A predictive understanding of ecological processes requires identifying the factors that explain variation in the organismal traits that drive these processes. Integrating evolutionary history and ecology has been shown to be essential to understand variation in traits that determine species interactions in community ecology. However, the extent to which these factors determine traits relevant for ecosystem dynamics (and thus ecosystem ecology) is poorly understood. Nutrient cycling is essential for reef ecosystem dynamics, and consumers are critical drivers of this process. We use a dataset of nine consumer “chemical traits” (e.g., body nutrient content and nutrient excretion rates) associated with nutrient cycling, collected from 1,572 individual coral reef fish (178 species spanning 41 families) in two biogeographic regions, the Caribbean and Polynesia, to quantify the relative importance of phylogenetic history and ecological context as a driver of chemical trait variation on coral reefs. We find: (1) phylogenetic history is a better predictor of variation in all chemical traits, overwhelming the influence of ecological factors, (2) phylogenetic conservatism in chemical traits is greater in the Caribbean than Polynesia, where our data suggests that ecological forces may have a greater influence on chemical trait variation, and (3) differences in chemical traits between regions can be explained by differences in nutrient limitation associated with our study locations. Our study provides multiple lines of evidence that phylogenetic conservatism is a critical determinant of contemporary nutrient dynamics on coral reefs. More broadly our findings highlight the utility of evolutionary history to improve prediction in ecosystem ecology.

Predators can strongly influence disease transmission and evolution, particularly when they prey selectively on infected hosts. Although selective predation has been observed in numerous systems, why predators select infected prey remains poorly understood. Here, we use a model of predator vision to test a longstanding hypothesis as to the mechanistic basis of selective predation in a Daphnia-microparasite system, which serves as a model for the ecology and evolution of infectious diseases. Bluegill sunfish feed selectively on Daphnia with a variety of parasites, particularly in water uncolored by dissolved organic carbon. The leading hypothesis for selective predation in this system is that infection-induced changes in the appearance of Daphnia render them more visible to bluegill. Rigorously evaluating this hypothesis requires that we quantify the effect of infection on the visibility of prey from the predator’s perspective, rather than our own. Using a model of the bluegill visual system, we show that the three common parasites, Metschnikowia bicuspidata, Pasteuria ramosa and Spirobacillus cienkowskii, increase the opacity of Daphnia, rendering infected Daphnia darker against the background of downwelling light. As a result of this increased brightness contrast, bluegill can see infected Daphnia at greater distances than uninfected Daphnia – between 19-33% further, depending on the parasite. Pasteuria and Spirobacillus also increase the chromatic contrast of Daphnia. Contrary to expectations, the visibility Daphnia was not strongly impacted by water color in our model. Our work generates hypotheses about which parasites are most likely affected by selective predation in this important model system and establishes visual models as a valuable tool for understanding ecological interactions that impact disease transmission.