Abstract
Quantitative approaches to predator–prey interactions are central to understanding the structure of food webs and their dynamics. Different predatory strategies may influence the occurrence and strength of trophic interactions likely affecting the rates and magnitudes of energy and nutrient transfer between trophic levels and stoichiometry of predator–prey interactions. Here, we used spider–prey interactions as a model system to investigate whether different spider web architectures—orb, tangle, and sheet‐tangle—affect the composition and diet breadth of spiders and whether these, in turn, influence stoichiometric relationships between spiders and their prey. Our results showed that web architecture partially affects the richness and composition of the prey captured by spiders. Tangle‐web spiders were specialists, capturing a restricted subset of the prey community (primarily Diptera), whereas orb and sheet‐tangle web spiders were generalists, capturing a broader range of prey types. We also observed elemental imbalances between spiders and their prey. In general, spiders had higher requirements for both nitrogen (N) and phosphorus (P) than those provided by their prey even after accounting for prey biomass. Larger P imbalances for tangle‐web spiders than for orb and sheet‐tangle web spiders suggest that trophic specialization may impose strong elemental constraints for these predators unless they display behavioral or physiological mechanisms to cope with nutrient limitation. Our findings suggest that integrating quantitative analysis of species interactions with elemental stoichiometry can help to better understand the occurrence of stoichiometric imbalances in predator–prey interactions.
Highlights
Biological communities are composed of networks of trophic interactions, whose structure plays a major role in shaping the dynamics and functioning of ecological systems (Montoya, Pimm, & Solé, 2006; Olff et al, 2009; Pimm, 1982)
We addressed the following questions: (1) How does spider web architecture influence prey species richness and composition? and (2) Does web architecture influence the stoichiometry of spider–prey interactions? We hypothesized that if web architecture influences spider–prey interactions, spiders that build webs of different architectures will differ in the prey communities they capture, resulting in relative prey capture variability and degree of generalist trophic behavior as a function of web type
We investigated how spider web architecture influenced the structure of spider–prey interactions on the basis of prey frequency and biomass as well as the stoichiometry of spider–prey interactions
Summary
Biological communities are composed of networks of trophic interactions, whose structure plays a major role in shaping the dynamics and functioning of ecological systems (Montoya, Pimm, & Solé, 2006; Olff et al, 2009; Pimm, 1982) Such networks, which look at the degree to which predators feed upon a prey community, can be used to observe both qualitative properties—which species are interacting—or quantitative measures that consider the strength of the species interactions (Ings et al, 2009; Williams & Martinez, 2000). Specialist consumers being restricted to a narrower range of prey types may face nutrient limitation if a single prey taxon does not satisfy the nutritional needs of the consumer (Westoby, 1978) In such a case, we expect that specialization will result in spiders with greater elemental imbalances than those faced by generalist spiders. We expect that specialization will result in spiders with weaker elemental imbalances than generalist spiders
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