The mechanics of predator-prey interactions: first principles of physics predict predator-prey size ratios

Portalier, Sebastien M. J.; Fussmann, Gregor F.; Loreau, Michel; Cherif, Mehdi

doi:10.1101/313239

“…The field has also not yet reached an effective synthesis of metabolic and foraging theories. Our study joins the recent work of Portalier et al (2019) to provide the first major advances in that direction since the ADBM (Petchey et al 2008). Food webs represent the roles of species as both consumers and resources, and considering the joint constraints on foraging behaviour of these dual roles (Naisbit et al 2012) is a necessary step towards truly capturing the complexity of real ecosystems.…”

Section: Discussionmentioning

confidence: 75%

Predation risk influences food‐web structure by constraining species diet choice

Ho

¹

,

Tylianakis

²

,

Zheng

³

et al. 2019

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The foraging behaviour of species determines their diet and, therefore, also emergent food‐web structure. Optimal foraging theory (OFT) has previously been applied to understand the emergence of food‐web structure through a consumer‐centric consideration of diet choice. However, the resource‐centric viewpoint, where species adjust their behaviour to reduce the risk of predation, has not been considered. We develop a mechanistic model that merges metabolic theory with OFT to incorporate the effect of predation risk on diet choice to assemble food webs. This ‘predation‐risk‐compromise’ (PR) model better captures the nestedness and modularity of empirical food webs relative to the classical optimal foraging model. Specifically, compared with optimal foraging alone, risk‐mitigated foraging leads to more‐nested but less‐modular webs by broadening the diet of consumers at intermediate trophic levels. Thus, predation risk significantly affects food‐web structure by constraining species’ ability to forage optimally, and needs to be considered in future work.

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“…Our observation that predators are larger than their prey follows logically from the implemented optimal predator–herbivore body mass ratio as observed in nature. From a functional perspective, too high or too low predator–prey body mass ratios are not favourable as too small prey are difficult to trace and offer low energy profit, whereas too large prey may be difficult to control and capture (Brose, Jonsson, et al, ; Brose, ; Portalier et al, ). Larger (active) predators experience an additional benefit as they are able to follow their mobile prey in space more efficiently, hence to keep track with shifts in the prey spatial distribution.…”

Section: Discussionmentioning

confidence: 99%

“…Since increases in trophic position are associated with additional energetic and mechanical constraints, body size will be subject to ecological and/or evolutionary dynamics in food webs (Govaert et al, ). Too small prey are difficult to locate for predators and provide insufficient energy, whereas too large prey can be difficult to control and capture (Brose, Jonsson, et al, ; Portalier, Fussmann, Loreau & Cherif, ). This trade‐off results in a hump‐shaped function for predation rate, with a maximum at intermediate predator–prey ratios (Brose et al, ; Rall, Kalinkat, Ott, Vucic‐Pestic & Brose, ; Viveiros De Castro & Fernandez, ; Vucic‐Pestic, Rall, Kalinkat & Brose, ).…”

Section: Introductionmentioning

confidence: 99%

“…In case prey of all sizes are unlimitedly available, a realized predator–prey body mass ratio converges to this theoretical optimum (the preferred ratio; Tsai, Hsieh & Nakazawa, ). As a general principle, optimal sizes of predators are larger than those of their prey (Brose, Jonsson, et al, ; Portalier et al, ). This first principle corresponds to one of the earliest observations in ecology (Elton, ).…”

Section: Introductionmentioning

confidence: 99%

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Habitat loss and fragmentation increase realized predator–prey body size ratios

Hillaert

¹

,

Vandegehuchte

²

,

Hovestadt

³

et al. 2019

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In the absence of predators, habitat fragmentation favours large body sizes to facilitate gap crossing. The size of primary consumers is, however, also shaped by top‐down effects as predators select prey of a certain size. Therefore, higher trophic levels should be taken into consideration when studying the effect of habitat loss and fragmentation on size distributions of herbivores. We built a model to study the effect of habitat loss and fragmentation within a tri‐trophic food chain. Body size is directly linked to movement capacity and metabolic processes and considered as a master trait under selection. We show that basal resources accumulate locally if a predator causes top‐down control of the herbivore. Due to this increasing spatiotemporal variability in resource availability, larger herbivores are selected than in scenarios without predator as they are able to move further. As predators cause herbivores to be intrinsically much larger than the optimal sizes selected by habitat fragmentation in the absence of predators, habitat fragmentation is no longer a significant driver of herbivore size. However, there is selection for increased predator size with habitat fragmentation as herbivores become less abundant, hence favouring gap‐crossing ability of the predator. Since herbivore and predator body size respond differently to habitat loss and fragmentation, realized predator–herbivore body size ratios increase along this fragmentation gradient. Our model demonstrates how feedbacks between the abundance, body size and mobility of predators and prey ultimately determine body size distributions in food webs. These new insights shed light on the impact of habitat destruction and fragmentation on overall food web structure. A free Plain Language Summary can be found within the Supporting Information of this article.

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“…The model observation 399 that predators are larger than their prey follows logically from the implemented optimal predator-400 herbivore body mass ratio as observed in nature. Too high or too low predator-prey body mass ratios 401 are not favorable as too small prey are hard to trace and offer low energy profit, whereas too large 402 prey may be hard to control and capture Brose, 2010;Portalier et al, 2018). 403…”

Section: Pressure 397mentioning

confidence: 99%

Habitat loss and fragmentation increase realized predator-prey body size ratios

Hillaert

¹

,

Vandegehuchte

²

,

Hovestadt

³

et al. 2018

Preprint

View full text Add to dashboard Cite

In the absence of predators, habitat fragmentation favours large body sizes to facilitate gap crossing. The size of primary consumers is, however, also shaped by top‐down effects as predators select prey of a certain size. Therefore, higher trophic levels should be taken into consideration when studying the effect of habitat loss and fragmentation on size distributions of herbivores. We built a model to study the effect of habitat loss and fragmentation within a tri‐trophic food chain. Body size is directly linked to movement capacity and metabolic processes and considered as a master trait under selection. We show that basal resources accumulate locally if a predator causes top‐down control of the herbivore. Due to this increasing spatiotemporal variability in resource availability, larger herbivores are selected than in scenarios without predator as they are able to move further. As predators cause herbivores to be intrinsically much larger than the optimal sizes selected by habitat fragmentation in the absence of predators, habitat fragmentation is no longer a significant driver of herbivore size. However, there is selection for increased predator size with habitat fragmentation as herbivores become less abundant, hence favouring gap‐crossing ability of the predator. Since herbivore and predator body size respond differently to habitat loss and fragmentation, realized predator–herbivore body size ratios increase along this fragmentation gradient. Our model demonstrates how feedbacks between the abundance, body size and mobility of predators and prey ultimately determine body size distributions in food webs. These new insights shed light on the impact of habitat destruction and fragmentation on overall food web structure. A free Plain Language Summary can be found within the Supporting Information of this article.

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The mechanics of predator-prey interactions: first principles of physics predict predator-prey size ratios

Cited by 29 publications

References 48 publications

Predation risk influences food‐web structure by constraining species diet choice

Predation risk influences food‐web structure by constraining species diet choice

Habitat loss and fragmentation increase realized predator–prey body size ratios

Habitat loss and fragmentation increase realized predator-prey body size ratios

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