Short-term spatial stability in trophic interactions

Summary: The concept of stability in ecological theory has been a subject of debate for more than 40 years. Its value lies in being the explanatory principle underlying equilibrium in nature. Until now, the possibility of spatial stability in trophic interactions, defined as resilience of trophic activity (e.g. herbivore/algae or predator/prey) within patches after a disturbance, has not been explored. This concept requires the demonstration of two properties: (i) the return after a strong disturbance to a reference level of intensity of the trophic interaction (intensity criterion), and (ii) positive spatial correlation between pre- and post-disturbance intensity of the trophic interaction (spatial determinism criterion). The first criterion can be assessed by checking the consistency of intensities of grazing effects between years and the second criterion by correlating the intensities of grazing between years on the same set of patches. We used a spatially explicit test, repeated after experimental disturbance of the same plots in two consecutive years, to test for the existence of spatial stability in the effects of grazing on rocky shore algal assemblages. The detection of spatial stability depended on the level of resolution at which the prey assemblages were examined (species, functional group and trophic level) and allowed us to demonstrate stability in grazing effects, which shape the mosaic of patches on the high rocky shore at scales of 10s of meters. The community analysed was highly resilient due to its domination by species that can quickly re-colonize and recover to pre-disturbance levels and showed spatial determinism because of the tendency of both grazers and algae to colonize particularly favourable areas. Synthesis. The most important findings are as follows: (i) spatial stability was confirmed for a trophic interaction, and (ii) spatial determinism in these systems was detectable. We suggest that patches exhibiting predictability in trophic interaction strength can function as initiators of recovery after disturbance and at the same time represent the deterministic initial condition that might shape long-term spatial configurations within the landscape. © 2014 British Ecological Society.