The ecology of fear and inverted biomass pyramids

Abstract

In inverted biomass pyramids (IBPs) prey are outnumbered by their predators when measured by biomass. We investigate how prey should behave in the face of danger from higher predator biomass, and how anti‐predator behavior (in the form of vigilance) can, in turn, affect the predator–prey system. In this study, we incorporate anti‐predator behaviors into a Lotka–Volterra predator–prey model in the form of fixed and facultative vigilance. Facultative vigilance models behavior as a dynamic foraging game, allowing us to assess optimal behavioral responses in the context of IBPs using a dynamical fitness optimization approach. We model vigilance as a tradeoff between safety and either the prey's maximum growth rate or its carrying capacity. We assess the population dynamics of predators and prey with fear responses, and investigate the role fear plays on trophic structure. We found that the ecology of fear plays an important role in predator–prey systems, impacting trophic structure and the occurrence of IBPs. Fixed vigilance works against IBP structure by always reducing the predator–prey biomass ratio at equilibrium with increasing levels of vigilance. Facultative vigilance can actually promote IBPs, as prey can now adjust their vigilance levels to cope with increased predation and the costs associated with vigilance. This is especially true when the effectiveness of vigilance is low and predators are very lethal. In general, these trends are true whether the costs of vigilance are felt on the prey's maximum growth rate or its carrying capacity. Just as the ecology of fear, when first introduced, was used to explain why top carnivores are rare in terrestrial systems, it can also be used to understand how big fierce predators can be common in IBPs.

Reefscapes of fear assess tradeoffs of risk and reward on coral reefs

“…It also means that risk may vary in a 3dimensions (Harvey and White 2017; Lester et al 2020). Finally, prey on pristine coral reefs must cope with high biomass of erce predators, which is not typical of terrestrial predator-prey systems (Malone et al 2020).…”

Using functional groups to predict the spatial distribution of large herbivores on the Palaeo‐Agulhas Plain, South Africa, during the Last Glacial Maximum

“…The distribution of resources and predators (top‐down and bottom‐up drivers) are key factors influencing how herbivores distribute themselves in the landscape (Anderson et al ., 2010; Jarman, 1974) through a ‘landscape of fear’ (Laundré et al ., 2010). Herbivores need to balance their acquisition of resources against predation risk and energy expenditure (Fortin et al ., 2004; Venter et al ., 2019) and the landscape of fear gauges how species infer risk from environmental features and predation (Malone et al ., 2020). On the PAP, forage and associated vegetation type, distribution of water, vegetation cover and density (Smit, 2011), pressure from humans (Marean et al ., 2014) and animal physical and behavioural characteristics (Searle et al ., 2010) all would have played a role in influencing the distribution of herbivores.…”

Non-consumptive effects stabilize herbivore control over multiple generations

“…Increasing the temporal scale of non-consumptive studies to accommodate reproduction provides insight into how non-consumptive effects may influence population cycles [7][8][9]. Studies of sufficient duration to include prey reproduction reveal carryover of non-consumptive effects on subsequent generations of prey [10][11][12].…”

“…The common expectation based on consumption is that a decline in prey abundance will lead to an increase in predator abundance as predators eat prey and convert prey biomass into predator biomass through reproduction [16][17][18][19]. However, non-consumptive suppression of prey, which decouples prey suppression from predator reproduction, can provide alternative explanations for common predator-prey patterns documented in nature [7][8][9].…”