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At least 883 records · Page 49Linked to original sources
PubMed2006

A Vibrio cholerae protease needed for killing of Caenorhabditis elegans has a role in protection from natural predator grazing.

Vibrio cholerae is the causal bacterium of the diarrheal disease cholera, and its growth and survival are thought to be curtailed by bacteriovorous predators, e.g., ciliates and flagellates. We explored Caenorhabditis elegans as a test organism after finding that V. cholerae can cause lethal infection of this nematode. By reverse genetics we identified an extracellular protease, the previously uncharacterized PrtV protein, as being necessary for killing. The killing effect is associated with the colonization of bacteria within the Caenorhabditis elegans intestine. We also show that PrtV is essential for V. cholerae in the bacterial survival from grazing by the flagellate Cafeteria roenbergensis and the ciliate Tetrahymena pyriformis. The PrtV protein appears to have an indirect role in the interaction of V. cholerae with mammalian host cells as judged from tests with tight monolayers of human intestinal epithelial cells. Our results demonstrate a key role for PrtV in V. cholerae interaction with grazing predators, and we establish Caenorhabditis elegans as a convenient organism for identification of V. cholerae factors involved in host interactions and environmental persistence.

Animals↗
PubMed1998

Paleoindian large mammal hunters on the plains of North America.

From approximately 11,200 to 8,000 years ago, the Great Plains of North America were populated by small Paleoindian hunting groups with well developed weaponry and the expertise to successfully hunt large mammals, especially mammoths and bison. Mammoths became extinct on the Plains by 11,000 years ago, and, although paleoecological conditions were worsening, their demise may have been hastened by human predation. After this, the main target of the Plains Paleoindian hunters consisted of subspecies of bison, Bison antiquus and Bison occidentalis. As bison populations gradually diminished, apparently because of worsening ecological conditions, by approximately 8,000 years ago, human subsistence was forced into a greater dependence on small animal and plant foods. Human paleoecology studies of the Paleoindian time period rely heavily on multidisciplinary efforts. Geomorphologists, botanists, soil scientists, palynologists, biologists, and other specialists aid archaeologists in data recovery and analysis, although, with few exceptions, their contributions are derived from the fringes rather than the mainstream of their disciplines.

Animals↗
PubMed2004

Demographic theory of coral reef fish populations with stochastic recruitment: comparing sources of population regulation.

The effects of three forms of density-dependent regulation were explored in model coral reef fish populations: top-down (predation), bottom-up (competition for food), and pelagic (non-reef-based mechanisms) control. We describe the demographic responses of both biomass and numbers of adult fish, predicting the mean and the variance of temporal fluctuations resulting from stochastic recruitment of juveniles. We find that top-down control acts by suppressing variability of numbers of fish, which in turn suppresses the variability of biomass. Bottom-up control has no effect on fluctuations of numbers of fish, though it strongly reduces fluctuations of biomass. Because fecundity of fish is directly linked to body mass, the regulation of biomass tightly regulates reproductive output independently of the number of individuals in the population. Finally, populations under pelagic control experience bounded fluctuations of biomass and numbers directly proportional to the bounded fluctuations of recruitment. The demographic signatures predicted from both bottom-up and pelagic control are consistent with current evidence supporting the recruitment limitation hypothesis in reef fish ecology. We propose tests to discriminate the dominant mode of density-dependent regulation using qualitative trends in time series demographic data across environmental clines.

Animals↗
PubMed2004

Coexistence of cycling and dispersing consumer species: Armstrong and McGehee in space.

Two competing consumer species may coexist using a single homogeneous resource when the more efficient consumer--the one having the lowest equilibrium resource density--has a more nonlinear functional response that generates consumer-resource cycles. We extend this model of nonequilibrium coexistence, as proposed by Armstrong and McGehee, by putting the interaction into a spatial context using two frameworks: a spatially explicit individual-based model and a spatially implicit metapopulation model. We find that Armstrong and McGehee's mechanism of coexistence can operate in a spatial context. However, individual-based simulations suggest that decreased dispersal restricts coexistence in most cases, whereas differential equation models of metapopulations suggest that a low rate of dispersal between subpopulations often increases the coexistence region. This difference arises in part because of two potentially opposing effects on coexistence due to the asynchrony in the temporal dynamics at different locations. Asynchrony implies that the less efficient species is more likely to be favored in some spatial locations at any given time, which broadens the conditions for coexistence. On the other hand, asynchrony and dispersal can also reduce the amplitude of local population cycles, which restricts coexistence. The relative influence of these two effects depends on details of the population dynamics and the representation of space. Our results also demonstrate that coexistence via the Armstrong-McGehee mechanism can occur even when there is little variation in the global densities of either the consumers or the resource, suggesting that empirical studies of the mechanisms should measure densities on several spatial scales.

Animal Migration↗
PubMed2005

Transient dynamics limit the effectiveness of keystone predation in bringing about coexistence.

We analyze the transient dynamics of simple models of keystone predation, in which a predator preferentially consumes the dominant of two (or more) competing prey species. We show that coexistence is unlikely in many systems characterized both by successful invasion of either prey species into the food web that lacks it and by a stable equilibrium with high densities of all species. Invasion of the predator-resistant consumer species often causes the resident, more vulnerable prey to crash to such low densities that extinction would occur for many realistic population sizes. Subsequent transient cycles may entail very low densities of the predator or of the initially successful invader, which may also preclude coexistence of finite populations. Factors causing particularly low minimum densities during the transient cycles include biotic limiting resources for the prey, limited resource partitioning between the prey, a highly efficient predator with relatively slow dynamics, and a vulnerable prey whose population dynamics are rapid relative to the less vulnerable prey. Under these conditions, coexistence of competing prey via keystone predation often requires that the prey's competitive or antipredator characteristics fall within very narrow ranges. Similar transient crashes are likely to occur in other food webs and food web models.

Animals↗
PubMed1996

Growth hormone increases predation exposure of rainbow trout.

The energetic state of an animal strongly influences decisions that balances feeding against predation risk. Growth hormone increases the metabolic demands, which should elevate the feeding motivation of an animal. This, in turn, may increase the willingness to risk exposure to predators during feeding. To test this hypothesis, we studied the effect of growth hormone on the behavioural response of rainbow trout (Oncorhynchus mykiss) to simulated attacks from a model heron. After attacks, growth hormone treated trout foraged closer to the water surface, resumed feeding earlier, and ate more food than did control trout. Such behaviour should increase the susceptibility to aerial predation. Thus, predation may select against high endogenous growth hormone secretion in wild fish. Furthermore, genetic manipulations to increase growth hormone levels, intended to improve growth performance in aquaculture, may result in individuals with substantially altered behavioural patterns. In light of the increasing potential for interactions between farmed and wild fish, growth hormone transgenic fish may pose a threat to wild fish populations.

Animals↗
PubMed2001

Fruit or aposematic insect? Context-dependent colour preferences in domestic chicks.

Colours are common stimuli in signalling systems. Requirements to function well as a signal sometimes conflict between different signallers, and the same colour stimulus is used to convey completely different messages to the same receiver. Fruits and aposematic insects both use red coloration as a signal, in the former case to signal profitability and in the latter case as a warning signal. In two experiments, we investigated whether the domestic chick, an omnivorous predator, differed in its unconditioned preference or avoidance of red and green stimuli depending on whether or not the stimulus was an insect. The experiments were designed as preference tests between red and green painted prey. The prey were live insects and artificial fruits (experiment 1), and, to investigate the effect of movement, live and dead insects (experiment 2). The chicks did not show any difference in pecking preference between red and green when fruit-like stimuli were used, but when the prey were insects, green prey were strongly preferred to red prey, and prey movement did not affect this bias. Thus, young chicks may recognize prey as insects and then discriminate between different prey colorations, or one type of food may elicit an unlearned colour preference-avoidance response that is absent with another type of food.

Animals↗
PubMed2006

Behavioural and hormonal responses to predation in female chacma baboons (Papio hamadryas ursinus).

In humans, bereavement is associated with an increase in glucocorticoid (GC) levels, though this increase can be mitigated by social support. We examined faecal GC levels and grooming behaviour of free-ranging female baboons to determine whether similar effects were also evident in a non-human species. Females who lost a close relative experienced a significant increase in GC levels in the weeks following their relative's death compared with the weeks before, whereas control females showed no such increase. Despite the fact that females concentrate much of their grooming on close kin, females who lost a close female relative did not experience a decrease in grooming rate and number of grooming partners; instead, both grooming rate and number of grooming partners increased after a relative's death. While the death of a close relative was clearly stressful over the short term, females appeared to compensate for this loss by broadening and strengthening their grooming networks. Perhaps as a result, females' GC levels soon returned to baseline. Even in the presence of familiar troop-mates and other relatives, females experienced a stress response when they lost specific companions, and they apparently sought to alleviate it by broadening and strengthening their social relationships.

Animals↗
PubMed2006

Food-limitation in a generalist predator.

Investigating food-limitation in generalist predators is difficult, because they can switch to alternative prey, when one of their staple prey becomes scarce. Apart from data on the dynamics of the predator population, a robust study requires: (i) a documentation of the predator's entire prey base; and (ii) an experimental or natural situation, where profitable dietary shifts are impossible, because several preferred prey species decline simultaneously. Here, we provide a detailed description of how food-supply has limited a generalist avian top predator, the northern goshawk Accipiter gentilis. In our study area, populations of several principal goshawk prey species crashed simultaneously during 1975-2000, whereas other extrinsic factors remained essentially unchanged. The breeding and non-breeding segments of the local goshawk population declined markedly, associated with a significant increase in nest failures. Brood size of successful pairs remained unaffected by changes in prey availability. Breeding recruitment ceased at a time when potential replacement birds ('floaters') were still present, providing a rare empirical demonstration of an 'acceptance threshold' in raptor territory choice. To investigate how goshawk diet changed in response to varying food-supplies, we make novel use of an analytical tool from biodiversity research-'abundance-biomass-comparison curves' (ABC curves). With increasing levels of food-stress, the dominance of principal prey species in the diet decreased, and the number of small-bodied prey species increased, as did intra-guild predation. Our finding that breeder and non-breeder segments declined in concert is unexpected. Our results carry the management implication that, in food-limited raptor populations, externally induced breeder mortality can rapidly depress population size, as losses are no longer buffered when floaters reject breeding opportunities.

Animals↗
PubMed2004

Stochastic models in population biology and their deterministic analogs.

We introduce a class of stochastic population models based on "patch dynamics." The size of the patch may be varied, and this allows one to quantify the departures of these stochastic models from various mean-field theories, which are generally valid as the patch size becomes very large. These models may be used to formulate a broad range of biological processes in both spatial and nonspatial contexts. Here, we concentrate on two-species competition. We present both a mathematical analysis of the patch model, in which we derive the precise form of the competition mean-field equations (and their first-order corrections in the nonspatial case), and simulation results. These mean-field equations differ, in some important ways, from those which are normally written down on phenomenological grounds. Our general conclusion is that mean-field theory is more robust for spatial models than for a single isolated patch. This is due to the dilution of stochastic effects in a spatial setting resulting from repeated rescue events mediated by interpatch diffusion. However, discrete effects due to modest patch sizes lead to striking deviations from mean-field theory even in a spatial setting.

Adaptation, Physiological↗
PubMed2005

Instability of defensive alliances in the predator-prey model on complex networks.

A model of six-species food web is studied in the viewpoint of spatial interaction structures. Each species has two predators and two preys, and it was previously known that the defensive alliances of three cyclically predating species self-organize in two dimensions. The alliance-breaking transition occurs as either the mutation rate is increased or interaction topology is randomized in the scheme of the Watts-Strogatz model. In the former case of temporal disorder, via the finite-size scaling analysis, the transition is clearly shown to belong to the two-dimensional Ising universality class. In contrast, the geometric or spatial randomness for the latter case yields a discontinuous phase transition. The mean-field limit of the model is analytically solved and then compared with numerical results. The dynamic universality and the temporally periodic behaviors are also discussed.

Animals↗
PubMed2002

Phenotypic lability and the evolution of predator-induced plasticity in tadpoles.

The hypothesis that predator-induced defenses in anuran larvae are maintained by divergent selection across multiple predation environments has not been fully supported by empirical results. One reason may be that traits that respond slowly to environmental variation experience a fitness cost not incorporated in the standard adaptive model, due to a time lag between detecting the state of the environment and expressing the phenotypic response. I measured the rate at which behavior and morphology of Rana temporaria tadpoles change when confronted with a switch in the predation environment at two points in development. Hatchling tadpoles that had been exposed during the egg stage to Aeshna dragonfly larvae were not phenotypically different from those exposed as eggs to predator-free conditions, and both responded similarly to post-hatching predator treatments. When 25-day-old tadpoles from treatments with and without dragonflies were subjected to a switch in the environment, their activity budgets reversed completely within 24-36 h, and their body and tail shape began changing significantly within 4 days. The behavioral response was conservative: Tadpoles switched from high-risk to predator-free treatments were slower to adjust their activity. The study confirmed that behavioral traits are relatively labile and exhibit strong plasticity, but it did not reveal such a pattern at the level of individual traits: Morphological traits that developed slowly did not show the least plasticity. Thus, I found that differences in lability of traits were useful for predicting the magnitude of plasticity only for fundamentally different kinds of characters.

Aging↗
PubMed2006

Recruitment pulses induce cannibalistic giants in Arctic char.

1. Recent theoretical studies on the population dynamic consequences of cannibalism have focused on mechanisms behind the emergence of large cannibals (giants) in size-structured populations. Theoretically, giants emerge when a strong recruiting cohort imposes competition induced mortality on stunted adults, but also provides a profitable resource for a few adults that accelerate in growth and reach giant sizes. 2. Here the effects of a recruitment pulse on the individual and population level in an allopatric Arctic char population have been studied over a 5-year period and these results were contrasted with theoretical model predictions for the conditions necessary for the emergence of cannibalistic giants. 3. The recruitment pulse had negative effects on invertebrate resource abundance, and the decrease in body condition and increase in mortality of adult char suggested that strong intercohort competition took place. 4. The frequency of cannibalism increased and a few char accelerated in growth and reached 'giant' sizes. 5. The main discrepancy between model predictions and field data was the apparently small effect the recruited cohort had on resources and adult char performance during their first summer. Instead, the effects became pronounced when the cohort was 1 year old. This mismatch between model predictions and field observations was suggested to be due to the low per capita fecundity in char and the restricted nearshore habitat use in young-of-the-year (YOY) char. 6. This study provides empirical evidence that the emergence of giants is associated with the breakthrough of a strong recruiting cohort and also suggests that the claimed stable char populations with large cannibals may instead be populations with dynamic size structure that results in intermittent breakthroughs of recruitment pulses, providing the conditions necessary for char to enter the cannibalistic niche. 7. The data suggest that increased recruit survival through restricted habitat use may destabilize dynamics and cause the emergence of giants. However, they also suggest that this does not necessarily develop into populations with bi-modal size structure in populations with low per capita fecundity and size- and density-dependent habitat use of recruiting cohorts.

Animals↗
PubMed2006

Predator-induced phenotypic plasticity in tadpoles: extension or innovation?

Phenotypic plasticity, the ability of a trait to change as a function of the environment, is central to many ideas in evolutionary biology. A special case of phenotypic plasticity observed in many organisms is mediated by their natural predators. Here, we used a predator-prey system of dragonfly larvae and tadpoles to determine if predator-mediated phenotypic plasticity provides a novel way of surviving in the presence of predators (an innovation) or if it represents a simple extension of the way noninduced tadpoles survive predation. Tadpoles of Limnodynastes peronii were raised in the presence and absence of predation, which then entered a survival experiment. Induced morphological traits, primarily tail height and tail muscle height, were found to be under selection, indicating that predator-mediated phenotypic plasticity may be adaptive. Although predator-induced animals survived better, the multivariate linear selection gradients were similar between the two tadpole groups, suggesting that predator-mediated phenotypic plasticity is an extension of existing survival strategies. In addition, nonlinear selection gradients indicated a cost of predator-induced plasticity that may limit the ability of phenotypic plasticity to enhance survival in the presence of predators.

Animals↗
PubMed2006

Prey selectivity of bacterivorous protists in different size fractions of reservoir water amended with nutrients.

An experiment designed to examine food preferences of heterotrophic nanoflagellates (HNF) grazing on bacterioplankton was performed in the freshwater Rímov reservoir (Czech Republic). Water samples were size-fractionated to obtain < 5 microm filtrate containing bacteria and HNF. To manipulate resource availability, < 5 microm treatments were incubated in dialysis bags submerged in the barrels filled with the unfiltered reservoir water amended with either orthophosphate or glucose or combination of both. We employed rRNA-targeted probes to assess HNF prey preferences by analysing bacterial prey in HNF food vacuoles compared with available bacteria. Actinobacteria (the HGC69a probe) were avoided by HNF in all treatments. Cytophaga-Flavobacterium-Bacteroidetes bacteria (the CF319a probe) were positively selected mainly in treatments in which bacteria were heavily grazed, the < 5 microm treatments, but this trend was less pronounced towards the end of the study. The members of a small subcluster of Betaproteobacteria (the R-BT065 probe) were mostly positively selected. The nutrient amendments differentially affected bacterioplankton dynamics in almost all treatments, and together with the size fractionation, altered HNF overall bacterivory as well as prey selection. Analyses of bacterivores in unfiltered treatments allowed to detect the effect of different protists on shifts in HNF selectivity observed in < 5 microm compared with unfiltered treatments.

Actinobacteria↗
PubMed2005

Nutrient-specific foraging in invertebrate predators.

Many herbivores and omnivores adjust their food selection behavior to regulate the intake of multiple nutrients. Carnivores, however, are generally assumed to optimize the rate of prey capture rather than select prey according to nutrient composition. We showed experimentally that invertebrate predators can forage selectively for protein and lipids to redress specific nutritional imbalances. This selection can take place at different stages of prey handling: The predator may select among foods of different nutritional composition, eat more of a prey if it is rich in nutrients that the predator is deficient in, or extract specific nutrients from a single prey item.

Animals↗