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At least 181 records · Page 10Linked to original sources

Co‐occurrence dynamics of endangered Lower Keys marsh rabbits and free‐ranging domestic cats: Prey responses to an exotic predator removal program

The Lower Keys marsh rabbit ( Sylvilagus palustris hefneri ) is one of many endangered endemic species of the Florida Keys. The main threats are habitat loss and fragmentation from sea‐level rise, development, and habitat succession. Exotic predators such as free‐ranging domestic cats ( Felis catus ) pose an additional threat to these endangered small mammals. Management strategies have focused on habitat restoration and exotic predator control. However, the effectiveness of predator removal and the effects of anthropogenic habitat modifications and restoration have not been evaluated. Between 2013 and 2015, we used camera traps to survey marsh rabbits and free‐ranging cats at 84 sites in the National Key Deer Refuge, Big Pine Key, Florida, USA. We used dynamic occupancy models to determine factors associated with marsh rabbit occurrence, colonization, extinction, and the co‐occurrence of marsh rabbits and cats during a period of predator removal. Rabbit occurrence was positively related to freshwater habitat and patch size, but was negatively related to the number of individual cats detected at each site. Furthermore, marsh rabbit colonization was negatively associated with relative increases in the number of individual cats at each site between survey years. Cat occurrence was negatively associated with increasing distance from human developments. The probability of cat site extinction was positively related to a 2‐year trapping effort, indicating that predator removal reduced the cat population. Dynamic co‐occurrence models suggested that cats and marsh rabbits co‐occur less frequently than expected under random conditions, whereas co‐detections were site and survey‐specific. Rabbit site extinction and colonization were not strongly conditional on cat presence, but corresponded with a negative association. Our results suggest that while rabbits can colonize and persist at sites where cats occur, it is the number of individual cats at a site that more strongly influences rabbit occupancy and colonization. These findings indicate that continued predator management would likely benefit endangered small mammals as they recolonize restored habitats.

Florida

Increasing artificial light at night enhances salmonid predator foraging efficiency in an urbanized lake

Artificial light at night (ALAN) poses a threat to ecosystems globally. It includes both direct and indirect light, or skyglow, which occurs when ALAN scatters in the atmosphere, extending beyond its original source. We analyzed ALAN trends in Lake Washington, WA, from 2014 to 2023 using Visible Infrared Imaging Radiometer Suite (VIIRS) nighttime light measurements, evaluated the relationship between in situ and satellite measurements, and modeled predator search volumes for a juvenile salmon predator, cutthroat trout ( Oncorhynchus clarki ), as a function of ambient light and turbidity conditions. Open water regions experienced significant increases in ALAN, while nearshore areas primarily showed no or negative trends, revealing the role of skyglow in shaping open water light environments. Using a visual foraging model for cutthroat trout, we found that juvenile salmon at the shallow southern pelagic site experienced light 28 times brighter, resulting in a 168% greater predation vulnerability than those at the northern site. In the Ship Canal, a narrow corridor for outmigrating salmon, predator search volumes were 249% higher than at the southern site. These contrasts in predation vulnerability demonstrate how local conditions influence predator–prey dynamics and provide critical insight for targeting mitigation of both nearshore and distant light sources.

Washington

Sea otter predator avoidance behavior

Predators directly affect their prey as a source of mortality, and prey respond by employing antipredator strategies. Sea otters are a keystone predator within the nearshore community, but higher trophic level avian, terrestrial, and pelagic predators (e.g., bald eagles, brown bears, wolves, white sharks, and killer whales) prey on them. Three antipredator strategies used by sea otters are vigilance (group or sentinel detection of danger), avoidance (seeking a location that is inaccessible to predators), and crypsis (the ability to avoid observation or detection). Vigilant behavior allowed sea otters to escape total extinction during the Maritime Fur Trade of the eighteenth and nineteenth centuries. Female otters with pups practice vigilance when they reduce their foraging time and move along meandering paths. Sea otters usually rest at sea, and when they rest on shore, they usually haul out on offshore rocks, reefs, and small islands—possibly a behavioral response to terrestrial predators (brown bears and wolves can kill non-vigilant sea otters on shore). In areas where many sea otters haul out together, group vigilance may be important in detecting an approaching threat. Along the coast of central California, white sharks are a significant source of sea otter mortality, and the only antipredator strategy is avoidance or crypsis by resting in kelp beds. Despite the threat, sea otters still forage in open water, so the perception of risk may be low. In the western Aleutian Islands, killer whale predation is believed to be the cause of a > 90% decline in sea otters. As a result, sea otters perceive killer whales as a threat and limit their movements to shallow, complex habitats where the risk of attack is low. This behavioral response is so strong in the western Aleutian Islands that it may it limit sea otter dispersal among islands, with implications for the connectivity and genetic health of the small, isolated populations that remain.

Book chapter

Nest predation research: Recent findings and future perspectives

Nest predation is a key source of selection for birds that has attracted increasing attention from ornithologists. The inclusion of new concepts applicable to nest predation that stem from social information, eavesdropping or physiology has expanded our knowledge considerably. Recent methodological advancements now allow focus on all three players within nest predation interactions: adults, offspring and predators. Indeed, the study of nest predation now forms a vital part of avian research in several fields, including animal behaviour, population ecology, evolution and conservation biology. However, within nest predation research there are important aspects that require further development, such as the comparison between ecological and evolutionary antipredator responses, and the role of anthropogenic change. We hope this review of recent findings and the presentation of new research avenues will encourage researchers to study this important and interesting selective pressure, and ultimately will help us to better understand the biology of birds.

Journal of Ornithology

Habituation of adult sea lamprey repeatedly exposed to damage-released alarm and predator cues

Predation is an unforgiving selective pressure affecting the life history, morphology and behaviour of prey organisms. Selection should favour organisms that have the ability to correctly assess the information content of alarm cues. This study investigated whether adult sea lamprey Petromyzon marinus habituate to conspecific damage-released alarm cues (fresh and decayed sea lamprey extract), a heterospecific damage-released alarm cue (white sucker Catostomus commersonii extract), predator cues (Northern water snake Nerodia sipedon washing, human saliva and 2-phenylethylamine hydrochloride (PEA HCl)) and a conspecific damage-released alarm cue and predator cue combination (fresh sea lamprey extract and human saliva) after they were pre-exposed 4 times or 8 times, respectively, to a given stimulus the previous night. Consistent with our prediction, adult sea lamprey maintained an avoidance response to conspecific damage-released alarm cues (fresh and decayed sea lamprey extract), a predator cue presented at high relative concentration (PEA HCl) and a conspecific damage-released alarm cue and predator cue combination (fresh sea lamprey extract plus human saliva), irrespective of previous exposure level. As expected, adult sea lamprey habituated to a sympatric heterospecific damage-released alarm cue (white sucker extract) and a predator cue presented at lower relative concentration (human saliva). Adult sea lamprey did not show any avoidance of the Northern water snake washing and the Amazon sailfin catfish extract (heterospecific control). This study suggests that conspecific damage-released alarm cues and PEA HCl present the best options as natural repellents in an integrated management program aimed at controlling the abundance of sea lamprey in the Laurentian Great Lakes.

Environmental Biology of Fishes

Impact of smallmouth bass predation on subyearling fall Chinook salmon over a broad river continuum

Smallmouth bass ( Micropterus dolomieu ) predation on subyearling fall Chinook salmon ( Oncorhynchus tshawytscha ) was examined in the Snake River (USA) to identify seasonal and habitat-related changes in bass diets, and associated subyearling consumption and loss in various riverine and impounded reaches. Smallmouth bass diets reflected opportunistic foraging that at times showed predation on subyearlings is influenced by the consumption of other prey such as crayfish, sand roller ( Percopsis transmontana ), and smaller invertebrates. Estimated loss of subyearlings was influenced by bass abundance and consumption rates. The highest bass abundances (> 1,000 bass/river kilometer) were observed in the upper reach of Hells Canyon early in April and May, and in Lower Granite Reservoir. Peak consumption rates of subyearlings (≥ 0.12 subyearlings/bass/day) occurred in the upper reach of Hells Canyon during May and in most reservoir reaches in June. Predation losses accumulated evenly along the river continuum from riverine to reservoir habitats. We estimated that 869,371 subyearlings could be lost to smallmouth bass predation between riverine production areas and Lower Granite Dam in a given year. To provide a context for this estimated loss, we provide an illustration of its potential effect on the adult population. Assuming no juvenile mortality occurred downstream of the dam and depending on smolt-to-adult return rates, this represented up to 3.9–16.0% of the potential adult run that could have returned to Lower Granite Dam had no subyearling predation by smallmouth bass occurred upstream of the dam. Although this study was limited by a number of assumptions and constraints, it does provide an illustration of how predation affects juvenile and adult salmon loss over a broad, changing river landscape.

Idaho, Oregon, Washington

When introduced prey violates trophic hierarchy: Conservation of an endangered predator

Introduced species often disrupt established food webs, but some native predators can come to rely on introduced prey. Understanding the net effects of the non-natives on imperiled predators is crucial for planning conservation measures. The invasive American bullfrog ( Lithobates catesbeianus ) can be prey, predator, and competitor for the critically endangered San Francisco garter snake ( Thamnophis sirtalis tetrataenia ). We examined the seasonal prey use of a San Francisco garter snake population that co-occurs with American bullfrogs to examine intraguild predation between these species. Juvenile and adult snakes mainly consumed native anurans instead of American bullfrogs, and this diet pattern peaked in spring, a critical foraging period for the snakes. In spring, large adult American bullfrogs also foraged heavily on native anurans and displayed a high degree of diet overlap with San Francisco garter snakes. Invasive American bullfrogs are detrimental to San Francisco garter snakes mainly through seasonal competition rather than reciprocal predation. Removal of invasive species provided further evidence that eliminating American bullfrogs can benefit San Francisco garter snakes by reducing predation pressure on their shared amphibian prey. Better understanding the interactions of invasive species with native species of conservation concern informs management practices and improves conservation outcomes.

Biological Conservation

Investigating apparent misalignment of predator-prey dynamics: Great Lakes lake trout and sea lampreys

Interpreting ecological dynamics is challenging when observed patterns are not aligned with presumed models. Investigating possible sources of uncertainty is critical to understand the underlying system and ultimately inform management decisions. In this study, we used simulation to investigate the hypothesis that observed inconsistencies in Great Lakes lake trout ( Salvelinus namaycush ) and sea lamprey ( Petromyzon marinus ) predator-prey dynamics were caused by measurement error in the abundance and predation metrics. When lake trout abundances increase and sea lamprey abundances decrease, predation rates are expected to decline (and vice versa). Occasionally predation rates do not change as expected, leading to an inconsistency in expected predator-prey dynamics. We used a Type II functional response model to align lake trout relative abundance, adult sea lamprey abundance, and sea lamprey marking rates of lake trout in each Great Lake. Then we added measurement error to each of the simulated metrics to see how it contributed to observed inconsistencies in the marking rates. The simulated inconsistency rate was far less than the observed inconsistency rate in Lakes Superior and Erie, indicating that measurement error was not primarily responsible for the misalignment of metrics, contrary to our hypothesis. Rather than ignoring these inconsistencies as unfortunate consequences of imperfect assessments, we recommend that future inconsistencies be scrutinized for possible mechanistic explanations. We suspect that predator-prey dynamics are being influenced by spatially structured within-lake components and the presence of alternative hosts, neither of which were accounted for in the functional response model we used.

Great Lakes

Dynamics of prey moving through a predator field: a model of migrating juvenile salmon

The migration of a patch of prey through a field of relatively stationary predators is a situation that occurs frequently in nature. Making quantitative predictions concerning such phenomena may be difficult, however, because factors such as the number of the prey in the patch, the spatial length and velocity of the patch, and the feeding rate and satiation of the predators all interact in a complex way. However, such problems are of great practical importance in many management situations; e.g., calculating the mortality of juvenile salmon (smolts) swimming down a river or reservoir containing many predators. Salmon smolts often move downstream in patches short compared with the length of the reservoir. To take into account the spatial dependence of the interaction, we used a spatially-explicit, individual-based modeling approach. We found that the mortality of prey depends strongly on the number of prey in the patch, the downstream velocity of prey in the patch, and the dispersion or spread of the patch in size through time. Some counterintuitive phenomena are predicted, such as predators downstrean capturing more prey per predator than those upstream, even though the number of prey may be greatly depleted by the time the prey patch reaches the downstream predators. Individual-based models may be necessary for complex spatial situations, such as salmonid migration, where processes such as schooling occur at fine scales and affect system predictions. We compare some results to predictions from other salmonid models. (C) 2000 Elsevier Science Inc.

Mathematical Biosciences

Predation of freshwater fish in environments with elevated carbon dioxide

Carbon dioxide (CO 2 ) in fresh-water environments is poorly understood, yet in marine environments CO 2 can affect fish behaviour, including predator–prey relationships. To examine changes in predator success in elevated CO 2 , we experimented with predatory Micropterus salmoides and Pimephales promelas prey. We used a two-factor fully crossed experimental design; one factor was 4-day (acclimation) CO 2 concentration and the second factor CO 2 concentration during 20-min predation experiments. Both factors had three treatment levels, including ambient partial pressure of CO 2 ( p CO 2 ; 0–1000 μatm), low p CO 2 (4000–5000 μatm) and high p CO 2 (8000–10 000 μatm). Micropterus salmoides was exposed to both factors, whereas P. promelas was not exposed to the acclimation factor. In total, 83 of the 96 P. promelas were consumed ( n = 96 trials) and we saw no discernible effect of CO 2 on predator success or time to predation. Failed strikes and time between failed strikes were too infrequent to model. Compared with marine systems, our findings are unique in that we not only saw no changes in prey capture success with increasing CO 2 , but we also used CO 2 treatments that were substantially higher than those in past experiments. Our work demonstrated a pronounced resiliency of freshwater predators to elevated CO 2 exposure, and a starting point for future work in this area.

Marine and Freshwater Research

Nest predation risk explains variation in avian clutch size

Questions about the ecological drivers of, and mechanistic constraints on, productivity have driven research on life-history evolution for decades. Resource availability and offspring mortality are considered among the 2 most important influences on the number of offspring per reproductive attempt. We used a factorial experimental design to manipulate food abundance and perceived offspring predation risk in a wild avian population (red-faced warblers; Cardellina rubrifrons ) to identify the mechanistic cause of variation in avian clutch size. Additionally, we tested whether female quality helped explain the extant variation in clutch size. We found no support for the Food Limitation or Female Quality Hypotheses, but we did find support for both predictions of the Nest Predation Risk Hypothesis. Females that experienced an experimentally heightened perception of offspring predation risk responded by laying a smaller clutch than females in the control group. Additionally, predation rates at artificial nests were highest where red-faced warbler clutch size was smallest (at high elevations). Life-history theory predicts that an individual should invest less in reproduction when high nest predation risk reduces the likely benefit from that nesting attempt and, indeed, we found that birds exhibit phenotypic plasticity in clutch size by laying fewer eggs in response to increasing nest predation risk.

Behavioral Ecology

Using the risk-disturbance hypothesis to assess the relative effects of human disturbance and predation risk on foraging American Oystercatchers

The risk-disturbance hypothesis asserts that animals perceive human disturbance similar to nonlethal predation stimuli, and exhibit comparable responses in the form of optimization tradeoffs. However, few studies have examined how natural predation risk factors interact with human-disturbance stimuli to elicit such responses. We observed American Oystercatcher ( Haematopus palliatus ) vigilance behavior from September–December 2002 on the Cape Romain National Wildlife Refuge, South Carolina. A set of models was constructed based on 340 focal-animal samples and models revealed relationships between vigilance behavior, predator density, and boat activity. Oystercatchers increased vigilance in response to aerial predators, particularly late in the season when predator species composition was dominated by Northern Harriers ( Circus cyaneus ). At a broader temporal scale, oystercatchers exhibited the highest vigilance rates during simultaneous peaks in boating disturbance and Osprey ( Pandion haliaetus ) activity. Due to this temporal overlap of stimuli, it is difficult to interpret what may have been driving the observed increased in vigilance. Foraging rates appeared to be primarily driven by habitat and tidal stage indicating that time lost to vigilance did not effectively reduce intake. Taken together, these findings provide some support for the risk-disturbance hypothesis, underscore the sensitivity of disturbance studies to temporal scale, and draw attention to the potential confounding effects of natural predation risk.

South Carolina

Risk of predation on offspring reduces parental provisioning, but not flight performance or survival across early life stages

Developmental responses can help young animals reduce predation risk but can also yield costs to performance and survival in subsequent life stages with major implications for lifetime fitness. Compensatory mechanisms may evolve to offset such costs, but evidence from natural systems is largely lacking. In songbirds, increased nest predation risk should favour reduced provisioning, but also young that fledge (leave their nest) at an earlier age. Both responses can result in fledglings with shorter wings, reduced mobility and decreased survival. Young may compensate for shorter wings developmentally by reallocating resources towards feather development or behaviourally by adjusting flight kinematics or habitat use. However, underfed young may lack the capacity to express these phenotypes due to insufficient resources or an inability to adjust allocation of resources. Using predation risk experiments and 29 years of observational field data, we test whether increased nest predation risk reduces flight performance and survival during the fledgling stage and explore potential mechanisms that might underlie these effects. We show that young from high-risk nests did not leave the nest earlier on average, but wing growth was slower likely due to observed reductions in parental feeding rates. Wings were shorter in high-risk nests when fledglings left the nest early. Yet, fledglings from high-risk nests showed improved flight performance for a given wing length such that flight performance at fledging did not differ between young from high-risk and low-risk nests. Young from high-risk nests may have offset the costs of shorter wings on flight performance by accelerating the emergence of flight feathers from their sheaths to reduce wing porosity, though evidence for this mechanism was mixed. Fledglings from high-risk nests also selected habitat with denser woody vegetation compared with young from low-risk nests. Together, these developmental and behavioural responses seem to mitigate the expected effects of increased nest predation risk on fledgling survival. Ultimately, our results show that offspring predation risk can affect parental provisioning and offspring morphology without major implications for performance and survival in subsequent life stages.

Arizona

Trade-offs of predation and foraging explain sexual segregation in African buffalo

1. Many studies have investigated why males and females segregate spatially in sexually dimorphic species. These studies have focused primarily on temperate zone ungulates in areas lacking intact predator communities, and few have directly assessed predation rates in different social environments. 2. Data on the movement, social affiliation, mortality and foraging of radio-collared African buffalo (Syncerus caffer) were collected from 2001-06 in the Kruger National Park, South Africa. 3. The vast majority of mortality events were due to lion (Panthera leo) predation, and the mortality hazard associated with being an adult male buffalo in a male-only 'bachelor' group was almost four times higher than for adult females in mixed herds. The mortality rates of adult males and females within mixed herds were not statistically different. Mortality sites of male and female buffalo were in areas of low visibility similar to those used by bachelor groups, while mixed herds tended to use more open habitats. 4. Males in bachelor groups ate similar or higher quality food (as indexed by percentage faecal nitrogen), and moved almost a third less distance per day compared with mixed herds. As a result, males in bachelor groups gained more body condition than did males in breeding herds. 5. Recent comparative analyses suggest the activity-budget hypothesis as a common underlying cause of social segregation. However, our intensive study, in an area with an intact predator community showed that male and female buffalo segregated by habitat and supported the predation-risk hypothesis. Male African buffalo appear to trade increased predation risk for additional energy gains in bachelor groups, which presumably leads to increased reproductive success. ?? 2008 The Authors.

Journal of Animal Ecology

A multispecies statistical age-structured model to assess predator-prey balance: application to an intensively managed Lake Michigan pelagic fish community

Using a Bayesian model fitting approach, we developed a multispecies statistical catch-at-age model to assess trade-offs between predatory demands and prey productivities, focusing on the Lake Michigan pelagic fish community. We assessed these trade-offs in terms of predation mortalities and productivities of alewife (Alosa pseudoharengus) and rainbow smelt (Osmerus mordax) and functional responses of salmonines. Our predation mortality estimates suggest that salmonine consumption has been a major driver of historical fluctuations in prey abundance, with sharp declines in alewife abundance in the 1980s and 2000s coinciding with estimated increases in predation mortalities. While Chinook salmon (Oncorhynchus tshawytscha) were food limited during periods of low alewife abundance, other salmonines appeared to maintain a (near) maximum per-predator consumption across all observed prey densities, suggesting that feedback mechanisms are unlikely to help maintain a balance between predator consumption and prey productivity in Lake Michigan. This study demonstrates that a multispecies modeling approach that combines stock assessment methods with explicit consideration of predator–prey interactions could provide the basis for tactical decision-making from a broader ecosystem perspective.

Lake Michigan

Climate-induced trends in predator–prey synchrony differ across life-history stages of an anadromous salmonid

Differential climate-induced shifts in phenology can create mismatches between predators and prey, but few studies have examined predator–prey mismatch across multiple life-history stages. We used long-term data from a warming stream with shifting salmonid migration timings to quantify intra-annual migration synchrony between predatory Dolly Varden ( Salvelinus malma ) and Pacific salmon prey and examined how predator–prey synchrony has been influenced by climate change. We demonstrate that Dolly Varden have become increasingly mismatched with spring downstream migrations of abundant pink salmon ( Oncorhynchus gorbuscha ) juveniles. However, Dolly Varden have remained matched with fall upstream migrations of spawning Pacific salmon, including coho ( Oncorhynchus kisutch ), sockeye ( Oncorhynchus nerka ), and pink salmon. Downstream predator–prey migration synchrony decreased over time and with higher temperatures, particularly with pink salmon. In contrast, upstream migration synchrony was temporally stable and increased with rising temperatures. Differing trends in Dolly Varden predator–prey synchrony may be explained by the direct use of salmon to cue upstream migration, but not downstream migration. Overall, we show that climate change can have differing impacts on predator–prey synchrony across life-history stages.

Alaska

Effect of suspended sediment on vulnerability of young razorback suckers to predation

The decline of native fishes in North America is principally a result of altered habitats, and the impact of mainstream dams has accounted for many of the habitat changes. Diminished turbidity, and introduced nonnative predators were investigated as possible reasons for the decline of endangered razorback suckers Xyrauchen texanus in the Colorado River. In laboratory tests, young razorback suckers selected clear water over two water samples with higher concentrations of suspended sediment. In clear water, however, young razorback suckers were extremely susceptible to predation; native Colorado squawfish Ptychocheilus lucius consumed 90% of test razorback suckers, and nonnative green sunfish Lepomis cyanellus consumed 99.6%. As turbidity increased, razorback sucker predator avoidance improved and differences in predator success disappeared. Winter–spring spawning by razorback suckers in Lake Mohave, along with the extreme susceptibility of larvae to predation in clear water, may account for total recruitment failure in that lake. However, in upper basin rivers, suspended sediments remain high enough to limit predation by fishes tested, suggesting that other impacts, including contaminants and lack of floodplain habitat, may be thwarting recruitment in those rivers.

Transactions of the American Fisheries Society

Influence of thiamine deficiency on Lake Trout larval growth, foraging, and predator avoidance

Diet‐related thiamine deficiency increases the acute mortality, known as early mortality syndrome, of salmonines from some of the Great Lakes. The consequences of thiamine deficiency as measured at the egg stage for other important early life stage processes like growth, foraging efficiency, and predator avoidance that may also result in mortality, are unknown. Accordingly, we investigated the impacts of low thiamine on the specific growth rate (SGR) of first‐feeding fry, the ability of first‐feeding fry to capture Daphnia , fry emergence in the presence of a potential predator (round goby Apollina (formerly Neogobius ) melanostomus ), and predation by slimy sculpin Cottus cognatus . We used a combination of thiamine‐deficient and thiamine‐replete wild stocks of lake trout Salvelinus namaycush for this purpose. From these investigations we developed predictive relationships. Specific growth rate was related to egg thiamine concentration. From the exponential relationship, it was predicted that the threshold egg thiamine concentrations associated with 20% and 50% reductions in SGR are 8.1 and 5.1 nmol/g, respectively. The foraging rate on Daphnia was also related to egg thiamine concentration by an exponential relationship. It was predicted that the threshold concentrations associated with 20% and 50% reductions in this rate are 6.9 and 2.9 nmol/g, respectively. The presence of a round goby significantly reduced emergence success, but the level of goby predation was unrelated to egg thiamine concentration. Sculpin predation was related, although weakly, to the initial egg thiamine concentration. This research found that thiamine deficiency affected growth, foraging, and predator avoidance in lake trout fry. Growth effects resulting from thiamine deficiency may represent the most sensitive means of monitoring the impact of the secondary consequences of thiamine deficiency. Mortality associated with the combined effects of reduced growth and foraging has the potential to seriously impair lake trout recruitment.

Journal of Aquatic Animal Health