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 size. 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 remarkable heterogeneity suggests that environmental variation might overshadow species-specific traits or that methodological variation among studies constrains our ability to perceive drivers. Our results underscore the need for future efforts to identify the factors that drive this variability in population regulation.

Foundation species recovery is often assumed to restore associated communities to their pre-disturbance state. However, community dynamics may differ due to species-specific responses, altered environmental conditions, or changes in biotic interactions that can override the influence of the recovering foundation species. In a 14-year experiment, we studied the loss and recovery of giant kelp and its associated rocky reef community. Alongside reference plots, we removed giant kelp for 6–7 years, then tracked recovery for another 6–7 years. After cessation of removal, giant kelp and community (understory macroalgae and sessile invertebrates) biomass rapidly converged on the reference condition. However, the composition of the community diverged from the starting point, indicating that recovery of community biomass can disguise species turnover in response to foundation species recovery. Our results highlight how stochastic forces can overwhelm the influence of foundation species to determine the structure of communities when recovering from disturbance.

Size-scaling relationships generated across huge variation in body mass from zooplankton to elephants offer critical insight into understanding similarities in species interactions across ecosystems. Yet to what extent ecologists can borrow from these relationships to effectively predict interactions between a single species pair remains poorly understood. Here, we combine experiments and long-term data to test how accurately published size-scaling relationships predict interactions between an economically and ecologically important predator-prey pair. We demonstrate that interaction strength is highly dependent on predator size, prey size, and prey density. We then used this relationship to predict plausible interaction strengths across ten years of data at five sites. Our analysis reveals that variation in body size accounts for up to 91% of the variation in interaction strength compared to density. However, predictions generated from even the closest size-scaling relationship from the literature underestimated the strength of interactions by a factor of 4.

A growing body of literature has documented myriad effects of human activities on animal behavior, yet the ultimate ecological consequences of these behavioral shifts remain largely uninvestigated. While it is understood that, in the absence of humans, variation in animal behavior can have cascading effects on species interactions, community structure, and ecosystem function, we know little about whether the type or magnitude of human-induced behavioral shifts translate into meaningful ecological change. Here we synthesize empirical literature and theory to create a novel framework for examining the range of behaviorally mediated pathways through which human activities may affect different ecosystem functions. We highlight the few empirical studies that show the potential realization of some of these pathways, but also identify numerous factors that can dampen or prevent ultimate ecosystem consequences. Without a deeper understanding of these pathways, we risk wasting valuable resources on mitigating behavioral effects with little ecological relevance, or conversely mismanaging situations in which behavioral effects do drive ecosystem change. The framework presented here can be used to anticipate the nature and likelihood of ecological outcomes and prioritize management among widespread human-induced behavioral shifts, while also suggesting key priorities for future research linking humans, animal behavior, and ecology.