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ABSTRACT Debates over whether and how populations are regulated have recently shifted away from detecting and instead towards quantifying the strength of density dependence and its variation among systems. Yet, the degree of variation in density‐dependent mortality and the factors driving this variation remain poorly understood. Here, we conducted a meta‐analysis of 38 reef fish species across 56 studies, which yielded 147 estimates of intraspecific density‐dependent mortality, primarily during early or small life stages. The magnitude of density‐dependent mortality (the increase in the per capita mortality rate due to one fish per unit area of habitat) was surprisingly inconsistent both within and among species. Several factors emerged as drivers of variation. Predators amplified the negative effects of density, and density‐dependent mortality was greater for species that typically colonize at low densities or achieve larger maximum sizes. However, even within a single species, the strength of density‐dependent mortality varied dramatically—often by several orders of magnitude—and sometimes changed sign. This heterogeneity likely reflects multiple processes acting together, including environmental context (e.g., predator density or refuge availability), traits of the focal organism (e.g., size) and methodological differences (e.g., study design) among studies. Our results underscore the need for future efforts to quantify and report ancillary variables and strive to identify how much these factors contribute to population regulation. 

Abstract Meta‐analysis (MA), a powerful tool for synthesizing reported results, is influential in ecology. While ecologists have long been well‐informed on the potential problems associated with nonindependence in experimental work (e.g., pseudoreplication), they have, until recently, largely neglected this issue in MA. However, results used in MAs are likely much more similar when they come from the same locality, system, or laboratory. A simple and common form of nonindependence in MA arises when multiple data points, that is, observed effect sizes, come from the same paper. We obtained original data from 20 published MAs, reconstructed the published analyses, and then, for 14 that had not accounted for a paper effect, used three approaches to evaluate whether within‐paper nonindependence was a problem. First, we found that “nonsense” explanatory variables added to the original analyses were statistically significant (p < 0.05) far more often than the expected 5% (25%–50% for four nonsense variables). For example, the number of vowels in the first author's name had a significant effect 50% of the time. Second, we found that an added dummy variable, which was randomly assigned at one of two levels, was statistically significant an average of 38% of the time, far exceeding the expected 5%. Even after including a random paper effect in the analyses, there was still an excess of significant results, suggesting that the within‐paper nonindependence was more complex than modeled with the random paper effect. Third, we repeated the original MAs that did not include random paper effects (n = 14 MAs) but added a random paper effect to each revised analysis. In 12 out of the 14 MAs, an added random effect was statistically significant (indicating group nonindependence that was not accounted for in the original analyses), and often the original inferences were substantially altered. Further, incorporating random paper effects was not a sufficient solution to nonindependence. Thus, problems resulting from nonindependence are often substantial, and accounting for the problem will likely require careful consideration of the details of the potential dependence among observed effect sizes. MAs that do not properly account for this problem may reach unwarranted conclusions. 

Abstract Field studies of cleaning mutualisms use a variety of methods to quantify behavioral dynamics. Studies in marine systems typically utilize data recorded by human observers on scuba or snorkel or via remote underwater video. The effects of these different methods on cleaner–client behaviors have not been rigorously assessed. We quantified cleaner–client interactions at 13 bluestreak cleaner wrasse (Labroides dimidiatus) cleaning stations in Moorea, French Polynesia using hand‐held and remote videos. We found that cleaning, cheating, and client posing rates, cleaning duration, and client species richness were all greater in the remote than in the hand‐held videos, suggesting that human presence disrupts cleaning interactions by inducing antipredator responses among clients. Some metrics, such as the ratio of cleaner chasing to cleaning behavior and the cleaners' benthic feeding rate, were higher for the hand‐held than the remote videos, possibly due to limited access of cleaners to clients in the presence of humans. Other metrics, such as cleaner and client chasing rates, the ratio of cleaning to cheating behaviors, and the duration of cleaner chases, did not differ between video types. Finally, piscivorous clients were far more abundant in the remote than the hand‐held videos, suggesting that piscivores are particularly sensitive to human presence, likely because they are targeted by fishers. Overall, our study suggests that human presence can bias studies of cleaning behavior and cleaner–client interactions, and that remote cameras should be used to conduct behavioral studies. These potential biases should be considered when interpreting existing behavioral data. 

ABSTRACT We observed a novel, nocturnal cleaning interaction between a cleaner shrimp (GenusUrocaridella) and the giant moray eel (Gymnothorax javanicus) on a lagoonal patch reef in Moorea, French Polynesia. Over the course of an 85‐min foraging bout (recorded on video by a snorkeler), we observed three separate, stereotyped cleaning interactions betweenG. javanicusand a cleaner shrimp in the genus Urocaridella (which surveys of Moorea biodiversity previously visually identified asUrocaridella antonbruunii). During these interactions, the shrimp would slowly crawl along one of the eel's flanks towards its head, enter its mouth, emerge on the other side of its head, then crawl back towards the reef along the eel's opposite flank, often causing it to jolt in response. On each of the visits, the moray spent roughly 9–12 min at the cleaning station and was observed being cleaned for a total of 62 s. Although this was a chance observation of only a few instances of cleaning, it may have several important implications for our understanding of the behavioral ecology of cleaning mutualisms, including (1) indicating potential temporal trade‐offs between being cleaned and foraging in eels, (2) suggesting a degree of temporal niche partitioning among sympatric cleaner species and (3) updating our understanding of cleaner‐client communication, given the nocturnal nature of our observations. 

Abstract Standing dead structures of habitat‐forming organisms (e.g., dead trees, coral skeletons, oyster shells) killed by a disturbance are material legacies that can affect ecosystem recovery processes. Many ecosystems are subject to different types of disturbance that either remove biogenic structures or leave them intact. Here we used a mathematical model to quantify how the resilience of coral reef ecosystems may be differentially affected following structure‐removing and structure‐retaining disturbance events, focusing in particular on the potential for regime shifts from coral to macroalgae. We found that dead coral skeletons could substantially diminish coral resilience if they provided macroalgae refuge from herbivory, a key feedback associated with the recovery of coral populations. Our model shows that the material legacy of dead skeletons broadens the range of herbivore biomass over which coral and macroalgae states are bistable. Hence, material legacies can alter resilience by modifying the underlying relationship between a system driver (herbivory) and a state variable (coral cover). 

Abstract Multispecies mutualisms are embedded in a network of interactions that include predation, yet the effects of predation on mutualism function have not been well integrated into mutualism theory. Where predators have been considered, the common prediction is that predators reduce mutualist abundance and, as a consequence, decrease service provision. Here, we use a mathematical model of a predatory fish that consumes two competing coral mutualists to show that predators can also have indirect positive effects on hosts when they preferentially consume competitively dominant mutualists that are also lower in quality. In these cases, predation reverses the outcome of competition, allowing the higher quality mutualist to dominate and enhancing host performance. The direction and strength of predator effects depend on asymmetries in mutualist competition, service provision, and predation vulnerability. Our findings suggest that when the strength of predation shifts (e.g., due to exploitative harvest of top predators, introduction of new species, or range shifts in response to climate change), mutualist communities will exhibit dynamic responses with nonmonotonic effects on host service provision. 

Abstract Remote coral reefs are thought to be more resilient to climate change due to their isolation from local stressors like fishing and pollution. We tested this hypothesis by measuring the relationship between local human influence and coral community resilience. Surprisingly, we found no relationship between human influence and resistance to disturbance and some evidence that areas with greater human development may recover from disturbance faster than their more isolated counterparts. Our results suggest remote coral reefs are imperiled by climate change, like so many other geographically isolated ecosystems, and are unlikely to serve as effective biodiversity arks. Only drastic and rapid cuts in greenhouse gas emissions will ensure coral survival. Our results also indicate that some reefs close to large human populations were relatively resilient. Focusing research and conservation resources on these more accessible locations has the potential to provide new insights and maximize conservation outcomes.