Foraging behavior by Daphnia in stoichiometric gradients of food quality

Abstract

Mismatches in the elemental composition of herbivores and their resources can impact herbivore growth and reproduction. In aquatic systems, the ratio of elements, such as C, P, and N, is used to characterize the food quality of algal prey. For example, large increases in the C:P ratio of edible algae can decrease rates of growth and reproduction in Daphnia. Current theory emphasizes that Daphnia utilize only assimilation and respiration processes to maintain an optimal elemental composition, yet studies of terrestrial herbivores implicate behavioral processes in coping with local variation in food quality. We tested the ability of juvenile and adult Daphnia to locate regions of high-quality food within a spatial gradient of algal prey differing in C:P ratio, while holding food density constant over space. Both juveniles and adults demonstrated similar behavior by quickly locating (i.e., <10 min) the region of high food quality. Foraging paths were centred on regions of high food quality and these differed significantly from paths of individuals exposed to a homogeneous environment of both food density and food quality. Ingestion rate experiments on algal prey of differing stoichiometric ratio show that individuals can adjust their intake rate over fast behavioral time-scales, and we use these data to examine how individuals choose foraging locations when presented with a spatial gradient that trades off food quality and food quantity. Daphnia reared under low food quality conditions chose to forage in regions of high food quality even though they could attain the same C ingestion rate elsewhere along a spatial gradient. We argue that these aspects of foraging behavior by Daphnia have important implications for how these herbivores manage their elemental composition and our understanding of the dynamics of these herbivore-plant systems in lakes and ponds where spatial variation in food quality is present.

Evolution of Nutrient Uptake Reveals a Trade‐Off in the Ecological Stoichiometry of Plant‐Herbivore Interactions

“…The underlying assumption that herbivores can detect the nutritional value of their food is supported by several experimental studies (Cowles et al 1988;DeMott 1989;Buskey 1997;John and Davidson 2001;Schatz and McCauley 2007;Martel 2009). For instance, various zooplankton species can sense the nutrient content of their prey through chemical cues such as the chemical composition of their outer cell surface (Martel 2009) and leakage of nutrientrich molecules (Buskey 1997;Kiørboe 2008).…”

“…The primary producers compete for nutrients according to a variable-internal-stores model (Droop 1973;Grover 1991;Ducobu et al 1998). The herbivore preys on the primary producers, with a preference for the most nutritious species (Cowles et al 1988;Schatz and McCauley 2007;Kiørboe 2008). The nutrient uptake rate of primary producers is an evolving trait.…”

Food Web Paradigms: The Biochemical View on Trophic Interactions

“…The properties of a food particle can be different for the sequential steps in the chain of reactions of food intake. This encompasses food detection, including texture and taste (PAFFENHÖFER et al, 1982;DEMOTT, 1986;Butler et al, 1989;DEMOTT, 1989;SCHATZ and MCCAULEY, 2007), filtration, ingestion (BURNS, 1968;ROTHHAUPT, 1990a;ROTH-HAUPT, 1990b), andassimilation properties (e.g., PORTER, 1975; VAN DONK, 1997).…”

Single dietary amino acids control resting egg production and affect population growth of a key freshwater herbivore

“…For example, the mineral content and primary and secondary metabolite contents of plants and algae can influence herbivore foraging behaviour (Berner et al 2005;Schatz and McCauley 2007), somatic growth and reproduction (Sterner and Elser 2002;Von Elert 2002;MartinCreuzburg et al 2009), life history strategy (Twombly et al 1998), immune function (Bukovinszky et al 2009;Smilanich et al 2009), anti-predator defence (Kazana et al 2007) and genetic diversity (Weider et al 2008). As a consequence, the elemental and biochemical composition of herbal food sources potentially affects the population dynamics of herbivores and thus the efficiency with which carbon and organic matter are transferred to higher trophic levels (Müller-Navarra et al 2000;Wacker and Von Elert 2001;Sterner and Elser 2002).…”