Abstract
Individual size is a major determinant of mobile organisms’ ecology and behavior. This study aims to explore whether allometric scaling principles can provide an underlying framework for general patterns of resource patch use. To this end, we used giving‐up densities (GUDs), that is, the amount of resources remaining in a patch after a forager has quit feeding, as a comparative measure of the amount of resources exploited by a forager of any given size. We specifically tested the hypothesis that size‐dependent responses to both internal (energy requirement) and external (risk management) forces may have an effect on GUDs. We addressed this topic by conducting an extensive meta‐analysis of published data on granivorous rodents, including 292 GUD measurements reported in 25 papers. The data set includes data on 22 granivorous rodent species belonging to three taxonomic suborders (Castorimorpha, Myomorpha, and Sciuromorpha) and spans three habitat types (desert, grassland, and forest). The observations refer to both patches subject to predation risk and safe patches. Pooling all data, we observed positive allometric scaling of GUDs with average forager size (scaling exponent = 0.45), which explained 15% of overall variance in individual GUDs. Perceived predation risk during foraging led to an increase in GUDs independently of forager size and taxonomy and of habitat type, which explained an additional 12% of overall GUD variance. The size scaling exponent of GUDs is positive across habitat types and taxonomic suborders of rodents. Some variation was observed, however. The scaling coefficients in grassland and forest habitat types were significantly higher than in the desert habitat type. In addition, Sciuromorpha and Myomorpha exhibited a more pronounced size scaling of GUDs than Castorimorpha. This suggests that different adaptive behaviors may be used in different contexts and/or from different foragers. With body size being a fundamental ecological descriptor, research into size scaling of GUDs may help to place patch‐use observations in a broader allometric framework.
Highlights
Body size is one of the most fundamental characteristics of an organism
We tested the hypotheses (1) that giving-up densities (GUDs) will scale as a positive allometric function of forager size (M), in accordance with GUD = aMb, because of increasing total metabolic cost with increasing body size; (2) that GUDs scaling with the forager size in safe patches will differ from risky patches because of potential size dependency of predator avoidance costs, that is, that GUDs in risky patches will scale with a lower or higher scaling coefficient than in safe patches if, respectively, larger or smaller foragers have an advantage in managing predator avoidance costs; and (3) that observed trends will be consistent across a range of taxonomic groups and habitats. We addressed these topics by conducting an extensive meta-analysis of published data on granivorous rodents, including 292 GUD treatments reported in 25 studies (Data S1, Metadata S1)
Higher GUDs were measured in the forest (813 kJ/m2 [Æ566 SD]) and grassland (724 kJ/m2 [Æ333 SD]) than in the desert (227 kJ/m2 [Æ158 SD]) habitat types
Summary
It is linked to fundamental individual parameters such as metabolic, growth, and reproduction rates (Peters 1983, Calder 1984, West et al 1997, Brown et al 2004), as well as to physical aspects such as locomotion, dispersal, and space use (Bekoff and Mech 1984, Ritchie and Olff 1999, Jetz et al 2004, Woodward et al 2005). Larger organisms have higher total metabolic energy demand per unit of time (West et al 1997, Kooijman 2000, Capellini et al 2010) and must maintain higher rates of resource harvesting and ingestion (Peters 1983, Hendriks 1999).
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