Adult frogs are sensitive to the predation risks of olfactory communication

Olfaction is a common sensory mode of communication in much of the Vertebrata, although its use by adult frogs remains poorly studied. Being part of an open signalling system, odour cues can be exploited by 'eavesdropping' predators that hunt by smell, making association with odour a high-risk behaviour for prey. Here, we show that adult great barred frogs (Mixophes fasciolatus) are highly attracted to odour cues of conspecifics and those of sympatric striped marsh frogs (Limnodynastes peronii). This attraction decreased significantly with the addition of odours of a scent-hunting predator, the red-bellied black snake (Pseudechis porphyriacus), indicating that frogs perceived predation risks from associating with frog odours. Male frogs, however, maintained some attraction to unfamiliar conspecific scents even with predator odours present, suggesting that they perceived benefits of odour communication despite the risk. Our results indicate that adult frogs can identify species and individuals from their odours and assess the associated predation risk, revealing a complexity in olfactory communication previously unknown in adult anurans.     

Plankton predation rates in turbulence: a study of the limitations imposed on a predator with a non-spherical field of sensory perception

This paper presents an extension to previously published work which studied encounter rates of planktonic predators with restricted perception fields, to examine the related problems of prey capture and predation rates. Small-scale turbulence influences planktonic predation in two ways: the extra energy of the flow enhances the number of encounter events between individual predator and prey meso/micro-zooplankton, but it lowers the capture probability (because the time spent by the predator and prey in close proximity is reduced). Typically, an 'encounter' has usually been defined as an event when a potential prey swims (or is advected) to within a distance R of the predator in any direction. However, there is a considerable body of experimental evidence showing that predators perception fields are far from spherical; often they are wedge shaped (e.g. fish larvae), or strongly aligned with the directions of sensory antennae (e.g. copepods); and this is certain to influence optimal predation strategies. This paper presents a theoretical model which for the first time examines the combined problems of both encounter and capture for a predator with a restricted perception field swimming in a turbulent flow. If such a predator adopts a cruising strategy (continuous swimming, possibly with direction changes) the model predictions suggest that predation rates actually vary little with swimming speed, in contrast to predictions made for spherical perception fields. Consequently, cruising predators are predicted to swim at relatively low speeds whilst foraging. However, application of the model to examine the net energy gain of a typical pause-travel predator (the Atlantic cod larva), does predict the existence of an optimal ratio of the length of pauses to time spent swimming (specifically one pause phase to every two travel phases), in line with experimental observations. Kinematic simulations are presented which support these findings.     

Predators and the breeding bird: behavioral and reproductive flexibility under the risk of predation

A growing body of work suggests that breeding birds have a significant capacity to assess and respond, over ecological time, to changes in the risk of predation to both themselves and their eggs or nestlings. This review investigates the nature of this flexibility in the face of predation from both behavioural and reproductive perspectives, and also explores several directions for future research. Most available work addresses different aspects of nest predation. A substantial change in breeding location is perhaps the best documented response to nest predation, but such changes are not always observed and not necessarily the best strategy. Changes in nesting microhabitat (to more concealed locations) following predation are known to occur. Surprisingly little work addresses the proactive avoidance of areas with many nest predators, but such avoidance is probably widespread. Individual birds could conceivably adopt anti‐predator strategies based on the nest predators actually present in an area, but such effects have yet to be demonstrated. In fact, the ways in which birds assess the risk of nest predation is unclear. Nest defence in birds has historically received much attention, but little is known about how it interacts with other aspects of decision‐making by parents. Other studies concentrate on predation risk to adults. Some findings suggest that risk to adults themselves influences territory location, especially relative to raptor nests. An almost completely unexplored area concerns the sorts of social protection from predators that might exist during the breeding season. Flocking typical of the non‐breeding season appears unusual while breeding, but a mated pair may sometimes act as a “flock of two”. Opportunistic heterospecific sociality may exist, with heterospecific protector species associations more prevalent than currently appreciated. The dynamics of singing during the breeding season may also respond to variation in predation risk, but empirical research on this subject is limited. Furthermore, a few theoretical and empirical studies suggest that changes in predation risk also influence the behaviour of lekking males. The major influence of predators on avian life histories is undoubtedly expressed at a broad phylogenetic scale, but several studies hint at much flexibility on an ecological time scale. Some species may forgo breeding completely if the risk of nest predation is too high, and a few studies document smaller clutch sizes in response to an increase in nest predation. Recent evidence suggests that a female may produce smaller eggs rather than smaller clutches following an increase in nest predation risk. Such an increase may also influence decisions about intraspecific brood parasitism. There are no clear examples of changes in clutch/egg size with changes in risk experienced by adults, but parental responses to predators have clear consequences for offspring fitness. Changes in risk to adults may also influence body mass changes across the breeding season, although research here is sparse. The topics highlighted herein are all in need more empirical attention, and more experimental field work whenever feasible.     

高寒草甸生态系统中高原鼠兔和高原鼢鼠的捕食风险及生存对策

调查青藏高原高寒草甸生态系统中两种主要啮齿动物及其天敌动物的种群密度,分析天敌动物对两种啮齿类的捕食方式、捕食强度,探讨啮齿类动物的捕食风险及生存对策。研究结果表明,高原鼠兔和高原鼢鼠的种群密度分别为4．97只／hm^2和10．6只／hm^2,而它们的主要天敌赤狐、艾虎和香鼬的种群密度分别为0．16只／100hm^2、0．37只／100hm^2、3只／100hm^2。艾虎和香鼬在取食过程中主要搜寻啮齿类的洞道系统,全部食物几乎都来源于洞道系统内;赤狐或取食地面活动的鼠兔,或挖掘洞口待高原鼢鼠封闭洞口时取食猎物。高原鼠兔在赤狐、艾虎和香鼬的食物中所出现的频次分别为100％、96．1％、100％,高原鼢鼠在3种天敌动物的食物中所出现的频次分别为87．5％、73．2％、0％。3种天敌动物对高原鼠兔和高原鼢鼠的捕食强度分别为0．703％和0．038％,高原鼠兔和高原鼢鼠所承受的捕食风险分别为0．780和0．393。高原鼠兔在高的捕食风险下通过行为对策和繁殖对策增加其适合度,而承受捕食风险较小的高原鼢鼠主要通过封闭的洞道系统和高的存活率增加其适合度。     

Vigilance and fitness in grey partridges Perdix perdix: the effects of group size and foraging-vigilance trade-offs on predation mortality

1. Vigilance increases fitness by improving predator detection but at the expense of increasing starvation risk. We related variation in vigilance among 122 radio-tagged overwintering grey partridges Perdix perdix (L.) across 20 independent farmland sites in England to predation risk (sparrowhawk Accipiter nisus L., kill rate), use of alternative antipredation behaviours (grouping and use of cover) and survival. 2. Vigilance was significantly higher when individuals fed in smaller groups and in taller vegetation. In the covey period (in early winter when partridges are in flocks), vigilance and use of taller vegetation was significantly higher at sites with higher sparrowhawk predation risk, but tall vegetation was used less by larger groups. Individuals were constrained in reducing individual vigilance by group size and habitat choice because maximum group size was determined by overall density in the area during the covey period and by the formation of pairs at the end of the winter (pair period), when there was also a significant twofold increase in the use of tall cover. 3. Over the whole winter individual survival was higher in larger groups and was lower in the pair period. However, when controlling for group size, mean survival decreased as vigilance increased in the covey period. This result, along with vigilance being higher at sites with increasing with raptor risk, suggests individual vigilance increases arose to reduce short-term predation risk from raptors but led to long-term fitness decreases probably because high individual vigilance increased starvation risk or indicated longer exposure to predation. The effect of raptors on survival was less when there were large groups in open habitats, where individual partridges can probably both detect predators and feed efficiently. 4. Our study suggests that increasing partridge density and modifying habitat to remove the need for high individual vigilance may decrease partridge mortality. It demonstrates the general principle that antipredation behaviours may reduce fitness long-term via their effects on the starvation-predation risk trade-off, even though they decrease predation risk short-term, and that it may be ecological constraints, such as poor habitat (that lead to an antipredation behaviour compromising foraging), that cause mortality, rather than the proximate effect of an antipredation behaviour such as vigilance.     

A test of the risk allocation hypothesis: tadpole responses to temporal change in predation risk

The risk allocation hypothesis predicts that temporal variationin predation risk can influence how animals allocate feedingbehavior among situations that differ in danger. We testedthe risk allocation model with tadpoles of the frog Rana lessonae,which satisfy the main assumptions of this model because theymust feed to reach metamorphosis within a single season, theirbehavioral defense against predators is costly, and they canrespond to changes in risk integrated over time. Our experiment switched tadpoles between artificial ponds with different numbersof caged dragonfly larvae and held them at high and low riskfor different portions of their lives. Tadpoles responded stronglyto predators, but they did not obey the risk allocation hypothesis:as the high-risk environment became more dangerous, there wasno tendency for tadpoles to allocate more feeding to the low-riskenvironment, and as tadpoles spent more time at risk, they didnot increase feeding in both environments. Our results suggestthat the model might be more applicable when the time spentunder high predation risk is large relative to the time requiredto collect resources.     

Seasonal colour change by moult or by the abrasion of feather tips: a comparative study

Many birds undergo seasonal changes in plumage coloration by prebreeding moult, abrasion of cryptic feather tips, or both. Seasonal dichromatism is thought to result from optimizing coloration to the conflicting demands of different life-cycle periods, sexual selection for conspicuousness being substantial during the mating season, whereas selection for camouflage and for social signals may act in all seasons. Furthermore, energetic and time demands may constrain the extent of moult, thereby limiting colour change. We investigated the relative importance of several factors in shaping this variation in a songbird clade using phylogenetic comparative methods. We found that prebreeding moult relates most strongly to breeding onset and winter diet, demonstrating that both time and food availability constrain feather replacement. Feather abrasion was best predicted by winter flocking behaviour, and secondarily by open habitats, implying that exposure to predators and the simultaneous need for social signalling may favour the expression of partially obscured ornaments in the non-breeding season. The combined occurrence of prebreeding moult and feather abrasion was associated with the polygynous mating system, suggesting that species under strong sexual selection may employ both strategies of colour change to ensure the full expression of breeding coloration.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 711–721.     

Perch selection by singing chaffinches: a better view of surroundings and the risk of predation

Predation risk varies among perches, and the vulnerability ofsinging chaffinches (Fringilla coelebs) might differ dependingon where they perch in a tree. To find out how singing of thechaffinch is associated with antipredatory behavior, I studiedperch selection in mature pine forest and in pine saplings,two habitats differing in the amount of cover for protection from predators. My results show that male chaffinches preferto sing below the canopy of mature pines and in the uppermostparts of sapling pines. Although these are the canopy partsmost exposed to sparrowhawk (Accipiter nisus) attacks, stayingin open sites may be a beneficial strategy for singing chaffinchesbecause it makes it possible to improve antipredatory vigilance.This assumption was supported by the hawk experiments. Afterbeing exposed to the sparrowhawk model, all of the singingbirds selected the conspicuous perch below the canopy of maturepines. The males that perched higher in the canopy before theexperiment moved to the lower canopy, whereas those males thatsang below the canopy did not change their singing perch.     

Planktonic encounter rates in homogeneous isotropic turbulence: the case of predators with limited fields of sensory perception

It is a well-established fact that encounter rates between different species of planktonic microorganism, either swimming, or passively advected by the flow, are enhanced in the presence of turbulence. However, due to the complexity of the various calculations involved, current encounter rate theories are based on a number of simplifying approximations, which do not reflect reality. In particular, a typical planktonic predator is usually assumed to have perfect 'all round vision', i.e. it can perceive a prey particle at any relative orientation, provided it lies within some given contact radius R. Unfortunately, there is a wide body of experimental evidence that this is not the case. In this study the encounter problem for a predator with a limited field of sensory perception, swimming in a turbulent flow, is examined from first principles and a number of new modelling ideas proposed. A wide range of kinematic simulations are also undertaken to test these predictions. Particular attention is paid to the swimming strategy such a predator might undertake to enhance its encounter rate. It turns out that the predicted optimum swimming strategies differ radically from the results of previous work. Empirical evidence is also presented which appears to support these new findings.     

Estimating predation risk in zooplankton communities: the importance of vertical overlap

In order to estimate predation risk in nature, two basic components of predation need to be quantified: prey vulnerability, and density risk. Prey vulnerability can be estimated from clearance rates obtained from enclosure experiments with and without predators. Density risk is a function of predator density, and the spatial and temporal overlap of the predator and prey populations. In the current study we examine the importance of the vertical component of overlap in making accurate estimates of predation risk from the invertebrate predator Mesocyclops edax on rotifer versus crustacean prey. The results indicate that assumptions of uniform predator and prey densities cause a significant underestimation of predation risk for many crustacean prey due to the coincident vertical migration of these prey with the predator. The assumption of uniformity is more reasonable for estimating predation risk for most rotifer prey.     

Potential risks of olfactory signaling: the effect of predators on scent marking by beavers

Mammals scent mark their territories to advertise occupancyand ownership. However, signaling with scent for territorialdefense can have a negative effect by advertising an individual'spresence and location to predators. In this study, we measuredresponses to a simulated territorial intrusion by conspecificadult male Eurasian beavers (Castor fiber) either in the localizedpresence or in the absence of odor of a predator to test thehypothesis that the territorial defense of free-living beaverswould be disrupted by the presence of predation risk in theirnatural environment. We predicted that beavers would significantlyreduce their willingness to countermark intruder's scent inthe presence of the scent of predators (wolf [Canis lupus] andlynx [Lynx lynx]), compared with a control (no odor), as responsesare in general stronger to predator scent marks than nonpredatorscent. Therefore, we also predicted that the effects of nonpredatorymammal scent (neophobic control) (eland [Taurotragus oryx] andhorse [Equus cabalus]) are to be expected somewhere in betweenthe effects of the predator odor and a control. Our resultssuggest that both predator and nonpredator scents reduce beaversresponse to a simulated intruder's scent mounds and thereforedisrupt their territorial defense. However, predator scent hada stronger effect than nonpredator scent. Beavers may thereforebe at great risk on territories with predators present becauseof the trade-off between predator avoidance and territorialdefense. Our study demonstrates the potential of predation riskas a powerful agent of counterselection on olfactory signalingbehavior.     

Bearding the scorpion in his den: desert isopods take risks to validate their ‘landscape of fear’ assessment

Animals balance the risk of predation against other vital needs by adjusting their spatial behavior to match spatiotemporal variation in predation risk. To map this ‘landscape of fear’, prey use evolutionary rules of thumbs that are associated with the activity and hunting efficiency of predators. In addition, prey acquire perceptual information about the presence, identity and state of potential predators and use these cues to focus their acute anti‐predatory responses. Our goal was to explore if and how prey also use such perceptual information that decays with time to update their spatiotemporal risk assessment. We placed scorpions in freshly dug burrows and recorded the spatial activity and defense behavior of their isopod prey upon encountering the burrows straight after settling the scorpions and seven days later. To corroborate our understanding, we also examined the isopods’ detailed reactions towards deserted scorpion burrows. The isopods reacted defensively to scorpion burrows during their first encounter. After seven days, proportionally more isopods approached the scorpion burrows on their way out for foraging and fewer isopods encountered it on their way back. No changes in the spatial activity were observed towards deserted burrows. In addition, on the eighth day, more isopods entered the risky area near the scorpion burrows when leaving their own burrow than on the first encounter. The results suggest that isopods used predator cues to readjust the ‘landscape of fear’. Yet, rather than avoiding the dangerous areas altogether, the isopods implemented risky inspection behavior, validating whether the danger is actual. Our findings imply that inspection behavior toward predators can be used for future planning of prey spatial activity, offsetting possible ‘information decay costs’.     

Quantifying insect predation with predator exclusion cages: the role of prey antipredator behavior as a source of bias

There are limitations imposed by current methodologies to detect and quantify insect predation. However, there has been relatively little effort to experimentally document the sources of biases associated with the various methodologies. In this study, we examined how predation estimates in the field using predator exclusion cages may be biased when one fails to account for antipredator behavioral responses. To do this, we did the usual comparison of the number of insects missing from plants where predators were allowed access to the number missing from plants where predators were excluded, but also determined how many of the missing insects reacted to predators by dropping from plants and how many were actually preyed upon. Our results provide evidence that estimates of insect mortality in the field are significantly reduced if prey antipredator behavior is taken into account. As it is commonly assumed that prey missing in the field are predated, documenting the incidence of predator‐mediated ‘disappearance’ and capturing insect prey before they escape can provide with a relevant estimate of bias.     

When food fights back: Cebid primate strategies of larval paper wasp predation and the high-energy yield of high-risk foraging

Optimal foraging theory predicts that well-defended potential foods should be exploited only when energy pay-offs are great. Although stinging hymenopteran nests are both well-defended and predated by primates, their larvae's energy yields rarely have been calculated, and predation-linked foraging behaviours by primates infrequently documented. Based on 58 opportunistic observations of primates raiding wasp nests for larvae, we calculated energetic yields of low- and high-risk wasp nest predation for Cebus albifrons, Saimiri collinsi, S. sciureus and Sapajus apella, and tested predictions derived from optimal foraging theory. We recorded how nests were processed and by which age-sex classes, eaten nest fragment sizes, number of occupied and empty cells, and nest occupancy patterns (percent larvae/pupae, eggs, empty cells). Basal metabolic rate (BMR) calculations showed energetic yields from 15 min foraging on low-risk nests (Polybia quadricincta) would meet energy needed to sustain adult female and male C. albifrons BMR for 4.9 and 4.5 h, respectively; yields from high-risk (Chartergus artifex) nests for 6.5 and 6.2 h; Mischocyttarus sp. nest yields (low risk, but mimetically resembling other wasps) would meet S. collinsi BMR for 2.9 h (female) and 2.3 h (male), and 2.6 and 2.1 h, for the slightly larger S. sciureus, respectively. The Chartergus energetic-yield value is nearly 20% of a 36 g chocolate bar (741 kJ). Our data provide quantitative support for the common assertion that wasp larvae and pupae are high-yield foods for primates. As predicted by optimal foraging, energetic yield is sufficient to offset the risk and pain of being stung.     

The benefits of stealing from a predator: foraging rates, predation risk, and intraspecific aggression in the kleptoparasitic spider Argyrodes antipodiana

In the trade-off between food and safety, the role of aggressiveintraspecific interactions has not been extensively examined.Here I present information on this system using a kleptoparasiticspider, Argyrodts antipodiana, and its host spider and potentialpredator, Eriophora pustulosa. A. antipodiana can feed eitherat a potentially dangerous site (the hub of its host's web withthe host), or at a relatively safe site (on food bundles aroundthe edge of the host's web). I found that A. antipodiana cangain food very quickly when feeding with the host, apparentlyby exploiting the host's ability to digest the prey. Thus A.antipodiana follows predictions based on foraging models inthat it accepts a higher predation risk at the hub because ofthe higher food payoff. A. antipodiana also aggressively competesfor access to more food. However, aggressive competition increasesthe predation risk from the host, especially at tile hub wherethe host is very close. Consequently, A. antipodiana modifiesits level of intraspecific aggressiveness in accordance withits position on the web: at the hub, where the cost of aggressionis high (due to predation risk), A. antipodiana reduces itsaggressiveness, but it is aggressive away from the hub whencompeting for food bundles. The ability of A. antipodiana tochange interaction intensity as a function of its position onthe web enables it to exploit a rich, but risky, food sourceand provides a new angle for examining food and safety tradeoffs in light of intraspecific competition for food     

黄土高原区主导生态风险识别及分异性研究——以黄河流域中游为例

黄河流域作为典型的生态脆弱区,其生态问题复杂多样,亟待全面的生态治理和修复。同时,黄河流域生态保护和高质量发展是当前我国发展战略之一。明确黄河流域存在的生态问题,做好区域生态修复,开展综合治理是黄河流域可持续发展的重点。因此把握黄河流域的自然条件的区域差异,开展综合性的生态风险识别与评价,明确区域风险空间异质性分布与特点,是服务于区域生态修复、促进黄河流域高质量发展的重点。结合黄河流域中游气候、地形、植被等多自然本底情况识别风险源,建立服务于研究区生态保护和修复的区域生态风险评价体系,并通过GEE和GIS平台,可视化和量化了各类生态风险,并采用空间相关分析明确了生态风险的主要成因。结果表明：1）研究区的生态风险空间分布具有显著的区域特征,各个要素的生态风险呈现明显的东南和西北的差异、不同土地覆被情况的差异、人类活动带与非人类活动带的差异以及河流沿河与非沿岸的差异;2）植被净生态系统生产力呈现东南高西北低的特征,温度植被干旱指数显示西北部、山西、陕西南部存在较高的干旱风险,土壤侵蚀风险主要存在于黄河沿岸、其他河谷地带以及西北部,防风固沙服务能力在山西省山区以及植被生长较好的地区较高;3）综合生态风险评价显示宁夏以及陕西北部多数地区属于高风险区,低风险区主要分布在研究区西南部以及山西省西部沿线地区;4）双变量的Moran''s I指数显示地表温度、植被覆盖和汛期降水是导致综合生态风险西北和东南差异的主要原因,坡度是导致局部风险差异的主要原因。