Feeding Experience Modifies the Assessment of Ambush Sites by the Timber Rattlesnake, a Sit-and-Wait Predator

To effectively ambush prey, sit‐and‐wait predators must locate sites where profitable prey are likely to return. One means by which predators evaluate potential ambush sites is by recognizing high‐use areas through chemical cues deposited inadvertently by their prey. However, it is unknown whether ambush predators can use chemical cues associated with past prey items in the assessment of potential ambush sites. I examined selection of ambush sites by timber rattlesnakes (Crotalus horridus) exposed to trails made from chemical extracts of the integument of various prey species. I evaluated the role of feeding experience in ambush site selection by comparing the behavior of timber rattlesnakes before and after feeding experience with different sized prey items. Timber rattlesnakes are more likely to select ambush sites adjacent to chemical trails from prey with which they have had feeding experience, but only those fed relatively large prey showed an increase in responsiveness. Increased responsiveness after feeding experience was exhibited in experiments using integumentary extracts of mammals (the natural prey of timber rattlesnakes), but not in those using extracts of fish. These results indicate that ambush predators may learn to recognize chemicals on the integument of profitable food items, and use that experience when subsequently selecting ambush sites. Additionally, these findings provide evidence that size‐dependent predation by snakes may be, in some species, a result of active prey selection.     

Fine‐scale foraging habitat selection by two diving central place foragers in the Northeast Atlantic

Habitat selection and spatial usage are important components of animal behavior influencing fitness and population dynamic. Understanding the animal–habitat relationship is crucial in ecology, particularly in developing strategies for wildlife management and conservation. As this relationship is governed by environmental features and intra‐ and interspecific interactions, habitat selection of a population may vary locally between its core and edges. This is particularly true for central place foragers such as gray and harbor seals, where, in the Northeast Atlantic, the availability of habitat and prey around colonies vary at local scale. Here, we study how foraging habitat selection may vary locally under the influence of physical habitat features. Using GPS/GSM tags deployed at different gray and harbor seals’ colonies, we investigated spatial patterns and foraging habitat selection by comparing trip characteristics and home‐range similarities and fitting GAMMs to seal foraging locations and environmental data. To highlight the importance of modeling habitat selection at local scale, we fitted individual models to colonies as well as a global model. The global model suffered from issues of homogenization, while colony models showed that foraging habitat selection differed markedly between regions for both species. Despite being capable of undertaking far‐ranging trips, both gray and harbor seals selected their foraging habitat depending on local availability, mainly based on distance from the last haul‐out and bathymetry. Distance from shore and tidal current also influenced habitat preferences. Results suggest that local conditions have a strong influence on population spatial ecology, highlighting the relevance of processes occurring at fine geographical scale consistent with management within regional units.     

Managing predators: The influence of kangaroo rat antipredator displays on sidewinder rattlesnake hunting behavior

Upon sensing predators in their vicinity, many prey species perform antipredator displays that are thought to provide information to the predator that deters it from attacking (predator‐deterrent signals). These displays can be complex, incorporating a variety of signaling elements as well as direct physical harassment of the predator. Although the display behaviors in these communication systems are often well characterized, evidence of the efficacy of these displays in deterring predators is limited due to the challenges associated with studying free‐ranging predators. Here, we examine how the anti‐snake signals of the desert kangaroo rat (Dipodomys deserti) influence the ambush hunting behaviors of sidewinder rattlesnakes (Crotalus cerastes). We found that, although desert kangaroo rats incorporate a number of signal elements into their antipredator display, only sand kicking behavior was a significant factor in motivating sidewinder rattlesnakes to cease hunting: high rates of sand kicking led to early abandonment of ambush coils. These results indicate that anti‐snake displays of small mammals may be especially effective at mitigating the threat posed by rattlesnakes when those displays incorporate physical harassment as well as signaling.     

Ground squirrel tail-flag displays alter both predatory strike and ambush site selection behaviours of rattlesnakes

Many species approach, inspect and signal towards their predators. These behaviours are often interpreted as predator-deterrent signals-honest signals that indicate to a predator that continued hunting is likely to be futile. However, many of these putative predator-deterrent signals are given when no predator is present, and it remains unclear if and why such signals deter predators. We examined the effects of one such signal, the tail-flag display of California ground squirrels, which is frequently given both during and outside direct encounters with northern Pacific rattlesnakes. We video-recorded and quantified the ambush foraging responses of rattlesnakes to tail-flagging displays from ground squirrels. We found that tail-flagging deterred snakes from striking squirrels, most likely by advertising squirrel vigilance (i.e. readiness to dodge a snake strike). We also found that tail-flagging by adult squirrels increased the likelihood that snakes would leave their ambush site, apparently by elevating the vigilance of nearby squirrels which reduces the profitability of the ambush site. Our results provide some of the first empirical evidence of the mechanisms by which a prey display, although frequently given in the absence of a predator, may still deter predators during encounters.     

Trophic resource partitioning drives fine‐scale coexistence in cryptic bat species

Understanding the processes that enable species coexistence has important implications for assessing how ecological systems will respond to global change. Morphology and functional similarity increase the potential for competition, and therefore, co‐occurring morphologically similar but genetically unique species are a good model system for testing coexistence mechanisms. We used DNA metabarcoding and high‐throughput sequencing to characterize for the first time the trophic ecology of two recently described cryptic bat species with parapatric ranges, Myotis escalerai and Myotis crypticus. We collected fecal samples from allopatric and sympatric regions and from syntopic and allotopic locations within the sympatric region to describe the diets both taxonomically and functionally and compare prey consumption with prey availability. The two bat species had highly similar diets characterized by high arthropod diversity, particularly Lepidoptera, Diptera and Araneae, and a high proportion of prey that is not volant at night, which points to extensive use of gleaning. Diet overlap at the prey item level was lower in syntopic populations, supporting trophic shift under fine‐scale co‐occurrence. Furthermore, the diet of M. escalerai had a marginally lower proportion of not nocturnally volant prey in syntopic populations, suggesting that the shift in diet may be driven by a change in foraging mode. Our findings suggest that fine‐scale coexistence mechanisms can have implications for maintaining broad‐scale diversity patterns. This study highlights the importance of including both allopatric and sympatric populations and choosing meaningful spatial scales for detecting ecological patterns. We conclude that a combination of high taxonomic resolution with a functional approach helps identify patterns of niche shift.     

Beyond the encounter: Predicting multi‐predator risk to elk (Cervus canadensis) in summer using predator scats

1. There is growing evidence that prey perceive the risk of predation and alter their behavior in response, resulting in changes in spatial distribution and potential fitness consequences. Previous approaches to mapping predation risk across a landscape quantify predator space use to estimate potential predator‐prey encounters, yet this approach does not account for successful predator attack resulting in prey mortality. An exception is a prey kill site that reflects an encounter resulting in mortality, but obtaining information on kill sites is expensive and requires time to accumulate adequate sample sizes.
2. We illustrate an alternative approach using predator scat locations and their contents to quantify spatial predation risk for elk (Cervus canadensis) from multiple predators in the Rocky Mountains of Alberta, Canada. We surveyed over 1300 km to detect scats of bears (Ursus arctos/U. americanus), cougars (Puma concolor), coyotes (Canis latrans), and wolves (C. lupus). To derive spatial predation risk, we combined predictions of scat‐based resource selection functions (RSFs) weighted by predator abundance with predictions that a predator‐specific scat in a location contained elk. We evaluated the scat‐based predictions of predation risk by correlating them to predictions based on elk kill sites. We also compared scat‐based predation risk on summer ranges of elk following three migratory tactics for consistency with telemetry‐based metrics of predation risk and cause‐specific mortality of elk.
3. We found a strong correlation between the scat‐based approach presented here and predation risk predicted by kill sites and (r = .98, p < .001). Elk migrating east of the Ya Ha Tinda winter range were exposed to the highest predation risk from cougars, resident elk summering on the Ya Ha Tinda winter range were exposed to the highest predation risk from wolves and coyotes, and elk migrating west to summer in Banff National Park were exposed to highest risk of encountering bears, but it was less likely to find elk in bear scats than in other areas. These patterns were consistent with previous estimates of spatial risk based on telemetry of collared predators and recent cause‐specific mortality patterns in elk.
4. A scat‐based approach can provide a cost‐efficient alternative to kill sites of quantifying broad‐scale, spatial patterns in risk of predation for prey particularly in multiple predator species systems.

     

To minimize foraging time,use high‐efficiency,energy‐expensive search and capture methods when food is abundant but low‐efficiency,low‐cost methods during food shortages

Based on a mathematical model, I show that the amount of food in the habitat determines which among alternative methods for search of prey, respectively, for pursuit‐and‐capture give the shortest daily foraging time. The higher the locomotor activity, the higher the rate of energy expenditure and the larger the habitat space a predator can search for prey per time unit. Therefore, I assume that the more efficient a foraging method is, the higher its rate of energy expenditure. Survival selection favors individuals that use foraging methods that cover their energy needs in the shortest possible time. Therefore, I take the optimization criterion to be minimization of the daily foraging time or, equivalently, maximization of the rate of net energy gain. When time is limiting and food is in short supply, as during food bottleneck periods, low‐efficiency, low‐cost foraging methods give shorter daily foraging times than high‐efficiency, energy‐expensive foraging methods. When time is limiting, food is abundant and energy needs are large, as during reproduction, high‐efficiency high‐cost foraging methods give shorter daily foraging times than low‐efficiency low‐cost foraging methods. When time is not limiting, food is abundant, and energy needs are small, the choice of foraging method is not critical. Small animals have lower rates of energy expenditure for locomotion than large animals. At a given food density and with similar diet, small animals are therefore more likely than large ones to minimize foraging time by using high‐efficiency energy‐expansive foraging methods and to exploit patches and sites that require energy‐demanding locomotion modes. Survival selection takes place at food shortages, while low‐efficiency low‐cost foraging methods are used, whereas reproduction selection occurs when food is abundant and high‐efficiency energy‐expensive foraging methods do better. In seasonal environments, selection therefore acts on different foraging methods at different times. Morphological adaptation to one method may oppose adaptation to another. Such conflicts select against foraging and morphological specialization and tend to give species‐poor communities of year‐round resident generalists. But a stable year‐round food supply favors specialization, niche narrowing, and dense species packing.     

Match and mismatch: Integrating consumptive effects of predators,prey traits,and habitat selection in colonizing aquatic insects

Predators are a particularly critical component of habitat quality, as they affect survival, morphology, behavior, population size, and community structure through both consumptive and non‐consumptive effects. Non‐consumptive effects can often exceed consumptive effects, but their relative importance is undetermined in many systems. Our objective was to determine the consumptive and non‐consumptive effects of a predaceous aquatic insect, Notonecta irrorata, on colonizing aquatic beetles. We tested how N. irrorata affected survival and habitat selection of colonizing aquatic beetles, how beetle traits contributed to their vulnerability to predation by N. irrorata, and how combined consumptive and non‐consumptive effects affected populations and community structure. Predation vulnerabilities ranged from 0% to 95% mortality, with size, swimming, and exoskeleton traits generating species‐specific vulnerabilities. Habitat selection ranged from predator avoidance to preferentially colonizing predator patches. Attraction of Dytiscidae to N. irrorata may be a natural ecological trap given similar cues produced by these taxa. Hence, species‐specific habitat selection by prey can be either predator‐avoidance responses that reduce consumptive effects, or responses that magnify predator effects. Notonecta irrorata had both strong consumptive and non‐consumptive effects on populations and communities, while combined effects predicted even more distinct communities and populations across patches with or without predators. Our results illustrate that an aquatic invertebrate predator can have functionally unique consumptive effects on prey, attracting and repelling prey, while prey have functionally unique responses to predators. Determining species‐specific consumptive and non‐consumptive effects is important to understand patterns of species diversity across landscapes.     

Interactions of multiple predators with different foraging modes in an aquatic food web

Top predators can have different foraging modes that may alter their interactions and effects on food webs. Interactions between predators may be non-additive resulting from facilitation or interference, whereas their combined effects on a shared prey may result in emergent effects that are risk enhanced or risk reduced. To test the importance of multiple predators with different foraging modes, we examined the interaction between a cruising predator (largemouth bass, Micropterus salmoides) and an ambush predator (muskellunge, Esox masquinongy) foraging on a shared prey (bluegill sunfish, Lepomis macrochirus) with strong anti-predator defense behaviors. Additive and substitution designs were used to compare individual to combined predator treatments in experimental ponds. The multiple predator interaction facilitated growth of the cruising predator in the combined predator treatments, whereas predator species had substitutable effects on the growth of the ambush predator. The combined predator treatments created an emergent effect on the prey; however, the direction was dependent on the experimental design. The additive design found a risk-reducing effect, whereas the substitution design found a risk-enhancing effect for prey fish. Indirect effects from the predators weakly extended to lower trophic levels (i.e., zooplankton community). Our results highlight the need to consider differences in foraging mode of top predators, interactions between predators, and emergent effects on prey to understand food webs.     

Integrating disparate datasets to model the functional response of a marine predator: A case study of harbour porpoises in the southern North Sea

1. Quantifying consumption and prey choice for marine predator species is key to understanding their interaction with prey species, fisheries, and the ecosystem as a whole. However, parameterizing a functional response for large predators can be challenging because of the difficulty in obtaining the required data on predator diet and on the availability of multiple prey species.
2. This study modeled a multi‐species functional response (MSFR) to describe the relationship between consumption by harbour porpoises (Phocoena phocoena) and the availability of multiple prey species in the southern North Sea. Bayesian methodology was employed to estimate MSFR parameters and to incorporate uncertainties in diet and prey availability estimates. Prey consumption was estimated from stomach content data from stranded harbour porpoises. Prey availability to harbour porpoises was estimated based on the spatial overlap between prey distributions, estimated from fish survey data, and porpoise foraging range in the days prior to stranding predicted from telemetry data.
3. Results indicated a preference for sandeels in the study area. Prey switching behavior (change in preference dependent on prey abundance) was confirmed by the favored type III functional response model. Variation in the size of the foraging range (estimated area where harbour porpoises could have foraged prior to stranding) did not alter the overall pattern of the results or conclusions.
4. Integrating datasets on prey consumption from strandings, predator foraging distribution using telemetry, and prey availability from fish surveys into the modeling approach provides a methodological framework that may be appropriate for fitting MSFRs for other predators.

     

Environmental heterogeneity amplifies behavioural response to a temporal cycle

Resource acquisition is integral to maximise fitness, however in many ecosystems this requires adaptation to resource abundance and distributions that seldom stay constant. For predators, prey availability can vary at fine spatial and temporal scales as a result of changes in the physical environment, and therefore selection should favour individuals that can adapt their foraging behaviour accordingly. The tidal cycle is a short, yet predictable, temporal cycle, which can influence prey availability at temporal scales relevant to movement decisions. Here, we ask whether black‐legged kittiwakes Rissa tridactyla can adjust their foraging habitat selection according to the tidal cycle using GPS tracking studies at three sites of differing environmental heterogeneity. We used a hidden Markov model to classify kittiwake behaviour, and analysed habitat selection during foraging. As expected for a central‐place forager, we found that kittiwakes preferred to forage nearer to the breeding colony. However, we also show that habitat selection changed over the 12.4‐h tidal cycle, most likely because of changes in resource availability. Furthermore, we observed that environmental heterogeneity was associated with amplified changes in kittiwake habitat selection over the tidal cycle, potentially because environmental heterogeneity drives greater resource variation. Both predictable cycles and environmental heterogeneity are ubiquitous. Our results therefore suggest that, together, predictable cycles and environmental heterogeneity may shape predator behaviour across ecosystems.     

Ambush site selection and ontogenetic shifts in foraging strategy in a semi-aquatic pit viper, the Eastern cottonmouth

Although habitat selection has been studied in a variety of snake taxa, little is known about habitat selection in aquatic snake species. Additionally, due to their small size and secretive nature, juvenile snakes are seldom included in habitat selection studies. The Eastern cottonmouth Agkistrodon piscivorus is a semi-aquatic pit viper known to use ambush, sit-and-wait foraging strategies. Ambush hunters are likely to select habitats that increase opportunity for successful prey capture while minimizing predation risk and maintaining appropriate thermal and hydric conditions. We characterized the foraging strategy and microhabitat use of cottonmouths at Ellenton Bay, an isolated Carolina bay freshwater wetland on the Savannah River Site in SC, USA. We measured habitat characteristics of 55 ambush sites used by 51 individual cottonmouths located during nighttime visual surveys, as well as 225 randomly selected sites within our search area. Cottonmouths exhibited an ontogenetic shift in foraging strategy with juveniles using predominately ambush foraging around the edge of the wetland while adults were most often encountered actively moving within the wetland. Principal components analysis revealed that juveniles selected foraging microhabitats that were different from random and consisted of mud substrate with sparse vegetation, whereas adults occupied a greater variety of microhabitats that did not differ from random. Concomitantly, free-ranging cottonmouths exhibited ontogenetic shifts in diet: juveniles consumed mostly salamanders, while adults ate a greater variety of prey including other snakes and birds. Our results highlight the importance of understanding how ontogenetic changes in coloration, diet and predation risk influence foraging strategy and microhabitat selection in snakes.     

Jaguar (Panthera onca) feeding ecology: distribution of predator and prey through time and space

Jaguars Panthera onca inhabiting tropical or subtropical evergreen moist forest have often been classified as opportunistic predators because they consume prey relative to its availability. However, these studies failed to address simultaneously the distribution of predator and prey through time and space, which may lead to an incomplete or erroneous understanding of jaguar foraging strategies. In this study, we reconstructed jaguar diet from scat, and used camera traps to investigate jaguar prey availability and the distribution of jaguar and its prey through space and time. We focused our examination of predator–prey temporal and spatial relations on forest infrastructure comprising man-made paths, small mammal trails, tapir Tapirus bairdi trail and trail-less, forested areas as they represent distinct habitats for prey selection. Overall, we observed high overlap between the prey used and available, suggestive of opportunistic foraging. However, jaguars exhibited selective tendencies in discriminating between larger prey. Jaguars used collared peccary Tayassu tajacu greater than its availability, while preying upon the equally abundant and similarly distributed white-lipped peccary Tayassu pecari and tapir less than predicted based upon availability. Armadillo Dasypus novemcinctus and paca Agouti paca , 56.6% of total consumption, were consumed relative to availability but exhibited low spatial overlap with jaguar. Armadillo and paca used trail-less, forested areas and small mammal trails not used by jaguar and were photographed more frequently at greater distances from man-made paths, major thoroughfares for jaguars. This study suggests that although forest jaguars use prey relative to its abundance, jaguars may rely on foraging strategies other than chance encounters for exploiting prey.     

Solitary Floral Specialists Do Not Respond to Cryptic Flower-Occupying Predators

The impacts of predators on bee foraging behavior are varied, but have been suggested to depend on both the type of predator (namely their hunting strategy) and also risk assessment by the prey (i.e., ability to perceive predators and learn to avoid them). However, nearly all studies have explored these impacts using social bees, despite the fact that solitary bees are extremely diverse, often specialized in their floral interactions, and may exhibit different behaviors in response to flower-occupying predators. In this study, we examined foraging behaviors of wild solitary long-horned bees (Melissodes spp.) in response to a cryptic predator, the ambush bug (Phymata americana) on the bees’ primary floral host, the prairie sunflower (Helianthus petiolaris). We found sex-specific differences in foraging behaviors of bees, but little evidence that ambush bugs affected either pre-landing or post-landing foraging behaviors. Male bees visited flowers three times more often than females but female bees were five times more likely to land than males. Ambush bugs did not reduce visitation in either sex. Spectral analysis through a bee vision model indicated that ambush bug dorsal coloration was indistinguishable from the disc flowers of sunflowers, suggesting that ambush bugs are indeed cryptic and likely rarely detected by solitary bees. We discuss the implications of these findings for the perceived risk of predation in solitary bees and compare them to other studies of social bees.     

Greater sage‐grouse respond positively to intensive post‐fire restoration treatments

Habitat loss is the most prevalent threat to biodiversity in North America. One of the most threatened landscapes in the United States is the sagebrush (Artemisia spp.) ecosystem, much of which has been fragmented or converted to non‐native grasslands via the cheatgrass‐fire cycle. Like many sagebrush obligates, greater sage‐grouse (Centrocercus urophasianus) depend upon sagebrush for food and cover and are affected by changes to this ecosystem. We investigated habitat selection by 28 male greater sage‐grouse during each of 3 years after a 113,000‐ha wildfire in a sagebrush steppe ecosystem in Idaho and Oregon. During the study period, seeding and herbicide treatments were applied for habitat restoration. We evaluated sage‐grouse responses to vegetation and post‐fire restoration treatments. Throughout the 3 years post‐fire, sage‐grouse avoided areas with high exotic annual grass cover but selected strongly for recovering sagebrush and moderately strongly for perennial grasses. By the third year post‐fire, they preferred high‐density sagebrush, especially in winter when sagebrush is the primary component of the sage‐grouse diet. Sage‐grouse preferred forb habitat immediately post‐fire, especially in summer, but this selection preference was less strong in later years. They also selected areas that were intensively treated with herbicide and seeded with sagebrush, grasses, and forbs, although these responses varied with time since treatment. Wildfire can have severe consequences for sagebrush‐obligate species due to loss of large sagebrush plants used for food and for protection from predators and thermal extremes. Our results show that management efforts, including herbicide application and seeding of plants, directed at controlling exotic annual grasses after a wildfire can positively affect habitat selection by sage‐grouse.     

White‐tailed deer exploit temporal refuge from multi‐predator and human risks on roads

Although most prey have multiple predator species, few studies have quantified how prey respond to the temporal niches of multiple predators which pose different levels of danger. For example, intraspecific variation in diel activity allows white‐tailed deer (Odocoileus virginianus) to reduce fawn activity overlap with coyotes (Canis latrans) but finding safe times of day may be more difficult for fawns in a multi‐predator context. We hypothesized that within a multi‐predator system, deer would allocate antipredation behavior optimally based on combined mortality risk from multiple sources, which would vary depending on fawn presence. We measured cause‐specific mortality of 777 adult (>1‐year‐old) and juvenile (1–4‐month‐old) deer and used 300 remote cameras to estimate the activity of deer, humans, and predators including American black bears (Ursus americanus), bobcats (Lynx rufus), coyotes, and wolves (Canis lupus). Predation and vehicle collisions accounted for 5.3 times greater mortality in juveniles (16% mortality from bears, coyotes, bobcats, wolves, and vehicles) compared with adults (3% mortality from coyotes, wolves, and vehicles). Deer nursery groups (i.e., ≥1 fawn present) were more diurnal than adult deer without fawns, causing fawns to have 24–38% less overlap with carnivores and 39% greater overlap with humans. Supporting our hypothesis, deer nursery groups appeared to optimize diel activity to minimize combined mortality risk. Temporal refuge for fawns was likely the result of carnivores avoiding humans, simplifying diel risk of five species into a trade‐off between diurnal humans and nocturnal carnivores. Functional redundancy among multiple predators with shared behaviors may partially explain why white‐tailed deer fawn predation rates are often similar among single‐ and multi‐predator systems.     

The possible role of predator–prey dynamics as an influence on early hominin use of burned landscapes

Foraging in burned areas has been suggested to represent the earliest stage in the use and control of fire by early hominins. Recently burned areas offer immediate foraging benefits including increased search efficiency for high‐ranked food items and decreased hunting opportunities for ambush predators. As such, they provide a triple‐bonus (reduced risk from ambush, ease of terrestrial travel and higher foraging returns) for some primates. However, previous studies have not yet accounted for other types of predators e.g., coursing (endurance predators that can pursue prey over long distances) which were sympatric with hominins and may also have exploited these environments. Behavioral ecology studies on the use of burned landscapes by extant carnivores demonstrate that while some ambush predators avoid recently burned areas, coursing predators do take advantage of their immediate hunting opportunities. Research examining habitat selection by animals under the simultaneous threat of multiple predator species with different modes of hunting, and the diversity of Plio‐Pleistocene carnivore guild is suggestive of two possible evolutionary scenarios in which hominins could either have selected or avoided burned areas (3–2 mya), based on whether ambush or coursing predators were perceived as presenting the greatest risk.     

History of canids in Chile and impacts on prey adaptations

Artiodactyl prey species of Chile, especially guanacos (Lama guanicoe), are reported to be very susceptible to predation by pack‐hunting feral dogs. It has been previously suggested that guanacos and endemic South American deer may have evolved in the absence of pack‐hunting cursorial predators. However, the paleoecology of canid presence in southern South America and Chile is unclear. Here, we review the literature on South American and Chilean canids, their distributions, ecologies, and hunting behavior. We consider both wild and domestic canids, including Canis familiaris breeds. We establish two known antipredator defense behaviors of guanacos: predator inspection of ambush predators, for example, Puma concolor, and rushing at and kicking smaller cursorial predators, for example, Lycalopex culpaeus. We propose that since the late Pleistocene extinction of hypercarnivorous group‐hunting canids east of the Andes, there were no native species creating group‐hunting predation pressures on guanacos. Endemic deer of Chile may have never experienced group‐hunting selection pressure from native predators. Even hunting dogs (or other canids) used by indigenous groups in the far north and extreme south of Chile (and presumably the center as well) appear to have been used primarily within ambush hunting strategies. This may account for the susceptibility of guanacos and other prey species to feral dog attacks. We detail seven separate hypotheses that require further investigation in order to assess how best to respond to the threat posed by feral dogs to the conservation of native deer and camelids in Chile and other parts of South America.     

Zebra mussels affect benthic predator foraging success and habitat choice on soft sediments

The introduction of zebra mussels (Dreissena spp.) to North America has resulted in dramatic changes to the complexity of benthic habitats. Changes in habitat complexity may have profound effects on predator-prey interactions in aquatic communities. Increased habitat complexity may affect prey and predator dynamics by reducing encounter rates and foraging success. Zebra mussels form thick contiguous colonies on both hard and soft substrates. While the colonization of substrata by zebra mussels has generally resulted in an increase in both the abundance and diversity of benthic invertebrate communities, it is not well known how these changes affect the foraging efficiencies of predators that prey on benthic invertebrates. We examined the effect of zebra mussels on the foraging success of four benthic predators with diverse prey-detection modalities that commonly forage in soft substrates: slimy sculpin (Cottus cognatus), brown bullhead (Ameirus nebulosus), log perch (Percina caprodes), and crayfish (Orconectes propinquus). We conducted laboratory experiments to assess the impact of zebra mussels on the foraging success of predators using a variety of prey species. We also examined habitat use by each predator over different time periods. Zebra mussel colonization of soft sediments significantly reduced the foraging efficiencies of all predators. However, the effect was dependent upon prey type. All four predators spent more time in zebra mussel habitat than in either gravel or bare sand. The overall effect of zebra mussels on benthic-feeding fishes is likely to involve a trade-off between the advantages of increased density of some prey types balanced against the reduction in foraging success resulting from potential refugia offered in the complex habitat created by zebra mussels.     

Carbohydrates complement high‐protein diets to maximize the growth of an actively hunting predator

In nature, food is often variable in composition and availability. As a consequence, predators may need to seek non‐prey food sources. Some predators are known to feed on nectar when food is limited. Nectar and other carbohydrate resources could also be beneficial when prey are more abundant if it helps predators balance protein‐biased diets. We tested if an actively hunting predator, the jumping spider, Phidippus audax, benefited from liquid carbohydrates when prey were not limited. We also tested if the benefit of carbohydrates varied with the nutrient content of prey (i.e., from protein to lipid biased). Spiders were reared on one of six live prey, Drosophila melanogaster, treatments that ranged from high protein to high lipid. Half of the spiders were given access to a 20% sucrose solution. After 2 months, we measured spider mass, cephalothorax width, instar duration, percent body fat, survival, and estimated number of prey eaten. Spiders reared on high‐protein diets with carbohydrates were larger and heavier than spiders on other treatments. Access to carbohydrates also increased percent body fat and survival across prey treatments. Our results suggest that carbohydrates may be a valuable component of spider diets, especially when prey have high protein and low lipid content as is commonly observed in prey in the field. Our results highlight the importance of diet balancing for predators, and that liquid carbohydrates can be an important nutrient to supplement a diet of prey rather than just being an energy supplement during periods of starvation.