Abstract:
With an increase in the rate of biodiversity loss, much research has been focused on
understanding the relationship between biodiversity and ecosystem functioning. Past
research has shown that both the diversity and density of functional groups is positively
related to ecosystem functions. This thesis explores the relationship between the variation in
macroalgal and coral cover and five herbivorous fish functional groups on 51 reefs in the
Caribbean. The main aims are to determine which functional groups significantly affect
macroalgal cover and coral cover, both direct and indirect proxies for herbivory, and to
understand the relative importance of functional group diversity and density in the function
of herbivory. Linear mixed effect models are used to determine the relationships. The
primary findings are 1) large parrotfish are negatively associated with macroalgal cover.
These fish are known to consume large quantities of macroalgae, suggesting that this
functional group is playing an important role in the function of herbivory, and 2) the density
of territorial damselfish is negatively associated with macroalgal cover and positively with coral cover. A more detailed analysis of the functional group revealed high densities of only
two species-Stegastes partitus and Stegastes adustus. It is known that these species do not exclude
macroalgae from their territories, but prefer habitats with high coral cover and low
macroalgal cover, suggesting that the relationship between territorial damselfish density and
benthic cover is a result of habitat preference rather than herbivory. In addition to these
findings, diversity was not a robust predictor of benthic cover, suggesting that merely
increasing the species richness of an assemblage will not result in increased functioning; a
proportional increase in fish density is required.
