Introduced Prey Species Research Articles

Management of invasive mesopredators in the Flinders Ranges, South Australia: effectiveness and implications

Abstract ContextSignificant resources have been devoted to the control of introduced mesopredators in Australia. However, the control or removal of one pest species, such as, for example, the red fox (Vulpes vulpes), may inadvertently benefit other invasive species, namely feral cats (Felis catus) and rabbits (Oryctolagus cuniculus), potentially jeopardising native-species recovery. AimsTo (1) investigate the impact of a large-scale, long-term fox-baiting program on the abundance of foxes, feral cats and introduced and native prey species in the Flinders Ranges, South Australia, and (2) determine the effectiveness of a short time period of cat removal in immediately reducing feral cat abundance where foxes are absent. MethodsWe conducted an initial camera-trap survey in fox-baited and unbaited sites in the Flinders Ranges, to quantify the impact of fox baiting on the relative abundance of foxes, feral cats and their prey. We then conducted a secondary survey in sites where foxes were absent, following an intensive, but short, time period of cat removal, in which 40 cats were shot and killed. Key resultsNo foxes were detected within baited sites, but were frequently detected in unbaited sites. We found a corresponding and significant increase in several native prey species in fox-baited sites where foxes were absent. Feral cats and rabbits were also more frequently detected within baited sites, but fox baiting did not singularly predict the abundance of either species. Rather, feral cats were less abundant in open habitat where foxes were present (unbaited), and rabbits were more abundant within one predominantly open-habitat site, where foxes were absent (fox-baited). We found no effect of short-term cat removal in reducing the local abundance of feral cats. In both camera-trap surveys, feral cat detections were positively associated with rabbits. ConclusionsLong-term fox baiting was effective in fox removal and was associated with a greater abundance of native and introduced prey species in the Flinders Ranges. To continue to recover and conserve regional biodiversity, effective cat control is required. ImplicationsOur study showed fox removal has likely resulted in the local release of rabbits and an associated increase in cats. Because feral cat abundance seemingly fluctuated with rabbits, we suggest rabbit control may provide an alternative and more effective means to reduce local feral cat populations than short-term removal programs.

A native top predator relies on exotic prey inside a protected area: The puma and the introduced ungulates in Central Argentina

Top predators play an important role to preserving healthy and functional ecosystems. Predatory interactions among generalist predators and native prey may be altered due to occurrence and availability of introduced prey species. These interactions seldom receive attention in biodiversity conservation, particularly when establishing protected area management guidelines. In this study we described puma (Puma concolor) diet in a protected area from central Argentina, where red deer (Cervus elaphus) and wild boar (Sus scrofa) were regionally introduced for game a hundred years ago. We aimed to evaluate if the puma effectively bases its diet on native prey species maintaining natural ecological interactions despite the occurrence and availability of these introduced prey species. We analyzed 83 puma scats in a landscape containing both native and introduced species susceptible to predation. Results indicate that puma diet was composed mostly by introduced species, which represented 80.8% of the total biomass consumed (Cervus elaphus 40.6%, Sus scrofa 39.4%, and Ovis aries 0.8%). Pumas mainly preyed on introduced ungulates in the protected area, where management guidelines do not account for puma-native prey interactions. We suggest implementation of management actions to reduce densities of these introduced ungulates to restore natural ecological interactions between the puma and native prey.

Effects of historically familiar and novel predator odors on the physiology of an introduced prey.

Predator odors can elicit fear responses in prey and predator odor recognition is generally associated with physiological responses. Prey species are often more likely to respond to the odor of familiar rather than alien predators. However, predator naïvety in an introduced prey species has rarely been investigated. We examined the physiological response, as shown by changes in ventilatory variables, of an introduced terrestrial herbivore, the European rabbit Oryctolagus cuniculus, in Australia, to the odor of potential predators and to control odors (distilled water and horse), to explore if responses were limited to historical (cat and fox) predators, or extended to historically novel predators (snake and quoll). All odors except distilled water elicited a response, with rabbits showing long-term higher respiratory frequencies and lower tidal volumes after introduction of the odors, indicating an increase in alertness. However, the intensity of the rabbits’ reaction could not be directly linked to any pattern of response with respect to the history of predator–prey relationships. Rabbits exhibited significantly stronger reactions in response to both cat and quoll odors than they did to distilled water, but responses to horse, fox, and snake odor were similar to that of water. Our results show that the introduced rabbit can respond to both historical and novel predators in Australia, and suggest that shared evolutionary history is not necessarily a prerequisite to predator odor recognition.

No longer naïve? Generalized responses of rabbits to marsupial predators in Australia

Predation is an important selective force on prey species, but avoiding predators can be costly. Efficient decisions on who to avoid (predator recognition) and when (situations with different predation risk) will determine the chances of prey survival. In coevolved predator-prey systems, detection of predator odours generally induces a response in potential prey to reduce predation risk. However, prey may not necessarily respond to odours of predators with which they have no previous experience, as predicted by the prey naivete hypothesis. In turn, perceived predation risk may also modulate predator recognition and the intensity of antipredator responses. In this study, we investigate the responses of an introduced prey species, the European rabbit (Oryctolagus cuniculus), to odours from coevolved and non-coevolved, sympatric and allopatric predators in situations of high and low numbers of predators in Australia. We used pellet counts to quantify rabbits’ use of space on experimental plots treated with predator odours. Rabbit avoidance of plots scented with coevolved predator odours was strongest, but they also responded to non-coevolved, marsupial predators. Predator abundance did not affect predator recognition in rabbits, although responses were more intense in situations where perceived predation risk was low and the intensity of responses decreased over time. Our results suggest that rabbits may have learned to recognize novel marsupial predators after 150 years of exposure in their introduced range.

What motivates hunters to target exotic or endemic species on the island of São Tomé, Gulf of Guinea?

AbstractHunting and invasive species are amongst the main causes of species extinctions on oceanic islands. On the island of São Tomé hunting of introduced mammals (monkeys, civets and pigs) and endemic bird species has contrasting effects in terms of conservation. Hunting of introduced mammals may benefit native fauna and flora but pressure on endemic birds poses a threat to some species. We conducted semi-structured interviews with 119 hunters to assess the relative importance of native and introduced prey species, gathering information on personal profiles, preference and practice, and hunters’ perceptions of trends in prey populations. Eleven species were hunted, including five invasive mammals and five endemic birds of high conservation importance. Based on species hunted, techniques used and final destination of the quarry we distinguished three groups of hunters, using cluster analyses: bird, monkey and feral-pig hunters. Bird hunters were all from urban areas but most pig hunters were rural. Monkey hunters were mostly rural workers but a small proportion were from urban areas. Bird and monkey hunters were primarily motivated by commercial gains but they also hunted for enjoyment and food. In general, hunting of mammals is an opportunistic activity that, if regulated, can be sustainable and contribute to mitigating the effects of invasive species on local fauna as well contributing to local livelihoods. Given the economic drivers involved in hunting of birds, intervention to reduce or eliminate this form of hunting will require enforcement of legislation and raising awareness of the issues involved.

Habitat use of lake trout (Salvelinus namaycush) following species introduction

Abstract – Although introductions of prey species have the potential to significantly alter habitat use by top predatory fish, this aspect has rarely been directly quantified. Introduction of yellow perch (Perca flavescens), a littoral–pelagic prey species, to a small boreal lake previously dominated by littoral cyprinids provided a unique opportunity to examine how a change in forage base influenced habitat use by the sole top predator, lake trout (Salvelinus namaycush). We monitored lake trout pelagic and spatial distribution using acoustic telemetry before (2001) and after (2008) the introduction of perch to determine whether habitat use reflected a deeper, offshore prey community. After accounting for differences in water temperature and dissolved oxygen concentrations between years and the inclusion of a control lake, our data suggest that lake trout habitat use changed after the introduction of yellow perch. Lake trout, on average, were 1.4 m deeper (P < 0.01), reduced their use of littoral habitat by 55% (P = 0.03) and experienced a 71% decrease in home range size (P < 0.01), consistent with a greater offshore habitat overlap between predator and prey after the introduction of yellow perch. This study illustrates how introduced prey species may have a significant influence on habitat use by top predatory fish, while also showing the importance of using direct measurements to quantify behavioural changes.

Prey naiveté in an introduced prey species: the wild rabbit in Australia

Early detection of predators by their prey is an essential element of antipredator tactics, and for many mammalian predator prey interactions, detection comes mainly via a predators olfactory cues. The avoidance of predator odors can reduce the likelihood of encountering predators and increases the chances of prey survival. However, the role of coevolutionary history in the exploitation of odors in mammalian predator-prey interactions is not so well understood. The prey naivetehypothesis predicts the lack of effective antipredator behaviors given the lack of a coevolution between predator and prey but has so far been only tested on native prey. In this study, we describe the short-time responsiveness of an introduced prey species, the European rabbit (Oryctolagus cuniculus), to scents from coevolved and novel predators in Australia. We quantified rabbit activity rates by means of pellet counting and activity indices based on footprints, in a series of experimental plots treated with predator odors, and both methods yielded consistent results. Rabbits responded to coevolved predators by reducing their activity rates to scented exper- imental plots, whereas no avoidance was found for novel allopatric predators. These results suggest a shared evolutionary history between the antipredatory responses of rabbits and their natural predators. Key words: antipredator response, avoidance behav- ior, coevolutionary history, Oryctolagus cuniculus, predation, space use. (Behav Ecol)

Research Article: Foraging and prey handling behaviors of the generalist Thamnophis hammondii offered various prey types

Foraging success is critical to the survival of any predator. When encountering introduced prey species, predatory generalists often adapt more readily to the prey than do predatory specialists. The foraging and prey handling behaviors of Thamnophis hammondii offered three different prey types (Lepomis spp., larval Rana catesbeiana, and juvenile X. laevis) were examined. Durations of foraging and prey handling behaviors were analyzed to determine if these behaviors varied by snake gender, collection locality, or prey type. Differences in behavior type and duration as a function of gender or location were not detected. Snake behaviors varied between prey types, with differences in the duration of the following behaviors: time overland, cruising, margin wandering, midwater diving, prey-orienting underwater, and ingesting. Snakes successfully captured all prey types, with the highest attack and success rates when foraging for R. catesbeiana. The results indicate that T. hammondii exhibits a variable repertoire of foraging behaviors when presented various prey types. The generalist nature of this species may allow it to forage effectively for prey types that may be unavailable to other natricine snakes.

SNAKE (COLUBRIDAE: THAMNOPHIS) PREDATORY RESPONSES TO CHEMICAL CUES FROM NATIVE AND INTRODUCED PREY SPECIES

Abstract Several aquatic vertebrates have been introduced into freshwater systems in California over the past 100 years. Some populations of the two-striped garter snake (Thamnophis hammondii) have lived in sympatry with these species since their introduction; other populations have never encountered them. To assess the possible adaptation to a novel prey, we tested the predatory responses of T. hammondii from different populations to different chemosensory cues from native and introduced prey species. We presented chemical extracts from potential prey types and 2 control odors to individual snakes on cotton swabs and recorded the number of tongue flicks and attacks directed at each swab. Subject response was higher for prey odors than control substances. Odors from introduced centrarchid fish (Lepomis) elicited higher response levels than other prey types, including native anuran larvae (Pseudacris regilla). The pattern of response was similar for both populations of snakes (experienced and naive, with r...

Adaptability of great cormorants Phalacrocorax carbo in a coastal environment demonstrated by their exploitation of introduced prey species and use of artificial breeding sites

An analysis of the contents of regurgitations of great cormorant Phalacrocorax carbo chicks at two coastal colonies in South Africa, one on an offhore island (St Croix) and the other at a saltworks in an estuary (Swartkops), revealed that the diet was dominated by introduced freshwater and estuarine fish. Most other prey species were indigenous euryhaline fish, and from the size ranges of the estuary-dependent species it was clear that they had been obtained in estuaries. Great cormorants in this coastal environment have learned to exploit introduced fish species, but use offshore islands as safe breeding sites, unless suitably safe artificial sites are created near their preferred foraging areas. Keywords: chick regurgitations, diet, St Croix Island, Swartkops River African Journal of Marine Science 2002, 24: 317–321

Rabbits killing birds: modelling the hyperpredation process

1. Introduced rabbits are known to have catastrophic effects on oceanic islands, either by direct destruction of the vegetative cover, or by the resulting disturbance of indigenous vertebrates. 2. Another dramatic effect, less well known, but potentially of major importance, is the hyperpredation process. This process, related to apparent competition, predicts that an introduced prey species, well adapted to high predation pressure, could induce the extinction of an indigenous prey, through the sudden increased population size of an introduced predator. In many island ecosystems, the simultaneous presence of introduced feral cats and rabbits is thus potentially a further threat for small vertebrates endemic of these islands. 3. Through a mathematical model, we tested this hypothesis, using a tri‐trophic system comprising an indigenous prey (birds), an introduced prey (rabbits) and an introduced predator (cats), and we demonstrated the theoretical existence of the hyperpredation process. 4. In addition, the numerical analysis of the model allowed a quantification of this process. It shows that the conditions required for an indigenous species to cope with the hyperpredation process imply very high intrinsic growth rates and/or carrying capacity, as well as behavioural anti‐predator response to the introduced predator. Since these conditions are unlikely to be met, this process is a further potential threat to most indigenous vertebrate prey. 5. Finally, our model shows that, although it can be induced by both types of adaptation together or alone, behavioural adaptations alone are more powerful in generating the hyperpredation process, than are life history traits adaptations.

The diet of the Barn OwlTyto albain southern Ireland, with reference to a recently introduced prey species— the Bank VoleClethrionomys glareolus

The diet of the Barn Owl in Ireland was investigated from pellet collections containing a total of 8229 individual prey items. The pellets were obtained from 15 roosts, 6 of which were within the established range of the Bank Vole Clethrionomys glareolus, a recent introduction to the island. Barn Owls were found to feed principally upon rodents, which formed 90% of prey weight consumed and, as in previous Irish studies, Field Mice, House Mice and Brown Rats were important prey items. The Bank Vole was a significant prey species where it occurs, constituting 15–22% of the diet. Other items such as Pygmy Shrews, birds and frogs were generally of seasonal or local importance only. The Barn Owl is an opportunistic feeder specializing in small mammals.