Differences in the behavior and diet between shoaling and solitary surgeonfish (Acanthurus triostegus).

Variation in behavior within marine and terrestrial species can influence the functioning of the ecosystems they inhabit. However, the contribution of social behavior to ecosystem function remains underexplored. Many coral reef fish species provide potentially insightful models for exploring how social behavior shapes ecological function because they exhibit radical intraspecific variation in sociality within a shared habitat. Here, we provide an empirical exploration on how the ecological function of a shoaling surgeonfish (Acanthurus triostegus) may differ from that of solitary conspecifics on two Pacific coral reefs combining insight from behavioral observations, stable isotope analysis, and macronutrient analysis of gut and fecal matter. We detected important differences in how the social mode of A. triostegus affected its spatial and feeding ecology, as well as that of other reef fish species. Specifically, we found increased distance traveled and area covered by shoaling fish relative to solitary A. triostegus. Additionally, shoaling A. triostegus primarily grazed within territories of other herbivorous fish and had piscivorous and nonpiscivorous heterospecific fish associated with the shoal, while solitary A. triostegus grazed largely grazed outside of any territories and did not have any such interactions with heterospecific fish. Results from stable isotope analysis show a difference in δ15N isotopes between shoaling and solitary fish, which suggests that these different social modes are persistent. Further, we found a strong interaction between social behavior and site and carbohydrate and protein percentages in the macronutrient analysis, indicating that these differences in sociality are associated with measurable differences in both the feeding ecology and nutrient excretion patterns. Our study suggests that the social behavior of individuals may play an important and underappreciated role in mediating their ecological function.

Life history mediates the association between parasite abundance and geographic features.

Although parasites are ubiquitous in marine ecosystems, predicting the abundance of parasites present within marine ecosystems has proven challenging due to the unknown effects of multiple interacting environmental gradients and stressors. Furthermore, parasites often are considered as a uniform group within ecosystems despite their significant diversity. We aim to determine the potential importance of multiple predictors of parasite abundance in coral reef ecosystems, including reef area, island area, human population density, chlorophyll-a, host diversity, coral cover, host abundance and island isolation. Using a model selection approach within a database of more than 1,200 individual fish hosts and their parasites from 11 islands within the Pacific Line Islands archipelago, we reveal that geographic gradients, including island area and island isolation, emerged as the best predictors of parasite abundance. Life history moderated the relationship; parasites with complex life cycles increased in abundance with increasing island isolation, while parasites with direct life cycles decreased with increasing isolation. Direct life cycle parasites increased in abundance with increasing island area, although complex life cycle parasite abundance was not associated with island area. This novel analysis of a unique dataset indicates that parasite abundance in marine systems cannot be predicted precisely without accounting for the independent and interactive effects of each parasite's life history and environmental conditions.

Human impacts decouple a fundamental ecological relationship-The positive association between host diversity and parasite diversity.

Human impacts on ecosystems can decouple the fundamental ecological relationships that create patterns of diversity in free-living species. Despite the abundance, ubiquity, and ecological importance of parasites, it is unknown whether the same decoupling effects occur for parasitic species. We investigated the influence of fishing on the relationship between host diversity and parasite diversity for parasites of coral reef fishes on three fished and three unfished islands in the central equatorial Pacific. Fishing was associated with a shallowing of the positive host-diversity-parasite-diversity relationship. This occurred primarily through negative impacts of fishing on the presence of complex life-cycle parasites, which created a biologically impoverished parasite fauna of directly transmitted parasites resilient to changes in host biodiversity. Parasite diversity appears to be decoupled from host diversity by fishing impacts in this coral reef ecosystem, which suggests that such decoupling might also occur for parasites in other ecosystems affected by environmental change.

Dispersal at a snail's pace: historical processes affect contemporary genetic structure in the exploited wavy top snail (Megastraea undosa).

We used population genetics to assess historical and modern demography of the exploited wavy top snail, Megastraea undosa, which has a 5-10 day pelagic larval duration. Foot tissue was sampled from an average of 51 individuals at 17 sites across the range of M. undosa. Genetic structure at the mtDNA locus is strikingly high (ΦST of 0.19 across 1000 km), and a major cline occurs in northern Baja California (ΦCT of 0.29 between northern and southern populations). Genetic data indicate that the northern region is highly connected through larval dispersal, whereas the southern region exhibits low genetic structure. However, additional analyses based on patterns of haplotype diversity and relationships among haplotypes indicate that M. undosa has likely recently expanded into the Southern California Bight or expanded from a small refugial population, and analysis using isolation by distance to calculate dispersal distance indicates surprisingly short estimates of dispersal from 30 m to 3 km. This scenario of a northward expansion and limited larval dispersal is supported by coalescent-based simulations of genetic data. The different patterns of genetic variation between northern and southern populations are likely artifacts of evolutionary history rather than differences in larval dispersal and this may have applications to management of this species. Specifically, these data can help to inform the scale at which this species should be managed, and given the potentially very small dispersal distances, this species should be managed at local scales. Consideration of the evolutionary history of target species allows for a more accurate interpretation of genetic data for management.

Patterns, causes and consequences of regional variation in the ecology and life history of a reef fish.

Many species vary in their ecology across their geographic ranges in response to gradients in environmental conditions. Such variation, which can influence life history traits and subsequent demography of populations, usually occurs over large spatial scales. However, describing and understanding the causes of such variation is difficult precisely because it occurs over such large spatial scales. In this study, we document spatial variation in the ecology of a common reef fish, Stegastes beebei, in the Galápagos Islands and test a number of potential causal mechanisms. The pattern resembles that seen in latitudinal variation: individuals are larger, occur in higher densities, and live longer in the coldest region of the islands than those in the warmest region. However, in this system, demography varies among regional populations separated by <150 km. Preferred nutritious algae are more available in the cold region and comprise a greater proportion of the diet of fish in this region. Per gram reproductive effort appears to be strongly related to temperature, despite differences in the gross magnitude and timing of reproduction in different regions. A model of reproductive output suggests that fish in the warmest region are allocating a greater proportion of available energy to reproduction, resulting in apparent regional life history tradeoffs. Our data suggest that regional demographic differences in S. beebei may be driven by a combination of variation in food availability and an environmentally mediated life history tradeoff.