Perceived Predation Risk Research Articles

Age‐based shifts in habitat selection of wild turkey broods

AbstractAnimals exhibit pronounced age‐based shifts in habitat selection, often because of increasing body size. Body size affects how animals access resources, traverse landscapes, and perceive predation risk. While adults may be habitat generalists, offspring may be constrained by diet, predation avoidance methods, and mobility given smaller body size, and thus be more specialized. Observed declines in eastern wild turkey (Meleagris gallopavo silvestris) productivity and recruitment across the southeastern United States has necessitated evaluations of availability and composition of brood habitat. As poults are smaller and have more specialized resource requirements than adults, selection of vegetation likely changes as poults age. We evaluated aged‐based shifts in selection relative to vegetation communities, normalized difference vegetation indices (NDVI), and distances to trails by eastern wild turkey brooding females in a pine (Pinus spp.)‐dominated landscape in Georgia, USA, from April–July during 2017–2020. We used step‐selection functions and conditional logistic regression to evaluate resource selection of 36 brooding females. Of 175 nests monitored, 36 (20.6%) successfully hatched a brood and only 12 broods had at least 1 poult survive ≥28 days post‐hatch (i.e., 6.9% of nests produced a poult that was recruited into the population). Overall, brooding females selected for pastures (β = 0.730; 95% CI = 0.5144–0.9452), hardwoods (β = 0.324; 95% CI = 0.1608–0.4865), areas closer to trails (β = −0.002; 95% CI = −0.0023–−0.0014), and areas with greater NDVI values (β = 2.714; 95% CI = 1.7897–3.6380). Habitat selection shifted as broods aged, suggesting resource needs shift to scale allometrically with body size as broods get older. For example, selection strength waned as broods aged and broods were 2.47 times less likely to select pastures on day 28 relative to day 1 post‐hatch. Pastures were selected for after broods hatched, whereas selection for young pines increased as poults aged. Despite pine‐dominated cover types comprising nearly a third of the usable landscape, young pine communities were avoided by females with recently hatched broods. Managers may create better brood habitat by promoting early successional vegetation communities amidst a diversity of other land cover types to account for changing resource needs and predator avoidance capabilities as poults age.

Experimental variation of perceived predation risk does not affect coordination of parental care in long-tailed tits

To maximise fitness, parents should optimise their investment in each breeding attempt. When there are multiple carers, the optimal strategy may also depend on the relative timing of their investment, with coordination of care hypothesised to maximise its efficiency and reduce predation risk. The aim of this study was to test the hypothesis that carers coordinate provisioning as an antipredator measure that reduces the time that a brood’s location is advertised to predators (‘predation hypothesis’). We presented predatory and non-predatory model birds to provisioning long-tailed tit Aegithalos caudatus parents and helpers, predicting that coordination would increase, and carer activity near the nest would decrease following predator presentation, relative to controls. First, carers reduced provisioning rates and took longer to resume provisioning following the predator presentation. Second, contrary to predictions, we found no significant change in any metric of coordination following predator presentations, relative to controls. Moreover, following predator presentation carers spent more time near the nest, resulting in greater near-nest activity compared to controls. In conclusion, although provisioning long-tailed tits are sensitive to perceived predation risk, our findings do not support the prediction of the predation hypothesis that carers adjust coordination behaviour in response to that threat.Significance statementParental care improves offspring condition and is often necessary for their survival but may also confer risk. In birds, provisioning a brood may advertise its location to predators. When multiple individuals provision the same brood, they are hypothesised to coordinate their visits to limit the time that a brood’s location is advertised. This hypothesis has not yet been experimentally tested, so in this study, we investigated whether carers increase their level of provisioning coordination in response to elevated brood predation risk by presenting predatory and non-predatory model birds near 22 long-tailed tit Aegithalos caudatus nests. As anticipated, carers stopped provisioning during predator presentation. However, contrary to expectations, carers did not coordinate more in watches following predator presentation, but instead spent longer near the nest before provisioning, suggesting an increase in risk aversion or vigilance behaviour.

Landscape of fear in freshwater ecotones: How predation risk and light conditions affect mesopredator activity and foraging in springs

Abstract Springs are environments that can provide general insights into factors favouring diversity in ecotones, but they are often neglected in freshwater studies. One of the challenging processes acting in ecotones is the landscape of fear (LOF), the space–time variation of perceived predation risk. Spring exploitation often involves species that are mesopredators in surface fresh water and that can become apex predators in ground water, as in the case of the fire salamander larvae (Salamandra salamandra). Here, we aim to determine whether the activity and foraging patterns of the fire salamander in springs are affected by LOF. We surveyed the night‐ and daytime abundance of fire salamander larvae in 15 springs to assess predator occurrence. We also reared 48 salamander larvae with and without non‐lethal exposure to predators within tanks simulating groundwater or surface freshwater light features. Before and after a month of rearing, we tested larva efficiency in catching prey when exposed to predator chemical cues, both in light and dark conditions. In the field, the number of active fire salamander larvae was significantly higher during the night. At night, the number of active larvae across the transition area between ground water and surface water was higher in plots closer to the surface. Testing and rearing conditions significantly affected larva behaviour, and prey capture was significantly more effective in light conditions. It was less successful in larvae reared with predator chemical cues and in the presence of predators. Moreover, larvae reared with predators under light conditions were slower than those raised with predators in dark conditions. Our results show that LOF can interact with extant environmental features and constitute a significant behavioural pressure for mesopredator species living in freshwater ecotones.

Increasing perceived predation risk through playbacks reduces Red-winged Blackbird abundance in agriculture late in the breeding season

Abstract Perceived predation and brood parasitism risks strongly influence nesting habitat selection in several bird species. Here, we report on a playback experiment evaluating whether perceived predation or brood parasitism risk can reduce Red-winged Blackbird (Agelaius phoeniceus) abundances in agricultural nesting habitat. We broadcast Cooper’s Hawk vocalizations (Accipiter cooperii, a predator of adult blackbirds and nests), Brown-headed Cowbird vocalizations (Molothrus ater, a brood parasite of many passerine species, including blackbirds), and the “Sonic Net” as treatments, the latter of which is broadcast of frequencies that overlap with blackbird vocalizations and prevent blackbirds from accessing intraspecific communication informing of predator and brood parasite risks. Neither the hawk, cowbird, nor Sonic Net treatments reduced blackbird abundances at sites early in the breeding season (April to May), when blackbirds were selecting nesting habitat. In contrast, late in the breeding season (July to August), hawk vocalizations and the Sonic Net reduced blackbird abundances at sites, but cowbird vocalizations did not. Our late-breeding season results suggest that blackbirds may flexibly change responses to perceived predation risk based on their stage of reproductive investment. Perceived predation risk could potentially be used to manage pest birds that nest in agricultural landscapes, at least for crops that are vulnerable to birds late in the breeding season.

So many choices, so little time: Food preference and movement vary with the landscape of fear.

Spatial and temporal variation in perceived predation risk is an important determinant of movement and foraging activity of animals. Foraging in this landscape of fear, individuals need to decide where and when to move, and what resources to choose. Foraging theory predicts the outcome of these decisions based on energetic trade-offs, but complex interactions between perceived predation risk and preferences of foragers for certain functional traits of their resources are rarely considered. Here, we studied the interactive effects of perceived predation risk on food trait preferences and foraging behavior in bank voles (Myodes glareolus) in experimental landscapes. Individuals (n = 19) were subjected for periods of 24 h to two extreme, risk-uniform landscapes (either risky or safe), containing 25 discrete food patches, filled with seeds of four plant species in even amounts. Seeds varied in functional traits: size, nutrients, and shape. We evaluated whether and how risk modifies forager preference for functional traits. We also investigated whether perceived risk and distance from shelter affected giving-up density (GUD), time in patches, and number of patch visits. In safe landscapes, individuals increased time spent in patches, lowered GUD and visited distant patches more often compared to risky landscapes. Individuals preferred bigger seeds independent of risk, but in the safe treatment they preferred fat-rich over carb-rich seeds. Thus, higher densities of resource levels remained in risky landscapes, while in safe landscapes resource density was lower and less diverse due to selective foraging. Our results suggest that the interaction of perceived risk and dietary preference adds an additional layer to the cascading effects of a landscape of fear which affects biodiversity at resource level.

Larval and/or Adult Exposure to Intraguild Predator Harmonia axyridis Alters Reproductive Allocation Decisions and Offspring Growth in Menochilus sexmaculatus

Maternal effects can reduce offspring susceptibility to predators by altering resource allocation to young and reproducing larger offspring. While the perception of predation risk can vary according to a prey’s life stage, it is unclear whether maternally experienced intraguild predation (IGP) risk during different life stages influences the maternal effects of predatory insects. We investigated the influence of exposure to intraguild predators (Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae)) during the larval and/or adult stages on reproductive decisions and offspring growth in Menochilus sexmaculatus (Fabricius). Independent of the life stage, when M. sexmaculatus females experienced IGP risk, their body weight and fecundity decreased, but the proportion of trophic eggs produced increased. However, egg mass, egg clutch number, and egg clutch size were not influenced by the treatment. Next, when offspring encountered H. axyridis, mothers experiencing IGP risk during the larval and/or adult stages could increase their offspring’s weight. Moreover, offspring in IGP environments reached a similar size as those with no-IGP environments when mothers experienced IGP risk during the larval and/or adult stages. Overall, M. sexmaculatus larval and/or adult exposure to IGP risk had no influence on egg size, but increased offspring body size when faced with H. axyridis. Additionally, mothers experiencing IGP risk during different life stages showed increased production of trophic eggs. Because IGP is frequently observed on M. sexmaculatus and favours relatively larger individuals, different stages of M. sexmaculatus express threat-sensitively to IGP risk; inducing maternal effects can be an adaptive survival strategy to defend against H. axyridis.

Multiple antipredator behaviors in wild red-tailed monkey (Cercopithecus ascanius) groups reveal spatially distinct landscapes of fear

Abstract Foraging opportunity and predation risk act as opposing influences on an animal’s habitat use. “Landscapes of fear” (LOF), whereby one predicts the spatial distribution of predators or perceived predator presence using prey responses, are an important tool for modeling this conflict. LOF models examining perceived predation risk are often generated using a single behavioral metric, even though individuals can respond to predation pressure with multiple potential behaviors. Here, we expanded traditional LOF approaches by measuring three antipredator behaviors in wild red-tailed monkeys (Cercopithecus ascanius): aggregation, alarm calling, and vigilance. We predicted that each behavior would reveal spatially explicit regions of high risk, as each behavior may attend to different aspects of perceived predation risk. The use of different behaviors may depend upon factors such as vegetation type, age/sex class of an individual, and which other antipredator behaviors are being exhibited by group members. We collected data on two troops of monkeys in the Issa Valley, Tanzania for over 19 months and conducted 3189 group follows. We found that vegetation type varied in its effect on antipredator behavior. Monkeys conducted more antipredator behavior in more open vegetation types compared to more closed, riparian forests. The LOF models generated for each behavior mapped distinct and predominantly non-overlapping spatial regions of perceived predation risk, which was replicated across the two groups. This suggested that monkeys responded differently across their home range to specific perceived risks. Such spatially explicit behavior may indicate vegetation-specific predation risk or unique trade-offs in antipredator behavior throughout a heterogenous habitat.

Multiple Sentinels in a Cooperative Breeder Synchronize Rather Than Coordinate Gazing.

Sentinels can detect predators and rivals early by monitoring their surroundings from vantage points. Multiple sentinels in a group may reduce the perceived predation risk by diluting the risk and increasing collective detection, especially if sentinels monitor different areas at the same time. We investigated sentinel behavior in groups of the Florida scrub jay (Aphelocoma caerulescens). Sentinels in this species turn their heads frequently to monitor different areas for threats. As predicted, we found that sentinels turned their heads less frequently in the presence of other sentinels. Multiple sentinels, however, tended to gaze in the same direction at the same time more often than predicted by chance alone. Gaze synchronization reduces the efficiency of collective detection by reducing visual coverage at any one time at the group level. Despite the benefits of the presence of other sentinels, our results highlight the limits to collective detection when multiple individuals are vigilant at the same time.

Red deer Cervus elaphus blink more in larger groups.

Most animals need to spend time being vigilant for predators, at the expense of other activities such as foraging. Group-living animals can benefit from the shared vigilance effort of other group members, with individuals reducing personal vigilance effort as group size increases. Behaviors like active scanning or head lifting are usually used to quantify vigilance but may not be accurate measures of this. We suggest that measuring an animal's blinking rate gives a meaningful measure of vigilance: increased blinking implies reduced vigilance, as the animal cannot detect predators when its eyes are closed. We describe an observational study of a captive population of red deer, where we measured the blinking rates of individual deer from groups of differing sizes (where mean group size ranged between 1 and 42.7 individuals). We demonstrate that as group size increases in red deer, individuals increase their blink rate, confirming the prediction that vigilance should decrease. Blinking is a simple non-invasive measure and offers a useful metric for assessing the welfare of animals experiencing an increase in perceived predation risk or other stressors.

Do non-direct heterospecific cues of avian predator activity alter reproductive modes of a passerine bird?

Predators affect prey by killing them or inducing changes in their physiology and behaviour through a fear effect associated with predation risk. In birds, perceived predation risk influences reproductive decisions, such as the reduction of parental investment in offspring during both egg production and nestling rearing. Visual and vocal cues of predator presence have been widely used to test the direct effects of predation risk. However, few studies have examined the indirect cues of predator activity such as dead avian prey or their remains. In this study, for the first time, we experimentally studied whether piles of feathers, simulating the remains of avian prey, induce changes in the reproductive decisions of adult birds. Before and during egg laying, great tit, Parus major, pairs were exposed to piles of bright down and cover feathers from domestic goose (treatment), woodchips (procedural control), or were not exposed (control). Our experiment affected maternal investment in individual eggs, but did not influence other reproductive parameters. Females from the treatment group laid larger and more asymmetrical (pointed) eggs than control females. Moreover, females from the procedural control group laid larger eggs than those from the control group, but without differences in egg shape. However, the eggs from the treatment and procedural control groups did not differ. This indicates that great tit females can perceive feathers and woodchips as informative cues, such as potential predation risk or habitat suitability, or as novel items in the environment. Importantly, females respond to such cues by changing their maternal investment in eggs, which may result from an adaptive mechanism aimed at increasing offspring fitness in the face of specific environmental conditions experienced by a female. Our study contributes to the understanding of how female songbirds adjust their maternal reproductive investment in response to publicly available social and environmental cues.

Lockdown effects on fear revealed direct and indirect effects of human presence on perceived predation risk

The Covid-19 lockdown reduced drastically human presence outdoors, providing an uncontrolled experiment for disentangling direct and indirect effects of human presence on animal fearfulness. We measured 18,494 flight initiation distances (FIDs, the distance at which individual animals fly away when approached by a human) from 1333 populations of 202 bird species taken in four European cities both before, during and after the lockdown. FIDs decreased during lockdown in rural habitats but increased in urban habitats, especially for singing birds. Height above ground increases during lockdown in non-singing birds only, and birds adjusted horizontal tolerance to approach according to height outside lockdown, in rural habitats and while not singing. Responses showed lagged effects after lockdown in urban but not in rural habitats. Differential responses to lockdown among habitats and between signing and non-singing birds were consistent with relaxation of direct disturbance effects on birds in rural habitats during lockdown, as well as with increased indirect fear effects mediated by predator release in cities. FIDs seemed to measure the balance of direct and indirect effects of humans on predations risk and food needs rather than direct effects of humans on fear.

Heat stress increases risk taking in foraging shorebirds

Abstract Animals often face a trade‐off between food acquisition and predation/disturbance avoidance. Yet, the extent to which this trade‐off is affected by modulating factors such as thermal risk and foraging opportunities has been largely overlooked. Here, we examined the influence of temporal and environmental gradients on the flight initiation distance (FID, the distance at which animals flee from an approaching human‐simulated predator) and escape mode (flying/low risk versus running/low cost) in 16 species of shorebirds foraging on tidal flats of the Bijagós Archipelago, Guinea‐Bissau. We measured escape responses throughout the low tide period during wet and dry seasons and simultaneously recorded microclimate variables and occurrence of heat‐reduction behaviour (ptiloerection). Furthermore, we measured corticosterone metabolites (CORTm) from droppings in red knots Calidris canutus to assess whether ptiloerection is associated to a physiological stress response to hot conditions. Overall, birds tolerated a closer approach at higher environmental temperatures and when showing ptiloerection. They also had shorter FIDs during the dry season and towards the start/end of the low tide period. FIDs also increased with body mass and decreased in areas with more human presence. In red knots, individuals showing ptiloerection had higher levels of CORTm, demonstrating a link between physiological and behavioural stress coping responses to heat events. Our results suggest that heat‐stressed shorebirds take greater risks, supporting the idea of a thermoregulation–predation risk trade‐off. They also indicate that shorebirds adjust risk taking to tidal and seasonal cycles, generally reducing FIDs when the energetic costs of escape are expected to be large. Finally, they suggest that shorebirds habituate to non‐lethal human presence and respond to perceived predation risk in accordance with the predictions of optimal escape theory. These results are relevant to many animals that face a tight window for foraging activity while being exposed to predation/disturbance and heat during the day. We discuss management implications of our results in the context of global change. Read the free Plain Language Summary for this article on the Journal blog.

Artificial lighting affects the landscape of fear in a widely distributed shorebird

Fear influences almost all aspects of a prey species’ behaviour, such as its foraging and movement, and has the potential to cause trophic cascades. The superior low-light vision of many predators means that perceived predation risk in prey is likely to be affected by light levels. The widespread and increasing intensity of artificial light at night is therefore likely to interfere with this nocturnal visual arms race with unknown behavioural and ecological consequences. Here we test how the fear of predation perceived by wintering Eurasian curlew foraging on tidal flats is influenced by lighting. We quantified flight initiation distance (FID) of individuals under varying levels of natural and artificial illumination. Our results demonstrate that FID is significantly and substantially reduced at low light levels and increases under higher intensity illumination, with artificial light sources having a greater influence than natural sources. Contrary to the sensory-limitation hypothesis, the curlews’ unwillingness to take flight in low-light appears to reflect the risks posed by low-light flight, and a desire to remain on valuable foraging grounds. These findings demonstrate how artificial light can shape the landscape of fear, and how this interacts with optimal foraging decisions, and the costs of taking flight.

Vegetation cover and food availability shapes the foraging activity of rodent pests in and around maize fields

Evidence-based information for smallholder farmers on where and when to conduct rodent management is vital given that most are resource poor and depend on agriculture for food and income. However, there is scarce information on how the foraging activity of rodent pests changes over agricultural cropping seasons. We used the concepts of giving-up-density (GUD) and landscape of fear to monitor how the foraging activity of rodent pests changes in and around maize (Zea mays) fields over the cropping season. We tested the hypothesis that the foraging activity of rodent pests will be influenced by vegetation cover, perceived predation risk and food availability. Mastomys natalensis was the dominant species in all maize fields (n = 3, 87.05 % of the total captures). We observed that the foraging activity of rodents was influenced by vegetation cover and food availability. During the germination stage, rodent activity in the natural habitat and along the border was higher than inside the maize fields. During land preparation, planting, weeding, maize tasselling, maturity, and post-harvest stages, there was no difference in the foraging activity in and around the maize fields. During the harvest stage, the foraging activity was higher in the maize fields than along the border and in the natural habitat. These results can be used to guide smallholder farmers where and when to focus rodent control measures during different stages of the cropping season. An additional approach would be to develop strategies that could potentially increase rodent fear perceptions in cropping landscapes.

Predation risk and personality influence seed predation and dispersal by a scatter‐hoarding small mammal

AbstractSmall mammals are key scatter hoarders in forest ecosystems, acting as both seed predators and dispersers. The outcome of their interactions (i.e., predation vs. dispersal) is determined by a series of decisions made by small mammals, such as the choice of seed, whether the seed is immediately consumed or cached, and where it is cached. These decisions are influenced by a variety of factors, including the intrinsic traits of the seed, the individual personality of the scatter hoarder, and the perceived risk of predation while foraging. Furthermore, these factors may all interact to dictate the fate of the seed, with consequences for forest regeneration. Nevertheless, the ways in which perceived predation risk and personality interact to affect the seed dispersal decisions of scatter hoarders are still poorly understood. To contribute in filling this knowledge gap, we tested the hypotheses that southern red‐backed voles (Myodes gapperi), an important scatter hoarder in forest ecosystems, would exhibit personality‐mediated foraging and that predation risk would alter associations between personality and seed dispersal. We conducted a large‐scale field experiment, offering seed trays at stations with altered risk levels and recorded foraging decisions of free‐ranging voles with known personalities. We found that personality and perceived predation risk influenced decisions made by foraging voles. Specifically, docility, and boldness predicted foraging site selection, boldness predicted seed species selection and the number of seeds individuals selected, and the tendency to explore of an individual predicted whether voles would remove or consume seeds. Predation risk, mediated by the amount of cover at a site and by moon illumination, affected which foraging site individuals chose, seed species selection, and the probability of removal versus consumption. We did not find support for an interaction between personality and predation risk in predicting foraging decisions. These findings highlight the importance of scatter hoarder personality and perceived predation risk in affecting foraging decisions, with important consequences for seed dispersal and implications for altered patterns of forest regeneration in areas with different small mammal personality distributions or landscapes of fear.

Can predators influence small rodent foraging activity rates immediately after wildfires?

Background Habitat complexity, predation risk, and intraspecific competition shape rodent communities and impact foraging. Wildfires remove vegetation shelter, which increases the predation risk perception and leads to changes in trophic resources availability. Consequently, prey adjust their foraging activity levels to minimise the likelihood of encounters with predators. Rodents select safe habitats and can detect predators’ scents, which allows them to reduce the predation risk when foraging. Aims To evaluate the effects of carnivore occurrence and habitat structure on rodent foraging activity rates immediately after fires using mixed models and structural equation modelling. Methods This study used 900-m linear transects to analyse environmental variables, acorn removal by rodents, and carnivore activity in three recently burnt areas. Results In areas with higher stone marten abundances, rodents removed more acorns. However, acorn removal was also higher in structurally complex habitats with greater rodent abundance. Conclusions Rodents’ foraging activity is driven by increased interspecific competition and the predation risk perception due to the simplicity of the burnt habitat. Additionally, stone martens and rodents share the same preferences for habitat complexity after fires. Implications Habitat complexity increases seed holding by rodents, which positively contributes to fire recovery and attracts predators, thereby increasing species diversity.

Sex matters: predator presence induces sexual dimorphism in a monomorphic prey, from stress genes to morphological defences.

Inducible defences allow prey to increase survival chances when predators are present while avoiding unnecessary costs in their absence. Many studies report considerable inter-individual variation in inducible defence expression, yet what underlies this variation is poorly understood. A classic vertebrate example of a predator-induced morphological defence is the increased body depth in crucian carp (Carassius carassius), which reduces the risk of predation from gape-size limited predators. Here, we report that among-individual variation in morphological defence expression can be linked to sex. We documented sexual dimorphism in lakes in which crucian carp coexisted with predators, where females showed shallower relative body depths than males, but not in a predator-free lake. When exposing crucian carp from a population without predators to perceived predation risk in a laboratory environment (presence/absence of pike, Esox lucius), we found that males expressed significantly greater morphological defence than females, causing sexual dimorphism only in the presence of predators. We uncovered a correlative link between the sex-specific inducible phenotypic response and gene expression patterns in major stress-related genes (POMC, MC3R, and MC4R). Together, our results highlight that sex-specific responses may be an important, yet underappreciated, component underlying inter-individual differences in the expression of inducible defences, even in species without pronounced sexual dimorphism.

Under the influence of light: How light pollution disrupts personality and metabolism in hermit crabs

Anthropogenic disturbances are known to cause significant physiological and behavioural changes in animals and, thus, are the critical focus of numerous studies. Light pollution is an increasingly recognised source of disturbance that has the potential to impact animal physiology and behaviour. Here, we investigate the effect of constant light on a personality trait and metabolic rate in the European hermit crab Pagurus bernhardus. We used Bayesian mixed models to estimate average behavioural change (i.e. sample mean level behavioural plasticity) and between- and within-individual variation in boldness in response to laboratory light. Hermit crabs experiencing constant light were consistently less bold and had a higher metabolic rate than those kept under a standard laboratory light regime (12:12 h light/dark). However, there was no effect of light on individual consistency in behaviour. As boldness is associated with coping with risk, hermit crabs exposed to light pollution at night may experience increased perceived predation risk, adjusting their behaviour to compensate for the increased conspicuousness. However, reduced boldness could lead to lower rates of foraging and this, in combination with elevated metabolic rate, has the potential for a reduction in energy balance.

Forager-mediated cascading effects on food resource species diversity.

Perceived predation risk varies in space and time. Foraging in this landscape of fear alters forager-resource interactions via cascading nonconsumptive effects. Estimating these indirect effects is difficult in natural systems. Here, we applied a novel measure to quantify the diversity at giving-up density that allows to test how spatial variation in perceived predation risk modifies the diversity of multispecies resources at local and regional spatial levels. Furthermore, we evaluated whether the nonconsumptive effects on resource species diversity can be explained by the preferences of foragers for specific functional traits and by the forager species richness. We exposed rodents of a natural community to artificial food patches, each containing an initial multispecies resource community of eight species (10 items each) mixed in sand. We sampled 35 landscapes, each containing seven patches in a spatial array, to disentangle effects at local (patch) and landscape levels. We used vegetation height as a proxy for perceived predation risk. After a period of three nights, we counted how many and which resource species were left in each patch to measure giving-up density and resource diversity at the local level (alpha diversity) and the regional level (gamma diversity and beta diversity). Furthermore, we used wildlife cameras to identify foragers and assess their species richness. With increasing vegetation height, i.e., decreasing perceived predation risk, giving-up density, and local alpha and regional gamma diversity decreased, and patches became less similar within a landscape (beta diversity increased). Foragers consumed more of the bigger and most caloric resources. The higher the forager species richness, the lower the giving-up density, and alpha and gamma diversity. Overall, spatial variation of perceived predation risk of foragers had measurable cascading effects on local and regional resource species biodiversity, independent of the forager species. Thus, nonconsumptive predation effects modify forager-resource interactions and might act as an equalizing mechanism for species coexistence.

Early nest initiation and vegetation density enhance nest survival in Wild Turkeys

Abstract The theory of adaptive habitat selection suggests resource selection by animals should reflect underlying quality, such that individual selection confers an adaptive advantage via increased fitness. Using resource selection functions and nest survival models, we demonstrated that visual obstruction at the nest site was adaptively significant but timing of nest initiation had the greatest effect on nest survival for eastern Wild Turkeys (Meleagris gallopavo silvestris). Predation risk is a selective pressure, and if individuals can perceive predation risk, they may respond by altering the selection of nest site characteristics based on prior experience. We evaluated patterns in nest site selection of 387 Wild Turkeys and the consequences of selection on reproductive success across the southeastern United States from 2014 to 2019. We monitored 549 nest sites and found that nest initiation date had the strongest effect on daily nest survival rates, wherein adult females at our earliest nest initiation date were ~4 times more likely to successfully nest than females at our latest nest initiation date. Selection of nest sites with greater visual obstruction also increased daily nest survival rates, and females were 1.17 (95% CI: 1.100–1.234) and 1.37 (95% CI: 1.258–1.486) times more likely to select sites for every 10-cm increase in visual obstruction and maximum vegetation height, respectively. Collectively, our results indicate that nest initiation date is likely the critical parameter driving Wild Turkey nest success, whereas vegetative conditions play a lesser role in influencing nest success. Females nesting earlier may be in better body condition and show increased nest attentiveness, which may mediate nest success more than vegetation conditions around nest sites. Our work indicates that increasing the reproductive success of Wild Turkeys may hinge on females being able to nest as early as possible within the reproductive season.