Ecological stoichiometry of the black widow spider and its prey from desert, urban and laboratory populations

Ecological stoichiometry (ES) offers a framework to identify the mechanisms that allow pest species to thrive following human-induced rapid environmental change (HIREC). Specifically, ES links the biochemical composition of an organism to their growth and reproduction, which influences population growth and ecosystem dynamics. We used ES to quantify the nutrient composition (C: N, C: P, and N: P) of the western black widow spider (Latrodectus hesperus) and its prey (from desert and urban) and laboratory populations. Urban field spider and cricket subpopulations exhibited spatial variation in their C: N ratios. Urban field spider C: N, C: P, and N: P ratios were significantly different from urban crickets, but in the laboratory population, spiders and cricket C: N, C: P, and N: P ratios did not vary. Relative to urban spiders, desert spiders had lower C: P and N: P, but C: N did not differ. In the laboratory population, spiders had higher C: N, C: P, N: P ratios than field-caught spiders. Moreover, cannibalism by laboratory-reared spiders lowered C: P and N: P ratios, but not C: N ratios. We suggest such intraspecific variation may be one mechanism that allows urban pests to thrive following HIREC.