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Predator Populations (predator + population)

Distribution by Scientific Domains

Life Sciences	70%

Selected Abstracts

Metabolic rate models and the substitutability of predator populations

JOURNAL OF ANIMAL ECOLOGY, Issue 2 2004
David R. Chalcraft
Summary 1Much of the debate surrounding the consequences of biodiversity loss centres around the issue of whether different species are functionally similar in their effects on ecological processes. In this study, we examined whether populations consisting of smaller, more abundant individuals are functionally similar to populations of the same species with larger, fewer individuals. 2We manipulated the biomass and density of banded sunfish (Enneacanthus obesus) and measured their impact on populations of Southern leopard frog (Rana sphenocephala) larvae. We also evaluated the ability of models relating metabolic rate to body size to predict the relative impacts of populations that differ in average body size and population density. 3Our results indicate that population biomass, density and their interaction each play a large role in determining the effect of a predator population on its food resource. Populations with smaller but more abundant individuals had effects as large or larger than those populations with larger but fewer individuals. 4Although we found qualitative agreement between the observed relative effects of populations with that predicted by allometric models, we also found that density-dependence can cause effects of a population to differ from that expected based on allometry. 5The substitutability of populations differing in average body size appears to depend on complex relationships between metabolic rate, population density and the strength of density-dependence. The restrictive conditions necessary to establish functional equivalence among different populations of the same species suggests that functional equivalence should be rare in most communities. [source]

Extinction and permanence of the predator,prey system with stocking of prey and harvesting of predator impulsively

MATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 4 2006
Lingzhen Dong
Abstract In this paper, a predator,prey system with stocking of prey and harvesting of predator impulsively is studied. Here, the prey population is stocked with a constant quantity and the predator population is harvested at a rate proportional to the species itself at fixed moments. Under some conditions, the existence and global asymptotic stability of the boundary periodic solution are proved, which implies that the system will be extinct; and given some different restrictions, ultimate positive upper and lower bounds of all solutions are obtained, showing the system being permanent. At last, two examples are given to illustrate our results. Copyright © 2005 John Wiley & Sons, Ltd. [source]

A ratio-dependent eco-epidemiological model of the Salton Sea

MATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 2 2006
Kusumika Kundu
Abstract Ratio-dependent models set up a challenging issue for their rich dynamics incomparison to prey-dependent models. Little attention has been paid so far to describe the importance of transmissible disease in ecological situation by considering ratio-dependent models. In this paper, by assuming the predator response function as ratio-dependent, we consider a model of a system of three non-linear differential equations describing the time evolution of susceptible and infected Tilapia fish population and their predator, the Pelican. Existence and stability analysis of different equilibria of the system lead to different realistic thresholds in terms of system parameters. The condition for extinction of the species is also worked out. Our analytical and numerical studies may be helpful to chalk out suitable control strategies for minimizing the extinction of the Pelicans. We also suggest that supply of alternative food source for predator population may be used as a possible solution to save the predator from their extinction. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Ecological repercussions of historical fish extraction from the Southern Ocean

FISH AND FISHERIES, Issue 1 2009
David G Ainley
Abstract A major mid-1980s shift in ecological structure of significant portions of the Southern Ocean was partially due to the serial depletion of fish by intensive industrial fishing, rather than solely to climate factors as previously hypothesized. Over a brief period (1969,1973), several finfish stocks were on average reduced to <50%, and finally (mid-1980s) to <20%, of original size. Despite management actions, few stocks have recovered and some are still declining. Most affected species exhibit K-selected life-history patterns, and before exploitation presumably fluctuated in accordance with infrequent strong year classes, as is true of such fish elsewhere. A climate regime, the Southern Annular Mode, once oscillated between two states, but has remained in its ,positive mode' since the time of the fish extraction. This may have increased finfish vulnerability to exploitation. As breeding stocks decreased, we hypothesize that availability of annually produced juvenile fish fed upon by upper-level predators remained low. Correlations between predator populations and fish biomass in predator foraging areas indicate that southern elephant seal Mirounga leonina, Antarctic fur seal Arctocephalus gazella, gentoo penguin Pygoscelis papua, macaroni penguin Eudyptes chrysolphus and ,imperial' shag Phalacrocorax spp. , all feeding extensively on these fish, and monitored at Marion, Crozet, Kerguelen, Heard, South Georgia, South Orkney and South Shetland Islands, where fishing was concentrated , declined simultaneously during the two periods of heavy fishing. These patterns indicate the past importance of demersal fish as prey in Antarctic marine systems, but determining these interactions' ecological mechanisms may now be impossible. [source]

Trophic role of Atlantic cod in the ecosystem

FISH AND FISHERIES, Issue 1 2009
Jason S. Link
Abstract As the world's oceans continue to undergo drastic changes, understanding the role of key species therein will become increasingly important. To explore the role of Atlantic cod (Gadus morhua Gadidae) in the ecosystem, we reviewed biological interactions between cod and its prey, predators and competitors within six ecosystems taken from a broad geographic range: three are cod-capelin (Mallotus villosus Osmeridae) systems towards cod's northern Atlantic limit (Barents Sea, Iceland and Newfoundland,Labrador), two are more diverse systems towards the southern end of the range (North Sea and Georges Bank,Gulf of Maine), and one is a species-poor system with an unusual physical and biotic environment (Baltic Sea). We attempt a synthesis of the role of cod in these six ecosystems and speculate on how it might change in response to a variety of influences, particularly climate change, in a fashion that may apply to a wide range of species. We find cod prey, predators and competitors functionally similar in all six ecosystems. Conversely, we estimate different magnitudes for the role of cod in an ecosystem, with consequently different effects on cod, their prey and predator populations. Fishing has generally diminished the ecological role of cod. What remains unclear is how additional climate variability will alter cod stocks, and thus its role in the ecosystem. [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]

The anatomy of predator,prey dynamics in a changing climate

JOURNAL OF ANIMAL ECOLOGY, Issue 6 2007
CHRISTOPHER C. WILMERS
Summary 1Humans are increasingly influencing global climate and regional predator assemblages, yet a mechanistic understanding of how climate and predation interact to affect fluctuations in prey populations is currently lacking. 2Here we develop a modelling framework to explore the effects of different predation strategies on the response of age-structured prey populations to a changing climate. 3We show that predation acts in opposition to temporal correlation in climatic conditions to suppress prey population fluctuations. 4Ambush predators such as lions are shown to be more effective at suppressing fluctuations in their prey than cursorial predators such as wolves, which chase down prey over long distances, because they are more effective predators on prime-aged adults. 5We model climate as a Markov process and explore the consequences of future changes in climatic autocorrelation for population dynamics. We show that the presence of healthy predator populations will be particularly important in dampening prey population fluctuations if temporal correlation in climatic conditions increases in the future. [source]

Metabolic rate models and the substitutability of predator populations

Individual responses of seabirds to commercial fisheries revealed using GPS tracking, stable isotopes and vessel monitoring systems

JOURNAL OF APPLIED ECOLOGY, Issue 2 2010
Stephen C. Votier
Summary 1.,The large amount of discards produced by commercial fisheries can have major impacts on marine predator populations: this abundant food may increase populations of some scavengers or decrease others via accidental bycatch. Yet, despite the conservation implications of discard practices, the ecology of individual scavengers is poorly understood. 2.,Here, we assess the influence of commercial fisheries' activity on the foraging behaviour of individual breeding northern gannets Morus bassanus. Using recent developments in stable isotope mixing models (Stable Isotope Analysis in R or SIAR) we estimate individual discard consumption. Using GPS tracking and the Vessel Monitoring System (VMS), we investigate behavioural responses to trawlers. 3.,Analysis of conventional diet samples, as well as stable isotope ratios of carbon and nitrogen in blood (plasma and cells), highlight marked individual differences in the proportion of fishery discards in the diet. Individual differences in foraging behaviour revealed by stable isotopes show evidence of both short-term consistency and behavioural flexibility. 4.,At-sea path tortuosity of 25 gannets (tracked using GPS loggers) revealed scale-dependent adjustments in response to VMS-derived fishing vessel locations, as well as to sea surface temperature, chlorophyll a concentration and copepod abundance. The results also indicate individual variability in behavioural response to trawlers. 5.,Individual differences in the amount of discards estimated from SIAR were negatively correlated with differences in foraging trip length and body condition, indicating potential fitness consequences. 6.,Synthesis and applications. The management of commercial fisheries and apex predators is a daunting task. Ultimately, reducing bycatch and removing dependency on discards remain key conservation priorities, but managers should also ensure that scavenging species have sufficient alternative food to meet their energetic needs, to ameliorate potential unforeseen knock-on consequences. The results of Stable Isotope Analysis (SIAR) reveal intra-population differences in discard consumption by gannets; differences that have impacts on foraging effort and body condition. The use of GPS tracking and Vessel Monitoring Systems (VMS) reveal that gannet at-sea behaviour is influenced by fishing vessels, although this also varies among individuals. A combination of SIAR, GPS tracking and VMS can be used to study fishery/scavenger interactions in detail at the individual level, to answer fundamental questions about scavenging behaviour. [source]

Influence of non-crop plants on stink bug (Hemiptera: Pentatomidae) and natural enemy abundance in tomatoes

JOURNAL OF APPLIED ENTOMOLOGY, Issue 8 2010
C. G. Pease
Abstract We investigated the effects of weed hosts on stink bug density and damage (Euschistus conspersus Uhler and Thyanta pallidovirens Stal), and a nectar bearing plant on natural enemies of stink bugs in the Sacramento Valley of California. Stink bug density and fruit damage were evaluated in processing tomatoes adjacent to weedy and cultivated borders. The density of E. conspersus was significantly greater in tomatoes adjacent to weedy borders in July but not during August/September. Thyanta pallidovirens was less abundant overall (19%), but was found in significantly greater densities adjacent to cultivated borders in July but not in August/September. Mean percent fruit damage by stink bugs was greater adjacent to the weedy border than the cultivated border, but this difference was not significant. Stink bug egg parasitism and generalist predator density were evaluated in fresh market tomatoes adjacent to a sweet alyssum (Lobularia maritima L.) border and an unplanted control border at three sites. Egg parasitism was significantly greater in the alyssum treatment for the 9,12 September sampling period. Jalysus wickhami VanDuzee (Hemiptera: Berytidae) density was significantly greater in the alyssum treatment in mid-June. No other significant differences in predator populations were detected. Results of these two studies show that habitat manipulations have the potential to reduce densities of E. conspersus in tomato, the first step in developing a farmscape management plan for stink bug control. [source]

Seed predation during general flowering events of varying magnitude in a Malaysian rain forest

JOURNAL OF ECOLOGY, Issue 4 2007
I-FANG SUN
Summary 1The lowland dipterocarp forests of Southeast Asia exhibit interspecifically synchronized general flowering (GF) and mast fruiting at irregular multi-year intervals of 1 to 11 years. The predator satiation hypothesis (PSH) posits that GF events enhance seed survival by reducing the survival, reproduction and population sizes of seed predators between GF events, and then satiating the reduced seed predator populations during GF events. 2Three GF events of different magnitudes occurred in Pasoh Forest Reserve, Peninsular Malaysia, during 2001, 2002 and 2005. We exploited this natural experiment to test two predictions of the PSH. The first prediction was that seed survival should increase with the magnitude of the GF event. The second prediction was that seed predation should decrease with time since the previous GF event. 3A reproductive survey of all (c. 900) dipterocarp trees 30 cm d.b.h. in a 50 ha plot showed that flowering pervasiveness (the proportion of dipterocarp species participating) was high and similar in all three GF events. However, relative flowering magnitudes (measured by an index of individual tree participation and flowering intensity in Shorea species) were 2, 5 and 8 for the 2001, 2002 and 2005 GF events, respectively. 4The percentage of Shorea seeds surviving pre- and post-dispersal predation increased with the magnitude of GF events, which is consistent with the first prediction. 5Pre-dispersal insect seed predators consumed 12.9%, 11.2% and 3.4% of Shorea seeds in the 2001, 2002 and 2005 GF events, respectively, which is consistent with both predictions. 6Pre-dispersal seed predation by primates (mainly leaf monkeys) increased from 11.9% to 38.6% then fell to 9.3% in the 2001, 2002 and 2005 GF events, respectively. 7Predator satiation occurred only at population and community levels. At the individual tree level there was no relationship between the percentage of seeds surviving pre- and post-dispersal seed predation and variation in seed crop size or seed density beneath the tree. This suggests that attempts to test the PSH on the scale of individual trees may miss key community level effects. 8Our results suggest a more significant role of pre-dispersal seed predation in the evolution of reproductive synchrony than was recognized in the original statement of the PSH. [source]

A predator,prey model with disease in the prey species only

MATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 8 2007
David Greenhalgh
Abstract A predator,prey model with transmissible disease in the prey species is proposed and analysed. The essential mathematical features are analysed with the help of equilibrium, local and global stability analyses and bifurcation theory. We find four possible equilibria. One is where the populations are extinct. Another is where the disease and predator populations are extinct and we find conditions for global stability of this. A third is where both types of prey exist but no predators. The fourth has all three types of individuals present and we find conditions for limit cycles to arise by Hopf bifurcation. Experimental data simulation and brief discussion conclude the paper. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Direct and indirect effects of masting on rodent populations and tree seed survival

OIKOS, Issue 3 2002
Jaclyn L. Schnurr
Many plant species are thought to benefit from mast seeding as a result of increased seed survival through predator satiation. However, in communities with many different masting species, lack of synchrony in seed production among species may decrease seed survival by maintaining seed predator populations through the intermast cycle. Similarly, masting by different plant species may have different effects on the seed predator community. We conducted a three-year study in a northeastern USA temperate deciduous forest to determine if production of large seed crops by several tree species was synchronous, and if they had similar effects on all small mammal species. We found that red oak mast crops resulted in increased densities of Peromyscus leucopus and P. maniculatus, but had no effect on Clethrionomys gapperi abundance. Conversely, C. gapperi populations, but not Peromyscus populations, appeared to increase in response to a large red maple seed crop. Differences in small mammal abundance resulted in changes in species-specific seed survival: in the year of abundant C. gapperi, experimentally placed red oak acorns had significantly higher survival than in the year of high Peromyscus abundance. Red oak acorn removal was positively correlated with Peromyscus abundance, while red maple seed removal was significantly higher with increased C. gapperi abundance. Thus, species-specific seed production had differential effects on subsequent small mammal abundance, which in turn affected seed survival. We suggest that at the level of the community, even short-term lack of synchrony in production of large seed crops can cause variation in postdispersal seed survival, through differential effects on the community of small mammal seed predators. [source]

Endangered, apparently: the role of apparent competition in endangered species conservation

ANIMAL CONSERVATION, Issue 4 2010
N. J. DeCesare
Abstract Conservation biologists have reported growing evidence of food-web interactions as causes of species endangerment. Apparent competition is an indirect interaction among prey species mediated by a shared predator, and has been increasingly linked to declines of prey species across taxa. We review theoretical and empirical studies of apparent competition, with specific attention to the mechanisms of asymmetry among apparently competing prey species. Asymmetry is theoretically driven by niche overlap, species fitness traits, spatial heterogeneity and generalist predator behavior. In real-world systems, human-induced changes to ecosystems such as habitat alteration and introduced species may be ultimate sources of species endangerment. However, apparent competition is shown to be a proximate mechanism when resultant changes introduce or subsidize abundant primary prey for predator populations. Demonstration of apparent competition is difficult due to the indirect relationships between prey and predator species and the potential for concurrent exploitative competition or other community effects. However, general conclusions are drawn concerning the characteristics of prey and predator species likely to exhibit asymmetric apparent competition, and the options for recovering endangered species. While short-term management may be required to avoid imminent extinction in systems demonstrating apparent competition, we propose adaptive conservation efforts directed at long-term recovery. [source]

Inbreeding and density-dependent population growth in a small, isolated lion population

ANIMAL CONSERVATION, Issue 4 2010
M. Trinkel
Abstract In South Africa, more than 30 small, enclosed game reserves have reintroduced lions over the last two decades, which now house more than 500 individuals. There is a high risk of inbreeding in these fragmented, fenced and isolated populations, which may be compounded by a lack of management guidelines. A population of 11 founder lions Panthera leo was reintroduced to Madikwe Game Reserve in 1995, and this population has in turn become a source for reestablishing other populations. Only four lineages were reintroduced, founder males were related to founder females, and since 1997, only one male lineage maintained tenure for >9 years, resulting in breeding with direct relatives. Interventionist management to limit lion population growth and inbreeding in Madikwe has taken the form of translocating, trophy hunting and culling of mainly sub adult lions. Despite this management, inbreeding started 5 years after reintroduction. Reproductive performance and thus population growth in Madikwe were dependent on the overall lion population density. When lion density was low, females first gave birth at a significantly younger age and produced larger litters, resulting in a high population growth rate, which decreased significantly when lion density in the park reached carrying capacity, that is, 61 lions. This might have profound consequences for future reestablishment of lion populations when restocking new reserves: our study illustrates the need for founder populations of reintroduced endangered predator species to be as large and genetically diverse as possible, and thereafter new genetic material should be supplemented. The development of such management guidelines is becoming very important as large predator populations become increasingly fragmented and managed as metapopulations. [source]

Recolonisation and distribution of spiders and carabids in cereal fields after spring sowing

ANNALS OF APPLIED BIOLOGY, Issue 2 2006
S. Öberg
Abstract Generalist predators are important for pest suppression during pest establishment because they may occur in the crop before and during pest arrival. However, different crop management practices can have a negative effect on predator populations. If so, there is a need for recolonisation by the predators to the crop fields. An important pest in Sweden is the bird cherry-oat aphid, Rhopalosiphum padi, which migrates to cereal fields in spring. In turn, many cereal fields are spring sown and thus are disturbed by harrowing and sowing a short time before aphid arrival. In this study, three different questions about the populations of spiders and carabids in spring cereal crops were asked. First, does sowing in spring have a negative effect on the predators present in the fields? Second, if sowing has a negative effect on predator populations, do they recolonise the fields before pest arrival? Third, how are the predators distributed in the fields? We found that most carabids and most lycosid spiders were not affected by sowing and were distributed uniformly in the fields after sowing. Most linyphiid spiders were negatively affected by sowing, but then they recolonised the fields and were uniformly distributed in the fields after recolonisation. Thus, many spiders and carabids are present in the fields after sowing in spring and have the opportunity to suppress aphids during their establishment phase, which in turn may prevent a possible outbreak. [source]