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PubMed2000

Provisioned Parastrachia japonensis (Hemiptera: Cydnidae) nymphs gain access to food and protection from predators.

Females of the shield bug Parastrachia japonensis Scott progressively provision nymph-containing nests with drupes of the host tree, Schoepfia jasminodora (Olicaceae: Rosidae: Santales). The majority of nests are 5-15 m from the host tree, a distance thought to have been a major impetus for the occurrence of provisioning in this species. However, the function of provisioning is not well understood. We carried out two field experiments to determine whether provisioning is nutritionally important and whether it affords protection against predation. Development of nymphs was significantly delayed and their survival was low in the absence of provisioning, even when nests were within the area of ground on to which the drupes fell, apparently because of the poor quality of the majority of the drupes. Selective provisioning of good-quality drupes by female P. japonensis, a semelparous species, was thus necessary for young nymphs to obtain enough food for their development. Furthermore, even without a female in attendance, having drupes in the nest significantly reduced early mortality in the presence of a predator. Copyright 2000 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed2000

Self-organization, scale and stability in a spatial predator-prey interaction.

Simple predator-prey models often predict extreme instability in interactions where the prey are depressed well below their carrying capacity. Although the behaviour of some laboratory systems conforms to this pattern, field and mesocosm studies generally show prolonged co-existence of prey and predator. Prominent among the possible causes of this discrepancy are the effects of spatial heterogeneity. In this paper we show that both discrete and continuous representations of the spatial Rosenzweig-McArthur model with immobile prey can be stabilized by self-organized prey heterogeneity. This concordance of behaviour closely parallels that which we have previously established in the context of invasion waves. We use the continuous model variant to calculate the characteristic spatial scales of the self-organized structures. The discrete variant forms the basis of a simulation study demonstrating the variety of stable structures and elucidating their relation to the history of the system. We note that all stable prey distributions take the form of a network of occupied patches separated by prey-free regions, and liken the process which generates such assemblages to the formation of a landscape mozaic.

Animals↗
PubMed2001

Prey patchiness, predator survival and fish recruitment.

A simple mathematical model is presented for the population dynamics of fish larvae when the main food supply, in this case copepods, is spatially patchy in its distribution. Encounters by an individual predator (larva) with prey patches, and with individual prey within patches, are represented by Poisson processes. It is demonstrated analytically, and confirmed by numerical experiments, that prey patchiness fails to alter mean predator-prey encounter rates from their values for homogeneous prey distributions. Individual variance in encounter rate is, however, much affected. This has significant consequences for the (small) numbers of larvae surviving to metamorphosis and recruitment to the adult fish population.

Animals↗
PubMed1998

Implications of predator foraging on aphid pathogen dynamics.

The foraging behavior of starved and nonstarved second and fourth instar Coccinella septempunctata larvae on dead Acyrthosiphon pisum aphids, either infected with the entomopathogenic fungus Erynia neoaphidis (sporulating) or uninfected, was examined. Larvae searched for longer and fed less when presented with infected rather than uninfected A. pisum. Although no sporulating infected aphids were completely consumed, both adult and larval ladybirds can still be considered as intraguild predators. In a further study, fourth instar larvae fed on dying infected, dead infected (not sporulating), and dead uninfected aphids for similar periods of time but again the infected aphids were seldom entirely consumed. Live uninfected aphids were fed upon for significantly longer than any other prey. Infected aphids which were damaged at an early stage of infection (0, 1, or 2 days after inoculation) did not sporulate, whereas damaged moribund aphids (3 days after inoculation) did subsequently sporulate. Damaged sporulating cadavers continued to sporulate. However, damage to moribund and sporulating infected aphids, both mechanical or due to C. septempunctata feeding, reduced the number of conidia subsequently produced. Larval feeding caused the most significant reduction. Under laboratory conditions, C. septempunctata foraging on infected aphids did, therefore, reduce the pathogen density. However, conidia produced from a damaged cadaver resulted in levels of transmission to healthy aphids comparable to that resulting from an intact cadaver. Furthermore, the presence of a foraging adult ladybird resulted in a significant increase in transmission of the fungus to healthy aphids. Preliminary studies to assess the potential of other aphid natural enemies as intraguild predators illustrated that adults of the generalist carabid, Pterostichus madidus, entirely consumed sporulating cadavers. Third instar lacewing, Chrysoperla carnea, and hoverfly, Episyrphus balteatus, larvae never fed on sporulating cadavers. The ecological implications of these results are discussed.

Animals↗
PubMed2000

A simple model for the interplay of predators, rodents and food.

This paper presents a simple mathematical model for multiannual population cycles, in particular the periods, for the triple of small rodents and their predators and food. The parameters used are average birth rates of rodents and predators. The period lengths fit observations of lemmings and voles rather well and the model explains why the observed periods cluster around 4 years and around 10 years.

Animals↗
PubMed2001

The influence of predator--prey population dynamics on the long-term evolution of food web structure.

We develop a set of equations to describe the population dynamics of many interacting species in food webs. Predator-prey interactions are nonlinear, and are based on ratio-dependent functional responses. The equations account for competition for resources between members of the same species, and between members of different species. Predators divide their total hunting/foraging effort between the available prey species according to an evolutionarily stable strategy (ESS). The ESS foraging behaviour does not correspond to the predictions of optimal foraging theory. We use the population dynamics equations in simulations of the Webworld model of evolving ecosystems. New species are added to an existing food web due to speciation events, whilst species become extinct due to coevolution and competition. We study the dynamics of species-diversity in Webworld on a macro-evolutionary time-scale. Coevolutionary interactions are strong enough to cause continuous overturn of species, in contrast to our previous Webworld simulations with simpler population dynamics. Although there are significant fluctuations in species diversity because of speciation and extinction, very large-scale extinction avalanches appear to be absent from the dynamics, and we find no evidence for self-organized criticality.

Animals↗
PubMed2000

Patch choice under predation hazard.

In this paper we study optimal animal movement in heterogeneous environments consisting of several food patches in which animals trade-off energy gain versus predation risk. We derive a myopic optimization rule describing optimal animal movements by fitness maximization assuming an animal state is described by a single quantity (such as weight, size, or energy reserves). This rule predicts a critical state at which an animal should switch from a more dangerous and more profitable patch to a less dangerous and less profitable patch. Qualitatively, there are two types of behavior: either the animal switches from one patch to another and stays in the new patch for some time before it switches again, or the animal switches between two patches instantaneously. The former case happens if animal state growth is positive in all patches, while the latter case happens if animal state growth is negative in one patch. In particular, this happens if one patch is a refuge. We consider in detail two special cases. The first one assumes a linear animal state growth while the second assumes a saturating animal state growth described by the von Bertalanffy curve. For the first model the proportion of time spent in the more profitable and more risky patch increases with profitability of this patch when state growth is positive in both patches. On contrary, if state growth is negative in the less profitable and safer patch, animals spend proportionally less time in the more profitable and more risky patch as its profitability increases. As a function of the predation risk in the more profitable patch the time spent there proportionally decreases. When animal state growth is described by the saturating curve, time spent in the more risky patch is a hump-shaped curve if state growth is positive in both patches. Our results extend the mu/f rule, which predicts that animals should behave in such a way as to minimize mortality risk to resource intake ratio.

Animals↗
PubMed2002

Stabilizing dispersal delays in predator-prey metapopulation models.

Time delays produced by dispersal are shown to stabilize Lotka-Volterra predator-prey models. The models are formulated as integrodifferential equations that describe local predator-prey dynamics and either intrapatch or interpatch dispersal. Dispersing individuals may (or may not) differ in the duration of their trips; these differences are captured via a distributed delay in the models. Our results include those of previous studies as special cases and show that the stabilizing effect continues to operate when the dispersal process is modeled more realistically.

Animals↗
PubMed1991

Models for the effect of toxicant in single-species and predator-prey systems.

Models of single-species and predator-prey systems in a polluted closed environment are developed and partially analyzed. Three cases are considered: a single influx of toxicant, a constant influx of toxicant, and a periodic pollution of the environment. In the case of single-species growth we are able to determine some local and global dynamics. In the case of predator-prey systems, we investigate the existence of steady states for a small constant influx of toxicant.

Environmental Pollution↗
PubMed1982

Models of the influence of predation on aspect diversity in prey populations.

By considering a model incorporating behavioral changes by predators and prey evolution, we demonstrate how under certain conditions apostatic predation influences the maintenance of diversity within prey populations, and among different prey species. Further, we estimate the intrinsic "diversity" wavelength of the system when apostasy combines with other factors to lead to nonuniform distributions of prey along aspect gradients.

Animals↗
PubMed1982

Top predator persistence in differential equation models of food chains: the effects of omnivory and external forcing of lower trophic levels.

Persistence criteria are given for the highest trophic level predator in ordinary differential equation models of food chains exhibiting arbitrary omnivory and external supplementation of food source or an intermediate predator. The results are expressed in terms of inequalities involving the bounds on the intrinsic growth and interaction rates. Whether omnivory or external forcing enhances persistence is discussed, particularly for the examples of three-, four-, and five-link Lotka-Volterra food chains.

Animals↗
PubMed1987

Cannibalism and autotomy as predator-prey relationship for monoxenous Sarcosporidia.

In search for the final host of Sarcocystis gallotiae, sarcocysts of naturally infected Canarian lizards, Gallotia galloti, were fed to vertebrate predators of the lizard. Repeated transmission experiments remained negative. Routine check of the feces of the wild G. galloti revealed shedding of sporocysts. The sporocysts were administered to small vertebrates, which may function as prey for G. galloti. The transmission experiments remained negative. The observation of a high intraspecific aggression of G. galloti, including cannibalism and autotomy, seemed to support the hypothesis that this behavior might be the base of a an unexpected predator-prey relationship. Sarcocysts of S. gallotiae, fed to two laboratory-bred G. galloti resulted in excretion of sporulated sporocysts measuring 9.7 (9.2-12.2) X 7.7 (6.6-9.2) microns. Oral inoculation of two laboratory-bred G. galloti with experimentally gained sporocysts, led to the development of sarcocysts of 150-200 microns in length and 80-110 microns in width in the musculature of the lizards 153 days p.i. The sarcocysts were identified as S. gallotiae by light and electron microscopy. In epithelial cells of the intestine of G. galloti, which had experimentally been infected with sarcocysts of S. gallotiae, stages of gamogony and sporogony were found. We suggest that the life cycle of S. gallotiae is monoxenous and not obligatorily heteroxenous. The genus Sarcocystis seems to be more flexible in its biologic adaptability to utilize autotomy and cannibalism for completing its cycle than had heretofore been assumed.

Animals↗
PubMed1991

The toxic effect of deltamethrin on linyphiid and erigonid spiders in connection with ambient temperature, humidity, and predation.

The first part of this study concerns the effect of temperature and air humidity on the toxicity of deltamethrin to the erigonid Oedothorax apicatus. The second part concerns the effect of deltamethrin on behavior of linyphiids and erigonids with respect to their ability to escape from predators and to select between unfavorable (dry) and favorable (moist) habitat conditions. The toxic effect of deltamethrin was highest at the combination of high temperature and low air humidity. It was concluded that the spider's sensitivity to drought is increased by this pyrethroid. Affected spiders, however, are less able to select moist habitat conditions than unaffected ones. Walking speed of spiders was decreased by exposure to deltamethrin and their predation by carabid beetles was increased. It was concluded that the effect observed under field conditions is the result of a combination of neurological, physiological, and behavioral disturbance.

Animals↗
PubMed1991

Predators of the tick Amblyomma variegatum (Acari: Ixodidae) in Guadeloupe, French West Indies.

Some vertebrate species in Guadeloupe are predators of free or parasitic stages of Amblyomma variegatum (Fabricius). Among birds, 1.9% of the 421 identified animals found in the stomachs of grackles (Quiscalus lugubris), 1.6% of the 364 animals found in the stomachs of free-ranging chickens, and 0.3% of the 4642 animals found in the stomach of cattle egrets (Bubulcus ibis) were A. variegatum ticks. The most efficient predator of ticks was the tropical fire ant, Solenopsis geminata, which was observed to only attack engorged stages of ticks. An average of 8% of the 564 individual ticks or batch of ticks released on the ground, mainly in a grass environment, were attacked by this ant species. Mice (Mus musculus) and mongooses (Herpestes auropunctatus) feed on engorged nymphs and female ticks. None of the 15 strains of entomophagous nematodes, genera Steinernema and Heterorhabditis, experimentally put in contact with engorged larvae and nymphs were able to parasitize them. In the laboratory, the insects Megaselia scalaris (Diptera) and Tineola sp. (Lepidoptera) were occasionally found to feed on engorged and unfed ticks, respectively.

Animals↗
PubMed1996

Evolutionary dynamics of predator-prey systems: an ecological perspective.

Evolution takes place in an ecological setting that typically involves interactions with other organisms. To describe such evolution, a structure is needed which incorporates the simultaneous evolution of interacting species. Here a formal framework for this purpose is suggested, extending from the microscopic interactions between individuals--the immediate cause of natural selection, through the mesoscopic population dynamics responsible for driving the replacement of one mutant phenotype by another, to the macroscopic process of phenotypic evolution arising from many such substitutions. The process of coevolution that results from this is illustrated in the context of predator-prey systems. With no more than qualitative information about the evolutionary dynamics, some basic properties of predator-prey coevolution become evident. More detailed understanding requires specification of an evolutionary dynamic; two models for this purpose are outlined, one from our own research on a stochastic process of mutation and selection and the other from quantitative genetics. Much of the interest in coevolution has been to characterize the properties of fixed points at which there is no further phenotypic evolution. Stability analysis of the fixed points of evolutionary dynamical systems is reviewed and leads to conclusions about the asymptotic states of evolution rather different from those of game-theoretic methods. These differences become especially important when evolution involves more than one species.

Animals↗
PubMed1995

Bifurcation and stability analysis of a temperature-dependent mite predator-prey interaction model incorporating a prey refuge.

The non-linear behavior of a differential equations-based predator-prey model, incorporating a spatial refuge protecting a constant proportion of prey and wit temperature-dependent parameters chosen appropriately for a mite interaction on fruit trees, is examined using the numerical bifurcation code AUTO 86. The most significant result of this analysis is the existence of a temperature interval in which increasing the amount of refuge dynamically destabilizes the system; and on part of this interval the interaction is less likely to persist in that predator and prey minimum population densities are lower than when no refuge is available. It is also shown that increasing the amount of refuge can lead to population outbreaks due to the presence of multiple stable states. The ecological implications of a refuge are discussed with respect to the biological control of mite pests.

Animals↗
PubMed2001

Parasite-altered host behavior in the face of a predator: manipulation or not?

Parasitologists have generally accepted the idea that parasite-induced alterations in host behavior increase the chance for parasite survival and transmission or ensure the completion of its life cycle. The aim of the present study was to investigate modifications in the behavior of Taenia crassiceps-infected BALB/c mice in the face of a predator. The experiments showed modifications in the response of infected mice in comparison with uninfected controls on exposure to a predator final host. However, different studies lead us to suggest that the observed modifications are likely to be a secondary effect of the impact of the parasite on host physiology and immunity that favors its development and proliferation.

Animals↗
PubMed2004

Effects of phytoplankton-induced turbidity on predation success of piscivorous Eurasian perch (Perca fluviatilis): possible implications for fish community structure in lakes.

Turbidity can strongly influence predation success of visually oriented fish, especially piscivores such as adult Eurasian perch (Perca fluviatilis). This purely carnivorous species usually becomes a facultative piscivore after two discrete food niche shifts. Perch biomass has been observed to decrease in lakes along the productivity gradient, and then be replaced by cyprinids in non-manipulated eutrophic systems. Until now, this change has been mainly attributed to the competitive superiority of cyprinids for zooplankton prey during the juvenile phase of perch, while the piscivorous phase--as a possible factor influencing the recruitment success of perch--has been neglected. As the abundance of suitably sized prey fish should not be limiting in highly productive systems, we hypothesise that the switch from benthivorous feeding to preying on fish is inhibited by the reduced visibility in eutrophic lakes. We tested this hypothesis in laboratory experiments, where perch were fed two size classes of juvenile cyprinids at different phytoplankton- and bentonite-induced turbidity levels. Predation success was significantly influenced by turbidity level and turbidity source, but not by prey size. These experimental results suggest for the first time that piscivory of Eurasian perch is negatively influenced by different sources of turbidity, and hence low visibility might delay the onset of the food niche shift to fish prey.

Animals↗