High Predator Densities Research Articles

A cat among the dogs: leopardPanthera pardusdiet in a human-dominated landscape in western Maharashtra, India

AbstractThe ecology and predator–prey dynamics of large felids in the tropics have largely been studied in natural systems where wild ungulates constitute the majority of the prey base. However, human-dominated landscapes can be rich in potential prey for large carnivores because of the high density of domestic animals, especially in tropical countries where pastoralism is an important livelihood activity. We report the almost complete dependence of leopardsPanthera parduson domestic animals as prey in the crop lands of Ahmednagar district, Maharashtra, India. From analysis of 85 confirmed leopard scats, 87% of the leopard's prey biomass consisted of domestic animals, with 39% consisting of domestic dogsCanis lupus familiarisalone. The only wild species that occurred in the leopard's diet were rodents, small indian civetViverricula indica, bonnet macaqueMacaca radiataand other primatesSemnopithecusspp., mongooseHerpestesspp., and birds. Interviews conducted in 77 households distributed randomly in the study area documented a high density of domestic animals: adult cattleBos taurus, calves, goatsCapra aegagrus, dogs and catsFelis catusoccurred at densities of 169, 54, 174, 24 and 61 per km2, respectively. Ivlev's electivity index indicated that dogs and cats were over-represented in the leopard's diet, given the higher densities of goats and cattle. The standing biomass of dogs and cats alone was sufficient to sustain the high density of carnivores at the study site. Our results show that the abundance of potential domestic prey biomass present in human-use areas supports a relatively high density of predators, although this interaction could result in conflict with humans.

Hemigrapsus sanguineus in Long Island salt marshes: experimental evaluation of the interactions between an invasive crab and resident ecosystem engineers.

The invasive Asian shore crab, Hemigrapsus sanguineus, has recently been observed occupying salt marshes, a novel environment for this crab species. As it invades this new habitat, it is likely to interact with a number of important salt marsh species. To understand the potential effects of H. sanguineus on this ecosystem, interactions between this invasive crab and important salt marsh ecosystem engineers were examined. Laboratory experiments demonstrated competition for burrows between H. sanguineus and the native fiddler crab, Uca pugilator. Results indicate that H. sanguineus is able to displace an established fiddler crab from its burrow. Feeding experiments revealed that the presence of H. sanguineus has a significantly negative impact on the number as well as the biomass of ribbed mussels (Geukensia demissa) consumed by the green crab, Carcinus maenas, although this only occurred at high predator densities. In addition, when both crabs foraged together, there was a significant shift in the size of mussels consumed. These interactions suggests that H. sanguineus may have long-term impacts and wide-ranging negative effects on the saltmarsh ecosystem.

Field assessment of the predation risk-food availability trade-off in crab megalopae settlement.

Settlement is a key process for meroplanktonic organisms as it determines distribution of adult populations. Starvation and predation are two of the main mortality causes during this period; therefore, settlement tends to be optimized in microhabitats with high food availability and low predator density. Furthermore, brachyuran megalopae actively select favorable habitats for settlement, via chemical, visual and/or tactile cues. The main objective in this study was to assess the settlement of Metacarcinus edwardsii and Cancer plebejus under different combinations of food availability levels and predator presence. We determined, in the field, which factor is of greater relative importance when choosing a suitable microhabitat for settling. Passive larval collectors were deployed, crossing different scenarios of food availability and predator presence. We also explore if megalopae actively choose predator-free substrates in response to visual and/or chemical cues. We tested the response to combined visual and chemical cues and to each individually. Data was tested using a two-way factorial design ANOVA. In both species, food did not cause significant effect on settlement success, but predator presence did, therefore there was not trade-off in this case and megalopae respond strongly to predation risk by active aversion. Larvae of M. edwardsii responded to chemical and visual cues simultaneously, but there was no response to either cue by itself. Statistically, C. plebejus did not exhibit a differential response to cues, but reacted with a strong similar tendency as M. edwardsii. We concluded that crab megalopae actively select predator-free microhabitat, independently of food availability, using chemical and visual cues combined. The findings in this study highlight the great relevance of predation on the settlement process and recruitment of marine invertebrates with complex life cycles.

Multiple fish predators: effects of identity, density, and nutrients on lower trophic levels

The ongoing loss of predators is chang- ing the composition of food webs, with largely un - known consequences. In particular, the effects of multiple fish predators on food webs are difficult to predict due to the prevalence of omnivory and intra - guild predation. At the same time, many ecosystems experience high nutrient loads that fuel food webs from the bottom up. To test the combined effects of both multiple predators and nutrient enrichment on food web composition, we created monocultures of perch, roach, and stickleback as well as mixed assem- blages of all 3 species at 3 different density levels using an additive design, and induced nutrient en - richment in half of the cages. The biomass of inverte- brate herbivores and algae was measured. Stomach analyses of predators were used to detect prey switching. Herbivore biomass depended mainly on predator identity, while top-down effects on algae were mediated by predator density and nutrient en - richment. Specifically, perch strongly reduced amphi - pods and isopods, and roach mainly reduced gas- tropods but also isopods, while stickleback had weak overall effects on herbivores. These species-specific effects were attenuated in the mixed fish assem- blages, probably due to prey switching. Algal growth strongly increased under high fish density and nutri- ent enrichment, but was not affected by predator- induced changes in the herbivore composition. This study shows that identity effects from predators in isolation are attenuated in multiple predator assem- blages, probably due to increasing interference among the predators. Algal biomass was enhanced by nutrient enrichment and high predator density, which affected algae probably through non-lethal effects, such as reduced activity of the herbivores.

Human observers impact habituated samango monkeys’ perceived landscape of fear

Humans and human infrastructure are known to alter the relationship between predators and prey, typically by directly or indirectly shielding one of the species from the other. In addition to these overt changes to animals’ behavior, observers may have more subtle impacts on animals’ foraging decisions. However, the anthropogenic alteration of risk-taking behavior has rarely been acknowledged or quantified, particularly in behavioral ecological studies reliant on habituated animals. We tested the magnitude of the “human shield effect” experimentally on two groups of samango monkeys, Cercopithecus mitis erythrarcus, at a site with high natural predator density and no human hunting pressure. In general, giving up densities (GUDs) – the density of food remaining in a patch when a forager leaves – were greatest at ground level (0.1m) relative to three tree canopy levels (2.5m, 5m and 7.5m), highlighting a strong vertical axis of fear. When human followers were present, however, GUDs were reduced at all four heights; furthermore, for one group, the vertical axis disappeared in the presence of observers. Our results suggest that human observers lower monkeys’ perceived risk of terrestrial predators and thereby, affect their foraging decisions at or near ground level. These results have significant implications for future studies of responses to predation risk based on habituation and observational methods.

High intraguild predator density induces thinning effects on and increases temporal overlap with prey populations

AbstractIntraguild (IG) predator density can alter its effects on intraguild prey populations through several mechanisms, including density‐dependent processes that affect IG predator traits such as size or growth that enhance or limit its predatory abilities. We examined whether intraspecific density‐dependence altered IG predator traits, as well as the subsequent interspecific effects among its intraguild prey within a larval salamander guild. Four densities of ringed salamanders (Ambystoma annulatum), the IG predator, were combined with the presence/absence of spotted salamanders (A. maculatum), the IG prey, within experimental mesocosms. We modeled the effects of A. annulatum density on both conspecific and heterospecific responses that would be indicative of density‐dependent competition and predation, respectively. We also modeled the reciprocal interspecific effects of A. maculatum on A. annulatum. We found that increasing intraspecific density negatively affected morphological traits but not survival of A. annulatum. No interspecific effects of A. maculatum on A. annulatum were observed. Alternatively, traits of A. maculatum showed nonlinear relationships with increasing A. annulatum density. Thinning effects of A. annulatum on A. maculatum were observed, as survival was positively and size negatively related for A. maculatum with IG predator density. The temporal overlap of the IG predator and prey also increased nonlinearly with IG predator density, intensifying the potential encounter rate of the two species. Overall, this study shows that density‐dependent processes in IG predators can significantly affect traits of both themselves, as well as IG prey, which could ultimately change whether competition or predation occurs between the two groups.

Characteristics of African wild dog natal dens selected under different interspecific predation pressures

To successfully reproduce, many carnivorous mammals need access to suitable den sites. Den site selection is often based on fitness related criteria like escape from predators, food availability and shelter from extreme weather conditions. African wild dogs are cooperative breeders that use a den to give birth to their offspring. They often co-exist with lions and spotted hyenas, both of which are known to kill African wild dog pups. Little is known about den site selection by African wild dogs. In this study, we compared vegetation characteristics and distribution of roads and waterholes around den sites and random sites, in areas with high and low lion and spotted hyena densities. In both areas, African wild dogs selected den sites in closed woodland with little visibility, which is likely to reduce detection by predators, increase the likelihood of escape when detected, and might provide shelter from extreme weather conditions. In the high predator density area, African wild dogs seemed to spatially avoid predators by selecting den sites in this type of habitat relatively further away from waterholes and roads. African wild dogs have high energetic costs of gestation. Therefore, even when predation risk is relatively low, they are likely to try to maximise their fitness by choosing a den site in habitat that will provide optimal protection for their offspring, leaving little additional options to respond to a higher predation pressure.

Larvae of cryptic species of Anopheles gambiae respond differently to cues of predation risk

Summary Predation is a major evolutionary force driving speciation. Identifying the stimuli prompting anti‐predator responses is essential for unravelling the proximate mechanisms of anti‐predator adaptations and for understanding how predation impacts species diversification. Here, we explore for the first time the divergence in the use of cues of predation risk by different incipient species of mosquitoes within the Anopheles gambiae complex. We examined the anti‐predator responses to various predation cues by the aquatic larvae of Anopheles arabiensis and the two molecular forms, M and S, of Anopheles gambiae s.s. sampled from wild populations in Burkina Faso naturally exposed to different predator densities. The larvae altered their behaviour in response to various predation cues, shifting from the surface of the water to a less exposed location on the walls of the experimental arena. There were important differences in the use of predation cues between populations sharing the same larval development sites and, within the M form, related to predation pressure at their site of origin. Anopheles arabiensis larvae, which develop in small temporary waterbodies, relied only on physical cues signalling the presence of a predator to mount a vigilance response, whereas the sympatric larvae of the M and S forms of An. gambiae used both physical and chemical cues to fine‐tune their response. M‐form larvae, developing in permanent aquatic habitats with high densities of predators, responded chiefly to chemical stimuli ensuing from acute predation. Our results suggest that predation might play a role as a disruptive selective force promoting ecological divergence within the An. gambiae complex and, more recently, between the M and S molecular forms. Notably, beyond interspecific differences in the use of predation cues, our study also documented phenotypic differences within the M form based on predation pressure at their site of origin, suggesting that a process of ecological divergence is generating species ‘forerunners’ within the An. gambiae complex in the wild.

Fearing the feline: domestic cats reduce avian fecundity through trait‐mediated indirect effects that increase nest predation by other species

Summary Urban areas contain high densities of non‐native species, which in the UK include the domestic cat Felis catus (Linnaeus 1758) and the grey squirrel Sciurus carolinensis (Gmelin 1788). The direct predation effects of domestic cats on prey populations attract intense debate, and such influences of the nest‐predatory grey squirrel are receiving increasing attention. In contrast, theory predicts that sublethal and indirect effects are more important, but empirical evidence is currently lacking. We conducted controlled model presentation experiments at active urban blackbird Turdus merula (Linnaeus 1758) nests to provide the first empirical evidence that quantifies the potential sublethal and indirect effects of predators (domestic cat and grey squirrel) on avian reproductive success. Domestic cat models reduced subsequent parental provisioning rates, a strong indicator of sublethal effects, by one‐third relative to a nonpredatory rabbit Oryctolagus cuniculus (Linnaeus 1758) control. There was no compensatory increase in food load size. Previous experiments demonstrate that this magnitude of reduced food delivery will reduce nestling growth rates by c. 40%. The grey squirrel model induced similar but weaker effects. Following the brief presence of the domestic cat model, subsequent daily nest predation rates, chiefly by corvids, increased by an order of magnitude relative to the squirrel and rabbit models. The intensity of parental nest defence elicited in response to model presentations predicts the probability of such third‐party predator predation events, and the domestic cat model generated significant increases in nest defence behaviour. Synthesis and applications. The brief presence of a domestic cat at avian nest sites reduces subsequent provisioning rates and induces lethal trait‐mediated indirect effects. We provide the first robust evidence for these latter effects in any avian predator–prey system, although they are likely to be common in many avian assemblages with high predator densities. It is imperative that future assessments of the impact of predatory species on avian prey species take lethal trait‐mediated indirect effects into account, as so doing will prevent biased estimates of predator effects and facilitate the design of more effective control strategies. Full mitigation of the sublethal and indirect effects of domestic cats would problematically require permanent indoor housing.

Top-down control of epifauna by fishes enhances seagrass production

Predators can influence the structure and function of ecosystems by altering the composition or behavior of herbivore communities. Overexploitation of predators, therefore, may lead to habitat loss by altering important top-down interactions that facilitate habitat-forming species. In seagrass beds, top-down control of algal growth by mesograzers appears to facilitate seagrass production. The indirect consequences of higher-order trophic interactions, however, remain unclear. Although predators may limit the beneficial effects of algal mesograzers, it is also possible that they limit the abundance of invertebrates that consume and foul seagrasses. We used experimental enclosure and exclosure cages to explore the direct and indirect effects of microcarnivorous fishes on epifaunal invertebrates, epiphytic loads, and seagrass growth in a natural eelgrass (Zostera marina) bed in San Diego Bay, California, USA. Contrary to expectations, when fishes were excluded, invertebrate abundance increased by 300-1000%, fouling on eelgrass leaves increased by 600%, and eelgrass production declined by 50%. Despite high densities of predators in enclosures, subsequent effects did not differ from ambient conditions. When predators were excluded, however, abundances of epifauna (including tube-building crustaceans and an eelgrass-grazing limpet) increased dramatically, resulting in reduced seagrass production. Our results are supported by several studies of eelgrass communities in the northeastern Pacific, characterized by coastal upwelling, inverse estuaries, and a voracious seagrass-consuming limpet. These strong, positive, indirect effects of microcarnivores on seagrass production contrast with the beneficial mesograzer paradigm, highlighting the need for hypotheses to be tested across a variety of ecosystems with varying biophysical characteristics.

The non‐consumptive effects of a predator on spider mites depend on predator density

AbstractPredators can have non‐consumptive effects on their prey by causing anti‐predator responses such as changes in behaviour. These effects may vary with the number of predators, which determines per capita predation risk. Predator density and cue concentration have been shown to affect prey responses in aquatic predator–prey systems; however, there are fewer tests in terrestrial systems. Here, we test the effects of predator density on prey dispersal and body growth in a system of predatory mites and their spider mite prey reared on leaf patches. Groups of prey were exposed to a low or high predator density level, or no predators. Prey dispersed in the presence of a predator and higher predator density led to greater prey dispersal. Growth in adult body size after maturation was reduced in the presence of a predator, and this effect was greater with a higher predator density, most likely related to a reduction in time spent feeding. Experiments were also conducted to test the effects of predator density mediated by predatory cues alone (previous presence of predators on the leaf patch). Spider mites were more likely to disperse when the patch had previously contained a higher density of predators; however, there was no effect of previous density level on body growth. These findings show that the non‐consumptive effects of a predator on spider mites can depend on predator density and provide some evidence that chemical cues play a role in this density dependence. As these changes are likely to affect the predation rate and prey population growth rate, they are also likely to have consequences for the predator–prey dynamics.

Habitat functionality for the ecosystem service of pest control: reproduction and feeding sites of pests and natural enemies

Landscape management for enhanced natural pest control requires knowledge of the ecological function of the habitats present in the landscape mosaic. However, little is known about which habitat types in agricultural landscapes function as reproduction habitats for arthropod pests and predators during different times of the year. We studied the arthropod assemblage on six crops and on the seven most abundant native plant species in two landscapes over 1 year in Australia. Densities of immature and adult stages of pests and their predators were assessed using beat sheet sampling. The native plants supported a significantly different arthropod assemblage than crops. Native plants had higher predator densities than crops over the course of the year, whereas crops supported higher pest densities than the native plants in two out of four seasonal sampling periods. Crops had higher densities of immature stages of pests than native plants in three of four seasonal sampling periods, implying that crops are more strongly associated with pest reproduction than native plants. Densities of immature predators, excluding spiders, were not different between native plants and crops. Spiders were, however, generally abundant and densities were higher on native plants than on crops but, because some species disperse when immature, there is less certainty in identifying their reproduction habitat. Because the predator to pest ratio on native plant species showed little variation, and spatial variation in arthropod assemblages was limited, the predator support function of native vegetation may be a general phenomenon. Incentives that maintain and restore native remnant vegetation can increase the predator to pest ratio at the landscape scale, which could enhance pest suppression in crops.

Huemul heresies: beliefs in search of supporting data. 2. Biological and ecological considerations

Scarce information from remnant huemul (Hippocamelus bisulcus) populations in marginal habitats can lead to erroneous interpretations of the species’ natural history, such as assumptions of being a highly inflexible species. We evaluated discrepancies between historical accounts and recent interpretations regarding biological and ecological traits to better understand factors preventing recovery of highly endangered huemul. Early information supports the theory that huemul are currently living under suboptimal conditions. We find variability to be the norm for huemul, as with other cervids, in regard to antler characteristics, group size and density, sexual segregation, and social and feeding behaviours. No evidence supports competition and disease from livestock or red deer as having caused declines or preventing recovery. Instead, livestock management, particularly presence of people and dogs, creates incompatibilities. Where red deer are sympatric with huemul, red deer are outnumbered by livestock by 2100%, and being regularly inspected at slaughter, livestock provide a good proxy for diseases afflicting red deer. Inadequate antipredator responses due to evolutionary absence of cursorial predators are unsupported as several Canis species coexisted with huemul, overlapping with dogs that arrived with Paleoindians. Three populations have increased despite high predator density. Age at maturity for huemul is 1 year, with evidence that fawns may also breed. Reported twinning needs confirmation, but occurs in congeneric taruca (H. antisensis) and other Odocoilines, and huemul frequently raise fawns successfully every year; life cycle calculations should apply these parameters. Like taruca, dominance group breeding systems have been described repeatedly. Although huemul bucks were recently claimed unique by displaying territoriality year-round, data do not support such behaviour. Two sole dispersal records (8 and 15.5 km) are unlikely to represent maximum dispersal capacity and do not support barriers assumed from few kilometres of unsuitable habitat. Huemul using 500 ha could predictably disperse up to 90 km, well within the ranges of other cervids. Mistakenly assuming barriers and underestimating reproductive capacity may distract from discovering the factors affecting recolonisations. Sustained recovery may depend on re-establishing source populations on more productive habitats, guided by zooarcheological and historical data.

Temporal variation in nest predation risk along habitat edges between grassland and secondary forest in Central Europe

Habitat fragmentation alters many ecological processes, including trophic cascades. For example, increased predation pressure along habitat edges has often been observed in fragmented landscapes. Here, we studied how nest predation risk varies along the transition zone between grassland and mixed forest in Central Europe. Using artificial nests, we tested the two mechanisms that are expected to underlie higher predation rates along edges: (1) the matrix effect model that supposes predator penetration from a habitat type with higher predator density to one with lower predator density and (2) the ecotonal effect model that assumes specific predator preferences for habitat edges. Although our results do not fully support either of these scenarios, our data show high temporal instability in nest predation along forest–grassland edges. Predation was higher in habitat interiors compared to edges during the first year, whereas the opposite pattern was observed during the subsequent year. In addition, dramatic between-year differences in the species composition of nest predators were observed. Therefore, we hypothesise that the effect of edges on nest predation is difficult to predict in landscapes with high predator diversity. In addition, our data indicate that a high abundance of wild boar considerably increases the risk of predation for ground-nesting birds.

The advantage of alternative tactics of prey and predators depends on the spatial pattern of prey and social interactions among predators

AbstractIndividual variation in behavioral strategies is ubiquitous in nature. Yet, explaining how this variation is being maintained remains a challenging task. We use a spatially‐explicit individual‐based simulation model to evaluate the extent to which the efficiency of an alternative spacing tactic of prey and an alternative search tactic of predators are influenced by the spatial pattern of prey, social interactions among predators (i.e., interference and information sharing) and predator density. In response to predation risk, prey individuals can either spread out or aggregate. We demonstrate that if prey is extremely clumped, spreading out may help when predators share information regarding prey locations and when predators shift to area‐restricted search following an encounter with prey. However, dispersion is counter‐selected when predators interact by interference, especially under high predator density. When predators search for more randomly distributed prey, interference and information sharing similarly affect the relative advantage of spreading out. Under a clumped prey spatial pattern, predators benefit from shifting their search tactic to an area‐restricted search following an encounter with prey. This advantage is moderated as predator density increases and when predators interact either by interference or information sharing. Under a more random prey pattern, information sharing may deteriorate the inferior search tactic even more, compared to interference or no interaction among predators. Our simulation clarifies how interactions among searching predators may affect aggregation behavior of prey, the relative success of alternative search tactics and their potential to invade established populations using some other search or spacing tactics.

Local management and landscape drivers of pollination and biological control services in a Kenyan agro-ecosystem

Arthropods that have a direct impact on crop production (i.e. pests, natural enemies and pollinators) can be influenced by both local farm management and the context within which the fields occur in the wider landscape. However, the contributions and spatial scales at which these drivers operate and interact are not fully understood, particularly in the developing world. The impact of both local management and landscape context on insect pollinators and natural enemy communities and on their capacity to deliver related ecosystem services to an economically important tropical crop, pigeonpea was investigated. The study was conducted in nine paired farms across a gradient of increasing distance to semi-native vegetation in Kibwezi, Kenya. Results show that proximity of fields to semi-native habitats negatively affected pollinator and chewing insect abundance. Within fields, pesticide use was a key negative predictor of pollinator, pest and foliar active predator abundance. On the contrary, fertilizer application significantly enhanced pollinator and both chewing and sucking insect pest abundance. At a 1 km spatial scale of fields, there were significant negative effects of the number of semi-native habitat patches within fields dominated by mass flowering pigeonpea on pollinators abundance. For service provision, a significant decline in fruit set when insects were excluded from flowers was recorded. This study reveals the interconnections of pollinators, predators and pests with pigeonpea crop. For sustainable yields and to conserve high densities of both pollinators and predators of pests within pigeonpea landscapes, it is crucial to target the adoption of less disruptive farm management practices such as reducing pesticide and fertilizer inputs.

Predator biomass, prey density, and species composition effects on group size in recruit coral reef fishes

Group incidence and size are described for recruit parrotfishes, wrasses, and damselfishes on Hawaiian reefs over 3 years (2006–2008) at sites spanning the archipelago (20–28°N, 155–177°W). Coral-poor and coral-rich areas were surveyed at sites with both low (Hawaii Island) and high (Midway Atoll) predator densities, facilitating examination of relations among predator and recruit densities, habitat, and group metrics. Predator and recruit densities varied spatially and temporally, with a sixfold range in total recruit densities among years. Group (≥2 recruits) metrics varied with time and tracked predator and recruit densities and the proportion of schooling species. Groups often included heterospecifics whose proportion increased with group size. A non-saturating relationship between group size and recruit density suggests that the anti-predator benefits of aggregation exceeded competitive costs. Grouping behavior may have overarching importance for recruit survival–even at high recruit densities–and merits further study on Hawaiian reefs and elsewhere.

Survival and cause‐specific mortality of elk Cervus canadensis calves in a predator rich environment

AbstractQuantification of basic demographic parameters such as survival rates and cause‐specific mortality is important for effective species management. We conducted a 4‐year study (during May 2005‐June 2009) of elk Cervus canadensis calf survival and cause‐specific mortality in Pennsylvania, USA. We captured and radio‐collared 93 elk calves ≤ 7 days old and monitored them weekly to detect mortality and cause of death. Of the 93 radio‐collared elk calves, 15 (16%) died during our study. Despite high black bear Ursus americanus and coyote Canis latrans densities, none of the mortalities were the result of predation. Causes of death included poaching (N = 3), legal harvest (N = 2), road kill (N = 2), pneumonia (N = 1) and rumen acidosis (N = 1). We were unable to determine the cause of mortality for six of the elk calves; however, predation was eliminated as a possible source of mortality in all unknown cases. Survival probabilities were similar between sexes and among years. Summer survival (birth‐31 October) was 0.92 (SE = 0.03, N = 93) and winter survival (1 November ‐ 1 April) was 0.90 (SE = 0.04, N = 79). Annual estimated elk calf survival was 0.82 (SE = 0.04, N = 93). Our findings suggest that Pennsylvania elk calves have a > 80% chance of survival to one‐year of age, despite high densities of predators known to influence elk calf survival elsewhere. The high calf survival rates that we observed indicate the availability of high quality habitat leading to excellent physical condition of elk.

The impact of a coastal invasive predator on infaunal communities: Assessing the roles of density and a native counterpart

Our understanding of the influence of many predatory invaders in areas of increasing overlap with native counterparts remains elusive. In Atlantic Canada, the European green crab, Carcinus maenas, overlaps with the native rock crab, Cancer irroratus, but surprisingly little is known about their effects in the light of their potential interactions. In this study we used short-term cage inclusion experiments to assess the impact of low and high green crab densities upon infaunal communities. Then, we re-assessed this impact by running identical manipulations combining green crabs with rock crabs of comparable size and at similar overall predator densities. Our results indicate that both low and high green crab densities accounted for severe declines in infaunal organisms with respect to ambient cages. Polychaetes, the group best represented in this trial, accounted for most of such decline with densities at least 50% lower in the green crab inclusions. A similar (~ 50%) decline in infaunal density was observed when green crabs and rock crabs were combined at low predator densities. However, at high predator densities their impact on polychaetes, molluscs and total infauna was less severe and non-significant with respect to ambient cages. Our results indicate that between-predator interactions have serious indirect effects on benthic prey and contrast previous results on the role played by these crab species. We propose a re-assessment of the role played by native counterparts while searching for management alternatives to minimize the impact of invasive predators in areas heavily invaded.

Mitigating carnivore–livestock conflict in Europe: lessons from Slovakia

AbstractConflicts with human interests have reappeared following recovery of large carnivores in Europe. Public acceptance is higher than historically but there is a need to identify effective, acceptable techniques to facilitate coexistence. We present a case study of predation on livestock in Slovakia. Damage, mitigation measures and public opinion were assessed using compensation records, analysis of farm conditions, questionnaire surveys, semi-structured interviews, diet analysis and on-farm trials of livestock-guarding dogs. Economic damage was inconsequential on a national scale but high locally: c. 80% of reported losses occurred at 12% of sheep flocks. Grey wolvesCanis lupuswere held responsible for four to six times more damage than brown bearsUrsus arctos, although livestock occurred in only 2 of 78 wolf faeces during spring–autumn, when sheep and cattle were most vulnerable. Losses to Eurasian lynxLynx lynxwere negligible. Compared to other sectors of society shepherds had the most negative attitudes, particularly towards wolves, despite compensation payments. Appropriate use of livestock-guarding dogs was associated with fewer losses: median loss at trial flocks with predation was 70% lower than at control flocks. We conclude that identifying vulnerable farms and targeting them for mitigation could reduce damage, although lack of motivation and awareness are obstacles. This study shows that damage levels need not be excessive despite high predator densities in human-dominated landscapes. Conflicts were unevenly distributed, with much of the variation explained by local conditions and husbandry practices, especially preventive measures. Livestock-guarding dogs are particularly appropriate where wolves are present in proximity to unfenced pastures.