动物觅食行为对捕食风险的反应

动物进行任何活动时均面临被捕食的风险 ,分析捕食风险与猎物觅食行为的关系 ,有助于揭示捕食者与猎物的协同进化机制。捕食风险具有限制或调节猎物种群数量的功能。在进化时间内 ,对猎物形态和行为特征的进化是潜在的选择压力之一 ,可利用环境因子作为信息源估测食物可利用性和捕食风险大小的动物 ,具有更大的适合度。信息源可分为包括视觉的、听觉的和化学的。动物进行觅食活动时 ,依据信息源的变化确定环境中捕食风险的大小 ,并根据自身的质量在捕食风险的大小之间做出权衡 ,通过食物选择、活动格局和栖息地利用等行为的变化降低捕食风险     

捕食风险的种群动态效应及其作用机理研究进展

捕食者不但可以通过直接捕杀猎物而控制猎物的种群数量,还可以通过捕食风险效应影响猎物种群的繁殖和动态,并且在某些情况下,捕食风险效应对猎物种群动态的控制作用甚至大于捕食者的直接捕杀.关于捕食风险效应对猎物动物繁殖产出和种群动态变化的作用及其机理方面的野外研究越来越受到国内外学者重视.本文介绍了近年来捕食风险效应的研究进展,重点关注了美国黄石国家公园中捕食者对马鹿(Cervus elephus)、加拿大育空地区的捕食者对白靴兔(Lepus americanus)的捕食风险效应等案例研究,以阐明捕食风险效应对猎物种群动态影响的重要性,以及关于捕食风险效应影响猎物种群繁殖和动态机理的两个假说(捕食者敏感食物假说、捕食应激假说).并结合我国在捕食者与猎物之间关系的研究现状,提出了进一步在野外开展捕食风险效应对濒危有蹄类猎物种群动态影响研究的建议,阐释了开展这些研究的重要意义.     

急性捕食风险不能完全限制饥饿 雌性长爪沙鼠的觅食活动

觅食活动是动物生存和繁殖所必需的基本的活动,受个体生理状态（如饥饿）和环境状况（如捕食、食物可利用性）时空变化的影响,能量状态-风险分配假说指出,动物在应对不同风险时会优化觅食和反捕食努力的时间和能量分配。然而,有关啮齿动物觅食决策的能量状态-捕食风险分配假说的研究结论尚不统一。本研究在野外实验室以艾鼬（Mustela eversmannii）气味作为捕食风险刺激源,以非捕食者（马）气味源作为对照,首先通过Y型观测箱检验雌性饥饿长爪沙鼠（Meriones unguiculatus）对捕食者气味的辨别能力（Wilcoxon 秩检验）;在此基础上通过中立场行为观测箱分别测定饥饿雌鼠在“有食物和天敌气味源”与“有食物和非天敌气味源”环境下的觅食活动,采用Mann-Whitney Z检验比较两者间的行为差异,以验证急性捕食风险限制饥饿沙鼠觅食活动的假设,并探讨动物在饥饿风险与捕食风险共存情况下的觅食行为对策。结果显示,（1）长爪沙鼠对天敌气味反应明显,厌恶和回避有较高潜在捕食风险的空间;（2）虽然觅食潜伏期在捕食风险存在时有所增加,但急性捕食风险并未影响饥饿沙鼠的觅食频次,沙鼠通过缩短每次觅食的持续时间来应对捕食风险;与此同时,（3）饥饿沙鼠在急性捕食风险条件下对环境探究的次数明显增加,一定程度上提高反捕食努力,且自我修饰表现显著,以缓释捕食压力的恐惧效应。这些结果表明,急性捕食风险不能完全抑制饥饿沙鼠的觅食努力,在有捕食风险情况下,饥饿的长爪沙鼠会权衡觅食获取能量和避免捕食的收益和代价,优化觅食策略。本研究结果支持能量状态-风险分配假说关于在短期高风险情况下反捕食努力分配更多,但当动物在饥饿风险持续时间比例显著增加时,动物最终也必须在高风险情况下觅食的预测,也反映了长爪沙鼠对食物资源不可预测及捕食风险高的干旱半干旱荒漠环境的行为适应对策。     

水生生态环境中捕食信息素的生态学效应

捕食信息素是捕食者释放的,能够引发猎物反捕食反应的化学信号。在水生生态系统中,捕食信息素在捕食者和猎物之间信息传递及协同进化过程中发挥着重要的作用,其生态学效应在国际上受到广泛关注。捕食信息素的来源有多种形式,研究中常使用养殖过捕食者的水溶液作为捕食信息素的来源。捕食信息素的作用效果受到捕食者和猎物的种类、信息素的浓度、观察的指标等多方面因素的影响。捕食信息素可以对水生生物的行为、形态和生活史特征等方面造成影响。水生生物通过感知捕食信息素来提前预知潜在的被捕食风险,并作出适应性调整,以降低被捕食的风险。在某些情况下,捕食信息素可以与污染物产生交互作用,从而干扰污染物对水生生物的毒性。对水生环境中捕食信息素的研究现状做了综述,介绍了当前对捕食信息素来源和理化性质等本质问题的认识,总结捕食信息素对水生生物行为、形态和生活史特征的影响,以及捕食信息素对污染物毒性的干扰,并分析了这一研究领域尚存在的困难和今后的研究方向。加强对捕食信息素的研究,将为解析水生环境中捕食者和猎物的生态关系提供新依据。     

八斑鞘蛛对多种猎物的选择捕食作用研究

研究八斑鞘蛛在多种猎物共存时的日捕食量,功能反应,捕食作用率。在有棉铃虫和棉蚜共存且密度互补时,八斑鞘蛛对棉铃虫的功能反应属Holling Ⅲ型反应;一种猎物密度变化,其他种猎物密度固定时,功能反应呈Holling Ⅱ型反应。研究了捕食作用率与猎物共存种类,相对丰盛度,捕食者本身数量的关系。 计算机(IBM-PC)模拟结果表明:捕食者个体间的相互干扰、温度、猎物内禀增长率对系统稳定性有一定影响。     

不同栖息地破坏格局下具捕食偏爱似然竞争结局的模拟分析

使用元胞自动机模型,对具有捕食偏爱、不同栖息地破坏比例和不同空间破坏格局条件下的捕食-食饵系统中各物种的变化动态进行了模拟分析。在捕食者和两猎物物种共存时:栖息地破坏比例、栖息地破坏的聚集度对猎物物种间强弱关系产生相反的作用,若增加栖息地破坏比例不利于某一猎物生存,则提高聚集度对其有利;适当提高适宜栖息地的聚集度,对所有物种都有利,若聚集度过高,效果相当于减少了栖息地的破坏比例,可能对某些猎物物种不利,但对整体系统有利;被破坏栖息地的聚集度发生变化时,捕食者的反应更敏感;在一定条件下,增强弱势种群的捕食偏爱会有助于其生存。     

拟环纹狼蛛对褐飞虱的捕食作用及其模拟模型的研究Ⅲ.选择捕食作用

本文研究了拟环纹狼蛛雌成蛛对褐飞虱、稻纵卷叶螟的选择捕食作用。在不同猎物类型共存和不同总猎物密度下,测定了捕食者对猎物的喜好性和转换行为,分析了捕食者对猎物的功能反应形式,喜好性和转换行为与共存猎物种类、数量之间的关系;建立了在多种猎物类型共存时,雌成蛛对猎物的总捕食作用方程及对每一种猎物类型的捕食作用方程。室内验证实验表明:所建立的捕食作用方程具有一定的描述能力。     

温度变化对休耕期冬水田天敌捕食猎物的影响及天敌耐冷性分析

为评估冬水田休耕季节长达6-8个月温度变化对稻田主要捕食性天敌通过觅食策略维持其种群发生的影响,在室内测定了两种代表性温度下青翅蚁形隐翅甲Paederus fuscipes成虫、拟水狼蛛Pirata subpiraticus和拟环纹豹蛛Pardosa pseudoannulata成蛛、亚成蛛对天台刺齿虫兆Homidia tiantaiensis和白翅叶蝉Thaia rubiginosa成虫的捕食功能反应、搜寻效应、自身密度干扰效应以及捕食偏好性;测定了这些捕食者在这两种温度诱导下的过冷却点（Supercooling point,SCP）和结冰点（Freezing point,FP）。结果表明,温度变化显著影响了捕食性天敌的捕食功能反应、对猎物的搜寻效应以及自身密度的干扰反应。在22℃和12℃下,捕食者对刺齿虫兆和叶蝉的捕食功能反应均符合Holling II模型。由捕食功能反应可知,22℃下捕食者对两种猎物的捕食量均高于12℃下的捕食量,两种温度下捕食者对刺齿虫兆的捕食量要显著高于对叶蝉的捕食量。22℃下捕食者对两种猎物的瞬时攻击率、最大捕食量和a/T_h值均相应地高于12℃下的值,而22℃下它们对两种猎物的处理时间则相应地小于12℃下的处理时间。在同一猎物相同温度下,狼蛛和豹蛛亚成蛛的瞬时攻击率、最大捕食量和a/T_h值均相应地高于狼蛛和豹蛛成蛛的值,它们的处理时间则明显小于其成蛛的处理时间。隐翅甲的最大捕食量和a/T_h值在12℃叶蝉试验中均最大,而其处理时间则最小;其它条件下的隐翅甲参数值通常介于狼蛛和豹蛛成蛛、亚成蛛各参数值之间。捕食者对两种猎物的搜寻效应与猎物密度呈负相关;温度变化对捕食者搜寻效应的影响程度与捕食者和猎物的种类有关;22℃下的搜寻效应值均高于12℃下的搜寻效应值。捕食者对两种猎物的捕食作用均随自身密度升高而下降,22℃下对两种猎物和12℃下对刺齿虫兆的搜寻常数和干扰系数值均以狼蛛和豹蛛亚成蛛的为最高,而12℃下对叶蝉的这2个值以豹蛛亚成蛛和隐翅甲的为最高。两种温度下捕食者对这两种猎物存在选择偏好性,更嗜食刺齿虫兆,但温度变化没有对捕食者的这种猎物偏好性产生影响。在这两种温度快速冷驯化下这些捕食者间的SCP和FP均差异显著,通常温度降低能诱导亚成蛛的SCP和FP下降,而成蛛的升高,隐翅甲的变化很小或下降,说明不同捕食者适应温度降低的耐冷特性与其捕食作用间存在一定相关性。     

捕食风险对东方田鼠功能反应格局的作用

植食性哺乳动物对食物斑块的选择和利用不仅取决于食物的可利用性,且与觅食环境潜存的各种风险紧密关联。捕食风险是否通过作用于动物觅食活动中的警觉影响其功能反应格局。在新鲜白三叶叶片构成的各类食物密集斑块上,测定东方田鼠觅食行为,建立功能反应模型,检验捕食风险对其功能反应格局的作用。结果发现,捕食风险能显著地延长东方田鼠的觅食决定时间,但其摄入率保持稳定,功能反应构型亦未发生改变,仍为Ⅱ型功能反应;除了对照组个体的采食时间随叶片大小增大无明显变动规律外,处理组个体的采食时间及对照组和处理组个体的处理时间、觅食中断时间均随叶片大小及口量的增大呈线性增高趋势,处理组个体的觅食中断时间明显大于对照组个体的;对照组和处理组个体的采食率均随叶片大小及口量呈非线性渐近递减趋势,但处理组个体的采食率较对照组个体的略有降低。结果揭示,在捕食风险压力下,虽然上述觅食参数变异能潜在地降低摄入率,但个体能通过改变觅食活动中各种警觉行为动作如降低嗅闻和静听监视动作的发生频次,增大视觉监视动作比重,以此缓冲捕食风险压力,维持摄入率。摄入率测定值与模型预测值的线性回归极显著,表明,功能反应模型具有良好的预测性。在可利用植物密集斑块,动物觅食活动中的警觉能缓冲捕食风险压力;动物摄入率是由植物大小调控的口量决定的,且受采食与处理食物竞争及觅食中断的制约;其功能反应仍属Ⅱ型功能反应。     

确定棉蚜捕食性蜘蛛种类的血清学方法的可行性研究

在捕食性动物的生态学研究中,一个首要问题就是如何确定猎物的捕食者种类。对咀嚼式捕食者来说,其捕食对象可经解剖直接检查其消化道内猎物残骸来确定。但是,对吮吸猎物体液的捕食者来说,要鉴定其是否捕食过猎物,就需借助于更为复杂而精确的实验手段。自Brooke和Proke(1946)首次把血清学方法     

Indirect risk effects reduce feeding efficiency of ducks during spring

Indirect risk effects of predators on prey behavior can have more of an impact on prey populations than direct consumptive effects. Predation risk can elicit more vigilance behavior in prey, reducing the amount of time available for other activities, such as foraging, which could potentially reduce foraging efficiency. Understanding the conditions associated with predation risk and the specific effects predation risk have on prey behavior is important because it has direct influences on the profitability of food items found under various conditions and states of the forager. The goals of this study were to assess how ducks perceived predation risk in various habitat types and how strongly perceived risk versus energetic demand affected foraging behavior. We manipulated food abundance in different wetland types in Illinois, USA to reduce confounding between food abundance and vegetation structure. We conducted focal‐animal behavioral samples on five duck species in treatment and control plots and used generalized linear mixed‐effects models to compare the effects of vegetation structure versus other factors on the intensity with which ducks fed and the duration of feeding stints. Mallards fed more intensively and, along with blue‐winged teal, used longer feeding stints in open habitats, consistent with the hypothesis that limited visibility was perceived to have a greater predation risk than unlimited visibility. The species temporally nearest to nesting, wood ducks, were willing to take more risks for a greater food reward, consistent with an increase in a marginal value of energy as they approached nesting. Our results indicate that some duck species value energy differently based on the surrounding vegetation structure and density. Furthermore, increases in the marginal value of energy can be more influential than perceived risk in shaping foraging behavior patterns. Based on these findings, we conclude that the value of various food items is not solely determined by energy contained in the item but by conditions in which it is found and the state of the forager.     

Predator identity and consumer behavior: differential effects of fish and crayfish on the habitat use of a freshwater snail

Predators can alter the outcome of ecological interactions among other members of the food web through their effects on prey behavior. While it is well known that animals often alter their behavior with the imposition of predation risk, we know less about how other features of predators may affect prey behavior. For example, relatively few studies have addressed the effects of predator identity on prey behavior, but such knowledge is crucial to understanding food web interactions. This study contrasts the behavioral responses of the freshwater snail Physellagyrina to fish and crayfish predators. Snails were placed in experimental mesocosms containing caged fish and crayfish, so the only communication between experimental snails and their predators was via non-visual cues. The caged fish and crayfish were fed an equal number of snails, thereby simulating equal prey mortality rates. In the presence of fish, the experimental snails moved under cover, which confers safety from fish predators. However, in the presence of crayfish, snails avoided benthic cover and moved to the water surface. Thus, two species of predators, exerting the same level of mortality on prey, induced very different behavioral responses. We predict that these contrasting behavioral responses to predation risk have important consequences for the interactions between snails and their periphyton resources. Received: 1 June 1998 / Accepted: 12 October 1998     

Predator and Prey Models with Flexible Individual Behavior and Imperfect Information

To begin identifying what behavioral details might be needed to characterize community dynamics and stability, we examined the effect of prey behavioral responses to predation risk on community dynamics and stability. We considered the case of prey altering their foraging effort to trade off energy gain and predation risk. We used state-dependent dynamic optimization to calculate the optimal trade-off for four models of prey behaviorally responding to predation risk. We consider a fixed behavior model in which prey use constant levels of foraging effort and three flexible behavior models in which prey change their foraging effort according to their physiological state and their perceived level of predation risk. Flexible behavior was destabilizing at the community level as evidenced by higher predator-prey oscillations and lower community persistence times. The mechanisms by which prey estimated predation risk also affected community stability. We found that community dynamics resulting from prey with flexible behavior and fixed perception of risk approximated community dynamics resulting from prey with flexible behavior and perfect information about predation risk, however neither approximated the community dynamics resulting from prey with flexible behavior and flexible perception of risk. Thus, whether it might be possible to abstract complex behavior with simpler rules when modeling community dynamics depends on the prey's behavioral mechanisms, which are empirically poorly known.     

Detecting predators and locating competitors while foraging: an experimental study of a medium-sized herbivore in an African savanna

Vigilance allows individuals to escape from predators, but it also reduces time for other activities which determine fitness, in particular resource acquisition. The principles determining how prey trade time between the detection of predators and food acquisition are not fully understood, particularly in herbivores because of many potential confounding factors (such as group size), and the ability of these animals to be vigilant while handling food. We designed a fertilization experiment to manipulate the quality of resources, and compared awareness (distinguishing apprehensive foraging and vigilance) of wild impalas (Aepyceros melampus) foraging on patches of different grass height and quality in a wilderness area with a full community of predators. While handling food, these animals can allocate time to other functions. The impalas were aware of their environment less often when on good food patches and when the grass was short. The animals spent more time in apprehensive foraging when grass was tall, and no other variable affected apprehensive behavior. The probability of exhibiting a vigilance posture decreased with group size. The interaction between grass height and patch enrichment also affected the time spent in vigilance, suggesting that resource quality was the main driver when visibility is good, and the risk of predation the main driver when the risk is high. We discuss various possible mechanisms underlying the perception of predation risk: foraging strategy, opportunities for scrounging, and inter-individual interference. Overall, this experiment shows that improving patch quality modifies the trade-off between vigilance and foraging in favor of feeding, but vigilance remains ultimately driven by the visibility of predators by foragers within their feeding patches.     

Tradeoffs involved in site selection and foraging in a wolf spider: effects of substrate structure and predation risk

Understanding how animals weigh habitat features, exposure to predators and access to resources is important to determining their life history and distribution across the landscape. For example, when predators accumulate in structurally complex habitats, they face an environment with different competitive interactions, foraging opportunities and predatory risks. The wolf spider Pardosa milvina inhabits the soil surface of highly disturbed habitats such as agricultural fields throughout eastern North America. Pardosa displays effective antipredator behavior in the presence of chemical cues produced by a larger coexisting wolf spider, Hogna helluo . We used those cues to simulate predation risk in laboratory and field experiments designed to test the effects of habitat substrate and predation risk on site selection and prey consumption of Pardosa . In general, Pardosa preferred more complex substrates over bare dirt but those preferences were eliminated or reversed when cues from Hogna were present. Feeding trials revealed that substrate alone had few effects on Pardosa prey consumption, which we measured by documenting the change in the abdomen width. Although the presence of Hogna cues reduced prey consumption overall in field feeding trials, the negative effect of predation risk on prey consumption was only observed in grass and bare dirt substrates in the laboratory. We also found that prey capture was negatively affected by habitat complexity for both spider species but that same complexity offered Pardosa protection from predation by Hogna. This study provides insight into how two predator species interact to balance site selection and feeding in order to avoid predation. Shifts in foraging and distributional patterns of predators can have profound implications for their role in the food web.     

Effects of Structural Refuge and Density on Foraging Behaviour and Mortality of Hungry Tadpoles Subject to Predation Risk

Theoretical models of prey behaviour predict that food‐limited prey engage in risk‐prone foraging and thereby succumb to increased mortality from predation. However, predation risk also may be influenced by factors including prey density and structural cover, such that the presumed role of prey hunger on predation risk may be obfuscated in many complex predator–prey systems. Using a tadpole (prey) – dragonfly larva (predator) system, we determined relative risk posed to hungry vs. sated prey when both density and structural cover were varied experimentally. Overall, prey response to perceived predation risk was primarily restricted to increased cover use, and hungry prey did not exhibit risk‐prone foraging. Surprisingly, hungry prey showed lower activity than sated prey when exposed to predation risk, perhaps indicating increased effort in search of refuge or spatial avoidance of predator cues among sated animals. An interaction between hunger level and predation risk treatments indicated that prey state affected sensitivity to perceived risk. We also examined the lethal implications of prey hunger by allowing predators to select directly between hungry and sated prey. Although predators qualitatively favoured hungry prey when density was elevated and structural cover was sparse, the overall low observed variation in mortality risk between hunger treatments suggests that preferential selection of hungry prey was weak. This implies that hunger effects on prey mortality risk may not be readily observed in complex landscapes with additional factors influencing risk. Thus, current starvation‐predation trade‐off theory may need to be broadened to account for other mechanisms through which undernourished prey may cope with predation risk.     

Foraging speed in staging flocks of semipalmated sandpipers: evidence for scramble competition

Foraging speed is a key determinant of fitness affecting both foraging success and predator attack survival. In a scramble for food, for instance, evolutionary stable strategy models predict that speed should increase with competitor density and decrease when the risk of attack by predators increases. Foraging speed should also decrease in richer food patches where the level of competition is reduced. I tested these predictions in fall staging flocks of semipalmated sandpipers (Calidris pusilla) foraging for an evasive prey. Capture rate of these prey decreased with sandpiper density as the presence of competitors reduced the availability of resources for those behind. Foraging speed was evaluated indirectly by measuring the time needed to cross fixed boundaries on mudflats over 6 years. As predicted, foraging speed increased with sandpiper density and decreased with food density, but, unexpectedly, increased closer to obstructive cover where predation risk was deemed higher. When foraging closer to cover, from where predators launch surprise attacks, the increase in foraging speed may compensate for an increase in false alarms that interrupted foraging. While foraging in denser flocks decreases foraging success, joining such flocks may also increase safety against predators. In semipalmated sandpipers that occupy an intermediate position in the food chain, foraging behavior is influenced simultaneously by the evasive responses of their prey and by the risk of attack from their own predators.     

Patch use in time and space for a meso-predator in a risky world

Predator–prey studies often assume a three trophic level system where predators forage free from any risk of predation. Since meso-predators themselves are also prospective prey, they too need to trade-off between food and safety. We applied foraging theory to study patch use and habitat selection by a meso-predator, the red fox. We present evidence that foxes use a quitting harvest rate rule when deciding whether or not to abandon a foraging patch, and experience diminishing returns when foraging from a depletable food patch. Furthermore, our data suggest that patch use decisions of red foxes are influenced not just by the availability of food, but also by their perceived risk of predation. Fox behavior was affected by moonlight, with foxes depleting food resources more thoroughly (lower giving-up density) on darker nights compared to moonlit nights. Foxes reduced risk from hyenas by being more active where and when hyena activity was low. While hyenas were least active during moon, and most active during full moon nights, the reverse was true for foxes. Foxes showed twice as much activity during new moon compared to full moon nights, suggesting different costs of predation. Interestingly, resources in patches with cues of another predator (scat of wolf) were depleted to significantly lower levels compared to patches without. Our results emphasize the need for considering risk of predation for intermediate predators, and also shows how patch use theory and experimental food patches can be used for a predator. Taken together, these results may help us better understand trophic interactions.     

Quantifying Predation Risk for Refuging Animals: A Case Study with Golden Marmots

Although a variety of behaviors expose animals to some risk of predation, there is no accepted way to compare their relative risk. For animals that retreat to refugia when alarmed by predators, the proportion of time devoted to each out-of-refuge behavior multiplied by the total time required to return to a refuge can be used to compare a behavior's relative predation risk. Total time to return to a refuge is a function of both response time - the time required to respond to an increased risk of predation — and travel time — the time required to flee to a refuge once alarmed. Quantifying these components can illustrate how animals minimize exposure to predators. Golden marmots (Marmota caudata aurea) were a refuging prey species used to examine the utility of this measure and to understand how marmots minimized their risk of exposure to predation. Golden marmots devoted different amounts of time to looking, foraging, self-grooming, and playing. To estimate the behavior-specific time required to return to refugia, the location of different activities was noted and a behavior-specific travel time was calculated. Alarm calls were played back to marmots engaged in different behaviors to determine, in a standardized manner, if there were behavior-specific response times. Marmots appeared to minimize their predation risk by performing most behaviors close to refugia. Results suggest that foraging was the riskiest behavior, largely because marmots foraged far from refugia and spent about 30% of their time foraging. While sample sizes were small, results also suggested that play, a rare adult behavior, exposed animals to predation because of a relatively long response time.