PARENT SESSION
Contributed Oral Session 53: Trophic Communities and Modeling
Tuesday, August 9, 8:00 AM - 11:30 AM, Meeting Room 524 B, Level 5, Palais des congrès de Montréal
Nutritional constraints on omnivory in a mammalian generalist.
Shaner, Pei-Jen *,1, Macko, Stephen1, 1 Department of Environmental Sciences, University of Virginia, Charlottesville, VA, USA
ABSTRACT- Omnivory, defined as feeding on more than one trophic level, is ubiquitous in food webs and has profound consequences in population and food web dynamics. There are several adaptive advantages of omnivory, including nutritional balance, toxics dilution, food supplementation, and competition avoidance. These mechanisms are not mutually exclusive. For instance, when food availability is low, food supplementation should be the dominant driving force of omnivory, whereas when food is abundant, balancing diets to cope with nutrition deficiency should become more important. The study of omnivory in terrestrial ecosystems has a traditional focus on arthropods. However, omnivory is also common among terrestrial vertebrate taxa. Here we study a mammalian rodent species, the White-footed deermouse, and investigate how nutritional constraints in the form of C:N stoichiometry may affect omnivory in natural populations. Using stable isotopic tracing, food addition with seeds and beetle larvae that differ in C:N stoichiometry, and a suite of surrogates to consumer fitness, including survivorship, reproduction and weight gain, we demonstrate that, when supplied with abundant food of high energetic content, specialization on single food item is detrimental to survivorship and reproduction. Some degree of trophic mixing is especially needed for reproduction, and when trophic mixing could not be achieved, individuals seem to trade reproduction for survival. Furthermore, the weight of consumers increases with increased trophic specialization towards insectivory in seed-supplemented environments. On the contrary, consumer weights are independent of individual trophic position in larvae-supplemented environments. Considering beetle larvae have a low C:N ratio closer to the mice, while seeds have a relatively high C:N ratio, it is beneficial to individual mouse to be insectivorous in a seed-supplemented environment. Such nutritional constraints should not be important in a larvae-supplemented environment. Our results suggest that nutritional constraints, such as C:N stoichiometry, help maintain omnivory in mammalian generalists.
Key words: omnivory, stoichiometry, C:N ratio, nutritional constraint