EVOLUTION, Issue 9 2003
Stephan B. Munch
Abstract Several recent studies have demonstrated that rapid growth early in life leads to decreased physiological performance. Nearly all involved experiments over short time periods (<1 day) to control for potentially confounding effects of size. This approach, however, neglects the benefits an individual accrues by growing. The net effect of growth can only be evaluated over a longer interval in which rapidly growing individuals are allowed the time required to attain the expected benefits of large size. We used two populations of Menidia menidia with disparate intrinsic growth rates to address this issue. We compared growth and survivorship among populations subject to predation in mesocosms under ambient light and temperature conditions for a period of up to 30 days to address two questions: Do the growth rates of fish in these populations respond differently to the presence of predators? Is the previously demonstrated survival cost of growth counterbalanced by the benefits of increased size? We found that growth was insensitive to predation risk: neither population appeared to modify growth rates in response to predation levels. Moreover, the fast-growing population suffered significantly higher mortality throughout the trials despite being 40% larger than the slow-growing population at the experiment's end. These results confirm that the costs of rapid growth extend over prolonged intervals and are not ameliorated merely by the attainment of large size. [source]

ASYMMETRY IN STRUCTURAL DEFENSES: INSIGHTS INTO SELECTIVE PREDATION IN THE WILD

EVOLUTION, Issue 9 2003
C. A. Bergstrom
Abstract Assessment of geographical patterns in fluctuating asymmetry (small, random differences between sides of bilateral characters) among populations shows promise as a tool to resolve the relative biomechanical importance of traits, in addition to being a possible indicator of habitat quality. We used 115 endemic freshwater populations of threespine stickleback (Gasterosteus aculeatus) from Haida Gwaii (Queen Charlotte Islands), British Columbia, Canada, to explore the degree of concordance between geographical variation of asymmetry in a predator defense structure (bony lateral plates) and geographical variation in several indirect measures of predation regime as well as several abiotic habitat variables. We found a geographical cline in the population frequency of lateral plate asymmetries, with reduced asymmetry in the southern clear-water regions of the archipelago characterized by long reaction distances and greater chance of capture by predators, and elevated asymmetry in the northern stained-water regions with poor visibility and low chances of capture. Lateral plate asymmetry was strongly correlated with expression of several defensive armor traits, including total plate numbers among populations, mean cross-sectional diameter of stickleback with the dorsal and pelvic spines erect, and mean degree of overlap between the plates and spine supports. There were no significant correlations between frequency of asymmetric fish and any of our abiotic habitat variables. Stickleback with structural plate asymmetries had fewer trout-induced scars than symmetric fish in the significant majority of populations, and there was a decrease in structural plate asymmetry with age in stained-water habitats, suggesting that trout predators may be selectively removing asymmetric fish in some lakes. This study provides evidence that geographical variation in developmental stability of threespine stickleback, as seen in the frequencies of asymmetry, reflects differences among populations in the importance of structural defenses to fitness rather than differences in habitat quality, and that asymmetry may be a target of selection by predators in wild populations. [source]

THE ROLE OF SIZE-SPECIFIC PREDATION IN THE EVOLUTION AND DIVERSIFICATION OF PREY LIFE HISTORIES

EVOLUTION, Issue 5 2002
Troy Day
Abstract Some of the best empirical examples of life-history evolution involve responses to predation. Nevertheless, most life-history theory dealing with responses to predation has not been formulated within an explicit dynamic food-web context. In particular, most previous theory does not explicitly consider the coupled population dynamics of the focal species and its predators and resources. Here we present a model of life-history evolution that explores the evolutionary consequences of size-specific predation on small individuals when there is a trade-off between growth and reproduction. The model explicitly describes the population dynamics of a predator, the prey of interest, and its resource. The selective forces that cause life-history evolution in the prey species emerge from the ecological interactions embodied by this model and can involve important elements of frequency dependence. Our results demonstrate that the strength of the coupling between predator and prey in the community determines many aspects of life-history evolution. If the coupling is weak (as is implicitly assumed in many previous models), differences in resource productivity have no effect on the nature of life-history evolution. A single life-history strategy is favored that minimizes the equilibrium resource density (if possible). If the coupling is strong, then higher resource productivities select for faster growth into the predation size refuge. Moreover, under strong coupling it is also possible for natural selection to favor an evolutionary diversification of life histories, possibly resulting in two coexisting species with divergent life-history strategies. [source]

KILLER WHALE PREDATION ON SPERM WHALES: OBSERVATIONS AND IMPLICATIONS

MARINE MAMMAL SCIENCE, Issue 3 2001
Robert L. Pitman
Abstract In October 1997 we observed a herd of approximately 35 killer whales (Orcinus orca) attack a pod of nine sperm whales (Physeter macrocephalus) 130 km off the coast of central California. During the four hours we watched, adult female killer whales, including some with calves, attacked in waves of four to five animals in what was apparently a "wound and withdraw" strategy. Adult male killer whales stood by until the very end when one charged in and quickly killed a seriously wounded sperm whale that had been separated from the group. The sperm whales appeared largely helpless: their main defensive behavior was the formation of a rosette ("marguerite"-heads together, tails out). When the killer whales were successful in pulling an individual out of the rosette, one or two sperm whales exposed themselves to increased attack by leaving the rosette, flanking the isolated individual, and leading it back into the formation. Despite these efforts, one sperm whale was killed and eaten and the rest were seriously, perhaps mortally, wounded. We also present details of two other encounters between sperm whales and killer whales that we observed. Although sperm whales, because of various behavioral and morphological adaptations, were previously thought to be immune to predation, our observations clearly establish their vulnerability to killer whales. We suggest that killer whale predation has potentially been an important, and underrated, selective factor in the evolution of sperm whale ecology, influencing perhaps the development of their complex social behavior and at-sea distribution patterns. [source]

Patterns of Nest Predation on Artificial and Natural Nests in Forests

CONSERVATION BIOLOGY, Issue 2 2004
DAWN M. BURKE
ave de bosque; depredación de nidos; éxito de nidos; experimento de nidos artificiales; nidos naturales Abstract:,Artificial nest experiments have been used in an attempt to understand patterns of predation affecting natural nests. A growing body of literature suggests that neither relative rates nor patterns of predation are the same for artificial and natural nests. We studied nest predation and daily mortality rates and patterns at real and artificial ground and shrub nests to test the validity of artificial nest experiments. We monitored 1667 artificial and 344 natural nests, over seven trials, in three regions, across 58 sites in Ontario. We controlled for many of the factors thought to be responsible for previously reported differences between predation rates on natural and artificial nests. Although artificial nests in our study resembled natural nests, contained eggs of appropriate size, shape, and color of target bird species, and were placed in similar microhabitats as natural nests, the rates of predation on these nests did not parallel rates on natural nests for any region in terms of absolute rate or pattern. Predation rates on artificial nests did not vary between years, as they tended to for natural nests, and the magnitude of predation pressure on artificial ground nests compared with shrub nests did not show the same pattern as that on natural nests. In general, rates of predation on artificial nests were significantly higher than on natural nests. Our results suggest that conclusions derived from artificial nest studies may be unfounded. Given that many influential ideas in predation theory are based on results of artificial nest experiments, it may be time to redo these experiments with natural nests. Resumen:,Se han utilizado experimentos con nidos artificiales con la intención de entender los patrones de depredación que afectan a los nidos naturales. La bibliografía sugiere que ni las tasas relativas ni los patrones de depredación son iguales para nidos artificiales y naturales. Estudiamos las tasas y patrones de depredación de nidos y de mortalidad diaria en nidos reales y artificiales sobre el suelo y en matorrales para probar la validez de los experimentos con nidos artificiales. Monitoreamos 1667 nidos artificiales y 344 nidos naturales, en siete pruebas, en tres regiones, en 58 sitios en Notario. Controlamos muchos de los factores que se piensa son responsables de diferencias entre tasas de depredación en nidos naturales y artificiales reportadas previamente. Aunque los nidos artificiales en nuestro estudio se asemejaron a nidos naturales, contenían huevos de tamaño, forma y color adecuados para la especie de ave y fueron colocados en microhábitats similares a los de nidos naturales, las tasas de depredación en estos nidos no fueron similares a las tasas en nidos naturales en ninguna región en términos de tasa o patrón absoluto. Las tasas de depredación en nidos artificiales no variaron de un año a otro, como fue la tendencia en nidos naturales, y la magnitud de la presión de depredación en nidos sobre el suelo comparada con nidos en arbustos no mostró el mismo patrón que la depredación en nidos naturales. Nuestros resultados sugieren que las conclusiones derivadas de estudios con nidos artificiales pueden ser infundadas. Debido a que muchas ideas influyentes en la teoría de la depredación se basan en los resultados de experimentos con nidos artificiales, puede haber llegado el momento de volver a realizar estos experimentos utilizando nidos naturales. [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]

Predation on mutualists can reduce the strength of trophic cascades

ECOLOGY LETTERS, Issue 11 2006
Tiffany M. Knight
Abstract Ecologists have put forth several mechanisms to predict the strength of predator effects on producers (a trophic cascade). We suggest a novel mechanism , in systems in which mutualists of plants are present and important, predators can have indirect negative effects on producers through their consumption of mutualists. The strength of predator effects on producers will depend on their relative consumption of mutualists and antagonists, and on the relative importance of each to producer population dynamics. In a meta-analysis of experiments that examine the effects of predator reduction on the pollination and reproductive success of plants, we found that the indirect negative effects of predators on plants are quite strong. Most predator removal experiments measure the strength of predator effects on producers through the antagonist pathway; we suggest that a more complete understanding of the role of predators will be achieved by simultaneously considering the effects of predators on plant mutualists. [source]

Mortality dynamics and population regulation in Bemisia tabaci

ENTOMOLOGIA EXPERIMENTALIS ET APPLICATA, Issue 2 2005
Steven E. Naranjo
Abstract Natural mortality is an important determinant of the population dynamics of a species, and an understanding of mortality forces should aid in the development of better management strategies for insect pests. An in situ, observational method was used to construct cohort-based life tables for Bemisia tabaci (Gennadius) Biotype B (Homoptera: Aleyrodidae) over 14 generations on cotton in central Arizona, USA, from 1997 to 1999. In descending order, median marginal rates of mortality were highest for predation, dislodgment, unknown causes, egg inviability, and parasitism. The highest mortality occurred during the 4th nymphal stadium, and the median rate of immature survival over 14 generations was 6.6%. Predation during the 4th nymphal stadium was the primary key factor. Irreplaceable mortality was highest for predation and dislodgment, with the absence of these mortality factors leading to the greatest increases in estimated net reproduction. There was little evidence of direct or delayed density-dependence for any mortality factor. Wind, rainfall, and predator densities were associated with dislodgment, and rates of predation were related to densities of Geocoris spp., Orius tristicolor (White), Chrysoperla carnea s.l. Stephens, and Lygus hesperus Knight. Simulations suggest that immigration and emigration play important roles in site-specific dynamics by explaining departures from observed population trajectories based solely on endogenous reproduction and mortality. By a direct measurement of these mortality factors and indirect evidence of adult movement, we conclude that efficient pest management may be best accomplished by fostering greater mortality during the 4th stadium, largely through a conservation of predators and by managing immigrating adult populations at their sources. [source]

First Documentation of Cultural Transmission of Predator Recognition by Larval Amphibians

ETHOLOGY, Issue 6 2007
Maud C. O. Ferrari
Predation is a pervasive selective agent shaping a prey's behaviour, morphology and life history. To survive, prey animals have to respond adaptively to predation threats and this can be achieved through learned predator recognition. Cultural transmission of predator recognition is likely a widespread means of learning in social animals, including mammals, birds and fishes. However, no studies have investigated the cultural transmission of predator recognition in amphibians. In our study, we examined whether naïve woodfrog (Rana sylvatica) tadpoles can acquire the recognition of the odour of a predatory tiger salamander (Ambystoma tigrinum) from experienced conspecifics. After conditioning some tutors to recognize salamander odour, we paired naïve observer tadpoles with either a salamander-naïve or salamander-experienced tutor and exposed the pairs to either salamander odour or a water control. Observers were subsequently tested alone for a response to salamander odour. We found that when given salamander odour, observer tadpoles that were paired with a salamander-experienced tutor successfully learned to recognize the salamander odour as a threat, whereas the observers paired with salamander-naïve tutors did not. Likewise, tadpoles exposed to the water control did not learn to recognize the salamander regardless of whether they were paired with a naïve or experienced tutor. This is the first study demonstrating cultural transmission of predator recognition in an amphibian species. [source]

Survival of enteric bacteria in seawater

FEMS MICROBIOLOGY REVIEWS, Issue 5 2001
Yael Rozen
Abstract Enteric bacteria exposed to the marine environment simultaneously encounter a variety of abiotic and biotic challenges. Among the former, light appears to be critical in affecting seawater survival; previous growth history plays a major part in preadaptation of the cells, and stationary phase cells are generally more resistant than exponentially growing ones. Predation, mostly by protozoa, is probably the most significant biotic factor. Using Escherichia coli as a model, a surprisingly small number of genes was found that, when mutated, significantly affect seawater sensitivity of this bacterium. Most prominent among those is rpoS, which was also dominant among genes induced upon transfer to seawater. [source]

Predation by seals on salmonids in two Scottish estuaries

FISHERIES MANAGEMENT & ECOLOGY, Issue 3 2001
T. J. Carter
Detailed observations of the behaviour of harbour seals, Phoca vitulina L., at sites within the estuaries of the Rivers Dee and Don, in north-eastern Scotland, were made over two full years between 1993 and 1996. Small numbers of grey seals, Halichoerus grypus Fab., were also present. The presence of seals within the estuaries was strongly related to season, with maximum numbers observed in winter and early spring; seals were virtually absent in June and July. The River Don was used largely as a haul-out site, while the River Dee was used predominantly as a foraging site, although it was not possible to determine whether the same seals were using the two estuaries. More seals were hauled-out on the River Don during twilight and dark than in daylight. The seals were observed to eat mostly salmonids, Salmo salar L. and S. trutta L., unidentified roundfish and flounder, Pleuronectes flesus L. The otoliths identified in scats collected at the mouth of the River Don belonged to marine species indicating that the seals were also feeding outside the estuaries. A minimum estimate is given of the numbers of large salmonids eaten in each river during the course of the year. Although no information was available on the numbers of salmonids using the rivers or the reproductive status of the fish eaten by the seals, as a cause of mortality, seal predation on large salmonids in estuaries is apparently an order of magnitude less important than mortality caused by angling within the river. [source]

Variability in performance in wild Atlantic salmon, Salmo salar L., fry from a single redd

FISHERIES MANAGEMENT & ECOLOGY, Issue 6 2000
C. García De Leániz
Dispersal and growth were studied in Atlantic salmon, Salmo salar L., fry from a natural isolated redd. The distribution of fry leaving the redd was strongly peaked, 80% being caught within a 2-week period. Early in the dispersal period, all fry leaving the redd had remnants of yolk sac and had not fed; by half way through the dispersal period, no fry had any visible yolk, but 35% still had empty stomachs. Fry leaving the redd during the first half of the dispersal period tended to settle in different first feeding sites than those dispersing later. Predation on fry by larger salmonids was frequent, especially during dispersal. Coefficients of variation for length, weight and condition factor increased significantly over the study period and for individually recognised fry, growth rates varied markedly. Thus, individual salmon fry differ in physical status on emergence from the redd and these differences are amplified during the first few weeks after emergence. [source]

Predation by the tropical plant Utricularia foliosa

FRESHWATER BIOLOGY, Issue 11 2006
LIZANDRO SANABRIA-ARANDA
Summary 1. We examined the prey captured by individual plants of the tropical carnivorous plant Utricularia foliosa, located in different areas along a creek in the Colombian Amazon and the zooplankton and macroinvertebrate communities associated with the plants. The aims were: (i) to determine whether bladders of different sizes within each plant catch different numbers of prey or exploit different size ranges and types of prey, (ii) if the quantity and composition of prey captured varies temporally and/or spatially and (iii) if the plant has evolved effective mechanisms of attracting prey. 2. Utricularia foliosa captured the most abundant species of macroinvertebrates associated with the plant. Larger bladders captured more, larger and more diverse prey. However, benefits of the extra prey caught by large bladders were not offset by the greater cost of producing bladders larger than approximately 1650 ,m. 3. The number of prey captured was higher in those plants with more carbohydrates per bladder and with a higher ratio of antenna size/bladder length. The antennae enhance capture success by offering the prey a favourable substratum that exploits their natural locomotor and feeding behaviour. However, although carbohydrates may lure prey, carbohydrate production was not a strategy of the plant to enhance the capture of prey, because the amount of carbohydrates in the bladder was related to the abundance of periphyton. [source]

Characterizing the pigment composition of a variable warning signal of Parasemia plantaginis larvae

FUNCTIONAL ECOLOGY, Issue 4 2010
Carita Lindstedt
Summary 1.,Aposematic animals advertise their defences to predators via warning signals that often are bright colours combined with black patterns. Predation is assumed to select for large pattern elements and conspicuousness of warning signals because this enhances avoidance learning of predators. However, conspicuousness of the colour pattern can vary among individuals of aposematic species, suggesting that warning signal expression may be constrained by opposing selection pressures. If effective warning signals are costly to produce, variation in signal expression may be maintained via physiological trade-offs. To understand the costs of signalling that might underlay both physiological and ecological trade-offs, it is crucial to identify the pigments involved in aposematic traits, how they or their precursors are acquired and how their production and/or deposition interact with other physiological processes. 2.,We characterized the pigments responsible for the genetically and phenotypically variable orange-black warning signal of the hairy larvae of an Arctiid moth, Parasemia plantaginis. We tested orange and black coloured hairs for the presence of six candidate pigment types using high-performance liquid chromatography, spectral and solubility analyses. 3.,After excluding the presence of carotenoids, ommochromes, pterins and pheomelanins in orange hairs, our results suggest that tiger moth larvae produce their orange warning signal by depositing both diet-derived flavonoids and trace levels of synthesized eumelanin in their hairs. The nearby black hairs are coloured by eumelanin. 4.,In light of previous studies, we conclude that although a large orange patch increases the 1larvae's antipredator efficacy, variation in the size of orange patches within a population can be driven by scarcity of flavonoids in diet. However, traces of eumelanin found in the orange hairs of the larvae may also play a significant role in the maintenance of the signal pattern on poor quality diets. 5.,The goal of the future studies will be to test the condition dependence of pigment deposition in aposematic colour patterns by directly manipulating relevant nutritional parameters such as dietary flavonoid or nitrogen content (i.e. amino acid content). [source]

Policy Failure and Petroleum Predation: The Economics of Civil War Debate Viewed ,From the War-Zone'

GOVERNMENT AND OPPOSITION, Issue 2 2005
Jenny Pearce
The analysis of armed conflict in the post Cold War era has been profoundly influenced by neoclassical economists. Statistical approaches have generated important propositions, but there is a danger when these feed into policy prescriptions. This paper first compares the economics of civil war literature with the social movement literature which has also tried to explain collective action problems. It argues that the latter has a much more sophisticated set of conceptual tools, enriched by empirical study. The paper then uses the case of multipolar militarization in oil-rich Casanare, Colombia, to demonstrate complexity and contingency in civil war trajectories. State policy failure and civil actors can be an important source of explanation alongside the economic agendas of armed actors. [source]

Diagnosing the environmental causes of the decline in Grey Partridge Perdix perdix survival in France

IBIS, Issue 1 2001
ELISABETH BRO
We studied Grey Partridge Perdix perdix mortality during breeding to identify the environmental causes of a long-term decline in adult survival. We radiotagged and monitored daily from mid-March to mid-September 1009 females on ten contrasting study sites in 1995-97. Simultaneously, we recorded habitat features and estimated the abundance of Hen and Marsh Harriers Circus cyaneus and C. aeruginosus Red Fox Vulpes vulpes and mustelids. We experimentally tested whether scavenging could have biased predation rates. We also examined, through the necropsy of 80 carcasses of Grey Partridge, whether disease, parasites or poisoning could have been ultimate causes of high predation rates. The survival rate of radiotagged females during spring and summer ranged from 0.25 to 0.65 across study areas. Mortality peaked in May, June and July when females were laying and incubating. The direct negative impact of farming practices was low (6%). Predation was the main proximate cause of female mortality during breeding (73%) and determined the survival rate, suggesting no compensation by other causes of mortality. Ground carnivores were responsible for 64% of predation cases, and raptors for 29%, but this proportion varied across study sites. Disease and poisoning did not appear to favour predation, and scavenging was not likely to have substantially overestimated predation rates. The predation rate on breeding females was positively correlated with the abundance of Hen and Marsh Harriers, suggesting an additional mortality in areas where harriers were abundant. The proportion of raptor predation was linearly related to harrier abundance. The predation rate was not correlated with the abundance of the Red Fox and mustelids. A potential density-dependent effect on the predation rate was confounded by the abundance of harriers. We found no convincing relationship between the predation rate and habitat features, but we observed a positive relationship between the abundance of Hen and Marsh Harriers and the mean field size. This suggested that habitat characteristics may contribute to high predation rates through predator abundance or habitat-dependent predation. [source]

Top-Down Control of Reed Detritus Processing in a Lake Littoral Zone: Experimental Evidence of a Seasonal Compensation between Fish and Invertebrate Predation

INTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 2 2007
Giorgio Mancinelli
Abstract We investigated whether predatory fish exert a top-down control on reed leaf packs processing in a lake littoral zone through a trophic cascade. Exclosure experiments were repeated in summer and winter, under high and low natural fish abundance, respectively. Fish exclusion effects on detritus processing and fungal conditioning were consistent with trophic cascade predictions only in summer. In winter, however, results indicated that a trophic cascade was induced by predatory invertebrates. In both seasons, variations in detritivores abundance generally supported a cascade scenario, whereas several taxon-specific departures occurred during the experimental periods. We conclude suggesting that predators may continuously regulate leaf detritus processing in lake littoral zones, through a seasonal shift in the relative contribution of fish and invertebrate predation. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Cascading top-down effects of changing oceanic predator abundances

JOURNAL OF ANIMAL ECOLOGY, Issue 4 2009
Julia K. Baum
Summary 1Top-down control can be an important determinant of ecosystem structure and function, but in oceanic ecosystems, where cascading effects of predator depletions, recoveries, and invasions could be significant, such effects had rarely been demonstrated until recently. 2Here we synthesize the evidence for oceanic top-down control that has emerged over the last decade, focusing on large, high trophic-level predators inhabiting continental shelves, seas, and the open ocean. 3In these ecosystems, where controlled manipulations are largely infeasible, ,pseudo-experimental' analyses of predator,prey interactions that treat independent predator populations as ,replicates', and temporal or spatial contrasts in predator populations and climate as ,treatments', are increasingly employed to help disentangle predator effects from environmental variation and noise. 4Substantial reductions in marine mammals, sharks, and piscivorous fishes have led to mesopredator and invertebrate predator increases. Conversely, abundant oceanic predators have suppressed prey abundances. Predation has also inhibited recovery of depleted species, sometimes through predator,prey role reversals. Trophic cascades have been initiated by oceanic predators linking to neritic food webs, but seem inconsistent in the pelagic realm with effects often attenuating at plankton. 5Top-down control is not uniformly strong in the ocean, and appears contingent on the intensity and nature of perturbations to predator abundances. Predator diversity may dampen cascading effects except where nonselective fisheries deplete entire predator functional groups. In other cases, simultaneous exploitation of predator and prey can inhibit prey responses. Explicit consideration of anthropogenic modifications to oceanic foodwebs should help inform predictions about trophic control. 6Synthesis and applications. Oceanic top-down control can have important socio-economic, conservation, and management implications as mesopredators and invertebrates assume dominance, and recovery of overexploited predators is impaired. Continued research aimed at integrating across trophic levels is needed to understand and forecast the ecosystem effects of changing oceanic predator abundances, the relative strength of top-down and bottom-up control, and interactions with intensifying anthropogenic stressors such as climate change. [source]

Predation of beech seed by mice: effects of numerical and functional responses

JOURNAL OF ANIMAL ECOLOGY, Issue 6 2005
WENDY A. RUSCOE
Summary 1The functional response of post-dispersal seed predators (house mouse, Mus musculus) to absolute densities of southern beech seed (Nothofagus solandri var. cliffortioides) was studied in laboratory and field trials. House mice showed a Type II (hyperbolic) functional response to seed availability and this was not modified by the presence of an alternative food source. 2Maximum daily intake rate of beech seeds during field trials averaged 1042 seeds mouse,1. This is sufficient to provide house mice with both the energy and protein required for growth and reproduction. 3We explicitly incorporated the functional response into the numerical response of house mice to beech seed, measured for field populations monitored in a New Zealand beech forest. House mice showed a strong numerical response to beech seed intake rate that was modified by some density-dependent mechanism(s). 4We developed a model that simulated seedfall, house mouse population growth and seed reserve depletion over one year. We found that the previously reported decline in house-mouse populations in beech forests during spring and summer is likely to be related to spring beech seed germination that renders seed no longer available as a food source for house mice. 5From our simulation model it does not appear that house-mouse populations can completely eat-out beech seed reserves prior to germination in a year of large seedfall. ,Masting' behaviour in New Zealand native beech trees is therefore sufficient to satiate an eruptive population of an exotic mammalian omnivore, despite the lack of a long co-evolutionary interaction. [source]

Postdispersal seed predation and seed viability in forest soils: implications for the regeneration of tree species in Ethiopian church forests

AFRICAN JOURNAL OF ECOLOGY, Issue 2 2010
Alemayehu Wassie
Abstract Almost all dry Afromontane forests of Northern Ethiopia have been converted to agricultural, grazing or scrub lands except for small fragments left around churches (,Church forests'). Species regeneration in these forests is limited. We investigated (i) how intense postdispersal seed predation was in church forest, and if this seed predation varied with species and/or habitat, and (ii) for how long tree seeds maintained their viability while buried in forest soil. In the seed predation experiment, we monitored seeds of six tree species in four habitats for a period of 14 weeks (the peak seeding season). In the seed viability experiment, we assessed seed viability of five species in four habitats after being buried 6, 12, or 18 months. Ninety-two percent of the tree seeds were predated within 3.5 months. Predation was mainly dependent on species whereas habitat had a weaker effect. Seed viability decreased sharply with burial time in soil for all species except for Juniperus. To minimize seed availability limitation for regeneration of such species in the forest, the standing vegetation needs to be persistently managed and conserved for a continuous seed rain supply. Additional seed sowing, and seed and seedling protection (by e.g. animal exclosures) may increase successful regeneration of important species in these forests. Résumé Presque toutes les forêts afromontagnardes sèches du nord de l'Ethiopie ont été converties en terres agricoles, pâturages ou broussailles, à l'exception de petits fragments laissés autour des églises (« Forêts d'églises »). La régénération des espèces dans ces fragments reste limitée. Nous avons étudié (1) l'intensité de la prédation sur les semences après leur dispersion dans ces forêts et si cette prédation variait selon les espèces et/ou les habitats, (2) combien de temps les semences d'arbres gardaient leur viabilité lorsqu'elles étaient enterrées dans le sol d'une forêt. Dans l'expérience sur la prédation des semences, nous avons suivi des semences de six espèces d'arbres dans quatre habitats pendant 14 semaines (le pic de la saison des semences). Dans l'expérience sur la viabilité des semences, nous avons évalué la viabilité de semences de cinq espèces dans quatre habitats après avoir été enterrées depuis 6, 12 ou 18 mois. 92% des semences avaient été consommées en 3,5 mois. La prédation dépendait principalement de l'espèce, et l'habitat avait un effet moins important. La viabilité des semences diminuait fortement avec l'allongement de la durée d'enfouissement pour toutes les espèces sauf Juniperus. Pour diminuer autant que possible la limitation de la disponibilité des semences destinées à la régénération de telles espèces dans la forêt, il faut gérer continuellement la végétation présente et la conserver pour une production continue de semences. Un ensemencement supplémentaire ainsi que la protection des semences et des jeunes plants (par exemple en les clôturants pour écarter les animaux) pourraient améliorer la régénération des espèces importantes de ces forêts. [source]

Predation and the persistence of melanic male mosquitofish (Gambusia holbrooki)

JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 3 2004
L. Horth
Abstract The empirical reasons for the persistent rarity of a genotype are typically complex and tedious to identify, particularly in nature. Yet rare morphs occur in a substantial fraction of phenotypic polymorphisms. A colour polymorphism has persisted for decades in the eastern mosquitofish, yet why this is so remains obscure. Here, I report the results of (1) intensive sampling at 45 natural sites to obtain the frequency distribution of the melanic (black) mosquitofish morph in Florida, (2) predation trials, conducted independently in mesocosms, with three different predatory species and (3) two mark-recapture studies, conducted in nature. This work (1) documents the rarity of melanic mosquitofish in nature, (2) demonstrates that melanic males experience a selective advantage over silver males in the presence of predators, (3) indicates no difference in the colour morphs, survival at a natural site essentially devoid of these predators, although suggesting a higher rate of recapture for melanic males at a site rife with predators. Overall, selective predation appears to contribute to the persistence of the melanic morph, despite its rarity in nature. [source]

Predation by brown trout: a major mortality factor for sexually mature European minnows

JOURNAL OF FISH BIOLOGY, Issue 3 2003
J. Museth
Brown trout Salmo trutta in the subalpine lake, Øvre Heimdalsvatn, showed large temporal variation in the rate of predation on the introduced minnow Phoxinus phoxinus population. Minnows were found in the stomachs of brown trout between 16 and 38 cm LT. Significantly greater predation was recorded shortly after ice break at the end of June 1999, with frequencies of 9 and 20% within the LT classes 16,29·9 cm and ,30 cm, respectively. Predation on minnows was only occasionally detected during July, August and September. The high level of predation coincided with minnow spawning, and lengths of consumed minnows were equal to those of sexually mature individuals. Accepting a causal link between minnow spawning, which lasted c. 3 weeks, and the contemporary high rate of predation, the estimated annual consumption of minnows by the brown trout population would be 138 kg wet mass. Although most of the annual consumption of minnows by brown trout (90%) occurred within a very short period (3 weeks), it accounted for a significant proportion (60%) of the annual loss in biomass of the sexually mature part of the population. [source]

Predation on Atlantic salmon and sea trout during their first days as postsmolts

JOURNAL OF FISH BIOLOGY, Issue 3 2002
C. Dieperink
Radio-tagged smolts of Atlantic salmon Salmo salar and sea trout Salmo trutta were predated heavily by sea birds after crossing the saline limit in the estuary of the River Skjern, Denmark. Most predation took place within the first 9 h after estuarine entry. The field data do not contradict the hypothesis of maladaptive anti-predatory behaviour. [source]

Factors affecting the predation of otter (Lutra lutra) on European pond turtle (Emys orbicularis)

JOURNAL OF ZOOLOGY, Issue 2 2006
J. Lanszki
Abstract In this case study, the ecological background of an unusual hunting behaviour was investigated, when otters Lutra lutra preyed upon European pond turtles Emys orbicularis in a Hungarian fish pond system during an 18-month period. Predation on turtle was found only during cold periods (established by spraint analysis and also by the collection of 182 turtle carcasses in 2003). The relationship was not close between fish availability and turtle consumption (rP=,0.325, P=0.19). The crude protein content of the turtle head and leg was higher than that of fish, frog and turtle body, whereas the energy content of the samples was similar. The mean body weight of the killed turtles (460 g) fell within the range of the optimal prey size of the otter. Turtles were used as cache foods by otters during extreme environmental conditions (as in the long winter), but occurred only rarely as buffer foods during moderate winter. In fish ponds, the conservation of the coexistent otter and turtle depends on pond management. The maintenance of a higher fish availability in ponds during winter makes it possible to avoid the need to acquire a proper hunting technique on turtle, indicated by the scarcity of primary fish food. [source]

The predatory impact of the freshwater invader Dikerogammarus villosus on native Gammarus pulex (Crustacea: Amphipoda); influences of differential microdistribution and food resources

JOURNAL OF ZOOLOGY, Issue 1 2005
Calum MacNeil
Abstract Predation between invading and native species can produce patterns of exclusion and coexistence. Dikerogammarus villosus, a Ponto-Caspian amphipod species, has invaded many central European freshwaters in the past decade, replacing native Gammarus amphipod species. For instance, the arrival of D. villosus in Holland has been accompanied by the decline of Gammarus duebeni and G. tigrinus populations within invaded systems. This study examined what may happen when D. villosus eventually encounters native Dutch populations of Gammarus pulex, and how factors such as microhabitat and food resource availability could contribute to a future species replacement or coexistence. A laboratory simulation of a lake/pooled area of river indicated that G. pulex and D. villosus differed in distribution within the same habitat, and showed that although the distribution of the native differed in the presence of the invader, the presence of the native had no effect on the distribution of the invader. Gammarus pulex suffered severe intraguild predation (IGP) from D. villosus in mixed species treatments with no reciprocal predation of D. villosus by G. pulex. This IGP occurred regardless of whether no alternative food resource was available (91% of the G. pulex population eliminated after 7 days), or alternative foods/prey were available to excess, such as leaf material (85%), chironomids (77%) or fish food flakes (74%). We conclude that although differential microdistribution of the two species could promote coexistence, the presence of alternative foods/prey resources, merely slow the rate of IGP and replacement of the native by the invader. Our study joins one of an increasing number emphasizing the potential damaging impacts of D. villosus on native communities. [source]

Dining on diplopods: remarkable feeding behaviour in chlamydephorid slugs (Mollusca: Gastropoda)

JOURNAL OF ZOOLOGY, Issue 1 2000
D. G. Herbert
Abstract The diet of southern African carnivorous slugs of the endemic family Chlamydephoridae is discussed. At least three species, Chlamydephorus bruggeni, C. burnupi and C. sexangulus, are predators of pill-millipedes Sphaerotherium sp. The feeding behaviour of C. sexangulus is described in detail and illustrated. It is suggested that the prey, once captured, is killed or immobilized by the introduction of a toxin through the intersegmental membrane joining the millipede's skeletal plates. The source for such a toxin may be the anterior pedal mucous gland. Predation on sphaerotheriid millipedes may be a behavioural apomorphy associated with a clade within the Chlamydephoridae, including taxa with longitudinal body keels and distinctive radula morphology, but it is evidently not confined to this clade. Whether the diet of such millipede-eating slugs is limited to millipedes is unknown, but it is probable that at least some chlamydephorids feed on more conventional prey such as snails and earthworms. [source]

The role of Steller sea lions in a large population decline of harbor seals

MARINE MAMMAL SCIENCE, Issue 4 2010
Elizabeth A. Mathews
Abstract We provide the first direct evidence that Steller sea lions will prey on harbor seals. Direct observations of predation on marine mammals at sea are rare, but when observed rates of predation are extrapolated, predation mortality may be found to be significant. From 1992 to 2002, harbor seals in Glacier Bay declined steeply, from 6,200 to 2,500 (,65%). After documenting that Steller sea lions were preying on seals in Glacier Bay, we investigated increased predation by sea lions as a potential explanation for the large decline. In five independent data sets spanning 21,25 yr and including 14,308 d of observations, 13 predation events were recorded. We conducted a fine-scale analysis for an intensively studied haul-out (Spider Island) and a broader analysis of all of Glacier Bay. At Spider Island, estimated predation by sea lions increased and could account for the entirety of annual pup production in 5 of 8 yr since 1995. The predation rate, however, was not proportional to the number of predators. Predation by Steller sea lions is a new source of mortality that contributed to the seal declines; however, life history modeling indicates that it is unlikely that sea lion predation is the sole factor responsible for the large declines. [source]

Species-specific limitation of vole population growth by least weasel predation: facilitation of coexistence?

OIKOS, Issue 1 2008
Elina Koivisto
Interspecific competition is usually understood as different species competing directly with each other for limited resources. However, predators can alter such competitive interactions substantially. Predation can promote the coexistence of species in a situation where it would otherwise be impossible, for example if a tradeoff between the competitive abilities and predation resistance of the prey species exists. The field vole Microtus agrestis and the sibling vole M. rossiaemeridionalis are sympatric grassland species, which compete for the same resources. At the population level sibling voles are suggested to be superior competitors to field voles, yet more vulnerable to predation. We tested the effects of predation on the two species in 0.5 ha outdoor enclosures by exposing vole populations to radio-collared freely-hunting least weasels Mustela nivalis nivalis for three weeks. Lethal and non-lethal impacts of predation limited population densities of both species during and after the experimental period, but the effect was more pronounced in sibling voles in which population densities decreased markedly during the treatment period and even after that. Field vole population densities remained stable under weasel predation, while densities increased in controls. Survival in both species was lower in treatment populations compared to controls, but the effect tended to be more pronounced in sibling voles and in females of both species. The average mass of adults in both species declined in the treatment populations. These results suggest that predation by least weasels can limit vole populations locally, even during favourable summer conditions, and have extended negative effects on the dynamics of vole populations. In addition, predation alleviated interspecific competition between the vole species and is, therefore, a potential factor enabling the coexistence of them. [source]

From Predation to Accumulation?: The Second Transition Decade in Russia

THE ECONOMICS OF TRANSITION, Issue 3 2000
Willem H. Buiter
In this paper I argue that the insecure property rights and widespread predation that have characterized Russia during these past 12 or so years have depressed capital formation in all its dimensions, private, public, physical, human and environmental. The elimination of the conditions that gave rise to insecure property rights and predation is a necessary condition for the kind of sustained economic growth the Russian government anticipates in its new economic strategy, promulgated in June 2000. [source]

Predation and its rate of return: the sugar industry, 1887,1914

THE RAND JOURNAL OF ECONOMICS, Issue 1 2006
David Genesove
We show that the price wars following two major entry episodes were predatory. Our proof is twofold: by direct comparison of price to marginal cost, and by construction of a lower bound to predicted competitive price-cost margins that we show to exceed observed margins. Predation occurred only when its relative cost to the dominant firm, the American Sugar Refining Company (ASRC), was small. Its most clear effect was to lower the acquisition price of entrants and small incumbents. It may also have deterred future capacity additions and raised ASRC's share of industry profits. Predation operated by strengthening ASRC's reputation as a willing predator. [source]