The influence of landscape features on nest predation rates of grassland‐breeding waders

In Europe, lowland wet grasslands have become increasingly fragmented, and populations of waders in these fragments are subject to unsustainably high levels of nest predation. Patches of taller vegetation in these landscapes can support small mammals, which are the main source of prey for many predators. Providing such patches of habitat could potentially reduce levels of nest predation if predators preferentially target small mammals. However, predator attraction to patches of taller vegetation for foraging, shelter, perching and/or nesting could also result in local increases in predation rates, as a consequence of increased predator densities or spill‐over foraging into the surrounding area. Here we assess the influence of taller vegetation on wader nest predation rates, and the feasibility of managing vegetation structure to alter predator impacts. Between 2005 and 2011, the nest distribution and hatching success of Northern Lapwings Vanellus vanellus, which nest in the open, and Common Redshanks Tringa totanus, which conceal their nests in vegetation, were measured on a 487‐ha area of wet grassland in eastern England that is primarily managed for breeding waders. Predation rates of Lapwing nests increased significantly with distance from patches of taller vegetation, and decreased with increasing area of taller vegetation within 1 km of the nest, whereas neither variable influenced Redshank nest predation probability. These findings suggest that the distribution and activity of nest predators in lowland wet grassland landscapes may be influenced by the presence and distribution of areas of taller vegetation. For Lapwings at least, there may therefore be scope for landscape‐scale management of vegetation structure to influence levels of predation in these habitats.     

Temperature dependency of predation: Increased killing rates and prey mass consumption by predators with warming

Temperature dependency of consumer–resource interactions is fundamentally important for understanding and predicting the responses of food webs to climate change. Previous studies have shown temperature‐driven shifts in herbivore consumption rates and resource preference, but these effects remain poorly understood for predatory arthropods. Here, we investigate how predator killing rates, prey mass consumption, and macronutrient intake respond to increased temperatures using a laboratory and a field reciprocal transplant experiment. Ectothermic predators, wolf spiders (Pardosa sp.), in the lab experiment, were exposed to increased temperatures and different prey macronutrient content (high lipid/low protein and low lipid/high protein) to assess changes in their killing rates and nutritional demands. Additionally, we investigate prey mass and lipid consumption by spiders under contrasting temperatures, along an elevation gradient. We used a field reciprocal transplant experiment between low (420 masl; 26°C) and high (2,100 masl; 15°C) elevations in the Ecuadorian Andes, using wild populations of two common orb‐weaver spider species (Leucauge sp. and Cyclosa sp.) present along the elevation gradient. We found that killing rates of wolf spiders increased with warmer temperatures but were not significantly affected by prey macronutrient content, although spiders consumed significantly more lipids from lipid‐rich prey. The field reciprocal transplant experiment showed no consistent predator responses to changes in temperature along the elevational gradient. Transplanting Cyclosa sp. spiders to low‐ or high‐elevation sites did not affect their prey mass or lipid consumption rate, whereas Leucauge sp. individuals increased prey mass consumption when transplanted from the high to the low warm elevation. Our findings show that increases in temperature intensify predator killing rates, prey consumption, and lipid intake, but the responses to temperature vary between species, which may be a result of species‐specific differences in their hunting behavior and sensitivity to temperature.     

Density‐independent predation affects migrants and residents equally in a declining partially migratory elk population

Migration is expected to benefit individuals through exposure to higher quality forage and reducing predation rates more than non‐migratory conspecifics. Previous studies of partially migratory ungulates (with migrant and resident individuals) have focused on bottom–up factors regulating resident and migrant segments, yet differential predation between strategies could also be a density‐dependent regulatory mechanism. Our study tested for density‐dependence in mortality, as well as mechanisms of ­bottom–up or top–down regulation in the resident and migrant portions of the partially migratory Ya Ha Tinda elk population. We tested for density dependence in adult female and juvenile survival rates, and then discriminated between predator‐ and food‐regulation hypotheses by testing for density‐dependence amongst mortality causes for adult female elk. Notably, the population declined almost 70% from near previously published estimates of carrying capacity over 10 years, providing ideal conditions to test for density dependence. In contrast to predictions, we found only weak support for density dependence in adult survival and juvenile survival. We also found few differences between migrant and resident elk in adult or juvenile survival, though juvenile survival differences were biologically significant. Predation by humans and grizzly bears was density dependent, but similar between migratory strategies. Predation by wolves was the leading known cause of mortality, yet remained constant with declining elk density equally for both migrant and resident elk, indicating wolf predation was density‐independent. Instead of being strongly regulated by food or predation, we found adult female survival was driven by density‐independent predation and climatic factors. The few differences between migratory strategies suggest equivalent fitness payoffs for migrants and residents. This population is being limited by density‐independent predation leading to declines of both migratory strategies. Our results challenge classical predator–prey theory, and call for better integration between predator–prey and migration theory.     

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 water depth on predation frequency by diving beetles on mosquito larvae prey

Diving behavior and its frequency may differ among species of mosquito larvae because of differences in predation pressure. The present study aimed to investigate the relationship between water depth and predation frequency on two mosquito species, Culex tritaeniorhynchus (wetland breeder) and Aedes albopictus (container breeder), by the diving beetle Eretes griseus. Culex tritaeniorhynchus spends more time at the surface than A. albopictus, which spends more time thrashing underwater. When intact mosquito larvae of both species were present, the diving beetles consumed almost all A. albopictus larvae (98.3%). After all the A. albopictus larvae had been consumed, the diving beetles began to prey on C. tritaeniorhynchus. In order to compare the effect of position on the predation preference of the diving beetles, equal numbers of both species were heat‐killed and allowed to settle on the bottom of the container. When all the dead mosquito larvae had sunk to the bottom of a plastic container, the diving beetles caught both mosquito species at random. These results indicate that mosquito larvae near the surface were eaten less frequently by diving beetles than those at the bottom. The low diving frequency of C. tritaeniorhynchus is regarded as a form of anti‐predatory behavior.     

Carnivoran resource and habitat use in the context of a Late Miocene faunal turnover episode

We investigate resource and habitat use by apex predators through stable isotope analysis at two Spanish Late Miocene localities: Los Valles de Fuentidueña (~9.6 Ma, LVF) and Cerro de los Batallones (~9.1 Ma, BAT). The temporal window represented by LVF and BAT was crucial in the shaping of the current Iberian mammalian structure because it corresponds to the initial stages of a faunal turnover episode and regional environmental change at ~9.5–8.5 Ma (Vallesian–Turolian transition), associated with an increase in the seasonality of precipitation. Herbivore and carnivore δ¹³C and δ¹⁸O values do not point to significant changes in either the vegetation cover (a woodland to mesic C₃ grassland) or the hydrological regime during the time lapse represented between LVF and BAT. This suggests that the environmental shift recorded around the Vallesian–Turolian boundary may have occurred later in time, since LVF and BAT ages are synchronic with the onset of the turnover event. From the standpoint of predator–prey evaluation by means of stable isotope analysis, statistical post hoc tests, mixing model output, and the assessment of niche occupation by LVF and BAT carnivores point to high levels of interspecific competition among large active carnivores, albeit some genera, such as the amphicyonid Magericyon and specially the hyaenid Lycyaena, seemed to avoid competition by taking prey from a more open habitat. Despite the drop in diversity and change in faunal components observed between the LVF and BAT assemblages, a high degree of resource and habitat competition is evident from stable isotope data.     

Increasing the perceived predation risk changes parental care in female but not in male Great Tits Parus major

In birds, little is known about how the presence of predators alters parental food distribution decisions among nestlings. We found that experimentally increasing perceived predation risk changed parental care in female but not in male Great Tits Parus major. Females fed the lightest and average nestlings at similar rates under control conditions when predation risk was not manipulated but ignored the lightest nestling under increased perceived predation risk. Moreover, females reduced the duration of nest visits greatly after encountering a model predator, suggesting that the perception of predators may facilitate brood reduction mechanisms.     

Effects of density and predation risk on leaf litter processing by Phylloicus sp.

The allochthonous detritus that accumulates in the substrate of streams is used by aquatic invertebrate shredders for shelter and food. Shredders are considered rare in tropical systems, and little information is available about the role of density effects and predation risk (associated with the perception of predators by prey) in relationship to the resources used by these organisms. The aim of this study was to examine experimentally the effects of increased predation risk and of the density of Phylloicus sp. (i.e. of two types of biological relationships) on the processing of the leaf litter of Nectandra megapotamica (Spreng.) Mez. Phylloicus sp. can use leaf litter for case building and as a food resource. The density effect was measured using four treatments that differed only in the number of individuals (one, two, three or four). A second experiment with five treatments was performed to test the risk of non‐lethal predation on detritus consumption (shelter and food) by Phylloicus sp. (T1: Caddisfly; T2: Mayfly; T3: Astyanax sp./fish; T4: Damselflies; T5: Stonefly). A single Phylloicus and one other organism (a potential predator blocked with 0.5 mm fine mesh) were placed in each tank (0.002 m³ volume). We observed a negative effect of density on per capita litter consumption (experiment 1). The low density of Phylloicus may be a natural factor that decreases intraspecific competition. In the presence of fish, Phylloicus showed the lowest amount of litter processing observed in the experiment, indicating top‐down control (experiment 2). In treatments that involved the presence of invertebrates (non‐predatory and predatory), Phylloicus showed the highest amount and an intermediate amount of leaf litter processing, respectively (experiment 2). This observation also suggests that the predation effect is more probable for specific predator–prey pairs. Population density and predation risk in Phylloicus may be important factors controlling leaf litter processing.     

Shift in predation regime mediates diversification of foraging behaviour in a dragonfly genus

1. Behavioural adaptations to avoid and evade predators are common. Many studies have investigated population divergence in response to changes in predation regime within species, but studies exploring interspecific patterns are scant. Studies on interspecific divergence can infer common outcomes from evolutionary processes and highlight the role of environmental constraints in shaping species traits. 2. Species of the dragonfly genus Leucorrhinia underwent well‐studied shifts from habitats being dominated by predatory fish (fish lakes) to habitat being dominated by predatory invertebrates (dragonfly lakes). This change in top predators resulted in a set of adaptive trait modifications in response to the different hunting styles of both predator types: whereas predatory fish actively search and pursue prey, invertebrate predator follow a sit‐and‐wait strategy, not pursuing prey. 3. Here it is shown that the habitat shift‐related change in selection regime on larval Leucorrhinia caused species in dragonfly lakes to evolve increased larval foraging and activity, and results suggest that they lost the ability to recognise predatory fish. 4. The results of the present study highlight the impact of predators on behavioural trait diversification with habitat‐specific predation regimes selecting for distinct behavioural expression.     

Hypoxic refuges,predator–prey interactions and habitat selection by fishes

Localized hypoxic habitats were created in Delta Marsh, Manitoba, Canada to determine the potential of regions of moderate hypoxia to act as refuges for forage fishes from piscine predators. Minnow traps and giving‐up density (GUD) plates (plexiglas plates covered with trout crumble and fine gravel) were used to assess habitat use and perceived habitat quality for forage fishes, respectively, while passive integrated transponder tags provided data on habitat use by predator species to assess the level of predation risk. Data were collected both before and after a hypoxia manipulation (2–3 mg l^?1 dissolved oxygen, DO) to create a before–after control–effect style experiment. Fathead minnows Pimephales promelas were more abundant and consumed more food from GUD plates in hypoxic bays after the DO manipulation, indicating hypoxic locations were perceived as higher quality, lower‐risk habitats. The frequency of predator visits was not consistently affected. The duration of visits, and therefore the total time spent in these habitats, however, was significantly shorter. These predator data, combined with the prey information, are consistent with the hypothesis that hypoxic regions function as predator refuges. The refuge effect is not the result of predator exclusion, however; instead predators are rendered less capable of foraging and pose less of a threat in hypoxic locations.     

Predation risk and habitat complexity modify intermediate predator feeding rates and energetic efficiencies in a tri‐trophic system

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Factors affecting the vulnerability of cane toads (Bufo marinus) to predation by ants

Experimental evidence on the determinants of prey vulnerability is scarce, especially for vertebrates in the field. Invasive species offer robust opportunities to explore prey vulnerability, because the intensity of predation on or by such animals has not been eroded by coevolution. Around waterbodies in tropical Australia, native meat ants (Iridomyrmex reburrus) consume many metamorph cane toads (Bufo marinus, an invasive anuran). We document the determinants of toad vulnerability, especially the roles of toad body size and ant density. Larger metamorphs were attacked sooner (because they attracted more ants), but escaped more often. Overall, smaller toads were more likely to be killed. Ant densities influenced toad responses, as well as attack rate and success. Data on the immediate outcomes of attacks underestimate mortality: more than 73% of apparent ‘escapees’ died within 24 h. Because mortality during this period was independent of toad size, predation was less size selective than suggested by immediate outcomes. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 738–751.     

Post‐release predation on hatchery‐reared Japanese flounder Paralichthys olivaceus in the coast of Fukushima,Japan

To determine the predators of 100 mm total length hatchery‐reared juvenile Japanese flounder Paralichthys olivaceus, fishes and crabs were collected using gillnets and a small trawl net off the coast of Fukushima Prefecture, Japan. Predation on juvenile P. olivaceus by older conspecifics, the snailfish Liparis tanakai, ocellate spot skate Okamejei kenojei and the swimming crab Ovalipes punctatus, was detected based on analogical observation and molecular techniques. These predators are nocturnal feeders except for P. olivaceus. Liparis tanakai with body sizes large enough to consume juveniles only appeared in winter, whereas the large O. punctatus was abundant in early summer and in late autumn. Such seasonal variation in predator abundance indicates that the release season can be optimized for reducing predation mortality.     

Species‐level predation network uncovers high prey specificity in a Neotropical army ant community

Army ants are among the top arthropod predators and considered keystone species in tropical ecosystems. During daily mass raids with many thousand workers, army ants hunt live prey, likely exerting strong top‐down control on prey species. Many tropical sites exhibit a high army ant species diversity (>20 species), suggesting that sympatric species partition the available prey niches. However, whether and to what extent this is achieved has not been intensively studied yet. We therefore conducted a large‐scale diet survey of a community of surface‐raiding army ants at La Selva Biological Station in Costa Rica. We systematically collected 3,262 prey items from eleven army ant species (genera Eciton, Nomamyrmex and Neivamyrmex). Prey items were classified as ant prey or non‐ant prey. The prey nearly exclusively consisted of other ants (98%), and most booty was ant brood (87%). Using morphological characters and DNA barcoding, we identified a total of 1,103 ant prey specimens to the species level. One hundred twenty‐nine ant species were detected among the army ant prey, representing about 30% of the known local ant diversity. Using weighted bipartite network analyses, we show that prey specialization in army ants is unexpectedly high and prey niche overlap very small. Besides food niche differentiation, we uncovered a spatiotemporal niche differentiation in army ant raid activity. We discuss competition‐driven multidimensional niche differentiation and predator–prey arms races as possible mechanisms underlying prey specialization in army ants. By combining systematic prey sampling with species‐level prey identification and network analyses, our integrative approach can guide future research by portraying how predator–prey interactions in complex communities can be reliably studied, even in cases where morphological prey identification is infeasible.     

The indestructible insect: Velvet ants from across the United States avoid predation by representatives from all major tetrapod clades

Velvet ants are a group of parasitic wasps that are well known for a suite of defensive adaptations including bright coloration and a formidable sting. While these adaptations are presumed to function in antipredator defense, observations between potential predators and this group are lacking. We conducted a series of experiments to determine the risk of velvet ants to a host of potential predators including amphibians, reptiles, birds, and small mammals. Velvet ants from across the United States were tested with predator's representative of the velvet ants native range. All interactions between lizards, free‐ranging birds, and a mole resulted in the velvet ants survival, and ultimate avoidance by the predator. Two shrews did injure a velvet ant, but this occurred only after multiple failed attacks. The only predator to successfully consume a velvet ant was a single American toad (Anaxyrus americanus). These results indicate that the suite of defenses possessed by velvet ants, including aposematic coloration, stridulations, a chemical alarm signal, a hard exoskeleton, and powerful sting are effective defenses against potential predators. Female velvet ants appear to be nearly impervious to predation by many species whose diet is heavily derived of invertebrate prey.     

Early exposure to predation risk carries over metamorphosis in two distantly related freshwater insects

1. Predation and competition play a central role in ecological communities, and it is increasingly recognised that animals use early warning cues to reduce the impact of these antagonistic interactions. 2. Strategies to avoid risk can occur during embryo development through plasticity in egg hatching time. This strategy, and its associated costs and carryover effects on adults are little understood in insects. In this study, these are explored in two distantly related freshwater insects: the damselfly Ischnura elegans and the mosquito Aedes albopictus. 3. As predicted, damselfly eggs hatched earlier in response to larval predators cues, a treatment that also affected adult size. Risk cues did not affect mosquito egg hatching time, but they did affect larval development time in a sex‐dependent manner. 4. The results suggest that responses aimed at avoiding risks can be triggered during the egg stage, and although they can vary dramatically among species, they are likely to be widespread in insects. Early warning responses can be particularly important to understand the ecology of aquatic insects, some of them global vectors of human diseases.     

Impacts of temperature on giant panda habitat in the north Minshan Mountains

Understanding the impacts of meteorological factors on giant pandas is necessary for future conservation measures in response to global climate change. We integrated temperature data with three main habitat parameters (elevation, vegetation type, and bamboo species) to evaluate the influence of climate change on giant panda habitat in the northern Minshan Mountains using a habitat assessment model. Our study shows that temperature (relative importance = 25.1%) was the second most important variable influencing giant panda habitat excepting the elevation. There was a significant negative correlation between temperature and panda presence (ρ = −0.133, P < 0.05), and the temperature range preferred by giant pandas within the study area was 18–21°C, followed by 15–17°C and 22–24°C. The overall suitability of giant panda habitats will increase by 2.7%, however, it showed a opposite variation patterns between the eastern and northwestern region of the study area. Suitable and subsuitable habitats in the northwestern region of the study area, which is characterized by higher elevation and latitude, will increase by 18007.8 hm² (9.8% habitat suitability), while the eastern region will suffer a decrease of 9543.5 hm² (7.1% habitat suitability). Our results suggest that increasing areas of suitable giant panda habitat will support future giant panda expansion, and food shortage and insufficient living space will not arise as problems in the northwest Minshan Mountains, which means that giant pandas can adapt to climate change, and therefore may be resilient to climate change. Thus, for the safety and survival of giant pandas in the Baishuijiang Reserve, we propose strengthening the giant panda monitoring program in the west and improving the integrity of habitats to promote population dispersal with adjacent populations in the east.     

Diversity in thermal affinity among key piscivores buffers impacts of ocean warming on predator–prey interactions

Asymmetries in responses to climate change have the potential to alter important predator–prey interactions, in part by altering the location and size of spatial refugia for prey. We evaluated the effect of ocean warming on interactions between four important piscivores and four of their prey in the U.S. Northeast Shelf by examining species overlap under historical conditions (1968–2014) and with a doubling in CO₂. Because both predator and prey shift their distributions in response to changing ocean conditions, the net impact of warming or cooling on predator–prey interactions was not determined a priori from the range extent of either predator or prey alone. For Atlantic cod, an historically dominant piscivore in the region, we found that both historical and future warming led to a decline in the proportion of prey species’ range it occupied and caused a potential reduction in its ability to exert top‐down control on these prey. In contrast, the potential for overlap of spiny dogfish with prey species was enhanced by warming, expanding their importance as predators in this system. In sum, the decline in the ecological role for cod that began with overfishing in this ecosystem will likely be exacerbated by warming, but this loss may be counteracted by the rise in dominance of other piscivores with contrasting thermal preferences. Functional diversity in thermal affinity within the piscivore guild may therefore buffer against the impact of warming on marine ecosystems, suggesting a novel mechanism by which diversity confers resilience.