Predator Control Research Articles

Modelling transmission and control of Toxoplasma gondii in New Zealand farmland

Toxoplasma gondii is one of the world’s most prevalent parasites and has significant impacts on the health of humans, domestic animals and wildlife. In New Zealand’s rural environments, T. gondii creates economic losses for the farming industry and threatens vulnerable native avifauna and marine mammals. Predator control of rodents and feral cats has potential to reduce or even eliminate transmission of T. gondii on farms; however, the efficacy of such management is uncertain. We apply a mathematical model of T. gondii transmission dynamics in feral cat and rodent populations in New Zealand farmland and simulate varying intensities of predator control to predict changes in T. gondii prevalence and environmental contamination levels over time. The model predicts that predator control is relatively ineffective for reducing transmission in areas with high environmental contamination rates. However, assuming low rates of environmental contamination, local elimination of T. gondii could be achievable, for example, by control that sustains large reductions of 88%, 69% and 59% in feral cat, house mouse and ship rat populations, respectively, over 56 weeks. Predator control is, therefore, a potentially viable approach for managing T. gondii in some rural environments, but only if high levels of population control are sustained.

Corrigendum to “Understanding ground-nesting habitat selection by waterbirds to prioritize invasive predator control on islands” [Basic and Applied Ecology Volume 78, August 2024, Pages 14-22

Corrigendum to “Understanding ground-nesting habitat selection by waterbirds to prioritize invasive predator control on islands” [Basic and Applied Ecology Volume 78, August 2024, Pages 14-22

Identification and characteristics of refuges for the threatened swamp antechinus (Antechinus minimus maritimus) under climate change; targeted surveys across the Otway Ranges, south-east Australia

There is growing evidence that persistence of mammal fauna under climate change is reliant on refuges protected from disturbances such as extreme drought and fire. During the ‘millennium drought’ (1996–2010), the swamp antechinus (Antechinus minimus maritimus) declined precipitously in the eastern Otways, resulting in restriction to coastal dune refuges. Here, we evaluated the species’ distribution across the extended Otway landscape to identify the localities and characteristics of refuges. Targeted surveys (cameras, live-trapping) were conducted at sites of previous healthy populations and in putative habitat refuges (2018–2023). Eleven micro-refuges (<500 ha), located in Coastal Dune Scrub, were identified but are subject to destruction due to sea level rise. Three mid-connected refuges (500–1000 ha), providing habitat connection features (e.g. gullies), and three macro-refuges (>1000 ha) of unfragmented, complex vegetation were identified. The swamp antechinus remains absent from previously inhabited heathy woodland in the eastern Otways, and although it was initially (2021) trapped with high success in heathy woodlands of the Carlisle Heath, it was not captured subsequently, possibly related to incompatible fire, introduced predators and Phytophthora dieback. Management of refuges to ensure the future of the swamp antechinus will require effective control of Phytophthora infestation and predators, and protection from inappropriate fire.

Parasitoid avoidance of intraguild predation drives enemy complementarity in a multi-trophic ecological network.

How consumer diversity determines consumption efficiency is a central issue in ecology. In the context of predation and biological control, this relationship concerns predator diversity and predation efficiency. Reduced predation efficiency can result from different predator taxa eating each other in addition to their common prey (interference due to intraguild predation). By contrast, multiple predator taxa with overlapping but complementary feeding niches can generate increased predation efficiency on their common prey (enemy complementarity). When viewed strictly from an ecological perspective, intraguild predation and enemy complementarity are opposing forces. However, from an evolutionary ecology perspective, predators facing strong intraguild predation may evolve traits that reduce their predation risk, possibly leading to niche complementarity between enemies; thus, selection from intraguild predation may lead to enemy complementarity rather than opposing it. As specialized predators that live in or on their hosts, parasitoids are subjected to intraguild predation from generalist predators that consume the parasitoids' hosts. The degree to which parasitoid-predator interactions are ruled by interference versus enemy complementarity has been debated. Here, we address this issue with field experiments in a forest community consisting of multiple species of trees, herbivorous caterpillars, parasitoids, ants, and birds. Our experiments and analyses found no interference effects, but revealed clear evidence for complementarity between parasitoids and birds (not ants). Parasitism rates by hymenopterans and dipterans were negatively associated with bird predation risk, and the variation in the strength of this negative association suggests that this enemy complementarity was due to parasitoid avoidance of intraguild predation. We further argue that avoidance of intraguild predation by parasitoids and other arthropod predators may explain enigmatic patterns in vertebrate-arthropod-plant food webs in a variety of terrestrial ecosystems.

OPTIMAL HARVEST CONTROL OF PREDATOR–PREY SYSTEMS IN FISHERIES WITH STAGE STRUCTURE AND ADDITIONAL FOOD SUPPLY

In this paper, we consider a fishery predator–prey system with stage structure and additional food incorporating fluctuations in resource prices influenced by supply and demand. The fishery system can be regarded as a slow–fast system under some suitable assumptions. Through variable aggregation methods, we derive a simplified four-dimensional model governing the density of prey fish, the juvenile and adult predator densities, and fishing effort in the fishery. We perform a stability analysis of the simplified system and give the optimal harvesting policy by using Pontryagin’s maximum principle. In our analysis, we find that the catastrophe equilibrium point corresponding to overfishing leading to fish extinction is unstable, which indicates that the predator stage structure has an impact on the stability of the system. Moreover, we find that due to the additional food item the system appears to have prey-free equilibrium points, which indicates that the system does not collapse due to the extinction of one prey item. We also give thresholds for the amount of additional food needed to maintain the balance of the system under different circumstances.

The challenge of preventing extinctions: Lessons from managing threatened land snails on Norfolk Island.

Norfolk Island, situated between Australia, New Zealand and New Caledonia, has a rich, narrowly endemic land snail fauna, which has suffered considerably from habitat loss and introduced predators. Eleven species (Stylommatophora, Microcystidae) are currently listed by the IUCN and/or Australia's EPBC Act 1999 as Endangered, Critically Endangered or Extinct. Based on targeted surveys undertaken since 2020, we re-assess the threat status of these taxa. For three species assessed to be at imminent risk of extinction, we report on the implementation of in-situ and ex-situ conservation actions and assess their effectiveness after a three-year period. We document current distributions and abundances of these species and describe experimental conservation methods, such as increased predator control, the erection of predator-proof exclosures, and the establishment of an ex-situ breeding population. We found that the relative abundance of one subspecies, Advena campbellii campbellii, was strongly correlated with monthly rainfalls. Trials of predator-proof exclosures that retain adults but allow juveniles to disperse indicated that snails can be successfully secured from predation. Increased efforts in predator control led to the killing of more rodents and chickens; however, the impact on the snail population is unclear. The ex-situ breeding population had high birth rates initially followed by high adult mortality. Adjustments in husbandry conditions reduced stress levels leading to sustainable birth rates and increased survivorship with the result of rapid population growth. We determined that the ovoviviparous A. campbellii campbellii matures at the age of 3-4 months and has a lifespan of 10-12 months in captivity. We conclude that focused predation studies are needed to determine the impact of introduced predators. The use of exclosures requires further refinement especially regarding feeding schedules. In-situ breeding requires significant time for establishment but can be implemented successfully. We assess three endemic species as Extinct, four as Critically Endangered and two as Vulnerable.

Multi‐scale habitat selection and nest survival of whinchats and stonechats: implications for grassland conservation management

Effective management for endangered grassland birds requires a sound understanding of habitat requirements and factors shaping reproductive success. We studied multi‐level habitat selection of endangered whinchats Saxicola rubetra and locally increasing stonechats Saxicola rubicola in a nature reserve using Sentinel‐2 images, LiDAR data, and habitat variables measured onsite. We monitored nest fates, and estimated how the causes of nest mortality varied with nest initiation date. Further, we analyzed how nest‐site selection, precipitation, nest initiation date, and nest age influenced daily nest survival.At the landscape‐ and site‐level, both species primarily selected for territories in lightly farmed meadows. However, stonechats appeared to be less specialized and used most available habitat types. Within home‐ranges, both species selected for nest‐sites in fallow patches, but in contrast to stonechats, whinchats also selected for large viewsheds.In both species, the main causes of nest failure were predation by red foxes Vulpes vulpes, weather‐related factors, and nest desertion. In whinchats, the probability of nest desertion increased and predation risk decreased with nest initiation date, possibly due to better nest concealment in the later season. Daily nest survival decreased with nest age and precipitation in both species, and increased with nest initiation date in whinchats. None of the habitat variables examined were positively linked to daily nest survival, and viewshed was negatively related to whinchat daily nest survival.Our study suggests that extending core habitat may help to promote settlement and potentially reproductive success of whinchats. However, as habitat selection was not positively associated with daily nest survival, land management measures alone might not be sufficient to halt rapid population declines. To effectively conserve whinchats and other grassland bird populations, the causes of nest failures must be identified and addressed. Within the examined reserve and similar habitats, flood management and predator control may yield the biggest short‐term conservation gains.

Rifleman (Acanthisitta chloris sp.) population responses to aerial 1080 (sodium fluoroacetate) predator control in beech forests

Rifleman (Acanthisitta chloris sp.) population responses to aerial 1080 (sodium fluoroacetate) predator control in beech forests

Ecological erosion and expanding extinction risk of sharks and rays.

The true state of ocean biodiversity is difficult to assess, and there are few global indicators to track the primary threat of overfishing. We calculated a 50-year Red List Index of extinction risk and ecological function for 1199 sharks and rays and found that since 1970, overfishing has halved their populations and their Red List Index has worsened by 19%. Overfishing the largest species in nearshore and pelagic habitats risks loss of ecomorphotypes and a 5 to 22% erosion of functional diversity. Extinction risk is higher in countries with large human coastal populations but lower in nations with stronger governance, larger economies, and greater beneficial fisheries subsidies. Restricting fishing (including incidental catch) and trade to sustainable levels combined with prohibiting retention of highly threatened species can avert further depletion, widespread loss of population connectivity, and top-down predator control.

Optimising Control Device Luring Strategies for Invasive Predator Control: A Modelling Approach.

Invasive predators pose a serious threat to native biodiversity, with trapping being one of several methods developed to manage and monitor their populations. Many individuals in these predator populations have been found to display trap-shyness, which hinders eradication and results in inaccurate estimates of population size. Lures are used to help overcome trap-shyness by increasing the probability of interaction with the device, but the extent of trap-shyness in wild populations, and the best timing for the introduction of a new lure or combination of lures, are uncertain. A key challenge for wildlife managers is maximising the efficacy of invasive predator control, particularly in relation to baiting and trapping, so that pests are extirpated, or survivors are reduced to a minimum. We first use a Bayesian estimation method to quantify trap-shyness in a population of brushtail possum (Trichosurus vulpecula) in a New Zealand forest; the resulting estimated parameters are then used to calibrate a stochastic, individual-based model simulating the outcomes of different luring scenarios. We show that the brushtail possum population analysed was likely split into a smaller, very trappable group and a larger trap-shy group, with a low mean nightly probability of interaction with traps of 0.28 [0.14-0.56]. Furthermore, our results show that under the assumption of independent attraction levels towards different lures, using a combination of lures simultaneously can result in a greater and faster population knock-down than using a single lure, or than to switch from one lure to another. The model presented can be used to infer wildlife population trappability from capture data, and our simulation results highlight the potential of improved luring strategies to capture individuals in post-control residual populations.

Prey-carrying behavior of Lycalopex foxes in Chilean Patagonia

This study examines prey-carrying behavior in culpeo (Lycalopex culpaeus) and chilla (L. griseus) foxes within Chilean Patagonia's sheep farming lands. We used camera traps to register prey transportation. This behavior was more frequent during the reproductive season compared to the non-reproductive season, suggesting an association with pup-rearing activities. The presence of livestock guardian dogs and other predation control measures may also influence prey-carrying behavior, particularly in L. culpaeus, as foxes might adjust their activities in response to perceived risks. This research provides initial evidence of prey transport in these fox species and highlights the need for further study to understand its ecological implications and interactions with livestock management practices.

Consequences of terrestrial top predator control by Patagonian sheep farmers for coastal marine food webs

Most seabird species avoid predation by locating their breeding colonies in predator-free islands, inaccessible cliffs, capes, or on the mainland in Antarctica, the only continent without terrestrial predators. Departing from this general rule, a significant number of large Magellanic penguin (Spheniscus magellanicus) colonies exist nowadays in South American Atlantic mainland shores spanning a wide latitudinal range. Based on published radiocarbon dating of colonies, along with historical and archaeological records, we postulate that the current distribution of these colonies may be a response to predator eradication by sheep farmers. This would have made breeding habitats near marine food resources accessible and may have also reduced competition with neighboring colonies. We employed stable isotope analysis to estimate the penguin contribution to the diet of four pumas responsible for killing thousands of penguins in a breeding colony located within a coastal national park. Furthermore, we used a bioenergetic model to quantify the consumption of forage fish under different population distribution and abundance scenarios. We briefly discuss the implications of our results in the context of conservation policies aimed at establishing ecosystem baselines along the Patagonian shores.

Dynamical and Phase Analyses on Chaos Control of Discrete Predator–Prey Systems of Mixed Holling Types with Density-Dependent Birth Rates

This paper discusses the effect of density-dependent birth rate in a discrete predator–prey system with mixed functional responses of Holling types I and III. We use the Beverton–Holt function to modify the birth rate parameter of the prey species. The steady states and their stability are established. The criteria for flip bifurcation (FB) and Neimark–Sacker bifurcation (NSB) are proposed analytically using the center manifold theorem and normal bifurcation theory. Using the state feedback control method, it is shown that chaotic orbit can be stabilized at an unstable steady-state. This study deduces that the density of predator species is negatively affected by the density-dependent birth rate of prey species. Moreover, density-dependent birth rate can increase the possibility of extinction in prey species, which means that this birth rate may cause Allee effect. Some numerical simulations are given to verify these analytical results.

A landscape-based approach to design flower blocks may reduce mammalian predator activity and protect ground-nesting farmland birds

High predation rates threaten many ground-nesting farmland birds and are difficult to address through conventional measures such as lethal predator control or fencing. Landscape-based approaches for conservation measures promise an alternative by reducing predator - bird encounters, but require detailed knowledge of landscape effects on predation risk. Different habitat elements attractive to predators could have opposing effects on neighbouring nesting habitats, with implications for conservation: Increased predation risk due to higher predator activity (A) or reduced predation risk by distracting predators (B). Here we focus on the placement of conservation measures using flower blocks targeted at Grey Partridges in a Central European Farmland. Based on a three-year camera trap dataset, we investigated effects of landscape structure and composition on mammalian predator activity within flower blocks at two scales (100 m and 500 m radius around the camera) with generalized linear mixed models. Length of linear edge structures, i.e., field block borders, was most important, with a greater availability of linear edge structures leading to a decrease in predator activity at both scales (hypothesis B). Conversely, predator captures at both scales increased with increasing extensive vegetation area (i.e., permanent grassland, flower blocks and fallows) and in proximity to roads, indicating that these may attract predators and increase predator densities (hypothesis A). Our results suggest that a landscape-based approach can mitigate predation risk for ground-nesting birds in flower blocks and analogous conservation measures. Highly structured, small-scale agricultural landscapes seem to be particularly important for reducing mammalian predator activity in flower blocks.

The decline of ground nesting birds in Europe: Do we need to manage predation in addition to habitat?

Bird populations are declining globally with losses recorded in many European breeding birds. Habitat management measures have not resulted in widespread reversal of these declines. We analysed national bird population trends from ten European countries (France, Hungary, Ireland, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the UK) for which data on individual bird species was freely available online in relation to the species’ nesting strategy (‘ground-nesting’ or ‘other’), Annex I designation (‘designated’ or ‘not designated’) and association with agricultural habitats for breeding (‘associated’ or ‘not associated’). For each country in our dataset, we also broadly categorised the following factors: farming intensity; predator community complexity; and predator control effort. Our results showed additive effects of nesting strategy, designation, and breeding habitats on the likelihood of population decline. Ground-nesting birds were 86 % more likely to decline than birds with other nesting strategies. Annex I designated species of the Birds Directive were 50 % less likely to decline than non-designated birds. Birds breeding primarily in agricultural habitat were more likely to decline than birds breeding in other habitats, interactively with farming intensity. Homogenous trends across Europe (i.e. trends in two or more countries that were either not declining in all countries or declining in all countries), indicate that the probability of population decline was related to nesting strategy and breeding habitat. Ground-nesting birds were 15.6 times more likely than other birds to have a declining trend across Europe, and birds nesting in agricultural habitats were 17.8 times more likely to decline than birds nesting in other habitats. Our results highlight a widespread challenge, therefore widespread instruments (e.g. legislation, economic policies, agri-environment schemes) will be required to reverse these declines. Ground-nesting species requirements can be complex and multiple strategies will be needed to restore populations including the development of predation management tools.

Absence of predator control increases cod extirpation risk in a Northwest Atlantic ecosystem: inference from multispecies modelling

Atlantic cod Gadus morhua in the southern Gulf of St. Lawrence (sGSL) declined to low abundance in the early 1990s and have since failed to recover due to high natural mortality, which has been linked to predation by grey seals Halichoerus grypus. Increased grey seal harvests have been suggested to improve cod survival; however, predicting the response of cod to changes in seal abundance in the sGSL is complicated by a hypothesized triangular food web involving seals, cod, and small pelagic fishes, wherein the pelagic fishes are prey for cod and grey seals, but may also prey on young cod. Grey seals may therefore have an indirect positive effect on pre-recruit cod survival via predation on pelagic fish. Using a multispecies model of intermediate complexity fitted to various scientific and fisheries data, we found that seal predation accounted for the majority of recent cod mortality and that cod will likely be extirpated without a strong and rapid reduction in grey seal abundance. We did not find evidence that reducing grey seal abundance will impair cod recovery by causing large increases in pelagic biomass so long as pelagic fishing mortality continues at historical levels.

Livestock guarding dogs shape activity patterns of sympatric mesocarnivores in sheep ranches of the Patagonia region

Predation of livestock by wild carnivores is a source of human-wildlife conflict. Livestock Guarding Dogs (LGDs) are one of the most effective non-lethal methods used. LGDs could impact wildlife due to their possible top predator role; their effect on mesocarnivores has been studied mainly in terms of space use, however, temporal effects may also exist. Our study sought to determine the possible effects of LGD presence on the activity patterns of the native foxes Lycalopex griseus and L. culpaeus in southern Chile. Activity patterns were estimated from fox detections with camera traps set on ranches with and without LGDs in Isla Riesco, Magallanes region, Chile, between 2016 and 2018. We quantified the activity patterns of each fox species in presence/absence of LGDs, and under different conditions including breeding vs non-breeding season, moon phase and vegetation cover. Both species modified their daily activity pattern, avoiding times of day of high LGD activity; nevertheless, these modifications did not change the temporal interaction between the native foxes. Activity patterns of foxes without LGDs did not differ from those in natural areas. The effect of LGDs on fox activity patterns was stronger than other ecological variables (breeding season, moon phase or vegetation cover). Since LGDs change the activity patterns of foxes, they cannot be seen as a totally innocuous predation control tool; however, carnivores’ temporal avoidance of areas with a fear-evoking agent like LGDs would result in fewer livestock-predators encounters, thus reducing sheep predation risk. LGDs appear to exert non-lethal effects upon carnivores that would contribute to reduced predation rates and may help decrease producers’ economic losses, as well as the retaliatory hunting of wild carnivores. Thus, our results support that LGDs could be contributing to the co-existence with native predators in areas destined for livestock production.

Long-term anti-predator learning and memory differ across populations and sexes in an intertidal snail.

Anti-predator behaviours in response to predator cues can be innate, or they can be learned through prior experience and remembered over time. The duration and strength of continued anti-predator behaviour after predator cues are no longer present, and the potential for an enhanced response when re-exposed to predator cues later is less known but could account for the observed variation in anti-predator responses. We measured the carryover effects of past predation exposure and the potential for anti-predator learning and memory in the marine snail Nucella canaliculata from six populations distributed over 1000 km of coastline. We exposed lab-reared snails to cues associated with a common crab predator or seawater control in two serial experiments separated by over seven months. Responses were population- and sex-dependent, with some populations retaining anti-predator behaviours while others showed a capacity for learning and memory. Male snails showed a strong carryover of risk aversion, while females were able to return to normal feeding rates and grow more quickly. These behavioural differences culminated in strong impacts on feeding and growth rates, demonstrating that this variation has implications for the strength of trait-mediated indirect interactions, which can impact entire ecosystems.

Potential threats and habitat of the night parrot on the Ngururrpa Indigenous Protected Area

Context The Endangered night parrot (Pezoporus occidentalis) is one of the rarest birds in Australia, with fewer than 20 known to occur in Queensland and, prior to 2020, only occasional detections from a handful of sites in Western Australia (WA). Here, we provide an introduction to night parrots on the Ngururrpa Indigenous Protected Area (IPA) in WA from the perspectives of both Indigenous rangers and scientists working together to understand their ecology. Aims We aimed to identify night parrot sites on the Ngururrpa IPA, compare habitat and likely threats with those in Queensland and identify appropriate management practices. Methods Between 2020 and 2023, we used songmeters (a type of acoustic recorder) to survey for the presence of night parrots at 31 sites (>2 km apart). At sites where parrots were detected, we used camera-traps to survey predators and collected predator scats for dietary analysis. Forty years of Landsat images were examined to assess the threat of fire to roosting habitat. Key results Night parrots were detected at 17 of the 31 sites surveyed on the Ngururrpa IPA. Positive detections were within an area that spanned 160 km from north to south and 90 km from east to west. Ten roosting areas were identified, and these occurred in habitat supporting the same species of spinifex (lanu lanu or bull spinifex, Triodia longiceps) used for roosting in Queensland. However, the surrounding landscapes differ in their vegetation types and inherent flammability, indicating that fire is likely to be a more significant threat to night parrots in the Great Sandy Desert than in Queensland. Dingoes (Canis dingo) were the predator species detected most frequently in night parrot roosting habitat and the feral cat was found to be a staple prey for dingoes at night parrot sites. Conclusions Our surveys indicated that there could be at least 50 night parrots on the Ngururrpa IPA, which is the largest known population in the world. Fire is a key threat to roosting habitat, occurring in the surrounding sandplain country every 6–10 years. Dingoes are common in night parrot habitat and regularly eat feral cats, which are only occasionally detected in roosting habitat. Implications We recommend management that focuses on strategic burning to reduce fuel loads in the surrounding landscape, and limiting predator control to methods that do not harm dingoes.

Interactions between host plant quality and non‐consumptive predator effects on oviposition and larval behaviour of Plutella xylostella (Lepidoptera: Plutellidae)

Abstract The presence of predators can induce non‐consumptive effects on prey that result in subsequent changes to prey behaviour and defence. We investigate the interaction between top‐down non‐consumptive effects of various stages of the predator Coccinella septempunctata L.(Coleoptera: Coccinellidae) (larvae and adult) and bottom‐up effects of host nutrition on Plutella xylostella (L.) (Lepidoptera: Plutellidae) oviposition and larval host choice. We also compare the effect of presence of intact predators, predators without mandibles, confined predators and a no predator control treatment on P. xylostella larval growth, survival and herbivory. Host plant nutrition influenced the host choice of adult female P. xylostella; no interaction was observed between bottom‐up host plant nutrition and the presence of C. septempunctata adults or larvae on oviposition or larval host choice by P. xylostella. Predator presence impacted larval feeding and weight gain. The presence of free‐moving C. septempunctata adults without mandibles that could not predate P. xylostella reduced mean leaf consumption by P. xylostella larvae to 1.88 ± 0.21 cm2 and reduced weight gain to 2.12 ± 0.16 mg. Despite differences in leaf damage and larval weight gain, survival remained consistent across the non‐consumptive treatments. Intact C. septempunctata larvae reduced leaf damage and subsequent P. xylostella larval weight gain. The presence of larval predators across the non‐consumptive treatments, however, had no effect on feeding damage or weight gain. Results of our investigation indicate that C. septempunctata causes some non‐consumptive effects on P. xylostella that depend on predator life stage, level of confinement and prey life stage. It is likely that P. xylostella responds to multi‐modal cues in predator detection.