Food chain length and trophic niche of a key predator in montane desert streams

Abstract

Top predator foraging strategy and prey base community composition can influence food web structure and function. To investigate the role of functional trait diversity and taxonomic richness in determining food chain length and energy flow in high elevation desert streams, we examined aquatic invertebrate community data along with carbon and nitrogen stable isotope analysis of a top predator, Abedus herberti (giant water bug). We also examined isotopic niche differences across different levels of population structure and seasons. We hypothesized that communities with higher richness would have longer food chains. We found food chain length did not vary substantially across a wide taxonomic and functional richness gradient, which contradicts theoretical mechanisms stating that more resources or higher functional diversity should lead to longer food chains. The isotopic niche of A. herberti was conserved across seasons and sites, and the majority of carbon in tissues came from allochthonous materials. Stable isotopes suggested that A. herberti occupy similar feeding niches in spring and autumn, despite seasonal changes in stream conditions, leaf litter inputs, and invertebrate community structure. Due to the strong aquatic–terrestrial linkages we identified, human activities and climate-driven alterations to the adjacent terrestrial environment may affect the dynamics and integrity of the within-stream ecosystem.