Simulations allow us to explore what is often difficult or sometimes even intractable to test. I selected the paper ‘Local interactions drive size dependent space competition between coral and crustose coralline algae’ by Buenau et al. (doi: 10.1111/j.1600-0706.2010.18972.x) because I suspect and hope that it will become a really useful contribution to better understanding coral recovery.
This study examines the conditions associated with slow growing coral in competition with crustose coralline algae or CCA. Theory suggests that niche separation, disturbance, intransitive interactions etc. can all promote coexistence. Size dependence may be a critical aspect of many of these models in that size often directly relates to competitive ability (bigger is better) and indirectly relates to trade-offs associated with maturation, development, or life-history traits. Hence, this paper nicely links to broad theories but has profound conservation implications – i.e. how important is size as it relates to the capacity for an umbrella species to establish a competitive refuge. The overarching hypothesis is that corals require size refuges to effectively recolonize after disturbance. The hypothesis and associated predictions is tested using a spatially-explicit lattice based simulation and ordinary differential equations as a secondary and simpler test of the hypothesis.
Using my simple field ecology brain, I interpret the results as follows. Slow growing coral cannot use size-related refuges to escape being outcompeted from the aggressive (and evil?) algae. This is a really interesting finding (from the models) in that it suggests that alternative biological mechanisms must be present to encourage coexistence or to manage for conservation purposes. Hence, management must promote wide open space for coral recruitment. The other implication is that given the one-sidedness of these interactions, it likely that dead corals will be replaced by algae and that dead CCA will not be replaced by coral – ever. The only caveat is that if coral colonies fuse this does provide a limited competitive advantage. Coming from the plant ecology world where size is similarly important and we similarly seek an understanding of the mosaic that is a community, I really enjoyed this paper and found the big picture links to theory interesting, the models challenging and appropriate, and the conservation implication useful but disheartening. The empirical feedbacks suggested are however very clear – studies of competition for space, spatially structured, with size well documented would go a long way to informing conservation and theory in this instance.