Common Generalist Predator Research Articles

Effects of predation pressure and prey density on short‐term indirect interactions between two prey species that share a common predator

1. Generalist predators are important contributors to reliable conservation biological control. Indirect interactions between prey species that share a common generalist predator can influence both community dynamics and the efficacy of biological control.2. Laboratory cage experiments investigated the impact of the combined consumptive and non‐consumptive effects of predation by adult Hippodamia convergens as a shared predator on the population growth and relative abundance of Acyrthosiphon pisum and Aphis gossypii as prey species. Predation pressure and prey density were varied.3. At low predation pressure the indirect interaction between aphid species was asymmetrical with a proportionally greater negative impact of predation on A. gossypii than on A. pisum. At intermediate predation pressure, the indirect interaction became symmetrical. At high predation pressure and higher levels of prey density, it was asymmetrical with greater negative impact on A. pisum, often driven to local extinction while A. gossypii populations persisted.4. A linear mixed‐effects model including early population growth of both aphid species and predation pressure explained 96% and 92% of the variation in the population growth of A. pisum and A. gossypii, respectively, over an 8‐day period. The overall effect of shared predation on the indirect interaction between the two aphid species is best described as apparent commensalism, where A. pisum benefited from early population growth of A. gossypii, while A. gossypii was unaffected by early population growth of A. pisum. Considering these indirect interactions is important for conservation biological control efforts to be successful.

Volatiles from Sophora japonica flowers attract Harmonia axyridis adults (Coleoptera: Coccinellidae)

The multicolored Asian lady beetle, Harmonia axyridis (Coleoptera: Coccinellidae), is a common generalist predator in China and is occasionally found gathering on the Chinese pagoda tree, Sophora japonica, in summer. In a field investigation, we found that H. axyridis adults preferred S. japonica during its flowering period even though their optimal prey (aphid) is absent at this time. In addition, male and female adults were attracted to S. japonica flowers to a similar extent in a Y-tube olfactometer assay. Using coupled gas chromatography-electroantennogram detection (GC-EAD), we identified a flower odor component (nonanal) that elicited a significant electrophysiological response in H. axyridis. Electroantennogram (EAG) dose-dependent responses revealed that the amplitude of the adult beetle's EAG response increased with increasing concentration of nonanal, peaking at 10 mg mL−1. In Y-tube olfactometer behavioral tests, H. axyridis adults preferred a 10 mg mL−1 nonanal source over a 100 mg mL−1 diluent. Under field conditions, the adults were significantly attracted to both concentrations (10 and 100 mg mL−1), and high concentrations generally had greater attraction. All these results suggest that nonanal, a volatile compound of S. japonica flowers, greatly attracts H. axyridis adults. This study provides a basis for the development of synthetic attractants of H. axyridis, with the potential to promote biocontrol services of this generalist predator in the native area (e.g., China) and to suppress its population by mass trapping in its invasive areas.

Making the best of a bad situation: differential predator avoidance in a diminutive woodland salamander

Predator avoidance behaviour has been observed in many species and can strongly affect trophic interactions. Animals frequently adjust their response to predators in proportion to risk; however, when they are exposed to chronic predation risk, some animals reduce their antipredator responses in favour of resource acquisition. Animals that are subjected to predation pressure from multiple predator species may have to respond to different spatial and temporal distributions of risk; how they balance these risks will affect their choice of habitat or microhabitat patches. One species that is exposed to a wide range of predators is the pygmy salamander, Desmognathus wrighti. These miniaturized terrestrial plethodontids spend their entire life on the forest floor where they are exposed to a diversity of predators. We examined pygmy salamanders' ability to avoid potential predators based on the presence of substrate-borne chemical cues. The predator species included ground beetles (Carabidae: Pterostichus), Jordan's salamanders, Plethodon jordani, and ring-necked snakes, Diadophis punctatus. The ring-necked snake is a trophic specialist feeding on salamanders while the beetles and Jordan's salamanders are generalist predators. The pygmy salamanders were also exposed to chemical alarm cues from a congeneric salamander (Desmognathus fuscus) and odours from two unfamiliar species: corn snakes (Pantherophis gutattus) and herbivorous desert tortoises (Gopherus agassizii). We used a hierarchical Bayesian beta regression with a repeated measures design to model proportion of time spent in each treatment. Compared to controls, pygmy salamanders exhibited strong aversion to fed ring-necked snakes, a moderate avoidance of unfamiliar odours and a slight attraction to scents from the two common generalist predators. Our results suggest that pygmy salamanders accept modest risk from common generalist predators but avoid less common, specialist predators and unfamiliar species.

Wooded field margins increase potential for cultural and biological control of soybean pests

Crop field margins provide benefits to growers by inhibiting pest dispersal through cultural control and provisioning resources for predators through conservation biological control. The purpose of this study was to elucidate potential soybean insect pest control measures by determining the relationships between pests and spiders, common generalist predators in agroecosystems, and field margin type and distance from the field (0–3 and 3–6 m). Both margin type and distance were significantly correlated with in-field pest abundance (both pooled and taxa-specific). Generally, pest abundance was negatively correlated with the presence of wooded field margins at both distances and could be due to cultural control as hedgerows provide similar ecosystem services in other cropping systems. Spider abundance and spider-pest spatial associations (an indication of potential predation events) within fields were positively correlated with wooded margins from 3 to 6 m, indicating that conservation biological control in addition to cultural control might be contributing to diminished pest abundance in fields with these margins. The lack of wooded margin influence from 0 to 3 m might indicate a need for a minimum wooded area before margins can become a source for within-field spider populations. Furthermore, the number of spider-pest spatial associations was greatest early in the season when pest abundance was lowest and pests were more likely to be spatially aggregated. These data indicate that growers might be able to maintain their field margins, particularly wooded areas, to maximize both potential cultural control and conservation biological control resources, particularly early in the growing season.

Size matters: Body size determines functional responses of ground beetle interactions

Understanding patterns in predator:prey systems and the mechanisms that underlie trophic interactions provides a basis for predicting community structure and the delivery of natural pest control services. The functional response of predators to prey density is a fundamental measure of interaction strength and its characterisation is essential to understanding these processes. We used mesocosm experiments to quantify the functional responses of five ground beetle species that represent common generalist predators of north-west European arable agriculture. We investigated two mechanisms predicted to be key drivers of trophic interactions in natural communities: predator:prey body size ratio and multiple predator effects. Our results show regularities in foraging patterns characteristic of similarly sized predators. Ground beetle attack rates increased and handling times decreased as the predator:prey body-mass ratio rose. Multiple predator effects on total prey consumption rates were sensitive to the identity of the interacting species but not prey density. The extent of interspecific interactions may be a result of differences in body mass between competing beetle species. Overall these results add to the growing evidence for the importance of size in determining trophic interactions and suggest that body mass could offer a focus on which to base the management of natural enemy assemblages.

Understanding trophic interactions of Orius spp. (Hemiptera: Anthocoridae) in lettuce crops by molecular methods.

The aphid Nasonovia ribisnigri (Mosley) (Hemiptera: Aphididae) and the thrips Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) are common pests in Mediterranean lettuce crops, where Orius spp. are common generalist predators. Predation by Orius spp. was studied in a lettuce plot by conventional polymerase chain reaction (PCR) and real-time PCR analyses using specific primers of both main pests. Also, high-throughput sequencing was used to have a wider approach of the diet of these predators in natural field conditions. Molecular analyses indicated a higher predation on N. ribisnigri in spring and on F. occidentalis in summer. Predation on alternative prey, like Collembola, was also found in both seasons. Real-time PCR was more sensitive than conventional PCR in showing the target trophic links, whereas high-throughput sequencing revealed predation on other natural enemies - intraguild predation (IGP), showing other trophic interactions of Orius majusculus within the studied ecosystem. This study gives important information about the trophic relationships present in Mediterranean lettuce crops in different periods of the year. The detected predation by Orius spp. on alternative prey, as well as on other natural enemies, should be further investigated to clarify whether it adds or detracts to the biological control of N. ribisnigri and F. occidentalis.

Lethal and behavioral effects of pesticides on the insect predator Macrolophus pygmaeus

Macrolophus pygmaeus (Hemiptera: Miridae) is a common generalist predator in Mediterranean agro-ecosystems. We evaluated the lethal effects of six insecticides and a fungicide on M. pygmaeus nymphs exposed to the pesticides through three routes of exposure: direct, residual and oral. Chlorantraniliprole and emamectin-benzoate caused less than 25% mortality to M. pygmaeus and were classified as harmless according to the International Organization for Biological Control rating scheme. In contrast, thiacloprid and metaflumizone caused 100% and 80% mortality, respectively, and were classified as harmful. Indoxacarb and spinosad resulted in close to 30% mortality to the predator, and were classified as slightly harmful, while the fungicide copper hydroxide caused 58% mortality and was rated as moderately harmful. Chlorantraniliprole and thiacloprid were selected for further sublethal testing by exposing M. pygmaeus to two routes of pesticide intake: pesticide residues and feeding on sprayed food. Thiacloprid led to an increase in resting and preening time of the predator, and a decrease in plant feeding. Chlorantraniliprole resulted in a decrease in plant feeding, but no other behaviors were affected. In addition, thiacloprid significantly reduced the predation rate of M. pygmaeus, whereas chlorantraniliprole had no significant effect on predation rate. The results of the study suggest that thiacloprid is not compatible with M. pygmaeus, while further research needs to be carried out for metaflumizone and copper hydroxide. All other products seem to be relatively compatible with M. pygmaeus, though studies on their sublethal effects will shed more light into their safety.

Las arañas en agroecosistemas: bioindicadores terrestres de calidad ambiental

Spiders are common generalist predators in terrestrial ecosystems, broadly used in diversity studies. The landscape of extensive areas of Uruguay was transformed in a mosaic of patches between natural habitats and agroecosystems. What level of change in the spider community could we expect if these areas are situated near from one another? What percentage of the native species are replaced after the plantation? How this affects the local biodiversity? A study was carried out in four neighboring areas in INIA Las Brujas, Canelones: a riparian forest, an “Espinillo” forest, an Eucalyptus globulus plantation and an artificial prairie of Trifolium pratense and Avena sativa. Spiders were captured with pitfall traps, trunk traps, sweep netting, beating and by nocturnal hand collection. A total of 3.023 adults were collected. Higher values of abundance and species richness were observed in the riparian forest. In spite of the proximity between the studied areas, a high level of replacement of species was observed, especially between natural areas and agroecosystems. The collecting protocols used could be useful to evaluate the impact of differents managements of agroecosystems in the local biodiversity and its application in environmental quality certification.

Spider predation on a mirid pest in Japanese rice fields

Spiders are common generalist predators, and understanding their potential in biological control is important for the development of integrated pest management programs. In this study, predation by three groups of spiders on the mirid bug Stenotus rubrovittatus (Hemiptera: Miridae) in rice paddies was investigated using DNA-based gut-content analysis. A laboratory feeding study revealed that the detection half-lives of bug DNA in the spider gut at 25 °C was 3.4 days for Lycosidae and 1.5 days for Tetragnathidae. Individual spider predation on the mirid bug was investigated by detecting DNA of prey in field-collected spiders. In total, 1199 spiders were assayed from three spider groups: Pirata subpiraticus (Lycosidae), Tetragnatha spp. (Tetra-gnathidae), and Pachygnatha clercki (Tetra-gnathidae), which each differ in their preferred microhabitat as well as their predatory habits. Detection rates of prey DNA in spiders increased significantly with the density of prey across all spider groups. P. subpiraticus and Tetragnatha spp. predation showed a better fit to a saturated response curve to increasing prey density, while P. clercki showed a simple linear relationship with prey density. Densities of alternative prey species did not affect the detection rates of mirids. These results suggest that predation on pests by generalist predators in an agroecosystem is affected not only by prey abundance but also by predator preference for specific prey. Predator preference is therefore an important factor to consider when estimating the role of natural enemies as biological control agents.

Biological and behavioral effects of kaolin particle film on larvae and adults of Chrysoperla carnea (Neuroptera: Chrysopidae)

Several laboratory and field experiments were conducted to investigate the effect of kaolin particle film formulation Surround WP on the biology and behavior of the common generalist predator Chrysoperla carnea (Stephens). Kaolin 5% (w/v) suspension direct spray did not affect third instar larvae development to adulthood. The hatchability of recently laid eggs, subjected to the same spraying process, was also unaltered. However, third instar larvae coated with particle film after kaolin spraying showed slightly hampered movement capacity after measuring: distance moved, mean velocity, angular velocity and time spent in motion, obtained using the computerized system EthoVision. Parameters extracted from recorded larvae movement on a kaolin film surface showed similar decreased mobility results as well as preference for the clean control surface. Additionally, the larvae had difficulty grasping treated leaves. C. carnea adult females showed a predominant preference for treated leaves in oviposition choice tests. In the field trial, no difference in C. carnea adult abundance was found between kaolin-treated and control olive trees. These results indicate that disruption of movement capacity and dislodgement from the plant surface may be the principal negative effects of particle film on C. carnea larvae. Despite the positive trend in oviposition towards kaolin treated surfaces, a particle film attraction effect on adults was not observed at field level.

Invertebrate biodiversity affects predator fitness and hence potential to control pests in crops

Natural enemies that control pests usually allow farmers to avoid, or reduce, the use of pesticides. However, modern farming practices, that maximize yields, are resulting in loss of biodiversity, particularly prey diversity. Does this matter? Pests continue to thrive, and without alternative prey the predators should, perforce, concentrate their attentions upon the pests.We showed that a diverse diet significantly enhances predator fecundity and survival. Experiments were conducted using common generalist predators found in arable fields in Europe, the carabid beetle Pterostichus melanarius (Coleoptera: Carabidae) and the linyphiid spider Erigone atra (Araneae: Linyphiidae). We tested the hypothesis that mixed species diets were optimal, compared with restricted diets, with respect to parameters such as predator weights, egg weights, numbers of eggs laid, egg development times, egg hatching rates and predator survival. In carabids, an exclusive earthworm diet was as good as mixed diets containing earthworms for egg production and hatching, but less good than such mixed diets for increase in beetle mass and sustained egg laying. For spiders, aphids alone (Sitobion avenae) or with the Collembola Folsomia candida, drastically reduced survival. Aphids plus the Collembola Isotoma anglicana improved survival but only aphids with a mixed Collembola diet maximized numbers of hatching eggs.Predators offered only pests (slugs or aphids) had lowest growth rates and fecundity. We therefore demonstrated that conservation of a diversity of prey species within farmland, allowing predators to exploit a diverse diet, is essential if predators are to continue to thrive in crops and regulate agricultural pests.

Consumption of aphids by spiders and the effect of additional prey: evidence from microcosm experiments

Spiders are common generalist predators in agroecosystems and have been suggested to lower herbivore abundance in crops. It is not clear, however, if spiders can effectively suppress pest populations, and if so, by what mechanisms. In a microcosm experiment, we examined the consumption of the bird cherry-oat aphid, Rhopalosiphum padi L. (Homoptera: Aphididae), a pest species in wheat fields, by three spider species that differ in their hunting methods. We then tested the effect of additional prey type on the ability of erigonid spiders to reduce aphids. In a 48-h experiment Mermessus denticulatus (Banks) (Araneae: Linyphiidae; Erigoninae) consumed more aphids than did Enoplognatha gemina Bosmans and Van Keer (Araneae: Theridiidae) and Bathyphantes cf. extricatus (OP.-Cambridge) (Araneae: Linyphiidae; Linyphiinae). This difference may be due to the ability of erigonids to forage actively on the vegetation in addition to using their webs to catch prey. In a 7-week experiment, we provided springtails (Collembola) in high and low densities as additional prey to mated erigonids, prior to aphid introduction. Spiders in the low-density springtail treatment built more webs on the vegetation, and caused a 50% reduction in aphid populations. There were significantly fewer aphids in the low-density springtail treatment, but not in the high-density treatment, in comparison to the control (high-density springtails without spiders). The results suggest that additional prey density affects predatory interactions between M. denticulatus and R. padi and that erigonids, which occur in high densities in wheat fields in the Negev desert, may be involved in aphid suppression in these agroecosystems.

Predators reverse the direction of density dependence for juvenile salmon mortality

The effect of predators on prey populations depends on how predator-caused mortality changes with prey population density. Predators can enforce density-dependent prey mortality and contribute to population stability, but only if they have a positive numerical or behavioral response to increased prey density. Otherwise, predator saturation can result in inversely density-dependent mortality, destabilizing prey populations and increasing extinction risk. Juvenile salmon and trout provide some of the clearest empirical examples of density-dependent mortality in animal populations. However, although juvenile salmon are very vulnerable to predators, the demographic effects of predators on juvenile salmon are unknown. We tested the interactive effects of predators and population density on the mortality of juvenile Atlantic salmon (Salmo salar) using controlled releases of salmon in natural streams. We introduced newly hatched juvenile salmon at three population density treatments in six study streams, half of which contained slimy sculpin (Cottus cognatus), a common generalist predator (18 release sites in total, repeated over two summers). Sculpin reversed the direction of density dependence for juvenile salmon mortality. Salmon mortality was density dependent in streams with no sculpin, but inversely density dependent in streams where sculpin were abundant. Such predator-mediated inverse density dependence is especially problematic for prey populations suppressed by other factors, thereby presenting a fundamental challenge to persistence of rare populations and restoration of extirpated populations.

HARVESTING DISRUPTS BIOLOGICAL CONTROL OF HERBIVORES IN A SHORT-ROTATION COPPICE SYSTEM

Disturbances such as harvesting often interfere with the ecological processes that lead to the biological control of insect pests. For willows, grown as short-rotation coppice crops harvested every third to fifth year, it has been suggested that high plant quality in the resprouting shoots after harvesting may explain observed high densities of herbivorous insects, especially leaf beetles (Coleoptera: Chrysomelidae), in the plantations. In this study, we show that generalist predators may be important as regulators of leaf beetle populations. All three leaf beetle species, which were studied for five years in 12 plantations, showed a negative correlation between the population growth rate from spring to fall and the abundance of the most common generalist predator Orthotylus marginalis (Heteroptera: Miridae). For the most abundant leaf beetle, Phratora vulgatissima, we also found a significant positive correlation between its population growth rate and egg survival, indicating an overall effect of predation on herbivore population growth. Harvesting, which takes place during the winter, had a negative effect on the abundance of leaf beetles and predators. However, the first year after harvesting, all three leaf beetle species regained this loss with a very high population growth rate. A reason for the better ability of the herbivores to recover from the disturbance may be that they, unlike the predators, mainly overwinter outside the plantations. All three leaf beetles peaked in density three years after harvesting whereas the density of generalist natural enemies increased or leveled off during the five-year period after harvesting. We conclude that predation by generalist predators is potentially important for population control of leaf beetles in willow coppice, but that the intermediate disturbance regime of around five years between harvests, appears to be too short to avoid disruption of biological control. Alternatives for more efficient biological control in short-rotation coppice systems may be a longer period between harvests that enables the predators to fully respond numerically, to leave natural enemies refuges at harvest, or to harvest adjacent plantations asynchronously.

Mammal movements and foraging at remnant woodlands inside coniferous forest landscapes

Temporary or spatially restricted resources may affect population densities over more or less wide areas in the surrounding landscape or region. They may affect more than one trophic level by facilitation of predation. Areas of influence may differ between species. Such effects of mast-seeding in confined oak–hazel woodlands were examined for a guild of mainly seed-eating mammals and their predators. The mammals were tracked in snow in winter and the foraging of granivorous small mammals was assessed by experimental seed supplies in spring and autumn. Movements and foraging at various locations in and around the woodlands were distinguished from large-scale influences in the surrounding conifer forest landscape. Roe deer moved more abundantly inside the woodlands than in the conifer forest 50 m away and, less clearly, this was also the case for granivorous small mammals. Squirrels were particularly common at the edges while brown hares were somewhat less common at these edges. The edge effects appear therefore species-specific. Brown hares, squirrels, voles and granivorous small mammals were generally less common in the coniferous forest more than 500 m from the woodlands than in the coniferous forest 50 m from the woodlands. The most common generalist predator, the red fox, was as a mean equally common at all locations. However, it demonstrated a spatio-temporal variation in movements related to hare and, to a lesser extent, squirrel occurrence at open woodland sites. In order to sustain several mammalian species in conifer forest landscapes, not only granivorous ones, resource patches of oak and hazel should be retained, regenerated and, if possible, expanded. Such hot spots often need particular management.

GENERALIST PREDATORS DISRUPT BIOLOGICAL CONTROL BY A SPECIALIST PARASITOID

Two broad classes of arthropod natural enemies attack insect herbivores: specialists and generalists. The tight dynamical linkage of specialist natural enemies and their prey may make the specialists able to respond numerically to, and perhaps suppress, herbivore outbreaks. Because generalist predators may attack not only herbivores, but also the herbivores' specialist natural enemies, generalist predators may disrupt control of herbivore populations rather than contribute to it. We examined interactions between pea aphids (Acyrthosiphon pisum), a specialist parasitoid wasp (Aphidius ervi) that attacks the aphids, and a common generalist predator, carabid beetles (primarily Pterostichus melanarius). In two field experiments in alfalfa, we manipulated carabid densities to measure their direct (through predation) and indirect (through intraguild predation on A. ervi) impact on aphid population dynamics. The first experiment was initiated when plants were short (following cutting), and carabid predation of a...

Antipredatory Activity of the Weevil Oxyops vitiosa: A Biological Control Agent of Melaleuca quinquenervia

The larvae of the leaf-feeding weevil Oxyops vitiosa, a biological control agent of Melaleuca quinquenervia, are covered with a viscous orange coating that is thought to protect against generalist predators. This coating is gradually lost as the larvae drop to the ground and pupate in subterranean pupal cells. To test the antipredator activity of this species, four immature life stages (early instars, late instars, prepupae, pupae) were exposed to a common generalist predator, the red imported fire ant Solenopsis invicta. Choice tests were conducted by placing an O. vitiosa individual and a control larva of the weevil Neochetina eichhorniae into an arena containing a S. invicta colony and observing subsequent ant behaviors. S. invicta workers contacted O. vitiosa early instars, late instars, and prepupae less frequently than control N. eichhorniae larvae, and upon contact S. invicta was less likely to behave aggressively toward these O. vitiosa life stages than toward N. eichhorniae larvae. However, S. invicta contacted, attacked, and consumed naked (nonencased) O. vitiosa pupae and N. eichhorniae larvae with equal frequency. Encased O. vitiosa pupae buried in sand were not attacked compared to susceptible encased pupae on the sand surface. By shifting from a chemical defense during the larval stages to a physical defense during the pupal stage, O. vitiosa reduces the risk of attack by this generalist predator.

Cannibalism Regulates Densities of Young Wolf Spiders: Evidence From Field and Laboratory Experiments

We conducted field and laboratory experiments to examine the relative contributions of mortality from natural enemies and cannibalism to population regulation of the wolf spider Schizocosa ocreata. This cursorial spider is a common generalist predator in the leaf litter of forests of the eastern United States. In our study site in Maryland, densities of recently dispersed young S. ocreata can reach 60—90 individuals/m2, but decline to <15 spiders/m2 by early autumn. We investigated the cause of this rapid decline in spiderling density. We first performed a predator—exclusion field experiment to determine if natural enemies contributed significantly to spider mortality. Replicated enclosures with lip barriers to prevent emigration were stocked with newly dispersed S. ocreata spiderlings at either 0.75 X or 3 X mean field density, or had no S. ocreata added (0X). Before spiderlings were introduced, we reduced potential enemies in half of the plots by sifting the litter and removing other spiders, centipedes and predaceous beetles, and by installing 3—mm mesh netting to exclude birds, wasps and other predators of S. ocreata. Over a period of 2.5 mo we measured effects of natural enemies and spider density on prey (Collembola), spider growth, and spider survival. Spider mortality was high (≈ 80%) and strongly density dependent (DD). Survival in the 3$\times$ field—density plots was 50% lower than in the 0.75 X plots. Increasing spiderling density did not significantly reduce Collembola density and resulted only in a minor DD reduction in spiderling growth (≈ 10%). Although overall spider mortality was high, excluding natural enemies did not significantly improve spider survival. The absence of emigration and the high spider mortality rates in the predator—reduction treatment strongly implicate cannibalism as the major DD mortality factor. We then conducted two laboratory experiments in order to obtain direct measurements of the rates of cannibalism. Rates of cannibalism were measured in 0.3—m2 arenas stocked with S. ocreata at densities equivalent to those used in the field experiment. In Experiment 1, habitat complexity and prey availability were manipulated in arenas stocked with S. ocreata at 3 X mean field densities. In Experiment 2, we manipulated spider density (0.75 X and 3 X) and prey density to evaluate the DD component of cannibalism. The laboratory experiments confirmed the importance of cannibalism as a DD mortality factor. DD mortality from cannibalism was influenced by both prey abundance and habitat complexity. The presence of prey significantly reduced rates of cannibalism, and there was a significant interaction between habitat complexity and prey availability. When prey were present, rates of cannibalism were higher in the complex habitat than the simple habitat. In the absence of prey, increasing habitat complexity had no effect on rates of cannibalism. Rates of cannibalism in the treatment that most closely mimicked field conditions–complex leaf—litter with prey at natural densities–did not differ significantly from the rate of mortality of S. ocreata in the field experiment. Considered together, the results of our field and laboratory experiments lead to the conclusion that cannibalism can act as a strong DD mortality factor for young instars of S. ocreata, with the potential to regulate densities of this abundant cursorial spider.