molina 1782): A Model in Comparative Biology and Biomedicine

“…The ecological physiology of degus populations, in the seasonal Mediterranean and semiarid environment of Chile, indicates that degus’ thermal opportunities for activity shift seasonally/spatially along with the habitat's biotic and abiotic conditions (Bozinovic and Vásquez 1999). Seasonal changes in the availability and quality of food affect foraging, digestion, and nutritional ecology (Bozinovic 1995), as well as the level of seasonal and spatial metabolic expenditure (Bozinovic et al 2009).…”

Huddling behavior as critical phase transition triggered by low temperatures

“…Also, self-organization acting in concert with natural selection may be part of the whole evolutionary process [2,[42][43][44][45]. The importance of abiotic factors, mainly the thermal environment, in determining behavioral traits has been a central issue of discussion [46][47][48]. Physiological and environmental constraints are determinant in the relationship between abiotic variables and the spatial distribution of individuals and populations, but the processes driving such patterns remain poorly understood.…”