Predator Avoidance Strategies Research Articles

Variation in Predator Recognition Across Three Species of Jumping Spiders (Salticidae)

The ability to recognize threats and to respond in a timely and appropriate manner carries significant benefits. Depending on the recognition task, this can be cognitively demanding. The zebra jumping spider (Salticus scenicus) is capable of visually recognizing static predator stimuli and reacts via a robust “freeze and retreat,” a potentially innate response in this species. Here, we extend this finding, asking whether the ability of spiderlings to recognize a static predator and to initiate an escape response is common across juvenile salticids, and if so, whether there is species-specific variation of anti-predator responses. We found that captive-reared spiderlings of three European salticid species from different genera (Heliophanus cf. cupreus, Evarcha arcuata, Marpissa muscosa) were able to robustly recognize and retreat from a stationary predator stimulus. Additionally, we found differences in the reaction times between the species as well as different behavioral repertoires associated with the escape response which may reflect species-specific predator avoidance strategies.

Native fish abundance and habitat selection changes in the presence of nonnative piscivores

AbstractWe compared abundance patterns and developed resource selection models for imperilled native southwestern (USA) fishes in the presence and absence of Black Bass (Micropterus spp.) to evaluate how fishes alter their selection for habitats when sympatric with a nonnative piscivore. We collected data using snorkel surveys and in‐stream habitat sampling in Fossil Creek (AZ), upstream (native fish only) and downstream (native and nonnative fish) of a fish barrier. The abundance of all Roundtail Chub (Gila robusta), small (≤127 mm total length [TL]; vulnerable to predation) Sonora Sucker (Catostomus insignis) and Speckled Dace (Rhinichthys osculus) was significantly reduced, but the abundance of both small and large (>127 mm TL; invulnerable to predation) Desert Sucker (Catostomus clarkii) was similar in sampling reaches with and without Black Bass. When sympatric with Black Bass, small Roundtail Chub increased their selection for riffles by 2.57 times and small Desert Sucker reduce their selection for pools by 6.90 times while also selecting for faster flow velocity and finer substrates in lotic mesohabitats. Large native fishes altered selection least, notwithstanding an increased selection for canopy cover in sampling reaches with Black Bass. Observed shifts in resource selection are consistent with predator avoidance strategies. Our study highlights the behavioural consequences of nonnative piscivores on native fish communities and stresses the importance of maintaining lotic mesohabitats as potential refugia for vulnerable native fishes when nonnative piscivores are present.

Variation of shell ornamentation with latitude and water depth—A case study using living brachiopods

As a potential anti-predatory defensive structure, the shell ornamentation of marine calcifiers is usually used to understand the macro coevolution of the interactions between predators and preys. Marine calcifiers' shell ornamentation complexity is generally believed to vary negatively with latitude and water depth. In this paper, we explored the association between shell ornamentation and latitude/bathymetry using the latest global database of living brachiopods. We found that (1) ~59% of living brachiopods species are characterized by smooth shells and that (2) there is no statistically significant linear trend, either positive or negative, between the ornamentation index and latitudes nor with water depths. Both findings are puzzling for living brachiopods as they are sharply contrasted to the patterns of fossil brachiopods whereby the latter, especially Paleozoic brachiopods, are known to exhibit (1) a much greater ornamentation diversity and (2) (at least for the geological periods that have been studied) a linear latitudinal gradient of ornamentation complexity existed. The reasons why living brachiopods have such a high proportion of smooth or weakly ornamented shells and fail to demonstrate an unequivocal linear latitudinal ornamentation gradient were explored and are linked to a multitude of potential factors rather than uniquely only to the predation pressure. Among these, the most plausible factor seems to be the cryptic (refuge-type) habitats (e.g., deep waters, cold polar regions, and submarine rock caves) that living brachiopods have been adapted to due to their low metabolism, where predation pressure is low, allowing brachiopods to enact the predator avoidance strategy rather than having to manufacture robust shell ornamentation to survive in an otherwise highly engaged predator-prey global marine ecosystem.

Multivariate analysis of biologging data reveals the environmental determinants of diving behaviour in a marine reptile.

Diving behaviour of ‘surfacers' such as sea snakes, cetaceans and turtles is complex and multi-dimensional, thus may be better captured by multi-sensor biologging data. However, analysing these large multi-faceted datasets remains challenging, though a high priority. We used high-resolution multi-sensor biologging data to provide the first detailed description of the environmental influences on flatback turtle (Natator depressus) diving behaviour, during its foraging life-history stage. We developed an analytical method to investigate seasonal, diel and tidal effects on diving behaviour for 24 adult flatback turtles tagged with biologgers. We extracted 16 dive variables associated with three-dimensional and kinematic characteristics for 4128 dives. K-means and hierarchical cluster analyses failed to identify distinct dive types. Instead, principal component analysis objectively condensed the dive variables, removing collinearity and highlighting the main features of diving behaviour. Generalized additive mixed models of the main principal components identified significant seasonal, diel and tidal effects on flatback turtle diving behaviour. Flatback turtles altered their diving behaviour in response to extreme tidal and water temperature ranges, displaying thermoregulation and predator avoidance strategies while likely optimizing foraging in this challenging environment. This study demonstrates an alternative statistical technique for objectively interpreting diving behaviour from multivariate collinear data derived from biologgers.

Beetle bioluminescence outshines extant aerial predators.

We understand very little about the timing and origins of bioluminescence, particularly as a predator avoidance strategy. Understanding the timing of its origins, however, can help elucidate the evolution of this ecologically important signal. Using fireflies, a prevalent bioluminescent group where bioluminescence primarily functions as aposematic and sexual signals, we explore the origins of this signal in the context of their potential predators. Divergence time estimations were performed using genomic-scale datasets providing a robust estimate for the origin of firefly bioluminescence as both a terrestrial and as an aerial signal. Our results recover the origin of terrestrial beetle bioluminescence at 141.17 (122.63-161.17) Ma and firefly aerial bioluminescence at 133.18 (117.86-152.47) Ma using a large dataset focused on Lampyridae; and terrestrial bioluminescence at 148.03 (130.12-166.80) Ma, with the age of aerial bioluminescence at 104.97 (99.00-120.90) Ma using a complementary Elateroidea dataset. These ages pre-date the origins of all known extant aerial predators (i.e. bats and birds) and support much older terrestrial predators (assassin bugs, frogs, ground beetles, lizards, snakes, hunting spiders and harvestmen) as the drivers of terrestrial bioluminescence in beetles. These ages also support the hypothesis that sexual signalling was probably the original function of this signal in aerial fireflies.

Desert bighorn sheep habitat selection, group size, and mountain lion predation risk

AbstractBighorn sheep (Ovis canadensis) evolved for thousands of years in the presence of numerous predators, including mountain lions (Puma concolor). Bighorn sheep have presumably developed predator avoidance strategies; however, the effectiveness of these strategies in reducing risk of mountain lion predation is not well understood. These strategies are of increasing interest because mountain lion predation on bighorn sheep has been identified as a leading cause of mortality in some sheep populations. Therefore, we investigated how mountain lions affect both bighorn sheep habitat selection and risk of mortality in Arizona, USA. We used 2 approaches to investigate the predator‐prey relationship between mountain lions and bighorn sheep. We fit 103 bighorn sheep (81 females and 22 males) with global positioning system radio‐collars in 2 Arizona populations from 2013 to 2017, and used a negative binomial resource selection probability function to evaluate whether bighorn sheep selected for habitat features in accordance with presumed predator avoidance strategies, including terrain ruggedness, slope, topographic position, and horizontal obstruction, in 2 seasons (winter and summer). We then estimated how habitat features such as terrain ruggedness, slope, horizontal obstruction, and group size, influence the risk of mortality due to mountain lion predation using an Andersen‐Gill proportional hazards model. Generally, both sexes selected areas with lower horizontal obstruction and intermediate ruggedness and slope, but selection patterns differed between seasons and sexes. The use of more rugged areas and steeper slopes decreased the risk of mortality due to mountain lion predation, consistent with presumed predator avoidance strategies. Increased group size decreased risk of bighorn sheep mortality due to mountain lion predation but this effect became marginal at approximately 10 individuals/group. We did not identify a relationship between horizontal obstruction and bighorn sheep mortality risk. Our findings can be used in habitat and population management decisions such as the prioritization of habitat restoration sites or selection of translocation sites. In addition, we suggest that augmentation of low‐density bighorn sheep populations may reduce mountain lion predation risk by increasing group size, and that releasing large groups of bighorn sheep in population augmentation and reintroduction efforts may help to reduce mountain lion predation.

DNA barcoding of Austrian snow scorpionflies (Mecoptera, Boreidae) reveals potential cryptic diversity in Boreus westwoodi.

BackgroundSnow scorpionflies (genus Boreus) belong to a family of Mecoptera, Boreidae, that has been vastly neglected by entomological researchers due to their shift in seasonality to the winter months. Their activity during this time is regarded as a strategy for predator avoidance and regular sightings on snow fields suggest that this also facilitates dispersal. However, many aspects about snow scorpionflies, especially systematics, taxonomy, distribution of species, phylogenetics and phylogeography have remained fairly unexplored until today. In this study, we fill some of these gaps by generating a reference DNA barcode database for Austrian snow scorpionflies in the frame of the Austrian Barcode of Life initiative and by characterising morphological diversity in the study region.MethodsInitial species assignment of all 67 specimens was based on male morphological characters previously reported to differ between Boreus species and, for females, the shape of the ovipositor. DNA barcoding of the mitochondrial cytochrome c oxidase subunit 1 (COI) gene was carried out for all 67 samples and served as a basis for BIN assignment, genetic distance calculations, as well as alternative species delimitation analyses (ABGD, GMYC, bGMYC, bPTP) and a statistical parsimony network to infer phylogenetic relationships among individual samples/sampling sites.ResultsMorphological investigations suggested the presence of both Boreus hyemalis and Boreus westwoodi in Austria. DNA barcoding also separated the two species, but resulted in several divergent clades, the paraphyly of B. westwoodi in Austria, and high levels of phylogeographic structure on a small geographic scale. Even though the different molecular species delimitation methods disagreed on the exact number of species, they unequivocally suggested the presence of more than the traditionally recognized two Boreus species in Austria, thus indicating potential cryptic species within the genus Boreus in general and especially in B. westwoodi.

Assessing the effect of tagging and the vulnerability to predation in tigerfish (Hydrocynus vittatus, Castelnau 1861) in a water-stressed system using telemetry methods

Increase in anthropogenic pressures on freshwater ecosystems, globally and locally in South Africa, has made it difficult to meet environmental flow requirements and maintain these systems. The Letaba-Olifants catchment is one such example, where the upstream water demands place pressure on the river downstream as it flows through the Kruger National Park. We used the activity rates of Hydrocynus vittatus as a line of evidence to assess (1) the effects of telemeter tagging on their activity rates in three potential post-tagging recovery periods and (2) their vulnerability to predation and the causality related to the environmental stressors placed on the river catchment in the Olifants River Gorge, Kruger National Park, South Africa. We determined H. vittatus activity rates as locomotive movement using radio telemetry methods linked remotely to an online data management system. We telemeter tagged nine individuals from 08 May to 28 June 2018. However, only seven fish were successfully tracked for the duration of our study, and two individuals moved out of range of the remote network shortly after release and could not be located. The tagged H. vittatus individuals were found to have reduced activity at least within the first 7 days after tagging compared with the time after that. The results showed that three individuals were preyed on by predators after the tagging procedure recovery period. This coincided with abnormal low flow conditions, where the Letaba River ran dry. African fish eagles Haliaeestus vocifer were the only confirmed predator, whilst predation by other species was also evident.Conservation implications: Monitoring of H. vittatus using telemetry is a viable tool to use when assessing environmental stressors in remote locations. The abnormally low water levels in the Olifants and Letaba Rivers (cessation of flow in the Letaba River) during our study may have compromised the predator avoidance strategies of tagged H. vittatus and may further be affecting the viability of the H. vittatus populations in Kruger National Park. The synergistic effects of natural and anthropogenic stressors impact negatively H. vittatus populations and potentially other aquatic biotas.

Comparing the Individual and Combined Effects of Ant Attendance and Wing Formation on Aphid Body Size and Reproduction

AbstractSpecies employ multiple strategies to deal with stressful environments, but these strategies often incur costs. Aphids frequently utilize multiple predator avoidance strategies, including attracting mutualist ants for protection and dispersing by producing winged forms. While both strategies can be physiologically costly, the magnitudes of these costs have not been previously compared. In this study, we experimentally manipulated ant attendance in the field and measured the individual and interactive effects of ant attendance and wing formation on body size and reproduction of the ant-tended aphid Cinara schwarzii (Wilson) (Hemiptera: Aphididae). Aphid adult body size was smaller in the presence of ants (18%), but controlling for body size, there were no differences in embryo number or size. In contrast, wing formation did not affect adult body size but strongly reduced embryo number (46%) and size (8%). Although ant attendance reduced C. schwarzii wing formation, ant attendance and wing formation acted independently on aphid body size and reproduction. For comparison, we confirmed that the manipulation of ant presence had no effect on body size or reproduction of the untended co-existing congener Cinara solitaria (Gillette and Palmer) (Hemiptera: Aphididae). Complementing our empirical study, a meta-analysis of 78 responses from 24 publications showed that wing formation consistently and significantly reduces aphid body size and reproduction (37%), while the effects of ant attendance showed a mean positive effect (9%) that did not significantly differ from zero. Together, our empirical study and meta-analysis provide strong evidence for costs of wing formation but not ant attendance for aphids.

Resource‐use, body condition and parasite load metrics indicate contrasting health of stocked and native game fishes in Canadian prairie lakes

AbstractThis study evaluated the status of native and stocked fish species in 13 prairie lakes in central Canada over eight years (2007–14) using three metrics: resource‐use (benthic versus pelagic carbon via stable isotopes); body condition (relative weight index Wr); and parasite load (cestode gut enumerations). Analyses included game and non‐game fishes, like naturally occurring northern pike, Esox lucius L., and yellow perch, Perca flavescens Mitchill, but focused on stocked walleye, Sander vitreus (Mitchill) because it supports a robust recreational fishery. Walleye and northern pike were significantly more reliant on benthic carbon than yellow perch or forage fishes (p < 0.05), but this reliance was not associated with any measured environmental variables for any species. In lakes with game fishes, forage fishes exhibited higher reliance on benthic energy, possibly due to predator avoidance strategy, particularly yellow perch. Walleye body condition index was consistently lower (<95–105) than values exhibited by the other two game fishes (81–139), and parasites were only common in walleye and associated with lake‐water salinity (r2 = 0.93, p < 0.05) and sex (p < 0.05). Based on the results, the most desirable game fish, walleye, appears less resilient to environmental variability than northern pike and yellow perch, making this species more susceptible to impacts of future climate change.

Connectivity of Large-Bodied Fish with a Recovering Estuarine Tidal Marsh, Revealed Using an Imaging Sonar

Tidal wetlands represent important fish habitats, particularly as nurseries for many exploited species. However, usage of these habitats by large-bodied fish is poorly studied. Imaging sonar represents a relatively novel technology for ecologists and allows for the discrete observation of fish in conditions where a light-based camera is ineffective, such as turbid estuarine habitats. An imaging sonar uses sound waves to create video-like images where swimming direction, fish length and distance from the sonar can be inferred. This technology was applied to examine connectivity of large-bodied fish between a recovering Ramsar-listed wetland and the adjacent estuary, by censusing fish traversing the entrance to the wetland. Fish lengths ranged between ~ 8 and 109 cm. More fish were observed traversing the entrance to the wetland during the day (~ 365 fish h−1) compared with night (~ 198 fish h−1), possibly as a predator avoidance strategy. Under some conditions, biomass flux of large-bodied fish was estimated to exceed 100 kg fish h−1. Fish did not appear to have a consistent preference for moving with or against the flow of the tide. These novel findings highlight the utility of imaging sonar for conducting fish census in wetland habitats and also highlights that wetlands are valuable habitats for large-bodied fish.

Comparison of survival, growth and burying behavior of cultured and wild sandfish (Holothuria scabra) juveniles: Implications for ocean mariculture

The success of mariculture activities involving the release of cultured marine invertebrates into the ocean is contingent on high survival and appropriate growth rates. Physical, physiological or behavioral characteristics that differ from those of wild conspecifics may be acquired through hatchery rearing, or as a result of stress induced by the release process. Such differences may compromise the ‘fitness’ of cultured animals. We investigated the influence of hatchery rearing and transport/handling stress on a commercial sea cucumber, sandfish (Holothuria scabra), by comparing survival, growth and behavior of release-size (5–15 g) cultured juveniles to those of like-size wild conspecifics. At the conclusion of an 85-day growth experiment in natural habitat, there was no significant difference in weight between cultured and wild sandfish juveniles. Burying behavior of cultured and wild sandfish juveniles was observed over a 48-h period in natural habitat with or without seagrass. A generalized additive model showed that cultured juveniles were slower to bury in the substrate after release, less likely to be buried at most times, and more likely to be buried in substrate where seagrass was present. However, they became better synchronized with their wild counterparts after 30 h. Survival of cultured and wild sandfish was high in both experiments (>85%), but reduced burying by cultured individuals may increase the potential for predation because diel burying is the main predator avoidance strategy of sandfish juveniles.

Parental effects influence life history traits and covary with an environmental cline in common frog populations

Across latitudinal clines, the juvenile developmental rates of ectotherms often covary with the length of the growing season, due to life-history trade-offs imposed by the time-constrained environments. However, as the start of the growing season often varies substantially across years, adaptive parental effects on juvenile developmental rates may mediate the costs of a delayed season. By employing a meta-analysis, we tested whether larval developmental rates across a latitudinal cline of the common frog (Rana temporaria) are affected by fluctuating onsets of breeding, across years. We predicted that larval developmental rate will be inversely related to the onset of breeding, and that northern populations will be more prone to shorten their developmental rate in response to late breeding, as the costs of delayed metamorphosis should be highest in areas with a shorter growing season. We found that the larval period of both northern and southern populations responded to parental environmental conditions to a similar degree in absolute terms, but in different directions. In northern populations, a late season start correlated with decreased development time, suggesting that the evolution of parental effects aids population persistence in time-constrained environments. In southern populations, late season start correlated with increased development time, which could potentially be explained as a predator avoidance strategy. Our findings suggest that local ecological variables can induce adaptive parental effects, but responses are complex, and likely trade-off with other ecological factors.

Temporal patterns of waterhole use as a predator avoidance strategy

Abstract Animals that depend on water sources in dry environments must balance their water demands with predation risk. In settings of water scarcity, predators may strategically exploit prey’s dependence on water; prey may adjust their use of water sources either spatially or temporally to avoid overlapping with predators. To examine the spatiotemporal dynamics of predators and prey at water sources, we studied the use of semipermanent waterholes in the dry season by red-fronted lemurs (Eulemur rufifrons), a primate species that exhibits flexible circadian activity patterns and inhabits a dry deciduous forest in western Madagascar. We hypothesized that lemurs avoid predators in their spatiotemporal use of waterholes. We analyzed the patterns of camera trap activations at waterholes by red-fronted lemurs and their two main predators: fossa (Cryptoprocta ferox) and Madagascar harrier hawks (Polyboroides radiatus). We found that red-fronted lemurs were unlikely to use waterholes at times of day when predators were commonly present, and that the distributions of times of waterhole use differed between red-fronted lemurs and each of their predator species. Red-fronted lemurs frequently used waterholes that were also used by predators within the same week in part because the predators used a variable set of water resources. In this system, predators did not appear to exploit waterholes for the high density of red-fronted lemurs attracted to them, but instead likely used waterholes primarily to meet their own water demands. Our findings suggest that when predators and prey share water sources, prey may adjust their behavior to reduce their risk of overlap with predators, including through avoidance of indirect cues of predation, such as waterholes at particular times of day.

Convergent evolution of tail spines in squamate reptiles driven by microhabitat use

The repeated evolution of convergent or analogous traits is often used as evidence for adaptive evolution. Squamate reptiles show a high degree of convergence in a variety of morphological traits; however, the evolutionary mechanisms driving these patterns are not fully understood. Here, we investigate the evolution of tail spines, a trait that evolved multiple times in evolutionarily independent clades of lizards. Taking a comparative phylogenetic approach, we use 2877 squamate species to demonstrate that the evolution of spiny tails is correlated with microhabitat use, with species that live in rocky habitats significantly more likely to have evolved spiny tails. In the light of previous behavioural observations, our results suggest that spiny-tailed lizards have an advantage in rocky habitats through predation avoidance, where tail spines are used to prevent extraction from rocky crevices. In concordance with previous research on lizard body armour, our results suggest that the evolution of tail spines is coupled to both a rock-dwelling lifestyle and predator avoidance strategies, and highlight a complex interplay between different selective pressures on the evolution of defensive morphologies in reptiles.

Habitat and space use of wintering Sprague's Pipits (Anthus spragueii) in northern Mexico

Understanding home range size and habitat preferences is an important component of monitoring species in steep decline. Sprague's Pipit (Anthus spragueii) is a declining grassland specialist with a substantial portion of its population wintering in the highly threatened grasslands of the Chihuahuan Desert. We radio-tagged and tracked 10 wintering pipits between 2014 and 2017 at 3 sites across northern Mexico to generate baseline home range estimates and habitat preferences on their wintering grounds. We found that mean home range and core-use area size with 95% and 50% kernel density estimators were 11.4 ha and 2.4 ha, respectively, almost twice as large as some other grassland specialist passerines. Two birds left the study area and one individual shifted its home range 1.3 km after 20 d of monitoring, indicating that some individuals are flexible in their space use strategies. Within their home ranges, pipits selected grasslands with more bare ground and less “other cover” (litter, duff, animal excrement, and rocks) than what was available on the landscape. We found no relationship at the microhabitat scale between pipits and grass height nor shrub cover and heights, which in previous studies have been shown to influence habitat selection at larger scales. These findings may reflect different habitat use, diet, and predator avoidance strategies than other grassland passerines that select for denser grass cover during winter in the Chihuahuan Desert and highlight the importance of structurally heterogeneous grasslands. For this reason, strategies to manage and conserve Chihuahuan Desert grasslands and its avifauna must consider the diverse habitat and area needs of grassland birds to be effective.

Dietary polyunsaturated fatty acid supply improves Daphnia performance at fluctuating temperatures, simulating diel vertical migration

Abstract Diel vertical migration (DVM) is a common predator avoidance strategy of zooplankton. Migration to deeper water layers during the day to escape visually hunting predators is most likely to require physiological adaptations to periodically changing temperatures. Polyunsaturated fatty acids (PUFA) play crucial roles in membrane temperature acclimation. Exposure to cold temperatures typically results in an increase in the relative abundance of PUFA in cell membranes and PUFA requirements of Daphnia increase with decreasing temperatures. To assess the role of dietary PUFA in coping with temperature fluctuations experienced during DVM, we reared Daphnia magna at either constantly warm or fluctuating temperatures, simulating DVM both with and without dietary PUFA supplementation. We show that the well‐known positive effect of dietary eicosapentaenoic acid supplementation on offspring production and population growth rates of D. magna is more pronounced at alternating temperatures than at constantly warm temperatures. Exposure to alternating temperatures caused modification in body PUFA concentrations and, consequently, increased lipid peroxidation. However, detrimental effects of lipid peroxidation were not evident. Our data demonstrate that the capacity to cope with the distinct temperature fluctuations experienced during DVM increases with dietary eicosapentaenoic acid supplementation, suggesting that an adequate dietary PUFA supply is crucial especially for migrating Daphnia populations. A dietary deficiency in long‐chain PUFA may thus severely constrain predator evasion, potentially resulting in increased mortality and cascading effects on lower trophic levels.

Fine-scale movements of juvenile blacktip reef sharks Carcharhinus melanopterus in a shallow nearshore nursery

Limited information is available on the fine-scale movements and habitat use of juvenile sharks in very shallow (<1 m) nearshore areas and the factors that drive these behaviours. Active acoustic tracking was used to investigate movements and habitat use of juvenile (683 +/- 58 mm total length; mean +/- SD) blacktip reef sharks Carcharhinus melanopterus at Orpheus Island, Australia. Six juveniles were tracked by foot and boat for over 62 h. Juveniles moved in synchrony with tidal cycles, always remaining within very shallow (<1 m) sandy reef flat or reef crest waters during outgoing, low and incoming tides, and using inundated mangrove habitat during higher tides, indicating that tidal fluctuations were a major driver of movement and habitat use. Individuals never left the bay where they were captured or entered deep water beyond the fringing reef, restricting their movements within water <60 cm deep. In general, linearity and rate of movement were significantly higher during incoming or outgoing tides, whereas these measures were significantly lower during higher tide heights when juveniles were occupying mangrove habitats. The observed behaviour was most likely a predator-avoidance strategy, highlighting the importance of mangrove root habitat use by juvenile blacktip reef sharks in coastal nursery areas and indicating that this may be an essential habitat for the young of this species.

Cape fur seals (Arctocephalus pusillus pusillus) adjust traversing behaviour with lunar conditions in the high white shark (Carcharodon carcharias) density waters of Mossel Bay, South Africa

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 622:219-230 (2019) - DOI: https://doi.org/10.3354/meps13051 Cape fur seals (Arctocephalus pusillus pusillus) adjust traversing behaviour with lunar conditions in the high white shark (Carcharodon carcharias) density waters of Mossel Bay, South Africa P. Morse1,*, M. A. Mole2, M. N. Bester2, R. Johnson1, U. Scacco3, E. Gennari1,4,5 1Oceans Research Institute, PO Box 1767, Mossel Bay 6500, South Africa 2Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Private Bag X20, Hatfield 0028, Gauteng, South Africa 3ISPRA-Italian National Institute for Environmental Protection and Research, Via Vitaliano Brancati, 60, 00144 Roma, Italy 4South African Institute for Aquatic Biodiversity (SAIAB), Private Bag 1015, Grahamstown 6140, South Africa 5Department of Ichthyology and Fisheries Science, Rhodes University, PO Box 94, Grahamstown 6140, South Africa *Corresponding author: peter.morse@my.jcu.edu.au ABSTRACT: White sharks Carcharodon carcharias are highly visual predators, leading to the hypothesis that the predation risk for foraging Cape fur seals Arctocephalus pusillus pusillus might differ with ambient light conditions. This study investigated the relationship between environmental fluctuations of ambient light and the traversing behaviour of Cape fur seals in and out of their colony at Mossel Bay, South Africa, to better describe potential predator avoidance strategies. A total of 12 144 traversing events were observed over a 4-yr period and there was an overall trend for Cape fur seals to traverse less often but in relatively larger group sizes during periods when white sharks are suggested to be more active. Specifically, Cape fur seal activity was reduced during winter when white sharks are most actively hunting, and most traversing behaviour occurred at night when Cape fur seals were less likely to be detected by white sharks. However, among nocturnal observations, Cape fur seal group sizes increased significantly with moonlight. Although nocturnal predations of Cape fur seals by white sharks have been observed before in Mossel Bay, this is the first study to indicate Cape fur seals might respond to the increased risk of improved white shark visual acuity during moonlit nights by seeking safety in numbers while foraging. Further investigations are needed to assess the effect of the lunar cycle on white shark nocturnal hunting behaviour, but observations presented here suggest that white sharks may pose a bigger threat to Cape fur seals under the light of a full moon. KEY WORDS: Predator avoidance · Pinniped · Lunar cycle · Safety in numbers · Mobbing · Predator-prey Full text in pdf format PreviousCite this article as: Morse P, Mole MA, Bester MN, Johnson R, Scacco U, Gennari E (2019) Cape fur seals (Arctocephalus pusillus pusillus) adjust traversing behaviour with lunar conditions in the high white shark (Carcharodon carcharias) density waters of Mossel Bay, South Africa. Mar Ecol Prog Ser 622:219-230. https://doi.org/10.3354/meps13051 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 622. Online publication date: July 18, 2019 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2019 Inter-Research.

Nest predator avoidance during habitat selection of a songbird varies with mast peaks and troughs

Predation risk is vital in determining habitat quality. But landscapes of fear are complex and dynamic, such as temperate deciduous forests characterized by intermittent, synchronized production of large seed crops (mast peaks). These “resource pulses” elevate the magnitude of predation risk via direct or indirect effects, possibly altering also predator avoidance strategies of a prey. Yet, how animals manage predation risk via informed habitat selection and how this depends on ecological context remains poorly explored. We studied risk-sensitive settlement behavior of wood warbler Phylloscopus sibilatrix. We tested the hypothesis that warblers flexibly avoid predators (Eurasian jays Garrulus glandarius) during habitat selection but that their interactions are mediated by mast seeding, which is known to elevate the overall nest predation risk for warblers through its cascading effects on population dynamics of rodents and generalist predators. We used a playback experiment to manipulate warblers’ perceived risk of nest predation by jays. We replicated the experiment in two consecutive years, followed by high or low seed crop. In the spring following mast trough, risky jay plots featured low abundance, late settlement, and poor pairing success compared to other treatments. In contrast, no response differences were found in the spring following mast seeding. Our results suggest that the way wood warblers adjust habitat choices to jay predation risk is indirectly mediated by mast seeding. This highlights plasticity in predator avoidance during prey habitat selection in complex and dynamic landscapes of fear, and the potential effects of mast seeding on animal behavior via indirect interactions.Significance statementAvoiding places with high nest predation risk during settlement decisions is believed to be widespread in birds. However, the mechanistic understanding of how birds acquire and use information about ambient nest predation risk to fine-tune settlement decisions is still limited. Using a playback experiment, we show that wood warblers eavesdrop on predator calls and avoid settling at sites with high perceived risk of nest predation by Eurasian jays. However, the way warblers adjust habitat choices to the nest predation risk posed by jays appears to be affected by tree mast seeding. This is potentially due to cascading effects of masting on the population dynamics of rodents and generalist predators, creating temporal peaks of elevated nest predation risk for wood warblers. Our study highlights plasticity in predator avoidance during prey settlement behavior in temporally variable, pulsed-resources ecosystems.