What drives interaction strengths in complex food webs? A test with feeding rates of a generalist stream predator

AbstractDescribing the mechanisms that drive variation in species interaction strengths is central to understanding, predicting, and managing community dynamics. Multiple factors have been linked to trophic interaction strength variation, including species densities, species traits, and abiotic factors. Yet most empirical tests of the relative roles of multiple mechanisms that drive variation have been limited to simplified experiments that may diverge from the dynamics of natural food webs. Here, we used a field-based observational approach to quantify the roles of prey density, predator density, predator-prey body-mass ratios, prey identity, and abiotic factors in driving variation in feeding rates of reticulate sculpin (Cottus perplexus). We combined data on over 6,000 predator-prey observations with prey identification time functions to estimate 289 prey-specific feeding rates at nine stream sites in Oregon. Feeding rates on 57 prey types showed an approximately log-normal distribution, with few strong and many weak interactions. Model selection indicated that prey density, followed by prey identity, were the two most important predictors of prey-specific sculpin feeding rates. Feeding rates showed a positive, accelerating relationship with prey density that was inconsistent with predator saturation predicted by current functional response models. Feeding rates also exhibited four orders-of-magnitude in variation across prey taxonomic orders, with the lowest feeding rates observed on prey with significant anti-predator defenses. Body-mass ratios were the third most important predictor variable, showing a hump-shaped relationship with the highest feeding rates at intermediate ratios. Sculpin density was negatively correlated with feeding rates, consistent with the presence of intraspecific predator interference. Our results highlight how multiple co-occurring drivers shape trophic interactions in nature and underscore ways in which simplified experiments or reliance on scaling laws alone may lead to biased inferences about the structure and dynamics of species-rich food webs.

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Food web interaction strength distributions are conserved by greater variation between than within predator-prey pairs

10.1101/461921 ◽

2018 ◽

Author(s):

Daniel L. Preston ◽

Landon P. Falke ◽

Jeremy S. Henderson ◽

Mark Novak

Keyword(s):

Food Webs ◽

Prey Density ◽

Interaction Strength ◽

Feeding Rates ◽

Predator Prey ◽

Space And Time ◽

Individual Interaction ◽

Species Pairs ◽

The Mean ◽

Strength Distributions

AbstractSpecies interactions in food webs are usually recognized as dynamic, varying across species, space and time due to biotic and abiotic drivers. Yet food webs also show emergent properties that appear consistent, such as a skewed frequency distribution of interaction strengths (many weak, few strong). Reconciling these two properties requires an understanding of the variation in pairwise interaction strengths and its underlying mechanisms. We estimated stream sculpin feeding rates in three seasons at nine sites in Oregon to examine variation in trophic interaction strengths both across and within predator-prey pairs. We considered predator and prey densities, prey body mass, and abiotic factors as putative drivers of within-pair variation over space and time. We hypothesized that consistently skewed interaction strength distributions could result if individual interaction strengths show relatively little variation, or alternatively, if interaction strengths vary but shift in ways that conserve their overall frequency distribution. We show that feeding rate distributions remained consistently and positively skewed across all sites and seasons. The mean coefficient of variation in feeding rates within each of 25 focal species pairs across surveys was less than half the mean coefficient of variation seen across species pairs within a given survey. The rank order of feeding rates also remained relatively conserved across streams, seasons and individual surveys. On average, feeding rates on each prey taxon nonetheless varied by a hundredfold across surveys, with some feeding rates showing more variation in space and others in time. For most species pairs, feeding rates increased with prey density and decreased with high stream flows and low water temperatures. For nearly half of all species pairs, factors other than prey density explained the most variation, indicating that the strength of density dependence in feeding rates can vary greatly among a generalist predator’s prey species. Our findings show that although individual interaction strengths exhibit considerable variation in space and time, they can nonetheless remain relatively consistent, and thus predictable, compared to the even larger variation that occurs across species pairs. These insights help reconcile how the skewed nature of interaction strength distributions can persist in highly dynamic food webs.

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Use of size-based production and stable isotope analyses to predict trophic transfer efficiencies and predator-prey body mass ratios in food webs

Marine Ecology Progress Series ◽

10.3354/meps240011 ◽

2002 ◽

Vol 240 ◽

pp. 11-20 ◽

Cited By ~ 143

Author(s):

S Jennings ◽

KJ Warr ◽

S Mackinson

Keyword(s):

Stable Isotope ◽

Food Webs ◽

Body Mass ◽

Trophic Transfer ◽

Stable Isotope Analyses ◽

Predator Prey ◽

Mass Ratios ◽

Isotope Analyses

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Moving beyond linear food chains: trait-mediated indirect interactions in a rocky intertidal food web

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2016.2590 ◽

2017 ◽

Vol 284 (1851) ◽

pp. 20162590 ◽

Cited By ~ 15

Author(s):

Geoffrey C. Trussell ◽

Catherine M. Matassa ◽

Patrick J. Ewanchuk

Keyword(s):

Food Web ◽

Food Webs ◽

Predation Risk ◽

Community Dynamics ◽

Indirect Interactions ◽

Positive Interactions ◽

Food Chains ◽

Feeding Rates ◽

Basal Resources ◽

Crab Predation

In simple, linear food chains, top predators can have positive indirect effects on basal resources by causing changes in the traits (e.g. behaviour, feeding rates) of intermediate consumers. Although less is known about trait-mediated indirect interactions (TMIIs) in more complex food webs, it has been suggested that such complexity dampens trophic cascades. We examined TMIIs between a predatory crab ( Carcinus maenas ) and two ecologically important basal resources, fucoid algae ( Ascophyllum nodosum ) and barnacles ( Semibalanus balanoides ), which are consumed by herbivorous ( Littorina littorea ) and carnivorous ( Nucella lapillus ) snails, respectively. Because crab predation risk suppresses snail feeding rates, we hypothesized that crabs would also shape direct and indirect interactions among the multiple consumers and resources. We found that the magnitude of TMIIs between the crab and each resource depended on the suite of intermediate consumers present in the food web. Carnivorous snails ( Nucella ) transmitted TMIIs between crabs and barnacles. However, crab–algae TMIIs were transmitted by both herbivorous ( Littorina ) and carnivorous ( Nucella ) snails, and these TMIIs were additive. By causing Nucella to consume fewer barnacles, crab predation risk allowed fucoids that had settled on or between barnacles to remain in the community. Hence, positive interactions between barnacles and algae caused crab–algae TMIIs to be strongest when both consumers were present. Studies of TMIIs in more realistic, reticulate food webs will be necessary for a more complete understanding of how predation risk shapes community dynamics.

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Season and prey type influence size dependency of predator−prey body mass ratios in a marine fish assemblage

Marine Ecology Progress Series ◽

10.3354/meps09913 ◽

2012 ◽

Vol 466 ◽

pp. 167-175 ◽

Cited By ~ 5

Author(s):

JCP Reum ◽

ME Hunsicker

Keyword(s):

Body Mass ◽

Marine Fish ◽

Fish Assemblage ◽

Prey Type ◽

Predator Prey ◽

Size Dependency ◽

Mass Ratios

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Predator-prey relationship between the cyclopoid copepod Diacyclops bicuspidatus and a free-living bacterivorous nematode

Nematology ◽

10.1163/156854108783360203 ◽

2008 ◽

Vol 10 (1) ◽

pp. 55-62 ◽

Cited By ~ 20

Author(s):

Daniel Muschiol ◽

Mirjana Marković ◽

Ilka Threis ◽

Walter Traunspurger

Keyword(s):

Functional Response ◽

Body Mass ◽

Cyclopoid Copepod ◽

Type Ii ◽

Feeding Rates ◽

Free Living ◽

Predator Prey ◽

Freshwater Copepods ◽

Size Preference ◽

Type Ii Functional Response

Abstract The potential of copepods as predators of free-living nematodes was tested by presenting Diacyclops bicuspidatus, a common holarctic cyclopoid copepod, with Panagrolaimus sp. as prey in the laboratory. Diacyclops bicuspidatus readily fed on nematodes of all size classes, including prey longer than itself. No size preference was observed. Handling times varied between a few seconds and several minutes, depending on the size of the prey. At different prey densities, the feeding rates of D. bicuspidatus followed a type II functional response. Starved D. bicuspidatus consumed up to 45.1 nematodes in 2 h, equivalent to 43.5% of the copepod's body mass. Indications that nematophagous nutrition is common among freshwater copepods are discussed.

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How patch size and refuge availability change interaction strength and population dynamics: a combined individual- and population-based modeling experiment

PeerJ ◽

10.7717/peerj.2993 ◽

2017 ◽

Vol 5 ◽

pp. e2993 ◽

Cited By ~ 9

Author(s):

Yuanheng Li ◽

Ulrich Brose ◽

Katrin Meyer ◽

Björn C. Rall

Keyword(s):

Population Dynamics ◽

Habitat Complexity ◽

Patch Size ◽

Feeding Rate ◽

Interaction Strength ◽

Time Frame ◽

Feeding Rates ◽

Functional Responses ◽

Predator Prey ◽

Predator Prey Model

Knowledge on how functional responses (a measurement of feeding interaction strength) are affected by patch size and habitat complexity (represented by refuge availability) is crucial for understanding food-web stability and subsequently biodiversity. Due to their laborious character, it is almost impossible to carry out systematic empirical experiments on functional responses across wide gradients of patch sizes and refuge availabilities. Here we overcame this issue by using an individual-based model (IBM) to simulate feeding experiments. The model is based on empirically measured traits such as body-mass dependent speed and capture success. We simulated these experiments in patches ranging from sizes of petri dishes to natural patches in the field. Moreover, we varied the refuge availability within the patch independently of patch size, allowing for independent analyses of both variables. The maximum feeding rate (the maximum number of prey a predator can consume in a given time frame) is independent of patch size and refuge availability, as it is the physiological upper limit of feeding rates. Moreover, the results of these simulations revealed that a type III functional response, which is known to have a stabilizing effect on population dynamics, fitted the data best. The half saturation density (the prey density where a predator consumes half of its maximum feeding rate) increased with refuge availability but was only marginally influenced by patch size. Subsequently, we investigated how patch size and refuge availability influenced stability and coexistence of predator-prey systems. Following common practice, we used an allometric scaled Rosenzweig–MacArthur predator-prey model based on results from ourin silicoIBM experiments. The results suggested that densities of both populations are nearly constant across the range of patch sizes simulated, resulting from the constant interaction strength across the patch sizes. However, constant densities with decreasing patch sizes mean a decrease of absolute number of individuals, consequently leading to extinction of predators in the smallest patches. Moreover, increasing refuge availabilities also allowed predator and prey to coexist by decreased interaction strengths. Our results underline the need for protecting large patches with high habitat complexity to sustain biodiversity.

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How patch size and refuge availability change interaction strength and population dynamics: a combined individual- and population-based modeling experiment

10.7287/peerj.preprints.2190 ◽

2016 ◽

Author(s):

Yuanheng Li ◽

Ulrich Brose ◽

Katrin Meyer ◽

Björn C Rall

Keyword(s):

Population Dynamics ◽

Habitat Complexity ◽

Patch Size ◽

Feeding Rate ◽

Interaction Strength ◽

Time Frame ◽

Feeding Rates ◽

Functional Responses ◽

Predator Prey ◽

Predator Prey Model

Knowledge on how functional responses (a measurement of feeding interaction strength) are affected by patch size and habitat complexity (represented by refuge availability) is crucial for understanding food-web stability and subsequently biodiversity. Due to their laborious character, it is almost impossible to carry out systematic empirical experiments on functional responses across wide gradients of patch sizes and refuge availabilities. Here we overcame this issue by using an individual-based model (IBM) to simulate feeding experiments. The model is based on empirically measured traits such as body size dependent speed and capture success. We simulated these experiments in patches ranging from size of petri dishes to natural patches in the field. Moreover, we varied the refuge availability within the patch independently of patch size, allowing for an independent analyses of both variables. The maximum feeding rate (the maximum number of prey a predator can consume in a given time frame) is independent of patch size and refuge availability, as it is the physiological upper limit of feeding rates. Moreover, the results of these simulations revealed that a type III functional response, which is known to have a stabilizing effect on population dynamics, fits the data best. The half saturation density (the prey density where a predator consumes half of its maximum feeding rate) increased with refuge availability but was only marginally influenced by patch size. Subsequently, we investigated how patch size and refuge availability influence stability and coexistence of predator-prey systems. Following common practice, we used an allometric scaled Rosenzweig-MacArthur predator-prey model based on results from our in silico IBM experiments. The results suggested that densities of both populations are nearly constant across the range of patch sizes simulated, resulting from the constant interaction strength across the patch sizes. However, constant densities with decreasing patch sizes mean a decrease of absolute number of individuals, consequently leading to extinction of predators in smallest patches. Moreover, increasing refuge availabilities also allowed predator and prey to coexist by decreased interaction strengths. Our results underline the need for protecting large patches with high habitat complexity to sustain biodiversity.

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How patch size and refuge availability change interaction strength and population dynamics: a combined individual- and population-based modeling experiment

10.7287/peerj.preprints.2190v2 ◽

2016 ◽

Author(s):

Yuanheng Li ◽

Ulrich Brose ◽

Katrin Meyer ◽

Björn C Rall

Keyword(s):

Population Dynamics ◽

Habitat Complexity ◽

Patch Size ◽

Feeding Rate ◽

Interaction Strength ◽

Time Frame ◽

Feeding Rates ◽

Functional Responses ◽

Predator Prey ◽

Predator Prey Model

Knowledge on how functional responses (a measurement of feeding interaction strength) are affected by patch size and habitat complexity (represented by refuge availability) is crucial for understanding food-web stability and subsequently biodiversity. Due to their laborious character, it is almost impossible to carry out systematic empirical experiments on functional responses across wide gradients of patch sizes and refuge availabilities. Here we overcame this issue by using an individual-based model (IBM) to simulate feeding experiments. The model is based on empirically measured traits such as body size dependent speed and capture success. We simulated these experiments in patches ranging from size of petri dishes to natural patches in the field. Moreover, we varied the refuge availability within the patch independently of patch size, allowing for an independent analyses of both variables. The maximum feeding rate (the maximum number of prey a predator can consume in a given time frame) is independent of patch size and refuge availability, as it is the physiological upper limit of feeding rates. Moreover, the results of these simulations revealed that a type III functional response, which is known to have a stabilizing effect on population dynamics, fits the data best. The half saturation density (the prey density where a predator consumes half of its maximum feeding rate) increased with refuge availability but was only marginally influenced by patch size. Subsequently, we investigated how patch size and refuge availability influence stability and coexistence of predator-prey systems. Following common practice, we used an allometric scaled Rosenzweig-MacArthur predator-prey model based on results from our in silico IBM experiments. The results suggested that densities of both populations are nearly constant across the range of patch sizes simulated, resulting from the constant interaction strength across the patch sizes. However, constant densities with decreasing patch sizes mean a decrease of absolute number of individuals, consequently leading to extinction of predators in smallest patches. Moreover, increasing refuge availabilities also allowed predator and prey to coexist by decreased interaction strengths. Our results underline the need for protecting large patches with high habitat complexity to sustain biodiversity.

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Predator–prey interactions mediated by prey personality and predator hunting mode

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2016.0408 ◽

2016 ◽

Vol 283 (1828) ◽

pp. 20160408 ◽

Cited By ~ 54

Author(s):

Benjamin A. Belgrad ◽

Blaine D. Griffen

Keyword(s):

Predator Avoidance ◽

Community Dynamics ◽

Interaction Strength ◽

Avoidance Behaviour ◽

Blue Crabs ◽

Predator Species ◽

Predator Prey ◽

Hunting Mode ◽

Predator Hunting Mode ◽

Mud Crabs

Predator–prey interactions are important drivers in structuring ecological communities. However, despite widespread acknowledgement that individual behaviours and predator species regulate ecological processes, studies have yet to incorporate individual behavioural variations in a multipredator system. We quantified a prevalent predator avoidance behaviour to examine the simultaneous roles of prey personality and predator hunting mode in governing predator–prey interactions. Mud crabs, Panopeus herbstii , reduce their activity levels and increase their refuge use in the presence of predator cues. We measured mud crab mortality and consistent individual variations in the strength of this predator avoidance behaviour in the presence of predatory blue crabs, Callinectes sapidus , and toadfish, Opsanus tau . We found that prey personality and predator species significantly interacted to affect mortality with blue crabs primarily consuming bold mud crabs and toadfish preferentially selecting shy crabs. Additionally, the strength of the predator avoidance behaviour depended upon the predation risk from the predator species. Consequently, the personality composition of populations and predator hunting mode may be valuable predictors of both direct and indirect predator–prey interaction strength. These findings support theories postulating mechanisms for maintaining intraspecies diversity and have broad implications for community dynamics.

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