CANCELLED - Dynamics in competitive metacommunities: Fitness inequality and niche differentiation

Background/Question/Methods

Niche theory suggests that only one species should persist in ecological communities per niche or limiting resource, yet this prediction is routinely violated in non-laboratory environments. To solve this paradox ecologists have increasingly turned to examining the organization of competitive communities in terms of niches and neutrality, and more recently towards studying competition in terms of equalizing mechanisms (those governing fitness inequality) and stabilizing mechanisms (those governing niche differentiation). We present preliminary results from an experimental framework designed to allow manipulation of fitness inequality and niche differentiation in model communities of freshwater diatoms undergoing pairwise competition for a common limiting resource (silicate). Competition was carried out in semi-continuous batch culture, and generally run until competitive exclusion of one competitor, as defined by disappearance, or reduction to extremely low density, of one competitor from the community (typically over the course of 20 - 50 days). Model species used include Asterionella formosa, Fragilaria crotonensis, and Nitzschia palea.

Results/Conclusions

Preliminary results indicate that fitness inequality, quantified by the difference in competitors’ R* values for a limiting resource, is capable of predicting competitive exclusion in the absence of niche differentiation, both under conditions of single patch competition and in dispersal limited homogeneous metacommunities. Current work includes the creation of single patch communities with minimal fitness inequality, where competitive outcome is predicted to be primarily stochastic, and the creation of heterogeneous metacommunities, where niche differentiation is predicted to allow competitive coexistence even in patches with significant fitness inequality. We suggest that rephrasing competition theory in terms of fitness inequality and niche differentiation offers the potential to allow simultaneous attention to the importance of fitness inequality, stochasticity, dispersal, and niche differentiation without recourse to a niche-neutral dichotomy.