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At least 91 records · Page 5Linked to original sources
USGS2021

Broadening the ecology of fear: Non-lethal effects arise from diverse responses to predation and parasitism

Research on the ‘ecology of fear’ posits that defensive prey responses to avoid predation can cause non-lethal effects across ecological scales. Parasites also elicit defensive responses in hosts with associated non-lethal effects, which raises the longstanding, yet unresolved question of how non-lethal effects of parasites compare with those of predators. We developed a framework for systematically answering this question for all types of predator–prey and host–parasite systems. Our framework reveals likely differences in non-lethal effects not only between predators and parasites, but also between different types of predators and parasites. Trait responses should be strongest towards predators, parasitoids and parasitic castrators, but more numerous and perhaps more frequent for parasites than for predators. In a case study of larval amphibians, whose trait responses to both predators and parasites have been relatively well studied, existing data indicate that individuals generally respond more strongly and proactively to short-term predation risks than to parasitism. Apart from studies using amphibians, there have been few direct comparisons of responses to predation and parasitism, and none have incorporated responses to micropredators, parasitoids or parasitic castrators, or examined their long-term consequences. Addressing these and other data gaps highlighted by our framework can advance the field towards understanding how non-lethal effects impact prey/host population dynamics and shape food webs that contain multiple predator and parasite species.

Proceedings of the Royal Society B↗
USGS2022

Nesting and post-fledging predation risk influence diel patterns of songbird fledging

Among stages of avian ontogeny, the act of nest departure or fledging is an abrupt transition into a new environment and a major leap toward independence for offspring. In altricial birds, the timing of fledging is notable in that many species tend to fledge early in the morning. Past studies have proposed nest predation as a key factor driving birds to fledge earlier in the morning (the ‘survival hypothesis’), whereby offspring avoid peak times of nest predation that may occur later in the day. A natural extension of this hypothesis is the predation of offspring post-fledging, whereby offspring are also timing their fledging with future survival prospects outside of the nest. However, few studies have investigated fledging behavior in the context of both nesting and post-fledging predation. To help fill this knowledge gap, we investigated factors driving the timing and duration of fledging across six songbird species in the context of offspring predation: daily nest mortality, post-fledging mortality, and diel patterns of nest predation risk. We found that >60% of songbirds fledged early in the morning, while the peaks in nest predation risk occurred later in the day. Furthermore, species under greater risk of nest predation fledged earlier in the day and in closer succession to their siblings. Parameters of post-fledging mortality were poor predictors of fledging timing, but broods of species under higher risk of post-fledging mortality fledged more rapidly. These results provide evidence in support of the survival hypothesis, and suggest that songbirds fledge in the morning to avoid peak times of nest predation risk that occur later in the day (~8 hours after civil dawn). Such results corroborate past research highlighting predation on dependent offspring as a key factor driving variation in life histories across animal taxa, however, estimates of post-fledging mortality suggests that nest predation alone does not fully explain variation in fledging behavior among species. Future research is therefore needed to investigate the contribution of other factors, such as energetics, parent-offspring conflict, and diel patterns of post-fledging survival, that may help to mediate diel patterns of fledging within and among songbird species.

Illinois↗
USGS2005

Are all prey created equal? A review and synthesis of differential predation on prey in substandard condition

Our understanding of predator-prey interactions in fishes has been influenced largely by research assuming that the condition of the participants is normal. However, fish populations today often reside in anthropogenically altered environments and are subjected to many kinds of stressors, which may reduce their ecological performance by adversely affecting their morphology, physiology, or behaviour. One consequence is that either the predator or prey, or both, may be in a substandard condition at the time of an interaction. We reviewed the literature on predator-prey interactions in fishes where substandard prey were used as experimental groups. Although most of this research indicates that such prey are significantly more vulnerable to predation, prey condition has rarely been considered in ecological theory regarding predator-prey interactions. The causal mechanisms for increased vulnerability of substandard prey to predation include a failure to detect predators, lapses in decision-making, poor fast-start performance, inability to shoal effectively, and increased prey conspicuousness. Despite some problems associated with empirical predator-prey studies using substandard prey, their results can have theoretical and applied uses, such as in ecological modelling or justification of corrective measures to be implemented in the wild. There is a need for more corroborative field experimentation, a better understanding of the causal mechanisms behind differential predation, and increased incorporation of prey condition into the research of predator-prey modellers and theoreticians. If the concept of prey condition is considered in predator-prey interactions, our understanding of how such interactions influence the structure and dynamics of fish communities is likely to change, which should prove beneficial to aquatic ecosystems.

Journal of Fish Biology↗
USGS2007

Testing ecological and behavioral correlates of nest predation

Variation in nest predation rates among bird species are assumed to reflect differences in risk that are specific to particular nest sites. Theoretical and empirical studies suggest that parental care behaviors can evolve in response to nest predation risk and thereby differ among ecological conditions that vary in inherent risk. However, parental care also can influence predation risk. Separating the effects of nest predation risk inherent to a nest site from the risk imposed by parental strategies is needed to understand the evolution of parental care. Here we identify correlations between risks inherent to nest sites, and risk associated with parental care behaviors, and use an artificial nest experiment to assess site-specific differences in nest predation risk across nesting guilds and between habitats that differed in nest predator abundance. We found a strong correlation between parental care behaviors and inherent differences in nest predation risk, but despite the absence of parental care at artificial nests, patterns of nest predation risk were similar for real and artificial nests both across nesting guilds and between predator treatments. Thus, we show for the first time that inherent risk of nest predation varies with nesting guild and predator abundance independent of parental care. ?? Oikos.

Oikos↗
USGS2018

Entrapped carrion increases indirect plant resistance and intra‐guild predation on a sticky tarweed

Many plants employ indirect defenses against herbivores; often plants provide a shelter or nutritional resource to predators, increasing predator abundance, and lessening herbivory to the plant. Often, predators on the same plant represent different life stages and different species. In these situations intraguild predation (IGP) may occur and may decrease the efficacy of that defense. Recently, several sticky plants have been found to increase indirect defense by provisioning predatory insects with entrapped insects (hereafter: carrion). We conducted observational studies and feeding trials with herbivores and predators on two sticky, insect‐entrapping asters, Hemizonia congesta and Madia elegans , to construct food webs for these species and determine the prevalence of IGP in these carrion‐provisioning systems. In both systems, intraguild predation was the most common interaction observed. To determine whether IGP was driven by resource abundance, whether it reduced efficacy of this indirect defense and whether stickiness or predator attraction was induced by damage, we performed field manipulations on H. congesta . Carrion supplementation led to an increase in predator abundance and IGP. IGP was asymmetric within the predator guild: assassin bugs and spiders preyed on small stilt bugs but not vice versa. Despite increased IGP, carrion provisions decreased the abundance of the two most common herbivores (a weevil and a mealybug). Overall seed set was driven by plant size, but number of seeds produced per fruit significantly increased with increasing carrion, likely because of the reduction in the density of a seed‐feeding weevil. Observationally and experimentally, we found that carrion‐mediated indirect defense of tarweeds led to much intraguild predation, though predators effectively reduced herbivore abundance despite the increase in IGP.

Oikos↗
USGS2025

Smallmouth bass (Micropterus dolomieu) and chain pickerel (Esox niger) identified as Atlantic salmon (Salmo salar) smolt predators in a reservoir system

Reservoir predation has been identified as a leading mortality source for smolts migrating through impounded river systems. We investigated smolt predation risk for an endangered Atlantic salmon ( Salmo salar ) population in the Weldon Dam reservoir in the Penobscot River, Maine, USA. In spring 2022, we characterized the fates of 390 tethered smolts. Smolts were exclusively predated by two predator species not native to the study area: chain pickerel ( Esox niger , n = 43) and smallmouth bass ( Micropterus dolomieu , n = 42). Using Cox-proportional hazard analysis, we estimated that 23% (95% CI = 15%–29%) of tethered smolts were expected to be predated within a one-hour deployment. Water temperature was the primary driver of predation risk as predation probability increased from 10% to 33% when temperature increased from 5 to 15 °C. Smolts also incurred above-average predation risk when they were within 40 m of shore. We demonstrate that non-native fish predation may drive patterns of high impoundment mortality and that risk is spatially and temporally heterogeneous within these systems. Collectively, this study offers direct evidence of species-specific predation on Atlantic salmon smolts and illuminates potential strategies to mitigate predation risk during reservoir migration.

Maine↗
USGS2004

Determining nest predators of the Least Bell's Vireo through point counts, tracking stations, and video photography

We compared three methods to determine nest predators of the Least Bell's Vireo ( Vireo bellii pusillus ) in San Diego County, California, during spring and summer 2000. Point counts and tracking stations were used to identify potential predators and video photography to document actual nest predators. Parental behavior at depredated nests was compared to that at successful nests to determine whether activity (frequency of trips to and from the nest) and singing vs. non-singing on the nest affected nest predation. Yellow-breasted Chats ( Icteria virens ) were the most abundant potential avian predator, followed by Western Scrub-Jays ( Aphelocoma californica ). Coyotes ( Canis latrans ) were abundant, with smaller mammalian predators occurring in low abundance. Cameras documented a 48% predation rate with scrub-jays as the major nest predators (67%), but Virginia opossums ( Didelphis virginiana , 17%), gopher snakes ( Pituophis melanoleucus , 8%) and Argentine ants ( Linepithema humile , 8%) were also confirmed predators. Identification of potential predators from tracking stations and point counts demonstrated only moderate correspondence with actual nest predators. Parental behavior at the nest prior to depredation was not related to nest outcome.

Journal of Field Ornithology↗
USGS1999

Foraging trade-offs along a predator-permanence gradient in subalpine wetlands

We conducted a series of field and laboratory experiments to determine the direct and indirect effects of a top predator, the tiger salamander ( Ambystoma tigrinum nebulosum ), on larvae of two species of limnephilid caddisflies ( Limnephilus externus and Asynarchus nigriculus ) in subalpine wetlands in central Colorado. Asynarchus larvae predominate in temporary wetlands and are aggressive intraguild predators on Limnephilus larvae, which only predominate in permanent basins with salamanders. We first conducted a field experiment in mesocosms (cattle tanks) to quantify the predatory effects of different life stages of salamanders on the two caddisfly species. Two life stages of the salamanders (larvae and paedomorphs) preferentially preyed on Asynarchus relative to Limnephilus. Subsequent laboratory experiments revealed that high Asynarchus activity rates and relatively ineffective antipredatory behaviors led to higher salamander detection and attack rates compared to Limnephilus. In a second field experiment (full factorial for presence and absence of each of the three species), we found that salamander predation on Asynarchus had an indirect positive effect on Limnephilus : survival was higher in the presence of salamanders + Asynarchus than with just Asynarchus. In the laboratory we compared the predatory effects of salamanders with and without their mouths sewn shut and found the observed indirect positive effect on Limnephilus survival to be mainly the result of reduced numbers of Asynarchus rather than salamander-induced changes in Asynarchus behavior. We argue that indirect effects of predator–predator interactions on shared prey will be mainly density-mediated and not trait-mediated when one of the predators (in this case, Asynarchus ) is under strong selection for rapid growth and therefore does not modify foraging behaviors in response to the other predator. The reciprocal dominance of Limnephilus and Asynarchus in habitats with and without salamanders probably reflects a trade-off between competitive superiority and vulnerability to predation. The high activity levels and aggressiveness that enable Asynarchus to complete development in temporary habitats result in strong asymmetric competition (via intraguild predation) with Limnephilus. In permanent habitats these same behaviors increase Asynarchus vulnerability to salamander predation, which indirectly benefits Limnephilus. This and previous work implicate salamanders as keystone predators that exert a major influence on the composition of benthic and planktonic assemblages in subalpine wetlands.

Ecology↗
USGS2011

Identifying nest predators of American avocets (Recurvirostra americana) and black-necked stilts (Himantopus mexicanus) in San Francisco Bay, California

We evaluated predation on nests and methods to detect predators using a combination of infrared cameras and plasticine eggs at nests of American avocets ( Recurvirostra americana ) and black-necked stilts ( Himantopus mexicanus ) in Don Edwards San Francisco Bay National Wildlife Refuge, San Mateo and Santa Clara counties, California. Each technique indicated that predation was prevalent; 59% of monitored nests were depredated. Most identifiable predation ( n = 49) was caused by mammals (71%) and rates of predation were similar on avocets and stilts. Raccoons ( Procyon lotor ) and striped skunks ( Mephitis mephitis ) each accounted for 16% of predations, whereas gray foxes ( U rocyon cinereoargenteus ) and avian predators each accounted for 14%. Mammalian predation was mainly nocturnal (mean time, 0051 h ± 5 h 36 min), whereas most avian predation was in late afternoon (mean time, 1800 h ± 1 h 26 min). Nests with cameras and plasticine eggs were 1.6 times more likely to be predated than nests where only cameras were used in monitoring. Cameras were associated with lower abandonment of nests and provided definitive identification of predators.

California↗
USGS2000

Identifying predators and fates of grassland passerine nests using miniature video cameras

Nest fates, causes of nest failure, and identities of nest predators are difficult to determine for grassland passerines. We developed a miniature video-camera system for use in grasslands and deployed it at 69 nests of 10 passerine species in North Dakota during 1996-97. Abandonment rates were higher at nests <1 day after camera deployment (23%) than <1 day after nests were found (2%, P = 0.001). Most birds returned to nests 30 min after camera deployment, but clay-colored sparrows (Spizella pallida) took longer to return to nests than other species (P = 0.035). Cameras did not appear to increase nest predation rates. We videotaped predation by 11 species at 29 nests: eggs or nestlings were destroyed by mice, ground squirrels, weasel, badgers, canids, deer, cowbirds, and hawks. All eggs or nestlings were removed in <15 min at 14 depredated nests. Contents were removed during >1 day or night (22-116 hr) at 6 nests, 5 of which were depredated by ground squirrels or mice. For nests without cameras, estimated predation rates were lower for ground nests than aboveground nests (P = 0.055), but did not differ between open and covered nests (P = 0.74). Open and covered nests differed, however, when predation risk (estimated by initial-predation rate) was examined separately for day and night using camera-monitored nests; the frequency of initial predations that occurred during the day was higher for open nests than covered nests (P = 0.015). Thus, vulnerability of some nest types may depend on the relative importance of nocturnal and diurnal predators. Predation risk increased with nestling age from 0 to 8 days (P = 0.07). Up to 15% of fates assigned to camera-monitored nests were wrong when based solely on evidence that would have been available from periodic nest visits. There was no evidence of disturbance at nearly half the depredated nests, including all 5 depredated by large mammals. Overlap in types of sign left by different predator species, and variability of sign within species, suggests that evidence at nests is unreliable for identifying predators of grassland passerines.

Journal of Wildlife Management↗
USGS2010

Effects of subsidized predators, resource variability, and human population density on desert tortoise populations in the Mojave Desert, USA

Understanding predator–prey relationships can be pivotal in the conservation of species. For 2 decades, desert tortoise Gopherus agassizii populations have declined, yet quantitative evidence regarding the causes of declines is scarce. In 2005, Ft. Irwin National Training Center, California, USA, implemented a translocation project including 2 yr of baseline monitoring of desert tortoises. Unusually high predation on tortoises was observed after translocation occurred. We conducted a retrospective analysis of predation and found that translocation did not affect the probability of predation: translocated, resident, and control tortoises all had similar levels of predation. However, predation rates were higher near human population concentrations, at lower elevation sites, and for smaller tortoises and females. Furthermore, high mortality rates were not limited to the National Training Center. In 2008, elevated mortality (as high as 43%) occurred throughout the listed range of the desert tortoise. Although no temporal prey base data are available for analysis from any of the study sites, we hypothesize that low population levels of typical coyote Canis latrans prey (i.e. jackrabbits Lepus californicus and other small animals) due to drought conditions influenced high predation rates in previous years. Predation may have been exacerbated in areas with high levels of subsidized predators. Many historical reports of increased predation, and our observation of a range-wide pattern, may indicate that high predation rates are more common than generally considered and may impact recovery of the desert tortoise throughout its range.

Endangered Species Research↗
USGS2021

Avian predation of juvenile Lost River and Shortnose Suckers in Upper Klamath Lake: An assessment of Sucker assisted rearing program releases during 2018–2020

To bolster recruitment in Endangered Species Act (ESA) listed Lost River Suckers (Deltistes luxatus) and Shortnose Suckers (Chasmistes brevirostris) in the Upper Klamath Basin (UKB), the U.S. Fish and Wildlife Service (USFWS) and its partners have implemented the Sucker Assisted Rearing Program (SARP). As part of this program, juvenile suckers were reared in captivity, implanted with passive integrated transponder (PIT) tags (n= 8,857), and released into the Upper Klamath Lake or its tributaries during 2018–2020. Previous research suggests that predation by American White Pelicans (Pelecanus erythrorhynchos), Double-crested Cormorants (Nannopterum auritum), and Caspian Terns (Hydroprogne caspia) may negatively influence sucker survival, particularly predation on juvenile suckers. Estimates of predation impacts from past studies, however, represented minimum estimates of sucker mortality because analyses did not account for the proportion of consumed tags that were deposited by birds on their breeding colony where PIT tag recovery efforts took place. To estimate and account for deposition probabilities, we conducted a field study in which we fed pelicans PIT-tagged juvenile suckers (n = 401). We accounted for deposition probabilities of cormorants and terns by using previously published estimates. Sucker PIT tags were recovered from pelican, cormorant, and tern nesting sites in the UKB following each breeding season and a hierarchical Bayesian model was used to estimate predation rates (percentage of available tagged fish consumed) on SARP releases as well as naturally-reared or wild juvenile suckers and adult suckers that were PIT-tagged in Upper Klamath Lake and Clear Lake Reservoir. Pelican deposition probabilities were estimated at 0.47 (95% credible interval = 0.36–0.60), indicating that for every 100 PIT tags consumed, on average, 47 were deposited by pelicans on breeding colonies. Estimates of predation rates that incorporate corrections for deposition on SARP releases ranged annually from 4.4% (95% credible interval = 2.9–6.8%) to 8.8% (6.2–13.3%) during 2018–2020. Results suggest that colonial waterbird predation impacts on SARP releases likely constituted a small, but unknown, component of total mortality for suckers released into the Upper Klamath Lake system. Predation impacts on SARP juvenile suckers and wild juvenile suckers, which were estimated annually at 4.7% (1.0–13.9%) to 14.9% (7.6–29.3%), were consistently higher than those observed on adult suckers, with predation on adult suckers typically less than 4.0% of available fish annually. Future predation studies may consider models that integrate both live and dead detections of PIT-tagged suckers to generate more accurate and precise estimates of survival following release, as well as models that consider environmental factors that influence sucker susceptibility to colonial waterbird predation. Such models would provide a more holistic understanding of the degree to which avian predation limits the survival of ESA-listed suckers in the UKB.

Oregon↗
USGS2020

Response to terrestrial nest predators among endemic and introduced Hawaiian birds

Birds free from nest predators for long periods may either lose the ability to recognize and respond to predators or retain antipredator responses if they are not too costly. How these alternate scenarios play out has rarely been investigated in an avian community whose members have different evolutionary histories. We presented models of two nest predators (rat and snake) and a negative control (tree branch) to birds on Hawaiʻi Island. Endemic Hawaiian birds evolved in the absence of terrestrial predators until rats were introduced approximately 1,000 years ago. Introduced birds evolved with diverse predator communities including mammals and snakes, but since their introduction onto the island approximately one century ago have been free from snake predation. We found that (a) endemic and introduced birds had higher agitation scores toward the rat model compared with the branch, and (b) none of the endemic birds reacted to the snake model, while one introduced bird, the Red-billed Leiothrix (Leiothrix lutea), reacted as strongly to the snake as to the rat. Overall, endemic and introduced birds differ in their response to predators, but some endemic birds have the capacity to recognize and respond to introduced rats, and one introduced bird species retained recognition of snake predators from which they had been free for nearly a century, while another apparently lost that ability. Our results indicate that the retention or loss of predator recognition by introduced and endemic island birds is variable, shaped by each species' unique history, ecology, and the potential interplay of genetic drift, and that endemic Hawaiian birds could be especially vulnerable to introduced snake predators.

Hawaii↗
USGS2021

Diel patterns of predation and fledging at nests of four species of grassland songbirds

Although it is common for nestlings to exhibit a strong bias for fledging in the morning, the mechanisms underlying this behavior are not well understood. Avoiding predation risk has been proposed as a likely mechanism by a number of researchers. We used video surveillance records from studies of grassland birds nesting in North Dakota, Minnesota, and Wisconsin to determine the diel pattern of nest predation and fledging patterns of four ground-nesting obligate grassland passerines (Grasshopper Sparrow ( Ammodramus savannarum ), Savannah Sparrow ( Passerculus sandwichensis ), Bobolink ( Dolichonyx oryzivorus ), and Eastern Meadowlark ( Sturnella magna )). We used the nest predation pattern as a surrogate for predation activity to test whether nestlings minimized predation risk by avoiding fledging when predation activity was high and preferentially fledging when predation risk was low. Predation activity was significantly lower starting 3 hr before sunrise and ending 3 hr after sunrise, followed by a transition to a period of significantly higher activity lasting for 4 hr, before declining to an average activity level for the rest of the diel period. There was little evidence that the four grassland bird species avoided fledging during the high-risk period and Savannah Sparrow fledged at higher rates during that period. All four species had hours during the low-risk period where they fledged at higher rates, but only Grasshopper Sparrow fledged preferentially during that period. Bobolink and Eastern Meadowlark had multiple hours with high fledging rates throughout the daytime period, resulting in no relationship between probability of fledging and predation risk. Given the species variability in fledging pattern seen in our study, it is unlikely that there is a universal response to any driver that affects time of fledging. Further study is needed to understand the complex interplay between species ecology and drivers such as physiology, energetics, and predation in affecting grassland bird fledging behavior.

Minnesota, North Dakota, Wisconsin↗
USGS2020

Can oceanic prey effects on growth and time to fledging mediate terrestrial predator limitation of an at‐risk seabird?

Most seabird species nest colonially on cliffs or islands with limited terrestrial predation, so that oceanic effects on the quality or quantity of prey fed to chicks more often determine nest success. However, when predator access increases, impacts can be dramatic, especially when exposure to predators is extended due to slow growth from inadequate food. Kittlitz’s Murrelet ( Brachyramphus brevirostris ), a rare seabird having experienced serious declines, nests solitarily on the ground in barren, often alpine areas where exposure to predators is generally low. Nestling growth rates are exceptionally high and nestling periods very short relative to other Alcidae. This strategy reduces duration of exposure to predators, but demands adequate deliveries of high‐energy prey. In an area where foxes can access nests, we investigated whether varying energy content of prey fed to chicks could alter growth rates and resulting duration of predator exposure, and whether prolonged exposure appreciably reduced nest success. From 2009 to 2016, we monitored 139 nests; 49% were depredated (almost all by foxes) and 25% fledged. Prey fed to nestlings were 80% Pacific sand lance ( Ammodytes personatus ) and 19% capelin ( Mallotus villosus ), with capelin having 2.3× higher energy content per fish. In a year of slow chick growth, increased sand lance energy density of 31% (4.29–5.64 kJ/g, within published values), or increased proportion of capelin in the diet from 5.6% to 27.2%, would have allowed maximum chick growth. Maximum growth rates were attainable by delivering only 1.9 capelin/d versus 5.5 sand lance/d. Slow growth increased time to fledging by up to 5 d, decreasing survival by 7.7% (0.142–0.131). Breeding propensity of Kittlitz’s Murrelet averages only 20%, so even small changes in nest success could affect populations. Although nest success was limited mainly by predation, oceanic effects on prey quantity and quality had overriding impacts in one year (2015 heat wave), and small but substantive effects in other years by mediating exposure to predation. Climate warming that decreases availability of high‐energy forage fish, or increases expansion of predators into nesting habitats, may disproportionately affect this sensitive species and others with predator‐accessible nests and demands for energy‐rich prey.

Alaska↗
USGS2024

Using integrated step selection to determine effects of predation risk on bison habitat selection and movement

Animal movement is a fundamental mechanism that shapes communities and ecosystems. Ungulates alter the ecosystems they inhabit and understanding their movements and distribution is critical for linking habitat with population dynamics. Predation risk has been shown to strongly influence ungulate movement patterns, such that ungulates may select habitat where predation risk is lower (refugia), adjust movement rates, temporal patterns, or selection of cover variables in areas with greater predation risk. We evaluated potential predation avoidance behavior in a population of plains bison inhabiting the north rim of Grand Canyon National Park (GRCA) and adjacent Kaibab National Forest (KNF). The KNF has year-round hunting managed by Arizona Game and Fish Department, whereas hunting is not allowed in GRCA. Human-maintained water sources on the KNF are particularly important resources for bison wherein they may be exposed to higher predation risk to access these resources. We used 2-h GPS locations for three years from 31 bison ( n = 9 males; n = 22 females), and integrative step selection analysis to test four hypotheses about the potential for bison to reduce their risk from human predation by avoiding areas of high predation risk; moving faster in areas with high predation risk; entering high-risk areas at night when risk is reduced; and entering high-risk areas in habitats that provide cover (coniferous forest). The highest performing model indicated bison movement was 1.3 times faster per 2-h step interval than in areas with no hunting across all vegetation classes (coniferous forest, shrub, quaking aspen, grass-forb meadow) and across all topography classes (valley, slope, ridge). Bison moved more slowly in grass-forb meadows than all other vegetation types, and in valleys relative to slopes and ridges. Several radio-collared individuals had no GPS locations in KNF for the duration of the study. Bison avoided predation risk using two strategies: moving faster while in the KNF, and fully avoiding high-risk areas by remaining within GRCA. Management that manipulates or reduces timing of hunting seasons may reduce perceived predation risk and encourage bison to distribute into the KNF and across a broader range of available habitat.

Arizona↗
USGS2014

Partitioning the non‑consumptive effects of predators on preywith complex life histories

Non-consumptive effects (NCEs) of predators on prey can be as strong as consumptive effects (CEs) and may be driven by numerous mechanisms, including predator characteristics. Previous work has highlighted the importance of predator characteristics in predicting NCEs, but has not addressed how complex life histories of prey could mediate predator NCEs. We conducted a meta-analysis to compare the effects of predator gape limitation (gape limited or not) and hunting mode (active or sit-and-pursue) on the activity, larval period, and size at metamorphosis of larval aquatic amphibians and invertebrates. Larval prey tended to reduce their activity and require more time to reach metamorphosis in the presence of all predator functional groups, but the responses did not differ from zero. Prey metamorphosed at smaller size in response to non-gape-limited, active predators, but counter to expectations, prey metamorphosed larger when confronted by non-gape-limited, sit-and-pursue predators. These results indicate NCEs on larval prey life history can be strongly influenced by predator functional characteristics. More broadly, our results suggest that understanding predator NCEs would benefit from greater consideration of how prey life history attributes mediate population and community-level outcomes.

Oecologia↗
USGS2009

Modelling predation by transient leopard seals for an ecosystem-based management of Southern Ocean fisheries

Correctly quantifying the impacts of rare apex marine predators is essential to ecosystem-based approaches to fisheries management, where harvesting must be sustainable for targeted species and their dependent predators. This requires modelling the uncertainty in such processes as predator life history, seasonal abundance and movement, size-based predation, energetic requirements, and prey vulnerability. We combined these uncertainties to evaluate the predatory impact of transient leopard seals on a community of mesopredators (seals and penguins) and their prey at South Georgia, and assess the implications for an ecosystem-based management. The mesopredators are highly dependent on Antarctic krill and icefish, which are targeted by regional fisheries. We used a state-space formulation to combine (1) a mark-recapture open-population model and individual identification data to assess seasonally variable leopard seal arrival and departure dates, numbers, and residency times; (2) a size-based bioenergetic model; and (3) a size-based prey choice model from a diet analysis. Our models indicated that prey choice and consumption reflected seasonal changes in leopard seal population size and structure, size-selective predation and prey vulnerability. A population of 104 (90-125) leopard seals, of which 64% were juveniles, consumed less than 2% of the Antarctic fur seal pup production of the area (50% of total ingested energy, IE), but ca. 12-16% of the local gentoo penguin population (20% IE). Antarctic krill (28% IE) were the only observed food of leopard seal pups and supplemented the diet of older individuals. Direct impacts on krill and fish were negligible, but the "escapement" due to leopard seal predation on fur seal pups and penguins could be significant for the mackerel icefish fishery at South Georgia. These results suggest that: (1) rare apex predators like leopard seals may control, and may depend on, populations of mesopredators dependent on prey species targeted by fisheries; and (2) predatory impacts and community control may vary throughout the predator's geographic range, and differ across ecosystems and management areas, depending on the seasonal abundance of the prey and the predator's dispersal movements. This understanding is important to integrate the predator needs as natural mortality of its prey in models to set prey catch limits for fisheries. Reliable estimates of the variability of these needs are essential for a precautionary interpretation in the context of an ecosystem-based management. ?? 2009 Elsevier B.V.

Ecological Modelling↗