PARENT SESSION
Oral Session # 71: Trophic Structure I: Theory; Aquatic Systems.
Presiding: D Chalcraft
Thursday, August 7. 8:00 AM to 11:30 AM, SITCC Meeting Room 202.
Effects of resource diversity on the outcome of resource competition.
Fox, Jeremy*,1, Barreto, Cristine1, 1 Imperial College, Silwood Park, Ascot, Berkshire, UK
ABSTRACT- Many classical studies of resource partitioning demonstrate diet differences among coexisting consumers, but demonstrating that observed diet differences are either necessary or sufficient to explain coexistence is difficult. Here we take an alternative approach, by manipulating the diversity of resources (bacterial taxa) available to a pair of ciliate bacterivores coexisting in laboratory microcosms. Classical theory and intuition suggest that reducing bacterial diversity should reduce the scope for resource partitioning, and therefore coexistence. However, recent theory suggests that the intensity of competition may be a non-linear function of resource diversity when resources are self-reproducing. Self-reproducing resources can be driven extinct by their consumers. The equilibrial intensity of competition among consumers will depend on which resources persist at equilibrium, which in turn depends in a complex fashion on initial resource diversity and composition. We crossed four ciliate combinations (no ciliates, Tetrahymena, Colpidium, and both together) with five bacterial combinations (monocultures of each of three taxa, all three together, and all three plus 10 additional taxa). We sampled ciliate and bacterial abundance and composition after four weeks (=dozens of ciliate generations). Bacterial and ciliate composition have complex, reciprocal effects on one another. Resource partitioning only partially explains the observed coexistence of these ciliates. We speculate on the nature of other mechanisms of coexistence, and suggest that loss of biodiversity from one trophic level may have surprising consequences for biodiversity on adjacent trophic levels.
Key words: microcosms, resource competition, resource partitioning, protists