Alejandro Frid

Human-caused Disturbance Stimuli as a Form of Predation Risk

A growing number of studies quantify the impact of nonlethal human disturbance on the behavior and reproductive success of animals. Athough many are well designed and analytically sophisticated, most lack a theoretical framework for making predictions and for understanding why particular responses occur. Behavioral ecologists have recently begun to fill this theoretical vacuum by applying economic models of antipredator behavior to disturbance studies. In this emerging paradigm, predation and nonlethal disturbance stimuli create similar trade-offs between avoiding perceived risk and other fitness-enhancing activities, such as feeding, parental care, or mating. A vast literature supports the hypothesis that antipredator behavior has a cost to other activities, and that this trade-off is optimized when investment in antipredator behavior tracks short-term changes in predation risk. Prey have evolved antipredator responses to generalized threatening stimuli, such as loud noises and rapidly approaching objects. Thus, when encountering disturbance stimuli ranging from the dramatic, low- flying helicopter to the quiet wildlife photographer, animal responses are likely to follow the same economic principles used by prey encountering predators. Some authors have argued that, similar to predation risk, disturbance stimuli can indirectly affect fitness and population dynamics via the energetic and lost opportunity costs of risk avoidance. We elaborate on this argument by discussing why, from an evolutionary perspective, disturbance stimuli should be analogous to predation risk. We then consider disturbance effects on the behavior of individuals—vigilance, fleeing, habitat selection, mating displays, and parental investment—as well as indirect effects on populations and communities. A wider application of predation risk theory to disturbance studies should increase the generality of predictions and make mitigation more effective without over-regulating human activities.

Predicting ecological consequences of marine top predator declines

Recent studies document unprecedented declines in marine top predators that can initiate trophic cascades. Predicting the wider ecological consequences of these declines requires understanding how predators influence communities by inflicting mortality on prey and inducing behavioral modifications (risk effects). Both mechanisms are important in marine communities, and a sole focus on the effects of predator-inflicted mortality might severely underestimate the importance of predators. We outline direct and indirect consequences of marine predator declines and propose an integrated predictive framework that includes risk effects, which appear to be strongest for long-lived prey species and when resources are abundant. We conclude that marine predators should be managed for the maintenance of both density- and risk-driven ecological processes, and not demographic persistence alone.

Optimal diving under the risk of predation.

Many air-breathing aquatic foragers may be killed by aerial or subsurface predators while recovering oxygen at the surface; yet the influence of predation risk on time allocation during dive cycles is little known in spite of numerous studies on optimal diving. We modeled diving behavior under the risk of predation at the surface. The relationship between time spent at the surface and the risk of death is predicted to influence the optimal surface interval, regardless of whether foragers accumulate energy at a constant rate while at the food patch, deplete food resources over the course of the dive, or must search for food during the dive. When instantaneous predation risk during a single surface interval decreases with time spent at the surface, a diver should increase its surface interval relative to that which maximizes energy intake, thereby increasing dive durations and reducing the number of surfacings per foraging bout. When instantaneous risk over a single surface interval does not change or increases with increasing time at the surface, divers should decrease their surface interval (and consequently their dive duration) relative to that which maximizes energy intake resulting in more dives per foraging bout. The fitness consequences of selecting a suboptimal surface interval vary with the risk function and the way divers harvest energy when at depth. Finally, predation risk during surface intervals should have important consequences for habitat selection and other aspects of the behavioral ecology of air-breathing aquatic organisms.

Novel insights into green sea turtle behaviour using animal-borne video cameras

An animal-borne video camera and data-logger was used to collect behavioural data on green (Chelonia mydas) and loggerhead (Caretta caretta) turtles in Western Australia. This technique provided novel insights into the behaviour of green turtles including an apparent self-cleaning behaviour. Also, ctenophores and jelly¢sh might be more important in the diet of these turtles than previously thought.

Behavioral Indicators in Marine Conservation: Lessons from a Pristine Seagrass Ecosystem

In light of ongoing changes to marine ecosystems, there is a need for behavioral indicators that can identify critical habitats and assess anthropogenic impacts. Although the application of behavior to conservation has yielded mixed results, habitat selection behavior has promise as such an indicator. Terrestrial studies and a decade of work in Shark Bays pristine seagrass ecosystem show that habitat selection theory based on the ideal free distribution can be used to assess critical habitats based on food and safety and signal impacts of anthropogenic disturbance. One lesson from our studies of dugongs (Dugong dugon) and other species at risk from tiger sharks (Galeocerdo cuvier) is that physical attributes of habitats may influence the effects of predators, and, by extension, human disturbance. These species generally prefer seagrass bank edges, which facilitate escape from sharks, even though shark density is lower over interior portions of the banks. Thus, habitat selection indicates that a banks qu...

Predatory fishes affect trophic cascades and apparent competition in temperate reefs

We provide evidence for a trophic cascade involving apex predators and mesopredators of marine temperate reefs, lingcod and rockfish, respectively. We measured spatio-temporal variation in the relative abundance of lingcod, subadult rockfish and two shrimp groups eaten by rockfish (Pandalus sp. and three smaller-bodied genera aggregated). Lingcod had an indirect positive effect on shrimps, as mediated by the direct negative effects of lingcod on rockfish and of rockfish on shrimps. These top-down effects on shrimps, however, were stronger for Pandalus than for small-bodied shrimps. Further, abundances of Pandalus and small-bodied shrimps were negatively correlated and the latter had a stronger positive effect on rockfish, suggesting that rockfish mediated asymmetrical apparent competition between shrimps. Our results indicate mechanisms by which predatory fishes may influence the structure of marine communities.

Interspecific variation in life history relates to antipredator decisions by marine mesopredators on temperate reefs.

As upper-level predatory fishes become overfished, mesopredators rise to become the new ‘top’ predators of over-exploited marine communities. To gain insight into ensuing mechanisms that might alter indirect species interactions, we examined how behavioural responses to an upper-level predatory fish might differ between mesopredator species with different life histories. In rocky reefs of the northeast Pacific Ocean, adult lingcod (Ophiodon elongatus) are upper-level predators that use a sit-and-wait hunting mode. Reef mesopredators that are prey to adult lingcod include kelp greenling (Hexagrammos decagrammus), younger lingcod, copper rockfish (Sebastes caurinus) and quillback rockfish (S. maliger). Across these mesopredators species, longevity and age at maturity increases and, consequently, the annual proportion of lifetime reproductive output decreases in the order just listed. Therefore, we hypothesized that the level of risk taken to acquire resources would vary interspecifically in that same order. During field experiments we manipulated predation risk with a model adult lingcod and used fixed video cameras to quantify interactions between mesopredators and tethered prey (Pandalus shrimps). We predicted that the probabilities of inspecting and attacking tethered prey would rank from highest to lowest and the timing of these behaviours would rank from earliest to latest as follows: kelp greenling, lingcod, copper rockfish, and quillback rockfish. We also predicted that responses to the model lingcod, such as avoidance of interactions with tethered prey, would rank from weakest to strongest in the same order. Results were consistent with our predictions suggesting that, despite occupying similar trophic levels, longer-lived mesopredators with late maturity have stronger antipredator responses and therefore experience lower foraging rates in the presence of predators than mesopredators with faster life histories. The corollary is that the fishery removal of top predators, which relaxes predation risk, could potentially lead to stronger increases in foraging rates for mesopredators with slower life histories.

Conservation and Anti-Predator Behavior

Antipredator behavior and conservation are inextricably linked. Predators and human-caused disturbance stimuli cause animals to experience similar trade-offs between avoiding perceived risk and acquiring resources for growth and reproduction. Anthropogenic resource consumption and climate change may create resource shortages for mesoconsumers, limiting their scope for antipredator behavior and indirectly increasing predation rates. Notoriously, humans have been eliminating top predators, relaxing the need for mesoconsumers to invoke antipredator behavior and consequently, disrupting trophic cascades. These sorts of conservation challenges may be approached with predation risk theory, which can be used to predict how humans might influence predator–prey behavioral interactions and the ecological consequences of disrupting these relationships.