30 research outputs found

    Predator-dependent functional response in wolves: from food limitation to surplus killing

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    The functional response of a predator describes the change in per capita kill rate to changes in prey density. This response can be influenced by predator densities, giving a predator-dependent functional response. In social carnivores which defend a territory, kill rates also depend on the individual energetic requirements of group members and their contribution to the kill rate. This study aims to provide empirical data for the functional response of wolves Canis lupus to the highly managed moose Alces alces population in Scandinavia. We explored prey and predator dependence, and how the functional response relates to the energetic requirements of wolf packs. Winter kill rates of GPS-collared wolves and densities of cervids were estimated for a total of 22 study periods in 15 wolf territories. The adult wolves were identified as the individuals responsible for providing kills to the wolf pack, while pups could be described as inept hunters. The predator-dependent, asymptotic functional response models (i.e. Hassell-Varley type II and Crowley-Martin) performed best among a set of 23 competing linear, asymptotic and sigmoid models. Small wolf packs acquired >3 times as much moose biomass as required to sustain their field metabolic rate (FMR), even at relatively low moose abundances. Large packs (6-9 wolves) acquired less biomass than required in territories with low moose abundance. We suggest the surplus killing by small packs is a result of an optimal foraging strategy to consume only the most nutritious parts of easy accessible prey while avoiding the risk of being detected by humans. Food limitation may have a stabilizing effect on pack size in wolves, as supported by the observed negative relationship between body weight of pups and pack size

    Dynamics of a diffusive predator–prey model with herd behavior

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    This paper is devoted to considering a diffusive predator–prey model with Leslie–Gower term and herd behavior subject to the homogeneous Neumann boundary conditions. Concretely, by choosing the proper bifurcation parameter, the local stability of constant equilibria of this model without diffusion and the existence of Hopf bifurcation are investigated by analyzing the distribution of the eigenvalues. Furthermore, the explicit formula for determining the direction of Hopf bifurcation and the stability of the bifurcating periodic solutions are also derived by applying the normal form theory. Next, we show the stability of positive constant equilibrium, the existence and stability of periodic solutions near positive constant equilibrium for the diffusive model. Finally, some numerical simulations are carried out to support the analytical results

    Globally exponentially stable periodic solution in a general delayed predator-prey model under discontinuous prey control strategy

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    This paper studies the solution behaviour of a general delayed predator-prey model with discontinuous prey control strategy. The positiveness and boundeness of the solution of the system is firstly investigated using the comparison theorem. Then the sufficient conditions are derived for the existence of positive periodic solutions using the differential inclusion theory and the topological degree theory. Furthermore, the positive periodic solution is proved to be globally exponentially stable by employing the generalized Lyapunov approach. The global finite-time convergence is also discussed for the system state. Finally, the numerical simulations of four examples are given to validate the correctness of the theoretical results

    Predatory behaviour of wolves in Scandinavia

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    The study of predatory behaviour is essential for understanding the interactions that may affect the behaviour and population dynamics of the species involved and consequent cascading ecosystem effects. In the case of large carnivores feeding on large ungulate prey, predation is strongly impacted by humans who alter the habitat of both predators and their prey, control population sizes, and compete with large carnivores for the same prey species. The objectives of this thesis were to 1) establish a robust method to estimate kill rates of wolves (Canis lupus); 2) estimate kill rates during both summer and winter; 3) relate kill rates to prey availability in winter (functional response) and to the energetic requirements of the wolf packs; and 4) to study the impact of roads on predatory and other behaviour of wolves. To meet these objectives, the Scandinavian Wolf Research Project (SKANDULV) fitted wolves with Global Positioning System (GPS) collars and searched for kill remains on clusters of GPS-positions during defined time periods in winter and summer. Winter prey densities of cervids were assessed by spring counts of faecal pellet groups. High variation in the spatio-temporal movement pattern of wolves in relation to kill sites made it difficult to predictably identify kill sites along the wolf trajectory without fieldwork. Consequently, field personnel checked all clusters, and in addition some single positions, to obtain robust estimates of kill rate. Human disturbance at kill sites may be one possible reason for the high variation in the handling of kills, with a relatively short handling time associated with kills located in areas with a high potential for human disturbance. During summer, wolves preferred to be at intermediate distances to roads while handling prey. This was probably the result of a trade-off between avoidance of human presence and the preference for roads while traveling. In most wolf territories, moose (Alces alces) was the pre-dominant prey species during both summer and winter. Kill rates, measured as the acquired edible biomass per pack, did not differ between summer (mean ± SE = 24.0 ± 3.0 kg/day/pack) and winter (28.2 ± 2.3 kg/day/pack), but wolves killed twice as many moose per unit time in summer (0.60 ± 0.05 moose/day/pack) as during winter (0.31 ± 0.04 moose/day/pack). This difference occurred because wolves selected for moose calves and in summer these provided significantly less biomass per moose kill than in winter. In both seasons, per capita kill rates were negatively associated with wolf pack size. This negative association, combined with a positive association between kill rate and prey availability, resulted in a predator-dependent functional response in winter. Small wolf packs (2 – 4 wolves) acquired more than three times as much biomass as required to cover the energetic needs of the pack, while large packs (7 – 9 wolves) in territories with low to intermediate prey abundance seemed to be food-limited during winter. The average annual kill rate was estimated at 120 moose per wolf pack (95% CI 100 – 144) in territories where moose accounted for the majority of the kills. Predation rates during winter, i.e. the proportion of the moose population killed by predators, were not related to wolf pack size or kill rates, but were negatively correlated with the abundance of moose or the moose-to-wolf ratio within the wolf territory. Wolves did not regulate, but rather limited, the highly managed moose population in Scandinavia, with wolf-induced mortality being mainly additive to other sources of mortality. If the wolf population is to be controlled as a measure to reduce predation on moose, the removal of non-breeding pairs and small family groups will likely have a stronger effect on moose kill rates than a reduction in the number of wolves in larger packs

    Comparative feeding and foraging behaviour of the biocontrol agents Chilocorus spp. (Coccinellidae)

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    Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1991.This study focuses on the effective biocontrol agent Chilocorus nigritus (Fabricius). Its behaviour and ecology were compared with other Chilocorus spp. where appropriate, to elucidate why this species is such an effective biocontrol agent, and how to improve methodology for its deployment as a natural enemy. An artificial diet for C. nigritus was developed, but was still sub-optimal. Asterolecanium miliaris (Boisduval) was a suitable prey for all life stages of C. nigritus and the adults of Chilocorus bipustulatus (Linnaeus) and Chilocorus infernalis Mulsant, but was inadequate for larvae of the last two species. Adult weight, measured at one day after adult eclosion, was an appropriate indicator of the effects of larval treatment on their development and on the fitness of subsequent adults. There was no improvement in culture vigour due to a behavioural response of individuals within one generation to fluctuating as opposed to constant temperature. starvation for between 10h and 24h was appropriate for standardisation of hunger. Measuring feeding rate at a range of static temperatures did not reflect differences in the climatic adaptations of six Chilocorus spp., but mortality rates at increasingly high temperatures were useful. Chilocorus spp. showed little ability to choose between prey species. Prey substitutions adversely affected adults and larvae. Introduction of adults was the most effective method for field establishment. Giant bamboo Dendrocalamus giganteus Munro was a valuable site for field releases of C. nigritus, but less useful for C. bipustulatus and C. infernalis. Counter to assumptions on which interference models have been based, no significant intraspecific interference, reducing predatory efficiency, was observed. Visually prominent features on the horizon and a specific leaf shape, were attractive to foraging C. nigritus. The location of prey patches by adults was facilitated by prey odour, but not so for larvae. Adults detected individual prey olfactorily and visually over short distances, but physical contact was required for detection by larvae. Prey location by larvae and adults was facilitated by alterations in movement patterns in response to prey consumption. Differences in prey detection and the effects of prey substitutions, between the life stages, were related to field behaviour. The relevance to biological control, of responses to rearing conditions and feeding and foraging behaviour, was investigated

    The dynamics of feral pig populations in the semi-arid rangelands of Eastern Australia

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    An empirical study linking behaviour and population dynamics: altering spatial food availability in a mite model system.

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    Differences in the spatial availability of food can cause significant differences in the dynamics, age structure and size structure of a population. Replicated laboratory colonies of the soil mite Sancassania berlesei were fed the same absolute amount of food (yeast) daily, given either in a clumped form (or as a ball of yeast) or as a fine powder which was spread evenly. Animals were left to reproduce freely and population counts and measurements of animal length were taken every four days for 300 days. Animals in colonies fed clumped yeast have a higher initial oscillation in egg, juvenile and adult numbers than those fed a dispersed resource. In addition male and female lengths are larger in colonies fed clumped food, although the variance in length is also greater. Later in the time series adult numbers become similar between the two treatments, but the colonies fed clumped food maintained a roughly two-fold higher egg and juvenile number than colonies fed powder. The results are consistent with the idea that spatial arrangement of food can influence the type of competition acting at the individual level

    Pest and Pathogen Control: Strategic, Tactical, and Policy Models

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    This book describes mathematical models and systems analysis techniques applied to the study of insect pest, plant pathogens, and human diseases. The research programs of over 40 scientists from all over the world are compared and contrasted in detail to provide a state-of-the-art review on how such modeling can increase the effectiveness of more traditional ecological, biological, and chemical control methods. This is the first time such a synthesis has been attempted, and arises in part from a conference hosted by the International Institute for Applied Systems Analysis, Laxenburg, Austria. Papers from this event, plus additional solicited material, have been grouped by Professor Conway into three sections representing strategic, tactical, and policy decision models. An introduction and three linking chapters are provided to place these models in context. Discussing specific case histories in these mathematical terms and the consequent transfer of insights and methods will be of long-term interest to both professional and academic applied entomologists, plant pathologists, medical epidemiologists, applied ecologists, and systems analysts

    Predator-prey interactions in anthropogenic landscapes

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    Tre av fire artikler er fjernet fra den digitale versjonen, grunnet uklarhet om rettigheter. De kan leses i den trykte versjonen./ Three out of four articles have been removed from the digital version due to copyright. They can be read in the printed version.Interaksjoner mellom rovdyr og byttedyr er basert på flere faktorer, inkludert habitat og rovdyrets jaktmodus. Innenfor menneskepåvirkede landskap kan mennesker omforme interaksjoner mellom rovdyr og byttedyr ved å påvirke deres tetthet, atferd og overlevelse gjennom aktiviteter som jakt, skogsbruk og arealbruk. I menneskepåvirkede systemer er jakt den viktigste dødsårsaken for mange byttedyr, men med tilbakekomsten av store rovdyr står nå byttedyr overfor ytterligere dødlighetsrisiko. Målene med denne oppgaven var å 1) undersøke plasseringen av jegerdrepte og ulvedrepte elg i landskapet under og etter jaktsesongen og vurdere om det resulterte i kontrasterende eller overlappende spatio-temporære risikomønstre for elg; 2) undersøke elgers habitatvalg i forhold til fordelingen av jakt- og ulvpredasjonsrisiko i tid og rom; 3) undersøke dødeligheten til elgkalv sommer og vinter i forhold til risiko fra både mennesker og store rovdyr (ulver og brunbjørn), og klimatiske og miljømessige faktorer (produktivitet og snødybde); og 4) vurdere om ulvens tilbakekomst hadde forårsaket enten tetthets- eller atferdsutløste trofiske kaskader som involverte elg og deres viktigste fødeart, furu. For å gjøre dette har det Skandinaviske ulveforskningsprosjektet (SKANDULV) og GRENSEVILT-prosjektet innhentet lokaliseringer av elg drept av jegere og utstyrt både elg og ulv med Global Positioning System (GPS) halsbånd for å søke etter bytterester og innhente data om elgens habitatvalg om sommeren, høsten (dvs. jaktsesongen) og vinteren (dvs. etter jaktsesongen). I tillegg ble merkede elgkuer oppsøkt til fots i felt tre ganger i løpet av året (ved fødsel, ved starten av jaktsesongen og like før kalvenes spredning om vårenkalvespredning) for å telle antall kalver. Spatiotemporale Den romlige og tidsmessige variasjonen for jakt og predasjonsrisiko var korrelert med ulike naturlige og menneskeskapte faktorer. Jaktrisikoen var høyest nær åpne områder (f.eks. hogstflater og myrer) og veier, samt områder med lav bygningstetthet og liten grad av ulendt terreng. Ulvpredasjonsrisiko varierte tidsmessig og var høyest nær hogstflater/ungskog, lenger unna myr og i områder med lav bygningstetthet i jaktsesongen. Etter jaktsesongen var ulvepredasjonsrisikoen fortsatt høyest nærmere hogstflater/ungskog og i områder med lav bygningstetthet, men også nær hovedveier og i mer ulendt terreng. Når jeg sammenlignet de romlige egenskapene til jeger- og ulvedrept elg, fant jeg motsatte risikomønstre fra jegere og ulv. I løpet av jaktsesongen unngikk elgen områder med høy jaktrisiko på dagtid, mens habitatvalget deres ble ikke påvirket av jaktrisiko om natten. Etter jaktsesongen ble ikke elgens habitatvalg 6 påvirket av jaktrisiko verken på dag eller nattestid. Elg valgte områder med høy ulvepredasjonsrisiko både dag og natt under og etter jaktsesongen. Elgkalvdødeligheten om sommeren varierte betydelig mellom år, men var ikke relatert til verken predasjon fra ulv eller bjørn, klimatiske eller miljømessige variabler. Om vinteren var kalvedødeligheten positivt korrelert til snødybde og flatehogst/ungskog med nærvær av ulv, men også til økt jaktrisiko. Forekomst og tetthet av elg, samt beiteskader, var positivt korrelert til forekomst av ulv. Samlet sett var miljømessige og menneskeskapte faktorer viktigere for å forklare elgforekomst og beiteskader enn ulveforekomst. Selv om ulv ikke drepte elg tilfeldig i landskapet og at deres tilstedeværelse resulterte i en positiv korrelasjon mellom kalvedødelighet og visse landskapstrekk, oppdaget jeg ingen tegn til at elg unngikk områder eller perioder med høyere risiko. Følgelig ser det ut til at ulver ikke har fremkalt verken tetthets- eller atferdsutløste trofiske kaskader i det sør-sentrale Skandinavia. Resultatene mine tilsier at mens både jakt- og predasjonsrisiko varierte i tid og rom, responderte elg bare på jakt, som utgjør en større, men også mer forutsigbar risiko enn ulv. I løpet av det siste århundret har menneskers jakttradisjon på den Skandinaviske halvøy funksjonelt erstattet predasjon av ulv og bjørn på elg. Med tilbakekomsten av ulv justerte jegerne sine jaktkvoter på elg for å kompensere for den additive dødeligheten fra ulv. Elgens atferdsjustering på jaktrisiko kan tilsi at mennesker kan forårsake både tetthets- og atferdsutløste trofiske kaskader i menneskeskapte landskap. Ulver fremkalte derimot ikke atferdsresponser hos elg, som tilsier at elgen unngår risikofylte steder i risikofylte tider, og utløste heller ikke kaskadeeffekter på lavere trofiske nivåer. Den reduserte tilgjengeligheten av matressurser om vinteren kan tvinge elgen til å velge habitater med bedre næringstilgang som samtidig er kombinert med en større risiko for ulvepredasjon (f.eks. flatehogst/ungskog). Derfor kan ulvens potensiale til å sette i gang trofiske kaskader bli dempet, eller til og med kansellert, av elgens behov for næringstilgang om vinteren.ABSTRACT: Predator-prey interactions are shaped by several factors, including landscape features and hunting modes of predators. Within anthropogenic landscapes, humans can reshape predator prey interactions by influencing the density, behaviour and survival of both predators and prey through activities such as hunting, forestry practices and land use. Understanding the role that humans play within ecological communities is becoming increasingly important as large carnivores are recolonizing parts of their historical ranges. In anthropogenic systems, harvest is the main mortality source for many ungulate prey populations, and with the return of large carnivores, ungulates now face mortality risk from multiple sources. The objectives of this thesis were to: 1) assess the spatial attributes of hunter-killed and wolf (Canis lupus)-killed moose (Alces alces) during and after the hunting season and determine whether it resulted in contrasting or overlapping spatiotemporal patterns of risk for moose; 2) investigate habitat selection of moose in relation to the spatiotemporal distribution of hunting and wolf predation risk; 3) evaluate moose calf mortality during summer and winter in relation to risk from both humans and large carnivores (wolves and brown bears, [Ursus arctos]) and climatic and environmental variables (productivity and snow depth); and 4) assess whether the return of wolves had elicited either density- or behaviourally-mediated trophic cascades involving moose and their main browsing species, Scots pine. In order to do so, the Scandinavian Wolf Research Project (SKANDULV) and GRENSEVILT project obtained the locations of moose killed by hunters and fitted both moose and wolves with Global Positioning System (GPS) collars to search for kill sites and obtain data on moose habitat selection during summer, fall (i.e., the hunting season) and winter (i.e., after the hunting season). Additionally, female moose were approached three times during the year (at birth, at the onset of the hunting season and just before calf dispersal) from the ground to count the number of accompanying calves. Spatiotemporal patterns of hunting and predation risk correlated to both environmental and anthropogenic features. Hunting risk was highest close to open spaces (e.g., clearcuts and bogs) and roads and in areas with low building density and low terrain ruggedness. Wolf predation risk varied temporally and was highest close to clearcuts/young forests, further away from bogs and in areas of low building density during the hunting season. After the hunting season, wolf predation risk was still highest closer to clearcuts/young forests and in areas of low building 4 density, but also close to main roads and in more rugged terrain. When comparing the spatial characteristics of hunter-killed and wolf-killed moose, I found contrasting risk patterns from hunters and wolves. During the hunting season, moose avoided areas of high hunting risk during the day, while their habitat selection was not affected by hunting risk at night. After the hunting season, moose habitat selection was not influenced by hunting risk during the day or at night. Moose selected areas of high wolf predation risk during both day and night during and after the hunting season. Moose calf mortality in summer varied significantly between years but was not related to predation, climatic or environmental variables. In winter, calf mortality correlated positively to snow depth and clearcuts/young forests in the presence of wolves and increased hunting risk. Moose presence and abundance and browsing damage were positively correlated to the presence of wolves. Overall, environmental and anthropogenic features were more important in explaining moose presence and browsing damage than wolf presence. Although wolves did not kill moose randomly in the landscape and their presence resulted in a positive correlation between calf mortality and certain landscape features, I did not detect a behavioural response in moose consistent with the avoidance of places and times of higher risk. Consequently, wolves seem to not have elicited either density- or behaviourally-mediated trophic cascades in south-central Scandinavia. My results indicate that while both hunting and wolf predation risk varied spatiotemporally, moose responded only to the stronger, more predictable mortality source: hunting. During the last century in Scandinavia, hunting has functionally replaced predation by wolves and bears on moose. With the return of wolves, hunters adjusted their harvest quotas on moose to compensate for the additive mortality of wolves. Because moose adjusted their behavioural response to hunting risk, this may indicate that humans might have the potential to trigger both density- and behaviourally-mediated trophic cascades within anthropogenic landscapes. On the other hand, wolves did not elicit behavioural responses in moose consistent with the avoidance of risky places during risky times, nor triggered cascading effects on lower trophic levels. The decreased availability of food resources during winter may force moose to select habitats with greater forage opportunities that are simultaneously coupled with a greater risk of wolf predation (e.g., clearcuts/young forests). Hence, the potential for wolves to initiate trophic cascades might be dampened, or even cancelled, by the need for moose to find optimal foraging places during winter  publishedVersio
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