Prey Consumption Rates Research Articles

Plant and prey quality interact to influence the foraging behaviour of an omnivorous insect, Dicyphus hesperus

The foraging behaviour of omnivores is often difficult to predict and, thus, our understanding of their role in ecosystems is limited. The majority of our knowledge about omnivores comes from studies examining their preferences for different species of plants and prey under different conditions. The potential effect of intraspecific variation in food quality on omnivore foraging behaviour has received less attention. To enhance our understanding of the foraging behaviour of omnivores, we used focal observations in the laboratory to monitor the foraging behaviour and activity budget of an omnivorous insect, Dicyphus hesperus Knight (Hemiptera: Miridae), in arenas where a single species of plant food and a single species of prey food were provided at varying levels of quality based on nitrogen content. The activity budget of D. hesperus was not balanced; it was dominated by prey feeding, followed by plant feeding and probing. Foraging behaviour of D. hesperus was affected by the interaction of prey and plant quality, such that optimal foraging theory could predict its foraging behaviour in the presence of prey reared on high N-fertilized tomato plants, but not in the presence of low N-fertilized tomato plants. Neither prey quality nor plant quality affected the rate of prey consumption or the handling time of prey by D. hesperus during the observation period. Our results highlight the complexity of omnivore feeding behaviour and indicate that feeding decisions are not based only on the prey or plant species provided, but also on the quality of those resources.

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.

<p><strong>Sublethal effects of abamectin and fenpropathrin on the consumption of <em>Tetranychus urticae</em> eggs by <em>Scolothrips longicornis</em></strong></p>

Study of the sublethal effects of pesticide residues on predatory thrips is important for the design of integrated pest management programmes with biocontrol elements included. We estimated the sublethal effects of three concentrations of fenpropathrin and abamectin (LC10, LC20 and LC30) on prey consumption rates of exposed females of Scolothrips longicornis Priesner and their offspring when fed on Tetranychus urticae Koch eggs. Prey consumption of female thrips was significantly affected by treatment with all concentrations of the two pesticides with the effect of fenpropathrin being more severe than that of abamectin. Regarding the offspring of treated females, the prey consumption by thrips larvae was adversely affected by both pesticide treatments with no major differences between the two pesticides. The sublethal effects of these pesticides should be taken into account in the planning of integrated management programmes.

All's good in a famine? Hydrobia ulvae as a secondary prey for juveniles of Iceland moonsnails Amauropsis islandica at the White Sea sandflats

Many size-selective predators switch their diet during ontogeny. At the White Sea, the adult moonsnails Amauropsis islandica feed mostly on Macoma balthica clams. The diet of juveniles was largely unknown. We conducted a field survey and a caging experiment to find out if juvenile moonsnails can prey on Hydrobia ulvae, and whether they prefer this snail to their usual prey. Live molluscs and their intact or perforated shells were collected from 34 sediment cores. We exposed the single-prey cages with 50 Macoma (MP) or 50 Hydrobia (HP) together with five Amauropsis juveniles, as well as the cages where both prey species were in a 25:25 proportion (HMP). While live Hydrobia was more abundant in the natural assemblages, Amauropsis preferred Macoma, as indicated by proportions of perforated shells. The caging experiment produced similar results. Per capita Macoma consumption rate was significantly higher than Hydrobia consumption rate (6.4 ± 0.5 mg day−1 ind.−1vs. 1.4±0.2 mg day−1 ind.−1 in MP and HP respectively). Prey consumption rates in the single-prey treatments were higher than in mixed-prey cages regardless of prey species. Different mechanisms explain this variation: for Hydrobia it is a consequence of the dietary shift, while for Macoma it reflects the ‘floor’ effect in HMP cages, where virtually all Macoma had been drilled by the end of exposure term. While Macoma is the preferable prey of young Amauropsis, Hydrobia can supplement the diet of juveniles when Macoma is scarce in certain locations.

Species‐specific effects of subdaily temperature fluctuations on consumption, growth and stress responses in two physiologically similar fish species

AbstractFluctuations in water temperature can have important physiological consequences for fishes. Effects of daily thermal cycles are well studied and can be beneficial, increasing prey consumption and growth rates when mean and maximum temperatures of the fluctuations are at or below the species’ optimum temperature. While less studied, subdaily temperature fluctuations are also common in many aquatic habitats and can be caused by both natural and anthropogenic processes. We performed laboratory experiments to examine how two fish species (yellow perch, Perca flavescens, and walleye, Sander vitreus) with similar thermal preferences respond to chronic exposure to subdaily temperature variability. We selected temperature treatments that reflected observed thermal variation after examining water temperature data from multiple aquatic systems. We then separately exposed yellow perch and walleye to a stable 23 °C treatment and 12‐h cycles of 23 ± 2 °C or 23 ± 4 °C for 45 days. Adult yellow perch exposed to fluctuations of 23 ± 4 °C over 12 h expressed higher consumption, growth and food conversion efficiency than fish experiencing stable 23 °C. Temperature fluctuations, though, resulted in mortalities and the development of skin ulcers in yellow perch that did not occur under stable temperatures. In contrast, the same 12‐h temperature fluctuations did not result in mortalities or stress responses in juvenile walleye. Moreover, unlike yellow perch, growth rates of walleye were lower under 12‐h temperature fluctuations compared with the stable 23 °C treatment. Our results indicate that species with similar thermal preferences can respond differently to the same subdaily temperature fluctuations.

<p class="Body"><strong>Life history traits of predatory mite <em>Typhlodromus </em>(<em>Anthoseius</em>)<em> bagdasarjani</em> (Phytoseiidae) fed on <em>Cenopalpus irani </em>(Tenuipalpidae) under laboratory conditions </strong></p>

Biological traits of Typhlodromus (Anthoseius) bagdasarjani Wainstein & Arutunjan when exposed to the false spider mite, Cenopalpus irani Dosse (Tenuipalpidae), as a food source were determined at 27±1°C, with 16:8 h L: D, at an average daily relative air humidity of 60±10%. The developmental durations of egg, larva, protonymph, deutonymph stages and of all the juvenile phase (egg–adult) being 1.9±0.14, 0.9±0.05, 2.2±0.12, 2.5±0.12 and 7.6±0.18 days, respectively. Survivorship of the juvenile phase was 87%. Fecundity and daily oviposition rate was 33.8±2.60 eggs/female and 1.8 eggs/female/day, respectively. Oviposition period, adult longevity and total life span of females were 19.1±1.76, 36.8±1.88 and 44.3±1.84 days, respectively. The mean generation time (T), net reproductive rate (R0) and intrinsic rate of increase (rm) were 15.32±0.69 days, 14.38±1.11 female offspring and 0.174±0.005 day-1, respectively. Daily prey consumption rates by T. bagdasarjani protonymphs and deutonymphs were 6.0±0.21 and 5.1±0.17 prey individuals/day, respectively. Protonymphs and deutonymphs of T. bagdasarjani preferred the larval stages of C. irani to feed. The results of this study suggested that C. irani is a suitable prey for T. bagdasarjani, and that the predator might play a significant role in preventing that prey from reaching even higher population levels than it does on apple in western Iran.

Mysis zooplanktivory in Lake Champlain: A bioenergetics analysis

Abstract Mysid shrimp are important both as predators on zooplankton and as prey for a variety of fish species across most of the Laurentian Great Lakes. In Lake Champlain, where little is known about mysids, this may also be true. We evaluated the role of Mysis diluviana as a planktivore in Lake Champlain using hydroacoustics, gut content analysis, stable isotopes, cohort analysis, and bioenergetics models to estimate Mysis density, diets, growth rates, and prey consumption rates. Density of Mysis in the water column of the deeper Main Lake was lower in July–August of 2008–2011 (38, 38, 21, and 74 Mysis /m 2 , respectively) than historical values from the 1970s. Mysis selectively foraged for cladocerans, but also consumed cyclopoid and calanoid copepods in 2011. Stable isotope data suggest a mostly carnivorous diet, although agreement between isotope mixing models and observed diets varied. Cohort analyses revealed growth rates ranging from 2.7 mm/month in late spring to 1.3 mm/month in late summer. In contrast to the offshore areas of Lake Ontario and Lake Huron, zooplankton consumption by the Mysis population was low relative to zooplankton density and production indicating that Mysis are not currently a major zooplanktivore in Lake Champlain.

Testing assumptions of central place foraging theory: a study of Adélie penguins Pygoscelis adeliae in the Ross Sea

We investigated central place foraging (CPF) in the context of optimal foraging theory in Adélie penguins Pygoscelis adeliae of the southern Ross Sea by using satellite tracking and time‐depth recorders to explore foraging at two spatio‐temporal scales: within the day‐to‐day (sub‐mesoscale: single foraging trip, 10s of km2) and the entire breeding season (mesoscale: trips by multiple individuals across the collective foraging area, 100s of km2). Specifically, we examine whether three basic assumptions of the Orians–Pearson CPF model, shown to occur in other CPF species, are met: 1) within a patch, the rate of prey acquisition declines with time spent in that patch; 2) food is distributed in discrete patches and is not available between those patches; and 3) CPF species have knowledge of the potential (or average, at least) feeding rate within their universe of patches, and use this knowledge to determine their foraging strategy when planning or engaging in a foraging trip. We found that prey consumption rates did not decline with time spent in patches, and penguins foraged to some degree most of the time when at sea. Food availability, as measured by foraging dive rate, appeared to be predictable within the same day at the same location, but predictability broke down after 2 d at distances > 10 km away. We conclude that the assumptions of the Orians–Pearson CPF model are not a good fit to the circumstances of Ross Sea penguins, which clearly are central place foragers.

Predator‐free space, functional responses and biological invasions

SummaryPredator–prey interactions are mediated by the structural complexity of habitats, but disentangling the many facets of structure that contribute to this mediation remains elusive. In a world replete with altered landscapes and biological invasions, determining how structure mediates the interactions between predators and novel prey will contribute to our understanding of invasions and predator–prey dynamics in general.Here, using simplified experimental arenas, we manipulate predator‐free space, whilst holding surface area and volume constant, to quantify the effects on predator–prey interactions between two resident gammarid predators and an invasive prey, the Ponto‐Caspian corophiidChelicorophium curvispinum.Systematically increasing predator‐free space alters the functional responses (the relationship between prey density and consumption rate) of the amphipod predators by reducing attack rates and lengthening handling times. Crucially, functional response shape also changes subtly from destabilizingTypeIItowards stabilizingTypeIII, such that small increases in predator‐free space to result in significant reductions in prey consumption at low prey densities.Habitats with superficially similar structural complexity can have considerably divergent consequences for prey population stability in general and, particularly, for invasive prey establishing at low densities in novel habitats.

Biocontrol potential of the lynx spider Oxyopes javanus (Araneae: Oxyopidae) against the tea mosquito bug, Helopeltis theivora (Heteroptera: Miridae)

The tea (Camellia sinensis (L.) Kuntze) industry is the backbone of the agroeconomy of the North Bengal region located at the foothills of the Himalayas in North-East (NE) India. This region accounts for about 25% of the total tea production in India. The tea mosquito bug, Helopeltis theivora Waterhouse, is one of the most devastating sucking pests of tea in this region. Various kinds of synthetic insecticides are continuously sprayed to control this bug. The lynx spider Oxyopes javanus. Thorell has been found to remain associated with tea plants and feed on H. theivora. The present study investigated the predation potential and efficacy of the O. javanus spider against one of its most common prey species, H. theivora. In the laboratory, with an increase in H. theivora density, the predation rate of both male and female O. javanus increased. Per capita predation rates exhibited by male and female O. javanus per day against adult H. theivora were 3.67 ± 1.52 and 11.67 ± 1.53 (mean ± standard deviation), respectively. At a reasonably small prey density, the prey consumption rate was highest, reaching up to 100%, indicating that the spider predator has the potential to eliminate smaller populations of the pest. The predation effectiveness calculated using Holling’s disc equation was 6.08 and 356.58 for male and female O. javanus, respectively. The prey handling time was 0.138 day for male O. javanus and 0.012 day for female O. javanus. Female O. javanus exhibited about fivefold higher searching efficacy than male O. javanus. It appears that the conservation or augmentation of O. javanus in the tea ecosystem can provide effective biological management of the major tea pest, H. theivora, in sub-Himalayan foothills and plains of NE India.

Host plant mediates foraging behavior and mutual interference among adult Stethorus gilvifrons (Coleoptera: Coccinellidae) preying on Tetranychus urticae (Acari: Tetranychidae).

Physical plant characteristics can influence predator foraging and their behavioral responses to each other. This study examined the searching efficiency and functional response of adult female Stethorus gilvifrons Mulsant foraging for Tetranychus urticae Koch (Acari: Tetranychidae) on castor bean, common bean, and cucumber leaves. Experiments conducted on leaf discs in arenas for 12 h revealed a type II functional response for S. gilvifrons on all host plants. Per capita searching efficiency and killing power decreased with increasing predator density on all plants, but most notably on common bean, the plant with the highest prey consumption rates, due to greater mutual interference. Attack rates were highest on common bean and lowest on castor bean, whereas handling times were shortest on common bean and longest on cucumber, such that the daily predation rate was maximal on common bean. Host plant interacted with predator and prey densities to affect searching efficiency and functional response, the differences in mite consumption among host plants increasing with predator and prey densities. The waxy layers of castor bean leaves and high trichome counts of cucumber leaves appeared to reduce predator foraging efficiency. Thus, the efficacy of S. gilvifrons against T. urticae is likely to be greatest on plants such as Phaeseolus vulgaris L. that have relatively smooth leaves.

Why ratio dependence is (still) a bad model of predation.

The history of the idea that predation rates are functions of the ratio of prey density to predator density, known as ratio dependence, is reviewed and updated. When the term was introduced in 1989, it was already known that higher predator abundance often reduced an individual predator's average intake rate of prey. However, the idea that this effect was a universally applicable inverse proportionality was new. That idea was widely criticized in many articles in the early 1990s, and many of these criticisms have never been addressed. Nevertheless, ratio dependence seems to be gaining in popularity and is the subject of a recent monograph by the originators. This article revisits the most important objections to this theory, and assesses to what extent they have been answered by the theory's proponents. In this process, several new objections are raised. The counterarguments begin with the lack of a plausible, generally applicable mechanism that could produce ratio dependence. They include the fact that ratio dependence is a special case of predator-density effects, which, in turn, are only one of many non-prey species effects that influence the consumption rate of a particular prey. The proclaimed simplicity advantage of ratio dependence is at best small and is outweighed by its disadvantages; it predicts biologically implausible phenomena, and cannot easily be extended to describe multi-species systems, trait-mediated interactions, coevolution, and a number of other important ecological phenomena. Any potential small simplicity advantage disappears with corrections to remove unrealistic low-density dynamics caused by ratio dependence. The frequent occurrence of strong predator dependence does not make ratio dependence a better 'default' model of predation than prey dependence, and empirical studies of the full range of non-prey species effects on the consumption rates of predators are needed.

Light dependency of life trails, reproduction, locomotion, and predation in the polyphagous ladybird Hippodamia variegata

AbstractLight is regarded a key environmental cue influencing biological, physiological, and behavioral characteristics in insects. We compared the development, reproduction, locomotion, and predation ability of the predatory ladybird Hippodamia variegata (Goeze) (Coleoptera: Coccinellidae) under various photoperiods, light intensities, and light wavelengths. The results indicated long daylight, high light intensity, and particular colors light (blue, green, and yellow) could benefit H. variegata especially in shortening the period of immature development, increasing mating frequency (shorter mating and pre‐oviposition periods), higher fecundity, and a higher proportion of eggs hatched. Average locomotion speed and prey consumption rate of H. variegata increased with prolonged day length and increased light intensity. However, very high intensity of light could inhibit predation rates. Furthermore, green and yellow wavelength conditions increased locomotion speed of H. variegata, and the number of prey consumed increased with increased wavelength. The present study not only revealed significant influences of light conditions on the development and fertility of H. variegata, it also provided sufficient empirical data to improve the efficiency of mass rearing and field releases of this predatory ladybird by regulation of light conditions during biological control applications.

Eating between the lines: functional feeding response of bonnetheads (Sphyrna tiburo)

Mobile mesopredators can have strong influences in the structuring of marine food webs in shallow coastal ecosystems. Few quantitative estimates of the effects of predation on prey populations by highly mobile mesopredators exist, yet they are necessary to evaluate the impact mesopredators have on prey resources. Quantifying a predator’s functional response provides valuable information on how a predator’s per capita consumption rate of prey can influence community structure and prey populations. We examined the functional response of bonnetheads (Sphyrna tiburo) to one of its few natural prey items brown shrimp (Farfantepenaeus aztecus) to determine if per capita feeding rates would increase with increases in prey density. We simulated natural conditions in outdoor mesocosms and offered live prey at varying densities. The functional response of a predator can take one of three forms: linear (type I), rise to an asymptote (type II), and a sigmoid shape (type III). Bonnetheads consumed prey proportional to prey density and demonstrated a response that was in between a type I (R2 = 0.847, p < 0.01) and type II (R2 = 0.877, p < 0.01) functional response. Bonnetheads showed an increased rate of consumption with initial low prey densities but high densities of available prey did not consistently result in increased consumption rates. At the maximum prey density offered, bonnetheads consumed less prey than at intermediate densities. Bonnetheads may not have as strong of an influence on prey populations at high prey densities compared to predation impacts at low densities. Bonnethead per capita feeding rates did not conform to a type I, type II, or type III functional response and our results suggest that bonnetheads follow a functional response continuum more closely. This study highlights the importance and difficulty in understanding the feeding ecology of highly mobile mesopredators.

Complementarity and redundancy of interactions enhance attack rates and spatial stability in host-parasitoid food webs.

Complementary resource use and redundancy of species that fulfill the same ecological role are two mechanisms that can respectively increase and stabilize process rates in ecosystems. For example, predator complementarity and redundancy can determine prey consumption rates and their stability, yet few studies take into account the multiple predator species attacking multiple prey at different rates in natural communities. Thus, it remains unclear whether these biodiversity mechanisms are important determinants of consumption in entire predator-prey assemblages, such that food-web interaction structure determines community-wide consumption and stability. Here, we use empirical quantitative food webs to study the community-wide effects of functional complementarity and redundancy of consumers (parasitoids) on herbivore control in temperate forests. We find that complementarity in host resource use by parasitoids was a strong predictor of absolute parasitism rates at the community level and that redundancy in host-use patterns stabilized community-wide parasitism rates in space, but not through time. These effects can potentially explain previous contradictory results from predator diversity research. Phylogenetic diversity (measured using taxonomic distance) did not explain functional complementarity or parasitism rates, so could not serve as a surrogate measure for functional complementarity. Our study shows that known mechanisms underpinning predator diversity effects on both functioning and stability can easily be extended to link food webs to ecosystem functioning.

Top-down pressure on small pelagic fish by eastern Australian salmon Arripis trutta; estimation of daily ration and annual prey consumption using multiple techniques

Ecosystem-level models that trace flows of mass and energy to quantify species interactions are important tools in whole ecosystem-based approaches to managing marine resources. A critical input parameter for such models is an estimate of the consumption rates and biomasses of prey consumed by fish populations. Here we estimate the annual prey consumption of an abundant coastal piscivore, Arripis trutta, which may exert substantial top-down control on its prey over its broad latitudinal range (28–43°S) in the coastal waters off south-eastern (SE) Australia. Three independent techniques were used to estimate annual prey consumption at two environmentally-relevant temperatures, 15 and 20°C: experimental gastric evacuation experiments (coupled with stomach content analyses); bioenergetics modelling, and; empirical regression modelling. Each technique yielded a similar range of estimates with annual food consumed/biomass (Q/B) ranging from 3.20 to 4.02 at 15°C and 4.23 to 5.25 at 20°C. Using an estimated A. trutta stock biomass in SE Australia of 10,000t, total mean annual prey consumption was estimated to be 42,200t, consisting primarily (93%) of small zooplanktivorous teleosts, particularly Australian sardines Sardinops sagax (35%) and scads Trachurus spp. (30%). These results indicate that A. trutta do possess a top-down influence on the pelagic ecosystem of coastal SE Australia via consumption of considerable biomasses of small pelagic fish. However, despite the use of a maximum regional estimate of A. trutta abundance and the presence of at least two other ecologically similar predatory fish species with higher annual prey consumption rates in SE Australian coastal waters, A. trutta may remove only a small proportion (~15%) of the estimated spawning biomasses of its major prey species in this region annually. The multiple-technique approach used in this study has for the first time quantified the diet of A. trutta in SE Australia and provided broad and repeatable estimates of its annual prey consumption for use in ecosystem models designed to manage coastal fisheries resources in this region.

Functional response of Euseius concordis to densities of different developmental stages of the cassava green mite

Both prey density and developmental stage of pests and natural enemies are known to influence the effectiveness of biological control. However, little is known about the interaction between prey density and population structure on predation and fecundity of generalist predatory mites. Here, we evaluated the functional response (number of prey eaten by predator in relation to prey density) of adult females and nymphs of the generalist predatory mite Euseius concordis to densities of different developmental stages of the cassava green mite Mononychellus tanajoa, as well as the fecundity of adult females of the predator. We further assessed the instantaneous rate of increase, based on fecundity and mortality, of E. concordis fed on eggs, immatures and adults of M. tanajoa. Overall, nymphs and adults of E. concordis feeding on eggs, immatures and females of M. tanajoa had a type III functional response curve suggesting that the predator increased prey consumption rate as prey density increased. Both nymphs and adult females of the predator consumed more eggs than immatures of M. tanajoa from the density of 20 items per leaf disc onwards, revealing an interaction between prey density and developmental stage in the predatory activity of E. concordis. In addition, population growth rate was higher when the predator fed on eggs and immatures in comparison with females. Altogether our results suggest that E. concordis may be a good candidate for the biological control of M. tanajoa populations. However, the efficiency of E. concordis as a biological control agent of M. tanajoa is contingent on prey density and population structure.

Mercury and selenium ingestion rates of Atlantic leatherback sea turtles (Dermochelys coriacea): A cause for concern in this species?

Bodily accumulation of certain toxic elements can cause physiologic harm to marine organisms and be detrimental to their health and survival. The leatherback sea turtle (Dermochelys coriacea) is a broadly distributed marine reptile capable of consuming hundreds of kilograms of gelatinous zooplankton each day. Little is known about toxicants present in these prey items. Specifically, mercury is a known neurotoxin with no known essential function, while selenium detoxifies bodily mercury, but can be toxic at elevated concentrations. I collected 121 leatherback prey items (i.e., gelatinous zooplankton) from known leatherback foraging grounds and sampled the esophagus and stomach contents of stranded turtles. All samples were analyzed for total mercury and selenium. Additionally, two prey items and three liver samples were analyzed for methylmercury, the most toxic form of the element. Total mercury concentrations in prey items ranged from 0.2 to 17 ppb, while selenium concentrations ranged from <10 to 616 ppb; methylmercury concentrations in liver ranged from 25 to 236 ppb. Prey items had methylmercury concentrations below the limits of detection (<0.4 ppb). Hazard quotients and exposure rates indicate that leatherbacks of all life stages may be at risk for selenium toxicity. For endangered species like the leatherback, continued anthropogenic deposition of mercury and selenium into the environment is concerning, especially since bodily mercury and selenium concentrations increase as organisms age. Because leatherbacks are long-lived and have large daily prey consumption rates, mercury and selenium loads may increase to physiologically harmful levels in this imperiled species.

Investigating Habitat use, Prey Consumption, and Dispersal Response as Potential Coexistence Mechanisms using Morphologically Similar Species of Predaceous Diving Beetles (Coleoptera: Dytiscidae)

AbstractDifferences in habitat use and dispersal responses among competing species are mechanisms that may influence patterns of coexistence. Predaceous diving beetles (Coleoptera: Dytiscidae) are a model group for testing these potential coexistence mechanisms because they are abundant, interact in finite habitats, and are mobile among habitats. We focused on two morphologically similar species, Laccophilus fasciatus rufus (Aubé) and Laccophilus proximus (Say), to determine if mechanisms exist that help to explain patterns of their coexistence. Behavioral observations and feeding trials in the laboratory, a field experiment, and a mesocosm experiment were used to determine if habitat use, prey consumption, or dispersal rates of these two species were inherently different or changed when in the presence of intra- or interspecific competitors. We found no difference between habitat use or prey consumption between species in constant depth aquaria, and no effect of intra- or interspecifics on their behaviors. In variable depth aquaria, L. proximus occupied significantly shallower habitat when compared with L. ƒ. rufus; in the former this difference only occurred between conspecific treatments. Field collections confirmed that L. proximus occupied shallower habitats than L. f. rufus. In field mesocosms, L. proximus displayed higher dispersal rates than L. ƒ. rufus. These species also do not appear food limited in the field, suggesting that adult competition for food is unlikely. L.f. rufus and L. proximus exhibit different habitat use and dispersal responses, but this does not seem to be in response to intra- or interspecific competitive interactions.

Comparing rates of springtail predation by web‐building spiders using Bayesian inference

A major goal of gut-content analysis is to quantify predation rates by predators in the field, which could provide insights into the mechanisms behind ecosystem structure and function, as well as quantification of ecosystem services provided. However, percentage-positive results from molecular assays are strongly influenced by factors other than predation rate, and thus can only be reliably used to quantify predation rates under very restrictive conditions. Here, we develop two statistical approaches, one using a parametric bootstrap and the other in terms of Bayesian inference, to build upon previous techniques that use DNA decay rates to rank predators by their rate of prey consumption, by allowing a statistical assessment of confidence in the inferred ranking. To demonstrate the utility of this technique in evaluating ecological data, we test web-building spiders for predation on a primary prey item, springtails. Using these approaches we found that an orb-weaving spider consumes springtail prey at a higher rate than a syntopic sheet-weaving spider, despite occupying microhabitats where springtails are less frequently encountered. We suggest that spider-web architecture (orb web vs. sheet web) is a primary determinant of prey-consumption rates within this assemblage of predators, which demonstrates the potential influence of predator foraging behaviour on trophic web structure. We also discuss how additional assumptions can be incorporated into the same analysis to allow broader application of the technique beyond the specific example presented. We believe that such modelling techniques can greatly advance the field of molecular gut-content analysis.