NATURAL RESOURCE MODELING, Issue 2 2009
JEAN M. TCHUENCHE
Abstract The study of three-species communities have become the focus of considerable attention, and because the studies of ecological communities start with their food web, we consider a tritrophic food chain model comprised of the prey, the predator, and the super-predator. The classical assumption of the domino effect is supplemented with an adaptive parameter for the predator (in the absence of prey). Thus, the model exhibits an equilibrium with the predator-top-predator steady state, which is a saddle point. Dynamical behaviors such as boundedness, existence of periodic orbits, persistence, as well as stability are analyzed. The long-term coexistence of the three interacting species is addressed, and the stability analysis of the model shows that the biologically most relevant equilibrium point is globally asymptotically stable whenever it satisfies a certain criterion. Practical implications are explored and related to real populations. [source]

Environmental Manipulation to Avoid a Unique Predator: Drinking Hole Excavation in the Agile Wallaby, Macropus agilis

ETHOLOGY, Issue 2 2007
J. Sean Doody
The simplest way of avoiding an ambush predator is to entirely avoid the habitat in which it hunts. However, this strategy requires that the prey species find alternative, risk-free sources of essential resources. Herein we describe a novel strategy used by agile wallabies (Macropus agilis) to avoid saltwater crocodile (Crocodylus porosus) predation: the creation of risk-free sites to obtain water. We studied the anti-predator behaviour of agile wallabies for 3 yr during the dry season along the Daly River, Northern Territory, Australia. Wallabies excavated holes in the sand 0.5,18.0 m from the water's edge, and preferred to drink from these holes over drinking from the river. We determined a hierarchy of preferred drinking-site options for the wallabies: non-river sites: springs, puddles, excavated holes; and river sites: sites with cover, shallow water sites and deep water sites. Drinking holes were twice as far from the water's edge in a river stretch with high crocodile density (2/km) than those in a stretch with low crocodile density (0.08/km). However, site differences could also be explained by river bank morphology. Collectively, our findings indicate that agile wallabies excavate drinking holes to avoid crocodile predation. We contend that this behaviour represents environmental manipulation specifically to alter the risk associated with obtaining a key resource. [source]

Confusion Effect in a Reptilian and a Primate Predator

ETHOLOGY, Issue 8 2000
Carsten Schradin
The confusion effect is claimed to be one benefit of group living with respect to predator avoidance: it is more difficult for predators to capture prey that is surrounded by other conspecifics than to capture an isolated individual. So far, the predictions of the confusion effect have been tested mainly in aquatic predators. As the confusion effect is seen to be a general problem for predators, terrestrial predators of two different vertebrate classes were used to test it. The prey (mealworms and black beetles, Tenebrio molitor) was harmless and had no chance of predator avoidance. Thus, confounding effects of group defence and enhanced vigilance were controlled. Both leopard geckos (Eublepharis macularius) and common marmosets (Callithrix jacchus) took longer to catch one out of several prey compared to one single prey. Leopard geckos showed more fixations (changing of head position) when confronted with 20 mealworms than when confronted with only one mealworm, thus showing indications of being ,confused'. [source]

Predator,prey interactions in river networks: comparing shrimp spatial refugia in two drainage basins

FRESHWATER BIOLOGY, Issue 3 2009
ALAN P. COVICH
Summary 1.,Analysis of drainage networks provides a framework to evaluate the densities and distributions of prey species relative to locations of their predators. Upstream migration by diadromous shrimp (Atya lanipes and Xiphocaris elongata) during their life cycle provides access to headwater refugia from fish predation, which is intense in estuaries and coastal rivers. 2.,We postulate that geomorphic barriers (such as large, steep waterfalls >3.5 m in height), can directly limit the distribution of predatory fishes and, indirectly, affect the densities of their prey (freshwater shrimps) in headwater streams. 3.,We compared densities of shrimp in pools above and below waterfalls, in four headwater tributaries in two river basins of the Luquillo Mountains of northeastern Puerto Rico. We measured shrimp densities twice a year over 8 years (1998,2005) in Prieta, Toronja, Bisley 3 and Bisley 5 streams, which differ in drainage network positions relative to steep waterfalls in Río Espíritu Santo and Río Mameyes. 4.,Predatory fishes are absent in the Prieta and Toronja pools and present in Bisely 3 and in lower Bisley 5 pools. Atya lanipes and X. elongata rarely occur in the Bisley streams where predatory fishes are present but these shrimps are abundant in Prieta and Toronja, streams lacking predatory fishes. 5.,The mean carapace length of X. elongata is longer in pools where fish are present (Bisley 3 and lower Bisley 5) than in pools lacking fish (Prieta, Toronja, Upper Bisley 5). The increased body size is primarily due to significantly longer rostrums of individuals in stream reaches with fish (below waterfall barriers) than in those reaches lacking fish (above waterfall barriers). Rostrum length may be an adaptation to avoid predation by visually feeding fishes. 6.,Atya lanipes and X. elongata distributions and densities were predicted primarily by drainage network position relative to the presence or absence of predatory fishes. High, steep waterfalls effectively impeded fish from moving upstream and created a spatial refuge. Xiphocaris elongata may rely on size refugia (longer rostrum) to minimize predation where spatial refugia are lacking. [source]

Evidence for individualistic species assembly creating convergent predator:prey ratios among pond invertebrate communities

JOURNAL OF ANIMAL ECOLOGY, Issue 2 2002
Michael J. Jeffries
summary 1,Predator,:,prey ratios are cited as examples of a community level pattern, which suggests underlying assembly rules. Consistent ratios may result from either holistic community interactions or individualistic species assembly. This study tested for evidence of holistic or individualistic explanations for the predator : prey ratios among invertebrate communities of temporary ponds. 2,Macroinvertebrate species were recorded from 30 adjacent experimental ponds, in January and early summer over 4 years. After the first 2 years either additional predatory or prey taxa were added to treatment ponds to skew the natural predator : prey ratios. Species richness and ratios were monitored for the following 2 years comparing treatment ponds subject to augmented predator or prey richness against unmanipulated control ponds. 3,The majority of species added to treatments established in their respective ponds initially creating unusually high or low predator : prey ratios. In the 2 years following manipulation the ratios in treatment and control ponds converged. The convergence resulted from the spread of the additional species across all the ponds rather than acquisition or extinction of species within treatment ponds compensating for the skewed ratios. 4,Convergent predator : prey ratios resulted from the spread of the augmented local species pool across the site rather than holistic community level adjustment within separate ponds. The results support individualistic models of community assembly as the explanation for convergent predator : prey ratios in pond habitats. [source]

Predator,prey coupling: interaction between mink Mustela vison and muskrat Ondatra zibethicus across Canada

OIKOS, Issue 3 2009
Nina Holmengen
In this paper we explore variation in the predator-prey interaction between mink Mustela vison and muskrat Ondatra zibethicus across Canada based on 25 years of mink (predator) and muskrat (prey) data from the Hudson's Bay Company. We show that predator,prey interactions have stronger signatures in the west of Canada than in the east. In particular, we show that the observed phase plot trajectories of mink and muskrat rotate significantly clock-wise, consistent with predator,prey theory. We also investigate four phases of the mink muskrat interaction sequence (predator crash phase, prey recovery phase, etc.) and show that they are all consistent with a strong coupling in the west, whereas the presence of generalist predators and alternative preys can explain deviations from this pattern in the east. [source]

Predator, prey and pathogen interactions in introduced snail populations

ANIMAL CONSERVATION, Issue 3 2001
J. Gerlach
The introduction of the carnivorous snail Euglandina rosea to Pacific islands by biological control programmes has had a devastating effect on native snail populations. In most areas the target species, Achatina fulica, has not been affected, although some unsubstantiated reports have led to E. rosea being viewed as an effective control agent. Data from recent laboratory and field studies of E. rosea were combined into a simple model of the interactions between populations of E. rosea and A. fulica and a disease agent. Predictions from the model correspond closely with field data from a number of sites. The model suggests that apparent reductions in A. fulica numbers following E. rosea introduction are the result of a combination of predation and disease effects, and that although the maximum population levels are reduced the population is stabilized at a relatively high level. The model predicts that both A. fulica and E. rosea populations will persist. Partulidae will decline following E. rosea invasion although Samoana spp. may persist at reduced densities. More effective control of A. fulica can be achieved through manual collecting. Control of E. rosea requires the imposition of a significant novel mortality factor. [source]

Dynamics of intracohort cannibalism in cultured fish

AQUACULTURE RESEARCH, Issue 7 2002
E Baras
Abstract Cannibalism is a frequent phenomenon in fish, especially in culture environments where fish are unable to escape predation via habitat segregation or migration. Not all cultured fish species start to exhibit cannibalism at the same age or size, nor is cannibalism equally intense in different species or life stages. Predator to prey size ratios vary substantially between species and life stages, chiefly because cannibalism is governed by gape size limitations and allometric growth of mouthparts. The development of sense organs, hard body parts, swimming and escape capacities in both the predator and the prey also influence prey size selectivity. The dynamics of cannibalism are influenced by these, as well as by environmental, factors that have effects on feed intake, growth depensation and facilitate or complicate the displaying of cannibalistic behaviour. Knowledge about cannibalistic behaviour and the logistics of cannibalism along with environmental enhancement are prerequisites for the mitigation of cannibalism in aquaculture. Also, within the context of strain selection, it is of importance to determine whether cannibals are natural-born killers or just lottery winners. These factors are discussed, chiefly as they apply to intracohort cannibalism. In addition, guidelines are suggested for cannibalistic risk assessment, and methods for mitigation of cannibalism are discussed. [source]

Spatial Variation in the Strength of a Trophic Cascade Involving Ruellia nudiflora (Acanthaceae), an Insect Seed Predator and Associated Parasitoid Fauna in Mexico

BIOTROPICA, Issue 2 2010
Luis Abdala-Roberts
ABSTRACT Spatial variation in the strength of herbivore top-down control represents an important source of variation in plant fitness measures and community structure and function. By measuring seed predator (larvae of a Noctuid moth) and parasitoid impacts on Ruellia nudiflora across a broad spatial scale in Yucatan (Mexico), this study addressed the following: (1) to what extent does seed predator and parasitoid attack intensity associated with R. nudiflora vary spatially? (2) Does parasitoid attack result in a positive indirect effect on the plant, and does the intensity of this effect vary spatially? During the peak of fruit production (late June,early July) of 2005, we collected fruits from 21 R. nudiflora populations and grouped them into four regions: center, east, north and south. For each fruit we recorded: observed seed number, number of seeds eaten, seed predator presence, parasitoid presence and number of seeds ,saved' by parasitoids. Seed predators attacked ca 30 percent of fruits/plant on average, while parasitoids were found in 24 percent of seed predator-attacked fruits. Results indicated spatial variation in seed predator and parasitoid attack levels; interestingly, a contrasting spatial gradient of attack intensity was observed: populations/regions with greatest parasitoid attack levels usually had the lowest seed predator attack levels and vice versa, suggesting top-down control of parasitoids on seed predators. We observed a weak overall indirect impact of parasitoids on R. nudiflora (4% seeds ,saved' on average), which nonetheless varied strongly across populations (e.g., close to 14% seeds saved at one population). Findings indicate a geographical structuring of interaction strengths across populations, as well as spatial variation in the strength of parasitoid cascading effects on plant reproduction. Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp [source]

Escape Behavior of Neotropical Homopterans in Response to a Flush,Pursuit Predator

BIOTROPICA, Issue 4 2004
Mark L. Galatowitsch
ABSTRACT Insect defenses against avian predators often include both a primary defense that reduces the probability of being attacked and a secondary defense, typically escape behavior, employed if the primary defense fails. Escape behavior, however, can make insects potentially vulnerable to specialized flush,pursuit predators. Neotropical Redstarts of the genus Myioborus (Parulidae) exploit insect escape behavior by using their contrasting black-and-white plumage and animated foraging behavior to startle insect prey that are then pursued and captured in flight. We examined how insect primary defense strategy and natural variation in Myioborus plumage pattern influence escape behavior in six species of homopterans from Monteverde, Costa Rica. The six homopterans included two aposematic species of the family Cercopidae (Ocoaxo sp. and Sphenorhina sp.), two cryptic species of the family Cixiidae (both Bothriocera spp.), and two structurally defended species of the family Membracidae (Camfylocentrus sp. and Vestistilus variabilis). We measured the distance at which models of Myioborus Redstarts elicited escape behavior in insects under field conditions. Response distances varied significantly with both homopteran primary defense and Myioborus plumage pattern. Structurally defended homopterans were the most sensitive to the models and cryptic homopterans were the least sensitive. The model simulating the plumage of endemic M. miniatus comptus of Costa Rica elicited greater responses than did models of other Myioborus taxa with either less or more white in the plumage. Our results suggest that (1) primary defense strategies can have a significant effect on insect vulnerability to flush-pursuit predators, and (2) geographic variation in the plumage pattern of Myioborus Redstarts may reflect adaptation to regional prey and habitat characteristics that maximizes flush-pursuit foraging performance. RESUMEN Las defensas de los insectos contra aves depredadoras, frecuentemente incluye dos tipos de defensa: una primaria, que disminuye la probabilidad de ser atacado, y una defensa secundaria tipica de comportamiento de escape, la cual es empleada si falla la defensa primaria. Sin embargo, el comportamiento de escape puede ocasionar que los insectos scan potencialmente vulnerables a depredadores especializados en vuelo y persecusión. Los colirrojos neotropicales del género Myioborus (Parulidae) explotan el comportamiento de escape de los insectos usando su plumaje contrastante bianco-negro, y su comportamiento de forrajeo animado para sobresaltar a los insectos a cazar, que luego son perseguidos y capturados en vuelo. Nosotros examinamos cómo la defensa primaria de insectos y la variación natural del plumaje en Myioborus influye en el comportamiento de escape en seis especies de homópteros de Monteverde, Costa Rica. Los seis homópteros estudiados incluyeron dos especies conspicuas de la familia Cercopidae (Ocoaxo esp. y Sphenorhina esp.), dos especies enigmáticas de la familia Cixiidae (ambos Bothriocera esp.), y dos especies de la familia Membracidae (Campylocentrus esp. y Vestistilus variabilis) que se defienden estructuralmente. Nosotros medimos la distancia en la cual los modelos colirrojos de Myioborus provocan el comportamiento de escape en insectos bajo de condiciones de campo. Las respuestas a las distancias variaron significativamente en ambas, en defensa primaria de los homópteros y el partón del plumaje de los Myioborus. Los homópteros que se defienden estructuralmente fueron los más vulnerables a los modelos, y los homópteros enigmáticos los menos vulnerables. El modelo simulando el plumaje del colirrojo M. miniatus comptus endémico de Costa Rica, produjo mayor respuesta que los otros modelos Myioborus de otras taxas con menos o más color bianco en su plumaje. Los resultados de este estudio sugieren que: (1) las defensas de estrategia primaria pueden tener un efecto significative en la vulnerabilidad de los insectos a los depredadores que vuelan y persiguen; y (2) la variación geografica en el partón del plumaje de los Myioborus colirrojos puede indicar adaptaciones a presas por regiones y a caracteristicas del hábitat que maximizan su habilidad de volar y perseguir. [source]

Foraging behavior of an estuarine predator, the blue crab Callinectes sapidus in a patchy environment

ECOGRAPHY, Issue 1 2000
Mary E. Clark
To define general principles of predator-prey dynamics in an estuarine subtidal environment, we manipulated predator density (the blue crab, Callinectes sapidus) and prey (the clam, Macoma balthica) patch distribution in large field enclosures in the Rhode River subestuary of the central Chesapeake Bay. The primary objectives were to determine whether predators forage in a way that maximizes prey consumption and to assess how their foraging success is affected by density of conspecifics. We developed a novel ultrasonic telemetry system to observe behavior of individual predators with unprecedented detail. Behavior of predators was more indicative of optimal than of opportunistic foraging. Predators appeared responsive to the overall quality of prey in their habitat. Rather than remaining on a prey patch until depletion, predators appeared to vary their patch use with quality of the surrounding environment. When multiple (two) prey patches were available, residence time of predators on a prey patch was shorter than when only a single prey patch was available. Predators seemed to move among the prey patches fairly regularly, dividing their foraging time between the patches and consuming prey from each of them at a similar rate. That predators more than doubled their consumption of prey when we doubled the number of prey (by adding the second patch) is consistent with optimizing behaviors - rather than with an opportunistic increase in prey consumption brought about simply by the addition of more prey. Predators at high density, however, appeared to interfere with each other's foraging success, reflected by their lower rates of prey consumption. Blue crabs appear to forage more successfully (and their prey to experience higher mortality) in prey patches located within 15,20 meters of neighboring patch, than in isolated patches. Our results are likely to apply, at least qualitatively, to other crustacean-bivalve interactions, including those of commercial interest; their quantitative applicability will depend on the mobility of other predators and the scale of patchiness they perceive. [source]

Predation by an exotic lizard, Anolis sagrei, alters the ant community structure in betelnut palm plantations in southern Taiwan

ECOLOGICAL ENTOMOLOGY, Issue 5 2008
SHAO-CHANG HUANG
Abstract 1.,Predators can affect prey directly by reducing prey abundance and indirectly by altering behavioural patterns of prey. From previous studies, there is little evidence that ant community structure is affected by vertebrate predation. 2.,Researchers tend to consider the interactions between vertebrate predators and ants to be weak. The present study examined the impact of the exotic invasive lizard, Anolis sagrei, on the ant community structure by manipulating the density of lizards within enclosures. The natural density of A. sagrei in the field was surveyed and used as the stocking density rate in the lizard-present sub-enclosures. 3.,Before the lizard density was manipulated, there was no difference in the ant diversity between sub-enclosures. After the lizard density manipulation, the ant diversity in sub-enclosures with A. sagrei present was significantly different from that of enclosures where the lizards were absent, although the overall ant abundance did not differ significantly. 4.,The ant diversity difference was generated by a significant reduction of the ant species Pheidole fervens in sub-enclosures with A. sagrei present. Such an abundance change might be the result of direct predation by the lizards, or it might be generated by a foraging site shift by this ant. 5.,The results of this study thus demonstrated that the invasion of an exotic vertebrate can significantly alter the community structure of ants, perhaps through the combined direct and indirect effects of lizards on ants. [source]

Predator control of ecosystem nutrient dynamics

ECOLOGY LETTERS, Issue 10 2010
Oswald J. Schmitz
Abstract Predators are predominantly valued for their ability to control prey, as indicators of high levels of biodiversity and as tourism attractions. This view, however, is incomplete because it does not acknowledge that predators may play a significant role in the delivery of critical life-support services such as ecosystem nutrient cycling. New research is beginning to show that predator effects on nutrient cycling are ubiquitous. These effects emerge from direct nutrient excretion, egestion or translocation within and across ecosystem boundaries after prey consumption, and from indirect effects mediated by predator interactions with prey. Depending on their behavioural ecology, predators can create heterogeneous or homogeneous nutrient distributions across natural landscapes. Because predator species are disproportionately vulnerable to elimination from ecosystems, we stand to lose much more from their disappearance than their simple charismatic attractiveness. [source]

Predators temper the relative importance of stochastic processes in the assembly of prey metacommunities

ECOLOGY LETTERS, Issue 11 2009
Jonathan M. Chase
Abstract Communities assemble through a combination of stochastic processes, which can make environmentally similar communities divergent (high ,-diversity), and deterministic processes, which can make environmentally similar communities convergent (low ,-diversity). Top predators can influence both stochasticity (e.g. colonization and extinction events) and determinism (e.g. size of the realized species pool), in community assembly, and thus their net effect is unknown. We investigated how predatory fish influenced the scaling of prey diversity in ponds at local and regional spatial scales. While fish reduced both local and regional richness, their effects were markedly more intense at the regional scale. Underlying this result was that the presence of fish made localities within metacommunities more similar in their community composition (lower ,-diversity), suggesting that fish enhance the deterministic, relative to the stochastic, components of community assembly. Thus, the presence of predators can alter fundamental mechanisms of community assembly and the scaling of diversity within metacommunities. [source]

Top predator control of plant biodiversity and productivity in an old-field ecosystem

ECOLOGY LETTERS, Issue 2 2003
Oswald J. Schmitz
Abstract Predators can have strong indirect effects on plants by altering the way herbivores impact plants. Yet, many current evaluations of plant species diversity and ecosystem function ignore the effects of predators and focus directly on the plant trophic level. This report presents results of a 3-year field experiment in a temperate old-field ecosystem that excluded either predators, or predators and herbivores and evaluated the consequence of those manipulations on plant species diversity (richness and evenness) and plant productivity. Sustained predator and predator and herbivore exclusion resulted in lower plant species evenness and higher plant biomass production than control field plots representing the intact natural ecosystem. Predators had this diversity-enhancing effect on plants by causing herbivores to suppress the abundance of a competitively dominant plant species that offered herbivores a refuge from predation risk. [source]

Top-down and bottom-up diversity cascades in detrital vs. living food webs

ECOLOGY LETTERS, Issue 1 2003
Lee A. Dyer
Abstract Apex predators and plant resources are both critical for maintaining diversity in biotic communities, but the indirect (,cascading') effects of top-down and bottom-up forces on diversity at different trophic levels are not well resolved in terrestrial systems. Manipulations of predators or resources can cause direct changes of diversity at one trophic level, which in turn can affect diversity at other trophic levels. The indirect diversity effects of resource and consumer variation should be strongest in aquatic systems, moderate in terrestrial systems, and weakest in decomposer food webs. We measured effects of top predators and plant resources on the diversity of endophytic animals in an understorey shrub Piper cenocladum (Piperaceae). Predators and resource availability had significant direct and indirect effects on the diversity of the endophytic animal community, but the effects were not interactive, nor were they consistent between living vs. detrital food webs. The addition of fourth trophic level beetle predators increased diversity of consumers supported by living plant tissue, whereas balanced plant resources (light and nutrients) increased the diversity of primary through tertiary consumers in the detrital resources food web. These results support the hypotheses that top-down and bottom-up diversity cascades occur in terrestrial systems, and that diversity is affected by different factors in living vs. detrital food webs. [source]

The Bold and the Variable: Fish with High Heterozygosity Act Recklessly in the Vicinity of Predators

ETHOLOGY, Issue 1 2008
Sampsa Vilhunen
Variation in the innate behavioral response to predation threat is often assumed to reflect genetic differences among the prey individuals. To date, no published results, however, exist that would offer explanation for the origin of this behavioral variation within populations. Using microsatellites as markers, we estimated the genetic variability of juvenile brown trout (Salmo trutta) individuals whose behavior had been individually recorded in a trade-off situation where both predator chemical cues and food were present. Mean overall heterozygosity and the internal relatedness of fish associated significantly with their activity and foraging, so that the genetically more variable individuals showed more risk-prone behavior under predation risk. No association between genetic variability and behavior was found in trials where predator odors were not present. These results were consistent over the three study populations of brown trout with different backgrounds, suggesting that the phenomenon is of general nature in this species. Of the possible mechanisms suggested to enable the existence of the positive association between neutral microsatellite variation and fitness-related trait, the local effect hypothesis gained more support from our data than the general effect hypothesis. [source]

Persistence of Alarm-Call Behaviour in the Absence of Predators: A Comparison Between Wild and Captive-Born Meerkats (Suricata Suricatta)

ETHOLOGY, Issue 11 2007
Linda I. Hollén
Performing correct anti-predator behaviour is crucial for prey to survive. But, are such abilities lost in species or populations living in predator-free environments? How individuals respond to the loss of predators has been shown to depend on factors such as the degree to which anti-predator behaviour relies on experience, the type of cues evoking the behaviour, the cost of expressing the behaviour and the number of generations under which relaxed selection has taken place. Here we investigated whether captive-born populations of meerkats (Suricata suricatta) used the same repertoire of alarm calls previously documented in wild populations and whether captive animals, as wild ones, could recognize potential predators through olfactory cues. We found that all alarm calls that have been documented in the wild also occurred in captivity and were given in broadly similar contexts. Furthermore, without prior experience of odours from predators, captive meerkats seemed to distinguish between faeces of potential predators (carnivores) and non-predators (herbivores). Despite slight structural differences, the alarm calls given in response to the faeces largely resembled those recorded in similar contexts in the wild. These results from captive populations suggest that direct, physical interaction with predators is not necessary for meerkats to perform correct anti-predator behaviour in terms of alarm-call usage and olfactory predator recognition. Such behaviour may have been retained in captivity because relatively little experience seems necessary for correct performance in the wild and/or because of the recency of relaxed selection on these populations. [source]

Learned Recognition of Intraspecific Predators in Larval Long-Toed Salamanders Ambystoma macrodactylum

ETHOLOGY, Issue 6 2001
Erica L. Wildy
The ability of prey to detect predators and respond accordingly is critical to their survival. The use of chemical cues by animals in predator detection has been widely documented. In many cases, predator recognition is facilitated by the release of alarm cues from conspecific victims. Alarm cues elicit anti-predator behavior in many species, which can reduce their risk of being attacked. It has been previously demonstrated that adult long-toed salamanders, Ambystoma macrodactylum, exhibit an alarm response to chemical cues from injured conspecifics. However, whether this response exists in the larval stage of this species and whether it is an innate or a learned condition is unknown. In the current study, we examined the alarm response of naïve (i.e. lab-reared) larval long-toed salamanders. We conducted a series of behavioral trials during which we quantified the level of activity and spatial avoidance of hungry and satiated focal larvae to water conditioned by an injured conspecific, a cannibal that had recently been fed a conspecific or a non-cannibal that was recently fed a diet of Tubifex worms. Focal larvae neither reduced their activity nor spatially avoided the area of the stimulus in either treatment when satiated, and exhibited increased activity towards the cannibal stimulus when hungry. We regard this latter behavior as a feeding response. Together these results suggest that an anti-predator response to injured conspecifics and to cannibalistic conspecifics is absent in naïve larvae. Previous studies have shown that experienced wild captured salamanders do show a response to cannibalistic conspecifics. Therefore, we conducted an additional experiment examining whether larvae can learn to exhibit anti-predator behavior in response to cues from cannibalized conspecifics. We exposed larvae to visual, chemical and tactile cues of stimulus animals that were actively foraging on conspecifics (experienced) or a diet of Tubifex (naïve treatment). In subsequent behavioral treatments, experienced larvae significantly reduced their activity compared to naive larvae in response to chemical cues of cannibals that had recently consumed conspecifics. We suggest that this behavior is a response to alarm cues released by consumed conspecifics that may have labeled the cannibal. Furthermore, over time, interactions with cannibals may cause potential prey larvae to learn to avoid cannibals regardless of their recent diet. [source]

Detection and Avoidance of Predators in White-Tailed Deer (Odocoileus virginianus) and Mule Deer (O. hemionus)

ETHOLOGY, Issue 2 2001
Susan Lingle
In this paper, we investigate the relationship between early detection of predators and predator avoidance in white-tailed deer (Odocoileus virginianus) and mule deer (O. hemionus), two closely related species that differ in their habitat preferences and in their anti-predator behavior. We used observations of coyotes (Canis latrans) hunting deer to test whether the distance at which white-tails and mule deer alerted to coyotes was related to their vulnerability to predation. Coyote encounters with both species were more likely to escalate when deer alerted at shorter distances. However, coyote encounters with mule deer progressed further than encounters with white-tails that alerted at the same distance, and this was not due to species differences in group size or habitat. We then conducted an experiment in which a person approached groups of deer to compare the detection abilities and the form of alert response for white-tails and mule deer, and for age groups within each species. Mule deer alerted to the approacher at longer distances than white-tails, even after controlling for variables that were potentially confounding. Adult females of both species alerted sooner than conspecific juveniles. Mule deer almost always looked directly at the approacher as their initial response, whereas white-tails were more likely to flee or to look in another direction with no indication that they pinpointed the approacher during the trial. Mule deer may have evolved the ability to detect predators earlier than white-tails as an adaptation to their more open habitats, or because they need more time to coordinate subsequent anti-predator defenses. [source]

Freshwater crayfish farming technology in the 1990s: a European and global perspective

FISH AND FISHERIES, Issue 4 2000
H.E.G. Ackefors
This paper aims to describe the state of crayfish farming technology in the USA, Australia and Europe, and to discuss some of the prerequisites for this industry. Data from Europe are partly based on replies from a questionnaire sent out to scientists in all European countries. For other parts of the world, the crayfish literature has been reviewed and data from the August 2000 meeting of the International Association of Astacology are also included. Issues addressed in this review are cultivated species, production and productivity figures, production technique with regard to enclosures, reproduction and feed items, disease problems, predators, pond vegetation and water quality. Fewer than a dozen crayfish species are cultivated. The most attractive ones for culture and stocking in natural waters have been transferred to more than one continent. Pond rearing techniques predominate in all countries, and the technology required to achieve the spawning and rearing of juveniles is relatively simple. Pieces of fish, carrots and potatoes are frequent supplementary feed items; plants, cereals, pieces of meat, zooplankton and pellets are also common. Diseases are not usually a major concern, except in Europe where the American plague fungus, Aphanomyces astaci, has eradicated many European crayfish populations. Predators identified as common include insects and amphibians, as well as fishes, birds and mammals. Many water macrophytes are common in crayfish farms. These may either serve a useful function or cause problems for the crayfish farmer. Water temperature is the crucial factor for crayfish production. Water parameters such as pH and certain inorganic ion concentrations may also be of concern. Acidic waters that occur in some areas are generally detrimental to crayfish. The total yield from crayfish production from farming and fishery is in the order of 120 000,150 000 tonnes, more than four times the quantity given by FAO statistics. The largest crayfish producer is the Peoples' Republic of China, followed by the USA (70 000 and 50 000 tonnes in 1999, respectively). Of the quantity produced in the USA in 1999, about 35 000 tonnes was farmed. The yield in Europe was about 4500 tonnes in 1994, and of this quantity only 160 tonnes came from aquaculture. There are no official statistics for crayfish fishery production in Australia, but about 400 tonnes came from aquaculture in 1999. [source]

Taxon-specific reaction norms to predator cues in a hybrid Daphnia complex

FRESHWATER BIOLOGY, Issue 7 2007
JUSTYNA WOLINSKA
Summary 1. Previous studies have shown that interspecific hybridisation is common among taxa from the Daphnia galeata/hyalina/cucullata species complex. We investigated the influence of predator kairomones on the morphology and life histories of nine clones belonging to three taxa (pure D. galeata, F1 hybrids between D. galeata and D. hyalina, and backcrossed D. hyalina) of this species complex. Predators exerting positive (fish) and negative (Chaoborus larvae) size-selective predation were tested. 2. The most responsive traits were size at maturity and size of neonates. Despite large between-clone variation, discriminant analysis revealed that the three taxa were distinct from each other in key life-history traits. F1 hybrids did not react in an intermediate way compared to the other taxa: the multivariate distances between F1 hybrids and either taxon were larger than between pure D. galeata and backcrossed D. hyalina. 3. The average plasticity (calculated across all traits) was similar for all three taxa. With regard to the size at maturity and neonate body size, the strength of the response was a function of the intrinsic values of these traits expressed in the control. For example, for size at maturity, smaller individuals showed a significantly stronger reaction to Chaoborus kairomones than larger ones. 4. Finally, we monitored seasonal changes in body size, egg number and population density of pure D. galeata and F1 hybrids in Greifensee (Switzerland). The two taxa experienced similar seasonal changes in body size but, on some sampling dates, they differed in mean egg number. The observed seasonal changes in Daphnia body size were consistent with what would be expected if the predator assemblage shifted from fish to Chaoborus over the course of the summer. The fluctuations in the frequencies of Daphnia taxa, however, were not related to seasonal variation in Daphnia body size. 5. Experimental data suggest that temporally heterogeneous predation regimes might be an important condition stabilising the co-occurrence of Daphnia hybrids with parental taxa. Predation regimes, however, cannot solely explain dynamic changes in taxon frequency in Greifensee. [source]

Predators and cannibals modulate sex-specific plasticity in life-history and immune traits

FUNCTIONAL ECOLOGY, Issue 1 2008
D. J. Mikolajewski
Summary 1In organisms with complex life cycles, optimality models predict age and size at transition to translate larval condition into adult fitness. Recent studies, however, revealed that only a proportion of fitness is explained by age and size at transition. Moreover, sexes differ in the linkage of larval condition and adult fitness. 2In this study, we tested the hypothesis that immune traits may be partly decoupled from age and size at habitat transition and therefore contribute to the sex-specific linkage of larval condition and adult fitness. 3We reared larvae of the damselfly Coenagrion puella under the threat of predators and cannibals. We then examined sex-specific patterns in two life-history traits as well as two immune traits and tested for independency of the plastic responses among life-history and immune traits. 4Results revealed immune traits to be partly decoupled from life-history traits. Moreover, the sexes differed in the plasticity of life-history as well as immune traits. Our results give strong evidence that sex-specific translation of larval condition into adult fitness may be linked to immune traits as well as age and size at transition. [source]

Differential mortality of wintering shorebirds on the Banc d'Arguin, Mauritania, due to predation by large falcons

IBIS, Issue 2008
PIET J. VAN DEN HOUT
Predators may influence many aspects of the daily life and seasonal movements of their prey. Here we quantify direct, and evaluate indirect effects of predation by three falcon species (Lanner Falcon Falco biarmicus, Barbary Falcon Falco pelegrinoides and Peregrine Falcon Falco peregrinus) on coastal shorebirds wintering on the Banc d'Arguin, Mauritania, an area hosting approximately 30% of the East Atlantic Flyway population of shorebirds. On the basis of 754 h of observation over five winters, 97 witnessed attacks and 585 collected prey remains, we show that shorebirds were safer in larger flocks, which tended to be attacked less often. Furthermore, species that forage relatively close to shore and in small flocks were depredated more often than expected from their relative abundance. In three species, Red Knot Calidris canutus canutus, Bar-tailed Godwit Limosa lapponica taymyrensis and Dunlin Calidris alpina, the juveniles were more vulnerable than adults. We estimated that on average 1% of the juvenile and 0.1% of the adult Red Knots present were killed by large falcons each winter. For Red Knots we simultaneously quantified annual survival on the basis of an individual colour-marking programme: mortality due to predation by falcons accounted for an estimated 6.2% (juveniles) and 0.8% (adults) of annual mortality. We suggest that juvenile Red Knots are 10 times as likely to be killed by falcons because they use riskier habitats, i.e. early and late tide foraging areas closer to shores where surprise attacks are both more common and more successful. These results indicate that the strength of indirect effects of predation operating in a shorebird population largely outweigh the effects of mortality per se. [source]

Non-lethal effects of predation in birds

IBIS, Issue 1 2008
WILL CRESSWELL
Predators can affect individual fitness and population and community processes through lethal effects (direct consumption or ,density' effects), where prey is consumed, or through non-lethal effects (trait-mediated effects or interactions), where behavioural compensation to predation risk occurs, such as animals avoiding areas of high predation risk. Studies of invertebrates, fish and amphibians have shown that non-lethal effects may be larger than lethal effects in determining the behaviour, condition, density and distribution of animals over a range of trophic levels. Although non-lethal effects have been well described in the behavioural ecology of birds (and also mammals) within the context of anti-predation behaviour, their role relative to lethal effects is probably underestimated. Birds show many behavioural and physiological changes to reduce direct mortality from predation and these are likely to have negative effects on other aspects of their fitness and population dynamics, as well as affecting the ecology of their own prey and their predators. As a consequence, the effects of predation in birds are best measured by trade-offs between maximizing instantaneous survival in the presence of predators and acquiring or maintaining resources for long-term survival or reproduction. Because avoiding predation imposes foraging costs, and foraging behaviour is relatively easy to measure in birds, the foraging,predation risk trade-off is probably an effective framework for understanding the importance of non-lethal effects, and so the population and community effects of predation risk in birds and other animals. Using a trade-off approach allows us to predict better how changes in predator density will impact on population and community dynamics, and how animals perceive and respond to predation risk, when non-lethal effects decouple the relationship between predator density and direct mortality rate. The trade-off approach also allows us to identify where predation risk is structuring communities because of avoidance of predators, even when this results in no observable direct mortality rate. [source]

The Influence of Invertebrate Predators on Daphnia Spatial Distribution and Survival in Laboratory Experiments: Support for Daphnia Horizontal Migration in Shallow Lakes

INTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 1 2007
Adrianna Wojtal
Abstract The behavioural response of Daphnia cucullata to the presence of the pelagic invertebrate predator Leptodora kindtii, and the predation rate of littoral dragonfly nymphs on this species were investigated under laboratory conditions. Results of this study revealed a strong hiding response of Daphnia cucullata in the presence of the predatory cladoceran, L. kindtii, which was similar to the response of Daphnia in the presence of juvenile perch. This suggests that pelagic invertebrate predators may cause Daphnia to hide in the littoral zone which could result in increased exposure to predation by littoral invertebrates. A strong influence of dragonfly nymphs on D. cucullata, both in the presence and absence of macrophytes, was found. The average predation rate of Odonata larvae was about 5 prey ind,1 h,1 and did not differ significantly between treatments. Quantification of dragonfly pressure on Daphnia populations will require cross-verification with field experiments since in the natural conditions Daphnia seeks a shelter in the vegetation stands against predation by Leptodora, despite the occurrence of odonates. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Opportunists, Predators and Rogues: The Role of Local State Relations in Shaping Chinese Rural Development

JOURNAL OF AGRARIAN CHANGE, Issue 2 2005
MICHELLE S. MOOD
Chinese rural enterprises have developed in various ways in different parts of the country, giving rise to competing explanations of the variation in terms of the role of structure, historical legacies, norms, bureaucratic controls and agency. A new analysis seeks to resolve these contradictions by placing development in the context of township and village cadres' relationships. Townships can either enforce village compliance with county policy or not, and can promote economic development or not, resulting in bureaucratic controls working where compliance is enforced, and norms and agency guiding development where they are not. Perverse incentives allow compliance without achieving larger goals of economic development, and can trap villages in opportunistic or predatory townships. While structure and historical legacies do constrain development in general, inter-level relationships are key to understanding micro-variations. Village wealth and village elections further empower the village level and give agency greater salience. [source]

Predators, parasitoids and pathogens: species richness, trophic generality and body sizes in a natural food web

JOURNAL OF ANIMAL ECOLOGY, Issue 1 2000
J. Memmott
Summary 1.,A food web is presented which describes trophic interactions among the herbivores, parasitoids, predators and pathogens associated with broom, Cytisus scoparius (L.) Link. The data come from published work on the community at a single site. The web comprises a total of 154 taxa: one plant, 19 herbivores, 66 parasitoids, 60 predators, five omnivores and three pathogens. There are 370 trophic links between these taxa in the web. The taxa form 82 functionally distinct groups, called trophic species. 2.,Predators consumed significantly more species than did parasitoids: a median of two prey species per species of predator (range = 1,9), compared to a median of one host species per species of parasitoid (range = 1,4). Significant differences in the number of species consumed were also found among the five predator groups: birds (median = 4), spiders (median = 5), Coleoptera (median = 1), Diptera (median = 2) and Hemiptera (median = 7). 3.,Vulnerability, measured by numbers of consumer species, was significantly affected by the herbivores' feeding styles: externally feeding herbivores were most vulnerable and the concealed herbivores were least vulnerable. Miners were vulnerable to the most parasitoid species and externally feeding herbivores were the most vulnerable to predators. 4.,Resource species had a median vulnerability of 13 consumer species, a figure far higher than that in most published food webs. No significant relationship was found between species' vulnerability to predators and vulnerability to parasitoids. However, there was a strong negative relationship between the percentage mortality due to predation and percentage mortality due to parasitism. 5.,The broom food web contains nine orders of insects, a figure higher than previously recorded. The web also contains vertebrates, arachnids, bacteria and fungi. Most of the interactions between the orders were weak. Connectance was calculated for the complete web, the parasitoid sub-web and the predator sub-web. The connectance of the predator sub-web, a value of 0·0364, was more than an order of magnitude larger than the connectance of the entire web (0·0156) or the parasitoid sub-web (0·018). 6.,The body lengths of 52 species in the food web were estimated from field guides or museum specimens. Larger predators consumed smaller prey in 93% of predator,prey interactions. Smaller parasitoids consumed larger hosts in 79% of parasitoid,host interactions. Parasitoids were significantly smaller than predators. 7.,The 52 species were arranged in order of increasing body length along the columns and down the rows of a food web matrix. The predator sub-web was predominantly upper triangular with 8% of non-zero elements falling below the leading diagonal. The parasitoid sub-web was predominantly lower triangular with 21% non-zero elements falling above the leading diagonal. The entire web contains entries both above and below the main diagonal and thus violates a central assumption of the cascade model. [source]

Signalling conflict between prey and predator attraction

JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 5 2001
M. J. Bruce
Predators may utilize signals to exploit the sensory biases of their prey or their predators. The inclusion of conspicuous silk structures called decorations or stabilimenta in the webs of some orb-web spiders (Araneae: Araneidae, Tetragnathidae, Uloboridae) appears to be an example of a sensory exploitation system. The function of these structures is controversial but they may signal to attract prey and/or deter predators. Here, we test these predictions, using a combination of field manipulations and laboratory experiments. In the field, decorations influenced the foraging success of adult female St. Andrew's Cross spiders, Argiope keyserlingi: inclusion of decorations increased prey capture rates as the available prey also increased. In contrast, when decorations were removed, prey capture rates were low and unrelated to the amount of available prey. Laboratory choice experiments showed that significantly more flies (Chrysomya varipes; Diptera: Calliphoridae) were attracted to decorated webs. However, decorations also attracted predators (adult and juvenile praying mantids, Archimantis latistylus; Mantodea: Mantidae) to the web. St. Andrew's Cross spiders apparently resolve the conflicting nature of a prey- and predator-attracting signal by varying their decorating behaviour according to the risk of predation: spiders spun fewer decorations if their webs were located in dense vegetation where predators had greater access, than if the webs were located in sparse vegetation. [source]

Predators at bird nests in a northern hardwood forest in New Hampshire

JOURNAL OF FIELD ORNITHOLOGY, Issue 3 2006
David I. King
ABSTRACT Nest predation is the primary cause of nest failure in most passerine birds, and increases in nest predation associated with anthropogenic habitat disturbance are invoked as explanations for population declines of some bird species. In most cases, however, the identity of the nest predators is not known with certainty. We monitored active bird nests with infrared time-lapse video cameras to determine which nest predators were responsible for depredating bird nests in northern New Hampshire. We monitored 64 nests of 11 bird species during three breeding seasons, and identified seven species of predators during 14 predation events. In addition, we recorded two instances of birds defending nests from predators and, in both cases, these nests were ultimately lost to predation. These results contrast with other studies in terms of the relatively high proportion of nests depredated by raptors and mice, as well as the absence of any predation by snakes. The diverse suite of predators in this and other studies is likely to confound our understanding of patterns of nest predation relative to fragmentation and habitat structure. SINOPSIS La depredación de nidos es la causa principal del fracaso de anidamiento de muchos paserinos. El incremento en depredación ha sido asociado a disturbio antropogénico de habitat y considerado como la causa de la disminución poblacional de muchas especies de aves. En la mayoría de los casos, no se sabe a ciencia cierta quién es el depredador. Monitoreamos nidos activos con cámaras infrarojas de video que tomaban la acción en lapsos para determinar que depredadores eran responsables de la pérdida de nidos en el norte de New Hampshire. A lo largo de tres temporadas reproductivas monitoreamos 64 nidos, pertenecientes a 11 especies, e identificamos siete depredadores en 14 actos de depredación. Además, pudimos grabar dos casos en donde los aves defendieron sus nidos, aunque los nidos eventualmente fueron depredados posteriormente. Estos resultados contrastan con otros estudios en términos de la alta proporción de depredación por parte de rapaces y ratoncitos, y en la ausencia de depredación por parte de culebras. La diversidad de depredadores en este y otros estudios ampliará los conocimiento sobre los patrones de depredación en nidos, y su relación con la fragmentación y la estructura del hábitat. [source]