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PubMed1999

Coal tits, Parus ater, lose weight in response to chases by predators.

Theoretical models predict that birds should decrease their body mass in response to increased predation risk because lighter birds take off faster and are more manoeuvrable. We studied the effect of predation risk by chasing coal tits in large outdoor aviaries thus simulating an attempt to capture them. With this increase in predation risk, both perceived and actual, coal tits lost significantly more weight than in a control situation when they were not pursued. This pattern was attributable to a smaller gain in weight only during the day; nocturnal weight did not change in relation to diurnal predation risk. The lower daily weight gain was not consistent with predictions from models of interrupted foraging, but was consistent with predictions from risk adjustment models. Moreover, there was no difference in weight gain over 2-h periods that included a 1-h fast and those in which feeding was ad libitum, suggesting that coal tits could easily regain their body mass after a predator had interrupted their feeding. Our results therefore suggest that pursuit by predators leads to a decrease in the body mass of small birds. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗

PubMed1999

Honest signalling during prey-predator interactions in the lizard Anolis cristatellus.

Current theory on the evolution of pursuit-deterrent signals predicts that it may be advantageous for the prey to communicate to the predator its alertness and its ability to escape an attack. I tested these predictions by staging predator-prey encounters between A. cristatellus lizards and a model of one of its predators under natural conditions. Results supported the use of pushup displays as pursuit-deterrent signals. The intensity of signals, measured as the number of pushups given during predation episodes, was significantly positively correlated with individual physiological condition measured as endurance capacity. Because endurance capacity can be a critical aspect limiting the ability of A. cristatellus to escape a predatory attack, pushup displays can potentially communicate an individual's ability to escape an attack and, therefore, can be categorized as honest signals. Furthermore, because pushup displays are widely used during anoline social interactions, predation pressure and sexual selection may simultaneously favour the evolution of honest communication to allow both the predator and the potential mate or male rival to assess individual quality using the same signal. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗

PubMed2000

Parental investment strategies in two species of nuthatch vary with stage-specific predation risk and reproductive effort.

Life-history theory predicts that differences in reproductive effort and residual reproductive value among species should result in differences in the level of risk that parents are willing to tolerate to themselves versus their offspring. Specifically, highly fecund and shorter-lived species are expected to place greater value in current offspring than themselves, whereas less fecund and longer-lived species are expected to place greater value in their own survival and future breeding opportunities. Here, we test the prediction that parental investment decisions are correlated with life histories by comparing risk-taking behaviour in two species of nuthatch that differ in reproductive effort: the white-breasted nuthatch, Sitta carolinensis (more fecund, lower survival) and the red-breasted nuthatch, S. canadensis (less fecund, higher survival). We experimentally manipulated stage-specific predation risk by presenting models of an adult predator (hawk) and an egg predator (wren) and measured the willingness of males to feed incubating females on the nest. We found that both species of nuthatch responded to predators by increasing the length of time between visits and aborting more visits to the nest. However, as predicted by their life histories, S. carolinensis displayed a significantly stronger response to the egg predator, whereas S. canadensis responded more strongly to the adult predator. Thus, species can differ in their willingness to tolerate risk to themselves and their young, and such differences appear to be related to differences in investment in current reproduction and the probability of future survival. Copyright 2000 The Association for the Study of Animal Behaviour.

Journal Article↗

PubMed2000

Diet of a polyphagous arthropod predator affects refuge seeking of its thrips prey.

Antipredator behaviour of prey costs time and energy, at the expense of other activities. However, not all predators are equally dangerous to all prey; some may have switched to feeding on another prey species, making them effectively harmless. To minimize costs, prey should therefore invest in antipredator behaviour only when dangerous predators are around. To distinguish these from harmless predators, prey may use cues related to predation on conspecifics, such as odours released by a predator that has recently eaten conspecific prey or alarm pheromones released by attacked prey. We studied refuge use by a herbivorous/omnivorous thrips, Frankliniella occidentalis, in response to odours associated with a generalist predatory bug, Orius laevigatus, fed either with conspecific thrips or with other prey. The refuge used by thrips larvae is the web produced by its competitor, the two-spotted spider mite, Tetranychus urticae, where thrips larvae experience lower predation risk because the predatory bug is hindered by the web. Thrips larvae moved into this refuge when odours associated with predatory bugs that had previously fed on thrips were present, whereas odours from predatory bugs that had fed on other prey had less effect. We discuss the consequences of this antipredator behaviour for population dynamics. Copyright 2000 The Association for the Study of Animal Behaviour.

Journal Article↗

PubMed1998

Pattern Formation and the Spatial Scale of Interaction between Predators and Their Prey.

We study interactions of predators and prey that are characterized by a scale difference in their use of space. Prey are assumed to occupy patches, forming a metapopulation with low migration among patches. Predators are homogeneously distributed over these patches, due to broad-scale foraging behavior or long-range juvenile dispersal. The predator population thus exerts a globally uniform predation pressure on the prey subpopulations. Under these conditions a nonlinear predator functional response depending on local prey density leads to multiple equilibria that can occur for the same parameter values. These equilibria differ in the fraction of prey patches that are (nearly) empty. Equilibria with a larger fraction of empty prey patches are more stable. The system tends to approach equilibria with a sufficiently high number of empty prey patches, so that local and global population dynamics are stable. If unstable dynamics are observed at all, the fluctuations in local prey density exhibit predictable characteristics. Our main conclusion is that a nonlinear functional response of the predator to local prey density can induce the formation of static patterns in prey density and, hence, lead to stable local and global dynamics. It is shown that these results are sufficiently general to carry over to situations in which prey migration between patches does occur or the spatial domain occupied by the prey population is continuous instead of subdivided into patches. Copyright 1998 Academic Press.

Journal Article↗

PubMed1992

Differential sensitivity of Dugesia dorotocephala and Cheumatopsyche pettiti to water acidification: ecological implication for predator-prey interactions.

The initial hypothesis that predation pressure should decrease with decreasing pH in aquatic macrobenthic communities if predatory invertebrates are more sensitive to water acidification than prey invertebrates is tested. Short-term toxicity bioassays were conducted in soft water (average value of total hardness 38.0 mg CaCO3/L) to determine the differential sensitivity of the predator, Dugesia dorotocephala (Turbellaria, Tricladida), and the prey, larvae of Cheumatopsyche pettiti (Insecta, Trichoptera), to low pH. Test pH solutions were prepared with sulfuric acid (H2SO4). Test species were also exposed to high concentrations of sulfate ion (95 mg SO4 =/L for D. dorotocephala and 340 mg SO4 =/L for C. pettiti) as sulfate toxicity controls, using potassium sulfate (K2SO4). No mortality was observed during these toxicity controls, indicating that toxic effects generated by low pH were fundamentally due to H+ ions. The 72 and 96-h LC50s (as pH values) and their 95% confidence limits were 4.88 (4.72-5.05) and 5.04 (4.89-5.21) for D. dorotocephala, and 3.25 (3.00-3.51) and 3.48 (3.24-3.73) for C. pettiti. Net-spinning caddis-fly larvae migrated from their retreat nets and protruded their anal papillae before dying. After short-term bioassays, predation-pressure laboratory experiments were performed for 6 days. The cumulative mortality of C. pettiti by predation of D. dorotocephala decreased with decreasing sublethal pH values. The average predation rates at mean pH values of 7.7, 7.7, 6.6, 6.5, 6.2 and 6.0 were 2.5, 2.0, 1.33, 1.17, 0.67 and 0.33 larvae/day, respectively. The major biotic factor affecting predation pressure appears to be the reduction in the physiological activity of triclads at low pH.(ABSTRACT TRUNCATED AT 250 WORDS)

Acids↗

PubMed1987

A mathematical model with young predation.

We generalize the model of [21] in which the author considered a predator-prey system with predators eating only the young ones (or eggs) of the prey species. The prime assumption of the present paper is that the birth rate (per unit individual per unit time) of predators depends not only on the current prey egg-level but also on all previous prey egg-levels. It is seen that under this assumption an otherwise stable system may be stable as well as unstable leading to the conclusion that young predation with time delay is less stable than without it. Finally for the model of [21] we prove a result which shows that large predation rates help in the co-existence of both predator and prey species.

Aging↗

PubMed2004

Predation pattern and phylogenetic analysis of Bdellovibrionaceae from the Great Salt Lake, Utah.

The Bdellovibrionaceae are predatory, intraperiplasmic bacteria that prey upon a variety of Gram-negative bacteria. The prey susceptibility pattern is frequently used to characterize new isolates. The objective in this study was to isolate and characterize predators from the Great Salt Lake (GSL) by prey susceptibility testing. To recover the predators, water samples were inoculated into an enrichment medium with Vibrio parahaemolyticus as prey. After several days of incubation, the predators were isolated, pure DNA was extracted, and partial 16S rDNA gene was sequenced. Water samples were also plated for isolation of heterotrophic bacteria. The susceptibility of bacterial isolates from the lake and other sources to each predator isolate was determined. The results revealed that there are predators in the GSL, and they preferentially prey on bacteria from the lake. This is the first report of the isolation of Bdellovibrionaceae from GSL and the predators showing preferences for bacteria from the same habitat.

Bdellovibrio↗

PubMed2001

From chaos to chaos. An analysis of a discrete age-structured prey-predator model.

Discrete age-structured density-dependent one-population models and discrete age-structured density-dependent prey-predator models are considered. Regarding the former, we present formal proofs of the nature of bifurcations involved as well as presenting some new results about the dynamics in unstable and chaotic parameter regions. Regarding the latter, we show that increased predation may act both as a stabilizing and a destabilizing effect. Moreover, we find that possible periodic dynamics of low period, either exact or approximate, may not be generated by the predator, but it may be generated by the prey. Finally, what is most interesting from the biological point of view, is that given that the prey, in absence of the predator, exhibits periodic or almost periodic oscillations of low period, then the introduction of the predator does not alter this periodicity in any substantial way until the stabilizing effect of increased predation becomes so strong that a stable equilibrium is achieved.

Aging↗

PubMed2003

Herbivore host plant selection: whitefly learns to avoid host plants that harbour predators of her offspring.

Evidence is accumulating that herbivorous arthropods do not simply select host plants based on their quality, but also on the predation risk associated with different host plants. It has been suggested that herbivores exclude plant species with high predation risk from their host range. This assumes a constant, predictable predation risk as well as a rather static behaviour on the part of the herbivore; plants are ignored irrespective of the actual predation risk. We show that adult females of a small herbivore, the whitefly Bemisia tabaci, can learn to avoid plants with predatory mites that attack only juvenile whiteflies, while they accept host plants of the same species without predators. Predatory mites disperse more slowly than whiteflies; they cannot fly and walk from plant to plant. Hence, by avoiding plants with predators, the whiteflies create a temporary refuge for their offspring. We suggest that the experience of arthropod herbivores with risks associated with host plants plays an important role in their host plant selection.

Adaptation, Physiological↗

PubMed2003

Color change and color-dependent behavior in response to predation risk in the salamander sister species Ambystoma barbouri and Ambystoma texanum.

Although many organisms show multiple types of trait responses to predation risk (e.g., shifts in behavior, morphology, color, chemistry or life history), relatively few studies have examined how prey integrate these multiple responses. We studied the joint expression of color and behavioral responses to predation risk in two sister species of salamander larvae that live in habitats with different selection pressures. We examined responses to predation risk in three situations that differed in availability of refuge and substrate color heterogeneity, and thus availability of behavioral options for reducing risk. Relative to Ambystoma texanum, A. barbouri larvae were darker in color and showed a greater range of color change. With no variation in background color or refuge available, both species exhibited color change to better match the available background. The degree of color change showed by both species, however, did not depend on predation risk. Given the option to choose between light and dark substrates, A. texanum exhibited behavioral background matching (i.e., they preferred substrates that matched their own body color), while A. barbouri's substrate preferences did not depend on their initial body color. Instead, A. barbouri responded to risk by showing a strong preference for dark substrates, followed by a change to a darker body color. With refuge available, A. texanum's refuge use was color-dependent; larvae that were well camouflaged spent less time in refuge. In contrast, A. barbouri showed strong refuge use in response to risk, regardless of their body color. Overall, these results reflect how conflicting selection pressures (predation risk, habitat ephemerality, risk of UV damage) and species differences in mean color and ability to change color can govern the interplay of complementary and compensatory behavioral and color responses to predation risk.

Adaptation, Physiological↗

PubMed2003

Gender- and sequence-dependent predation within group colonizers of defended plants: a constraint on cheating among bark beetles?

Bark beetles engage in one of the most pronounced examples of group procurement of defended plants. Their aggregation pheromones attract both sexes and are essential to overcome constitutive and rapidly inducible lethal defenses. The relative benefits to senders versus receivers of these signals are only partly understood. Because the initial stage of host entry can be hazardous, there may be benefit to a cheating strategy, whose practitioners respond to pheromones but do not engage in host searching. Several disadvantages to cheating have been proposed, but the role of predators has not been considered. Predators exploit bark beetle pheromones to locate prey, accumulate at the breeding site, and consume adult bark beetles before they enter the tree. Preliminary experiments quantified arrival patterns in the field. We used a laboratory assay to investigate relative predation on pioneers (those that initially select and enter hosts) and responders (those that arrive at a host in response to pheromones) during host colonization. Our model system utilized the pine engraver, Ips pini, which exhibits male harem polygamy. We allowed male I. pini to colonize host tissue and added females 1 day later. Also 1 day later, we variably added additional males and predacious checkered beetles, Thanasimus dubius. These treatments included two densities of males and three densities of predators that were selected to emulate field conditions. Responding males experienced higher predation than pioneers. T. dubius ate more males than females, independent of the presence or absence of responding males. T. dubius affected the distribution of females per male, although the number of females that survived to construct ovipositional galleries was constant. We discuss the viability of cheating, implications for biological control, and predator-prey coevolution in this cooperative, group-colonizing herbivore.

Adaptation, Physiological↗

PubMed2004

Threat of predation negates density effects in larval gray treefrogs.

While density-dependence is central to most theory regarding population regulation and community structure, specific mechanisms that modify its effects in the absence of changes in consumer-resources ratios (e.g., thinning) are not well understood. To determine if the threat of predation alters effects of density, we investigated the interaction between density of larval treefrogs (Hyla chrysoscelis) and the non-lethal presence of a predatory fish (Enneacanthus obesus). A significant density by fish interaction was consistent for all response variables (e.g., larval survivorship, mass, and time to metamorphosis) driven by a complete lack of density effects in the presence of predators, while predator-free tanks showed classic density-dependent responses. Given that female H. chrysoscelis strongly avoid ovipositing in ponds containing fish, certain larval adaptations are apparently not constrained by maternal behavior and suggest redundancy in response to predators. Our data suggest that non-lethal effects of predators can determine larval performance irrespective of larval density, and that the non-lethal effects of predators can be strong whether lethal effects are strong or weak.

Animals↗

PubMed2004

Differential seed and seedling predation by crabs: impacts on tropical coastal forest composition.

Recently, the importance of seed predation by crabs on mangrove species distributions and densities has been established by several studies. In a tropical coastal terrestrial forest in Costa Rica, we investigated the relative importance of predation by land crabs, Gecarcinus quadratus, and hermit crabs, Coenobita compressus, on measured forest composition through a series of seed removal and seedling establishment experiments. We also used natural light-gaps and adjacent non-gap sites to test how canopy cover affects crab predation (seed removal) and seedling establishment. We found fewer tree species (S=18) and lower densities (seedlings, saplings, and adults) in the coastal zone within 100 m of coastline, than in the inland zone (S=59). Land crab densities were higher in the coastal zone (3.03+/-1.44 crabs m(-2)) than in the inland zone (0.76+/-0.78 crabs m(-2)), and hermit crabs were not present in the inland zone. Seed removal and seedling mortality also were higher in the coastal zone than in the inland zone, and in the open controls than in the crab exclosures. Mortality of seeds and seedlings was two to six times higher in the controls than exclosures for four of the five experiments. Crabs preferred seeds and younger seedlings over older seedlings but showed no species preferences in the seed (Anacardium excelsum, Enterolobium cyclocarpum, and Terminalia oblonga) and seedling (Pachira quinata and E. cyclocarpum) stages. We conclude that the observed differences in tree densities were caused by differential crab predation pressure along the coastal gradient, while the differences in species composition were due to predator escape (satiation) by seed quantity. Canopy cover did not affect seed removal rates, but did affect seedling survival with higher mortality in the non-gap versus gap environments. In summary, crab predation of seeds and seedlings, and secondarily canopy cover, are important factors affecting tree establishment in terrestrial coastal forests.

Animals↗

PubMed2005

Does predation contribute to tree diversity?

Seed and seedling predation may differentially affect competitively superior tree species to increase the relative recruitment success of poor competitors and contribute to the coexistence of tree species. We examined the effect of seed and seedling predation on the seedling recruitment of three tree species, Acer rubrum (red maple), Liriodendron tulipifera (yellow poplar), and Quercus rubra (northern red oak), over three years by manipulating seed and seedling exposure to predators under contrasting microsite conditions of shrub cover, leaf litter, and overstory canopy. Species rankings of seedling emergence were constant across microsites, regardless of exposure to seed predators, but varied across years. A. rubrum had the highest emergence probabilities across microsites in 1997, but Q. rubra had the highest emergence probabilities in 1999. Predators decreased seedling survival uniformly across species, but did not affect relative growth rates (RGRs). Q. rubra had the highest seedling survivorship across microsites, while L. tulipifera had the highest RGRs. Our results suggest that annual variability in recruitment success contributes more to seedling diversity than differential predation across microsites. We synthesized our results from separate seedling emergence and survival experiments to project seedling bank composition. With equal fecundity assumed across species, Q. rubra dominated the seedling bank, capturing 90% of the regeneration sites on average, followed by A. rubrum (8% of sites) and L. tulipifera (2% of sites). When seed abundance was weighted by species-specific fecundity, seedling bank composition was more diverse; L. tulipifera captured 62% of the regeneration sites, followed by A. rubrum (21% of sites) and Q. rubra (17% of sites). Tradeoffs between seedling performance and fecundity may promote the diversity of seedling regeneration by increasing the probability of inferior competitors capturing regeneration sites.

Ecosystem↗

PubMed2005

Putting prey back together again: integrating predator-induced behavior, morphology, and life history.

The last decade has seen an explosion in the number of studies exploring predator-induced plasticity. Recently, there has been a call for more comprehensive approaches that can identify functional relationships between traits, constraints on phenotypic responses, and the cost and benefits of alternative phenotypes. In this study, we exposed Helisoma trivolvis, a freshwater snail, to a factorial combination of three resource levels and five predator environments (no predator, one or two water bugs, and one or two crayfish) and examined ten traits including behavior, morphology, and life history. Each predator induced a unique suite of behavioral and morphological responses. Snails increased near-surface habitat use with crayfish but not with water bugs. Further, crayfish induced narrow and high shells whereas water bugs induced wide shells and wide apertures. In terms of life history, both predators induced delayed reproduction and greater mass at reproduction. However, crayfish induced a greater delay in reproduction that resulted in reduced fecundity whereas water bugs did not induce differences in fecundity. Resource levels impacted the morphology of H. trivolvis; snails reared with greater resource levels produced higher shells, narrower shells, and wider apertures. Resource levels also impacted snail life history; lower resources caused longer times to reproduction and reduced fecundity. Based on an analysis of phenotypic correlations, the morphological responses to each predator most likely represent phenotypic trade-offs. Snails could either produce invasion-resistant shells for defense against water bugs or crush-resistant shells for defense against crayfish, but not both. Our use of a comprehensive approach to examine the responses of H. trivolvis has provided important information regarding the complexity of phenotypic responses to different environments, the patterns of phenotypic integration across environments, and the potential costs and benefits associated with plastic traits.

Analysis of Variance↗

PubMed2005

Rodent seed predation promotes differential recruitment among bird-dispersed trees in temperate secondary forests.

We investigated the role of seed predation by rodents in the recruitment of the fleshy-fruited trees Taxus baccata, Ilex aquifolium and Crataegus monogyna in temperate secondary forests in NW Spain. We measured the densities of dispersed seeds, early emerged seedlings, established recruits and adults, at four sites over a period of 2 years. Seed predation among species was compared by seed removal experiments and analysis of rodent larder-hoards. The three species differed markedly in local regeneration patterns. The rank order in the seed rain following decreasing seed density was Ilex, Taxus and Crataegus. However, Crataegus established 3.3 times more seedlings than Taxus. For all species, there was a positive linear relationship between the density of emerged seedlings and seed density, suggesting that recruitment was seed- rather than microsite-limited. A consistent pattern of seed selection among species was exerted by rodents, which preferred Taxus and, secondarily, Ilex seeds to Crataegus seeds. Predation ranking was the inverse of that of seed protection against predators, measured as the mass of woody coat per mass unit of the edible fraction. Recruitment potential, evaluated as the ratio of seedlings to seeds, was negatively related to seed predation, with the rank order Crataegus > Ilex > Taxus. The selective early recruitment limitation exerted by predation may have a demographic effect in the long term, as judged by the positive relationship between early seedling emergence and the density of established recruits. By modulating the pre-emptive competition for seed safe sites, rodents may preclude the progressive exclusion of species that produce low numbers of seeds (i.e. Crataegus) by those dominant in seed number (i.e. Ilex, Taxus), or at least foster the evenness for site occupation among seedlings of different species.

Animals↗

PubMed2006

Spatial heterogeneity in predator activity, nest survivorship, and nest-site selection in two forest thrushes.

The ability of prey to find and use predator-free space has far-reaching consequences for their persistence and interactions with their predators. We tested whether nest survivorship of the ground-nesting veery (Catharus fuscescens) and shrub-nesting wood thrush (Hylocichla mustelina) was related to the local absence of a major nest predator, the white-footed mouse (Peromyscus leucopus). Mouse-free space was defined by trap stations that failed to trap a mouse during the avian breeding season (approximately May through July). In addition, mouse activity was quantified at individual trap stations based on the number of captures during the same period (six 2.25-ha trapping grids, each containing 121 trap stations trapped repeatedly throughout the summer between 1998 and 2002.) Annual mouse-free space was correlated with other measures of mouse activity based on trapping data. Both mouse-free space and activity metrics were significantly related to annual rates of nest predation (i.e., nest daily mortality rate) in veery but not wood thrush. Likewise, mouse-free space and mouse activity within the nest neighborhood (approximately 30x30 m2 surrounding each nest) was significantly related to nest survivorship in veery but not wood thrush. More trap stations had consistently greater (hotspots) and lesser (coldspots) mouse activity than expected by chance, and veeries were significantly more likely to nest near stations that had below the grid-average trapping success. Our study thus documented significant spatial variability in predator activity and its relationship to nest predation and nest-site selection in a ground-nesting songbird.

Animals↗