Seasonal variation and an “outbreak” of frog predation by tamarins

We report temporal variation and an “outbreak” of frog predation by moustached tamarins, Saguinus mystax, in north-eastern Peruvian Amazonia. Frog predation rates were generally very low, but strongly increased in October 2015. Other high rates, identified by outlier analyses, were also observed in September–November of other years. Over all study years, predation rates in this 3-month period were significantly higher than those in the remainder of the year, suggesting a seasonal pattern of frog predation by tamarins. Reduced fruit availability or increased frog abundance or a combination of both may be responsible for both the seasonal pattern and the specific “outbreak” of frog predation.     

Microhabitat use and behavior of voles under weasel and raptor predation risk: predator facilitation?

An example of predator facilitation is that a microhabitat shiftin a prey species induced by one predator increases the probabilityof the prey falling victim to other predators. Least weasels(Mustela nivalis) hunt in dense plant cover, whereas kestrels(Falco tinnunculus) hunt in habitats with sparse plant cover.Field voles (Microtus agrestis), the main food of weasels andkestrels, prefer open country with a high grass layer. We simulateda multipredator environment in an aviary (3.0 x 4.8 x 2.2 m)to find out whether predator facilitation plays a role in theinteractions between voles, small mustelids, and raptors. Ineach replicate, we placed a field vole in a pen including sidesof high and low grass layers (cover and open). In a predator-freesituation, voles preferred cover but shifted to open when aweasel was introduced to cover. In the presence of a kestrel,voles occupied cover and decreased their mobility. In the presenceof a weasel plus a kestrel, voles behaved as under the kestrelrisk alone. Therefore, in these aviary circumstances, volesperceived the kestrel risk as greater than the weasel risk.Predator facilitation in the assemblage of predators subsistingon rodent prey may contribute to the crash of the four-yearvole cycle: microhabitat shift due to an avoidance of weaseljaws may drive voles to raptor talons.     

Does dimethyl sulfoxide increase protein immunomarking efficiency for dispersal and predation studies?

Marking biological control agents facilitates studies of dispersal and predation. This study examines the effect of a biological solvent, dimethyl sulfoxide (DMSO), on retention of immunoglobulin G (IgG) protein solutions applied to Diorhabda carinulata (Desbrochers) (Coleoptera: Chrysomelidae), an important biological control agent of saltcedar, either internally by feeding them protein‐labeled foliage or externally by immersing them in a protein solution. In addition, we determined whether internally or externally marked DMSO‐IgG labels could be transferred via feeding from marked D. carinulata to its predator, Perillus bioculatus (Fabricius) (Heteroptera: Pentatomidae). The presence of rabbit and chicken IgG proteins was detected by IgG‐specific enzyme‐linked immunosorbent assays (ELISA). DMSO‐IgG treatments showed greater label retention than IgG treatments alone, and this effect was stronger for rabbit IgG than for chicken IgG. Fourteen days after marking, beetles immersed in rabbit IgG showed 100% internal retention of label, whereas beetles immersed in chicken IgG showed 65% internal retention. Immersion led to greater initial (time 0) label values, and longer label retention, than feeding beetles labeled foliage. The DMSO‐IgG label was readily transferred to P. bioculatus after feeding on a single marked prey insect. This investigation shows that addition of DMSO enhances retention of IgG labels, and demonstrates that protein marking technology has potential for use in dispersal and predator–prey studies with D. carinulata. Moreover, our observation of P. bioculatus feeding on D. carinulata is, to our knowledge, a new predator–prey association for the stink bug.     

Compensatory foraging in Trinidadian guppies： Effects of acute and chronic predation threats

In response to acute predation threats, prey may sacrifice foraging opportunities in favour of increased predator avoidance. Under conditions of high or frequent predation risk, such tradeoffs may lead to reduced fitness. Here, we test the pre diction that prey reduce the costs associated with lost opportunities following acute predation threats by exhibiting shortterm compensatory foraging responses. Under seminatural conditions, we exposed female guppies Poecilia reticulate from high and low predation risk sites to one of three levels of acute predation threat （high, intermediate or low concentrations of conspecific alarm cues）. Our results confirm previous reports, demonstrating that guppies from a high predation site were consistently ＇bolder＇ （shorter escape latencies） and exhibited graded threatsensitive responses to different simulated threat levels while those from the low predation site were ＇shyer＇ and exhibited nongraded responses. Most importantly, we found that when guppies from low predation sites resumed foraging, they did so at rates significantly lower than baseline rates. However, guppies from high preda tion sites resumed foraging either at rates equal to baseline （in response to low or intemaediate risk stimuli） or significantly in creased relative to baseline rates （in response to high risk stimuli）. Together, these results highlight a complex compensatory be havioral mechanism that may allow prey to reduce the longterm costs associated with predator avoidance [Current Zoology 60 （3）： 323-332, 2014 ].     

Prey habitat selection under shared predation: tradeoffs between risk and competition?

An individual's choice of habitat should optimize amongst conflicting demands in a way that maximizes its fitness. Habitat selection by one species will often be influenced by presence and abundance of competitors that interact directly and indirectly with each other (such as through shared predators). The optimal habitat choice will thus depend on competition for resources by other species that can also modify predation risk. It may be possible to disentangle these two effects with careful analysis of density‐dependent habitat selection by a focal prey species. We tested this conjecture by calculating habitat isodars (graphs of density assuming ideal habitat selection) of chital deer living in two adjoining dry‐forest habitats in Gir National Park and Sanctuary, western India. The habitats differed only in presence (Sanctuary) and absence (National Park) of domestic prey (cattle and buffalo). Both species are preyed on by Asiatic lions. The habitat isodar revealed at low densities, that chital live in small groups and prefer habitat co‐occupied by livestock that reduce food resources, but also reduce predation risk. At higher densities, chital form larger groups and switch their preference toward risky habitat without livestock. The switch in chital habitat use is consistent with theories predicting that prey species should trade off safety in favor of food as population density increases.     

As good as dead? Sublethal predation facilitates lethal predation on an intertidal clam

Although ecologists have speculated that sublethal predation can impact prey dynamics, consequences of these predator effects have seldom been experimentally tested. In soft‐sediment marine communities, fishes crop extended feeding siphons of buried clams, potentially causing clams to reduce their burial depth, thereby enhancing their susceptibility to excavating lethal predators. We simulated cropping of the confamilial clams, Protothaca staminea and Venerupis philippinarum, by removing the top 40% of siphons, which caused each species to burrow 33–50% shallower than conspecifics with intact siphons. To examine subsequent consequences of reduced burial depth, we exposed cropped and intact clams to natural levels of predation in the field. Because of a naturally longer siphon, Protothaca, even after cropping, remained at relatively safe burial depths. In contrast, siphon cropping nearly doubled the mortality rate of Venerupis. Thus, while sublethal predation facilitates lethal predation, this linkage depends on specific life history characteristics, even among ecologically similar species.     

How well do predation rates on artificial nests estimate predation on natural passerine nests?

Daily survival rates (DSR) of three nest types were compared among three passerine species in woodland habitats of the Czech Republic in 1998‐99. The species were: Yellowhammer (YH) Emberiza citrinella, Blackcap (BC) Sylvia atricapilla, Song Thrush (ST) Turdus philomelos. The nest types were: AA, artificial nests with artificial plastic eggs, both mimicking the real models (total n= 432); NA, natural nests left in their original position and baited with artificial plastic eggs (n= 706); and NN, active natural nests observed during the egg stage (n= 596). Rodents were dominant predators of the near‐ground YH nests while predation by corvids slightly prevailed in the shrub nests of BC and ST. There was no consistent relationship between nest type (AA vs. NA) and type of predator. Effects of nest type (AA vs. NA or AA vs. NN, respectively), species, date and study plot on DSR were examined by fitting logistic regression models. Marginally significant (< P < 0.05) differences were found between AA and NA nests in both years. Due to the interaction with date in 1998, the model predicted lower/higher DSR for AA nests before/after about 25 May respectively. In 1999 the DSR of AA nests was consistently higher (difference: 0.011; 95% CI: 0.001 to 0.021). Marginally significant differences between AA and NN nests were found only in 1998: the DSR of AA nests was consistently lower (‐0.014, 95% CI: ‐0.027 to ‐0.001). Comparisons of mean DSR within each species‐year sample showed that the differences between nest types were of both directions and varied from almost zero to 0.02 (ST, BC; ns) or 0.04 (YH; P < 0.05). Although the experimental nests accurately reflected the mean values as well as seasonal trends and interspecific differences in DSR of the real nests in some subsets of data, the pattern was not consistent across species and between years. This study suggests that artificial nests could not be used to assess survival of natural nests without careful validation of the experimental results.     

Does differential predation permit invasive and native mosquito larvae to coexist in Florida?

Abstract.  1. The hypothesis that selective predation on larvae of the invasive Aedes albopictus (Skuse) could account for its stable coexistence with the native mosquito species and inferior competitor Ochlerotatus triseriatus (Say) in Florida treeholes and container systems was tested experimentally.
2. Functional responses of the two dipteran predators Toxorhynchites rutilus (Coquillett) and Corethrella appendiculata (Grabham) were evaluated separately for A. albopictus and O. triseriatus prey. Both predators exhibited type II functional responses and consistently consumed more of the invasive species. Handling time of T. rutilus feeding upon O. triseriatus was significantly longer than when preying upon the invasive species.
3. When either predator species was offered varying ratios of the two prey species, A. albopictus was consumed preferentially. The absence of a prey ratio effect on preference indicated that switching probably does not occur.
4. The higher maximum feeding rate upon, and preference for, A. albopictus suggests that differential predation may foster coexistence of the invasive and native mosquito prey species in Florida.     

Does acoustically simulated predation risk affect settlement and reproduction of a migratory passerine?

Nest predation is one of the most important drivers of avian life history evolution and population dynamics. Increasing evidence suggests that birds are able to assess nest predation risk and avoid settling in high‐risk areas to increase their reproductive performance. However, the cues used for settlement decisions are poorly known in most species. Population sizes of the migratory wood warbler Phylloscopus sibilatrix are characterized by strong annual fluctuations, which are negatively correlated with the number of forest rodents. Wood warblers might avoid rodent‐rich areas to reduce predation risk arising either from rodents, from rodent‐hunting predators attracted to such areas or from predators not linked to rodents. To evaluate these hypotheses, we conducted a large‐scale field experiment to test whether wood warblers avoided settling in plots with high predation risk simulated by broadcasting vocalizations of rodents or predators. Moreover, we tested whether reproductive performance varied in relation to simulated predation risk. Settlement patterns did not differ between plots with rodent, predator and noise control treatments. Likewise, measures of reproductive performance did not seem to differ across treatments. Thus, the broadcasted vocalizations of rodents and predators did not seem to be perceived as threat by wood warblers. Alternatively, the species might use other cues than those presented here, either other acoustic cues, visual and/or olfactory cues or a combination of cue types during settlement. Further experimental investigations to pin point cues and senses relevant for settlement decisions in wood warblers and birds in general are needed to better understand their life history and population dynamics.     

Do the antipredator strategies of shared prey mediate intraguild predation and mesopredator suppression?

Understanding the conditions that facilitate top predator effects upon mesopredators and prey is critical for predicting where these effects will be significant. Intraguild predation (IGP) and the ecology of fear are hypotheses used to describe the effects of top predators upon mesopredators and prey species, but make different assumptions about organismal space use. The IGP hypothesis predicts that mesopredator resource acquisition and risk are positively correlated, creating a fitness deficit. But if shared prey also avoid a top predator, then mesopredators may not have to choose between risk and reward. Prey life history may be a critical predictor of how shared prey respond to predation and may mediate mesopredator suppression. We used hierarchical models of species distribution and abundance to test expectations of IGP using two separate triangular relationships between a large carnivore, smaller intraguild carnivore, and shared mammalian prey with different life histories. Following IGP, we expected that a larger carnivore would suppress a smaller carnivore if the shared prey species did not spatially avoid the large carnivore at broad scales. If prey were fearful over broad scales, we expected less evidence of mesopredator suppression. We tested these theoretical hypotheses using remote camera detections across a large spatial extent. Lagomorphs did not appear to avoid coyotes, and fox detection probability was lower as coyote abundance increased. In contrast, white‐tailed deer appeared to avoid areas of increased wolf use, and coyote detection probability was not reduced at sites where wolves occurred. These findings suggest that mesopredator suppression by larger carnivores may depend upon the behavior of shared prey, specifically the spatial scale at which they perceive risk. We further discuss how extrinsic environmental factors may contribute to mesopredator suppression.     

Are sweep net sampling and pitfall trapping compatible with molecular analysis of predation?

Molecular analysis of predation enables accurate and reliable elucidation of trophic linkages in complex food webs, but identifying the strength of such interactions can be subject to error. Currently two techniques dominate: monoclonal antibody-based enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR). Although the optimization and characterization of these systems ensures their sensitivity and specificity, predator collection protocols such as sweep-netting and vacuum sampling could overestimate feeding rates because of surface-level contamination, yielding positive reactivity or predation within the sampling device. Therefore, two sampling techniques (sweep-net sampling and hand collection) were compared within an alfalfa agroecosystem using a monoclonal antibody-based ELISA to test the hypothesis that cross-contamination is a source of error, i.e., significantly more predators (linyphiid spiders) would test positive for prey (Diptera) proteins. A concurrent study examining the viability of trapping predators into saline solution was also undertaken. No significant differences were found between the proportions of spiders screening positive for Diptera when collected by sweep-net versus hand collection, rejecting the hypothesis that sweep-netting predators for subsequent molecular gut content analysis overestimates predation frequency. ELISA was also capable of detecting prey proteins in predator guts from pitfall traps containing phosphate-buffered saline, indicating the suitability of this approach for the collection and analysis of epigeal predators. Although these results indicate that sweep netting and pitfall trapping into solution is appropriate in this predator-prey and ELISA analysis system, caution should be exercised with other interactions and PCR-based analysis. The likelihood for false-positive reactivity should therefore be considered on a case-by-case basis.     

Costly carotenoids: a trade‐off between predation and infection risk?

Carotenoid reserves in copepods seem costly in terms of predation risk because they make individuals conspicuous. However, carotenoids also seem to play an important role in immune defence as free radical scavengers. To test whether predation risk influences carotenoid levels and whether changes in carotenoid levels are related to changes in immune defence, I examined individual changes in large carotenoid and other lipid droplets upon exposure to predation risk and subsequent exposure to parasites in the copepod Macrocyclops albidus. Copepods reduced carotenoid reserves upon exposure to predators, through which they potentially avoided the costs of being conspicuous under predation risk. Thus, the size of carotenoid reserves is a plastic trait. Such a decrease in carotenoid reserves may also have a negative impact on the copepods' immune system as individuals that decreased their reserves suffered higher parasite prevalence upon exposure to the cestode Schistocephalus solidus. These results suggest that carotenoid reserves may be individually optimized to trade-off each individual's unique costs (predation risk) and benefits (immune defence) of having these reserves.     

Vulnerability of black grouse hens to goshawk predation: result of food supply or predation facilitation?

The plant cycle hypothesis says that poor-quality food affects both herbivorous voles (Microtinae spp.) and grouse (Tetraonidae spp.) in vole decline years, leading to increased foraging effort in female grouse and thus a higher risk of predation by the goshawk Accipiter gentilis. Poor-quality food (mainly the bilberry Vaccinium myrtillus) for these herbivores is induced by seed masting failure in the previous year, when the bilberry is able to allocate resources for chemical defence (the mast depression hypothesis; MDH). The predation facilitation hypothesis (PFH) in turn states that increased searching activity of vole-eating predators during or after the decline year of voles disturbs incubating and brooding grouse females. The behaviours used by grouse to avoid these terrestrial predators make them more vulnerable to predation by goshawks. We tested the main predictions of the MDH and PFH by collecting long-term (21-year) data from black grouse Tetrao tetrix hens and cocks killed by breeding goshawks supplemented with indices of bilberry crop, vole abundance and small carnivores in the vicinity of Oulu, northern Finland. We did not find obvious support for the prediction of the MDH that there is a negative correlation of bilberry crop in year t with vole abundance and with predation index of black grouse hens in year t + 1. We did find obvious support for the prediction of the PFH that there is a positive correlation between predator abundance and predation index of grouse hens, because the stoat Mustela erminea abundance index was positively related to the predation index of black grouse hens. We suggest that changes in vulnerability of grouse hens may mainly be caused by the guild of vole-eating predators, who shift to alternative prey in the decline phase of the vole cycle, and thus chase grouse hens and chicks to the talons of goshawks and other avian predators.     

Ethological and phenotypic divergence in insular fire salamanders: diurnal activity mediated by predation?

Phenotypic divergence can occur through both local adaptations and phenotypic plasticity in response to particular environmental pressures. Holocene land-bridge islands harbor recent isolated populations that offer an excellent natural framework to study the microevolutionary processes involved in rapid or ongoing phenotypic shifts. Two insular populations (Ons and San Martiño) of Salamandra salamandra in NW Iberian Peninsula exemplify these phenotypic shifts with a rapid evolutionary transition in reproductive mode and genetic differentiation since their isolation ca. 8000 years ago. We evaluate parallel phenotypic changes in body size and behavior. In particular, we (1) collected observational fieldwork data during diurnal and nocturnal transects in both islands for over a decade (2004–2016); (2) investigated the climatic conditions associated to fire salamanders’ activity; (3) compared physical condition between insular and mainland populations; and (4) used plasticine models and camera trapping to identify potential predators that might cause the observed diurnal activity in San Martiño Island. Our 13-year-long study shows that salamanders from San Martiño show mainly diurnal activity and are significantly smaller than salamanders from Ons and nearby continental populations. Overall, we present an exceptional case of behavior and phenotypic differentiation of an insular population of fire salamanders and suggest that this unusual behavior in the small population of San Martiño might be triggered by a response to predator pressure exerted by a dense population of Rattus rattus.     

Does predation maintain tit community diversity?

European tits of the genus Parus constitute a complex group of coexisting boreal birds. Here we present a survey of the distribution of three coniferous-living Parus species and one of their main predators, the pygmy owl ( Glaucidium passerinum ), on nine isolated islands in Scandinavia. On all islands the coal tit ( Parus ater ) is the sole tit species when the pygmy owl is absent. The two larger species, the willow tit ( P. montanus ) and the crested tit ( P. cristatus ), only coexist with the coal tit when pygmy owls are present. We suggest that the coexistence of willow tits, crested tits and coal tits is the result of a combination of competition for food and predator-safe foraging sites. The smaller coal tit is superior in exploitation competition for food, while the two larger species have an advantage in interference competition for predator-safe foraging sites. The association between the distribution of the pygmy owl and the two larger tit species on isolated islands in Scandinavia is consistent with the idea that the pygmy owl is a keystone predator.     

Intraguild predation: fiction or reality?

Intraguild predation has become a major research topic in biological control. Quantification of multipredator interactions and an understanding of the consequences on target prey populations are needed, which only highlights the importance of population dynamics models in this field. However, intraguild predation models are usually based on Lotka–Volterra equations, which have been shown not to be adequate for modeling population dynamics of aphidophagous insects and their prey. Here we use a simple model developed for simulation of population dynamics of aphidophagous insects, which is based on the type of egg distribution made by predatory females, to estimate the real strength of intraguild predation in the aphidophagous insects. The model consists of two components: random egg distribution among aphid colonies, and between-season population dynamics of the predatory species. The model is used to estimate the proportion of predatory individuals that face a conflict with a heterospecific competitor at least once during their life. Based on this, predictions are made on the population dynamics of both predatory species. The predictions are confronted with our data on intraguild predation in ladybirds.     

Does predation contribute to tree diversity?

Seed and seedling predation may differentially affect competitively superior tree species to increase the relative recruitment success of poor competitors and contribute to the coexistence of tree species. We examined the effect of seed and seedling predation on the seedling recruitment of three tree species, Acer rubrum (red maple), Liriodendron tulipifera (yellow poplar), and Quercus rubra (northern red oak), over three years by manipulating seed and seedling exposure to predators under contrasting microsite conditions of shrub cover, leaf litter, and overstory canopy. Species rankings of seedling emergence were constant across microsites, regardless of exposure to seed predators, but varied across years. A. rubrum had the highest emergence probabilities across microsites in 1997, but Q. rubra had the highest emergence probabilities in 1999. Predators decreased seedling survival uniformly across species, but did not affect relative growth rates (RGRs). Q. rubra had the highest seedling survivorship across microsites, while L. tulipifera had the highest RGRs. Our results suggest that annual variability in recruitment success contributes more to seedling diversity than differential predation across microsites. We synthesized our results from separate seedling emergence and survival experiments to project seedling bank composition. With equal fecundity assumed across species, Q. rubra dominated the seedling bank, capturing 90% of the regeneration sites on average, followed by A. rubrum (8% of sites) and L. tulipifera (2% of sites). When seed abundance was weighted by species-specific fecundity, seedling bank composition was more diverse; L. tulipifera captured 62% of the regeneration sites, followed by A. rubrum (21% of sites) and Q. rubra (17% of sites). Tradeoffs between seedling performance and fecundity may promote the diversity of seedling regeneration by increasing the probability of inferior competitors capturing regeneration sites.