The landscape of fear: the missing link to understand top‐down and bottom‐up controls of prey abundance?

Abstract

Identifying factors that may be responsible for regulating the size of animal populations is a cornerstone in understanding population ecology. The main factors that are thought to influence population size are either resources (bottom-up), or predation (top-down), or interspecific competition (parallel). However, there are highly variable and often contradictory results regarding their relative strengths and influence. These varied results are often interpreted as indicating "shifting control" among the three main factors, or a complex, nonlinear relationship among environmental variables, resource availability, predation, and competition. We argue here that there is a "missing link" in our understanding of predator-prey dynamics. We explore whether the landscape-of-fear model can help us clarify the inconsistencies and increase our understanding of the roles, extent, and possible interactions of top-down, bottom-up, and parallel factors on prey population abundance. We propose two main predictions derived from the landscape-of-fear model: (1) for a single species, we suggest that as the makeup of the landscape of fear changes from relatively safe to relatively risky, bottom-up impacts switch from strong to weak as top-down impacts go from weak to strong; (2) for two or more species, interspecific competitive interactions produce various combinations of bottom-up, top-down, and parallel impacts depending on the dominant competing species and whether the landscapes of fear are shared or distinctive among competing species. We contend that these predictions could successfully explain many of the complex and contradictory results of current research. We test some of these predictions based on long-term data for small mammals from the Chihuahuan Desert in the United States, and Mexico. We conclude that the landscape-of-fear model does provide reasonable explanations for many of the reported studies and should be tested further to better understand the effects of bottom-up, top-down, and parallel factors on population dynamics.

Diet quality in a wild grazer declines under the threat of an ambush predator

“…Further, the population consequences of the lower diet quality under the risk of predation will depend on whether the population is more limited by bottom-up or top-down factors and on how these effects interact. Across the landscape, the relative amounts of safe versus risky habitat seem to strongly affect which process dominates, with bottom-up forces more important in a landscape that is predominately safe and top-down forces more important when risky habitat predominates [38,39]. The Hwange zebra population is likely to be limited by predation (unpublished data), and hence individuals might make a trade-off between diet quality and the risk of predation with lower fitness costs.…”

Evaluating the landscape of fear between apex predatory sharks and mobile sea turtles across a large dynamic seascape

“…In summary, the landscape of fear model has recently been proposed as a possible unifying theme in ecology, also providing a ''missing link'' in understanding the population dynamics of species from a wide variety of taxa and ecosystems (Laundre´et al 2014). The present study is among the first to empirically evaluate the landscape of fear model across large (tens to hundreds of thousands of square kilometers) and dynamic seascapes involving highly mobile predators and prey.…”

“…The model has been expanded to explain the drivers of animal population dynamics (Laundre´et al 2014). Central to the model is that prey must forage and survive in both their home range and that of their predators; thus, an animal's knowledge of safe and risky areas within its home range is paramount for survival (Laundre´et al 2010).…”

Mesopredator suppression by an apex predator alleviates the risk of predation perceived by small prey

“…First, because predation risk is expected to reduce the amount of time individuals allocate to foraging, we predicted that the GUD of N. fuscus will be lower in areas where dingoes are common because the risk of predation is lower owing to dingoes' suppressive effects on mesopredator populations and activity. Second, because risk of predation can reduce foraging animals' use of 'risky' habitats [24], we predicted that the breadth of habitat used by N. fuscus should be greater in areas where dingoes are common because the risk of predation is lower [25,26]. In addition to the above hypotheses, because conspecific density dependence can potentially increase animals' allocation of time to foraging and increase the range of habitats exploited owing to intra-specific competition and/or 'safety in numbers' effects [27,28], we also predicted that the GUD of N. fuscus should be lower and the breadth of habitat use greater in areas with higher N. fuscus population densities.…”