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Abstract Predators mediate the strength of trophic cascades indirectly by decreasing the number of prey consuming a basal resource and by altering prey responses that dictate prey foraging. The strength of these indirect effects further depends on abiotic factors. For example, attributes of the environment, such as turbulent flows in aquatic habitats that disrupt spatial information available from chemical cues, can impose “sensory stresses” that impair the ability of predators or prey to detect each other. The multi-faceted impacts of sensory stress on both the predators and prey create challenges in predicting the overall effect on the trophic cascade. Here, we explore how sensory stress affects the strength of trophic cascades using a tri-trophic dynamical model that incorporates the sensory environment and anti-predatory responses. We explore two crucial parameters that govern outcomes of the model. First, we allow predation rates to either strengthen or weaken depending on whether prey or predators are more sensitive to sensory stress, respectively. Second, we explore scenarios where anti-predatory responses can either drive a strong or weak reduction in prey foraging. We find that sensory stress usually weakens trophic cascades except in scenarios where predators are relatively unaffected by sensory stress and the loss of anti-predatory responses does not affect prey foraging. The model finally suggests that “hydra effects” can manifest, whereby an increase in prey population occurs despite an increase in per capita predation. This last feature emerges due to the interaction between logistic growth of the basal resource and anti-predatory responses reducing the over-consumption of the basal resource. 

Abstract Dispersal of reproductive propagules determines recruitment patterns and connectivity among populations and can influence how populations respond to major disturbance events. Dispersal distributions can depend on propagule release strategies. For instance, the bull kelp,Nereocystis luetkeana, can release propagules (spores) from two heights in the water column (“bimodal release”): at the water surface, directly from the reproductive tissues (sori) on the kelp's blades, and near the seafloor after the sori abscise and sink through the water column.N. luetkeanais a foundation species that occurs from central California to Alaska and is experiencing unprecedented levels of population declines near its southern range limit. We know little of the kelp's dispersal distributions, which could influence population recovery and restoration. Here, we quantify how bimodal spore release heights affect dispersal outcomes based on a numerical model specifically designed forN. luetkeana. The model incorporates oceanographic conditions typical of the species' coastal range and kelp biological traits. With bimodal release heights, 34% of spores are predicted to settle within 10 m of the parental alga and 60% are predicted to disperse beyond 100 m. As an annual species, bimodal release heights can facilitate the local regeneration of adults within a source kelp forest while also supporting connectivity among multiple forests within broader bull kelp metapopulations. To leverage this pattern of bimodal spore dispersal in bull kelp restoration management, directing resources toward strategically located focal populations that can seed other ones could amplify the scale of recovery. 

Abstract In restoration ecology, the Field of Dreams hypothesis posits that restoration efforts that create a suitable environment could lead to the eventual recovery of the remaining aspects of the ecosystem through natural processes. Natural processes following partial restoration has led to ecosystem recovery in both terrestrial and aquatic systems. However, understanding the efficacy of a “Field of Dreams” approach requires a comparison of different approaches to partial restoration in terms of spatial, temporal, and ecological scale with what would happen given more comprehensive restoration efforts. We explore the relative effect of partial restoration and ongoing recovery on restoration efficacy with a dynamical model based on temperate rocky reefs in Northern California. We analyze our model for both the ability and rate of bull kelp forest recovery under different restoration strategies. We compare the efficacy of a partial restoration approach with a more comprehensive restoration effort by exploring how kelp recovery likelihood and rate change with varying intensities of urchin removal and kelp outplanting over different time periods and spatial scales. We find that, in the case of bull kelp forests, setting more favorable initial conditions for kelp recovery by implementing both urchin harvesting and kelp outplanting at the start of the restoration project has a bigger impact on the kelp recovery rate than applying restoration efforts through a longer period of time. Therefore, partial restoration efforts, in terms of spatial and temporal scale, can be significantly more effective when applied across multiple ecological scales in terms of both the capacity and rate for achieving the target outcomes. 

Many species are shifting their ranges to keep pace with climate change, but habitat fragmentation and limited dispersal could impede these range shifts. In the case of climate-vulnerable foundation species such as tropical reef corals and temperate forest trees, such limitations might put entire communities at risk of extinction. Restoring connectivity through corridors, stepping-stones or enhanced quality of existing patches could prevent the extinction of several species, but dispersal-limited species might not benefit if other species block their dispersal. Alternatively, managers might relocate vulnerable species between habitats through assisted migration, but this is generally a species-by-species approach. To evaluate the relative efficacy of these strategies, we simulated the climate-tracking of species in randomized competitive metacommunities with alternative management interventions. We found that corridors and assisted migration were the most effective strategies at reducing extinction. Assisted migration was especially effective at reducing the extinction likelihood for short-dispersing species, but it often required moving several species repeatedly. Assisted migration was more effective at reducing extinction in environments with higher stochasticity, and corridors were more effective at reducing extinction in environments with lower stochasticity. We discuss the application of these approaches to an array of systems ranging from tropical corals to temperate forests. This article is part of the theme issue ‘Ecological complexity and the biosphere: the next 30 years’. 

Anthropogenic environmental change is altering the behavior of animals in ecosystems around the world. Although behavior typically occurs on much faster timescales than demography, it can nevertheless influence demographic processes. Here, we use detailed data on behavior and empirical estimates of demography from a coral reef ecosystem to develop a coupled behavioral–demographic ecosystem model. Analysis of the model reveals that behavior and demography feed back on one another to determine how the ecosystem responds to anthropogenic forcing. In particular, an empirically observed feedback between the density and foraging behavior of herbivorous fish leads to alternative stable ecosystem states of coral population persistence or collapse (and complete algal dominance). This feedback makes the ecosystem more prone to coral collapse under fishing pressure but also more prone to recovery as fishing is reduced. Moreover, because of the behavioral feedback, the response of the ecosystem to changes in fishing pressure depends not only on the magnitude of changes in fishing but also on the pace at which changes are imposed. For example, quickly increasing fishing to a given level can collapse an ecosystem that would persist under more gradual change. Our results reveal conditions under which the pace and not just the magnitude of external forcing can dictate the response of ecosystems to environmental change. More generally, our multiscale behavioral–demographic framework demonstrates how high-resolution behavioral data can be incorporated into ecological models to better understand how ecosystems will respond to perturbations.