Affect Prey Capture Research Articles

Allometric shifts in foraging site selection and area increase energy intake for Yellowstone Cutthroat Trout but are constrained by functional limits to prey capture

AbstractObjectiveFor foraging animals, energy acquisition is often influenced by an interaction of prey abundance and the amount of space needed to capture sufficient food. Suitable habitat includes those locations where prey capture rates are sufficient to meet energetic requirements for growth and reproduction. Hence, quantifying how space use changes with energy requirements and how prey densities affect prey capture rates in foraging animals provides insight into the mechanisms that create suitable habitat. Here, we were interested in assessing how body size influences foraging site selection, space use, and energy intake by Yellowstone Cutthroat Trout Oncorhynchus virginalis bouvieri. Furthermore, we sought to quantify how foraging rates changed with increasing levels of food.MethodsWe recorded Yellowstone Cutthroat Trout foraging behavior in natural streams and measured space use and foraging rates using three‐dimensional videography.ResultWe found that physical habitat features, such as current velocity, water depth, and foraging distance, were positively correlated with fish body size, but when foraging area was compared to a model of space use, we found that Yellowstone Cutthroat Trout used less space to capture prey than the model predicted. Fish foraging rates and estimated energy intake also increased with increasing prey availability; however, trout captured prey according to a type II functional response, indicating an upper limit to prey capture from handling time constraints.ConclusionThese data demonstrate that Yellowstone Cutthroat Trout display allometric changes in foraging habitat use: larger fish can occupy deeper and faster areas that increase prey encounter rates, but as prey encounter rates increase, the foraging rates become limited by an individual's ability to identify, pursue, and handle prey items.

Effects of subchronic exposure to environmentally relevant concentrations of a commercial fluridone formulation on fathead minnows (Pimephales promelas).

Invasive aquatic plants are a widespread problem in United States' waterways, and aquatic herbicide treatments are a common tool used in their management. Fluridone is an active ingredient in aquatic herbicides used globally to control aquatic plants. In order to be effective, fluridone requires a long contact time with plants resulting in extended exposure to non-target organisms. While there has been limited studies exploring the effects of fluridone on non-target aquatic organisms, the effects of subchronic commercial fluridone exposure at concentrations representative of operational use rates for plant management on fish are poorly understood. Therefore, we conducted a series of three exposure experiments using environmentally relevant concentrations on different life stages of the fathead minnow (Pimephales promelas). We exposed fathead minnows to a commercial fluridone formulation, Spritflo®, at environmentally relevant concentrations of 0.00, 3.00, 12.00, 25.00, and 100.00 μg/L. Exposure times included subchronic periods up to 35 days and a trans-generation exposure of 65 days, which is a likely residence time of fluridone when applied for plant management. Following 30 days of fluridone exposure, adult male fish had an increased presence of nuptial tubercules, an indicator of endocrine disruption, and an enlarged liver compared to the control. Additionally, we conducted larval fish behavior experiments and found fluridone exposure negatively affected prey capture ability, locomotion, and position preference. Our findings suggest fluridone treatment concentrations used in aquatic plant management do not directly cause mortality in fathead minnows, though sub-lethal effects observed could cause a decline in biological fitness and pose potential ecological implications.

Moonlight influence on quality of nestlings of scops owls depends on paternal coloration

Abstract Lunar phases might favor the maintenance of color polymorphism via disruptive selection if the different color variants performed differently in terms of prey capture under different moonlight levels. Moonlight, however, may affect prey capture as a side effect of its influence on prey behavior. Here we combine data of parental provisioning and quality of owlets with one ex-situ study of grasshopper activity to test whether Eurasian scops owls (Otus scops) with different plumage color and their prey are differently affected by moonlight. Food provisioning increased from new- to full-moon. However, the effect of moonlight on owlet mass gain and immune response depended on paternal coloration. On the one hand, body mass gain of nestlings of the greyest fathers increased from nights with new- to full-moon, whereas it did not change with moonlight for the brownest fathers. On the other hand, PHA response of nestlings of the brownest fathers increased with high moonlight levels during the first week of life, whereas it did not change with moonlight levels for the greyest fathers. Grasshoppers were more active at new moon than at full or waning moon. Our study provides supporting evidence that moonlight influences the behavior of both scops owls and its prey and suggests that fluctuations in environmental conditions can modulate the advantages of morphs. These results are important because they provide a general insight into a little appreciated mechanism for the maintenance of color polymorphism in natural populations based on the interactive effect of different environmental factors.

Effects of methylmercury on the early life stages of an estuarine forage fish using two different dietary sources

Marine fish accumulate methylmercury (MeHg) to elevated concentrations, often higher than in freshwater systems. As a neurotoxic compound, high MeHg tissue concentrations could affect fish behavior which in turn could affect their populations. We examined the sublethal effects of MeHg on larvae of the Sheepshead minnow (Cyprinodon variegatus), an estuarine fish, using artificial or natural diets with varying MeHg concentrations (0–4.8 ppm). Larvae were fed control and MeHg-contaminated diets at low or normal (10% of their body mass) daily food rations from 7 to 29 days when they reached juvenile stage. Growth, respiration, swimming activity and prey capture ability were assessed. Food ration affected Hg toxicity in our study. Natural diets containing 3.2 ppm MeHg had no impacts on growth and swimming in fish that were fed normal food rations but depressed growth and swimming at low food rations. MeHg toxicity did not differ between artificial and natural foods, however fish accumulated more MeHg from the former. Artificial food containing 4.8 ppm MeHg only affected prey capture after 21 days of exposure. Sheepshead minnows, a forage fish species occupying a low trophic level in coastal waters, can be MeHg tolerant, especially when food is abundant, and can serve as an enriched Hg source for higher trophic level predators.

Non-random perch selection by cryptic lizards, Amphibolurus muricatus

Many animals make use of camouflage to avoid or reduce visual detection by predators or prey species. Among the diverse forms of animal camouflage, background matching—where an individual’s appearance helps it blend into the visual backdrop of a scene—is commonly observed as a major function of cryptic species’ patterning and coloration. While some animals can rapidly modify their pattern to match their surroundings and better avoid detection, most possess static patterns or coloration and cannot quickly adjust to suit the visual environment. We expect such animals to consider the cryptic suitability of a background they choose to occupy, ideally selecting one with features suitable relative to their own markings, thereby maximizing concealment. This relationship is complicated by the potential range of different substrates typically available in any one habitat, as conspicuousness may vary considerably when viewed against the different background options available. In the present study, we tested some of these assumptions, investigating whether cryptic lizards, Amphibolurus muricatus (jacky dragons), utilized perch options with features complementary to their dorsal camouflage patterns more so than unsuitable perches. In two experiments, lizards were provided with perch options differing in coloration and cover availability and pattern, respectively. Individuals spent significantly more time using perches with cover available in the first experiment, and those with more complex patterns in the second. These findings suggest cryptic lizards may be selecting basking sites in a non-random fashion with respect to the visual environment in order to enhance camouflage success and that cover may be more important to perch selection than previously thought. SIGNIFICANCE STATEMENT: Among animals that employ visual camouflage as a primary survival strategy, differences in conspicuousness caused by being viewed upon the various suitable and unsuitable backgrounds available in a habitat have the potential to drastically affect prey capture and predation, and hence survival. With respect to this, cryptic animals should prefer to occupy substrates that are relevant to their own patterns and offer better concealment. Research in this behavioral maintenance of camouflage has focused on spectral properties of camouflage and substrates, but studies on fine-scale pattern and behavior in camouflage are under-represented. In captive perch choice experiments, we found that male jacky dragons (Amphibolurus muricatus) preferred perches with more complex patterns and those with plant cover available nearby. This research highlights the important role of behavior in supporting camouflage strategies and some of the considerations made when cryptic individuals choose substrates.

Foraging behaviour and optimal microhabitat selection in Yukon River Basin nonanadromous Dolly Varden Charr (Salvelinus malma)

AbstractSpecies conservation requires understanding the mechanistic processes of habitat selection and their effects on fitness. Nonetheless, there are few fitness‐based habitat selection models for aquatic organisms. We examined multiple aspects of foraging behaviour of nonanadromous Dolly Varden Charr (Salvelinus malma) in Panguingue Creek, Alaska, USA and applied these data to test a fitness‐based microhabitat selection model. Velocity negatively affected prey capture success, positively affected holding velocity, and had no effect on reactive distance. Dominance was a better predictor of prey capture success than length difference between competitors, but there was no relationship between these variables and holding velocity or reactive distance. We used the velocity–prey capture success relationship to parameterise the microhabitat habitat selection model and compared the predicted optimal holding velocity to the 95% confidence interval (24.9–29.3 cm/s) of holding velocities occupied by Dolly Varden (N = 29) in Panguingue Creek. The prediction of 24.0 cm/s fell just slightly (0.9 cm/s) outside the lower limit of the confidence interval; the model barely failed to predict holding velocity for this species in Panguingue Creek. Although this discrepancy fell within measurement error, model failure also may have been due to influence of high turbulence on fish holding velocities in the creek, low sample sizes imposed by permitting limitations, or field logistical issues. The relationship between velocity and prey capture success is an important aspect of drift feeder habitat selection. Our optimal holding velocity prediction for Dolly Varden should aid in the management and conservation of this species.

Circadian Rhythms of Retinomotor Movement in a Marine Megapredator, the Atlantic Tarpon, Megalops atlanticus.

Many ecologically and economically important marine fish species worldwide spend portions of their lives in coastal regions that are increasingly inundated by artificial light at night. However, while extensive research illustrates the harmful effects of inappropriate light exposure on biological timing in humans, rodents and birds, comparable studies on marine fish are virtually nonexistent. This study aimed to assess the effects of light on biological clock function in the marine fish retina using the Atlantic tarpon (Megalops atlanticus) as a model. Using anti-opsin immunofluorescence, we observed robust rhythms of photoreceptor outer segment position (retinomotor movement) over the course of the daily light–dark cycle: cone outer segments were contracted toward the inner retina and rods were elongated during the day; the opposite occurred at night. Phase shifting the daily light–dark cycle caused a corresponding shift of retinomotor movement timing, and cone retinomotor movement persisted in constant darkness, indicating control by a circadian clock. Constant light abolished retinomotor movements of both photoreceptor types. Thus, abnormally-timed light exposure may disrupt normal M. atlanticus clock function and harm vision, which in turn may affect prey capture and predator avoidance. These results should help inform efforts to mitigate the effects of coastal light pollution on organisms in marine ecosystems.

Hierarchical influences of prey distribution on patterns of prey capture by a marine predator

Summary Prey distribution acts at multiple spatial scales to influence foraging success by predators. The overall distribution of prey may shape foraging ranges, the distance between patches may influence the ability of predators to detect and move between profitable areas, and individual patch characteristics may affect prey capture efficiency. In this study, we assessed relationships between spatially explicit patterns of prey capture by a central place forager, the little penguin (using GPS tracking and accelerometry), and the distribution of aggregations of potential forage fish prey (using boat‐based active acoustics) in eastern Australia. We used complementary resource selection functions to estimate the distribution of both prey captures and aggregations across the study area, based on a suite of habitat characteristics. We found that 99% of prey captures by penguins occurred in the top 20 m of the water column. The estimated distribution of prey captures across the study area was similar to the distribution of aggregations above 20 m depth, indicating that penguins effectively matched the local distribution of their prey. The distances between consecutive prey captures followed a bimodal distribution, with means of 8·1 ± 2·2 and 57·4 ± 1·7 m. Based on the length of aggregations and the distances separating aggregations along survey transects, this implies that foraging behaviour occurs on multiple spatial scales corresponding to within‐patch and between‐patch movements respectively. Morphological characteristics of aggregations above 20 m depth were important for explaining variance in the number of prey caught by penguins in an area, with penguins catching more prey where aggregations were relatively dense, compact and shallow. These results reveal spatially explicit patterns of prey capture, and provide a framework for understanding how features of prey distribution influence prey intake by predators in patchy environments. A lay summary is available for this article.

Effects of Turbidity on Foraging Behavior in the Endangered Fountain Darter (Etheostoma fonticola)

Abstract The fountain darter Etheostoma fonticola is a federally endangered species that is associated with primarily clear, spring-fed systems, suggesting even minor changes in turbidity have the potential to affect behavior. We examined the effects of turbidity [control: <1 Nephelometric Turbidity Unit (NTU), minimal turbidity: mean = 8.7 NTU, moderate turbidity: mean = 23.2 NTU, and high turbidity: mean = 74.6 NTU] on the total number of prey items consumed, time to initiate foraging, total prey consumed out of the time left to forage, and number of strikes made per prey items (prey capture success). Our results indicate elevated turbidity significantly affects the number of prey consumed, time to initiate foraging, and total prey consumed out of the time left to forage. Turbidity does not appear to affect prey capture success. These data suggest even a slight elevation in turbidity (≥8.7 NTU) can significantly impair foraging behavior in E. fonticola.

Exposure to spinosad affects orb-web spider (Agalenatea redii) survival, web construction and prey capture under laboratory conditions

Spinosad is a neurotoxic pesticide, which is currently used in IPM and organic agriculture. It can affect the survival and ecological function of spiders, which are natural enemies of important agricultural pests. In the laboratory, we carried out tests to determine lethal and sublethal effects of spinosad on mortality, web building, and web characteristics of Agalenatea redii. Spinosad has a lethal effect at the normal application rate (NAR, i.e., 96 g ha(-1)) causing 35 % mortality (vs 0 % for control) after 4 days and 62 % mortality (vs 14 % for control) after 30 days. For the sublethal effects, web building was affected and fewer spiders built webs when exposed to spinosad (10/37 at NAR and 28/39 at half the NAR vs 35/37 for control group). No delay in web building was observed following exposure. Spider webs showed irregularities in the spiral-thread spacing (parallelism) when exposed to higher doses of spinosad (NAR and half of the NAR). Spinosad also affected prey capture: spiders exposed to spinosad (NAR) showed decreased prey capture efficiency (32 vs 73 % for control). These results showed that spinosad affects the spider predatory behavior (agriculture auxiliaries), which could modify their role in pest biocontrol.

Feeding performance of king Mackerel, Scomberomorus cavalla.

Feeding performance is an organism's ability to capture and handle prey. Although bite force is a commonly used metric of feeding performance, other factors such as bite pressure and strike speed are also likely to affect prey capture. Therefore, this study investigated static bite force, dynamic speeds, and predator and prey forces resulting from ram strikes, as well as bite pressure of the king mackerel, Scomberomorus cavalla, in order to examine their relative contributions to overall feeding performance. Theoretical posterior bite force ranged from 14.0-318.7 N. Ram speed, recorded with a rod and reel incorporated with a line counter and video camera, ranged from 3.3-15.8B L/s. Impact forces on the prey ranged from 0.1-1.9 N. Bite pressure, estimated using theoretical bite forces at three gape angles and tooth cross-sectional areas, ranged from 1.7-56.9 MPa. Mass-specific bite force for king mackerel is relatively low in comparison with other bony fishes and sharks, with relatively little impact force applied to the prey during the strike. This suggests that king mackerel rely on high velocity chases and high bite pressure generated via sharp, laterally compressed teeth to maximize feeding performance.

Autotomy and its Effects on Wolf Spider Foraging Success

AbstractFew studies have attempted to determine how physical injury affects predators. One of the ways that physical injury can be expressed is by autotomy or the voluntary loss of a body part. Here, we examined whether the loss of specific legs affects the foraging success of the wolf spider Rabidosa santrita (predator) on another species, Pardosa valens (prey). We also wanted to identify whether the loss of legs in both the predator and prey would impact the outcome of a predation event. Both predator and prey were collected from a creek bed at Portal, AZ, in 2012. Predators were randomly assigned groups where all prey items were intact or all prey had one randomly chosen leg IV removed. Within these groups, predators were organized into a control, leg I autotomy, or leg IV autotomy treatment. All predators had their pre‐ and post‐foraging running speed determined. Predators were introduced into chambers with five prey items and allowed to forage for 1 h. The leg position autotomized or the comparison of pre‐ and post‐foraging trials had no effect on predator running speed. Additionally, there was no significant effect of either predator or prey leg treatment on the total proportion of prey items captured by the end of the foraging trials. Survival analyses indicated that intact prey items tended to have a higher survival rate when predators were missing a leg IV than when predators were intact. When both the predator and prey were missing legs, no significant difference in prey survival rates was detected. We suggest that for predators that inhabit complex, heterogeneous habitats and are classified as ambush predators, the loss of a limb may affect prey capture success, especially when the prey is intact, but that increased sample size is necessary to determine whether this trend is significant.

Aging and foraging efficiency in an orb-web spider

Aging is often associated with reduced behavioral performance such as decreased locomotion or food consumption, related to a deterioration in physiological functions. In orb-web spiders, webs are used to capture prey and aging can affect web-building behavior and web structure. Here, we investigated the effect of aging on prey capture in the orb-web spider Zygiella x-notata. The ability of adult females to capture flies was examined at different ages. The rate of prey capture did not change with age, but older spiders took more time to subdue and capture the prey. Alterations which appeared in web structure with age (increase in the number of anomalies affecting radii and capture spiral) affected prey capture behavior. Furthermore, the analysis of individual performance (carried out on 17 spiders at two different ages) showed that older females spent more time handling the prey and finding it in the web. Our results suggest that, in the laboratory, age does not affect prey capture rates but it influences prey capture behavior by affecting web structure or/and spider motor functions.

To Eat and Not Be Eaten: Modelling Resources and Safety in Multi-Species Animal Groups

Using mixed-species bird flocks as an example, we model the payoffs for two types of species from participating in multi-species animal groups. Salliers feed on mobile prey, are good sentinels and do not affect prey capture rates of gleaners; gleaners feed on prey on substrates and can enhance the prey capture rate of salliers by flushing prey, but are poor sentinels. These functional types are known from various animal taxa that form multi-species associations. We model costs and benefits of joining groups for a wide range of group compositions under varying abundances of two types of prey–prey on substrates and mobile prey. Our model predicts that gleaners and salliers show a conflict of interest in multi-species groups, because gleaners benefit from increasing numbers of salliers in the group, whereas salliers benefit from increasing gleaner numbers. The model also predicts that the limits to size and variability in composition of multi-species groups are driven by the relative abundance of different types of prey, independent of predation pressure. Our model emphasises resources as a primary driver of temporal and spatial group dynamics, rather than reproductive activity or predation per se, which have hitherto been thought to explain patterns of multi-species group formation and cohesion. The qualitative predictions of the model are supported by empirical patterns from both terrestrial and marine multi-species groups, suggesting that similar mechanisms might underlie group dynamics in a range of taxa. The model also makes novel predictions about group dynamics that can be tested using variation across space and time.

Effect of substrate density on behaviour of antlion larvae (Neuroptera: Myrmeleontidae)

Sand-dwelling antlion larvae are well known predators with a highly specialized prey-catching strategy, which either construct efficient pitfall traps or bury themselves in the sand ambushing prey on the surface. Although habitat selection in antlions has been extensively studied, little is known about the role substrate density plays in such behavioural decisions. We thus first quantified the natural substrate densities of 13 antlion species by collecting soil samples from 18 different field sites. We found that natural substrate densities varied from 121 g/l to 1562 g/l. The substrate densities of three non-pit-building species (Neuroleon microstenus, Distoleon tetragrammicus, Nophis teillardi) ranged from medium to high, while those of obligatory pit-builders (Euroleon nostras and eight Myrmeleon species) were more variable. The substrate density of the facultative pit-builder Cueta sp. was high. Next, we explored the responses of the pit-building antlion E. nostras to different substrate densities using both a habitat choice and a complementary no-choice experiment. We hypothesized that antlions should be capable of distinguishing between substrate types and that pit size should decrease with increased substrate density. When allowed to choose among eight substrate densities, E. nostras larvae preferred to build their pits in the fractions with low densities (i.e., 121, 353 and 512 g/l) and only a small proportion constructed pits in high density fractions (i.e., 1312 and 1546 g/l). A complementary no-choice experiment demonstrated that pit diameter, pit depth and pit angle were negatively correlated with substrate density. These reductions in pit size can negatively affect prey capture success.

Embryonic exposure to environmentally relevant concentrations of PCB126 affect prey capture ability of Fundulus heteroclitus larvae

Early life stages from a marine fish species, Fundulus heteroclitus, were exposed to sublethal doses of 3,3′,4,4′,5 pentachlorobiphenyl (PCB126) to evaluate its effects on ecologically relevant responses: growth and behavior. A few hours after fertilisation, eggs were treated topically with PCB126 (2.5–50 pg egg −1). Four days post-hatching (dph), morphological changes (body length and malformations), spontaneous locomotor activity (active swimming speed, rate of travel, % inactivity), prey capture ability ( Artemia franciscana nauplii) and whole body EROD activity were evaluated in larvae. Untreated larvae collected at 0.5, 1, 2, 3, 4 dph were also examined. PCB126 did not increase the mortality or malformation rates. Body length and spontaneous locomotor activity were altered only in larvae treated with the highest dose. Treatment with PCB126 caused a dose-responsive reduction in prey capture ability (rate of decline in the number of Artemia) and induction of EROD activity. The lowest observed effective dose for both of these responses was 5.0 pg PCB126 egg −1 or 5.0 TCDD-toxic equivalents pg g −1 egg, using a TCDD-toxic equivalent factor of 0.005 and an egg mass of 5 mg. Prey capture efficiency (number of Artemia captured per feeding strike) was reduced at ≥10.0 pg egg −1. In untreated developing larvae, prey capture ability and efficiency increased as post-hatching development progressed and EROD activity remained low. The pattern of behavioral responses observed in PCB126-exposed Fundulus larvae differed from that observed in less-developed larvae indicating that other mechanisms than retarded development were involved. Behavioral dysfunction was a more sensitive response to PCB126 than morphological alterations and it occurred at environmentally relevant concentrations.

Integrated diversification of locomotion and feeding in labrid fishes

An organism's performance of any ecological task involves coordination of multiple functional systems. Feeding performance is influenced by locomotor abilities which are used during search and capture of prey, as well as cranial mechanics, which affect prey capture and processing. But, does this integration of functional systems manifest itself during evolution? We asked whether the locomotor and feeding systems evolved in association in one of the most prominent and diverse reef fish radiations, the Labridae. We examined features of the pectoral fins that affect swimming performance and aspects of the skull that describe force and motion of the jaws. We applied a recent phylogeny, calculated independent contrasts for 60 nodes and performed principal components analyses separately on contrasts for fin and skull traits. The major axes of fin and skull diversification are highly correlated; modifications of the skull to amplify the speed of jaw movements are correlated with changes in the pectoral fins that increase swimming speed, and increases in force capacity of the skull are associated with changes towards fins that produce high thrust at slow speeds. These results indicate that the labrid radiation involved a strong connection between locomotion and feeding abilities.

Effect of dietary arachidonic acid, eicosapentaenoic acid and docosahexaenoic acid on survival, growth and pigmentation in larvae of common sole (Solea solea L.)

Evidence confirms that polyunsaturated fatty acids (PUFAs), arachidonic acid (ARA), eicosapentaenoic acid (EPA) and docosahexaenoic acid, DHA are involved in growth as well in pigmentation of marine fish larvae.In the present study we examined the performance of common sole larvae reared on Artemia enriched with 10 formulated emulsions, differing in inclusions of ARA, EPA, and DHA. The specific growth rate of the sole larvae until late metamorphosis, 21 days after hatching (dah) was 20 to 27% d−1. Even though the relative tissue essential fatty acid (EFA) concentrations significantly reflected dietary composition, neither standard growth nor larval survival were significantly related to the absolute concentrations of ARA, EPA and DHA or their ratios. This suggests low requirements for essential polyunsaturated fatty acids (PUFAs) in common sole. Malpigmentation was significantly related to increased dietary ARA content. However, pigmentation was not affected by inclusion levels of EPA or DHA when ARA was high. This, and no relation between DHA: EPA or ARA: EPA ratios and pigmentation and only a weak relation to ARA: DHA ratio, advocate for that it is the absolute concentration of ARA in larval tissues, that is responsible for malpigmentation rather than the relative concentration to other PUFAs.Within malpigmentation, the trait “albinism” was characterised by an abnormal incomplete eye migration, but this trait is suggested not to be related to dietary ARA. Furthermore, albinism resulted in a lower growth rate, which suggests that visual aberrations affected prey capture.

Between-sex Variation in Running Speed and a Potential Cost of Leg Autotomy in the Wolf Spider Pirata sedentarius

Leg autotomy in spiders is a relatively common occurrence, usually resulting from agonistic interactions with predators or conspecifics. While autotomy has immediate benefits, due to enhanced survival probability, it also potentially decreases future fitness. One possible cost of losing a leg is a reduction in burst running speed, which may affect prey capture and predator avoidance behaviors in wandering spiders. We examined sprint speed in intact and autotomized males and females of the wolf spider Pirata sedentarius from two stream banks in New York in an effort to determine if the sexes differed in either sprint speed or the potential cost of leg loss. Autotomy was fairly common in the field, with 18–22% of spiders missing at least one leg at our two sites. Males and females did not differ in frequency of leg loss. Females were larger than males (both in terms of mass and structural size) and ran significantly faster both before and after autotomy. Sprint speed was uncorrelated with body size (mass, carapace width or leg length) for males, while for females the only significant relationship was that between mass and pre-autotomy speed. Both sexes ran significantly faster when they had all legs compared to their speed after autotomy. We found no difference in speed between spiders which had lost a leg in the field and spiders from which we removed a leg in the laboratory or between intact spiders and spiders collected in the field with a leg missing. Overall, our results for P. sedentarius indicate that: (1) females are faster than males, (2) autotomy significantly reduces sprint speed in the lab for both sexes and (3) reductions in male sprint speed in the lab may result from a combination of autotomy and aging effects, while decreases in female speed are likely due primarily to autotomy.

Testing for the effect of detritus stabilimenta on foraging success in Cyclosa octotuberculata (Araneae: Araneidae)

This study tested the possibility that detritus stabilimenta of Cyclosa octotuberculata affect prey capture rate. Field experiments showed that there was no significant difference in prey capture rate between webs with and without detritus stabilimenta even after controlling for factors likely to affect foraging success. Thus, detritus stabilimenta appear to have no visual effects on insect prey despite their conspicuous appearance.