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Most carnivores undergo diet shift from smaller to larger prey items during ontogeny. The trophic relationship between a growing carnivore and larger prey is representative of a size‐structured predator–prey interaction. The strength of this interaction is, in part, determined by the recruitment of individuals from smaller predatory size classes into larger predatory size classes. Therefore, it is interesting to investigate how larger prey alter the recruitment of smaller predator size classes into larger predator size classes, since this can affect their own future predation risk. Past empirical studies have exclusively documented that large prey reduce predator recruitment by decreasing growth and/or survival of the smaller predators. In this study, we provide empirical evidence of the contrasting pattern: large prey enhance the recruitment of smaller predators into larger predators even though they increase cannibalism mortality of the smaller predators. We have done this here by studying the trophic interaction between predatory salamander larvae Hynobius retardatus and the frog tadpoles Rana pirica that represent their large prey. In a field experiment in which salamander hatchlings were exposed to the presence or absence of large frog tadpoles, we found that more giant salamanders emerged in the presence of frog tadpoles than in their absence. Reassignment of frog tadpoles (to both treatments) in the subsequent experimental period showed that the enhanced emergence of giant salamanders in the presence of frog tadpoles leads to the intensification of salamander predation on the frog tadpoles. In an additional laboratory experiment, to better understand the underlying mechanisms, we manipulated both the presence of frog tadpoles and the occurrence of cannibalism between salamander hatchlings. This experiment revealed that frog tadpoles intensify the cannibalism of salamander larvae during their hatchling stage, thus allowing more salamander larvae to become large‐sized predators. Our results suggest that frog tadpoles can inadvertently intensify their own future predation risk by intensifying cannibalistic interactions among predatory salamander hatchlings, thereby enhancing the degree of predator recruitment to a larger size class. Hence, large prey can enhance the recruitment of individuals from small predator size classes into larger predator size classes. Abstrakt 「サイズ構造のある捕食－被食系」の代表的な構造として、「成長する捕食者と大型餌種」の食う－食われるの関係がある。この構造において、捕食者種は成長することで大きな餌種を食えるようになるが、小さなサイズの段階においても大きな餌種と関係がないとは限らない。その成長や生存が大きな餌種によって影響を受ける場合がある。小さいサイズの捕食者個体の生存や成長は、大きなサイズの捕食者個体の加入に反映されるため、大きな餌種はその加入の程度を決めることで将来に被る捕食のリスクを自ら制御するといえる。このような系の性質から、サイズ構造のある捕食－被食系は、個体の特徴に種内変異がないことを前提とした従来の理論では予測できない個体群動態を示すと考えられてきた。このため、サイズ構造のある捕食－被食系の動態を理解するには、➀大きな餌種が小さいサイズ段階にある捕食者個体の生存や成長にどのような影響を与えるのか？②それが大きなサイズの捕食者個体の加入の程度を決め、結果的に大きな餌種の捕食リスクの強度にまで反映されるのか？を明らかにすることが重要である。 過去この問題に着目した研究は少なくないが、それらは一貫して、「大きな餌種が、大きなサイズの捕食者の加入を減らし、将来の捕食リスクを抑える」ことを示してきた。これは、大きな餌種と小さな捕食者が資源を巡って競争したり、大きな餌種が小さな捕食者を捕食することによって生じる。従来の研究とは対照的に、今回私たちは、「大きな餌種が大きなサイズの捕食者の加入を増やし、結果として、将来の捕食リスクを高める」場合があることを両生類2種のサイズ構造のある捕食－被食系で確かめた。 S. エゾサンショウウオ幼生は相手を丸のみにして食うタイプの捕食者種で、捕食できる餌の大きさは口の大きさで決まる。エゾサンショウウオ幼生は孵化直後に共食いをすると急激に成長し、大型の餌種であるエゾアカガエル幼生を食うことができる。私たちは、野外と室内で、エゾアカガエル幼生の在不在やエゾサンショウウオ幼生の共食いの有無を操作した実験を行った。 私たちは一連の実験によって、「エゾアカガエル幼生は、孵化直後のエゾサンショウウオ幼生の共食いを促進することで、大型化するエゾサンショウウオ幼生を増やし、結果的に将来自身が被る捕食圧を高めている」ことを明らかにした。大型の餌種と小さなサイズの捕食者との間に食う－食われる関係や競争関係がなかったとしても、大型餌種は小さなサイズの捕食者の採餌生態に関わることで捕食者の加入に影響するのだ。大きな餌種が捕食者の成長や加入に与える影響は多様であり、系特異的なプロセスとメカニズムに従っていると言えるだろう。 This study provides the first empirical evidence showing that large prey enhance recruitment of smaller predators into larger predatory stage by using a larval amphibian predator–prey interaction. In addition, the authors elucidated detailed mechanisms causing the effects. This paper advances our current understanding of the nature of size‐structured predator–prey interactions.

1. Ecologists have long searched for a framework of a priori species traits to help predict predator–prey interactions in food webs. Empirical evidence has shown that predator hunting mode and predator and prey habitat domain are useful traits for explaining predator–prey interactions. Yet, individual experiments have yet to replicate predator hunting mode, calling into question whether predator impacts can be attributed to hunting mode or merely species identity. 2. We tested the effects of spider predators with sit-and-wait, sit-and-pursue and active hunting modes on grasshopper habitat domain, activity and mortality in a grassland system. We replicated hunting mode by testing two spider predator species of each hunting mode on the same grasshopper prey species. We observed grasshoppers with and without each spider species in behavioural cages and measured their mortality rates, movements and habitat domains. We likewise measured the movements and habitat domains of spiders to characterize hunting modes. 3. We found that predator hunting mode explained grasshopper mortality and spider and grasshopper movement activity and habitat domain size. Sit-and-wait spider predators covered small distances over a narrow domain space and killed fewer grasshoppers than sit-and-pursue and active predators, which ranged farther distances across broader domains and killed more grasshoppers, respectively. Prey adjusted their activity levels and horizontal habitat domains in response to predator presence and hunting mode: sedentary sit-and-wait predators with narrow domains caused grasshoppers to reduce activity in the same-sized domain space; more mobile sit-and-pursue predators with broader domains caused prey to reduce their activity within a contracted horizontal (but not vertical) domain space; and highly mobile active spiders led grasshoppers to increase their activity across the same domain area. All predators impacted prey activity, and sit-and-pursue predators generated strong effects on domain size. 4. This study demonstrates the validity of utilizing hunting mode and habitat domain for predicting predator–prey interactions. Results also highlight the importance of accounting for flexibility in prey movement ranges as an anti-predator response rather than treating the domain as a static attribute.

Species exist within communities of other interacting species, so an exogenous force that directly affects one species can indirectly affect all other members of the community. In the case of climate change, many species may be affected directly and subsequently initiate numerous indirect effects that propagate throughout the community. Therefore, the net effect of climate change on any one species is a function of the direct and indirect effects. We investigated the direct and indirect effects of climate warming on corn leaf aphids, a pest of corn and other grasses, by performing an experimental manipulation of temperature, predators, and two common aphid-tending ants. Although warming had a positive direct effect on aphid population growth rate, warming reduced aphid abundance when ants and predators were present. This occurred because winter ants, which aggressively defend aphids from predators under control temperatures, were less aggressive toward predators and less abundant when temperatures were increased. In contrast, warming increased the abundance of cornfield ants, but they did not protect aphids from predators with the same vigor as winter ants. Thus, warming broke down the ant-aphid mutualism and counterintuitively reduced the abundance of this agricultural pest.

Protist grazing pressure plays a major role in controlling aquatic bacterial populations, affecting energy flow through the microbial loop and biogeochemical cycles. Predator-escape mechanisms might play a crucial role in energy flow through the microbial loop, but are yet understudied. For example, some bacteria can use planktonic as well as surface-associated habitats, providing a potential escape mechanism to habitat-specific grazers. We investigated the escape response of the marine bacterium Marinobacter adhaerens in the presence of either planktonic (nanoflagellate: Cafeteria roenbergensis) or surface-associated (amoeba: Vannella anglica) protist predators, following population dynamics over time. In the presence of V. anglica, M. adhaerens cell density increased in the water, but decreased on solid surfaces, indicating an escape response towards the planktonic habitat. In contrast, the planktonic predator C. roenbergensis induced bacterial escape to the surface habitat. While C. roenbergensis cell numbers dropped substantially after a sharp initial increase, V. anglica exhibited a slow, but constant growth throughout the entire experiment. In the presence of C. roenbergensis, M. adhaerens rapidly formed cell clumps in the water habitat, which likely prevented consumption of the planktonic M. adhaerens by the flagellate, resulting in a strong decline in the predator population. Our results indicate an active escape of M. adhaerens via phenotypic plasticity (i.e., behavioral and morphological changes) against predator ingestion. This study highlights the potentially important role of behavioral escape mechanisms for community composition and energy flow in pelagic environments, especially with globally rising particle loads in aquatic systems through human activities and extreme weather events.

Natural populations are heterogeneous mixtures of individuals differing in physiology, morphology, and behavior. Despite the ubiquity of phenotypic variation within natural populations, its effects on the dynamics of ecological communities are not well understood. Here, we use a quantitative genetics framework to examine how phenotypic variation in a predator affects the outcome of apparent competition between its two prey species. Classical apparent competition theory predicts that prey have reciprocally negative effects on each other. The addition of phenotypic trait variation in predation can marginalize these negative effects, mediate coexistence, or generate positive indirect effects between the prey species. Long-term coexistence or facilitation, however, can be preceded by long transients of extinction risk whenever the heritability of phenotypic variation is low. Greater heritability can circumvent these ecological transients but also can generate oscillatory and chaotic dynamics. These dramatic changes in ecological outcomes, in the sign of indirect effects, and in stability suggest that studies which ignore intraspecific trait variation may reach fundamentally incorrect conclusions regarding ecological dynamics.

Animal Vigilance builds on the author's previous publication with Academic Press (Social Predation: How Group Living Benefits Predators and Prey) by developing several other themes including the development and mechanisms underlying vigilance, as well as developing more fully the evolution and function of vigilance.Animal vigilance has been.

The functional response is a key element of predator–prey interactions, and variations in its parameters influence interaction strength and population dynamics. Recent studies have used the equation of the metabolic theory of ecology (MTE) to quantify the effect of temperature on the parameter Th, called “handling time,” and then predict the responses of predators and communities to climate change. However, our understanding of the processes behind Th and how they vary with temperature remains limited. Using a ladybeetle–aphid system, we compared estimates of Th to direct observations of handling time across a temperature gradient. We found estimated Th values to be greater than observed Th values, suggesting that predation rate is not limited by the time available for handling prey. We next estimated the corrected digestion time, i.e., digestion time corrected for gut capacity, by subtracting observed to estimated Th values. We finally plotted the relationships between temperature and handling or digestion rates. As predicted by MTE, the corrected digestion rate increased exponentially with warming whereas, in contrast to MTE prediction, the relationship between handling rate and temperature was hump shaped. The parameter Th is thus confusing because it combines handling and digestive processes that have different thermal responses. This may explain why general patterns in the relationship between Th and temperature have been difficult to identify in previous studies.

1. In response to multiple Stressors, coral reef health has declined in recent decades, with reefs exhibiting reduced living coral and structural complexity, and a concomitant rise in the dominance of algal resources. Reef degradation alters food availability and reduces the diversity and density of refuges for prey. These changes affect predator-prey interactions and can have cascading impacts on food webs and fisheries productivity. 2. We use a size-based ecosystem model of coral reefs that incorporates the influence of structural complexity, benthic primary production and detrital recycling to explore how predator-prey interactions and fisheries productivity respond to a gradient of reef degradation. 3. We show that fisheries productivity overall may be robust to initial stages of reef degradation because the benefits of increased resources outweigh the costs of moderate refuge decline. However, the assemblage composition and size structure of reef fish will differ on degraded reefs, with herbivores and invertivores contributing relatively more to productivity. 4. More significant losses of refuges associated with the erosion of structural complexity correspond to fisheries productivity losses of at least 35% compared to healthy reefs. 5. Synthesis and applications. Our model provides fisheries managers with quantitative predictions about how fisheries productivity may change in response to the ongoing degradation of coral reefs. We predict an initial increase in productivity at intermediate reef degradation, followed by a drastic decline when structural complexity is lost. We also capture subtle changes to potential catch composition and fish size, including increases in smaller herbivorous and invertivorous fish from degraded reefs, which will undoubtedly impact fisheries value. On the one hand, our results reassure for continued productivity in the short term, but on the other, we warn against complacency. Management must change to capture any potential benefits to fisheries, and long-term sustainability still depends on the maintenance of complex coral reef habitats.

Predator effects on prey dynamics are conventionally studied by measuring changes in prey abundance attributed to consumption by predators. We revisit four classic examples of predator—prey systems often cited in textbooks and incorporate subsequent studies of nonconsumptive effects of predators (NCE), defined as changes in prey traits (e.g., behavior, growth, development) measured on an ecological time scale. Our review revealed that NCE were integral to explaining lynx—hare population dynamics in boreal forests, cascading effects of top predators in Wisconsin lakes, and cascading effects of killer whales and sea otters on kelp forests in nearshore marine habitats. The relatives roles of consumption and NCE of wolves on moose and consequent indirect effects on plant communities of Isle Royale depended on climate oscillations. Nonconsumptive effects have not been explicitly tested to explain the link between planktonic alewives and the size structure of the zooplankton, nor have they been invoked to attribute keystone predator status in intertidal communities or elsewhere. We argue that both consumption and intimidation contribute to the total effects of keystone predators, and that characteristics of keystone consumers may differ from those of predators having predominantly NCE. Nonconsumptive effects are often considered as an afterthought to explain observations inconsistent with consumption-based theory. Consequently, NCE with the same sign as consumptive effects may be overlooked, even though they can affect the magnitude, rate, or scale of a prey response to predation and can have important management or conservation implications. Nonconsumptive effects may underlie other classic paradigms in ecology, such as delayed density dependence and predator-mediated prey coexistence. Revisiting classic studies enriches our understanding of predator—prey dynamics and provides compelling rationale for ramping up efforts to consider how NCE affect traditional predator—prey models based on consumption, and to compare the relative magnitude of consumptive and NCE of predators.

Predator functional responses describe predator feeding rates and are central to predator–prey theory. Ecologists have measured thousands of predator functional responses using the same basic experimental method. However, this design is ill-suited to address many current questions regarding functional responses. We derive a new experimental design and statistical analysis that quantifies functional responses using the times between a predators’ feeding events requiring only one or a few trials. We examine the feasibility of the experimental method and analysis using simulations to assess the ability of the statistical model to estimate functional response parameters and perform a proof-of-concept experiment estimating the functional responses of two individual jumping spiders. Our simulations show that the statistical method reliably estimates functional response parameters. Our proof-of-concept experiment illustrates that the method provides reasonable estimates of functional response parameters. By virtue of the fewer number of trials required to measure a functional response, the method derived here promises to expand the questions that can be addressed using functional response experiments and the systems in which they can be measured. Thus, we hope that our method will refine our understanding of functional responses and predator–prey interactions more generally.