Prey Suppression Research Articles

Non-additive effects of multiple predators alter the biological control of the coffee leaf miner (Leucoptera coffeella)

Although most prey are attacked by multiple predators, much of the ecological theory on prey suppression focuses on the effects of a single predator. The presence of multiple predators can lead to complex interactions such as trait-mediated interactions (TMIIs) and intraguild predation which can influence the suppression of pest populations. Here we explore the effect of two predators, a native anole lizard species Anolis cristatellus (Squamata: Dactyloidae) and a non-native ant species Wasmannia auropunctata (Hymenoptera: Formicidae), on the coffee leaf miner, Leucoptera coffeella (Lepidoptera: Lyonetiidae) (CLM). In a laboratory experiment we examined the effects of these two predators in isolation and when co-occurring. Our results show that when each predator is alone, they are able to consume the CLM in a comparable way. However, when they are together, their effect is not greater than when alone. This indicates that there is a negative effect when both predators co-occur. The results from this experiment have practical implications since both predators are present in coffee agroecosystems in Puerto Rico, where the CLM is considered the main insect pest. Furthermore, these results demonstrate the potential dynamics among several predators in agroecosystems and the potential implications for herbivore regulation.

Functional trait composition of carabid beetle communities predicts prey suppression through both mass ratio and niche complementarity mechanisms.

Several components of predator functional diversity have been hypothesized to influence prey suppression through either niche complementarity or mass ratio effects. Nevertheless, most studies have used a functional group approach when assessing the role of these predators in ecosystem functioning. By adopting a trait-based approach, we evaluated the relative contributions of carabid diversity components in predicting prey suppression. Our results highlight the importance of both taxonomic and functional diversity components of carabids as key drivers of prey suppression. Prey suppression was best predicted by carabid densities, with the dominance of Poecilus cupreus potentially driving the positive effect of community total abundance through the mass ratio effect. Prey suppression increased with increasing the density of large carabids. In addition, carabid eye diameter and antennal length were key functional traits for predicting prey suppression. Furthermore, prey suppression increased with increasing carabid functional richness following the niche complementarity effect. In contrast to functional richness, functional evenness and functional divergence of carabid communities were weakly correlated with prey suppression. By identifying which diversity components of carabid communities contribute the most to increase prey suppression, our results can guide efforts aiming to predict the relationship between diversity of these predators and ecosystem functioning.

The presence of multiple parasitoids decreases host survival under warming, but parasitoid performance also decreases.

Current global changes are reshaping ecological communities and modifying environmental conditions. We need to recognize the combined impact of these biotic and abiotic factors on species interactions, community dynamics and ecosystem functioning. Specifically, the strength of predator-prey interactions often depends on the presence of other natural enemies: it weakens with competition and interference or strengthens with facilitation. Such effects of multiple predators on prey are likely to be affected by changes in the abiotic environment, altering top-down control, a key structuring force in natural and agricultural ecosystems. Here, we investigated how warming alters the effects of multiple predators on prey suppression using a dynamic model coupled with empirical laboratory experiments with Drosophila-parasitoid communities. While multiple parasitoids enhanced top-down control under warming, parasitoid performance generally declined when another parasitoid was present owing to competitive interactions. This could reduce top-down control over multiple generations. Our study highlights the importance of accounting for interactive effects between abiotic and biotic factors to better predict community dynamics in a rapidly changing world and thus better preserve ecosystem functioning and services such as biological control.

Temporal Resource Continuity Increases Predator Abundance in a Metapopulation Model: Insights for Conservation and Biocontrol

The amount of habitat in a landscape is an important metric for evaluating the effects of land cover on biodiversity, yet it fails to capture complex temporal dimensions of resource availability that could be consequential for species population dynamics. Here, we use a spatially-explicit predator–prey metapopulation model to test the effect of different spatiotemporal resource patterns on insect predators and their prey. We examined population responses in model landscapes that varied in both the amount and temporal variability of basal vegetation. Further, we examined cases where prey comprised either a single generalist species or two specialist species that use different resources available either early or late in the growing season. We found that predators and generalist prey benefitted from lower temporal variance of basal resources, which increased landscape-scale abundances. However, increasing the amount of basal resources also increased the variability of generalist prey populations. Specialist prey, on the other hand, did not benefit from less temporally variable basal resources, as they were restricted by habitat type, while also suffering greater predation. Predators achieved greater prey suppression in landscapes with less temporally variable resources, but the overall effects on prey abundance depended on prey habitat specialization. Our simulations demonstrate the joint importance of both the amount and temporal variability of resources for understanding how landscape heterogeneity influences biodiversity and ecosystem services such as the biological control of agricultural pests.

Towards understanding factors influencing the benefit of diversity in predator communities for prey suppression

AbstractIt is generally assumed that high biodiversity is key to sustaining critical ecosystem services, including prey suppression by natural predator guilds. Prey suppression is driven by complex interactions between members of predator and prey communities, as well as their shared environment. Because of this, empirical studies have found both positive and negative effects of high predator diversity on prey suppression. However, we lack an understanding of when these different prey suppression outcomes will occur. In this work, we use a mechanistic, trait‐based model to unravel how intraguild interactions, species body mass, predator foraging area, and ambient temperature can combine to produce different levels of prey suppression. Surprisingly, we find that prey suppression is only improved by high biodiversity under a limited set of conditions. The most important factor in determining whether diversity improves prey suppression is the amount of overlap between predators' foraging areas. The degree of overlap in foraging areas shapes species interactions, and as the overlap between species increases, we see decreasing benefits from species‐rich communities. In contrast, diversity in body mass only improves prey suppression when there is significant variation in temperature.

Run rabbit run: spotted-tailed quoll diet reveals invasive prey is top of the menu

Information about the ecological functional roles of native predators may help inform the conservation of wildlife and pest management. If predators show preferences for certain prey, such as invasive species, this could potentially be used as a conservation tool to help restore degraded (e.g. overgrazed) ecosystems via the reintroduction of native predators and suppression of exotic prey (e.g. introduced herbivores). The diet of spotted-tailed quolls was studied in a fenced reserve in south-eastern Australia where native mammals have been reintroduced, foxes and cats removed, but invasive European rabbits still persist. A total of 80 scats were collected over 12 months and analysis of macroscopic prey remains was conducted to determine diet. Rabbits were by far the most commonly consumed prey species by volume (~76%) and frequency (~60%), followed by brushtail possums (~11% for both volume and frequency), and other small and medium-sized native mammals in much smaller amounts. Quoll scat analysis revealed 10 mammal species in total, eight of which were native. Bird, reptile and invertebrate remains were uncommon in quoll scats. This suggests that spotted-tailed quolls may show a preference for preying on invasive European rabbits in certain contexts, and this could potentially be used as part of quoll reintroductions to aid rabbit population suppression and ecosystem restoration.

Short-term pain before long-term gain? Suppression of invasive primary prey temporarily increases predation on native lizards

The control of invasive species can have cascading and at times undesirable effects on the wider ecological community. Effective management requires that the ecosystem-wide effects of removing invasive species be understood. We investigated the effects of large-scale rabbit control on the abundance (numerical response) and diet (functional response) of an invasive predator (ferret, Mustela putorius furo) that preys on rabbits (Oryctolagus cuniculus), as well as the subsequent predation pressure experienced by alternative prey species (total response), in New Zealand’s dryland habitats. Following rabbit control, ferret densities declined but surviving ferrets increased their per capita consumption of lizards and invertebrates, two key native prey groups. Rabbit control increased predation pressure on lizards, but reduced it on invertebrates. While rabbit control can negatively impact some groups of alternative prey up to 18 months post-control, it probably benefits them in the longer term because prey-switching by ferrets tended to reduce with time, and regeneration of vegetation previously over-grazed by rabbits is likely to reduce exposure of native prey to predation. While confirming these benefits will require longer-term monitoring, our results support management actions that limit short-term fluctuations in rabbit abundance and maintain them at low abundance.

Predator population size structure alters consumption of prey from epigeic and grazing food webs.

Numerous studies have found that predators can suppress prey densities and thereby impact important ecosystem processes such as plant productivity and decomposition. However, prey suppression by spiders can be highly variable. Unlike predators that feed on prey within a single energy channel, spiders often consume prey from asynchronous energy channels, such as grazing (live plant) and epigeic (soil surface) channels. Spiders undergo few life cycle changes and thus appear to be ideally suited to link energy channels, but ontogenetic diet shifts in spiders have received little attention. For example, spider use of different food channels may be highly specialized in different life stages and thus a species may be a multichannel omnivore only when we consider all life stages. Using stable isotopes, we investigated whether wolf spider (Pardosa littoralis, henceforth Pardosa) prey consumption is driven by changes in spider size. Small spiders obtained > 80% of their prey from the epigeic channel, whereas larger spiders used grazing and epigeic prey almost equally. Changes in prey consumption were not driven by changes in prey density, but by changes in prey use by different spider size classes. Thus, because the population size structure of Pardosa changes dramatically over the growing season, changes in spider size may have important implications for the strength of trophic cascades. Our research demonstrates that life history can be an important component of predator diet, which may in turn affect community- and ecosystem-level processes.

Reducing Native Ant Abundance Decreases Predation Rates in Midwestern Grasslands.

Diverse and robust predator communities are important for effective prey suppression in natural and managed communities. Ants are ubiquitous components of terrestrial systems but their contributions to natural prey suppression is relatively understudied in temperate regions. Growing evidence suggests that ants can play a significant role in the removal of insect prey within grasslands, but their impact is difficult to separate from that of nonant predators. To test how ants may contribute to prey suppression in grasslands, we used poison baits (with physical exclosures) to selectively reduce the ant population in common garden settings, then tracked ant and nonant ground predator abundance and diversity, and removal of sentinel egg prey for 7 wk. We found that poison baits reduced ant abundance without a significant negative impact on abundance of nonant ground predators, and that a reduction in ant abundance decreased the proportion of sentinel prey eggs removed. Even a modest decrease (~20%) in abundance of several ant species, including the numerically dominant Lasius neoniger Emery (Hymenoptera: Formicidae), significantly reduced sentinel prey removal rates. Our results suggest that ants disproportionately contribute to ground-based predation of arthropod prey in grasslands. Changes in the amount of grasslands on the landscape and its management may have important implications for ant prevalence and natural prey suppression services in agricultural landscapes.

Behavior, size, and body condition predict susceptibility to management and reflect post-treatment frequency shifts in an invasive snake

Foraging behavior can have population-level effects that are of interest for wildlife management. For invasive species, foraging behavior has been tied to establishment ability and rate of spread and is generally of import in understanding invasion biology. A major method for controlling invasive vertebrates is using food-based baits as attractants. Tool efficacy is therefore partially driven by individual decision-making during foraging, which may also affect population response to control. We used three studies on the invasive, arboreal brown treesnake (Boiga irregularis) on Guam to measure 1) size, body condition, and behavioral correlates with mortality in response to control using toxic baits, 2) shifts in prevalence of those traits after control treatments occurred and, based on the prior two findings, 3) interactive relationships between size, body condition, and behavioral traits at the landscape scale for untreated populations. Each trait was selected due to a potential relationship with foraging behavior or energetic state of an arboreal snake, as a method to estimate how foraging behavior can inform control tool efficacy. We found that snakes were more likely to be killed by toxiic baits if they had a lower body weight, were more active leading up to a bait application, and encountered on the ground more frequently. Across two treated populations, both body size and condition of sampled snakes increased after treatment, while the incidence of ground encounters decreased. Throughout forested habitat on Guam, ground encounter probability was positively correlated with snake size and inversely correlated to body condition. Additionally, size and condition had interactive effects such that snakes in good condition were more arboreal. Thus, body size and behavior (ground encounters) correlated with control-tool susceptibility and frequency shifts occurred in those traits within sampled post-treatment populations. Individual decision-making during foraging may thus inform population responses to bait-based control tools. Management decisions such as prey suppression are likely to directly influence removal efficacy through altered foraging behavior in snakes.

Conspecifics, not pollen, reduce omnivore prey consumption.

Pollen can decrease (via reduced consumption) or increase (via numerical response) an omnivores consumption of animal prey. Although pollen can increase predation pressure through numerical responses of omnivores, pollen may also suppress predation by increasing omnivore interactions with conspecifics. Despite this potential, studies of the impacts of pollen on predation by omnivores often overlook the effect of these tissues on intraspecific interactions between omnivores. We designed three studies to examine how Spartina foliosa pollen and conspecific density impact scale insect prey consumption by ladybeetle (Naemia seriata) omnivores. First, we assessed how pollen impacts scale insect consumption by isolated ladybeetles. Second, we measured how pollen influences ladybeetle prey suppression when numerical responses were possible. Third, because initial experiments suggested the consumption rates of individual ladybeetles depended on conspecific density, we compared per capita consumption rates of ladybeetles across ladybeetle density. Pollen did not influence prey consumption by isolated ladybeetles. When numerical responses were possible, pollen did not influence total predation on prey despite increasing ladybeetle density, suggesting that pollen decreased per capita prey consumption by ladybeetles. The discrepancy between these studies is likely a consequence of differences in ladybeetle density—the presence of only two other conspecifics decreased per capita prey consumption by 76%. Our findings suggest that pollen may not alter the population level effects of omnivores on prey when omnivore numerical responses are offset by reductions in per capita predation rate.

Functional diversity positively affects prey suppression by invertebrate predators: a meta-analysis.

The use of pesticides within agricultural ecosystems has led to wide concern regarding negative effects on the environment. One possible alternative is the use of predators of pest species that naturally occur within agricultural ecosystems. However, the mechanistic basis for how species can be manipulated in order to maximize pest control remains unclear. We carried out a meta‐analysis of 51 studies that manipulated predator species richness in reference to suppression of herbivore prey to determine which components of predator diversity affect pest control. Overall, functional diversity (FD) based on predator's habitat domain, diet breadth and hunting strategy was ranked as the most important variable. Our analysis showed that increases in FD in polycultures led to greater prey suppression compared to both the mean of the component predator species, and the most effective predator species, in monocultures. Further analysis of individual traits indicated these effects are likely to be driven by broad niche differentiation and greater resource exploitation in functionally diverse predator communities. A decoupled measure of phylogenetic diversity, whereby the overlap in variation with FD was removed, was not found to be an important driver of prey suppression. Our results suggest that increasing FD in predatory invertebrates will help maximize pest control ecosystem services in agricultural ecosystems, with the potential to increase suppression above that of the most effective predator species.

Subsistence Practices and the Occupational Histories of the Little Green Valley: A Prehistoric Central Arizona Frontier

The Transitional Zone of central Arizona is a mountainous region dissected by rivers that created barriers and drove movement between prehistoric Hohokam groups to the south and Ancestral Peoples groups to the northeast and northwest. Although never suitable for large-scale agricultural irrigation, this region provided small areas of arable land scattered across rugged terrain rich in wild foods and alboreal resources. Archaeological data recovery related to road improvement projects throughout Arizona Route 260 allowed us to examine paleobotanical and osteofaunal remains of five archaeological sites. We relate changes in diet breadth and anthropogenic land effects modeled and described using the methods of the optimal foraging theory, with modes of use modeled using concepts from the frontier theory. We found that brief intervals of prey suppression and concomitant expansion of diet breadth between low value resources coincide with intervals of prey recovery and diet amplitude contraction between low value resources and more intensive settlement. On the other hand, ranges of prey recovery and diet breadth contraction among low value resources coincide with a reduced population and seasonal, extractive, and short-term occupations.

Functional response and multiple predator effects of two generalist predators preying on Tuta absoluta eggs.

Interactions among invertebrate predators could affect a pest suppression. The hemipteran species Macrolophus pygmaeus (Rambur) and Nesidiocoris tenuis (Reuter) (Hemiptera: Miridae) are natural enemies of several pests in agroecosystems and coexist in tomato crops in Mediterranean countries. By using the multiplicative risk model (MRM) and the substitutive model, the multiple predator effects (MPEs) on prey suppression were calculated when two individuals of the predators foraged at the same densities on South American tomato pinworm, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), eggs. Egg consumption increased with increasing egg density and the two predators exhibited a type III functional response. Predation rates were strongly affected by prey density. Using the MRM, we found risk reduction at intraspecific treatments at high prey density. Applying the substitutive model, we detect risk enhancement at interspecific treatments at high egg density. At low prey densities, most of the interactions were independent, whereas at high densities most interactions were not independent and resulted in prey risk reduction, indicating antagonism between the individuals involved. We also showed that N. tenuis is a more competitive predator species for T. absoluta eggs than M. pygmaeus; however, combination of the two predator species will lead to better pest suppression at high T. absoluta population densities. © 2017 Society of Chemical Industry.

Substantial Mortality of Cabbage Looper (Lepidoptera: Noctuidae) From Predators in Urban Agriculture Is not Influenced by Scale of Production or Variation in Local and Landscape-Level Factors.

As Midwestern (United States) cities experience population decline, there is growing interest in converting underutilized vacant spaces to agricultural production. Urban agriculture varies in area and scope, yet most growers use similar cultivation practices such as avoiding chemical control of crop pests. For community gardens and farms that sell produce commercially, effective pest suppression by natural enemies is important for both societal, economic, and marketing reasons. To gauge the amount of prey suppression at 28 urban food-production sites, we measured removal of sentinel eggs and larvae of the cabbage looper Trichoplusia ni (Hubner), a caterpillar pest that defoliates Brassica. We investigated how landscape and local factors, such as scale of production, influence cabbage looper mortality caused by predators. Predators removed 50% of eggs and 25% of larvae over a 3-d period. Landscape factors did not predict mortality rates, and the amount of loss and damage to sentinel prey were similar across sites that differed in scale (residential gardens, community gardens, and farms). To confirm that removal of sentinel items was likely caused by natural enemies, we set up a laboratory assay that measured predation of cabbage looper eggs and larvae by several predators occurring in urban gardens. Lady beetles caused the highest mortality rates, suggesting their potential value for biocontrol; spiders and pirate bugs also consumed both eggs and larvae at high rates. Our results suggest that urban growers benefit from high consumption rates of cabbage looper eggs and larvae by arthropod predators.

Effects of predator richness and habitat heterogeneity on prey suppression in an estuarine food chain

Effects of predator richness and habitat heterogeneity on prey suppression in an estuarine food chain

Cascading effects of belowground predators on plant communities are density-dependent.

Soil food webs comprise a multitude of trophic interactions that can affect the composition and productivity of plant communities. Belowground predators feeding on microbial grazers like Collembola could decelerate nutrient mineralization by reducing microbial turnover in the soil, which in turn could negatively influence plant growth. However, empirical evidences for the ecological significance of belowground predators on nutrient cycling and plant communities are scarce. Here, we manipulated predator density (Hypoaspis aculeifer: predatory mite) with equal densities of three Collembola species as a prey in four functionally dissimilar plant communities in experimental microcosms: grass monoculture (Poa pratensis), herb monoculture (Rumex acetosa), legume monoculture (Trifolium pratense), and all three species as a mixed plant community. Density manipulation of predators allowed us to test for density-mediated effects of belowground predators on Collembola and lower trophic groups. We hypothesized that predator density will reduce Collembola population causing a decrease in nutrient mineralization and hence detrimentally affect plant growth. First, we found a density-dependent population change in predators, that is, an increase in low-density treatments, but a decrease in high-density treatments. Second, prey suppression was lower at high predator density, which caused a shift in the soil microbial community by increasing the fungal: bacterial biomass ratio, and an increase of nitrification rates, particularly in legume monocultures. Despite the increase in nutrient mineralization, legume monocultures performed worse at high predator density. Further, individual grass shoot biomass decreased in monocultures, while it increased in mixed plant communities with increasing predator density, which coincided with elevated soil N uptake by grasses. As a consequence, high predator density significantly increased plant complementarity effects indicating a decrease in interspecific plant competition. These results highlight that belowground predators can relax interspecific plant competition by increasing nutrient mineralization through their density-dependent cascading effects on detritivore and soil microbial communities.

Additive effects of predator diversity on pest control caused by few interactions among predator species

1. Studies of the impact of predator diversity on biological pest control have shown idiosyncratic results. This is often assumed to be as a result of differences among systems in the importance of predator–predator interactions such as facilitation and intraguild predation. The frequency of such interactions may be altered by prey availability and structural complexity. A direct assessment of interactions among predators is needed for a better understanding of the mechanisms affecting prey abundance by complex predator communities.2. In a field cage experiment, the effect of increased predator diversity (single species vs. three‐species assemblage) and the presence of weeds (providing structural complexity) on the biological control of cereal aphids were tested and the mechanisms involved were investigated using molecular gut content analysis.3. The impact of the three‐predator species assemblages of aphid populations was found to be similar to those of the single‐predator species treatments, and the presence or absence of weeds did not alter the patterns observed. This suggests that both predator facilitation and intraguild predation were absent or weak in this system, or that these interactions had counteracting effects on prey suppression. Molecular gut content analysis of predators provided little evidence for the latter hypothesis: predator facilitation was not detected and intraguild predation occurred at a low frequency.4. The present study suggests additive effects of predators and, therefore, that predator diversity per se neither strengthens nor weakens the biological control of aphids in this system.

Plant community composition determines the strength of top-down control in a soil food web motif.

Top-down control of prey by predators are magnified in productive ecosystems due to higher sustenance of prey communities. In soil micro-arthropod food webs, plant communities regulate the availability of basal resources like soil microbial biomass. Mixed plant communities are often associated with higher microbial biomass than monocultures. Therefore, top-down control is expected to be higher in soil food webs of mixed plant communities. Moreover, higher predator densities can increase the suppression of prey, which can induce interactive effects between predator densities and plant community composition on prey populations. Here, we tested the effects of predator density (predatory mites) on prey populations (Collembola) in monoculture and mixed plant communities. We hypothesized that top-down control would increase with predator density but only in the mixed plant community. Our results revealed two contrasting patterns of top-down control: stronger top-down control of prey communities in the mixed plant community, but weaker top-down control in plant monocultures in high predator density treatments. As expected, higher microbial community biomass in the mixed plant community sustained sufficiently high prey populations to support high predator density. Our results highlight the roles of plant community composition and predator densities in regulating top-down control of prey in soil food webs.

The importance of intraguild predation in predicting emergent multiple predator effects

Prey typically coexist with multiple predator species, each of which presents a predation risk related to its habitat domain and foraging mode. These predator characteristics can be used to predict how the risk from multiple predators will combine to create emergent multiple predator effects for shared prey. Interactions between predators, particularly intraguild predation, can strongly alter prey suppression, though the importance of intraguild predation in multiple predator effects has not been explicitly explored. Furthermore, the vast majority of studies on multiple predator effects has focused on shared prey that are herbivorous, thus experiments focused on mesopredators are needed to evaluate the generality of conclusions made about multiple predator effects. We used a suite of carnivorous arthropods to test a predictive framework of multiple predator effects and to evaluate the role of intraguild predation in shaping these effects. We allowed the wolf spiders Pardosa milvina, Tigrosa helluo, and Rabidosa rabida and the ground beetle Scarites quadriceps to interact and recorded the outcome of all predatory events. We used two tests of multiple predator effects to determine whether predators created risk enhancement, risk reduction, or were substitutable. We found that the occurrence of intraguild predation decreased the overall risk to prey, causing observed multiple predator effects to deviate from predictions. Additionally, we highlight the importance of considering predator identity, as predators were capable of increasing, decreasing, or not altering the success of their competitors. Our study demonstrates that intraguild predation is a critical factor in determining how the risk from multiple predators will combine to affect their prey.