Predator Feeding Rates Research Articles

Functional response of larval and adult Coccinella septempunctata to eggs and larvae of Plutella xylostella on canola

AbstractUnderstanding of functional responses (i.e., changes in predator feeding rates with prey density) of key predators to different crop pest stages is critical to strengthening biological control, particularly in view of climate change and temperature variation. We investigated prey preferences of Coccinella septempunctata L. (Coleoptera: Coccinelidae) to egg and larval stages of a key brassicaceous pest of canola (Brassica napus L., Brassicaceae), the diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae). First, laboratory choice and no‐choice bioassays tested the hypotheses that C. septempunctata accepts and differentially prefers two prey developmental stages (eggs and larvae). Then, C. septempunctata larvae and adults were exposed to six densities of P. xylostella eggs over 24 h in functional response bioassays that determined the number of eggs consumed. Finally, the functional response bioassays were repeated with larval prey and extended with three temperature regimes: 10, 22 and 32 °C. In both choice and no‐choice assays, C. septempunctata adults and larvae consumed more P. xylostella larvae than eggs. The functional response of C. septempunctata depended on predator developmental stage and temperature, with reduced handling time and increased attack rates and consumption under warmer conditions. At 10 and 22 °C, the functional responses of both C. septempunctata larvae and adults were of Type II, i.e., rates of prey consumption increase at decelerating rates and then plateau with increasing prey density. Our study demonstrates that both larvae and adults of C. septempunctata can consume high numbers of eggs and early instar P. xylostella larvae; these responses are temperature‐dependent with increased consumption rates at higher temperatures. This may lead to improvements in management of P. xylostella in canola.

Quantifying predator functional responses under field conditions reveals interactive effects of temperature and interference with sex and stage.

Predator functional responses describe predator feeding rates and are central to predator–prey theory. Originally defined as the relationship between predator feeding rates and prey densities, it is now well known that functional responses are shaped by a multitude of factors. However, much of our knowledge about how these factors influence functional responses is based on laboratory studies that are generally logistically constrained to examining only a few factors simultaneously and that have unclear links to the conditions organisms experience in the field.We apply an observational approach for measuring functional responses to understand how sex/stage differences, temperature and predator densities interact to influence the functional response of zebra jumping spiders on midges under natural conditions.We used field surveys of jumping spiders to infer their feeding rates and examine the relationships between feeding rates, sex/stage, midge density, predator density and temperature using generalized additive models. We then used the relationships supported by the models to fit parametric functional responses to the data.We find that feeding rates of zebra jumping spiders follow some expectations from previous laboratory studies such as increasing feeding rates with body size and decreasing feeding rates with predator densities. However, in contrast to previous results, our results also show a lack of temperature response in spider feeding rates and differential decreases in the feeding rates of females and juveniles with densities of different spider sexes/stages.Our results illustrate the multidimensional nature of functional responses in natural settings and reveal how factors influencing functional responses can interact with one another through behaviour and morphology. Further studies investigating the influence of multiple mechanisms on predator functional responses under field conditions will increase our understanding of the drivers of predator–prey interaction strengths and their consequences for communities and ecosystems.

Quantifying the effects of intraspecific variation on predator feeding rates through nonlinear averaging

Abstract Theory suggests that intraspecific trait variation will alter species interaction strengths through nonlinear averaging when interaction strengths are nonlinear functions of individuals' traits. This effect is expected to be widespread, yet what factors mediate its magnitude in nature and hence its potential effects on ecosystems and communities are unclear. We sought to quantify how nonlinear predator functional responses, variation in prey densities and counteracting variation in attack rates and handling times among predator individuals of similar body size alter their population‐level feeding rates through nonlinear averaging in a natural system, and to determine the processes influencing the net magnitude of this effect. We used a field caging experiment in the rocky intertidal of Oregon, USA to quantify attack‐rate variation and feeding rates of the whelk Nucella ostrina on its barnacle and mussel prey. We also used empirically parameterized simulations to examine the effects of handling‐time variation among individuals on population‐level feeding rates. Within cages, individual attack‐rate variation reduced population‐level whelk feeding rates. However, the magnitude of this reduction differed among prey species and cages depending on cage‐specific magnitudes of attack‐rate variation and functional‐response nonlinearity. The inferred effects of handling‐time variation among individuals were of smaller magnitude than those of attack‐rate variation, yet counteracted them to cause a net weakening of the effect of individual attack‐rate variation on population‐level feeding rates. Across cages, attack‐rate and prey‐density variation had non‐additive effects that produced greater feeding‐rate reductions at the experiment scale relative to the cage scale. Our results indicate that the effects of trait variation via nonlinear averaging depend critically on the features of systems that determine the magnitudes of nonlinearities and trait variation. Because of counteracting trait variation, nonlinear‐averaging effects may be quite complex, involving both the variances and covariances of all traits and environmental variables influencing the ecological process of interest. A free Plain Language Summary can be found within the Supporting Information of this article.

Estimating predator functional responses using the times between prey captures.

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.

Feeding rate and efficiency in an apex soil predator exposed to short-term temperature changes

As extreme climate events become more frequent and intense, short-term temperature responses of ectothermic organisms can lead to decreased performance and survival. However, organisms may acclimate to these conditions through behavioural and physiological mechanisms as exposure time increases. We used a reciprocal temperature (16 °C and 24 °C) transplant experiment to determine how feeding rate and body size of an apex soil mite predator (Stratiolaelaps scimitus) (formerly Hypoaspis miles) consuming prey (Carpoglyphus lactis) (dried-fruit-mite) changed along a gradient of acclimation time (1, 3, and 7 days, with control). In the control treatments, mites reared at 24 °C fed more, but were smaller than mites reared at 16 °C. When transferred to new temperature conditions, predators that experienced cooling events had reduced feeding efficiencies driven by decreased feeding performance, despite an absence of metabolic costs, while under warming events, predators also had reduced feeding activity, but feeding increased with acclimation time. Yet predators lost more weight the longer they were exposed to warming, and continued to experience reduced feeding efficiencies (i.e., lack of weight gain after feeding); this result suggests increased metabolic costs at higher temperatures and provides a mechanism for community downsizing under warming. Overall, our results suggest that ectothermic predators can acclimate to warming events with increased exposure time, but both warming and cooling events decrease overall performance.

Foraging strategy mediates ectotherm predator-prey responses to climate warming.

Climate warming and species traits interact to influence predator performance, including individual feeding and growth rates. However, the effects of an important trait-predator foraging strategy-are largely unknown. We investigated the interactions between predator foraging strategy and temperature on two ectotherm predators: an active predator, the backswimmer Notonecta undulata, and a sit-and-wait predator, the damselfly Enallagma annexum. In a series of predator-prey experiments across a temperature gradient, we measured predator feeding rates on an active prey species, zooplankton Daphnia pulex, predator growth rates, and mechanisms that influence predator feeding: body speed of predators and prey (here measured as swimming speed), prey encounter rates, capture success, attack rates, and handling time. Overall, warming led to increased feeding rates for both predators through changes to each component of the predator's functional response. We found that prey swimming speed strongly increased with temperature. The active predator's swimming speed also increased with temperature, and together, the increase in predator and prey swimming speed resulted in twofold higher prey encounter rates for the active predator at warmer temperatures. By contrast, prey encounter rates of the sit-and-wait predator increased fourfold with rising temperatures as a result of increased prey swimming speed. Concurrently, increased prey swimming speed was associated with a decline in the active predator's capture success at high temperatures, whereas the sit-and-wait predator's capture success slightly increased with temperature. We provide some of the first evidence that foraging traits mediate the indirect effects of warming on predator performance. Understanding how traits influence species' responses to warming could clarify how climate change will affect entire functional groups of species.

Predator‐dependent functional responses alter the coexistence and indirect effects among prey that share a predator

Predator functional responses describe predator feeding rates as a function of prey abundance and are central to predator–prey theory. Despite ample evidence that functional responses also depend on predator abundance, theory incorporating predator‐dependent functional responses has focused almost exclusively on specialist predator–prey pairs or linear food chains. This leaves a large gap in our knowledge as many predators feed on multiple prey, and in so doing, generate indirect effects among prey that can alter their coexistence. Here we investigate how predator‐dependent functional responses in a one predator–two prey model alter the coexistence among prey and their net effects on one another. We use two different functional response forms (the Beddington–DeAngelis and Crowley–Martin functional responses) and consider situations in which the prey do not directly interact and in which they directly compete with one another. We find that predator dependence can facilitate, hinder, or have no effect on prey coexistence depending on whether prey compete directly and the role of predation in mediating coexistence among the prey in the absence of predator dependence. We also show that the negative net effects of prey on one another are generally weakened by predator dependence and can become positive under the Crowley–Martin functional response. Together, these results suggest that predator dependence may have widespread effects on ecological communities by altering the coexistence among prey species and the strength and signs of the interactions among them.

Temperature and prey density jointly influence trophic and non‐trophic interactions in multiple predator communities

AbstractEnvironmental changes such as global warming can affect ecological communities by altering individual life histories and species interactions. Recent studies focusing on the consequences of environmental change on species interactions highlighted the need for a wider, multi‐species context including both trophic and non‐trophic interactions (e.g. predator interference). However, the effects of biotic and abiotic factors on trophic and non‐trophic interactions remain largely unexplored.To fill this gap, we combined laboratory experiments and functional response modelling to investigate how temperature and prey density influence trophic and non‐trophic interactions in multiple predator communities.The system under study consisted of predatory dragonfly larvae (Aeshna cyanea) and omnivorous marbled crayfish (Procambarus virginalis) preying on common carp fry (Cyprinus carpio). We estimated the functional response of each predator in single‐predator experiments and used this information to disentangle the trophic and non‐trophic interactions and their dependence on environmental conditions in multiple predator trials.We found that consumer identity, prey density, and temperature all affect the magnitude of trophic and non‐trophic interactions. Non‐trophic interactions mostly decreased predator feeding rates, corroborating previous observations that interference prevails in aquatic communities. Moreover, trophic interactions depended primarily on the environmental variables whereas non‐trophic interactions depended mainly on consumer identity.Our results indicate that non‐trophic interactions among true predators and omnivores can be substantial and that biotic and abiotic conditions further modify the magnitude and direction of these interactions, which can affect food web dynamics and stability.

Combined impacts of warming and salinisation on trophic interactions and mortality of a specialist ephemeral wetland predator

Abstract Wetlands are of enormous importance for biodiversity globally but are under increasing risk from multiple stressors driven by ongoing anthropogenic environmental change. As the trophic structure and dynamics of ephemeral wetlands are poorly understood, it is difficult to predict how these biodiverse ecosystems will be impacted by global change. In particular, warming and salinisation are projected to have profound impacts on these wetlands in future. The present study examined the combined effects of warming and salinisation on species interaction strengths and mortality rates for two ephemeral wetland species. Using an ephemeral pond specialist copepod, Lovenula raynerae Suárez‐Morales, Wasserman, & Dalu, (2015) as a model predator species, we applied a functional response approach to derive warming and salinisation effects on trophic interactions with a prey species. Furthermore, the effects of a salinisation gradient on mortality rates of adult copepods were quantified. The predatory copepod exhibited type II functional responses towards larval Culex pipiens mosquito prey, owing to high predation rates at low prey densities. Increased temperatures generally resulted in greater predator feeding rates, whilst increased salinities reduced consumption. However, the effects of temperature and salinity interacted: temperature effects on functional responses were suppressed under heightened salinities. Substantial mortality was observed in both male and female adult L. raynerae at salinity levels exceeding 10 parts per thousand. Warming and salinisation substantially altered interaction strengths in ephemeral wetland ecosystems, with implications for ecosystem function and stability. Furthermore, we demonstrated salinisation thresholds for mortality in an ephemeral wetland specialist, showing that salinisation may threaten the persistence of endemic species. The ongoing effects of warming and salinisation may therefore interact to alter trophic dynamics and species composition in ephemeral wetlands. These stressors should be considered synergistically within management practices.

Predation risk and habitat complexity modify intermediate predator feeding rates and energetic efficiencies in a tri‐trophic system

Abstract To understand the effects of environmental changes on ecosystems, it is important to determine the factors and mechanisms influencing the strength of species interactions in food webs. However, joint effects of predation risk and additional environmental factors on species interaction strengths in multitrophic systems remain largely unexplored, leaving a substantial gap in our understanding of the links between local environmental characteristics and food web properties. To fill this gap, we investigated the effects of habitat complexity and predation risk by top predatory dragonfly larvae (Aeshna cyanea) on feeding rates and energetic efficiency (i.e. the ratio of acquired and expended energy) of the larvae of three intermediate predatory odonate species (Libellula quadrimaculata, Sympetrum sanguineum, and Ischnura elegans) preying on cladocerans. We hypothesised that predation risk would decrease the feeding rate, especially in the structurally simple habitat, and increase the metabolic rate of all intermediate predators. We also expected higher feeding rates of intermediate predators using aquatic vegetation as a perching site (i.e. Sympetrum and Ischnura) in the structurally complex habitat. Finally, we expected to observe habitat‐ and predation risk‐dependent energetic efficiencies of the intermediate predators driven by changes in feeding and metabolic rates. The effect of predation risk on feeding rates was species specific and differed between the structurally simple and complex habitat. Habitat complexity increased feeding rates but only in the absence of predation risk. Moreover, predation risk signalled by chemical cues significantly increased Sympetrum vulgatum feeding rates but did not influence the feeding rates of the two other intermediate predators. Metabolic rates varied among the three intermediate predators but were not affected by predation risk. Estimated energetic efficiency decreased with intermediate predator body mass and depended, to a lesser extent, on the interactive effect of habitat complexity and predation risk. Our results imply that the effects of habitat complexity and predation risk on trophic interactions are likely to be determined by traits related to foraging and defence of the intermediate predators and their habitat domains, and that energetic efficiency is mainly determined by predator mass. Given that habitat complexity and predation risk can vary substantially across habitats, we conclude that it is important to consider habitat complexity and predation risk to better understand and predict the effects of environmentally driven variations on trophic interaction strength and metabolic rates that underlie the energetic efficiency of individual consumers. This has important implications for population and community dynamics as well as ecosystem functioning.

Ocean acidification may alter predator-prey relationships and weaken nonlethal interactions between gastropods and crabs

Predator–prey interactions often drive ecological patterns and are governed by factors including predator feeding rates, prey behavioral avoidance, and prey structural defenses. Invasive species can also play a large ecological role by disrupting food webs, driving local extinctions, and influencing evolutionary changes in prey defense mechanisms. This study documents a substantial reduction in the behavioral and morphological responses of multiple gastropod species (Nucella lapillus, N. ostrina, Urosalpinx cinerea) to an invasive predatory crab (green crab Carcinus maenas) under ocean acidification conditions. These results suggest that climate-related changes in ocean chemistry may diminish non-lethal effects of predators on prey responses including behavioral avoidance. While snails with varying shell mineralogies were similarly successful at deterring predation, those with primarily aragonitic shells were more susceptible to dissolution and erosion under high CO2 conditions. The varying susceptibility to predation among species with similar ecological roles could indicate that the impacts of invasive species like green crabs could be modulated by the ability of native and invasive prey to withstand ocean acidification conditions.

Hidden predators on coral reefs: muricid consumption of vermetids

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 615:121-131 (2019) - DOI: https://doi.org/10.3354/meps12920 Hidden predators on coral reefs: muricid consumption of vermetids A. L. Brown1,2,*, T. K. Frazer2,3, G. Li4, J. R. Hilsenroth2, J. S. Shima5, C. W. Osenberg1 1Odum School of Ecology, University of Georgia, Athens, GA 30602, USA 2School of Natural Resource and Environment, University of Florida, Gainesville, FL 32611, USA 3School of Forest Resources and Conservation, Fisheries and Aquatic Sciences Program, University of Florida, Gainesville, FL 32611, USA 4UC Berkeley Richard B. Gump Marine Station, BP 244, Maharepa 98728, Mo’orea, French Polynesia 5School of Biological Sciences, Victoria University of Wellington, Wellington 6140, New Zealand *Corresponding author: anyabrown@ufl.edu ABSTRACT: Predators, through their effects on prey densities, sizes, and behaviors, can shape ecological communities. Thus, quantitative assessments of predator-prey relationships are key to understanding these effects. Here, we documented the patterns and processes underlying the effects of 2 predatory muricid gastropods, Mancinella armigera and Menathais tuberosa, on the sessile vermetid gastropod Ceraesignum maximum. We used a combination of field surveys and manipulative lab and field experiments to quantify muricid abundances, predator feeding rates, and effects of predator density on vermetid mortality. The 2 predators exhibited spatial segregation, with M. armigera being more common close to the reef crest and M. tuberosa increasing in density away from and shoreward of the reef crest. We demonstrated that recently killed vermetids were more common in the vicinity of M. armigera. Laboratory assays revealed that M. armigera killed 0.55 C. maximum predator-1 d-1, a rate that was ~60% greater than for M. tuberosa. Although the 2 predators were spatially segregated in the field, they did not demonstrate interference competition or intraguild predation in the lab. Consumption rates of C. maximum by M. armigera in the field were approximately equal to those quantified in the lab, and although consumption rates decreased over time, predator density had no effect on predator consumption rate. In addition, we observed no evidence of size selectivity by predators. This study is the first to quantitatively examine predator-prey interactions involving C. maximum, and our findings suggests that muricids can limit vermetid populations where both are present. KEY WORDS: Predation · Ceraesignum maximum · Multiple predator effects · Coral reefs Full text in pdf format Supplementary material PreviousNextCite this article as: Brown AL, Frazer TK, Li G, Hilsenroth JR, Shima JS, Osenberg CW (2019) Hidden predators on coral reefs: muricid consumption of vermetids. Mar Ecol Prog Ser 615:121-131. https://doi.org/10.3354/meps12920 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 615. Online publication date: April 18, 2019 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2019 Inter-Research.

A Beddington–DeAngelis type one-predator two-prey competitive system with help

In this paper, we present and study a two competing prey and one predator system where during predation both the teams of prey help each other and the rate of predation on both the teams are different. The prey consumption rate per individual of predator is considered as Beddington–DeAngelis type. Beddington–DeAngelis type functional response describes predator feeding rate depending on both the prey and predator density. Ecological significance of considering this type of functional response depends on how frequently a predator encounters another predator while feeding on the same type of prey, resulting in strong intraspecific competition and thereby reducing the predator feeding rate. Firstly we establish persistence and permanence of the system and examine the role of cooperation coefficient. Different conditions for the coexistence of equilibrium solutions are discussed. Then the local asymptotic stability of various equilibrium points and the existence of Hopf bifurcation at the positive equilibrium are carried out to understand the dynamics of the model system. The Kolmogorov analysis of subsystems suggests for the existence of transcritical bifurcation. Sufficient conditions for the nonexistence of periodic orbits of the considered model system have been presented. The analytical results found in this paper are illustrated with the help of numerical examples.

Impacts of deforestation‐induced warming on the metabolism, growth and trophic interactions of an afrotropical stream fish

Abstract In ectotherms, anthropogenic warming often increases energy requirements for metabolism, which can either impair growth (when resources are limiting) or lead to higher predator feeding rates and possibly stronger top–down trophic interactions. However, the relative importance of these effects in nature remains unclear because: (1) thermal adaptation or acclimation could lower metabolic costs; (2) greater prey production at warmer temperatures could compensate for higher predator feeding rates; and/or (3) temperature effects on trophic interactions via altered biological rates could be small relative to other, temperature‐unrelated human impacts on food webs. Here, we examined effects of deforestation‐associated warming on the minnow Enteromius neumayeri, occurring in both forested (cool) and deforested (warm) streams located inside or nearby an afrotropical rainforest. Combining approaches from physiological and community ecology, we quantified impacts of anthropogenic warming on the metabolism, growth and trophic interactions of this tropical ectotherm. We then compared these effects with impacts of land use unrelated to temperature. In a long‐term laboratory acclimation experiment quantifying the temperature dependence of growth and metabolism in E. neumayeri, warming increased metabolic rates and decreased growth (at a limited ration). We found no evidence of local (thermal) adaptation, with warming affecting farm and forest populations similarly. Then, using mark–recapture methods to quantify impacts of warming on performance in situ, we found similar growth rates in fish from deforested and forested streams despite their distinct thermal environments. This suggests higher prey consumption at deforested sites to compensate for greater metabolic costs, which could strengthen fish–invertebrate interactions. Finally, we developed a bioenergetics model to estimate fish–invertebrate interaction strength and quantify temperature‐related and unrelated impacts of land use on this interaction. We found that although warming increased fish consumption, it apparently increased invertebrate production even more and thus had a net‐weakening effect on estimated interaction strength. Most importantly, variation in both fish and invertebrate density not directly related to temperature had a much stronger influence on estimated interaction strength than temperature effects on predator consumption and prey growth. We conclude that ectotherms can sometimes offset the metabolic costs of warming with a small increase in consumption that hardly effects food web interactions compared to non‐metabolic impacts of anthropogenic disturbances. Future research should assess whether this is a common feature of heavily impacted ecosystems facing multiple stressors. A plain language summary is available for this article.

Using Survival Models to Estimate Invertebrate Prey Identification Times in a Generalist Stream Fish

AbstractEstimates of predator feeding rates are important for understanding trophic dynamics. One common method for quantifying feeding rates in fishes combines mass‐based diet data with gastric evacuation times to estimate prey mass consumed per predator. An alternative approach is to estimate the rates of prey individuals consumed using prey identification time—the time period over which prey remain identifiable in a predator's stomach. One challenge with the analysis of prey identification times, however, is that the response variable is likely to be censored because the “true” prey identification time cannot be observed directly. Here, we applied survival analysis that can incorporate censored data to estimate the effects of predator body size, water temperature, and prey characteristics (type, count, and body size) on identification times in Reticulate Sculpin Cottus perplexus. We focused on seven types of prey that are common in this generalist predator's diet: mayflies (Ephemeroptera), caddisflies (Trichoptera), stoneflies (Plecoptera), true flies (Diptera), beetles (Coleoptera), worms (Annelida), and sculpin eggs. An information‐theoretic model comparison approach indicated that an accelerated failure time Weibull model with all five covariates provided the best relative fit to the full data set. Prey type had a strong effect on prey identification time, with annelid worms having the shortest times (<1 h) and caddisflies having the longest times (>15 h). Water temperature decreased prey identification time (7.5% per 1°C increase), whereas prey count (i.e., meal size) increased prey identification time (15.5% per additional prey item). Predator body size had a weak negative effect on prey identification time (0.04% per 1‐mm increase). Body sizes of some prey taxa, including mayflies, caddisflies, and stoneflies, increased prey identification times, leading to an interaction between prey type and prey size. Our study highlights the utility of survival analysis for quantifying variation in prey identification times in the diets of generalist predators.

Functional Response of Phytoseiulus persimilis (Acari: Phytoseiidae) on Untreated and Beauveria bassiana - Treated Adults of Tetranychus urticae (Acari: Tetranychidae)

The functional response of the predatory mite, Phytoseiulus persimilis Athias- Henriot was examined on either non-inoculated or inoculated adults of the spider mite, Tetranychus urticae Koch by Beauveria bassiana DEBI008 with four time intervals; 0, 24, 48 and 72-h treatments, at 25 ± 1 °C, 60–70 % RH and a photoperiod of 16:8 h (L: D). Results indicated that functional responses of P. persimilis on both untreated and B. bassiana treated adults of T. urticae are type II. Data analysis showed that handling time of predator was increased on treated T. urticae with the increase of the time after spray in comparison with that of untreated adults of T. urticae (3.5143, 3.8152, 4.0735, 7.6829 and 11.7789 h.), respectively. Differences among treatments for handling time were significant. Attack rates were close to each others and there was no significant difference in attack rates of different time interval treatments. With the increase of the time after spray adults of the spider mite, T. urticae by B. bassiana caused intensive increasing in handling time of P. persimilis and accordingly it caused intensive decreasing in feeding rate of predator.

Using functional response modeling to investigate the effect of temperature on predator feeding rate and energetic efficiency

Temperature is one of the most important environmental parameters influencing all the biological processes and functions of poikilothermic organisms. Although extensive research has been carried out to evaluate the effects of temperature on animal life histories and to determine the upper and lower temperature thresholds as well as the optimal temperatures for survival, development, and reproduction, few studies have investigated links between thermal window, metabolism, and trophic interactions such as predation. We developed models and conducted laboratory experiments to investigate how temperature influences predator-prey interaction strengths (i.e., functional response) using a ladybeetle larva feeding on aphid prey. As predicted by the metabolic theory of ecology, we found that handling time exponentially decreases with warming, but--in contrast with this theory--search rate follows a hump-shaped relationship with temperature. An examination of the model reveals that temperature thresholds for predation depend mainly on search rate, suggesting that predation rate is primarily determined by searching activities and secondly by prey handling. In contrast with prior studies, our model shows that per capita short-term predator-prey interaction strengths and predator energetic efficiency (per capita feeding rate relative to metabolism) generally increase with temperature, reach an optimum, and then decrease at higher temperatures. We conclude that integrating the concept of thermal windows in short- and long-term ecological studies would lead to a better understanding of predator-prey population dynamics at thermal limits and allow better predictions of global warming effects on natural ecosystems.

Seasonal variation in the functional response of a coral-reef piscivore alters the inverse density-dependent mortality of its prey

Density-dependent processes are critical for regulating species' populations, and piscivory of coral-reef fishes is frequently density dependent. However, the mechanism driving this density-dependent mortality is poorly understood, but may be caused by changes in a predator's feeding rate at different prey densities (its functional response). An aquarium experiment replicated in winter and summer examined the functional response after 22 and 47 h of Cephalopholis cruentata feeding on Halichoeres pictus. With the exception of summer data after 47 h (density-independent mortality), mortality was inversely density dependent across all prey densities and increased with higher summer temperatures. The absence of an asymptotic pattern of inverse density-dependent mortality was caused by type II (summer) or dome-shaped type IV (winter) functional responses, with the benefits of schooling likely to cause the low mortality rates at higher prey densities. Predators' functional responses may underlie the inverse density-dependent mortality reported in field studies of aggregating fishes.

Differences in Relative Predation Vulnerability Between Native and Non-native Oyster Larvae and the Influence on Restoration Planning in an Estuarine Ecosystem

The costs and benefits of non-native introductions as a restoration tool should be estimated prior to any action to prevent both undesirable consequences and waste of restoration resources. The suggested introduction of non-native oyster species, Crassostrea ariakensis, into Chesapeake Bay, USA, provides a good example in which the survival of non-native oysters may differ from that of native oysters, Crassostrea virginica, during the larval stage. Experiments were conducted to compare the predation vulnerability of native and non-native oyster larvae to different predator types (visual vs. non-visual, benthic vs. pelagic). The results suggest that the non-native larvae are more vulnerable to visual and non-visual pelagic predators. Although vulnerability was similar for larvae exposed to benthic non-visual predators, the consumption of one non-native strain was higher than the consumption of native C. virginica larvae. When vulnerability data are combined with predator feeding rates, the predation mortality for non-native larvae in the wild can be much higher than for native larvae. Small changes in larval mortality rates can yield large changes in total larval delivery to the reef for settlement, so these differences among species may contribute to differences in settlement success. These results provide an example of how a comprehensive examination of the perceived benefits of non-native introductions into complex ecosystems can provide important information to inform management decisions.

Warming up the system: higher predator feeding rates but lower energetic efficiencies

Predictions on the consequences of the rapidly increasing atmospheric CO2 levels and associated climate warming for population dynamics, ecological community structure and ecosystem functioning depend on mechanistic energetic models of temperature effects on populations and their interactions. However, such mechanistic approaches combining warming effects on metabolic (energy loss of organisms) and feeding rates (energy gain by organisms) remain a key, yet elusive, goal. Aiming to fill this void, we studied the metabolic rates and functional responses of three differently sized, predatory ground beetles on one mobile and one more resident prey species across a temperature gradient (5, 10, 15, 20, 25 and 30 °C). Synthesizing metabolic and functional-response theory, we develop novel mechanistic predictions how predator–prey interaction strengths (i.e., functional responses) should respond to warming. Corroborating prior theory, warming caused strong increases in metabolism and decreases in handling time. Consistent with our novel model, we found increases in predator attack rates on a mobile prey, whereas attack rates on a mostly resident prey remained constant across the temperature gradient. Together, these results provide critically important information that environmental warming generally increases the direct short-term per capita interaction strengths between predators and their prey as described by functional-response models. Nevertheless, the several fold stronger increase in metabolism with warming caused decreases in energetic efficiencies (ratio of per capita feeding rate to metabolic rate) for all predator–prey interactions. This implies that warming of natural ecosystems may dampen predator–prey oscillations thus stabilizing their dynamics. The severe long-term implications; however, include predator starvation due to energetic inefficiency despite abundant resources.