COS 200-1 - Species diversity increases primary production more than behavioral diversity in a seagrass ecosystem

Abstract: In many ecosystems, primary production is driven by species-level attributes that dictate the rate of nutrient supply by consumers. Yet species-level traits are multifaceted, thus refining understanding of which traits most promote primary production is imperative to quantify the importance of biodiversity for ecosystem processes. Using a model artificial reef system in a seagrass bed we test 1) how species physiology and behavior individually affect seagrass primary production, and 2) the extent to which these two aspects of diversity interact at the community level to drive primary production. Artificial reefs (ARs) introduce three-dimensional structure to seagrass beds, initiating a feedback whereby reef-sheltering fish excrete nutrients, alleviate nutrient limitations, and increase seagrass production. We quantified the individual effect of species physiology (e.g., growth rate, body chemistry, etc.) and behavior (e.g., the extent to which they forage in open seagrass) for ecosystem primary production, by simulating populations of two different reef fish species, white grunts (Haemulon plumierii) and squirrelfish (Holocentrus rufus) under all possible combinations of physiology and behavior (e.g., swapped physiology with same behavior, and vice versa). Parameter swapping indicated that physiology has a greater effect on ecosystem primary production than behavior. Populations exclusively composed of recyclers resulted in greater primary production at the reef than populations of exclusively foragers, and forager fish populations resulted in more primary production in open seagrass; furthermore, forager fish populations resulted in more primary production per unit nutrient excreted, which is in line with ecological theory. To understand how species physiology and behavior may interact at the community level to influence primary production, we then simulated mixed fish communities composed of foragers and recyclers at 10% intervals for a given population size (e.g., for 10 individuals; 0 foragers:10 recyclers, 1:9, 2:8, 3:7, etc.). Primary production was greatest when communities were dominated by squirrelfish and lowest when communities were dominated by grunts irrespective of behavior. At the ecosystem scale, there were no emergent trends in primary production and behavior. At the reef scale, recycling communities resulted in the greatest primary production whereas foraging communities resulted in the greatest primary production at the open seagrass scale. Our findings highlight that species physiology tends to be more important than behavior for mediating primary production in a nutrient-poor ecosystem in both homogeneous populations and heterogeneous communities, providing a mechanistic basis for long-held assumptions about the importance of biodiversity for ecosystems.