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.
Degradation of coral reef habitats changes the abundance and community composition of fishes due in part to changes in the ecology of fear. The ecology of fear sees the predator-prey system as a dynamic game of behavioral responses to perceived risk with population and community level consequences. We measure spatial variation in predation risk as landscapes of fear. We consider changes in predation risk with habitat quality and examine the effects of fear on coral reefs in Kāne‘ohe Bay, O‘ahu, Hawai‘i. First, we associate fish and benthic communities on patch reefs with varying degradation due to invasive algae (Euchema spp. and Kappaphycus spp.). Next, we quantify the spatio-temporal variation of risk (reefscape of fear) of a common Hawaiian fish (saddle wrasse, hīnālea lau wili, Thalassoma duperrey) across reefs of varying degradation. Finally, we assess the tradeoffs in resource availability and predation risk on these reefs. At the scale of whole reefs, saddle wrasse responded to perceived risk. Intensity of patch use (measured by giving-up densities) by wrasse indicated risky reefs. Such reefs differed in benthic and fish community composition. We demonstrated the impact of an altered reefscape of fear due to habitat degradation. Habitat degradation seems to influence the tradeoff between resource availability and safety. From wrasse abundances and their patch use behavior we can classify the reefs into categories based on risk and resource availability. Allowing fish to reveal their perceptions of habitat qualities through their behaviors provides critical information for assessing and monitoring reefs.
Cooperation, defined as the act of an individual which benefits a recipient, is widely observed to occur within many species. There are strong implications of the addition of cooperation on population dynamics as cooperation allows for actor choice with individuals choosing group associations based usually on differences in fitness. There are at least two types of cooperative acts: facultative and obligate. Facultative cooperation such as starling murmurations, fish schools, and locust swarms grant the actors full choice over their associations since the consequences of non-cooperation are not severe. Obligate cooperation like that of social canids, cetaceans, primates, and eusocial insects only grant partial actor choice with the . CC-BY-NC-ND 4.0 International license peer-reviewed) is the author/funder. It is made available under aThe copyright holder for this preprint (which was not . http://dx.doi.org/10.1101/208934 doi: bioRxiv preprint first posted online Oct. 26, 2017; consequences of non-cooperation being more severe. The population dynamics of facultative cooperative species are well-modeled, but not so for obligate co-operators. This is because models assume no actor choice where individuals are permanently fixed to their group. Doing so implicitly engenders stability into the system leading to false conclusions regarding the nature of the species' population dynamics. In this paper, we created a model to analyze the population dynamics of obligate cooperators; it works by embedding a behavioral game of association with partial actor choice into a fitness dynamic. This model reveals three states based on strength of competition. In the first state under extremely strong competition, all groups will go extinct.Under the second state of moderately strong competition, the groups will exist at an unstable equilibrium. In the third state of weaker competition, the groups will show localized extirpations and constant turnover. As well, we generalize our results to show that obligate cooperative species can never achieve full stability due to the mismatch between the game's equilibrium and the fitness equilibrium. Our results, general enough to apply to most systems, show that the constant extirpation dynamics seen in obligately cooperative species are not necessarily a function of external stochastic events but instead inherent to their dynamics. The extirpation and group turnover seen among obligately cooperative societies are inherent to their population dynamics. While other factors may exacerbate the instability, they can only be secondary explanations. Because the instability arises out of a non-chaotic discrete process, it means that the dynamics are predictable and can be tested against experiments and simulations. Furthermore, our results lead to strong implications of for the conservation of obligately cooperative species. Firstly, it shows the importance of intergroup dynamics and the creation and destruction of new groups. Secondly, to conserve such species requires large areas with mu...
Cooperative acts is widely observed in nature. Because cooperation allows individuals to choose their associations based on differences in fitness opportunities, such behaviors directly influence population dynamics. Cooperative acts can be classified into two types: facultative and obligate. Facultative cooperation seen in starling murmurations, fish schools, and locust swarms grant the actors full choice over their associations since the consequences of non-cooperation are not severe. Obligate cooperation like that of canids, cetaceans, primates, and eusocial insects only grant partial actor choice as the consequences of non-cooperation are more severe. The population dynamics of facultative cooperative species are well-modeled, but not so for obligate co-operators. In this paper, we model and analyze the population dynamics of obligate cooperators by embedding a game theoretic behavioral dynamic into a within group population dynamic with additional between group dynamics. Our model confirms previous results showing within group cooperation leading to unstable population dynamics and go further by showing that more groups lead to greater population instability. Our behavioral analysis also shows that stable population equilibria will lead to behavioral instabilities. From there, we generalize our results to show that obligate cooperative species can never achieve full stability due to the fundamental mismatch between the stability of the behavioral equilibrium (ESS) and the stability of the population size equilibrium. Our results, general enough to apply to most systems, show that the constant group turnover seen in obligately cooperative species are not necessarily a function of external stochastic events but instead inherent to their dynamics..
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