Causes of species diversity differences: a comparative analysis of Markov models

While many dynamic processes have been proposed to produce diversity differences among communities, most empirical investigations focus on static system attributes. hn ideal analysis would consider multiple dynamic processes and their impact on many community members, but such analyses can be logistically daunting. I compared Markov chain models of ecological communities to explore general processes leading to diversity differences of sessile species between coral reefs and rocky intertidal mussel beds. As predicted by diversity theory, high diversity coral reefs had lower species replacement probabilities and higher disturbance rates than did lower diversity mussel beds. Intransitivities in species replacements, recruitment limitation and responses to perturbing species from equilibrium (Jacobian elements) did not differ significantly between systems. Tradeoffs between the displacement risk or displacement ability of a species and either disturbance risk or colonising ability were not apparent. Manipulating the coral reef model to eliminate disturbance or intransitivities caused declines in species diversity, whereas removing recruitment limitation or increasing the probability of interspecific replacement did not. Higher overall disturbance levels can explain part of the diversity difference between systems, but much remained unexplained, indicating that details of the pattern and strengths of species interactions were probably extremely important.