Evidence for intraguild predation by Podisus maculiventris on a ladybeetle, Coleomegilla maculata: Implications for biological control of Colorado potato beetle, Leptinotarsa decemlineata

The potential for intraguild predation (IGP) between larval and adult life stages of twopolyphagous arthropod predators common in NorthAmerican agroecosystems was studied in thelaboratory. Predators examined were the spinedsoldier bug, Podisus maculiventris Say,and the twelve-spotted ladybeetle, Coleomegilla maculata Lengi. A shared preyitem, eggs of the Colorado potato beetle (CPB),Leptinotarsa decemlineata Say, was alsoprovided to the predators, both to provide analternate food source and to quantify theimpact of IGP on the potential for pestsuppression by these two predators. Experimentswere conducted on single potato leaves inplastic cup arenas, and, subsequently, in cagesenclosing whole potato plants. IGP occurredasymmetrically, with P. maculiventrisadults and nymphs only attacking C. maculata larvae. Even though ladybeetle adultswere generally smaller than soldier bug adults,they were never preyed upon. This appears to bethe first documented case of a coccinellidshowing differential larval and adult immunityto attack by a larger invertebrate predator.The impact of IGP, when it did occur, on CPBegg consumption was equivocal. IGP did notconsistently influence levels of predation onthe eggs. Conversely, even when IGP did notoccur, predation on CPB eggs by both predatorstogether did not increase significantly overlevels inflicted by either predator alone. Theimplications for biological control of CPB bythese predators, which are being considered foraugmentative release in potato and tomato cropsin the United States, are discussed.     

Prey discrimination by a generalist coccinellid predator: effect of prey age or parasitism?

1. Patterns of prey discrimination by the generalist predatory coccinellid Coleomegilla maculata lengi Timb. (Coleoptera: Coccinellidae) were studied in relation to prey quality, under laboratory conditions. 2. Choice experiments were performed in which second‐ and fourth‐instar coccinellids had the choice between Trichoplusia ni (Lepidoptera: Noctuidae) eggs that were young or old, unparasitised or parasitised by Trichogramma evanescens Westwood (Hymenoptera: Trichogrammatidae). 3. Coleomegilla maculata larvae did not exhibit any preference for parasitised or unparasitised eggs at a similar stage of development but always preferred younger eggs, regardless of whether or not they were parasitised. Furthermore, the percentage of rejection was higher and handling time longer on the less preferred egg type. Pre‐imaginal development time, food intake to reach adulthood, and survival of coccinellid immatures were altered when coccinellid larvae were fed with parasitised and old unparasitised eggs. 4. These results indicate that C. maculata larvae select eggs based on their stage of development regardless of parasitism, and that prey quality of aged prey is lower. 5. Fourth‐instar coccinellid larvae spent less time in patches containing solely parasitised old eggs, and their level of exploitation was greatly reduced, compared with homogeneous patches containing unparasitised young eggs. This suggests that C. maculata larvae respond to variable patch quality by using flexible decision rules that reflect the payoff of the patch.     

Size-dependent predation by snakes: selective foraging or differential prey vulnerability?

I staged replicate encounters between unrestrained lizards andsnakes in outdoor enclosures to examine size-dependent predationwithin the common garden skink (Lampropholis guichenoti). Yellow-facedwhip snakes (Demansia psammophis) forage widely for activeprey and most often consumed large skinks, whereas death adders(Acanthophis antarcticus) ambush active prey and most oftenconsumed small skinks. Small-eyed snakes (Rhinoplocephalusnigrescens) forage widely for inactive prey and consumed bothsmall and large skinks equally often. Differential predationmay reflect active choice by the predator, differential preyvulnerability, or both. To test for active choice, I presentedforaging snakes with an inert small lizard versus an inertlarge lizard. They did not actively select lizards of a particularbody size. To test for differential prey vulnerability, I quantifiedvariation between small and large lizards in behavior thatis important for determining the outcome of predator—prey interactions. Snakes did not differentiate between integumentarychemicals from small and large lizards. Large lizards tendto flee from approaching predators, thereby eliciting attackby the visually oriented whip snakes. Small lizards were moremobile than large lizards and therefore more likely to passby sedentary death adders. Additionally, small skinks were more effectively lured by this sit-and-wait species and less likelyto avoid its first capture attempt. In contrast, overnightretreat site selection (not body size) determined a lizard'schances of being detected by small-eyed snakes. Patterns ofsize-dependent predation by elapid snakes may arise not becauseof active choice but as a function of species-specific predatortactics and prey behavior.     

Benefit by contrast: an experiment with live aposematic prey

Aposematic prey often have a coloration that contrasts withthe background. One beneficial effect of such conspicuous colorationis that it produces faster and more durable avoidance by predators.Another suggested benefit is that prey that contrast with thebackground are more quickly discerned and recognized as unpalatableby experienced predators. To further investigate the effectsof prey contrast on predator behavior, I conducted an experimentwith young chicks (Gallus gallus domesticus) as predators onlive aposematic and nonaposematic prey. Birds with prior experienceof both prey types were allowed into an arena with both palatableprey and aposematic prey on backgrounds that either closelymatched or contrasted with the coloration of the aposematicprey. Also, the time a bird had available to decide to attacka prey was manipulated by including a competing chick or not.The experienced birds showed greater attack latencies for aposematicprey on more contrasting backgrounds, and aposematic prey werealso attacked to a greater extent when on a matching background.The presence of a competitor generated similar effects, wherebirds in high competition attacked more and faster comparedto birds subjected to lower degree of competition, but therewas no interaction between competition and contrast. Thus,the experiment provides evidence that prey contrast againstthe background may produce better recognition and avoidance,independently of predator viewing time.     

Laboratory and field tests of predation on the cereal leaf beetle,Oulema melanopus (Coleoptera: Chrysomelidae)

The cereal leaf beetle (CLB), Oulema melanopus (L.) (Coleoptera: Chrysomelidae), is an invasive pest in North America recently reported in the Canadian Prairies. We performed a series of laboratory assays to identify potential predators and a field study to quantify predation of CLB eggs. In no-choice Petri dish assays, ground beetles (Carabidae), rove beetles (Staphylinidae), and several common lady beetle species (Coccinellidae) were the most consistent predators of eggs and larvae. Nabis spp. (Hemiptera: Nabidae) and wolf spiders (Araneae: Lycosidae) consumed many larvae, but did not consume eggs. Hippodamia spp., Coccinella septempunctata (L.) (Coleoptera: Coccinellidae), and Pterostichus melanarius (Illiger) (Coleoptera: Carabidae) also fed on CLB eggs on potted plants when an alternative food source was available, Sitobion avenae (Fabricius) (Hemiptera: Aphididae). In our field study, we found an average of 24.5% of sentinel eggs disappeared over a 24?h period, likely due to predation. Our results suggest that generalist predators can play an important role in the biological control of CLB, and warrant further study.     

Influence of prey foraging posture on flight behavior and predation risk: predators take advantage of unwary prey

Foraging in animals is often associated with characteristicbody postures, such as the head-down posture. When foragingconflicts with the ability to detect predators or to flee, individualsmay incur a greater risk of mortality to predation than otherwise.Here we investigate the influence of different foraging postures(horizontal versus nose-down body posture) on the ability ofindividuals to respond to approaching predators and on the riskof mortality to predation in the guppy (Poecilia reticulata).Individuals engaged in nose-down foraging were assumed to beable to visually scan a smaller area for predators and to escapeless effectively due to their body posture, and thus are morevulnerable to stalking predators than horizontally foragingones. In a first experiment, we separately exposed nonforaging,horizontally foraging, and nose-down foraging guppies to anapproaching cichlid fish predator model. Nonforaging guppiesreacted sooner to and initiated flight further away from theapproaching model than did foraging fish collectively, and horizontallyforaging individuals responded sooner to the model than nose-downforaging ones. Comparing all test guppies, nose-down foragingindividuals were the most likely not to exhibit any responseto the predator model. When presented with a simultaneous choiceof two guppies behind a one-way mirror, individual blue acaracichlid (Aequidens pulcher), a natural predator of the guppy,preferred to attack foraging guppies over nonforaging ones andnose-down foraging guppies over horizontally foraging individuals.In a final experiment with free-swimming cichlids and guppies,we demonstrated that individual risk of predation for guppiesforaging nose down was greater than for guppies foraging horizontally,and both were at greater risk than nonforaging guppies. Thislatter result is consistent with the above differences in theguppy's responsiveness to approaching predators depending ontheir foraging behavior, and with the finding that cichlid predatorspreferred fish that were less likely to show any response tothem. Our results therefore indicate that the ability to respondto approaching predators and the risk of mortality to predationin the guppy is strongly influenced by their foraging activity,and in particular their foraging posture, and that cichlid predatorspreferentially select less wary and more vulnerable guppies.[BehavEcol 7: 264–271 (1996)]     

Influence of six aphid prey species on development and reproduction of a ladybird beetle, Coccinella septempunctata

Pre-imaginal development, immaturesurvival, and reproduction of a ladybird, Coccinella septempunctata Linnaeus, werestudied in response to six aphid species, Aphiscraccivora Koch, Aphis gossypii Glover,Aphis nerii Boyer de Fonscolombe,Lipaphis erysimi (Kaltenbach), Myzuspersicae (Sulzer) and Uroleuconcompositae (Theobald) to quantify theirrelative suitability as prey. Pre-adultdevelopment was shortest (13.93 ± 0.12 days)when fed on L. erysimi and longest(22.85 ± 0.10 days) on A. nerii. Immaturesurvival, adult emergence, growth index,relative growth rate, development rate, maleand female longevity, oviposition period,fecundity and hatching percent were maximal, i.e. 73.47 ± 0.89%, 90.07 ± 1.43%,8.62 ± 0.23, 1.52 ± 0.02, 0.07,81.10 ± 1.26 days, 85.70 ± 1.45 days,69.80 ± 1.32 days, 1764.10 ± 8.46,and 87.88 ± 1.05, respectively when C.septempunctata were fed on L. erysimi.The same parameters were minimal, i.e.43.86 ± 1.33%, 71.65 ± 2.75%,2.02 ± 0.08, 0.49 ± 0.02, 0.04,44.40 ± 1.39 days, 53.50 ± 1.00 days,16.40 ± 0.60 days, 203.20 ± 11.83, and48.68 ± 2.06, respectively on A. nerii. Theweights of different ladybird life stages weremaximal after feeding on L. erysimi and minimalon A. nerii. Regression analyses of thedata revealed linear relationships betweendevelopment rate and weight of adult; dailyprey consumption and relative growth rate; logweight of adult male and female; and longevityand fecundity of female. On the basis of thesefindings, the order of suitability of aphidspecies for C. septempunctata is L. erysimi >M. persicae > A. craccivora > A. gossypii >U. compositae > A. nerii. Thus, the presentinformation can be utilized for the massrearing of C. septempunctata by supplyingthe best food and can also help in theprediction of the relative abundance of theladybird on different aphid infestations in thefields.     

Harmonia axyridis in Great Britain: analysis of the spread and distribution of a non-native coccinellid

Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) is native to Asia, and was widely introduced as a biocontrol agent of aphids and coccids in Europe and North America. In Europe H. axyridis is considered to be an invasive alien species. Although not known to have been deliberately introduced to Great Britain, it was first recorded there in 2004, in south-east England. Harmonia axyridis arrived in Great Britain by various means, primarily from mainland Europe, but also from Canada. Extensive national and local media coverage, and a dedicated website (), facilitated public involvement in recording H. axyridis in Great Britain; in excess of 4,000 verified records of the species were received between 2004 and 2006. Through detailed mapping, the objective of our study was to quantify and analyse the spread of H. axyridis in its early stages of invasion in Great Britain. Our data shows that between 2004 and 2006, the species spread north through Great Britain at the rate of 58 km year^-1 and west at the rate of 144.5 km year^-1. In England H. axyridis spread north to Yorkshire and west to Cornwall by the end of 2006, and also reached Wales. Recorded occurrence (of one or more H. axyridis individuals at larval, pupal and/or adult stage) in 10 km squares in Great Britain was: 2004—51; 2005—149; 2006—447. Records of juvenile H. axyridis extend through most of the recorded British range of the species, and we present evidence of bi-voltinism in the population in 2006.     

Quantifying insect predation with predator exclusion cages: the role of prey antipredator behavior as a source of bias

There are limitations imposed by current methodologies to detect and quantify insect predation. However, there has been relatively little effort to experimentally document the sources of biases associated with the various methodologies. In this study, we examined how predation estimates in the field using predator exclusion cages may be biased when one fails to account for antipredator behavioral responses. To do this, we did the usual comparison of the number of insects missing from plants where predators were allowed access to the number missing from plants where predators were excluded, but also determined how many of the missing insects reacted to predators by dropping from plants and how many were actually preyed upon. Our results provide evidence that estimates of insect mortality in the field are significantly reduced if prey antipredator behavior is taken into account. As it is commonly assumed that prey missing in the field are predated, documenting the incidence of predator‐mediated ‘disappearance’ and capturing insect prey before they escape can provide with a relevant estimate of bias.     

Harmonia axyridis in Europe: spread and distribution of a non-native coccinellid

Native to Asia, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) is considered an invasive alien ladybird in Europe and North America, where it was widely introduced as a biological control agent of aphids and coccids. In Europe, H. axyridis was sold by various biological control companies from 1995 in France, Belgium and the Netherlands, and was also intentionally released in at least nine other countries. It has spread very rapidly, particularly since 2002, and is now regarded as established in thirteen European countries. The established range extends from Denmark in the north to southern France in the south, and from Czech Republic in the east to Great Britain in the west. In this paper we map the spread and distribution of H. axyridis in Europe, and examine the situation on a country-by-country basis. We report first records of the species in five countries; Spain, Sweden, Denmark, Czech Republic and Italy; and first evidence of H. axyridis establishment in the latter three countries. Despite releases of H. axyridis in Portugal, Spain and Greece, there is little evidence of establishment in southern Europe. It is predicted that the spread and increase within Europe will continue and that H. axyridis will become one of the most widely distributed coccinellids in the continent.     

Model vs. playback experiments: The impact of sensory mode on predator-specific escape responses in saki monkeys

Although experimentally simulating predator presence helps improve sample sizes in studies of free-ranging animals, few studies have examined whether auditory playbacks and visual models produce similar results. Additionally, it is unclear if anti-predator strategies are specific to predator hunting styles in understudied Neotropical pitheciid primates, limiting what we can generalize about this phenomenon across this taxonomic order. We conducted predator simulation experiments to assess whether wild Rylands' bald-faced saki monkeys (Pithecia rylandsi) recognize predators based solely on acoustic cues, exhibit predator-specific responses to different predator types, and vary responses to presentations in different sensory modes. In our playback experiments, sakis had weak responses to non-predator control vocalizations compared to jaguar growls and harpy eagle shrieks. In most predator playbacks, subjects' first glance corresponded to the direction from which simulated predators would typically attack (above vs. below). However, although sakis exhibited appropriate movement responses to harpy playbacks (i.e., descending canopy), they exhibited no clear movement patterns when presented with jaguar playbacks. In contrast, jaguar model experiments consistently elicited fast approaches, mobbing-style responses, and long alarm calling bouts. Thus, if we had relied on playbacks alone, we might have concluded that sakis have only generalized responses to terrestrial ambush predators. In fact, in all variables measured (e.g., latency, number of calls, and response duration), models of both predator species elicited stronger reactions than playbacks. Results indicate that bald-faced sakis can identify predators based solely on vocalizations, but do not exhibit predator-specific escape responses to terrestrial predators based on acoustic cues alone. The differential response to playbacks and models calls into question the reliability of using acoustic-only stimuli to assess the specificity of anti-predator behavior to predator hunting styles in some primate species.     

A test of the risk allocation hypothesis: tadpole responses to temporal change in predation risk

The risk allocation hypothesis predicts that temporal variationin predation risk can influence how animals allocate feedingbehavior among situations that differ in danger. We testedthe risk allocation model with tadpoles of the frog Rana lessonae,which satisfy the main assumptions of this model because theymust feed to reach metamorphosis within a single season, theirbehavioral defense against predators is costly, and they canrespond to changes in risk integrated over time. Our experiment switched tadpoles between artificial ponds with different numbersof caged dragonfly larvae and held them at high and low riskfor different portions of their lives. Tadpoles responded stronglyto predators, but they did not obey the risk allocation hypothesis:as the high-risk environment became more dangerous, there wasno tendency for tadpoles to allocate more feeding to the low-riskenvironment, and as tadpoles spent more time at risk, they didnot increase feeding in both environments. Our results suggestthat the model might be more applicable when the time spentunder high predation risk is large relative to the time requiredto collect resources.     

Observation of epigeic predators and predation on artificial prey in a cereal field

Predation activity of different epigeic predators on artificially supplied prey was studied in a cereal field during several 24 h periods from spring to early summer 1993. Carabids were the most frequently observed predators. Among themPoecilus cupreus was the most voracious species during day-time, andAgonum muelleri during night-time. Predation rates were highest between 10.00 and 18.00 h and lowest between 02.00 and 10.00 h. Linear regressions showed significantly positive relations between temperature and predation rates, and between predation and activity density of epigeic predators. The latter relation was stronger when only activity density of predators which were observed to consume baits was included. Quadrat sampling and pitfall sampling showed that with the former only a small proportion of bait-consuming predators were caught whereas with the latter method this proportion was high.     

Effects of conspecific and heterospecific competitors on feeding and oviposition of a predatory ladybird: a laboratory study

Abstract There are several examples of intraguild interactions among insect predators of aphids, but little is known regarding the effects of interactions on feeding and oviposition of individual competitors in a guild. In the laboratory, we determined the feeding and oviposition responses of a ladybird predator to its conspecific and heterospecific competitors in an aphidophagous guild. Gravid females of Menochilus sexmaculatus (Fabricius) (Coleoptera, Coccinellidae) reduced oviposition, but not feeding, when exposed to immobilised conspecific or Coccinella transversalis (Fabricius) (Coleoptera, Coccinellidae) individuals in the short‐term (3 h) and long‐term (24 h). Feeding and oviposition responses were not affected when M. sexmaculatus females were exposed to larvae or adults of Scymnus pyrocheilus Mulsant (Coleoptera, Coccinellidae) beetles or larvae of the syrphid fly Ischiodon scutellaris (Fabricius) (Diptera: Syrphidae). The ratio of eggs laid to numbers of aphids consumed by M. sexmaculatus females was also affected by the presence of conspecific or C. transversalis larvae. The results suggest that fecundity of this predator may be affected by both conspecific and heterospecific competitors in a patchy resource.     

Predation and the evolution of prey behavior: an experiment with tree hole mosquitoes

We tested for facultative changes in behavior of an aquaticinsect in response to cues from predation and for evolutionof prey behavior in response to experimental predation regimes.Larvae of the tree hole mosquito Aedes triseriatus reducedfiltering, browsing, and time below the surface in responseto water that had held a feeding larva of the predator Toxorhynchitesrutilus. We subjected experimental A. triseriatus populationsto culling of 50% of the larval population, either by T. rutiluspredation or by random removal. After two generations of laboratoryculling, behavior of the two treatment groups diverged. Aedestriseriatus in control-culled lines retained their facultativeshift from filtering to resting, but tended to lose the response of reduced browsing below the surface in water that had helda feeding predator. Predator-culled lines lost their facultativeresponse of reduced filtering in water that had held a feedingpredator and evolved toward more time resting and less timefiltering in both water that had held a feeding predator andwater that had held only A. triseriatus. Predator-culled linesretained their facultative response of reduced browsing belowthe surface in water that had held a feeding predator. Twofield populations and their reciprocal hybrids responded similarlyto cues from predation and did not differ in their evolutionaryresponse to experimental culling. We conclude that consistentpresence or absence of predation can select rapidly for divergencein prey behavior, including facultative behavioral responsesto predators.     

Descriptions of a broad-nosed weevil (Eudiagogini: Curculionidae) and false ladybird beetle (Nilionini: Nilionidae) in Dominican amber

A broad-nosed weevil, Promecops tumidirostris n. sp. (Eudiagogini: Curculionidae), and a false ladybird beetle, Nilio dominicana n. sp. (Nilionini: Nilionidae), are described from Dominican amber. P. tumidirostris can be distinguished from extant species by the greatly swollen apical portion of its rostrum, large eyes almost meeting on top of its head and a V-shaped suture separating the first and second abdominal sternites. N. dominicana differs from extant species by its small size and 18 elytral striae with small interstrial punctures. Neither tribe is represented in Hispaniola today, supporting earlier studies showing a greater biodiversity in the region during the mid-Tertiary than at present.     

Female greater wax moths reduce sexual display behavior in relation to the potential risk of predation by echolocating bats

Female greater wax moths Galleria mellonella display by wing fanning in response to bursts of ultrasonic calls produced bymales. The temporal and spectral characteristics of these callsshow some similarities with the echolocation calls of batsthat emit frequency-modulated (FM) signals. Female G. mellonellatherefore need to distinguish between the attractive signalsof male conspecifics, which may lead to mating opportunities,and similar sounds made by predatory bats. We therefore predictedthat (1) females would display in response to playbacks of male calls; (2) females would not display in response to playbacksof the calls of echolocating bats (we used the calls of Daubenton'sbat Myotis daubentonii as representative of a typical FM echolocatingbat); and (3) when presented with male calls and bat callsduring the same time block, females would display more whenperceived predation risk was lower. We manipulated predationrisk in two ways. First, we varied the intensity of bat callsto represent a nearby (high risk) or distant (low risk) bat.Second, we played back calls of bats searching for prey (lowrisk) and attacking prey (high risk). All predictions weresupported, suggesting that female G. mellonella are able todistinguish conspecific male mating calls from bat calls, andthat they modify display rate in relation to predation risk.The mechanism (s) by which the moths separate the calls ofbat and moth must involve temporal cues. Bat and moth signalsdiffer considerably in duration, and differences in durationcould be encoded by the moth's nervous system and used in discrimination.     

Factors affecting detectability of prey DNA in the gut contents of invertebrate predators: a polymerase chain reaction-based method

This study aimed to determine factors that influence the detection of DNA of Plutella xylostella L. (Lepidoptera: Plutellidae) in the gut contents of arthropod predators when the polymerase chain reaction is used to amplify a diagnostic fragment of the gene coding for cytochrome oxidase subunit I. The effects of temperature, time since feeding, subsequent food intake, sex, weight, and species of predator on prey detectability were studied in the laboratory. Three types of predator were studied: the spider Venator spenceri Hogg. (Araneae: Lycosidae), a bug with sucking mouthparts, Nabis kinbergii (Reuter) (Heteroptera: Nabidae), and a coccinellid with chewing mouthparts, Hippodamia variegata (Goeze) (Coleoptera: Coccinellidae). In all experiments, the detectability of prey DNA was negatively correlated with time post‐feeding. The duration of detectability differed among the predator species. The time calculated for median detection success at 20 °C ranged from 49.6 h in V. spenceri to 36.1 h in N. kinbergii and 17.1 h in H. variegata. In H. variegata, but not in V. spenceri, the rate of detection decreased with increasing temperature. Subsequent food intake did not affect the detectability of DNA of P. xylostella in V. spenceri. In H. variegata, sex and weight of the predator did not influence detection of prey DNA. In addition, this study uncovered potential sources of error caused by detection of prey DNA following secondary cannibalistic and intraguild predation. The results provide essential information for the interpretation of prey detection data from field‐collected predators’ gut contents.     

食物、捕食及种间竞争对东方田鼠(Microtus fortis)种群攻击行为的作用

在野外围栏条件下,采用重复的2×2×2析因实验设计,测定食物、捕食和竞争物种黑线姬鼠对东方田鼠攻击行为作用的格局。东方田鼠各处理种群攻击水平与其种群密度的相关甚为复杂,与Chitty多态行为假设的预测不一致。东方田鼠双冲突个体间的攻击水平与其体重的相关不显著,而与冲突个体的体重差异则呈显著的负相关,体重差异越大,冲突个体间的攻击水平越低。雄体攻击水平与其繁殖特征无显著的相关关系,而雌体间攻击水平则受繁殖状态的影响,动情雌体间的攻击水平显著地高于非动情雌体。体重差异和食物对雄体的攻击行为具有极显著的独立作用,捕食和种间竞争对雄体攻击行为的独立作用不显著,而捕食与种间竞争交互作用对雄体攻击行为的效应则达到显著水平。体重差异、食物、捕食和种间竞争对动情雌体的攻击水平均有极显著的独立作用,3类外部因子交互作用的效应达到极显著水平;而3类外部因子交互作用对非动情雌体攻击行为的效应则不显著。结果检验了外部因子食物、捕食、种间竞争对田鼠类动物种群攻击行为具有独立和累加的整合效应的假设。     

Muskrat predation on a diverse unionid mussel community: impacts of prey species composition,size and shape

1. The muskrat, Ondatra zibethicus, is a predator known to affect species composition, population size and age structure of freshwater unionid mussel communities. Muskrats leave large piles of dead shells (middens) on the edges of rivers, lakes and streams. We compared the species composition and size structure of shells collected from muskrat middens to the nearby live unionid community in the lower Licking River (Kentucky, USA). 2. Like previous studies, our results suggest that muskrats are both size‐selective and species‐specific predators; however, our results indicate that mussel shape is also an important factor. 3. We generated a shape metric (‘cubocity’) sensitive to the overall shape of the mussel. Species with relatively lower cubocity values (around 0.85) are plate‐like or spike‐like, while mussels with more cuboidal shells have higher cubocity values (near 1.0). 4. Our results suggest muskrats prefer cuboidal mussels and generally avoid spike‐shaped mussels. The endangered fanshell, Cyprogenia stegaria, was the most favoured prey; the fanshell’s relative size and shape appear to make it particularly vulnerable to muskrats. 5. We believe the predictive capabilities of this shape metric will be of benefit to those who monitor and manage threatened mussel populations.