Biotic interactions shape the trait assembly of marine communities across time and latitude

Diana P. Lopez and Amy L. Freestone, Department of Biology, Temple University, Philadelphia, PA, Amy L. Freestone, Smithsonian Environmental Research Center, Edgewater, MD, Amy L. Freestone, Smithsonian Tropical Research Institute, Panama

Background/Question/Methods
Assembly processes are highly dynamic shifting with time, scale, latitude, or environmental gradients. Biotic filters operate more intensely at local scales, and the strength of biotic interactions is hypothesized to vary across time and latitude. Predation, for example, can be stronger at lower latitudes, while competition intensifies at later stages of community assembly due to resource limitation. Since biotic filters act upon functional traits of organisms, we explored trait-mediated community assembly using patterns of trait convergence, divergence, and shifts in mean traits in functionally diverse marine assemblages. We examined the effects of predation and assembly time on trait distribution across latitude in four regions along the Pacific coast of North and Central America using predator exclusion experiments and two assembly stages up to one year. We hypothesized non-random trait patterns would emerge during late assembly across latitudes due to competition and at low latitudes regardless of assembly stage due to predation.
Results/Conclusions
As expected, trait divergence occurred later in assembly across latitudes where competitive traits dominated, and in the tropics, predation caused trait convergence early in assembly. Shifts in the individual trait structure of communities confirmed these assembly patterns. For example, slower settlers with lower acquisition of organic matter dominated later assembly at higher latitudes, while in the tropics colonial and encrusting organisms were the dominant growth forms later in assembly. Moreover, in the tropics and during early in assembly, non-palatable traits such as calcification were favored under ambient predation. Therefore, biotic interactions resulted in deterministic assembly of nearshore communities at local scales across latitude with assembly time revealing changes in trait patterns. Assembly patterns continue to be a topic of debate and trait-based assembly explored at local scales and through time can provide a mechanistic understanding of community structure.