Predator Feeding Rates Research Articles

Reassessment of the Predatory Effects of Rainbow Smelt on Ciscoes in Lake Superior

AbstractEvidence from small lakes suggests that predation on larval ciscoes Coregonus artedi by nonnative rainbow smelt Osmerus mordax can lead to cisco suppression or extirpation. However, evidence from larger lakes has led to equivocal conclusions. In this study, we examine the potential predation effects of rainbow smelt in two adjacent but contrasting embayments in Lake Superior (Thunder and Black bays, Ontario). During May 2006, we sampled the ichthyoplankton, pelagic fish communities, and diet composition of rainbow smelt in both bays. Using acoustics and midwater trawling, we estimated rainbow smelt densities to be 476 ± 34/ha (mean ± SE) in Thunder Bay and 3,435 ± 460/ha in Black Bay. We used a bioenergetics model to estimate the proportion of cisco larvae consumed by rainbow smelt. Our results suggest that predation by rainbow smelt accounts for 15–52% and 37–100% of the mortality of larval ciscoes in Thunder and Black bays, respectively, depending on the predator feeding rate and the scale of predator–prey overlap. We also examined the sensitivity of past conclusions (based on 1974 field collections) to assumptions of temporal overlap between rainbow smelt and larval ciscoes and estimates of rainbow smelt abundance derived from bottom trawl samples. After adjusting these parameters to reflect current understanding, we found that the previous predation estimates may have been conservative. We conclude that rainbow smelt may have been a more important contributor to the demise and slow recovery of ciscoes in Lake Superior than previously thought.

Interaction between underwater and aerial body temperatures in influencing a top predator feeding rate in the intertidal

Interaction between underwater and aerial body temperatures in influencing a top predator feeding rate in the intertidal

Chemical information transfer in freshwater plankton

The structure of aquatic ecosystems is determined by complex interactions among individual organisms at different trophic levels. Although our basic understanding of how top-down and bottom-up processes interact to determine food-web dynamics has advanced, we still lack insights into how complex interactions and feedbacks affect the dynamics and structure of food webs. It is now becoming increasingly clear that, in addition to energy transfer from one trophic level to the other, there is exchange of information between these levels facilitated by the release of infochemicals by the organisms. There is evidence from recent studies that the exchange of chemical information in freshwater ecosystems is likely to play a decisive role in shaping structure and functioning of these systems. Chemical communication among freshwater organisms mediates many aspects of both predation and interspecific competition, which play key roles in determining community structure and ecosystem functioning. For example, consumer-induced defences in phytoplankton and zooplankton include modifications in the characteristics relating to life history, behaviour, morphology and biochemistry. These inducible defences affect trophic interactions by altering predator feeding rates through changes in attack rate or handling time, or both. Also host-specific fungal parasitism in phytoplankton is probably controlled by infochemicals. The motile fungi recognise their host by host-secreted compounds. Until now models describing the functioning of ecosystems mainly considered flows of biomass and energy. Integration of new knowledge about the role of chemical communication in these models may be one of the aims of ecological informatics. In this chapter I discuss how infochemicals may affect the dynamics and structure of planktonic food webs.

On the different nature of top‐down and bottom‐up effects in pelagic food webs

SUMMARY 1. Each individual planktonic plant or animal is exposed to the hazards of starvation and risk of predation, and each planktonic population is under the control of resource limitation from the bottom up (growth and reproduction) and by predation from the top down (mortality). While the bottom‐up and top‐down impacts are traditionally conceived as compatible with each other, field population‐density data on two coexisting Daphnia species suggest that the nature of the two impacts is different. Rates of change, such as the rate of individual body growth, rate of reproduction, and each species' population growth rate, are controlled from the bottom up. State variables, such as biomass, individual body size and population density, are controlled from the top down and are fixed at a specific level regardless of the rate at which they are produced.2. According to the theory of functional responses, carnivorous and herbivorous predators react to prey density rather than to the rate at which prey are produced or reproduced. The predator's feeding rate (and thus the magnitude of its effect on prey density) should hence be regarded as a functional response to increasing resource concentration.3. The disparity between the bottom‐up and top‐down effects is also apparent in individual decision making, where a choice must be made between accepting the hazards of hunger and the risks of predation (lost calories versus loss of life).4. As long as top‐down forces are effective, the disparity with bottom‐up effects seems evident. In the absence of predation, however, all efforts of an individual become subordinate to the competition for resources. Biomass becomes limited from the bottom up as soon as the density of a superior competitor has increased to the carrying capacity of a given habitat. Such a shift in the importance of bottom‐up control can be seen in zooplankton in habitats from which fish have been excluded.

Functional Responses with Predator Interference: Viable Alternatives to the Holling Type II Model

A predator's per capita feeding rate on prey, or its functional response, provides a foundation for predator–prey theory. Since 1959, Holling's prey-dependent Type II functional response, a model that is a function of prey abundance only, has served as the basis for a large literature on predator–prey theory. We present statistical evidence from 19 predator–prey systems that three predator-dependent functional responses (Beddington-DeAngelis, Crowley-Martin, and Hassell-Varley), i.e., models that are functions of both prey and predator abundance because of predator interference, can provide better descriptions of predator feeding over a range of predator–prey abundances. No single functional response best describes all of the data sets. Given these functional forms, we suggest use of the Beddington-DeAngelis or Hassell-Varley model when predator feeding rate becomes independent of predator density at high prey density and use of the Crowley-Martin model when predator feeding rate is decreased by higher predator density even when prey density is high.

FUNCTIONAL RESPONSES WITH PREDATOR INTERFERENCE: VIABLE ALTERNATIVES TO THE HOLLING TYPE II MODEL

A predator's per capita feeding rate on prey, or its functional response, provides a foundation for predator–prey theory. Since 1959, Holling's prey-dependent Type II functional response, a model that is a function of prey abundance only, has served as the basis for a large literature on predator–prey theory. We present statistical evidence from 19 predator–prey systems that three predator-dependent functional responses (Beddington-DeAngelis, Crowley-Martin, and Hassell-Varley), i.e., models that are functions of both prey and predator abundance because of predator interference, can provide better descriptions of predator feeding over a range of predator–prey abundances. No single functional response best describes all of the data sets. Given these functional forms, we suggest use of the Beddington-DeAngelis or Hassell-Varley model when predator feeding rate becomes independent of predator density at high prey density and use of the Crowley-Martin model when predator feeding rate is decreased by higher predator density even when prey density is high.

Effects of Multiple, Predator-Induced Behaviors on Short-Term Producer-Grazer Dynamics in Open Systems

We investigated the population consequences of multiple behavioral responses of grazers to a foraging return–predation risk trade‐off in an open system consisting of primary producers, grazers, and predators. Using a dynamical model where grazers adjust their foraging activity and emigration rate to the densities of predators and producers, we explored how changes in control variables (predator density, grazer immigration, and producer immigration and carrying capacity) affect the dynamics of producers and grazers at temporal scales shorter than consumer and predator reproduction. The model predicts that producer biomass increases and that both the density of foraging grazers and the feeding rate of predators decrease with predator density. These predictions hold although total ($$\mathrm{foraging}\,+\mathrm{nonforaging}\,$$) grazer density may actually increase with predator density. The latter will occur whenever the benefit of higher resource density outweighs the increased risk of predation. In this case, per capita grazer emigration decreases with predator density, which might be misinterpreted as a direct “freezing” response to predators. Increased grazer immigration is predicted to result in decreased producer density and increased densities of both foraging and total grazers, as well as increased grazer emigration and predator feeding rates. Increased producer immigration or carrying capacity should increase producer and grazer densities and predator feeding rate but decrease per capita grazer emigration. Manipulation of predator (trout) densities in a set of nine large (50 m2) stream channels produced results in broad agreement with model predictions. Most notably, a positive effect of trout on benthic algal biomass was mainly mediated through grazer behavior (changes in the use of epibenthic surfaces and in emigration rate) rather than through consumptive reductions of grazer numbers by trout.

Additive interactions between the moon snail Euspira heros and the sea star Asterias forbesi, two predators of the surfclam Spisula solidissima.

A laboratory experiment was conducted to determine whether the sea star Asterias forbesi and the naticid gastropod Euspira heros feed on surfclams, Spisula solidissima, in an additive or non-additive manner. Predators were allowed to feed on clams with conspecifics and in the presence of the other predator species. Clam mortality (measured as the rate of decline of clam number) and predator feeding rates were noted. To determine the effects of temperature on interactions among the predators, the experiment was conducted at three different temperatures. At all temperatures, feeding rate of each predator was not affected by the presence of the other species, and clam mortality in the presence of both predators was predictable from mortality in the presence of a single predator species. These additive interactions are most likely a result of habitat partitioning between the predators, with naticid snails being infaunal and sea stars being epifaunal. Previous studies in a variety of systems show no clear pattern of occurrence of non-additive interactions. Relatively small differences in predator or prey behavior may be responsible for the presence or absence of non-additive interactions.

Regulation of fish reproduction by a predatory gastropod: an experimental investigation of indirect effects in a seagrass community

The indirect effects of the horse conch, a predatory gastropod, on reproduction in a suite of fishes that use the shells of the gastropod's main prey (the pen shell Atrina rigida (Sol.)) as nest sites in St. Joseph Bay, Florida, was investigated by examining the two links (direct interactions) that create the indirect effect. The horse conch– A. rigida predator–prey interaction was quantified by measuring predator feeding rate and distribution across a range of prey density. To determine the effect of A. rigida mortality on fish reproduction, the rate of shell availability was experimentally manipulated and egg production measured in four fish species. Horse conch feeding rate and distribution were not functions of prey density, but A. rigida mortality was correlated with conch abundance, supporting previous evidence that horse conchs regulate new shell availability. Increased rates of shell availability caused increases in the number of clutches laid and average clutch size in one fish species, Chasmodes saburrae Jordan & Gilbert, probably because new shells provide a greater surface area for eggs compared to older shells. These results suggest that horse conchs indirectly affect C. saburrae reproduction both at the level of the individual (clutch size) and the population (egg production) by regulating the availability of new shells. Because prey density had little effect on the predator, variation in the indirect effect of conchs on fish reproduction will be primarily influenced by the distribution of the predator, not A. rigida.

Limitations to Lake Trout (Salvelinus namaycush) Rehabilitation in the Great Lakes Imposed by Biotic Interactions Occurring at Early Life Stages

We examine evidence that biotic factors, particularly predation, may be limiting early survival of wild lake trout (Salvelinus namaycush) juveniles in many areas of the Great Lakes. The Great Lakes contain numerous potential predators of lake trout eggs and fry, some of which are recent invaders, and most of which were probably absent when lake trout most recently re-invaded the Great Lakes after the last ice age. Simple quantitative models of predation suggest that plausible assumptions about prey densities, predator feeding rates, and duration of exposure of predator to prey can lead to very high estimates of predation mortality, in some instances approaching 100%. Indirect evidence from inter-Great Lake comparisons and inland lake examples also suggest that biotic factors may impede successful lake trout colonization. Our synthesis of the evidence leads to recommendations for research to better define field feeding rates of lake trout egg and fry predators and comparative studies of densities of potential egg and fry predators on lake trout spawning reefs. Management options should be designed to provide useful information as well as achieve short-term goals. From a management standpoint we recommend that: newly constructed lake trout reefs should be placed well away from concentrations of potential predators; offshore spawning reefs should be stocked; salmonine stocking, nutrient abatement, and commercial harvest of alewives should all be considered as options to enhance survival of young lake trout; hatchery lake trout should not be stocked at sites where wild lake trout are showing signs of recovery; and exotic species expansions or introductions must be curtailed to maintain or improve on our recent successes in lake trout rehabilitation.

Big-Eyed Bugs (Hemiptera: Lygaeidae) and the Striped Lynx Spider (Araneae: Oxyopidae): Intra- and Interspecific Interference on Predation of First Instar Corn Earworm (Lepidoptera: Noctuidae)

To understand agroecology and to increase the role of entomophages in pest management, it is important to understand interactions among arthropod predators. Laboratory studies were conducted with 1–2 adult big-eyed bugs, (BEB) Geocoris spp., 1–2 striped lynx spiders (SLS), Oxyopes salticus Hentz (lst–3rd instar), or one of each to investigate conspecific and interspecific interference of predation on 1st instar Heliothis zea Boddie in the laboratory. The number of 1st instar H. zea consumed per individual in 24 h fell significantly when two adult BEB were confined together compared with the number consumed by solitary BEB. Placing two juvenile SLS together did not reduce the number of larvae consumed per individual in 24 h. The combined feeding rate of one BEB and one SLS confined together fell well below the sum of the rates for solitary BEB and SLS, but it was unclear to what degree each predator's feeding rate was reduced. These results suggest that exceeding the optimum density of BEB and SLS in the field could reduce the biocontrol of H. zea provided by BEB.

ALLEE EFFECTS: POPULATION GROWTH, CRITICAL DENSITY, AND THE CHANCE OF EXTINCTION

This paper develops mathematical models to describe the growth, critical density, and extinction probability in sparse populations experiencing Allee effects. An Allee effect (or depensation) is a situation at low population densities where the per‐individual growth rate is an increasing function of population density.A potentially important mechanism causing Allee effects is a shortage of mating encounters in sparse populations. Stochastic models are proposed for predicting the probability of encounter or the frequency of encounter as a function of population density. A negative exponential function is derived as such an encounter function under very general biological assumptions, including random, regular, or aggregated spatial patterns. A rectangular hyperbola function, heretofore used in ecology as the functional response of predator feeding rate to prey density, arises from the negative exponential function when encounter probabilities are assumed heterogeneous among individuals. These encounter functions produce Allee effects when incorporated into population growth models as birth rates.Three types of population models with encounter‐limited birth rates are compared: (1) deterministic differential equations, (2) stochastic discrete birth‐death processes, and (3) stochastic continuous diffusion processes. The phenomenon of a critical density, a major consequence of Allee effects, manifests itself differently in the different types of models. The critical density is a lower unstable equilibrium in the deterministic differential equation models. For the stochastic discrete birth‐death processes considered here, the critical density is an inflection point in the probability of extinction plotted as a function of initial population density. In the continuous diffusion processes, the critical density becomes a local minimum (antimode) in the stationary probability distribution for population density. For both types of stochastic models, a critical density appears as an inflection point in the probability of attaining a small population density (extinction) before attaining a large one. Multiplicative (“environmental”) stochastic noise amplifies Allee effects. Harvesting also amplifies those effects.Though Allee effects are difficult to detect or measure in natural populations, their presence would seriously impact exploitation, management, and preservation of biological resources.

Predator-Prey Relationship of Geocoris punctipes1 and Heliothis virescens234

Predator-prey relationships between Geocoris punctipes (Say) and Heliothis virescens (F.) were studied in the laboratory by caging G. punctipes nymphs individually with H. virescens eggs or larvae. The primary objectives of the study were to determine which stages of H. virescens were acceptable as prey for each nymphal instar of G. punctipes and how this predation affected the developmental rate and percent survival of the predator's 5 instars. First-instar G. punctipes nymphs were discovered to be almost exclusively egg predators; the last 4 fed on both eggs and small larvae. All predator stages attained a survival rate of over 96% when they fed on eggs, but when feeding on 1st-instar larvae, survival ranged from 5.6–69.0% for all instars. Predator survival, feeding and development rates decreased as size (or age) of its prey increased; survival rate and feeding rates increased with each successive instar.

Effects of Feeding History on Short-Term and Long-Term Functional Responses in Notonecta hoffmanni

SUMMARY (1) Growth rate and size at moult increased with prey density for Notonecta hoffmanni Hungerford nymphs raised at various densities of their mosquito larvae prey. (2) The functional response of different sized instar IV nymphs was type-2, and large predators ate more at high prey densities than did small predators. (3) The feeding rate of individual predators did not vary in any regular way during the instar. Predator size at the start of the instar was a good predictor of the predators' functional responses for both long- and short-term experiments. Short-term experiments were good predictors of the long-term functional responses: the relationship between these two responses remains linear over a wide range of prey densities. These facts allow us to predict the functional response over the whole instar from a knowledge of predator weight. (4) Variation in predator size within one instar (IV) was as important as differences in the predators' size in different instars in determining the predator's feeding rate.