Functional Responses: A Question of Alternative Prey and Predator Density

Tschanz, B.; Bersier, Louis‐Félix; Bacher, Sven

doi:10.1890/06-1512

Cited by 40 publications

(32 citation statements)

References 37 publications

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“…Therefore as long as there is a most preferred prey present, then less preferred prey may show little direct predation (e.g. Tschanz et al 2007) and more importantly may also show relatively little decrease in fitness because of their non-lethal compensation.…”

Section: When Less Preferred Prey Have Lower Costs To Reduce Vulnerabmentioning

confidence: 99%

Predation in bird populations

Cresswell

2010

J Ornithol

237

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One of the classic ecological questions is how predators affect population size. This is often assessed by measuring how many individuals are killed by a predator, yet such direct effects may only be a relatively minor part of population dynamics. Predators frequently affect prey populations indirectly, with the fear of predation resulting in costly behavioural compensation leading to potentially large population and community effects. Large observable lethal effects may then just represent the most easily observed "special" cases of the effects of predation on populations, with the costs of non-lethal effects being ubiquitous and usually dominant. This review explores these two ideas: that cases where there are no population effects due to predation, and cases where lethal effects dominate, are unusual and involve special circumstances. First, systems where predation effects appear not to arise include complete avoidance of predators by prey; when other environmental factors limit populations so that predation is not additive to mortality; when there are other more vulnerable prey for a predator; when predators interact; because the relationship of perceived predation risk with predator abundance is usually a non-linear function, and simply because non-lethal effects have not been considered. Second, lethal effects tend to dominate over non-lethal effects when there is a high cost of compensating for predation risk associated with either resource constraint or a particularly vulnerable niche or life history stage (e.g. the nest stage generally for birds); when prey are the most popular prey of a predator or linear trophic chains operate; when there is evolutionary lag such as introduced predators and naïve prey populations; and when there are several predator species hunting the same prey in diverse ways. The presence of predators may or may not affect the size of a bird population at any particular life history stage, although in most cases it will through non-lethal effects and occasionally through lethal effects.But the presence of predators will always affect intra-and interspecific competition and so will always affect population dynamics. Studies that wish to fully demonstrate that predation has no effect on bird populations must show that lethal effects and the costs of non-lethal compensation by the prey do not significantly change its density and so the level of competition.3

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Section: When Less Preferred Prey Have Lower Costs To Reduce Vulnerabmentioning

confidence: 99%

Predation in bird populations

Cresswell

2010

J Ornithol

237

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“…While many studies have examined either the predator functional, numerical, or aggregative response in a system (e.g. Colton 1987, Settle et al 1996, Rott et al 1998, Murakami & Nakano 2002, few studies have integrated these responses because of the differences in temporal and spatial scales (Tschanz et al 2007). The functional response operates on a small spatial and temporal scale as it addresses predator feeding in a local prey patch over a short time period.…”

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confidence: 99%

Density-dependent indirect effects: apparent mutualism and apparent competition coexist in a two-prey system

Long¹,

Gamelin²,

Johnson³

et al. 2012

Mar. Ecol. Prog. Ser.

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A predator consuming multiple prey species usually causes indirect effects. Apparent mutualism results when multiple prey species reduce predation risk for each other by altering a predator's functional response. Short-term apparent competition occurs when multiple prey species increase predation risks for each other through the numerical response, i.e. increasing the predator's birth rate, or aggregative response, i.e. attracting a higher density of predators. Our objectives in this study were to determine the aggregative response and 2-prey functional response of a predator and to examine indirect effects over a range of prey densities. We used the clam Macoma balthica and juvenile blue crabs Callinectes sapidus as prey for adult blue crabs. In laboratory experiments, we determined the single-prey functional responses of the crabs to each prey species and the 2-prey functional response. We combined the 2-prey functional response with the known blue crab aggregative response to clams to estimate field predation rates. Our model predicts that at low prey densities, clams and juvenile blue crabs exhibit apparent mutualism, whereas at high clam densities, this relation switches to short-term apparent competition. These unexpected results highlight the need to incorporate multiple aspects of predation at multiple scales when considering indirect effects.KEY WORDS: Predator-prey interactions · Functional response · Indirect effects · Blue crab · Macoma balthicaResale or republication not permitted without written consent of the publisher Mar Ecol Prog Ser 456: 139-148, 2012 increases the predator density (i.e. changes either the predator's numerical or aggregative response), thus increasing predation on the other species (Holt & Lawton 1994). This occurs either through increasing the predator population growth rate (Settle et al. 1996, Carvalheiro et al. 2008 or through a local increase in predator density due to predator movement (Holt & Kotler 1987, Brown & Mitchell 1989, Murakami & Nakano 2002. Study organismsThe blue crab Callinectes sapidus Rathbun, 1896, is an important benthic predator in Chesapeake Bay (Virnstein 1977). Large adult crabs are opportunistic omnivores, feeding primarily on bivalves (~50% of diet) and crustaceans (~30%) as well as fish and polychaetes (Hines et al. 1990). Blue crabs are cannibalistic, with adults feeding on juveniles (Hines & Ruiz 1995). Because cannibalism represents a major source of mortality for juvenile blue crabs, juveniles congregate in shallow waters (<1 m), where adults are less abundant (Hines & Ruiz 1995, and in structured habitats that provide a predation refuge (Everett & Ruiz 1993).Macoma balthica Linnaeus, 1758, is a small (shell length < 40 mm) tellinid clam that is the dominant biomass in unvegetated mud habitats within the mesohaline regions of Chesapeake Bay (Holland et al. 1977) and is a major source of food for blue crabs (Baird & Ulanowicz 1989). M. balthica avoids predation by burying deeply, up to 35 cm, in the sediment (Hines & Comtois 1985)...

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“…As noted by Schenk and Bacher (2002), the acceleration of the predation rate at low prey densities could be due to the fact that P. dominulus is a generalist predator. Tschanz et al (2007) showed that prey switching between C. rubinigosa and larvae of flour beetles Tenebrio molitor, offered in an experiment as an alternative prey of P. dominulus, could not explain the type-III functional response, but they proposed alternative mechanisms, such as learning or the presence of still another prey than C. rubiginosa and T. molitor.…”

Section: Discussionmentioning

confidence: 99%

“…Although the predator abundance was treated as a constant number across various prey densities, the authors monitored the variations of wasp activity during the day from the video recordings of predation events. We use the latter data and similar observations obtained in later years (Tschanz et al 2007) to fit a gamma distribution in order to establish a predator activity profile during the day (Fig. 1).…”

Section: Experimental Datamentioning

confidence: 99%

Ratio‐dependent predation in a field experiment with wasps

et al. 2012

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Abstract. The functional response is a key component of trophic interactions since it quantifies the per capita rate of prey consumption. Determining whether this rate depends on the prey density only (which is the standard assumption), on both prey and predator densities, or simply on their ratio is essential to understand interacting populations. Several experiments have convincingly demonstrated ratio dependence but, with very few exceptions, they were conducted in laboratory conditions. The difficulty of collecting the required data (initial prey density, prey consumption, predator density) probably explains the lack of evidence from functional responses observed in natural systems. A field experiment was previously conducted with a paper wasp and its prey, shield beetle larvae. Both densities were manipulated and the prey consumption was measured. A first analysis led to the conclusion that the functional response of the wasps depended on both prey and predator densities but could not be considered being ratio dependent.Here, we perform an improved analysis of these data, making better justified assumptions and using more appropriate statistical methods. We fit several functional response models to the data and select the best one with information-theoretic criteria. We also estimate the model parameters and their confidence intervals. This more reliable analysis significantly modifies the original conclusion. Both model selection and parameter estimation indicate that ratio dependence governs the functional response of paper wasps preying on shield beetles in the field. Therefore, ratio dependence is not a laboratory artefact and should be more systematically considered as a potential model for describing functional responses.

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Functional Responses: A Question of Alternative Prey and Predator Density

Cited by 40 publications

References 37 publications

Predation in bird populations

Predation in bird populations

Density-dependent indirect effects: apparent mutualism and apparent competition coexist in a two-prey system

Ratio‐dependent predation in a field experiment with wasps

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