Reduce Predation Risk Research Articles

Small mammals reduce distance dependence and increase seed predation risk in tropical rainforest fragments

AbstractSeed predation and reduced predation risk with distance from conspecific trees are important influences on tree regeneration in tropical forests. Shifts in animal communities, such as an increase in rodents and other small mammals due to forest fragmentation, could alter patterns of seed predation and affect tree regeneration and community dynamics in forest fragments. We performed a field experiment on four native rainforest tree species in the Western Ghats, India, to test whether fragmentation increases seed predation by mammals and alters the distance dependence of seed predation. We monitored seed predation within open and mammal exclosure plots, near and far from the canopies of conspecific trees, in contiguous and fragmented forests. Seed predation of Cullenia exarillata, Ormosia travancorica, and Syzygium rubicundum was markedly higher in forest fragments, and more so within open plots than exclosures, while the predominantly insect‐predated Acronychia pedunculata experienced similar predation in contiguous forests and fragments. Seed predation of C. exarillata and S. rubicundum was unrelated to distance from conspecific trees in open plots in both contiguous forests and fragments, in contrast to exclosures that showed marked near versus far differences in seed predation. Our findings suggest that by increasing overall seed predation risk and imposing similar seed predation risk near and far from adults variably across the tree species, small mammals could alter processes that shape tree diversity and species composition in fragmented tropical rainforests.

Capybara responses to varying levels of predation risk

Predators can generate physiological and behavioural responses in prey individuals. Thus, carnivore reintroductions might cause profound changes in communities and ecosystems by modifying antipredator responses. Combining observational and experimental approaches, we compared the short- and long-term antipredator responses of capybaras, Hydrochoerus hydrochaeris , between a landscape with a high density of predators (Pantanal, Brazil) and a landscape where predators became extinct in the mid-20th century but where a jaguar reintroduction project was in progress (Iberá, Argentina). Generalized linear models were used to test whether the presence of natural predators affects capybara behavioural budgets, gregarious behaviour and the associated physiological stress responses and to test whether, in the short term, capybaras increase their vigilance levels after detecting the proximity of a simulated predator (a playback of jaguar, Panthera onca , calls). Capybaras in the Pantanal did not show higher levels of vigilance but they spent a greater proportion of time foraging than did capybaras in Iberá. Pantanal groups were smaller and foraged closer to water. The baseline levels of stress hormones tended to be higher in Iberá. In response to simulated stimuli, both populations responded to predator sound cues by increasing vigilance, but Iberá groups also increased vigilance in response to a control sound, suggesting that they did not recognize the predator stimulus as a greater risk than another stimulus. In areas with predators, capybaras may reduce predation risk by choosing safer areas, where they can spend more time foraging when predators are not nearby. Vigilance may be only a reactive response to cues of the predator's proximity. Understanding the capybara's antipredator responses may help predict the potential effects and the success of jaguar reintroduction in a region where the jaguar has been absent for over 80 years. • Capybaras facing regular jaguar predation spent more time foraging in safe zones. • Capybaras living without predators did not recognize predator sound stimuli. • Vigilance may be only a reactive response to cues of the predator's proximity. • Prey released from predation for generations may lose some antipredator behaviours. • Naïvety and high density of capybaras could predict successful jaguar reintroduction.

Recursive movements of eastern wild turkey broods in the southeastern United States

AbstractProductivity of wild turkey (Meleagris gallopavo) populations throughout the southeastern United States has declined over the past several decades. Although population trajectory is driven primarily by annual reproduction, wild turkey managers have little information regarding the behavioral ecology of broods immediately post‐hatch. Broods are known to revisit areas within their ranges, but revisitation behavior is poorly understood spatially and temporally. Thus, identifying patterns of visitation and revisitation can increase understanding of brood behavior. We monitored 94 brooding females until brood failure or 28 days after hatch to evaluate movements and to quantify landcover and vegetation density at revisited locations which we defined as a 100‐m radius circular buffer around each GPS location. Average time between revisitation was 1.05 days (SD = 2.01). Revisited areas were associated with increased proportions of open treeless, pine (Pinus spp.), and pine‐hardwood landcover types and decreased proportions of hardwood forest landcover. Our results indicate that broods frequently revisit areas, presumably due to understory structure that increases available forage and reduces predation risk. However, future research should evaluate recursion and its relationship to habitat selection as it could be driven by development (i.e., aging) of the brood over time.

A conservative oviposition preference in spider mites for complex habitats as a preventive strategy for reducing predation risk

A conservative oviposition preference in spider mites for complex habitats as a preventive strategy for reducing predation risk

Shoaling in the Trinidadian guppy: costs, benefits, and plasticity in response to an ambush predator

AbstractShoaling, the formation of social groupings in fish, can provide benefits including reduced predation risk. However, it can also inflict costs including increased competition for resources, transmission of parasites, and salience to predators. Trinidadian guppies exhibit inter-population variation in shoaling behavior where individuals coexisting with large piscivorous predators (high predation localities) spend most of their time in shoals and those coexisting with an ambush predator, Rivulus hartii (recently, Anablepsoides hartii), that preys primarily on smaller guppies (low predation localities) do not. It has been suggested that this predator selects for reduced shoaling because doing so reduces salience to the predator. Here, as far as we know, we perform the first test of this idea. First, we investigated the effectiveness of shoaling in encounters with this predator. In survival trials, where one rivulus interacted with a group of guppies, we found that the predator was more likely to attack individuals in shoals than singletons. However, we also found that attacks directed at shoals were less likely to succeed. This suggests that the optimal strategy for guppies co-existing with this predator is to reduce shoaling to reduce the probability of being attacked, and to form shoals when an attack is initiated. We then asked if guppies modified their shoaling behavior in response to visual and olfactory cues from this predator during development. We found changes in guppy behavior in response to the treatment: guppies increased shoaling behavior when there was heightened risk of predation.

Ontogeny and caudal autotomy fracture planes in a large scincid lizard, Egernia kingii

Many lizard species use caudal autotomy, the ability to self-amputate a portion of the tail, as an effective but costly survival strategy. However, as a lizard grows, its increased size may reduce predation risk allowing for less costly strategies (e.g., biting and clawing) to be used as the primary defence. The King’s skink (Egernia kingii) is a large scincid up to approximately 244 mm snout to vent length (SVL) in size when adult. Adults rely less on caudal autotomy than do juveniles due to their size and strength increase during maturation. It has been hypothesised that lower behavioural reliance on autotomy in adults is reflected in loss or restriction of caudal vertebrae fracture planes through ossification as caudal intra-vertebral fracture planes in some species ossify during ontogenetic growth. To test this, we used micro-CT to image the tails of a growth series of seven individuals of E. kingii. We show that fracture planes are not lost or restricted ontogenetically within E. kingii, with adults retaining between 39–44 autotomisable vertebrae following 5–6 non-autotomisable vertebrae. Even though mature E. kingii rely less on caudal autotomy than do juveniles, this research shows that they retain the maximum ability to autotomise their tails, providing a last resort option to avoid threats. The potential costs associated with retaining caudal autotomy are most likely mitigated through neurological control of autotomy and E. kingii’s longevity.

Significance of sea entry pathway of chum salmon Oncorhynchus keta fry, inferred from the differential expressions of Na+,K+-ATPase α-subunit genes in the gills

Na+,K+-ATPase (NKA) α-subunit 1a (α1a) and 1b (α1b) gene expressions in the gills are changeable in response to ambient salinity in a few salmonids. In this study, the expressions were compared among ambient salinities and used to infer sea entry migration of chum salmon Oncorhynchus keta fry. The expression of α1a decreased from the 2 days after seawater (SW) transfer from freshwater (FW) and was significantly lower in SW-acclimated fry than that in FW-fry. On the other hand, the expression of α1b peaked on the first to second day after SW transfer and then settled to a level 2-fold higher than in FW-fry. In fry caught in the waterfronts of the beaches, the expression levels were quite similar to those on the first and second days after SW transfer, whereas, in fry caught off beach, the expressions were identical to those of SW-acclimated fry. These suggest that fry adapt to SW with moving along the shoal in the bay, and move to off beach after completing SW adaptation. One of the physiological significances in a usage of waterfront may be to transform the gills to SW type. Only fry on the 2 days after SW transfer failed to exhibit condition factor-dependency of burst swimming, probably due to physiological perturbation, which may be related to poor predation avoidance. The physiological approach used in this study inferred sea entry migration of fry; furthermore, it shows the possible significance of adaptation to SW in the shoal is to reduce predation risk.

When can cropping rate compensate for increased vigilance?

Abstract Herbivores use vigilance to reduce predation risk and interact socially, yet it imposes a foraging efficiency cost. As individuals spend more time with their head up being vigilant, time available to search for and ingest food decreases. We explored whether ungulates can strategically modify behaviours to compensate for vigilance costs via increased cropping rate when food searching time was near-zero and bite sizes were small. We compared the proportion of time individuals had their head up to their cropping rate (bites/observation length) in 271 observations of Roosevelt elk (Cervus elaphus roosevelti). Using a linear mixed-effect model, we estimated the head up–cropping rate relationship and found that elk cropping rate was constant across varying lengths of time spent with their head up, indicating no vigilance compensation occurred via increased cropping rate. We discuss settings when cropping rate compensation is expected and other behaviours that might mitigate vigilance costs.

Effects of nest site selection and nest concealment on nest survival of Gosling's Bunting (Emberiza goslingi)

Selecting nest sites that provide access to resources and reduce predation risk is crucial to maximizing fitness in breeding birds. Therefore, understanding what habitat features influence nest site selection and nest success is a key component of avian conservation because it allows for identification and protection of habitat that will promote population growth. We examined drivers of nest success in Gosling's Bunting (Emberiza goslingi) by evaluating variables that influence nest site choice and nest survival at 23 nests and an equal number of random, paired, non-nesting locations in a tropical savannah landscape in north-central Nigeria. Gosling's Buntings exhibited a nonrandom nest-placement pattern. Nests were either on or in proximity to large rock surfaces with nesting probability increasing when the immediate nesting area (100 m radius around the nest) consisted of 30–60% bare rock. Compared to random non-nesting sites, buntings selected areas that were low in litter cover and/or had short grass height. Daily nest survival probability was high (0.96) and was positively associated with the proportion of bare rock around the nest but negatively with the amount of litter cover. Although hatching success was 56.9%, only 30% of all nesting attempts successfully fledged a chick suggesting that nest failure occurred mostly at advanced stages of nesting (nestling phase) when renesting is less likely. Nest survival was higher at low concealment, but only significantly higher than nest failure within a restricted concealment range of 45–54%. Our findings show that microhabitat features could benefit reproduction and daily nest survival. Furthermore, by linking nest-site attributes with fitness indices, we highlight the potential importance of fitness measures as a key component of habitat quality assessment for these buntings in tropical savannahs.

Fire as a driver and mediator of predator-prey interactions.

ABSTRACTBoth fire and predators have strong influences on the population dynamics and behaviour of animals, and the effects of predators may either be strengthened or weakened by fire. However, knowledge of how fire drives or mediates predator–prey interactions is fragmented and has not been synthesised. Here, we review and synthesise knowledge of how fire influences predator and prey behaviour and interactions. We develop a conceptual model based on predator–prey theory and empirical examples to address four key questions: (i) how and why do predators respond to fire; (ii) how and why does prey vulnerability change post‐fire; (iii) what mechanisms do prey use to reduce predation risk post‐fire; and (iv) what are the outcomes of predator–fire interactions for prey populations? We then discuss these findings in the context of wildlife conservation and ecosystem management before outlining priorities for future research. Fire‐induced changes in vegetation structure, resource availability, and animal behaviour influence predator–prey encounter rates, the amount of time prey are vulnerable during an encounter, and the conditional probability of prey death given an encounter. How a predator responds to fire depends on fire characteristics (e.g. season, severity), their hunting behaviour (ambush or pursuit predator), movement behaviour, territoriality, and intra‐guild dynamics. Prey species that rely on habitat structure for avoiding predation often experience increased predation rates and lower survival in recently burnt areas. By contrast, some prey species benefit from the opening up of habitat after fire because it makes it easier to detect predators and to modify their behaviour appropriately. Reduced prey body condition after fire can increase predation risk either through impaired ability to escape predators, or increased need to forage in risky areas due to being energetically stressed. To reduce risk of predation in the post‐fire environment, prey may change their habitat use, increase sheltering behaviour, change their movement behaviour, or use camouflage through cryptic colouring and background matching. Field experiments and population viability modelling show instances where fire either amplifies or does not amplify the impacts of predators on prey populations, and vice versa. In some instances, intense and sustained post‐fire predation may lead to local extinctions of prey populations. Human disruption of fire regimes is impacting faunal communities, with consequences for predator and prey behaviour and population dynamics. Key areas for future research include: capturing data continuously before, during and after fires; teasing out the relative importance of changes in visibility and shelter availability in different contexts; documenting changes in acoustic and olfactory cues for both predators and prey; addressing taxonomic and geographic biases in the literature; and predicting and testing how changes in fire‐regime characteristics reshape predator–prey interactions. Understanding and managing the consequences for predator–prey communities will be critical for effective ecosystem management and species conservation in this era of global change.

Large herbivores in a partially migratory population search for the ideal free home.

Migration is a tactic used across taxa to access resources in temporally heterogenous landscapes. Populations that migrate can attain higher abundances because such movements allow access to higher quality resources, or reduction in predation risk resulting in increased fitness. However, most migratory species occur in partially migratory populations, a mix of migratory and non-migratory individuals. It is thought that the portion of migrants in a partial migration population is maintained either through (1) a population-level evolutionary stable state where counteracting density-dependent vital rates act on migrants and residents to balance fitness or (2) conditional migration, where the propensity to migrate is influenced by the individual's state. However, in many respects, migration is also a form of habitat selection and the proportion of migrants and residents may be the result of density-dependent habitat selection. Here, we test whether the theory of Ideal Free Distribution (IFD) can explain the coexistence of different migratory tactics in a partially migratory population. IFD predicts individuals exhibit density-dependent vital rates and select different migratory tactics to maximize individual fitness resulting in equal fitness (λ) between tactics. We tested the predictions of IFD in a partially migratory elk population that declined by 70% with 19 years of demographic data and migratory tactic switching rates from >300 individuals. We found evidence of density dependence for resident pregnancy and adult female survival providing a fitness incentive to switch tactics. Despite differences in vital rates between migratory tactics, mean λ (fitness) was equal. However, as predicted by the IFD, individuals switched tactics toward those of higher fitness. Our analysis reveals that partial migration may be driven by tactic selection that follows the ideal free distribution. These findings reinforce that migration across taxa may be a polymorphic behavior in large herbivores where migratory tactic selection is determined by differential costs and benefits, mediated by density dependence.

Behavioral responses to predatory sounds predict sensitivity of cetaceans to anthropogenic noise within a soundscape of fear

SignificanceAcoustic signals travel efficiently in the marine environment, allowing soniferous predators and prey to eavesdrop on each other. Our results with four cetacean species indicate that they use acoustic information to assess predation risk and have evolved mechanisms to reduce predation risk by ceasing foraging. Species that more readily gave up foraging in response to predatory sounds of killer whales also decreased foraging more during 1- to 4-kHz sonar exposures, indicating that species exhibiting costly antipredator responses also have stronger behavioral reactions to anthropogenic noise. This advance in our understanding of the drivers of disturbance helps us to predict what species and habitats are likely to be most severely impacted by underwater noise pollution in oceans undergoing increasing anthropogenic activities.

Egg Laying Behaviour and Larval Shelter-Construction Patterns of the Endangered Mottled Duskywing (Erynnis martialis) Butterfly's Western Population in Canada

The Mottled duskywing (Erynnis martialis) butterfly is endangered, living in pine forests and oak barrens in Canada and the eastern United States of America. While host plants and larval behaviour is documented in Mottled duskywing's eastern range, these life components are poorly known in Manitoba. We observed adult behaviour, host plant species used and larval foraging to better understand these biological aspects of E. martialis. We observed eggs laid exclusively on Ceanothus herbaceus, and larvae consuming C. herbaceus in leaf shelters near the periphery of plants. Early instar larvae tied leaves together with cells of silk creating partly open shelters while later instar larvae completely sealed shelters. Shelters constructed out of young leaves at the edge of plants are likely easier to digest. Later-instar larvae may nocturnally harvest food to consume in shelters during the day to reduce predation risk. Larvae were found in clearings adjacent to Pinus banksiana dominated forests, with these openings likely providing suitable microhabitats for egg development and larval feeding. We observed newly emerged adults during weeks 1 to 5 of the flight period; eggs, larvae and adults overlapped. We recommend direct observations of larval foraging—during the day and night, as well as transitions into and out of diapause—to more accurately describe their behaviour and physiology. We started to characterise microhabitats, however further research is needed. Our research may help to guide critical habitat designations, leading to successful Mottled duskywing recovery in Manitoba.

Wild zebra finches are attracted towards acoustic cues from conspecific social groups

Abstract Social information gathered by observing others often supplements personal information collected from direct interactions with the physical environment during decision-making. Social information use may be particularly beneficial in harsh environments or if resources are distributed patchily, ephemeral, and unpredictable, and hence difficult to locate. We experimentally tested the use of acoustic cues in wild zebra finches (Taeniopygia guttata) as they flew around their arid habitat as a way of locating conspecifics on the ground, and potentially accessing useful social information. Joining a conspecific group may reduce the predation risk, and if they are foraging may also improve foraging efficiency, as the distribution of zebra finch food (grass seed) is scattered and unpredictable in their natural habitat, the Australian arid zone. We conducted playback experiments along vegetated creek lines radiating out from an artificial dam where all birds in the population were coming for drinking water. We broadcast recordings of vocalizations from foraging conspecific groups to birds using these creek lines to move to or from the water into the wider habitat. Zebra finches were more likely to land near the loudspeaker when conspecific vocalizations were broadcast compared to white noise. Birds flying low and close to the loudspeaker were most likely to land. Our results indicate that zebra finches use acoustic cues of conspecifics as a source of social information for grouping decisions. Use of such information may also enhance foraging efficiency in environments with unpredictable and scarce foraging locations, and reduce predation risk for calling and responding individuals.

Seascapes of fear and competition shape regional seabird movement ecology

Fear effects of predators on prey distributions are seldom considered in marine environments, especially over large spatial scales and in conservation contexts. To fill these major gaps, we tested the Seascape of Fear Hypothesis in the Benguela marine ecosystem off South Africa. Using electronic tracking data, we showed that Cape gannets and their predator, the Cape fur seal, co-occurred in daytime and competed with fisheries within coastal areas. At night, gannets are particularly vulnerable to seals, and 28% of the birds returned to the safety of their breeding colony. The remaining 72% slept at the sea surface, but shifted to offshore areas with lower seal attendance, reducing predation risk by 25%. Overall, our integrative study demonstrates how fear and competition shape the seascape of threatened Cape gannets within a marine environment perturbed by climate change and overfishing. Such knowledge has strong implications for the design of marine protected areas.

Odour-mediated Interactions Between an Apex Reptilian Predator and its Mammalian Prey

An important but understudied modality for eavesdropping between predators and prey is olfaction, especially between non-mammalian vertebrate predators and their prey. Here we test three olfactory eavesdropping predictions involving an apex reptilian predator, the sand goanna Varanus gouldii, and several species of its small mammalian prey in arid central Australia: 1) small mammals will recognize and avoid the odour of V. gouldii; 2) V. gouldii will be attracted to the odour of small mammals, especially of species that maximize its energetic returns; and 3) small mammals will be less mobile and will show higher burrow fidelity where V. gouldii is absent compared with where it is present. As expected, we found that small mammals recognized and avoided faecal odour of this goanna, feeding less intensively at food patches where the odour of V. gouldii was present than at patches with no odour or a pungency control odour. Varanus gouldii also was attracted to the odour of small mammals in artificial burrows and dug more frequently at burrows containing the odour of species that were energetically profitable than at those of species likely to yield diminishing returns. Our third prediction received mixed support. Rates of movement of three species of small mammals were no different where V. gouldii was present or absent, but burrow fidelity in two of these species increased as expected where V. gouldii had been removed. We conclude that olfaction plays a key role in the dynamic interaction between V. gouldii and its mammalian prey, with the interactants using olfaction to balance their respective costs of foraging and reducing predation risk. We speculate that the risk of predation from this apex reptilian predator drives the highly unusual burrow-shifting behaviour that characterizes many of Australia's small desert mammals.

Modeling vigilance in mixed‐species groups

AbstractMixed‐species groups are usually explained by foraging advantages and reduced predation risk for at least one of the participating species. Given that animals trade‐off foraging and vigilance, the optimal level of vigilance of individuals in mixed‐species groups depends partly on the vigilance levels of both conspecifics and heterospecifics. However, the benefits and costs of being part of a mixed‐species group do not need to be evenly distributed between the species in a group. In this paper, we modeled the evolutionary stable strategy (ESS) for the optimal level of vigilance of an individual in a mixed‐species group influenced by the effects of “many eyes,” “dilution” and “attraction,” and unequal costs and benefits between the species. Our model illustrates under what conditions associations with other species may facilitate reduced predation risk for at least one of the participating species. We show that vigilance of individuals in mixed‐species groups becomes a social game, and that the ESS of these vigilance games may predict the individual's adaptive level of vigilance. This paper provides the first step in the development of a predictive theory for the numerous empirical studies on mixed‐species groups.

Evidence of aggregation behavior in Erythrolamprus poecilogyrus caesius (Cope, 1862) (Serpentes: Dipsadidae) in the Dry Chaco

Aggregation among individuals of the same species is a common spatial pattern in nature, and has been well studied in insects, mammals, birds, and fishes. Among vertebrates, mammals, birds, and fishes are considered the most social. Among reptiles, snakes also form aggregations for mating, defense, or communal shedding, and this behavior can be associated to kin and conspecific recognition. Here, we report information on the aggregation behavior in Erythrolamprus poecilogyrus caesius. We made two observations in the Dry Chaco of Paraguay. In the first observation (2016) we found three adults of E. p. caesius under a fallen trunk. The second observation occurred in three temporary ponds (2020), where E. p. caesius aggregated in groups of five (juveniles), ten (juveniles and sub-adults), and two (juveniles). Aggregation can reduce predation risk, increase the survival or the reproductive success, and could occur in response to external cues. Future research must focus on aggregation context and define experimentally the factors that trigger it, and whether it depends on environmental resources, or if it is part of a social interaction.

Conspicuous cruciform silk decorations deflect avian predator attacks.

Although camouflage as an effective antipredator defense strategy is widespread across animals, highly conspicuous color patterning is not uncommon either. Many orb-web spiders adorn their webs with extra bright white silk. These conspicuous decorations are hypothesized to deter predators by warning the presence of sticky webs, camouflaging spiders, acting as a decoy, or intimidating predators by their apparent size. The decorations may also deflect predator attacks from spiders. However, empirical evidence for this deflection function remains limited. Here, we tested this hypothesis using the X-shaped silk cruciform decorations built by females of Argiope minuta. We employed visual modeling to quantify the conspicuousness of spiders and decorations from a perspective of avian predators. Then, we determined actual predation risk on spiders using naïve chicks as predators. Spider bodies and decorations were conspicuous against natural backgrounds to the avian visual systems. Chicks attacked the spider main bodies significantly less frequently on the decorated webs than on the undecorated webs, thus reducing predation risk. When both spiders and decorations were present, chicks also attacked the spider main bodies and their legs or decorations, and not randomly: they attacked the legs or decorations sooner and more frequently than they attacked the main bodies, independent of the ratio of the surface area between the decoration and spider size. Despite the increase in detectability, incorporating a conspicuous cruciform decoration to the web effectively defends the spider by diverting the attack toward the decoration or leg, but not by camouflaging or intimidating, thus, supporting the deflection hypothesis.

Trophic ecology of sympatric juvenile stingrays within a nursery area

Nursery areas are crucial for many elasmobranch species, providing advantages such as increased access to prey and reduced predation risk. This study investigated the trophic interactions of two juvenile stingray species within a coastal communal nursery using stable isotope analysis. Muscle, plasma and red blood cells samples were taken from the mangrove whipray Urogymnus granulatus and the cowtail stingray Pastinachus ater, and δ15N, δ13C and δ34S measured. Urogymnus granulatus had higher mean δ13C, δ15N and δ34S than P. ater. General linear models showed no significant trends between δ13C, δ15N or δ34S and body size or sex. Low isotopic niche overlap, combined with previous data on movement patterns, provided evidence of niche partitioning between stingrays that likely reflect differences in feeding grounds and prey selection. Despite the differences in feeding grounds and prey selection, previous studies showed that U. granulatus and P. ater share sand and reef flat areas for most of the day (~20 h). δ13C and δ34S values suggested that mangrove-derived carbon had little importance to stingrays’ diets in the study area. Results presented in this study bring new insights to the feeding ecology of two sympatric stingray species and their trophic interactions within a communal nursery area.