Influence of revegetation on predation rates by introduced red foxes (Vulpes vulpes) in south‐eastern Australian farmland

Interactions between wild carnivore abundance and landscape composition in agricultural landscapes are poorly understood despite their importance to both production and conservation. In Australia, introduced red foxes (Vulpes vulpes) prey on both native species and lambs in the temperate agricultural regions. Historically these areas were extensively cleared of native vegetation. Recently revegetation programmes have been implemented, but there is concern that this may benefit foxes and hence increase their impacts. We used an artificial prey placed in eight revegetated (6–12% cover) and 10 cleared (0–1.5% cover) landscapes of ～700 ha to assess how these landscapes influenced fox predation rates. In June and August 2006 (winter) when we expect fox populations to be relatively stable following juvenile dispersal, predation rates were 1.5–2 times higher in revegetated landscapes than in cleared landscapes. We found no evidence of microhabitat effects on predation rates suggesting these landscape‐level differences were probably due to differences in fox population density. In April 2007 (autumn) the results were more variable, possibly indicating more transient populations including dispersing juveniles at this time. Our results suggest that the impact of foxes on highly vulnerable prey could increase with revegetation. However, the benefits of revegetation to prey may offset negative impacts of foxes and future work is required to assess the likely net effects.     

Testing the validity of functional response models using molecular gut content analysis for prey choice in soil predators

Analysis of predator–prey interactions is a core concept of animal ecology, explaining structure and dynamics of animal food webs. Measuring the functional response, i.e. the intake rate of a consumer as a function of prey density, is a powerful method to predict the strength of trophic links and assess motives of prey choice, particularly in arthropod communities. However, due to their reductionist set‐up, functional responses, which are based on laboratory feeding experiments, may not display field conditions, possibly leading to skewed results. Here, we tested the validity of functional responses of centipede predators and their prey by comparing them with empirical gut content data from field‐collected predators. Our predator–prey system included lithobiid and geophilomorph centipedes, abundant and widespread predators of forest soils and their soil‐dwelling prey. First, we calculated the body size‐dependent functional responses of centipedes using a published functional response model in which we included natural prey abundances and animal body masses. This allowed us to calculate relative proportions of specific prey taxa in the centipede diet. In a second step, we screened field‐collected centipedes for DNA of eight abundant soil‐living prey taxa and estimated their body size‐dependent proportion of feeding events. We subsequently compared empirical data for each of the eight prey taxa, on proportional feeding events with functional response‐derived data on prey proportions expected in the gut, showing that both approaches significantly correlate in five out of eight predator–prey links for lithobiid centipedes but only in one case for geophilomorph centipedes. Our findings suggest that purely allometric functional response models, which are based on predator–prey body size ratios are too simple to explain predator–prey interactions in a complex system such as soil. We therefore stress that specific prey traits, such as defence mechanisms, must be considered for accurate predictions.     

Migratory herds of wildebeests and zebras indirectly affect calf survival of giraffes

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Prey diversity of Polistes rothneyi koreanus in different landscapes using DNA barcoding

For the present study, we investigated the prey of Polistes rothneyi koreanus, which is the most common social wasp in South Korea, and the relationship between prey diversity and vegetation cover around their nests. Prey was collected over two 6‐hr sampling from seven nests between July and mid‐August 2015 in Daegu, Gyeongsan and Gunwi in South Korea. To analyse the prey spectrum, we identified species using DNA barcodes; to analyse vegetation cover, we used the normalized difference vegetation index in a 200 m radius around the nests. A total of 338 prey samples were collected, and eight orders, 24 families, and 65 species were identified, demonstrating a much broader prey spectrum than those previously recorded for Polistes spp. Lepidoptera were the most prevalent, with 158 samples and 47 species. Nest 7, located in a rural area, had the highest numbers of samples and species per worker (5.2 and 1.9, respectively). Lepidoptera accounted for over half of the prey spectrum for all nests, and the families Noctuidae and Geometridae accounted for 60% of all Lepidoptera. Tenodera sinensis (Mantodea) and Gabala argentata (Noctuidae) were the most ubiquitous species, collected at five locations. Six species and some genera of prey are designated as pests in South Korea, indicating that P. r. koreanus also has a beneficial role in pest control. A higher vegetation cover was associated with significantly higher prey species diversity (R² = .4597, p < .1) and abundance (R² = .5986, p < .05), indicating that vegetation cover is an important factor for maintaining colonies. Therefore, the recent increase in green spaces in South Korean cities is probably a major contributor to the increased density of social wasps.     

Modeling ecological traps for the control of feral pigs

Ecological traps are habitat sinks that are preferred by dispersing animals but have higher mortality or reduced fecundity compared to source habitats. Theory suggests that if mortality rates are sufficiently high, then ecological traps can result in extinction. An ecological trap may be created when pest animals are controlled in one area, but not in another area of equal habitat quality, and when there is density‐dependent immigration from the high‐density uncontrolled area to the low‐density controlled area. We used a logistic population model to explore how varying the proportion of habitat controlled, control mortality rate, and strength of density‐dependent immigration for feral pigs could affect the long‐term population abundance and time to extinction. Increasing control mortality, the proportion of habitat controlled and the strength of density‐dependent immigration decreased abundance both within and outside the area controlled. At higher levels of these parameters, extinction was achieved for feral pigs. We extended the analysis with a more complex stochastic, interactive model of feral pig dynamics in the Australian rangelands to examine how the same variables as the logistic model affected long‐term abundance in the controlled and uncontrolled area and time to extinction. Compared to the logistic model of feral pig dynamics, the stochastic interactive model predicted lower abundances and extinction at lower control mortalities and proportions of habitat controlled. To improve the realism of the stochastic interactive model, we substituted fixed mortality rates with a density‐dependent control mortality function, empirically derived from helicopter shooting exercises in Australia. Compared to the stochastic interactive model with fixed mortality rates, the model with the density‐dependent control mortality function did not predict as substantial decline in abundance in controlled or uncontrolled areas or extinction for any combination of variables. These models demonstrate that pest eradication is theoretically possible without the pest being controlled throughout its range because of density‐dependent immigration into the area controlled. The stronger the density‐dependent immigration, the better the overall control in controlled and uncontrolled habitat combined. However, the stronger the density‐dependent immigration, the poorer the control in the area controlled. For feral pigs, incorporating environmental stochasticity improves the prospects for eradication, but adding a realistic density‐dependent control function eliminates these prospects.     

Dropping to escape: a review of an under‐appreciated antipredator defence

Dropping is a common antipredator defence that enables rapid escape from a perceived threat. However, despite its immediate effectiveness in predator–prey encounters (and against other dangers such as a parasitoid or an aggressive conspecific), it remains an under‐appreciated defence strategy in the scientific literature. Dropping has been recorded in a wide range of taxa, from primates to lizards, but has been studied most commonly in insects. Insects have been found to utilise dropping in response to both biotic and abiotic stimuli, sometimes dependent on mechanical or chemical cues. Whatever the trigger for dropping, the decision to drop by prey will present a range of inter‐related costs and benefits to the individual and so there will be subtle complexities in the trade‐offs surrounding this defensive behaviour. In predatory encounters, dropping by prey will also impose varying costs and benefits on the predator – or predators – involved in the system. There may be important trade‐offs involved in the decision made by predators regarding whether to pursue prey or not, but the predator perspective on dropping has been less explored at present. Beyond its function as an escape tactic, dropping has also been suggested to be an important precursor to flight in insects and further study could greatly improve understanding of its evolutionary importance. Dropping in insects could also prove of significant practical importance if an improved understanding can be applied to integrated pest‐management strategies. Currently the non‐consumptive effects of predators on their prey are under‐appreciated in biological control and it may be that the dropping behaviour of many pest species could be exploited via management practices to improve crop protection. Overall, this review aims to provide a comprehensive synthesis of the current literature on dropping and to raise awareness of this fascinating and widespread behaviour. It also seeks to offer some novel hypotheses and highlight key avenues for future research.     

Interactive effects of ocean acidification and rising sea temperatures alter predation rate and predator selectivity in reef fish communities

Ocean warming and acidification are serious threats to marine life. While each stressor alone has been studied in detail, their combined effects on the outcome of ecological interactions are poorly understood. We measured predation rates and predator selectivity of two closely related species of damselfish exposed to a predatory dottyback. We found temperature and CO₂ interacted synergistically on overall predation rate, but antagonistically on predator selectivity. Notably, elevated CO₂ or temperature alone reversed predator selectivity, but the interaction between the two stressors cancelled selectivity. Routine metabolic rates of the two prey showed strong species differences in tolerance to CO₂ and not temperature, but these differences did not correlate with recorded mortality. This highlights the difficulty of linking species‐level physiological tolerance to resulting ecological outcomes. This study is the first to document both synergistic and antagonistic effects of elevated CO₂ and temperature on a crucial ecological process like predator–prey dynamics.     

Effect of Willow Tit Poecile montanus alarm calls on attack rates by Pygmy Owls Glaucidium passerinum

One suggested anti‐predator function of alarm calls is to deliver a message to a predator that it has been detected. Moreover, giving the alarm call could provide a signal to the predator that capturing the individual giving the alarm is more difficult than capturing its silent group members, as the caller is probably the most aware of the predator's location. In an aviary experiment using stuffed dummy Willow Tits Poecile montanus, we assessed whether an authentic alarm call given by Willow Tit affected Pygmy Owl Glaucidium passerinum prey preference. In the experiment, the Owls attacked only the ‘silent’ dummy individuals, suggesting that alarm calling could offer direct fitness benefits to the caller by decreasing the attack risk of the caller relative to its group members.     

A ‘dynamic’ landscape of fear: prey responses to spatiotemporal variations in predation risk across the lunar cycle

Ambiguous empirical support for ‘landscapes of fear’ in natural systems may stem from failure to consider dynamic temporal changes in predation risk. The lunar cycle dramatically alters night‐time visibility, with low luminosity increasing hunting success of African lions. We used camera‐trap data from Serengeti National Park to examine nocturnal anti‐predator behaviours of four herbivore species. Interactions between predictable fluctuations in night‐time luminosity and the underlying risk‐resource landscape shaped herbivore distribution, herding propensity and the incidence of ‘relaxed’ behaviours. Buffalo responded least to temporal risk cues and minimised risk primarily through spatial redistribution. Gazelle and zebra made decisions based on current light levels and lunar phase, and wildebeest responded to lunar phase alone. These three species avoided areas where likelihood of encountering lions was high and changed their behaviours in risky areas to minimise predation threat. These patterns support the hypothesis that fear landscapes vary heterogeneously in both space and time.     

Coupling of canopy and understory food webs by ground‐dwelling predators

Understanding food‐web dynamics requires knowing whether species assemblages are compartmentalized into distinct energy channels, and, if so, how these channels are structured in space. We used isotopic analyses to reconstruct the food web of a Kenyan wooded grassland. Insect prey were relatively specialized consumers of either C₃ (trees and shrubs) or C₄ (grasses) plants. Arboreal predators (arthropods and geckos) were also specialized, deriving c. 90% of their diet from C₃‐feeding prey. In contrast, ground‐dwelling predators preyed considerably upon both C₃‐ and C₄‐feeding prey. This asymmetry suggests a gravity‐driven subsidy of the terrestrial predator community, whereby tree‐dwelling prey fall and are consumed by ground‐dwelling predators. Thus, predators in general couple the C₃ and C₄ components of this food web, but ground‐dwelling predators perform this ecosystem function more effectively than tree‐dwelling ones. Although prey subsidies in vertically structured terrestrial habitats have received little attention, they are likely to be common and important to food‐web organization.