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PubMed2001

Importance of predator diet cues in responses of larval wood frogs to fish and invertebrate predators.

We examined the effects of predator diet on the antipredator responses of larval woodfrogs (Rana sylvatica). We found that tadpoles showed stronger responses to fish (Perca flavescens) that were fed tadpoles than those fed invertebrates. Similarly, we found that tadpoles responded more strongly to larval dragonflies (Anax spp.) fed tadpoles than to dragonflies fed invertebrates. The overall intensity of response of tadpoles to fish was much stronger than that to dragonflies. Predator diet effects are not ubiquitous in predator-prey systems. We discuss possible reasons why predator diet effects are seen in some, but not all, predator-prey systems.

Animals↗
PubMed2003

A novel assay to monitor predator-prey interactions for Bdellovibrio bacteriovorus 109 J reveals a role for methyl-accepting chemotaxis proteins in predation.

Bdellovibrio bacteriovorus are Gram-negative bacteria that prey upon other Gram-negative bacteria, including some pathogens, in a wide variety of habitats including soil, sewage, marine and estuarine environments. In order to facilitate studies on predation by this organism, we have developed a method that assays killing of luminescent Escherichia coli by B. bacteriovorus. Moreover, we have used this assay to compare predation of cells by derivatives of B. bacteriovorus containing targeted mutations in genes we have identified. Two genes are described; one, mcp2, encoding a methyl-accepting chemotaxis protein (MCP) and the other, an mviN homologue. Bdellovibrio bacteriovorus mcp2::aphII were less efficient predators on luminescent E. coli than B. bacteriovorus containing a randomly inserted aphII gene via TnphoA transposition. These and other chemotaxis experiments implicated at least a minor role for chemotaxis in predation by B. bacteriovorus. They also open the way for further studies on Bdellovibrio ecology, genomics and predator-prey interactions. The results further confirm that Bdellovibrio uses a chemotaxis system in order to sense, and respond to, changes in its environment, including prey.

Bacterial Proteins↗
PubMed2006

Evolution of anti-predator traits in response to a flexible targeting strategy by predators.

Anti-predator benefits increase with vigilance rate and group size in many species of animal, while simultaneously resource intake rates usually decrease. This implies that there is an optimal group size and vigilance rate that will maximize individual fitness. While this basic theory of vigilance has been modelled and tested extensively, it has often been assumed that the predator represents a 'fixed-risk' such that groups of prey are essentially independent entities that exert little or no effect on one another either directly or indirectly. We argue that this is an over-simplification, and propose that the behaviour of one group of prey will likely affect the fitness of another local group of prey if the predator preferentially attacks the most vulnerable group-rather than attack both with constant rates. Using a numerical simulation model, we make the first examination of this game and allow the prey to dynamically evolve both optimal group size distributions between two habitats and vigilance rates in response to a predator with a preference for whichever group is the more vulnerable. We show that the density of prey in the population and the sensitivity of a predator to differences in prey vulnerability are likely to drive the dynamics of such a game. This novel approach to vigilance theory opens the door to several challenging lines of future research, both experimental and theoretical.

Animals↗
PubMed2002

Effect of diffusion and spatially varying predation risk on the dynamics and equilibrium density of a predator-prey system.

Starting from natural planktonic systems, we present a new mechanism involving spatial heterogeneity, and develop a new spatial structure model of planktonic predation systems. Firstly, the effect of diffusion on the dynamics of the system is investigated. We find that diffusion of only prey or both prey and predator between different patches with different predation risk may stabilize the dynamics, depending on the flow rate. Only a medium flow rate can lead to the stability of the system. Too large a rate can cause the system to approach the non-spatial limit case of a well-mixed system. Too large a rate can cause the system to approach the non-spatial limit case as a well-mixed system, which is characterized by its strongly oscillatory dynamics. When only prey diffuse, the smaller the parameter f (the proportion of the patchy volume with larger predation risk to the total volume), the more stable the system. If both populations can diffuse, however, only medium and very small f values may stabilize the system. Also, the response of the spatially averaged equilibrium densities of the system to the increasing of the flow rate is examined. With increasing flow rate, the spatial-averaged equilibrium density of prey decreases, while that of predator depends on which species can diffuse. For the case of prey diffusion only, it first remains unchanged and then slightly decreases, while it increases for the case of combinations as the flow rate increases. Our results are, qualitatively, determined by the spatially heterogeneous mechanism that we propose, and further regulated by top-down forces. Of practical importance, the results reported here indicate that which species diffuse plays a key role in the ways in which diffusion influences the dynamics and the spatial-average equilibrium densities of the system responses to the flow rate's increasing.

Animals↗
PubMed2004

Effects of opportunistic predation on anti-predator behavioural responses in a guild of ground foragers.

We studied factors that affect prey selection by a generalist predator that opportunistically attacks prey species, and the associated inter- and intra-specific responses of prey to this type of predation. Our model system was a guild of ground-foraging birds that are preyed upon by magpies ( Pica pica) during the breeding season. We found that magpies attacked up to 12 species during three consecutive breeding seasons. The overall capture success was estimated to be 4.9%. Magpies tended to attack from the air, targeting solitary prey, either on the ground or flying. Inter-specific prey responses to the risk of magpie predation included a reduction in the mean number of species occupying a foraging patch when magpies were present and a decrease in the distance between heterospecific neighbours. Intra-specific responses to magpie predation varied between species that were subject to different attack rates. Preferentially attacked prey enhanced their risk responses (increase in scanning time and scanning rate in the presence of magpies) relative to those species attacked in proportion to their abundance (increase only in scanning rate with magpies). Species attacked infrequently, relative to their abundance, showed no antipredator response. The probability of being attacked, rather than mortality rate, appears to be the factor to which prey species respond.

Animals↗
PubMed2005

Costs and limits of dosage response to predation risk: to what extent can tadpoles invest in anti-predator morphology?

Inducible defences have long been considered as a polyphenism opposing defended and undefended morphs. However, in nature, preys are exposed to various levels of predation risk and scale their investment in defence to actual predation risk. Still, among the traits that are involved in the defence, some are specific to one predator type while others act as a more generalised defence. The existence of defence costs could prevent an individual investing in all these traits simultaneously. In this study, we investigate the impact of an increasing level of predator density (stickleback, Gasterosteus aculeatus) on the expression of morphological inducible defences in tadpoles of Rana dalmatina. In this species, investment in tail length and tail muscle is a stickleback-specific response while increased tail fin depth is a more general defence. As expected, we found a relationship between investment in defence and level of risk through the responses of tail fin depth and tail length. We also found an exponential increase of defence cost, notably expressed by convex decrease of growth and developmental rates. We found a relative independence of investment in the different traits that compose the defence, revealing a high potential for fine tuning the expression of defended phenotypes with respect to local ecological conditions.

Adaptation, Biological↗
PubMed2006

Hard clams (Mercenaria mercenaria) evaluate predation risk using chemical signals from predators and injured conspecifics.

Hard clams, Mercenaria mercenaria, are sessile, filter-feeding organisms that are heavily preyed upon by blue crabs, which find their clam prey using chemical cues. Clams may evade blue crabs by reducing their pumping (feeding) behavior when a threat is perceived. The purpose of this study was to determine the type of signals that clams use to detect consumers. Clams decreased their pumping time in response to blue crabs and blue crab effluent, but not to crab shells, indicating that chemical signals and not mechanical cues mediated the response of clams to distant predators. Because predator diet can influence prey evaluation of predatory threats, we compared clam responses to blue crabs fed a steady diet of fish, clams, or that were starved prior to the experiment. In addition, we used injured clams as a stimulus because many organisms detect predators by sensing the odor of injured con- or heterospecifics. Clams reduced feeding in response to injured conspecifics and to blue crabs that had recently fed. Clams reacted similarly to fed crabs, regardless of their diet, but did not respond to starved blue crabs. Because blue crabs are generalist predators and the threat posed by these consumers is unrelated to the crab's diet, we should expect clam reactions to blue crabs to be independent of the crab's diet. The failure of clams to react to starved blue crabs likely increases their vulnerability to these consumers, but clam responses to injured conspecifics may constitute a strategy that allows animals to detect an imminent threat when signals emanating from blue crabs are not detectable.

Animal Communication↗
PubMed1992

The subcritical collapse of predator populations in discrete-time predator-prey models.

Many discrete-time predator-prey models possess three equilibria, corresponding to (1) extinction of both species, (2) extinction of the predator and survival of the prey at its carrying capacity, or (3) coexistence of both species. For a variety of such models, the equilibrium corresponding to coexistence may lose stability via a Hopf bifurcation, in which case trajectories approach an invariant circle. Alternatively, the equilibrium may undergo a subcritical flip bifurcation with a concomitant crash in the predator's population. We review a technique for distinguishing between subcritical and supercritical flip bifurcations and provide examples of predator-prey systems with a subcritical flip bifurcation.

Animals↗
PubMed2001

The effects of temporal variation in predation risk on anti-predator behaviour: an empirical test using marine snails.

Foraging animals must often balance the conflicting demands of finding food and avoiding predators. Temporal variation in predation risk is expected to influence how animals allocate time to these behaviours. Counterintuitively, the proportion of time spent foraging during both high- and low-risk periods should increase with increasing time exposed to high risk. We tested this prediction using intertidal marine snails (Littorina spp.) that were exposed to temporal variation in perceived predation risk from crabs (Cancer productus and Cancer magister). Our results were consistent with those predicted for high-risk, but not low-risk, periods. During high-risk periods, a greater number of snails foraged (versus those that left the water or remained in their shells) as time at high perceived risk increased. For low-risk periods, there was no relationship between the number of snails foraging and time at high risk. This might be due to snails in all treatments foraging maximally in the low-risk periods. As a consequence, the difference in the number of snails foraging between high- and low-risk periods decreased with increasing time subject to high risk. These results indicate that the commonly used protocol of exposing foragers to a single pulse of heightened risk might tend to overestimate their typical investment in anti-predator behaviour.

Adaptation, Biological↗
PubMed2003

Managing a subsidized predator population: reducing common raven predation on desert tortoises.

Human communities often are an inadvertent source of food, water, and other resources to native species of wildlife. Because these resources are more stable and predictable than those in a natural environment, animals that subsist on them are able to increase in numbers and expand their range, much to the detriment of their competitors and species they prey upon. In the Mojave Desert, common ravens (Corvus corax) have benefited from human-provided resources to increase in population size precipitously in recent years. This trend has caused concern because ravens prey on juvenile desert tortoises (Gopherus agassizi), a federally threatened species. In this paper, I discuss management strategies to reduce raven predation on desert tortoises. The recommendations fall into three categories: (1) managing raven populations by reducing access to anthropogenic resources; (2) removing offending ravens or other birds in specially targeted tortoise management zones; and (3) continuing research on raven ecology, raven behavior, and methods of reducing raven predation on tortoises. I also recommend approaching the problem within an adaptive management framework: management efforts should first be employed as scientific experiments--with replicates and controls--to yield an unbiased assessment of their effectiveness. Furthermore, these strategies should be implemented in concert with actions that reduce other causes of desert tortoise mortality to aid the long-term recovery of their populations. Overall, the approaches outlined in this paper are widely applicable to the management of subsidized predators, particularly where they present a threat to a declining species of prey.

Animals↗
PubMed2005

Predation by Allothrombium pulvinum on the spider mites Tetranychus urticae and Amphitetranychus viennensis: predation rate, prey preference and functional response.

The deutonymphs of Allothrombium pulvinum Ewing (Acari: Trombidiidae) are among the most important natural enemies of spider mites in North, North East and West Iran. In this study, maximum predation rate and preference experiments were conducted with A. pulvinum deutonymphs on apple leaf discs, to determine their preference for either of two spider mite species: Amphitetranychus viennensis (Zacher) and Tetranychus urticae Koch (Acari: Tetranychidae). Maximum predation rate tests showed that the predatory mite consumed more eggs and females of T. urticae than of A. viennensis. Furthermore, the Manly's preference index for eggs and females of T. urticae confirmed that T. urticae were the preferred prey. The functional response of A. pulvinum deutonymphs on females of T. urticae was examined over a 24-h period. Predation of A. pulvinum deutonymphs presented with females of T. urticae followed a type III functional response. Estimated handling time for the predatory mites was 4.51 h and attack coefficient b, which describes the changes in attack rate with prey densities in a type III functional response, was 0.021.

Animals↗
PubMed2000

Predator-prey relations between age-1+ summer flounder (Paralichthys dentatus, Linnaeus) and age-0 winter flounder (Pseudopleuronectes americanus, Walbaum): predator diets, prey selection, and effects of sediments and macrophytes.

Laboratory experiments and weekly trammel net surveys in the Navesink River, New Jersey (USA) were used to examine the predator-prey interaction between age-1+ summer flounder (Paralichthys dentatus) and age-0 winter flounder (Pseudopleuronectes americanus). Winter flounder (24-67 mm TL) were the dominant piscine prey of summer flounder (n=95, 252-648 mm TL) collected in trammel nets. We observed a temporal shift in summer flounder diets from sand shrimp (Crangon septemspinosa) and winter flounder, dominant during June and early July, to blue crabs (Callinectes sapidus) and other fishes (primarily Atlantic silversides, Menidia menidia and Atlantic menhaden, Brevortia tyrannus) later in the summer. Variations in prey selection appeared to be related to changes in the spatial distribution of predators and spatio-temporal variation in prey availability. In laboratory experiments, summer flounder (271-345 mm total length, TL) preferred demersal winter flounder to a pelagic fish (Atlantic silversides) and a benthic invertebrate (sand shrimp) prey, and the vulnerability of winter flounder increased with increasing prey body size from 20 to 90 mm TL. Experiments testing habitat effects showed that mortality of winter flounder in three different size classes (20-29, 40-49, 60-69 mm TL) was not influenced by sediment grain sizes permitting differential burial of the prey. However, vegetation enhanced survival, with fish suffering lower mortality in eelgrass (Zostera marina, 15+/-0.04%) than in sea lettuce (Ulva lactuca, 38+/-0.04%) or bare sand (70+/-0.07%) when the macrophytes were planted to produce similar leaf surface areas (5000 cm(2) m(-2)). Prey vulnerability appeared to be related to the role of vision in the predator's attack strategy and prey activity levels.

Journal Article↗
PubMed2001

PCR-based gut content analysis of insect predators: using ribosomal ITS-1 fragments from prey to estimate predation frequency.

We used polymerase chain reaction to determine whether Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae) DNA was present in the guts of larvae and adult males and females of the generalist predator Coleomegilla maculata De Geer (Coleoptera: Coccinellidae). The predators were fed Ostrinia nubilalis egg masses and allowed to digest at either 20 degrees C or 27 degrees C for time spans ranging from 0 to 12 h. Four primer pairs, specific for O. nubilalis were developed, using a nuclear ribosomal RNA sequence including part of the 18S gene, the complete internal transcribed spacer (ITS-1) region and part of the 5.8S gene. These primers amplified four sequences that were 492, 369, 256 and 150 base pairs long. We found a significant negative effect of time since feeding on the number of bands that could be detected. The shortest fragment was detected for the longest time after feeding (up to 12 h). We found no effect of predator weight, sex, developmental stage, or meal size on the time course over which bands of varying lengths could be detected.

Animals↗
PubMed2006

Predation and cathemerality. Comparing the impact of predators on the activity patterns of lemurids and ceboids.

The removal, or absence, of predatory species could be a contributing proximate factor to the rise of primate cathemerality. But predators themselves can also be cathemeral, so cathemerality could well be an evolutionary stable strategy. From a comparative perspective, it appears that the effect of predatory species cannot provide a unitary explanation for cathemerality. Varying distributions and population densities of predators, especially raptors, may be key factors in owl monkey (Aotus) cathemerality, but temperature and lunar cycle variation have also been implicated. In Madagascar, while raptors are potential predators of lemur species, the cathemerality of Eulemur species coincides with that of the fossa (Cryptoprocta ferox), a major predatory threat to lemurs. Thus, lemurid cathemerality may be more parsimoniously explained as an evolutionary stable strategy.

Animals↗
PubMedDate not supplied

Modelling prey-predator cycles using hemipteran predators of mosquito larvae for reducing world-wide mosquito-borne disease incidence.

Diplonychus indicus is an aquatic hemipterous bug known to be a voracious predator of dipteran larvae, among others, and to show a selective predation for mosquito larvae when exposed to a mixed prey diet. A datum consisted of the percentage of the fourth instar of (25) culicine mosquitoes killed by the bug. Data around the clock, published earlier (from starved adult males of this bug), reanalyzed by single cosinor, reveal a circasemidian rhythm (p = 0.004). This result prompts the recommendation of studying the time structure of prey-predator cycles further to evaluate the merits or demerits of introducing the bug in the field with the aim of reducing worldwide mosquito-borne disease incidence.

Animals↗
PubMed2004

Analysis of a predator-prey system with predator switching.

In this paper, we consider an interaction of prey and predator species where prey species have the ability of group defence. Thresholds, equilibria and stabilities are determined for the system of ordinary differential equations. Taking carrying capacity as a bifurcation parameter, it is shown that a Hopf bifurcation can occur implying that if the carrying capacity is made sufficiently large by enrichment of the environment, the model predicts the eventual extinction of the predator providing strong support for the so-called 'paradox of enrichment'.

Animals↗
PubMed2006

The prey-dependent consumption two-prey one-predator models with stage structure for the predator and impulsive effects.

In this paper, we consider the prey-dependent consumption two-prey one-predator models with stage structure for the predator and impulsive effects. By applying the Floquet theory of linear periodic impulsive equation, we show that there exists a globally asymptotically stable pest-eradication periodic solution when the impulsive period is less than some critical value, that is, the pest population can be eradicated totally. But from the point of ecological balance and saving resources, we only need to control the pest population under the economic threshold level instead of eradicating it totally, and thus, we further prove that the system is uniformly permanent if the impulsive period is larger than some critical value, and meanwhile we also give the conditions for the extinction of one of the two preys and permanence of the remaining species. Thus, we can use the stability of the positive periodic solution and its period to control insect pests at acceptably low levels. Considering population communities always are imbedded in periodically varying environments, and the parameters in ecosystem models may oscillate simultaneously with the periodically varying environments, we add a forcing term into the prey population's intrinsic growth rate. The resulting bifurcation diagrams show that with the varying of parameters, the system experiences process of cycles, periodic windows, periodic-doubling cascade, symmetry breaking bifurcation as well as chaos.

Animals↗
PubMed2001

Predators as stressors? Physiological and reproductive consequences of predation risk in tropical stonechats (Saxicola torquata axillaris).

Tropical birds usually lay smaller clutches and are less likely to initiate a second brood than their temperate-zone relatives. This reduction in annual fecundity is generally explained as an adaptation either to higher rates of nest predation or to a more limited food supply concurrent with higher adult survival in the tropics. However, the physiological parameters associated with lower annual fecundity in tropical birds have not been well investigated. We compared the annual fecundity, behaviour and a number of physiological parameters of stonechat parents feeding fledged juveniles in territories with and without fiscal shrikes, a predator on adult and fledged birds. Stonechat pairs in territories with shrikes were less likely to initiate a second brood and delayed successive broods compared to pairs in territories without shrikes. After fledging of their young, males showed a greater propensity than females to initiate distraction calls after a human intrusion into their territory and, therefore, invested more in the defence of their young. In territories with shrikes stonechat males had higher initial plasma corticosterone levels and lower body conditions than males in territories without shrikes, suggesting that they were chronically stressed. In contrast, the females from both types of territory had low initial plasma corticosterone levels. We conclude that shrike presence might account for the delay in initiation of a second brood and the reduction in the tendency to initiate a second brood. Whether these effects are mediated by the elevated levels of corticosterone remains to be demonstrated.

Animals↗