CONSUMER MOBILITY AND THE RELATIVE IMPORTANCE OF CONSUMPTION AND COMPETITION FOLLOWING PHYSICAL DISTURBANCE

Simple models and an example from the published Literature suggest how consumer mobility can alter the relative importance to producers of c onsumption (predation and herbivory) and competition following a distu rbance that opens habitat for colonization. Highly mobile consumer spe cies often can colonize disturbed habitat at juvenile and adult life s tages with high per capita consumption rates. In contrast, consumers w ith limited mobility, as well. as sessile or sedentary prey, can be re stricted to colonization of disturbed habitat by reproductive propagul es, and initially have low per capita consumption, and low biomass and per capita production, respectively. Following a disturbance, the rel ationship between potential consumption and production can differ in i mportant ways from that prior to the disturbance if consumer and prey species differ markedly in mobility, but may be similar to that prior to the disturbance if consumers and prey are both limited to colonizat ion by reproductive propagules. Functional responses of consumers, and growth rates of consumers relative to producers, can determine how st rongly consumer mobility will influence post-disturbance interactions. In California (USA) kelp forests, sea urchins may be able to colonize disturbed patches as adults or can be restricted to colonization by l arval settlement depending on habitat characteristics and how their fo raging behavior affects sea urchin susceptibility to winter storms. On Naples Reef, near Santa Barbara, California, recovery of macroalgae i ncluding giant kelp was inhibited under grazing by adult urchins but w as rapid when sea urchins colonized through larval settlement.