scholarly journals Food‐web interaction strength distributions are conserved by greater variation between than within predator–prey pairs

Ecology ◽  
2019 ◽  
Vol 100 (10) ◽  
Author(s):  
Daniel L. Preston ◽  
Landon P. Falke ◽  
Jeremy S. Henderson ◽  
Mark Novak
Keyword(s):  
Food Web ◽  
Interaction Strength ◽  
Predator Prey ◽  
Strength Distributions

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

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.

Macroecological patterns and niche structure in a new marine food web

2008 ◽  
Vol 3 (1) ◽  
pp. 91-103 ◽  
Author(s):  
Gabriel Yvon-Durocher ◽  
Jose Montoya ◽  
Mark Emmerson ◽  
Guy Woodward
Keyword(s):  
Food Web ◽  
Body Mass ◽  
Weak Interactions ◽  
Interaction Strength ◽  
Niche Overlap ◽  
Irish Sea ◽  
Strong Interactions ◽  
Predator Prey ◽  
Marine Food Web ◽  
Lough Hyne

AbstractThe integration of detailed information on feeding interactions with measures of abundance and body mass of individuals provides a powerful platform for understanding ecosystem organisation. Metabolism and, by proxy, body mass constrain the flux, turnover and storage of energy and biomass in food webs. Here, we present the first food web data for Lough Hyne, a species rich Irish Sea Lough. Through the application of individual-and size-based analysis of the abundance-body mass relationship, we tested predictions derived from the metabolic theory of ecology. We found that individual body mass constrained the flux of biomass and determined its distribution within the food web. Body mass was also an important determinant of diet width and niche overlap, and predator diets were nested hierarchically, such that diet width increased with body mass. We applied a novel measure of predator-prey biomass flux which revealed that most interactions in Lough Hyne were weak, whereas only a few were strong. Further, the patterning of interaction strength between prey sharing a common predator revealed that strong interactions were nearly always coupled with weak interactions. Our findings illustrate that important insights into the organisation, structure and stability of ecosystems can be achieved through the theoretical exploration of detailed empirical data.

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

2018 ◽  
Author(s):  
Daniel L. Preston ◽  
Jeremy S. Henderson ◽  
Landon P. Falke ◽  
Leah M. Segui ◽  
Tamara J. Layden ◽  
...  
Keyword(s):  
Food Webs ◽  
Body Mass ◽  
Prey Density ◽  
Scaling Laws ◽  
Community Dynamics ◽  
Abiotic Factors ◽  
Interaction Strength ◽  
Feeding Rates ◽  
Predator Prey ◽  
Mass Ratios

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.

Community Ecology of Stream Fishes: Concepts, Approaches, and Techniques

2010 ◽  
Keyword(s):  
Life History ◽  
Food Web ◽  
Interaction Strength ◽  
Ecosystem Dynamics ◽  
Stream Fishes ◽  
Migratory Fish ◽  
Migratory Species ◽  
Different Types ◽  
Migratory Stream ◽  
Migratory Fishes

<em>Abstract</em>.—Migratory fishes are common in freshwaters throughout the world and can fundamentally alter recipient ecosystems. We describe different types of fish migrations and consider their importance from the perspective of ecosystem subsidies—that is, landscape-scale flows of energy, materials, and organisms that are important in driving local food web and ecosystem dynamics. We distinguish between two general categories of subsidies, which we term here material subsidies and process subsidies. Material subsidies are the transfer of energy, nutrients, and other resources resulting in direct changes in resource pools within ecosystems. We posit that material subsidies occur under only a subset of life history strategies and ecological settings, and the potential for migratory fish to represent major material subsidies is greatest when (1) the biomass of migrants is high relative to recipient ecosystem size, (2) the availability of nutrients and energy is low in the recipient ecosystem (i.e., oligotrophic), and (3) there are effective mechanisms for both liberating nutrients and energy from migratory fishes and retaining those materials within the food web of the recipient ecosystem. Thus, anadromous semelparous Pacific salmon <em>Oncorhynchus </em>spp. with en masse programmed senescence in oligotrophic Pacific Northwest streams can be large material subsidies. In contrast, process subsidies arise from feeding or other activities of migratory species that directly affect process rates within recipient ecosystems. For example, the physical and chemical effects of grazing and sediment-feeding fishes such as prochilodontids, as well as seed dispersal by large-bodied frugivorous characins, represent potentially key process subsidies by migratory fishes in some of the great rivers of South America. We speculate that process subsidies are more widespread than material subsidies from migratory stream fishes because they are independent of the type of migration patterns, life history, and distance traveled. Nevertheless, the magnitude of process subsidies is likely to be greatest under a specific subset of ecological conditions, which can differ from those where material subsidies might be most important. In addition to migrant biomass, the potential for migratory fish to represent strong process subsidies is regulated by migrant interaction strength and the degree to which a migratory species is functionally unique in a particular ecological setting. Unlike material subsidies, which require high migrant biomass as conveyor belts of materials, migratory fishes can be crucial process subsidies, even when migrant biomass is low, if they are functionally unique and strong interactors. We provide specific examples of these different types of subsidies and outline key directions of research for furthering our understanding of the functional significance of migratory stream fishes. Our aim is to highlight the diversity of subsidies provided by migratory fishes in order to foster a more comprehensive perspective on fishes as essential components of riverine ecosystems.

Coupled predator-prey oscillations in a chaotic food web

2009 ◽  
Vol 12 (12) ◽  
pp. 1367-1378 ◽  
Author(s):  
Elisa Benincà ◽  
Klaus D. Jöhnk ◽  
Reinhard Heerkloss ◽  
Jef Huisman
Keyword(s):  
Food Web ◽  
Predator Prey

Cycle lengths and phase portrait characteristics as probes for predator–prey interactions: comparing simulations and observed data

2009 ◽  
Vol 87 (1) ◽  
pp. 20-30 ◽  
Author(s):  
Nina Holmengen ◽  
Knut Lehre Seip
Keyword(s):  
American Mink ◽  
Interaction Strength ◽  
Simulation Models ◽  
Ondatra Zibethicus ◽  
Clockwise Rotation ◽  
Predator Prey ◽  
Strength Of Interaction ◽  
Cycle Lengths ◽  
The Relationship ◽  
Best Fit

In this paper we explore the cyclic interactions of prey–predator systems by examining the relationship between cycle lengths of both species and the strength of their interaction. As a probe of interaction strength, we use the degree of counter-clockwise rotation in phase plots with the prey on the x axis and the predator on the y axis. We compare the results from a 25-year time series from the Hudson’s Bay Company data on American mink ( Neovison vison (Schreber, 1777)) and muskrat ( Ondatra zibethicus (L., 1766)) with results from three simulation models. We found that the strength of interaction (rotation range: –0.4 to 1.1 rad/year) was strongest when the two cycle lengths were similar and that it increased with the amplitude of the cycles (cycle range: 4–10 years). The time difference between prey and predator cycles that corresponded to the highest interaction strength was 2–3 years. Similar results were obtained with simulation models; the most complex Hanski model showing the overall best fit with observations. However, none of the models were able to reproduce long ranges of stable cycles by only changing one of their parameters at a time (ranges 2–4 years), whereas the observed range of stable cycles was 4–10 years.

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