A term paper on PREDATION (original) (raw)
Scientific Reports
Understanding the factors governing predation remains a top priority in ecology. Using a dragonfly nymph-tadpole system, we experimentally varied predator density, prey density, and prey species ratio to investigate: (i) whether predator interference varies between prey types that differ in palatability, (ii) whether adding alternate prey influences the magnitude of predator interference, and (iii) whether patterns of prey selection vary according to the predictions of optimal diet theory. In single-prey foraging trials, predation of palatable leopard frog tadpoles was limited by prey availability and predator interference, whereas predation of unpalatable toad tadpoles was limited by handling time. Adding unpalatable prey did not affect the predator’s kill rate of palatable prey, but the presence of palatable prey increased the influence of predator density on the kill rate of unpalatable prey and reduced unpalatable prey handling time. Prey selection did not change with shifts in ...
Predator Functional Responses: Discriminating between Handling and Digesting Prey
Ecological Monographs, 2002
We present a handy mechanistic functional response model that realistically incorporates handling (i.e., attacking and eating) and digesting prey. We briefly review current functional response theory and thereby demonstrate that such a model has been lacking so far. In our model, we treat digestion as a background process that does not prevent further foraging activities (i.e., searching and handling). Instead, we let the hunger level determine the probability that the predator searches for new prey. Additionally, our model takes into account time wasted through unsuccessful attacks. Since a main assumption of our model is that the predator's hunger is in a steady state, we term it the steady-state satiation (SSS) equation.
Marine Ecology Progress Series, 1992
We investigated the influence of variations in the size of prey (Mallotus villosus) and a vertebrate predator (Gasterosteus aculeatus) on larval fish mortality rates during the period of yolk absorption using mid-size mesocosms (2.7 m". Increasing predator size increased mortality rates of capelin larvae. Variations in larval capelin size resulted in 2 distinct patterns. Between experimental trials, greater mean size of larval capelin in the mesocosm reduced mortality due to predation. Within an experimental mesocosm, larger larvae suffered higher mortality than smaller individuals. Contrasting patterns of size-dependent vulnerability to predation reflect the hierarchy of processes that determine the probability that a larval fish will be preyed upon. The broad scale response of the predator was determined by the mean relative sizes of prey and predator which govern the average probabilities of encounter, attack and capture. Within the search ambit of a predator (e.g area or volume searched within a complete diurnal foraging cycle) active prey selection for larger prey due to either greater visibility or higher energy reward was an important factor. A comparison of our results with estimated predation rates by the jellyfish Aurelia aurita indicates that at a similar size a gelatinous zooplankter consumes fewer larvae than a stickleback and is a less efficient predator as measured by the energy ingested relative to energy demands. For both vertebrate and invertebrate predators, the ratio of prey to predator lengths was a strong predictor of the daily mortality rate due to predation. Relative prey-predator sizes may provide a useful perspective to assess changes in larval fish vulnerability as they grow through a predator field.
An experimental test of the nature of predation: neither prey- nor ratio-dependent
Journal of Animal Ecology, 2004
There is a current debate about the appropriateness of prey-dependent vs. ratiodependent functional responses in predator-prey models. This is an important issue as systems governed by these models exhibit quite different dynamical behaviour. However, the issue is not yet resolved on a theoretical basis, and there is a lack of experimental evidence in natural systems. We used a paper wasp-shield beetle system in a natural setting to assess the validity of either approach. 2. We manipulated the abundance of herbivorous insect prey on thistle plants and of predatory paper wasps in the immediate environment of the prey by opening or closing cages containing wasp nests. 3. The number of wasps foraging at the site increased when cages were opened, but rapidly reached an asymptote, indicating predator interference. The predation rate per predator decreased with the number of wasps in the environment. Thus, the functional response depended on both prey and predator density. 4. Neither a pure prey-nor a pure ratio-dependent model fitted perfectly our observations. However, the functional response of the paper wasps towards shield beetle larvae was closer to ratio-dependence. To our knowledge, this is the first experimental evidence discriminating between ratio-and prey-dependence in a natural setting with unconfined predators and prey. 5. Predator interference was most probably responsible for the specific form of the functional response found. We found indications that both direct (e.g. aggression) and indirect interference mechanisms (e.g. depletion of easy-to-find prey) were at work in our system. We conclude that predator density cannot be ignored in models of predatorprey interactions.
Body Sizes of Animal Predators and Animal Prey in Food Webs
The Journal of Animal Ecology, 1993
1. We measured the body sizes (weights or lengths) of animal species found in the food webs of natural communities. In c. 90% of the feeding links among the animal species with known sizes, a larger predator consumes a smaller prey. 2. Larger predators eat prey with a wider range of body sizes than do smaller predators. The geometric mean predator size increases with the size of prey. The increase in geometric mean predator size is less than proportional to the increase in prey size (i.e. has a slope less than 1 on log-log coordinates). 3. The geometric mean sizes of prey and predators increase as the habitat of webs changes from aquatic to terrestrial to coastal to marine. Within each type of habitat, mean prey sizes are always less than mean predator sizes, and prey and predator sizes are always positively correlated. 4. Feeding relations order the metabolic types of organisms from invertebrate to vertebrate ectotherm to vertebrate endotherm. Organisms commonly eat other organisms with the same or lower metabolic type, but (with very rare exceptions) organisms do not eat other organisms with a higher metabolic type. Mean sizes of prey increase as the metabolic type of prey changes from invertebrate to vertebrate ectotherm to vertebrate endotherm, but the same does not hold true for predators. 5. Prey and predator sizes are positively correlated in links from invertebrate prey to invertebrate predators. In links with other combinations of prey and predator metabolic types, the correlation between prey and predator body sizes is rarely large when it is positive, and in some cases is even negative. 6. Species sizes are roughly log-normally distributed. 7. Body size offers a good (though not perfect) interpretation of the ordering of animal species assumed in the cascade model, a stochastic model of food web structure. When body size is taken as the physical interpretation of the ordering assumed in the cascade model, and when the body sizes of different animal species are taken as log-normally distributed, many of the empirical findings can be explained in terms of the cascade model.
How Prey Respond to Combined Predators: A Review and an Empirical Test
Ecology, 2003
Studies of phenotypic plasticity frequently ask how organisms respond to a change in their environment, but most organisms do not experience single environmental changes. Therefore, we need to move to the next step and understand how organisms respond to combinations of environmental changes. Recent studies of predator-induced plasticity have addressed how prey respond to different combinations of predators. I briefly review 22 studies of combined predator effects on prey phenotypes and identify four factors that make it difficult to interpret the results of these studies: (1) uncontrolled prey consumption, (2) a low number of prey traits, (3) a low number of predator combinations, and (4) confounded predator composition and total predator density. I address these challenges in an experiment that examined how wood frog tadpoles (Rana sylvatica) altered 12 behavioral, morphological, and life historical traits in response to four different caged predators (Erythemis, Belostoma, Dytiscus, and Anax). The predators were present alone at low density, alone at high density (2ϫ), or combined into six pairwise combinations. When each predator was alone (at either low or high density), tadpoles discriminated among different predators and produced predator-specific phenotypes. The doubling of predator density rarely induced more extreme prey phenotypes. When predators were combined, the tadpoles generally developed phenotypes that were similar to those induced by the more risky predator alone (90% of all traits examined, at either low or high density). These results suggest that tadpoles perceive the risk of combined predators as being similar to the risk of the most dangerous predator in the pair, and not as a summed or averaged predation risk. The actual risk from these predator combinations remains to be tested. This appears to be the first study to take a comprehensive approach that controls prey consumption, examines a large number of prey traits, uses a large number of predator combinations, and separates the effects of predator composition and predator density. There is a clear need for more such studies to determine whether these results can be generalized to other taxa.
Joint evolution of predator body size and prey-size preference
Evolutionary Ecology, 2007
We studied the joint evolution of predator body size and prey-size preference based on dynamic energy budget theory. The predators' demography and their functional response are based on general eco-physiological principles involving the size of both predator and prey. While our model can account for qualitatively different predator types by adjusting parameter values, we mainly focused on 'true' predators that kill their prey. The resulting model explains various empirical observations, such as the triangular distribution of predator-prey size combinations, the island rule, and the difference in predator-prey size ratios between filter feeders and raptorial feeders. The model also reveals key factors for the evolution of predator-prey size ratios. Capture mechanisms turned out to have a large effect on this ratio, while prey-size availability and competition for resources only help explain variation in predator size, not variation in predator-prey size ratio. Predation among predators is identified as an important factor for deviations from the optimal predator-prey size ratio.
Why can a predator increase its consumption of prey when it is released along with a parasitoid?
Entomologia Generalis, 2019
The mixed release of predators and parasitoids to control a target pest can produce different results. In some cases, this mixed introduction can induce an increase in the predation rates of the pest and even of the parasitoid. To explain this phenomenon, it has been hypothesized that the presence of parasitoids (revealed by their mobility or related products) and interspecific competition (parasitoid vs predator) could influence such rates of predation. Therefore, in the present study we tested the effect of parasitoid mobility, host hemolymph (produced by parasitoid host-feeding) and parasitoid species (competing vs. non-competing species of the predator) on the number of prey consumed by the predator. Additionally, to add weight to the results of the bioassays, we determined whether the gender of the predators and parasitoids induced an effect on prey consumption by the predator by performing three bioassays under randomized block designs. Our results showed that neither parasitoid mobility nor host hemolymph presence modified the number of whitefly nymphs preyed upon by the predator. However, the number of whitefly nymphs consumed was significantly higher when the predator was introduced together with the competing parasitoid species relative to treatments with the non-competing parasitoid. In addition, we found that the predator preyed upon more mobile than immobile parasitoids and more competing than noncompeting parasitoids. As for predator gender, we found that female predators consumed more whitefly nymphs relative to male predators and wasp gender did not affect predation. Overall, our results suggest that interspecific competition may be a more important factor regulating predator consumption than parasitoid mobility or the presence of the host hemolymph.