Trophic structure and the role of predation in shaping hot desert communities

Low precipitation and high temperatures in deserts limit primary productivity, and reduce rates of herbivory and microbial decomposition. As a result, the small amount of plant tissue produced in deserts dies unconsumed and turns to litter that is consumed by macrodetritivorous arthropods, which are preyed upon by small ectothermic arthropods and reptiles. This ectotherm-based food chain is energetically efficient and, despite the low productivity of the desert habitat, is able to support a fourth trophic level of endothermic predators, i.e. mammals and birds, that forage over large areas and locate their prey visually from a distance. This four-link chain results in trophic interactions that run from the large endothermic predators through the ectothermic ones to the macrodetritivores. Thus, macrodetritivores are released from predation and become food-limited. However, the full expression of these interactions occurs only in low productivity habitats with low plant cover. In productive habitats, plant cover blocks the vision of endothermic predators and provides refuge to small ectothermic ones. This results in ectothermic predators becoming abundant in habitats with high plant cover and controlling their prey, the macrodetritivores. Thus, the increase in productivity in deserts decreases the amount of energy that reaches top predators as it has a mainly structural effect: to increase plant cover and mediate predation interactions.