Differences In Predation Risk Research Articles

Altitudinal differences in foraging decisions under predation risk in great tits

Abstract Foraging decisions under risk of predation are crucial for survival as predation risk can contribute to a reduction of food intake over time leading to a trade-off between starvation and predation. Environmental variation can provoke changes in food accessibility or predation risk that will in turn affect foraging decisions. Specifically, less predictable or harsher environments, such as those found at high elevation, should lead to more risk-prone foraging in order to prevent risk of starvation, but empirical confirmation of this hypothesis is lacking. In the current study, we used video playbacks combined with an automatic feeder to measure continuous foraging choices between control and predator videos by wild great tits originating from high and low elevations and tested under controlled conditions. Great tits discriminated between two conditions representing differences in predation risk and visited the feeder less frequently when a predator was shown. Moreover, we found that birds from low elevation populations were more risk-averse and visited the feeder significantly less when a predator video playback was broadcasted compared with high elevation individuals. This elevation-related contrast was also dependent on the season, body mass, and fat reserves of individuals, and was more marked in females. Furthermore, adults visited the feeder less in the presence of a predator compared with yearlings. These results are consistent with predictions from life-history theory and starvation–predation trade-off hypotheses and could have implications for individual movements and population dynamics in changing environments.

Habitat openness and predator abundance determine predation risk of warningly colored longhorn beetles (Cerambycidae) in temperate forest.

Organisms have evolved different defense mechanisms, such as crypsis and mimicry, to avoid detection and recognition by predators. A prominent example is Batesian mimicry, where palatable species mimic unpalatable or toxic ones, such as Clytini (Coleoptera: Cerambycidae) that mimic wasps. However, scientific evidence for the effectiveness of Batesian mimicry in Cerambycids in natural habitats is scarce. We investigated predation of warningly and nonwarningly colored Cerambycids by birds in a temperate forest using beetle dummies. Dummies mimicking Tetropium castaneum, Leptura aethiops, Clytus arietis, and Leptura quadrifasciata were exposed on standing and laying deadwood and monitored predation events by birds over one season. The 20 surveyed plots differed in their structural complexity and canopy openness due to different postdisturbance logging strategies. A total of 88 predation events on warningly colored beetle dummies and 89 predation events on nonwarningly colored beetle dummies did not reveal the difference in predation risk by birds. However, predation risk increased with canopy openness, bird abundance, and exposure time, which peaked in July. This suggests that environmental factors have a higher importance in determining predation risk of warningly and nonwarningly colored Cerambycidae than the actual coloration of the beetles. Our study showed that canopy openness might be important in determining the predation risk of beetles by birds regardless of beetles' warning coloration. Different forest management strategies that often modify canopy openness may thus alter predator-prey interactions.

Digest: More than just a pretty fin: The evolution of sexual ornaments in killifish.

What conditions favor the evolution of elaborate sexual ornaments? In freshwater killifishes, Sowersby etal. found that larger sexual ornaments were negatively associated with locomotive performance. Although selection clearly favored large ornamental fins in environments with fewer predators, there was no clear association between large ornamental fins and differences in life-history strategy. This finding illustrates that habitat differences in predation risk have the potential to influence the evolution of secondary sexual traits such as ornaments through natural selection.

The relative effects of pace of life-history and habitat characteristics on the evolution of sexual ornaments: A comparative assessment.

Selection may favor greater investment into sexual ornaments when opportunities for future reproduction are limited, for example, under high adult mortality. However, predation, a key driver of mortality, typically selects against elaborate sexual ornaments. Here, we examine the evolution of sexual ornaments in killifishes, which have marked contrasts in life-history strategy among species and inhabit environments that differ in accessibility to aquatic predators. We first assessed if the size of sexual ornaments (unpaired fins) influenced swimming performance. Second, we investigated whether the evolution of larger ornamental fins is driven primarily by the pace of life-history (investment into current vs. future reproduction) or habitat type (a proxy for predation risk). We found that larger fins negatively affected swimming performance. Further, males from species inhabiting ephemeral habitats, with lower predation risk, had larger fins and greater sexual dimorphism in fin size, compared to males from more accessible permanent habitats. We show that enlarged ornamental fins, which impair locomotion, evolve more frequently in environments that are less accessible to predators, without clear associations to life-history strategy. Our results provide a rare link between the evolution of sexual ornaments, effects on locomotion performance, and natural selection on ornament size potentially through habitat differences in predation risk.

Morphological divergence, tail loss, and predation risk in urban lizards

Urbanisation changes the structure of natural habitats and alters trophic interactions, pressuring urban species to adjust and adapt. Unlike behavioural shifts that tend to be more flexible, morphological characteristics in vertebrates are less plastic and changes may come at a greater cost. We explored the hypothesis that morphological characteristics in a tropical agamid lizard Psammophilus dorsalis are not only selected to suit altered habitat conditions in urbanised areas but reflect predation risk in urban habitats. In addition, we explored differences in tail loss in both sexes from urban and rural habitats. First, we find that predation risk did not differ between urban and rural habitats, but differed between sexes. Conspicuous courtship-coloured male lizards were more likely to be attacked compared to cryptically-coloured female lizards. Next, we find that P. dorsalis differed in key morphological characteristics, with greater urban-rural differences in males than females. Urban lizards had shorter proximal limb elements, longer 4th digits and greater body mass than rural lizards; and among males, urban lizards had significantly larger head sizes and longer distal limb elements than rural lizards. Finally, we find that the rates of tail loss differed between habitats and sexes, with urban male lizards having greater rates of tail loss than rural males and all females. Inter-sexual difference in tail loss was consistent with the difference in predation risk between sexes, but tail loss differences between urban and rural habitats could not be explained by predation risk. In sum, we find that adaptations to novel urban environments are not exclusively driven by a single promoter (e.g. predation risk) but are influenced by multiple selection pressures with associated fitness costs, such as tail loss.

Testing Whether Camera Presence Influences Habitat Specific Predation Pressure on Artificial Shorebird Nests in the Arctic

When monitoring the breeding ecology of birds, the causes and times of nest failure can be difficult to determine. Cameras placed near nests allow for accurate monitoring of nest fate, but their presence may increase the risk of predation by attracting predators, leading to biased results. The relative influence of cameras on nest predation risk may also depend on habitat because predator numbers or behaviour can change in response to the availability or accessibility of nests. We evaluated the impact of camera presence on the predation rate of artificial nests placed within mesic tundra habitats used by Arctic-breeding shorebirds. We deployed 94 artificial nests, half with cameras and half without, during the shorebird-nesting season of 2015 in the East Bay Migratory Bird Sanctuary, Nunavut. Artificial nests were distributed evenly across sedge meadow and supratidal habitats typically used by nesting shorebirds. We used the Cox proportional hazards model to assess differential nest survival in relation to camera presence, habitat type, placement date, and all potential interactions. Artificial nests with cameras did not experience higher predation risk than those without cameras. Predation risk of artificial nests was related to an interaction between habitat type and placement date. Nests deployed in sedge meadows and in supratidal habitats later in the season were subject to a higher risk of predation than those deployed in supratidal habitats early in the season. These differences in predation risk are likely driven by the foraging behaviour of Arctic fox (Vulpes lagopus), a species that accounted for 81% of observed predation events in this study. Arctic fox prey primarily on Arvicoline prey and goose eggs at this site and take shorebird nests opportunistically, perhaps more often later in the season when their preferred prey becomes scarcer. This study demonstrates that, at this site, cameras used for nest monitoring do not influence predation risk. Evaluating the impact of cameras on predation risk is critical prior to their use, as individual study areas may differ in terms of predator species and behaviour.

Selection of calling sites by Pelophylax porosus porosus (Anura: Ranidae)

In frogs, males generally use calls to attract conspecific females for breeding. Previous studies suggest that male frogs can effectively attract females by calling from an open environment, which has the advantages of avoiding the diminishing of their calls and increasing attractiveness to females by bimodal (acoustic + visual) signal. However, males calling from open sites, would be more easily detected by predators due to their exposed bodies. Male frogs may need to select a calling site that is suitable for environmental conditions to enhance their survival rate and mating success. In the present study, we examined the selection of calling sites by Pelophylax porosus porosus male, whose predators are mostly diurnal. As a results, P. p. porosus males tended to select vegetation-shaded water surfaces as daytime calling sites and select open water surfaces as night calling sites. Our results suggest that choice of calling sites by P. p. porosus males depends on whether it is daytime or night, because of differences in predation risk between daytime and night. The selection of a calling site suitable for each situation is expected to increase the fitness of the male frogs.

Predation risk alters life history strategies in an oceanic copepod.

The ubiquitous oceanic copepod Calanus finmarchicus is the major link between primary producers and important fish stocks in the North Atlantic Ocean and adjacent seas. Despite over a century of research on growth and development of this key species, the effect of predation risk on these processes remains elusive. We tested how food level and chemical cues from a fish predator influence growth and development of C. finmarchicus, using a predator naïve laboratory population. Copepods reached adult stage earlier both in response to high food and to predator cues in our experiment. High food also increased growth and lipid accumulation. In contrast, perceived predation risk triggered reduced size and lipid fullness, indicating a decoupling of growth and development rates. Our results demonstrate that chemical predator cues can influence life history strategies in C. finmarchicus, and suggest that present and future patterns in oceanic zooplankton size and population dynamics may also reflect differences in predation risk.

Environmental conditions as proximate cues of predation risk inducing defensive response in Daphnia pulex

Daphnia pulex from a pond in Northern Italy shows four distinct defensive morphotypes, varying in the number, location and thickness of neckteeth, as the results of phenotypic plasticity. Because the frequency of the morphotypes was not related to the density of Chaoborus flavicans larvae, the main predators of D. pulex, it has been suggested that environmental factors such as long-day photoperiod, temperature or crowding might act as proximate cues for the predation risk. Here, we analysed the morphotypes of newborn D. pulex produced by mothers not exposed to chemical cues (kairomones) released by Chaoborus, but reared under environmental conditions simulating seasonal differences in predation risk. Three experimental treatments, low temperature and short-day photoperiod (16 °C 12:12 L:D), high temperature and long-day photoperiod (20 °C 14:10 L:D), and crowding under high temperature and long-day photoperiod, were compared for three clonal lineages. Almost 70% of neonates produced one or more neckteeth, but the frequencies of different morphotypes varied significantly among clones and treatments, indicating that both abiotic (temperature and photoperiod) and biotic (crowding) environmental factors affected the development of neckteeth. A characteristic S-shaped relationship between percentages of neckteethed and total juveniles per female further suggests an antipredator adaptation to high prey density. Our findings support that environmental conditions serve as proximate cues of predation risk in D. pulex contributing to the phenotypic plasticity of the neckteeth number.

Giraffe diurnal recumbent behavior and habitat utilization in Katavi National Park, Tanzania

AbstractResting behaviors play an important role in animals’ daily activities by minimizing energy consumption. Although this may be equally important to other behavioral states for sustaining life, it has not been well studied in the giraffe (Giraffa camelopardalis). This study characterized the bout duration, frequency, and age–sex class differences in diurnal recumbent behavior of free‐ranging giraffe. Additionally, it is currently unknown whether giraffe utilize shady or safe areas for diurnal recumbency, as many other animals do. Therefore, we also investigated this in the present study. Data were collected in Katavi National Park, Tanzania, during four time periods. The duration of recumbency bouts was calculated from 170 episodes, and the frequency of recumbency was determined by following 24 individuals for more than 10 h each. Habitat type was categorized into wooded grassland or miombo woodland, and habitat preference was analyzed based on 173.6 h of observations. We found no significant difference in the duration of recumbency bouts among the four age‐classes and between sexes in adults. On the other hand, calves (n = 2) rested more frequently than did other age‐groups, possibly due to differences in predation risk or activity budgets. Adult males had a higher frequency of recumbency compared to adult females, possibly because pregnant/nursing females were hindered in adopting this posture. We also found that giraffe primarily utilized the miombo woodland for daytime recumbency, likely because the high tree density reduces heat stress, and its seclusion from the river reduces predation risk.

Stay home, stay safe-Site familiarity reduces predation risk in a large herbivore in two contrasting study sites.

Restricting movements to familiar areas should increase individual fitness as it provides animals with information about the spatial distribution of resources and predation risk. While the benefits of familiarity for locating resources have been reported previously, the potential value of familiarity for predation avoidance has been accorded less attention. It has been suggested that familiarity should be beneficial for anti-predator behaviour when direct cues of predation risk are unclear and do not allow prey to identify well-defined spatial refuges. However, to our knowledge, this hypothesis has yet to be tested. Here, we assessed how site familiarity, measured as the intensity of use of a given location, is associated with the probability of roe deer Capreolus capreolus being killed by two predators with contrasting hunting tactics, the Eurasian lynx Lynx lynx and human hunters. While risk of human hunting was confined to open habitats, risk of lynx predation was more diffuse, with no clear refuge areas. We estimated cause-specific mortality rates in a competing risk framework for 212 GPS-collared roe deer in two ecologically distinct areas of Central Europe to test the hypothesis that the daily risk of being killed by lynx or hunters should be lower in areas of high familiarity. We found strong evidence that site familiarity reduces the risk of being predated by lynx, whereas the evidence that the risk of being hunted is linked to site familiarity was weak. We suggest that local knowledge about small-scale differences in predation risk and information about efficient escape routes affect an individual's ability to avoid or escape an attack by an ambush predator. Our study emphasizes the role of site familiarity in determining the susceptibility of prey to predation. Further research will be required to understand better how a cognitive map of individual spatial information is beneficial for avoiding predation in the arms race that drives the predator-prey shell game.

Anthropogenic Disturbance and Population Viability of Woodland Caribou in Ontario

ABSTRACTOne of the most challenging tasks in wildlife conservation and management is to clarify how spatial variation in land cover due to anthropogenic disturbance influences wildlife demography and long‐term viability. To evaluate this, we compared rates of survival and population growth by woodland caribou (Rangifer tarandus caribou) from 2 study sites in northern Ontario, Canada that differed in the degree of anthropogenic disturbance because of commercial logging and road development, resulting in differences in predation risk due to gray wolves (Canis lupus). We used an individual‐based model for population viability analysis (PVA) that incorporated adaptive patterns of caribou movement in relation to predation risk and food availability to predict stochastic variation in rates of caribou survival. Field estimates of annual survival rates for adult female caribou in the unlogged ( 0.90) and logged ( 0.76) study sites recorded during 2010–2014 did not differ significantly (P > 0.05) from values predicted by the individual‐based PVA model (unlogged: = 0.87; logged: 0.79). Outcomes from the individual‐based PVA model and a simpler stage‐structured matrix model suggest that substantial differences in adult survival largely due to wolf predation are likely to lead to long‐term decline of woodland caribou in the commercially logged landscape, whereas the unlogged landscape should be considerably more capable of sustaining caribou. Estimates of population growth rates (λ) for the 2010–2014 period differed little between the matrix model and the individual‐based PVA model for the unlogged (matrix model = 1.01; individual‐based model = 0.98) and logged landscape (matrix model = 0.88; individual‐based model = 0.89). We applied the spatially explicit PVA model to assess the viability of woodland caribou across 14 woodland caribou ranges in Ontario. Outcomes of these simulations suggest that woodland caribou ranges that have experienced significant levels of commercial forestry activities in the past had annual growth rates <0.89, whereas caribou ranges that had not experienced commercial forestry operations had population growth rates >0.96. These differences were strongly related to regional variation in wolf densities. Our results suggest that increased wolf predation risk due to anthropogenic disturbance is of sufficient magnitude to cause appreciable risk of population decline in woodland caribou in Ontario. © 2020 The Authors. The Journal of Wildlife Management published by Wiley Periodicals, Inc. on behalf of The Wildlife Society.

Is the predation risk of mate-searching different between the sexes?

In animals that communicate for pair formation, generally one sex invests more effort in mate searching. Differential predation risk of mate searching between the sexes is hypothesised to determine which sex invests more effort in mate searching. Although searching by males is prevalent in most animals, in orthopteran insects and some other taxa females physically move to localise signalling males who are predominantly sedentary. Although the two sexes thus share mate searching effort in orthopterans, their behavioural strategies are different and sexual selection theory predicts that signalling males may be following the riskier strategy and incurring higher costs. However, relative levels of risk posed by the two mate searching strategies remain largely unexplored. Hence, we estimated the relative predation risk experienced in natural populations by signalling males and responding females. We did this by quantifying predation risk as a probability of mortality in the context of acoustic communication in a tree cricket, Oecanthus henryi from its ecologically relevant predator, a lynx spider, Peucetia viridans. Spiders may perceive calling in males and movement in females by their ability to detect both airborne acoustic cues and substrate-borne vibratory cues. Probability of mortality was quantified by partitioning it into three spatial components at which crickets and spiders interact, using a combination of extensive field observations and manipulative experiments in a semi-natural setup. We found no differences in predation risk faced by calling males and responding females, supporting the prediction that similar sex-specific costs can explain shared mate searching responsibilities. Our findings therefore suggest that direct benefits offered by males to females upon pair formation may better explain shared mate searching effort between the sexes in orthopterans.

Spatial structure of foraging meerkat groups is affected by both social and ecological factors

Group-living animals need to trade off the benefits and the costs of close proximity to conspecifics. Benefits can be increased, and costs reduced by preferentially choosing specific locations within a group best adjusted to an individual’s needs or by associating with specific group members and/or avoiding others. We investigated the spatial structure of meerkat (Suricata suricatta) groups and whether it was shaped by social factors such as affiliation or aggression among group members, predation risk, foraging success, or a mix of these different factors. Using social network analyses, based on spatial networks, we found associations between the dominant pair, among males and among same aged individuals, and dis-assortment by sex only in one to two of the six groups. In addition, the structure of meerkat groups was highly variable, as individual strength within the calculated networks was not repeatable over time. Meerkats seemed to adjust their location to their physical environment, as dominant individuals were located further toward the front of the group, where foraging success is likely higher and young individuals located further toward the back of the group, where they can benefit most from the vigilance effort of their conspecifics. We conclude that meerkat groups display a dynamic spatial structure depending on both the current social and physical environmental. Group-living animals can achieve greater benefits from close association with conspecifics by choosing specific locations within a group or associating with specific group members and/or avoiding others. A considerable body of work has examined how differences in predation risk or foraging success affect the relative location of individuals within a group. Several studies investigated the association between individuals, in order to draw conclusions on the social structure. However, it is important to disentangle the impact of all of these different aspects on the spatial structure of a group. Here, we provide evidence that both the social and physical environment is important for the spatial assortment of meerkats, a social mongoose foraging in cohesive groups.

Predation risk and microhabitat selection by cave salamanders, Eurycea lucifuga (Rafinesque, 1822)

Abstract Habitat selection is driven by many factors, but no one location is likely to be best for all factors; thus, individuals are subject to trade-offs when selecting habitat. Caves provide a clear example of such trade-offs because these habitats are energy deprived. Cave salamanders (Eurycea lucifuga) commonly inhabit caves at least in part because this habitat is cool and wet. We tested the hypothesis that caves also provide cave salamanders with a reduction in predation risk. We used clay models to test for differences in predation risk in caves vs. forests and at low (e.g., ground) vs. elevated (e.g., cave wall) positions, and recorded locations of cave salamanders to assess vertical (i.e., wall) vs. non-vertical (e.g., ground) substrate selection in a cave. Overall, a mean of 3.2 models in caves were damaged and a mean of 8.2 were damaged in forests. Cave salamanders selected vertical substrate more often than non-vertical substrate (, ), and in caves, low-positioned models were more likely to be damaged than models on walls, although there was no effect of model height in forests. This study suggests that caves provide salamanders a refuge from increased predation pressure, a benefit that likely compensates for the costs of moving between caves and the richer foraging grounds outside them.

Female response to predation risk alters conspecific male behaviour during pre‐copulatory mate guarding

AbstractMating behaviour often increases predation risk, but the vulnerability within mating pairs differs between the sexes. Such a sex difference is expected to lead to differences in responses to predation risk between the sexes. In the two‐spotted spider mite Tetranychus urticae, males engage in pre‐copulatory mate guarding because only the first mating results in fertilisation. We investigated (i) whether pre‐copulatory pairs are more conspicuous to the predatory mite Phytoseiulus persimilis than solitary females, (ii) whether the vulnerability to the predator differs between sexes within the pre‐copulatory pair, (iii) whether each sex of T. urticae responds to predation risk during pre‐copulatory mate guarding and (iv) whether T. urticae's response to predation risk affects predator behaviour. Because T. urticae females are immobile during pre‐copulatory mate guarding, we observed male behaviour to evaluate effects of predation risk. We found that the predators detect more pre‐copulatory pairs than solitary females and that more females than males of the pre‐copulatory pairs are preyed upon by the predators. The preference of spider mite males for pre‐copulatory pairs versus solitary females was affected by whether or not the female had been exposed to predators during development. Male T. urticae exposed to predation risk did not alter their behaviour. These results suggest that only the most vulnerable sex, that is the female, responds to predation risk, which modifies male behaviour. Regardless of T. urticae females’ experience, however, P. persimilis detected more T. urticae pre‐copulatory pairs than solitary females, suggesting that pre‐copulatory mate guarding itself is dangerous for T. urticae females when these predators are present. We discuss our results in the context of sex‐dependent differences in predation risk.

Habitat‐specific capture timing of deer mice (Peromyscus maniculatus) suggests that predators structure temporal activity of prey

AbstractTiming is an essential component of the choices that animals make: The likelihood of successful resource capture (and predator avoidance) depends not just on what an animal chooses to do, but when it chooses to do it. Despite the importance of activity timing, our ability to understand the forces that constrain activity timing has been limited because this aspect of animal behavior is shaped by several factors (e.g., interspecific competitors, predators, physical conditions), and it is difficult to examine activity timing in a setting where only a single factor is operating. Using an island system that makes it possible to focus on the effect of predation risk in the absence of interspecific competition, we examine how the onset of activity of the deer mouse (Peromyscus maniculatus) varies between habitats with unique predation risks (i.e., minimal‐shrub cover versus abundant‐shrub cover sites). Using capture time to assess the timing of mouse activity, we found that mice in habitats with minimal shrub cover were captured 1.7 hr earlier than mice in habitats with abundant shrub cover. This difference in timing between habitats was likely a direct response to differences in predation risk between the two habitats: There were no differences in thermal conditions between the two habitats, and the difference in activity timing disappeared during a night when overcast skies reduced island‐wide predation risk. Our results demonstrate that predation risk, independent of interspecific competition, can generate significant changes in animal activity timing. Our work suggests that habitat structure that provides safety (i.e., refuge habitats) plays a direct role in the timing of prey activity and that habitat modification that alters refuge availability (e.g., shrub dominance) may alter the timing of animal activity.

Motile behavior and predation risk in planktonic copepods

AbstractPredation is an important source of mortality in zooplankton but factors governing predation risk in marine food webs are still not well understood. Here, we examine the role of zooplankton behavior in determining predation risk. We first quantified motility of copepods with different feeding behaviors (ambush feeding, cruising, and feeding‐current feeding). Second, we estimated remote predator detection and escape characteristics of the studied copepods. Third, we proposed a simple behavior‐dependent encounter model to predict copepod predation risk from rheotactic predators. Finally, we compared our predictions with predation risk previously determined experimentally. For similar sized copepods, predicted predation risks were similar between feeding‐current feeders and cruising feeders, whereas predation was up to 8.5 times lower (range: 1.5–8.5) for ambush feeders. Predicted predation risks further differed between males and females depending on feeding behavior: in ambush feeders males actively search for non‐motile females and their predation risk was up to 6 times higher (range 1.2–6) than for females. In contrast, feeding current‐ and cruising feeders showed small differences in predation risk between genders. In all cases, predicted relative predation risks between particular behaviors were confirmed by empirical data from previous predation experiments. Our results demonstrate that prey behavior of zooplankton may lead to a predictable variation in predation risk from rheotactic predators of up to an order of magnitude, and therefore that individual behavior is an important factor in structuring zooplankton communities.

Diel activity patterns of northern Australian small mammals: variation, fixity, and plasticity

The temporal niche has received less attention than the spatial niche in ecological research on free-ranging animals. Most studies that have examined the effect of season on the diel activity patterns of small mammals have been conducted in temperate climates where daily temperatures and day length are important predictors of activity. Extremely seasonal rainfall in northern Australia possibly exerts a strong influence on mammalian activity due to the influx of food resources. Using camera traps set over a 3-year period, we documented the diel activity patterns of 5 species of small mammals co-occurring on Groote Eylandt, in the wet-dry tropics of northern Australia. All species were strictly nocturnal but some responded differently to the effect of season. The northern quoll (Dasyurus hallucatus) displayed a bimodal activity pattern that did not differ between the seasons. The northern brown bandicoot (Isoodon macrourus) displayed bimodal activity in the wet season and unimodal activity in the dry. The more sustained activity of I. macrourus in the dry season may be the result of this species utilizing more cellulose-rich food in times of lower insect abundance, whereas D. hallucatus possibly exhibits lower dietary plasticity. The northern hopping-mouse (Notomys aquilo) was consistently active throughout the night in both seasons. Conversely, the delicate mouse (Pseudomys delicatulus) showed great plasticity in its nocturnal activity which altered significantly depending on both season and habitat. The disparity in activity pattern between these 2 rodents possibly reflects differences in predation risks. The grassland melomys (Melomys burtoni) was recorded only during the dry season in coastal grassland habitat, when its activity peaked sharply after nightfall. Our study highlights the interspecific variation in small mammal activity between the wet and dry seasons in northern Australia, which may be explained by differences in diet, habitat use, and predation risk in these species.

Intimidating courtship and sex differences in predation risk lead to sex-specific behavioural syndromes

Behavioural correlations between mating behaviour and antipredator behaviour are expected when sexual behaviour increases predation risk. However, the correlation would be different between males and females, particularly when the sexes experience different levels of predation risk. Here, we tested this idea using a water strider species, Gerris gracilicornis (Heteroptera: Gerridae). G. gracilicornis males employ an unusual intimidating courtship strategy capitalizing on predator behaviours and female response to predators. Since mounted females are more vulnerable than males to predatory attacks from below, we predicted that changes in female mating behaviours across predation contexts (boldness in a mating context) should be associated with female antipredator behaviours (boldness in a nonmating context), but that the correlation would be weaker for male mating behaviours. In a series of behavioural assays, we measured water striders' (1) mating behaviour in the absence of predators, (2) mating behaviour in the presence of predation risk, (3) boldness in the mating context (changes in female mating behaviour after predator attacks) and (4) boldness in the nonmating context. We found that females behaved more cautiously around predators in both the mating and nonmating contexts. We also found that females' boldness in the mating context was significantly correlated with their boldness in the nonmating context. In contrast to females, antipredator behaviour of males in the nonmating context did not correlate with their boldness in the mating context. Thus we suggest that sex differences in boldness across predation contexts appear to cause sex-specific behavioural syndromes.