Prey Survival Research Articles

Ontogenetic diversity buffers communities against consequences of species loss.

Biodiversity can be measured at multiple organizational scales. While traditional studies have focused at taxonomic diversity, recent studies have emphasized the ecological importance of diversity within populations. However, it is unclear how these different scales of diversity interact to determine the consequence of species loss. Here we asked how predator diversity and presence of ontogenetic diversity within predator populations influences community structure. Ontogenetic diversity arises from shifts in the traits and ecology of individuals during ontogeny and it is one of the biggest sources of intraspecific diversity. However, whether it dampens or strengthens the negative consequences of with species loss is poorly understood. To study the interaction of species diversity and ontogenetic diversity, we experimentally manipulated predator species diversity and diversity of developmental stages within focal predator species and analysed their joint effect on predator and prey survival, biomass and prey community structure in experimental pond systems. While individual effects of ontogenetic diversity were often species specific, losing predator species from the community often had a much smaller or no effect on prey survival, biomass or community structure when all predator populations had high ontogenetic diversity. Thus, ontogenetic diversity within populations buffered against some of the consequences of biodiversity loss at higher organizational levels. Because the experiment controlled mean per capita size and biomass across structured versus unstructured populations, this pattern was not driven by differences in biomass of predators. Instead, results suggest that effects were driven by changes in the functional roles and indirect interactions across and within species. This indicates that even if all environmental conditions are similar, differences in the intrinsic structure of populations can modify the consequences of biodiversity loss. Together, these results revealed the importance of ontogenetic diversity within species for strengthening the resilience of natural communities to consequences of biodiversity loss and emphasize the need to integrate biodiversity patterns across organizational scales.

Asymmetrical effects of temperature on stage‐structured predator–prey interactions

Abstract Warming can impact consumer–resource interactions through multiple mechanisms. For example, warming can both alter the rate at which predators consume prey and the rate prey develop through vulnerable life stages. Thus, the overall effect of warming on consumer–resource interactions will depend upon the strength and asymmetry of warming effects on predator and prey performance. Here, we quantified the temperature dependence of both (a) density‐dependent predation rates for two dragonfly nymph predators on a shared mosquito larval prey, via the functional response, and (b) the development rate of mosquito larval prey to a predator‐invulnerable adult stage. We united the results of these two empirical studies using a temperature‐ and density‐dependent stage‐structured predation model to predict the effects of temperature on the number of larvae that survive to adulthood. Warming accelerated both larval mosquito development and increased dragonfly consumption. Model simulations suggest that differences in the magnitude and rate of predator and prey responses to warming determined the change in magnitude of the overall effect of predation on prey survival to adulthood. Specifically, we found that depending on which predator species prey were exposed to in the model, the net effect of warming was either an overall reduction or no change in predation strength across a temperature gradient. Our results highlight a need for better mechanistic understanding of the differential effects of temperature on consumer–resource pairs to accurately predict how warming affects food web dynamics. A free plain language summary can be found within the Supporting Information of this article.

Hide-and-seek strategies and post-contact immobility.

To understand why an animal might gain by playing dead, or more precisely, exhibit post-contact immobility (PCI), we consider the context in which this behaviour occurs. Is it, for example, a method by which a potential victim encourages a predator to direct its attention elsewhere? We investigate this possibility by using the marginal value theorem to analyse predator behaviour in the context of this defence strategy by potential prey. We consider two models. In the first, (random revisiting) the predator may return to sites it has already depleted within the patch. In the second, (systematic search) the predator goes only to new sites within the patch. The results of the two models are qualitatively extremely similar. We show that when prey occur in patches, PCI favours prey survival. Indeed, certain antlion larvae have PCI durations characterized by very long half-lives. These appear to be of such long durations that further increases would convey no substantial benefits in redirecting potential predators to other antlions within the patch and subsequently to other patches.

Detectability is in the eye of the beholder—the role of UV reflectance on tadpole detection and predation by a passerine bird

The evolution of defensive coloration is dependent upon a complex combination of variables related to the prey itself, the environmental context, and predator vision/behavior. Some animals reflect ultraviolet (UV) light, which is visible to predators such as birds. Here, we report the first case of UV reflectance by a tadpole (Ololygon machadoi, Hylidae) and we investigate whether it influences tadpole detection/predation by a bird (Saltator similis, Passeriformes) on backgrounds of three different colors (two blending – yellow and dark – and one not blending – blue – to tadpole colors). We also tested whether a previous experience of the birds with the prey species would influence the search/attack effort. Although many predation attempts were recorded, birds did not consume many tadpoles. Birds attempted to/preyed upon more tadpoles on dark backgrounds in the presence rather than the absence of the UV portion of the spectrum; attempt/predation on the other backgrounds (yellow, blue) did not change between the UV conditions. The differential contrast of dark and yellow tadpole body parts against specific backgrounds may aid to disruptive properties. The interruption of tadpole body contour was probably enough to prevent detection on yellow and blue backgrounds based on low achromatic contrasts of yellow and dark body parts against such backgrounds, respectively. On dark backgrounds, however, an increase in the chromatic contrast of yellow bars caused by UV reflectance may have reached a threshold and increased tadpole detectability. Birds spent more time searching for tadpoles and visited more frequently the trays in the first than in the second trial, and several tadpoles were regurgitated after ingestion, suggesting that the existence of a potential aposematic role of the UV reflectance cannot be disregarded. Birds also spent more time inspecting blue backgrounds, which may relate to their unfamiliarity with such backgrounds. UV reflectance in O. machadoi tadpoles unveals a potential adaptative value of this feature for the larval stage, and our results indicate influence on tadpole detection by birds. The effects of such adaptation in natural habitats and its occurrence in other species deserve further studies. Defensive colorations that hamper prey detection can play an important role on prey survival, which depends on background matching ability, prey and predator behavior, and predator visual system. Tadpoles are preyed upon by a variety of visually oriented predators and background matching is likely to aid survivorship through decreased detectability. We show for the first time that tadpoles of Ololygon machadoi, although apparently benefited by camouflage, reflect UV wavelenghts, becoming more visible and maybe providing some kind of aversiveness signaling to birds. In natural conditions, however, the water column on deep stream microhabitats usually occupied by the tadpoles is expected to filter UV wavelengths and improve background matching, at least for some specific background colors.

The key role of inter-row vegetation and ants on predation in Mediterranean organic vineyards

Biodiversity-friendly farming practices are taking centre stage, with herbicide use sparking major public debate on human health. Vegetation cover is increasingly used to enhance agroecosystem biodiversity and functions, providing important ecosystem services like biological pest control. However, further information is required on the relationship between vegetation cover, natural enemies, and pest predation. Using a sentinel prey experiment set up in 26 Mediterranean organic vineyards, we analysed the response of generalist predators, and the associated final predation and dynamics under three inter-row management types: bare soil, one out of two inter-rows vegetated and all inter-rows vegetated. Predation on sentinel prey was monitored on the ground and on the vine trunk throughout the daytime and after a night of exposure. Generalist predator abundance was quantified using pitfall traps. Final sentinel prey predation both on vine trunks and on the ground were significantly higher in fully vegetated vineyards, with a shorter prey survival time than in tilled vineyards. Both diurnal and nocturnal predation were significantly related to increased vegetation cover and richness. Moreover, 96 % of the identified predation events involved ants. We demonstrated the key role of vegetation cover in improving the predation function through a spill-over from the inter-row to the grapevine. Contrary to what is commonly observed in agrosystems, we clearly identified ants as the predominant predator both on the ground and on the vine trunk. Our study has important implications for Mediterranean vineyard management, promoting vegetation as a nature-based solution. Sustainable management of vineyard vegetation favouring the natural predator community may contribute to a reduction in pesticide use and fossil fuel consumption.

Predator Attack Strategy and Prey Behaviour Drive Individual Predation Risk in Schooling Prey

Predation is one of the main drivers of animal grouping. However, predation risk is not shared equally within groups. Despite long-standing theoretical work and strong empirical insights, very little work has examined the real-time dynamics of predators attacking groups of prey nor quantified the features that predict prey predation risk and survival. Here we used high resolution tracking of Northern pike (Esox lucius) attacking large schools of prey (golden shiner fish, Notemigonus crysoleucas) to get a mechanistic quantification of predation at every stage of the attack. We found that pike tended to attack the groups head-on, but did so stealthily, often striking only when partly within the school. From the predator’s perspective, relative position to the prey was the most important feature, with shiners very close and directly in front of the pike being most at risk. From the prey’s perspective, we found that central individuals, with relatively low local neighbour density and alignment, face increased risk. While the majority of attacks were successful, escape was associated with individuals achieving high maximum movement speeds, relative to others. Our study highlights both predator attack strategy and prey behaviour are key factors underlying the predation risk of grouping prey, and our results contradict the long-held assertion arising from Hamilton’s “selfish herd” concept that central positions are safer. To ultimately understand the cost-benefits that underly the evolution of animal grouping it is thus key to consider the multifaceted, and dynamical, nature of predator-prey relationships.

A systematic study of autonomous and nonautonomous predator–prey models with combined effects of fear, migration and switching

In this paper, we study the dynamics of a predator–prey system under the combined effects of fear, migration and switching phenomena. This study is new in the sense that the dynamics of such system was studied either through fear or migration, or switching, but the combined effects of such three factors are yet to be explored. We observe oscillatory behavior of the system in the absence of fear, migration and switching, whereas the system shows stable dynamics if anyone of these three factors is introduced. After analyzing the behavior of system with fear, migration and switching, we find that the system does not possess periodic solution whenever the predator population experiences intraspecies competition, but in the absence of intraspecies competition among predator population, fear of predators destabilizes the system, whereas on increasing the migration rates, the system first undergoes subcritical Hopf-bifurcation and then supercritical Hopf-bifurcation settling the system to stable coexistence. Existence of multiple limit cycles is also observed. Our results show that switching behavior of predator population supports the survival of prey and predator populations. We extend our model by assuming the fear parameters as time dependent. We find that the nonautonomous system exhibits periodic solutions, whereas the corresponding autonomous system shows stable focus. Moreover, we observe that if the autonomous system undergoes a Hopf-bifurcation through limit cycle oscillations, the corresponding nonautonomous system shows higher periodic solutions. Almost periodic behavior of the system is also observed by setting the fear parameters as almost periodic functions of time.

Applying the mean free-path length model to juvenile Chinook salmon migrating in the Sacramento River, California

Population vital rates, such as stage-specific survival, are influenced by individual behavior and movement patterns. Yet few methods exist to incorporate behavior into predator-prey models, omitting a potentially important source of variability in population dynamics. Here were combine results from an acoustic telemetry study of juvenile Chinook salmon (Oncorhynchus tshawytscha) with an existing predator prey model, called the mean free-path length model, originally presented in Anderson et al. (2005). The model describes the probability of predator-prey encounters as a function of the predator density and the movement patterns of predators and prey. Greater predator densities and greater variation in movement vectors should result in higher predator-prey encounter rates, and lower survival for the prey. Fitting this model to data provides insight into mechanisms of mortality for migrating fishes. Here we estimate model parameters for two flow conditions in the Sacramento River, California, examining the importance of natural environmental variation in shaping encounters and prey survival. Survival estimates were similar between the high and low flow conditions, yet travel time was slower at lower flows. The model estimates of mean free-path length were lower when compared to those estimated in the Snake River system, corresponding with lower survival. We discuss the value of model parameters estimated from telemetry data in providing a tool for forecasting population-level responses to structural or hydrodynamic modifications in large river systems, and we explore how the XT model can provide insight into nonlinear and threshold-like responses of migratory fish survival to flow.

Positive indirect effects of top‐predators on the behaviour and survival of juvenile fishes

Top‐predators can suppress mesopredator behaviour through risk effects. However, there is limited understanding of whether such behavioural suppression can dampen the lethal and sub‐lethal effects of mesopredators on bottom level prey. Here, we document a field experiment that examines whether the presence of top‐predator cues (visual and chemical stimuli from a coral trout) can cascade to indirectly influence the behaviour and survival of juvenile fish prey of different species (Pomacentrus amboinensis and P. chrysurus) and size (small = 1.18 cm SL versus large = 1.32 cm SL). Results showed that habitat patches exposed to top‐predator cues received fewer visits and foraging attacks from mesopredators, leading to higher space use (~ 46%), feeding rate (~ 95%) and survival (~ 67%) from juvenile fish prey. Survival was always higher for individuals of P. amboinensis and of large‐size, independent of the presence or absence of top‐predator cues. Our data indicate that predation risk from the top‐predator indirectly favoured the persistence and behaviour of juvenile fishes by promoting risk‐averse behavioural responses in mesopredators. This study underscores the behavioural mechanisms by which risk effects can cascade through the food web and highlights the consequences that harvesting top‐predators may have on the replenishment of bottom prey populations.

Antipredator tactics: a kin‐selection benefit for defensive spines in coral catfish?

Morphological features that impair a predator's ability to consume a prey item may benefit individual prey; but what of features that prolong prey‐handling but do not enhance prey survival? For example, a striped eel catfish Plotosus lineatus will be fatally envenomated if struck by its specialist predator, the greater sea snake Hydrophis major. Nonetheless, the catfish typically erects long, toxic pectoral and dorsal spines that increase prey‐handling times for the snake by around eightfold. Because the catfish travel in swarms of closely‐related individuals, the delay enforced by spines may enable the victim's swarm‐mates to disperse before the snake is able to search for another meal. In keeping with that hypothesis, defensive spines tend to be longer in catfish from regions where the greater sea snake occurs, than from areas where the snake does not occur.

Native and Invasive Macrophytes Differ in Their Effectiveness as Nurseries for Juvenile Endangered Salmon

For marine biogenic habitats, such as kelp and seagrass, declines and local extinction events cause concern because of the loss of ecosystem services they provide. Many of these habitats function as valuable nurseries, but this function may be eroded when invasive species alter the structure of the habitats. For anadromous salmonids along the northeast Pacific, there is little known about the nursery role of coastal habitats, which presents a challenge for scientists to fully understand their complex life histories necessary for informing resource managers in decision-making processes regarding habitat protection and restoration. To address these issues, we ran a 3-week experiment testing the nursery functions of seagrass (Zostera marina), the invasive alga Sargassum muticum, mixed seagrass-Sargassum, and bare sand plots on the growth, survival, and prey availability for endangered Chinook salmon (Oncorhynchus tshawytscha) smolts. We found mixed effects of each habitat type when compared with each other. Chinook salmon smolts grew less in seagrass when compared with the three other habitats (bare sand, Sargassum, mixed seagrass-Sargassum). However, fish survival was lower in Sargassum habitat compared with seagrass and bare sand. Prey availability was greatest in mixed seagrass-Sargassum habitat compared with bare sand, Sargassum, or seagrass. We used a principal components analysis (PCA) to develop a nursery index using the smolts’ growth rate, percent survival, prey availability, and density of prey in gut contents. The nursery index showed that mixed seagrass-Sargassum habitat had the most positive effects on nursery performance. These results suggest that invasive species can serve positive habitat functions, but only when in the presence of a habitat-forming native species. Our study supports the theory that habitat diversity leads to greater nursery function of coastal ecosystems.

Measuring the Additive Effects of Predation on Prey Survival Across Spatial Scales

The degree to which predation is an additive vs. compensatory source of mortality is fundamental to understanding the effects of predation on prey populations and evaluating the efficacy of predator management actions. In the Columbia River basin, USA, predation by Caspian Terns (Hydroprogne caspia) on U.S. Endangered Species Act (ESA)-listed juvenile salmonids (smolts; Oncorhynchus spp.) has led to predator management actions to reduce predation; however, the assumption that reduced predation translates into greater salmonid survival, either within the life stage where predation occurs or across their lifetime, has remained untested. To address this critical uncertainty, we analyzed a long-term (2008-2018) mark-recapture-recovery data set of ESA-listed steelhead trout (O. mykiss) that were tagged (n = 78,409) and subsequently exposed to predation during smolt out-migration through multiple river reaches (spatial scales), jointly estimating weekly probabilities of steelhead survival, mortality due to bird predation, and mortality due to other causes. This concurrent estimation across time-stratified cohorts allowed for the direct measurement of the strength, magnitude, and direction of relationships between survival and Caspian Tern predation. Estimates of Tern predation on steelhead were substantial in most years, with cumulative annual estimates ranging from 0.075 (95% creditable interval = 0.058-0.099) to 0.375 (0.290-0.461). Increases in Tern predation probabilities were associated with statistically significant decreases in steelhead survival probabilities in all evaluated years and salmonid life stages (smolt out-migration and smolt-to-adult returns). Results provide novel evidence that predation by Caspian Terns may have been a super-additive source of mortality during the smolt life stage and a partially additive source of mortality to the adult life stage. Annual estimates of the difference between observed survival and baseline survival (i.e., in the absence of Tern predation) ranged from 0.052 (0.017-0.103) to 0.314 (0.172-0.459) during the steelhead smolt life stage and from 0.011 (0.001-0.029) to 0.049 (0.025-0.078) to the adult life stage. The estimated levels of compensation have important implications for predator management actions aimed at increasing the survival of endangered salmonids, and the modeling approach developed herein provides a framework to directly quantify the impacts of source-specific mortality factors on prey populations.

The truth is in the detail: predators attack aposematic prey with less aggression than other prey types

AbstractAposematic organisms are often unprofitable to predators (e.g. because of defensive chemicals) which they advertise with a conspicuous signal (e.g. bright and conspicuous colour signals). Aposematism is thought to reduce predation of prey because the colour signal increases the ability of predators to learn, recognize and remember the prey’s defensive properties. The efficacy of aposematism has been extensively documented in laboratory studies, although its benefits seem to be harder to demonstrate in the field. In this study, we compared the levels of partial and overall predation among four prey types (undefended and cryptic, undefended and warning coloured, defended and cryptic, and aposematic prey). Overall, predation of warning coloured and defended (aposematic) prey was lower than the predation for cryptic and undefended prey; however, it was the same as predation of cryptic and defended prey. Moreover, aposematic prey had higher levels of partial predation (where prey was not wholly consumed by the predator) and lower attack intensities. This suggests that prey were being taste sampled, but also might be better able to survive attacks. Therefore, the benefits of aposematism may lie not only in reducing outright predation, but also in altering a predator’s post-attack behaviour, thus leading to greater escape opportunities and post-attack survival of prey. These results reinforce the importance of examining predation in more detail rather than simply examining attack rates.

<p class="Body"><strong>Under pressure: predation risk defining mating investment in matured spider mite <em>Tetranychus urticae</em></strong></p>

The emergence of anti-predatory strategies for prey survival are ruled by the minimization of the encounters/interactions with potential predators, but at the same time by maximizing the access to limiting resources such as food or mating partners. Cues indicating predatory activity influence decision-making activities in the two-spotted spider mite Tetranychus urticae, such as dispersion, foraging activities, and reproductive effort. However, anti-predatory strategies studied in spider mites generally considers mainly the female perspective (e.g. oviposition), leaving a gap in how T. urticae couples deal with predatory risk. Here, through laboratory experiments, we observed that matured spider mite couples were only affected by predation risk during the pre-copulatory stages of the mating process, especially when deciding to proceed in a mating opportunity. The mating performance of individuals was independent of their exposure to predation risk, suggesting that couples would adopt full investment behavior after opting to proceed in a mating attempt. Though our working hypothesis predicted predation risk interference throughout the entire mating process, we conclude that decision-making activities by spider mite during pre-copulatory stages act independently from copulatory stages associated to insemination.

Measuring the additive effects of predation on prey survival across spatial scales.

The degree to which predation is an additive vs. compensatory source of mortality is fundamental to understanding the effects of predation on prey populations and evaluating the efficacy of predator management actions. In the Columbia River basin, USA, predation by Caspian Terns (Hydroprogne caspia) on U.S. Endangered Species Act (ESA)-listed juvenile salmonids (smolts; Oncorhynchus spp.) has led to predator management actions to reduce predation; however, the assumption that reduced predation translates into greater salmonid survival, either within the life stage where predation occurs or across their lifetime, has remained untested. To address this critical uncertainty, we analyzed a long-term (2008-2018) mark-recapture-recovery data set of ESA-listed steelhead trout (O. mykiss) that were tagged (n=78,409) and subsequently exposed to predation during smolt out-migration through multiple river reaches (spatial scales), jointly estimating weekly probabilities of steelhead survival, mortality due to bird predation, and mortality due to other causes. This concurrent estimation across time-stratified cohorts allowed for the direct measurement of the strength, magnitude, and direction of relationships between survival and Caspian Tern predation. Estimates of Tern predation on steelhead were substantial in most years, with cumulative annual estimates ranging from 0.075 (95% creditable interval=0.058-0.099) to 0.375 (0.290-0.461). Increases in Tern predation probabilities were associated with statistically significant decreases in steelhead survival probabilities in all evaluated years and salmonid life stages (smolt out-migration and smolt-to-adult returns). Results provide novel evidence that predation by Caspian Terns may have been a super-additive source of mortality during the smolt life stage and a partially additive source of mortality to the adult life stage. Annual estimates of the difference between observed survival and baseline survival (i.e., in the absence of Tern predation) ranged from 0.052 (0.017-0.103) to 0.314 (0.172-0.459) during the steelhead smolt life stage and from 0.011 (0.001-0.029) to 0.049 (0.025-0.078) to the adult life stage. The estimated levels of compensation have important implications for predator management actions aimed at increasing the survival of endangered salmonids, and the modeling approach developed herein provides a framework to directly quantify the impacts of source-specific mortality factors on prey populations.

Effect of parasitized prey on prey consumption, survival, growth, and development of Coccinella septempunctata L. (Coleoptera: Coccinellidae) under laboratory conditions

A study of interactions among natural enemies is important to develop a better biological control program. Among these interactions, one that is crucial is the consumption of parasitized prey by a predator. Feeding on aphid mummies could affect the predator as well as the parasitoid species. In this study, the effect of parasitized prey on prey consumption, survival, growth, and development of 4th instar larvae of the predatory species, Coccinella septempunctata L. (Coleoptera: Coccinellidae), as an active predator of aphids, was studied. Moreover, the effect of parasitized and mummified aphids on female fecundity was also evaluated. The green peach aphid, Myzus persicae Sulzer (Hemiptera: Aphididae) was used. Obtained results showed that the parasitized aphids, as a predatory food, significantly affected the predator. The prey consumption was highest on parasitized (24.10 ± 0.53) and lowest on mummified (9.75 ± 0.40) aphids. The survival rate was in the order of non-parasitized > parasitized > mummified. The mass gained by the 4th instar larvae of C. septempunctata was in the order of parasitized (26.25 mg ± 0.89) > non-parasitized (19.25 mg ± 0.86) > mummified aphids (10.20 mg ± 0.52), when fed on different prey. Developmental time of the predator was recorded highest, when it consumed mummified aphids (13.6 ± 0.39). As well, female fecundity was affected positively. The female was observed to lay the most eggs (323.55 ± 1.57) to have the highest number of hatched eggs (38.70 ± 0.92), and to have the highest egg mass (196.10 μg ± 1.22), when it consumed the parasitized aphids in contrast to non-parasitized and mummified aphids. It was also found that the type of prey did not affect the incubation period of the eggs.

Woodlice change the habitat use of spiders in a different food chain.

BackgroundIn old field systems, the common woodlouse may have an indirect effect on a nursery web spider. Woodlice and nursery web spiders feed in different food chains, yet previous work demonstrated that the presence of woodlice is correlated with higher predation success by nursery web spiders upon their grasshopper prey. This finding suggested a new hypothesis which links two seemingly disparate food chains: when woodlice are present, the spider predator or the grasshopper prey changes their location in the vegetative canopy in a way that increases their spatial overlap and therefore predation rate. However, warming temperatures may complicate this phenomenon. The spider cannot tolerate thermal stress, meaning warming temperatures may cause the spider to move downwards in the vegetative canopy or otherwise alter its response to woodlice. Therefore, we would expect warming and woodlice presence to have an interactive effect on predation rate.MethodsWe conducted behavioral experiments in 2015, 2017, and 2018 to track habitat domains—the use of the vegetative canopy space by grasshoppers and spiders—in experimental cages. Then, we used three models of spider movement to try to explain the response of spiders to woodlice: expected net energy gain, signal detection theory, and individual-based modelling.ResultsHabitat domain observations revealed that spiders shift upward in the canopy when woodlice are present, but the corresponding effect on grasshopper prey survival was variable over the different years of study. Under warming conditions, spiders remained lower in the canopy regardless of the presence of woodlice, suggesting that thermal stress is more important than the effect of woodlice. Our modelling results suggest that spiders do not need to move away from woodlice to maximize net energy gain (expected net energy gain and signal detection theory models). Instead spider behavior is consistent with the null hypothesis that they move away from unsuccessful encounters with woodlice (individual-based simulation). We conclude that mapping how predator behavior changes across biotic (e.g. woodlouse presence) and abiotic conditions (e.g. temperature) may be critical to anticipate changes in ecosystem dynamics.

Intraspecific Behavioral Variation Mediates Insect Prey Survival via Direct and Indirect Effects

Conspecific individuals often exhibit behavioral differences that influence susceptibility to predation. Yet, how such trait differences scale to affect prey population regulation and community structure remains unclear. We used an 8 day field mesocosm experiment to explore the effects of intraspecific prey behavioral trait variation on survival in an herbivorous insect community. We further manipulated spider predator composition to test for top-down context-dependence of behavioral effects. Insect prey behavioral trait variance influenced survival through both direct (i.e., variation among conspecifics) and indirect (i.e., variation among heterospecifics) mechanisms. The behavioral variance of two prey species, Philaenus and Orchelimum, directly reduced their survival, though for Philaenus, this direct negative effect only occurred in the presence of a single spider predator species. In contrast, the survival of Scudderia was enhanced by the behavioral trait variance of the surrounding insect community, an indirect positive effect. Taken together, these results emphasize the importance of accounting for intraspecific variation in community ecology, demonstrating novel pathways by which individual-level behavioral differences scale to alter population and community level patterns.

Impact of Allee effect on an eco-epidemiological system

In this paper, we propose a general ratio-dependent prey-predator model with disease in predator subject to the strong Allee effect in prey. We obtain the complete dynamics of both models: (a) full model with Allee effect; (b) full model without Allee effect. Model (a) may have more than one interior equilibrium point, but model (b) has only one interior equilibrium point. Numerical results reveal that the coexistence of all the populations at the endemic state is possible for both the models. But for the model with Allee effect, the coexistence can be destroyed by an increased supply of alternative food for the predators. It can also be proved that for the full model with Allee effect, the disease can be suppressed under certain parametric conditions. Also by comparing models (a) and (b), we conclude that Allee effect can create or destroy the interior attractor. Finally, we have studied the disease free-submodel (prey and susceptible predator model) with and without Allee effect. The comparative study between these two submodels leads to the following conclusions: 1) In the presence of Allee effect, the number of interior equilibrium points can change from zero to two whereas the submodel without Allee effect has unique interior equilibrium point; 2) Both with and without Allee effect, initial conditions play an important role on the survival and extinction of prey as well as its corresponding predator; 3) In the presence of Allee effect, bi-stability occurs with stable or periodic coexistence of prey and susceptible predator and the extinction of prey and susceptible predator; 4) Allee effect can generate or destroy the interior equilibrium points.

Effects of a habitat-modifying eelgrass epibiont on predator success and epifaunal survival

Structural complexity plays an important role in mediating predator-prey interactions. Structural elements can limit predator mobility and ability to detect prey, increasing prey survival. Seagrasses are marine plants that provide refuge for many fishes and invertebrates by increasing the structural complexity of the benthos. Though prey survival often is positively correlated with seagrass biomass or shoot density, seagrasses frequently are colonized by epibiotic organisms such as algae and colonial invertebrates, which could affect this relationship. In San Diego Bay, Thalamoporella californica Levinsen is a common rigid branching bryozoan that creates a three-dimensional structure within eelgrass (Zostera marina L.) canopies. We conducted laboratory mesocosm experiments in which we examined fish Heterostichus rostratus predator foraging behaviors and shrimp Hippolyte californiensis prey escape behavior with (i) different densities of artificial seagrass, both with and without artificial bryozoans, and (ii) constant seagrass density, but varying amounts of artificial bryozoans. We also conducted a laboratory habitat selection experiment to determine if H. rostratus prefer to forage in artificial eelgrass with or without the presence of artificial bryozoans, and a field experiment to determine whether bryozoan, eelgrass and algal biomasses influenced survivorship of tethered H. californiensis. In the lab, we found that increasing eelgrass density reduced predator foraging efficiency, but bryozoans did not alter this relationship. We also found that fish preferred foraging in artificial eelgrass without artificial bryozoans. In the field, the biomass of bryozoans, eelgrass and algae did not influence tethered shrimp relative survival. Our results suggest that it should not be assumed that alterations to habitat complexity alter the outcomes of predator-prey interactions in seagrass habitat.