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PubMed2004

Effects of dung and seed size on secondary dispersal, seed predation, and seedling establishment of rain forest trees.

Seeds dispersed by tropical, arboreal mammals are usually deposited singly and without dung or in clumps of fecal material. After dispersal through defecation by mammals, most seeds are secondarily dispersed by dung beetles or consumed by rodents. These post-dispersal, plant-animal interactions are likely to interact themselves, as seeds buried by dung beetles are less likely to be found by rodents than unburied seeds. In a series of three experiments with seeds of 15 species in central Amazonia (Brazil), we determined (1) how presence and amount of dung associated with seeds influences long-term seed fate and seedling establishment, (2) how deeply dung beetles bury seeds and how burial depth affects seedling establishment, and (3) how seed size affects the interaction between seeds, dung beetles, and rodents. Our overall goal was to understand how post-dispersal plant-animal interactions determine the link between primary seed dispersal and seedling establishment. On average, 43% of seeds surrounded by dung were buried by dung beetles, compared to 0% of seeds not surrounded by dung ( n=2,156). Seeds in dung, however, tended to be more prone than bare seeds to predation by rodents. Of seeds in dung, probability of burial was negatively related to seed size and positively related to amount of dung. Burial of seeds decreased the probability of seed predation by rodents three-fold, and increased the probability of seedling establishment two-fold. Mean burial depth was 4 cm (0.5-20 cm) and was not related to seed size, contrary to previous studies. Probability of seedling establishment was negatively correlated with burial depth and not related to seed size at 5 or 10 cm depths. These results illustrate a complex web of interactions among dung beetles, rodents, and dispersed seeds. These interactions affect the probability of seedling establishment and are themselves strongly tied to how seeds are deposited by primary dispersers. More generally, our results emphasize the importance of looking beyond a single type of plant-animal interaction (e.g., seed dispersal or seed predation) to incorporate potential effects of interacting interactions.

Animals↗
PubMed2004

Potent cytotoxins produced by a microbial symbiont protect host larvae from predation.

Larvae of the sessile marine invertebrate Bugula neritina (Bryozoa) are protected by an effective chemical defense. From the larvae, we isolated three bryostatin-class macrocyclic polyketides, including the novel bryostatin 20, that deterred feeding by a common planktivorous fish that co-occurs with B. neritina. A unique bacterial symbiont of B. neritina, Endobugula sertula, was hypothesized as the putative source of the bryostatins. We show that: (1) bryostatins are concentrated in B. neritina larvae and protect them against predation by fish; (2) the adults are not defended by bryostatins; and (3) E. sertula produces bryostatins. This study represents the first example from the marine environment of a microbial symbiont producing an anti-predator defense for its host and, in this case, specifically for the host's larval stage, which is exceptionally vulnerable to predators.

Adaptation, Physiological↗
PubMed2004

Selective predation for low body condition at the larval-juvenile transition of a coral reef fish.

Mortality is known to be high during the transition from larval to juvenile life stages in organisms that have complex life histories. We are only just beginning to understand the processes that influence which individuals survive this period of high mortality, and which traits may be beneficial. Here we document a field experiment that examines the selectivity of predation immediately following settlement to the juvenile population in a common tropical fish, Pomacentrus amboinensis (Pomacentridae). Newly metamorphosed fish were tagged and randomly placed onto replicated patches of natural habitat cleared of resident fishes. After exposure to transient predators for 3 days, fish were recollected and the attributes of survivors from patch reefs that sustained high mortality were compared to individuals from patch reefs that experienced low mortality. Seven characteristics of individuals, which were indicative of previous and present body condition, were compared between groups. Predation was found to be selective for fish that grew slowly in the latter third of their larval phase, were low in total lipids, and had a high standardized weight (Fulton's K). Traits developed in the larval phase can strongly influence the survival of individuals over this critical transition period for organisms with complex life cycles.

Adaptation, Physiological↗
PubMed2005

Relative importance of fertiliser addition to plants and exclusion of predators for aphid growth in the field.

Herbivore dynamics and community structure are influenced both by plant quality and the actions of natural enemies. A factorial experiment manipulating both higher and lower trophic levels was designed to explore the determinants of colony growth of the aphid Aphis jacobaeae, a specialist herbivore on ragwort Senecio jacobaea. Potential plant quality was manipulated by regular addition of NPK-fertiliser and predator pressure was reduced by interception traps; the experiment was carried out at two sites. The size and persistence of aphid colonies were measured. Fertiliser addition affected plant growth in only one site, but never had a measurable effect on aphid colony growth. In both habitats the action of insect predators dominated, imposing strong and negative effects on aphid colony performance. Ants were left unmanipulated in both sites and their performance on the aphid colonies did not significantly differ between sites or between treatments. Our results suggest that, at least for aphid herbivores on S. jacobaea, the action of generalist insect predators appears to be the dominant factor affecting colony performance and can under certain conditions even improve plant productivity.

Analysis of Variance↗
PubMed2005

Experimental manipulation of predation risk and food quality: effect on grazing behaviour in a central-place foraging herbivore.

The relative importance of predation risk and food quality on spatial grazing pressure and activity patterns was tested in a central-place foraging herbivore: the European rabbit. Rabbits grazed less with increasing distance from their burrows into adjacent grassland, thereby creating a gradient of increasing vegetation height and plant biomass and decreasing plant nutrient concentration. When nitrogen concentration was experimentally increased by 150% through fertilizing and mowing, rabbits visited these plots four times more frequently than the untreated control plots. Addition of predator scent (mink pellets) did not result in different patch use by rabbits. The combined addition of fertilizer and mink pellets had the same effect as addition of fertilizer alone. However, the mink pellets changed the temporal activity pattern of rabbits as measured with infrared detectors. Rabbits were predominantly nocturnal but shifted their activities to the day when mink pellets were added, resulting in equal activities during night and day. We conclude that rabbits are sensitive to perceived predation risk, but that this does not influence their spatial grazing pressure. A selection for the highest food quality on the other hand can explain the observed natural rabbit grazing gradient. Food quality was highest close to the burrows, therefore rabbits selecting for high quality food should forage most intensely close to the burrows and only move further away for higher quality items or when the vegetation close to their burrows is depleted. Through intensive grazing close to the burrows rabbits facilitated for themselves either through stimulating fresh protein rich re-growth or the return of nutrients through faeces or both. This is in contrast with central-place foraging theory where intense feeding close to the burrow is assumed to lead to reduced food resources.

Animals↗
PubMed2006

Predator avoidance in phytophagous mites: response to present danger depends on alternative host quality.

We studied whether volatiles released by putative host plants affect the antipredator response of an herbivorous mite, Tetranychus urticae, when the patch was invaded by Phytoseiulus persimilis. Tetranychus urticae laid a lower number of eggs on tomato leaves than on lima bean leaves, suggesting that lima bean is a preferred host food source for T. urticae. In addition, T. urticae preferred lima bean plant volatiles to tomato plant volatiles in a Y-tube olfactometer test. To investigate the antipredator response of T. urticae, we examined the migration of T. urticae from a lima bean leaf disc to a neighbouring leaf disc (either a tomato or lima bean leaf disc) when ten predators were introduced into the original lima bean disc. A Parafilm bridge allowed for migration between the leaf discs. No migrations occurred between leaf discs when there were no predators introduced to the original leaf disc. However, when predators were introduced migrations did occur. When the neighbouring leaf disc was upwind of the original disc, the migration rate of the mite from original lima bean leaf disc to a neighbouring tomato leaf disc was significantly lower than that to a neighbouring lima bean leaf disc. By contrast, when the neighbouring leaf disc was downwind of the original leaf disc, there was no difference in the migration rates between lima bean leaf discs and tomato leaf discs. The number of T. urticae killed by P. persimilis for each treatment was not different, and this clearly shows that the danger was the same in all treatments regardless of the decision made by T. urticae. From these results, we conclude that T. urticae change their antipredator response by evaluating the difference in host plant volatiles in the patch they inhabit.

Analysis of Variance↗
PubMed2005

Lethal and sub-lethal selectivity of fenbutatin oxide and sulfur to the predator Iphiseiodes zuluagai (Acari: Phytoseiidae) and its prey, Oligonychus ilicis (Acari: Tetranychidae), in Brazilian coffee plantations.

Lethal concentration (LC) has been widely used to estimate pesticide toxicity. However, it does not consider the sub-lethal effects. Therefore we included the instantaneous rate of increase in association with LC to estimate population-level effects of the acaricides fenbutatin oxide and sulfur on the predator Iphiseiodes zuluagai and its prey, the phytophagous southern red mite, Oligonychus ilicis. The predator was 32.84x and 17.20x more tolerant to fenbutatin oxide and sulfur, respectively, than its prey, based on LC50 estimates obtained from acute concentration-mortality bioassays. The instantaneous rate of population growth in both mite species decreased with increasing acaricide concentration. Both acaricides provided effective control of O. ilicis at their recommended concentrations, but sulfur drastically compromised the predator populations quickly leading them to extinction due to the low reproductive potential of this species compared with its prey.

Acari↗
PubMed1990

A model of predator-prey dynamics as modified by the action of a parasite.

A predator-prey population is described in which the prey population may be either a secondary host or a primary host to a parasite, but the predator is always a primary host. Those prey that have been invaded by the parasite have their behavior modified so as to make them more susceptible to predation. The model is described by a system of three autonomous ordinary differential equations. Conditions for persistence of all populations are given in the case that both populations are primary hosts. A brief discussion of the stability of the interior equilibrium is given.

Animals↗
PubMed1988

Brief exposure to a natural predator, the short-tailed weasel, induces benzodiazepine-sensitive analgesia in white-footed mice.

Exposure to a natural predator, the short-tailed weasel, Mustela erminea, elicited significant increases in the nociceptive responses of wild male white-footed mice, Peromyscus leucopus. A short (30 sec), ecologically relevant, nonvisual exposure to a weasel elicited a relatively brief (15 min) analgesia that was insensitive to the opiate antagonist, naloxone (1.0 mg/kg), and was blocked by either pre- or post-exposure injections of the benzodiazepine antagonist, Ro15-1788 (10 mg/kg), or agonist, diazepam (4.0 mg/kg). A 5 min exposure to the weasel elicited an analgesic response of longer duration (15-30 min) that was sensitive to both naloxone and the benzodiazepine agonist and antagonist. A 15 min exposure to the weasel induced a higher amplitude analgesia that was of relatively long duration (45 min), blocked by naloxone, and insensitive to the benzodiazepine manipulations. Exposures of 5 and 15 min to a nonpredator, the European rabbit, Oryctolagus cuniculus, elicited low amplitude, naloxone-reversible analgesic responses that were unaffected by the benzodiazepine manipulations. Thirty-sec exposures to the rabbit had no significant effects on the nociceptive response of the rabbit. These results indicate that a brief, ecologically appropriate, exposure to a predator elicits a benzodiazepine-mediated analgesia while a more prolonged exposure to a predator induces opioid-mediated analgesia. These results show that the opioid and nonopioid distinction between the effects of long- and short-term laboratory stresses is also evident with a natural, ecologically relevant, stressor.

Analgesia↗
PubMed1985

The effect of long time delays in predator-prey systems.

Past studies have indicated that a time delay longer than the natural period of a system will generally cause instability; however here it is shown that including long maturational time delays in a general predator-prey model need not have this effect. In each of the three cases studied (a predator delay, a prey delay, and both), local stability can persevere despite the presence of arbitrarily long time delays. This perseverence depends upon an interaction between delayed and undelayed features of the model. Delayed processes always act to destabilize the model. For example, prey self-regulation, usually a source of stability, becomes destabilizing if subject to a long delay. However, the effect of such a delay is offset by undelayed regulatory processes, such as a stabilizing functional response. In addition, the adverse effects of delayed predator recruitment can be reduced by the nonreproductive component of the numerical response, a feature not usually involved in determining stability. Finally, it is shown that long time delays are not necessarily more disruptive than short delays; it cannot be assumed that lengthening a time delay progressively reduces stability.

Aging↗
PubMed1991

Variation in the appearance of guppy color patterns to guppies and their predators under different visual conditions.

Color patterns of natural populations of guppies (Poecilia reticulata) are a compromise between sexual selection and predation avoidance. Field data on ambient light spectra, water transmission spectra, courtship and attack distances, and cone pigments of guppies and their predators were used to calculate measures of conspicuousness of guppies under various combinations of visual conditions and vision. The results suggest that color patterns are relatively more conspicuous to guppies at the times and places of courtship and relatively less conspicuous at the times and places of maximum predator risk. Some implications to the evolution of vision, visual communication and behavior are discussed.

Animals↗
PubMed1991

Predation on livestock ticks by chickens.

Chickens were shown to be natural predators of ticks. Rhipicephalus appendiculatus were recovered in large numbers from the crops and gizzards of chickens which had scavenged for 30 min-1 h among tick-infested cattle. Other ticks recovered were Amblyomma variegatum and Boophilus decoloratus. The numbers of ticks recovered ranged from 3 to 331, with an average of 81 per chicken. Cattle facilitated the predation of ticks by certain behavioural actions. Chickens also picked up both engorged and unengorged ticks seeded on vegetation, but unengorged ticks were preferred. The possibility of tick predation by chickens forming a viable biological control component in an integrated tick management system in Africa is discussed.

Animals↗
PubMed1996

Antennal response and field attraction of the predator Elatophilus hebraicus (Hemiptera: Anthocoridae) to sex pheromones and analogues of three Matsucoccus spp. (Homoptera: Matsucoccidae).

The predator Elatophilus hebraicus is closely associated with its prey, the pine bast scale, Matsucoccus josephi, and utilizes the M. josephi sex pheromone as a kairomone. Kairomonal activity of E. hebraicus was studied by GC-EAD and field bioassays. The sex pheromone of M. josephi [2E,5R,6E,8E)-5,7-dimethyl-2,6,8-decatrien-4-one [(R)-E-M.j.] elicited a strong EAD response and attracted large numbers of the predator. The sex pheromone of two allopatric Matsucoccus spp., Matsucoccus feytaudi, (3S,7R,8E,10E)-3,7,9-trimethyl-8,10-dodecadien-6-one [(S,R)-E-M.f.] and Matcucossus matsumurae, (2E, 4E,6R,10R)-4,6,10,12-tetramethyl-2,4-tridecadien-7-one [(R,R)-E-M.m.], were also EAD-active and attracted significant numbers of E. hebraicus in the forest. Increasing the lure load of (S,R)-E-M.f. and (R,R)-E-M.m., in order to compensate for their lower volatility relative to (R)-E-M.j., resulted in similar attraction of E. hebraicus to each of the three pheromones. Other Matsucoccus pheromone stereoisomers displayed no behavioral activity. There was a significant difference in the activity of sex pheromone analogues, (6E/Z,8E)-5,7-dimethyl-6,8-decadien-4-one (52% E + 48% Z, ANLG 1) and (6E/Z,8E)-2,4,6-trimethyl- 1,6,8-nonatrien-3-one (60% E + 40% Z, ANLG 2). The (E) isomer of ANLG 1 evoked a strong EAD response from E. hebraicus and the mixture of E/Z ANLG 1 attracted the predator in moderate numbers, whereas ANLG 2 was inactive both in EAD and field tests. Conversely, M. josephi males were not attracted to M. feytaudi and M. matsumurae pheromones or pheromone analogues. Cross-activity of E. hebraicus to M. feytaudi and M. matsumurae pheromones may be based on structural similarity of the compounds. Alternatively, E. hebraicus may respond specifically to the pheromones of two allopatric Matsucoccus spp. If true, kairomonal attraction of E. hebraicus to these pheromones may have evolved during speciation of Matsucoccidae and may have been preserved despite the allopatry of M. josephi, M feytaudi and matsumurae.

Animals↗
PubMed2004

Balancing variable patch quality with predation risk.

Patch choice is almost always under the influence of multiple factors. Patch quality and the threat of predation are two such factors that have been shown to influence the foraging decisions of animals. In addition, aspects of patch quality may also vary with time, and consequently animals should incorporate temporal information to reduce their uncertainty about current patch conditions. The temporal weighting rule (TWR), which has been validated in previous studies, describes how animals should choose among variable options with the passage of time. In this study, we varied an additional factor, predation risk, along with certainty about patch yields in a field experiment, utilizing individually marked, free-ranging least chipmunks, Tamias minimus. We gave the animals in each condition experience at our experimental patches and then recorded patch choices a few minutes or one to 2 days later. The results show that animals combined perceived predation risk with a progressively shifting assessment of patch quality to form estimates of overall patch value as modeled by TWR. Based on the information available, the animals' patch choices were, arguably, the most adaptive choices.

Animals↗
PubMed2005

Anxiety levels and wild running susceptibility in rats: assessment with elevated plus maze test and predator odor exposure.

It is reported in the literature that nearly 20% of rats are susceptible to displays of wild running (WR) behavior when submitted to high intensity acoustic stimulation. Some characteristics of WR suggest that it can be viewed as a panic-like reaction. This work aimed to test whether WR-sensitive rats show higher levels of anxiety in elevated-plus-maze (EPM) and predator-odor exposure paradigms in comparison with WR-resistant ones. Male adult Wistar rats were submitted to two trials of acoustic stimulation (104 dB, 60 s) in order to assess WR susceptibility. Seven WR-sensitive and 15 WR-resistant rats were evaluated by the EPM test. Other 13 WR-sensitive and 18 WR-resistant animals were submitted to the predator-odor exposure test which consisted of a 10 min-session of free exploration in a specific apparatus containing two odoriferous stimuli: cotton swab imbedded with snake cloacal gland secretion or with iguana feces (control). WR-sensitive rats presented a significantly higher closed-to open-arm-entry ratio in the EPM test. All rats responded with anxiety-like behaviors to the predator odor exposure, although the WR-sensitive ones showed a marked behavioral inhibition regardless of the odor condition. We conclude that WR-sensitive rats present elevated levels of anxiety manifested by means of passive behavioral strategies.

Acoustics↗
PubMed2006

A delayed prey-predator system with parasitic infection.

This paper analyzes a prey-predator system in which some members of the prey population and all predators are subjected to infection by a parasite. The predator functional response is a function of a weighted sum of prey abundances. Persistence and extinction criteria are derived. The stability of the interior equilibrium point is discussed. The role of delay is also addressed. Lastly the results are verified through computer simulation. Numerical simulation suggests that the delay has a destabilizing effect.

Animals↗
PubMedDate not supplied

Corticosterone controls the developmental emergence of fear and amygdala function to predator odors in infant rat pups.

In many altricial species, fear responses such as freezing do not emerge until sometime later in development. In infant rats, fear to natural predator odors emerges around postnatal day (PN) 10 when infant rats begin walking. The behavioral emergence of fear is correlated with two physiological events: functional emergence of the amygdala and increasing corticosterone (CORT) levels. Here, we hypothesize that increasing corticosterone levels influence amygdala activity to permit the emergence of fear expression. We assessed the relationship between fear expression (immobility similar to freezing), amygdala function (c-fos) and the level of corticosterone in pups in response to presentation of novel male odor (predator), littermate odor and no odor. CORT levels were increased in PN8 pups (no fear, normally low CORT) by exogenous CORT (3 mg/kg) and decreased in PN12 pups (express fear, CORT levels higher) through adrenalectomy and CORT replacement. Results showed that PN8 expression of fear to a predator odor and basolateral/lateral amygdala activity could be prematurely evoked with exogenous CORT, while adrenalectomy in PN12 pups prevented both fear expression and amygdala activation. These results suggest that low neonatal CORT level serves to protect pups from responding to fear inducing stimuli and attenuate amygdala activation. This suggests that alteration of the neonatal CORT system by environmental insults such as alcohol, stress and illegal drugs, may also alter the neonatal fear system and its underlying neural control.

Amygdala↗
PubMed2006

Direct effects of snowdrop lectin (GNA) on larvae of three aphid predators and fate of GNA after ingestion.

Plants genetically modified to express Galanthus nivalis agglutinin (GNA) have been found to confer partial resistance to homopteran pests. Laboratory experiments were conducted to investigate direct effects of GNA on larvae of three species of aphid predators that differ in their feeding and digestive physiology, i.e. Chrysoperla carnea, Adalia bipunctata and Coccinella septempunctata. Longevity of all three predator species was directly affected by GNA, when they were fed a sucrose solution containing 1% GNA. However, a difference in sensitivity towards GNA was observed when comparing the first and last larval stage of the three species. In vitro studies revealed that gut enzymes from none of the three species were able to break down GNA. In vivo feed-chase studies demonstrated accumulation of GNA in the larvae. After the larvae had been transferred to a diet devoid of GNA, the protein stayed present in the body of C. carnea, but decreased over time in both ladybirds. Binding studies showed that GNA binds to glycoproteins that can be found in the guts of larvae of all three predator species. Immunoassay by Western blotting of haemolymph samples only occasionally showed the presence of GNA. Fluorescence microscopy confirmed GNA accumulation in the midgut of C. carnea larvae. Implications of these findings for non-target risk assessment of GNA-transgenic crops are discussed.

Animals↗