Endothermic Predators Research Articles

Temperature-dependent predation predicts a more reptilian future.

Diversity increases toward the tropics, but the strength of this pattern diverges with thermoregulatory strategy. Synthesizing over 30,000 species distributions, we quantified patterns of richness in terrestrial vertebrates, and present evidence for a latitudinal gradient of community composition. We observe a two orders of magnitude shift in comparative diversity with temperature, from endothermic mammal and avian dominance near the poles, toward ectothermic reptile and amphibian majority in the tropics. Next, we provide mechanistic support for a corresponding latitudinal gradient of predatory interactions. Using automated video tracking in >4500 trials, we show that differences in thermal sensitivity of locomotion in endothermic predators and ectothermic prey favors endotherms in colder environments and yields theoretically predicted foraging outcomes across thermal conditions, including the number of strikes, the distance traveled, and the time to capture prey. We also present evidence that endotherms use thermal cues to anticipate prey behavior, modulating the impact of temperature. Finally, we integrate theory and data to forecast future patterns of diversity, revealing that as the world get warmer, it will become increasingly reptilian. Overall, our results point toward a broad reorganization of vertebrate diversity with latitude, elevation, and temperature: from endotherm dominance in cold systems toward ectotherm dominance in warm.

Determining early marine survival and predation by endothermic predators on acoustically tagged Atlantic salmon (Salmo salar) post-smolts

Many Atlantic salmon ( Salmo salar) populations have experienced significant declines for decades throughout North America and Europe. Mortality due to marine mammal predation during their early marine life could be an important factor contributing to these declines and limiting their population recoveries. However, quantifying predation events, and particularly the extent of marine mammal predation on Atlantic salmon, remains a challenge. In this study, we estimated the contribution of mesothermic and endothermic species predation to the mortality of Atlantic salmon post-smolts during their early marine life using acoustic telemetry. Predation events were inferred from changes in temperatures and depths experienced by acoustically tagged hatchery-reared Atlantic salmon smolts. No salmon were consumed by mesothermic predators, with most endothermic predation events being classified as marine mammals. Post-smolt mortality during the study period was low overall in both years (13.1%–16.7%), with endothermic predation accounting for 33.1%–42.9% of all marine mortality events (5.2%–5.6% mortality). Our results suggest that the current low return of adult Atlantic salmon observed in this area in recent years was not heavily influenced by endothermic predation on post-smolts in the first weeks at sea.

Feeding on epibenthic zooplankton by Long‐tailed Ducks: patch structure, profitability, and food web implications

AbstractModels of the trophic needs and impacts of mobile predators in food web networks typically do not consider interactions between prey dispersion and threshold prey densities needed for profitable foraging. As a result, the biomass of predators that can be supported, or direct and indirect impacts of those predators on other food web components, may be poorly estimated. In Simpson Lagoon on the U.S. Arctic coast, epibenthic amphipods and especially mysid shrimp comprised most of the diets of fish, and of Long‐tailed Ducks (Clangula hyemalis) which strongly dominated prey consumption. Based on mean prey densities and gross estimates of prey biomass consumed, earlier studies estimated that continuous immigration of mysids into the lagoon was needed to support the predators. Comparison of variances from net samples vs. different probability density functions (PDFs) around reported means indicated that prey were not normally distributed, and instead occurred in patches with a skewed and wide range of densities. We used the functional response of captive Long‐tailed Ducks eating mysids, and a foraging energetics model, to identify minimum prey densities these diving ducks needed to feed profitably. Based on PDFs that assumed prey densities in all 1‐m2 cells (patches for single feeding dives on potential mysid swarms) were independent, we simulated prey grids with slightly skewed to highly skewed distributions for the reported sample means. Results showed that the greater the range of patch densities, the smaller the fraction of prey biomass that was profitably available to the ducks, thereby increasing the requisite immigration of mysids. Consumption by ectothermic predators further decreased prey available and advanced the date and increased the amount of mysid influx required. The models also showed that the birds had to seek areas with non‐independent clusters of high‐density feeding patches as prey declined in late summer. Thus, spatially continuous measures of patch structure over larger scales are needed to estimate the fraction of prey that is functionally available. Our study emphasizes that when estimating trophic needs and impacts of mobile endothermic predators, simple means of prey density can be misleading, owing to interactions of prey patch structure with profitability thresholds.

Sediment organic carbon integrates changing environmental conditions to predict benthic assemblages in shallow Arctic seas

Abstract In marine spatial planning, conserving adequate habitats and the food webs they support requires delineating habitats and projecting future trends. For bottom‐feeding marine birds and mammals, repeated benthic sampling over large areas to document changes and to develop predictive models of prey dispersion is quite costly. More easily monitored variables that relate strongly to the biomass and structure of benthic assemblages, and are more readily predicted from physical models of climate change, would facilitate planning efforts. The organic carbon (OC) content of sediments integrates diverse physical and biotic processes, and can be less variable over time than primary production, salinity, temperature, or position of water masses. Sediment OC further subsumes inputs at the base of food webs that can limit carbon flows to higher taxa. For the northern Bering Sea, this study explored the utility of sediment OC as a predictor of benthic assemblage types. Cluster analysis and multi‐dimensional scaling distinguished three main types along a gradient of sediment OC. The assemblage for highest sediment OC had a much greater biomass of brittlestars, diverse marine worms, and two mid‐sized, thinner‐shelled bivalves selected as prey by diving sea ducks. The assemblage for lowest sediment OC lacked brittlestars, had a much greater biomass of amphipods sought by gray whales (Eschrichtius robustus), and had a much higher biomass of two often larger or thicker‐shelled bivalves commonly targeted by walruses (Odobenus rosmarus). Areas of exceptionally low sediment OC tended towards dominance by sand dollars with low foraging value. Our study shows that sediment OC has promise as a proxy for monitoring and predicting changes in important prey assemblages in a given region. Models that link predicted hydrographic patterns to lateral advection of phytodetritus, and the resulting sediment OC, may further allow the use of physical climate models to project the future dispersion of benthic habitats for endothermic predators.

Consumption of pelagic tunicates by cetaceans calves in the Mediterranean Sea

Gelatinous zooplankton, including jellyfish, ctenophores and pelagic tunicates, constitutes fragile marine animals that live in the water column, and represent an important resource for marine food webs through their seasonal pulses. Although there is scarce evidence on the occurrence of gelatinous zooplankton in stomach contents of apex, endothermic predators such as cetaceans, the ecological significance of such observations requires consideration. In this study, we report on the occurrence of pelagic tunicates in the stomach of three individual calves of two cetacean species from the western Mediterranean, and collate all previous reports of gelatinous zooplankton in cetacean diets. We then briefly discuss the possible dietary significance of these observations.

Seed ingestion and germination in rattlesnakes: overlooked agents of rescue and secondary dispersal.

Seed dispersal is a key evolutionary process and a central theme in the population ecology of terrestrial plants. The primary producers of most land-based ecosystems are propagated by and maintained through various mechanisms of seed dispersal that involve both abiotic and biotic modes of transportation. By far the most common biotic seed transport mechanism is zoochory, whereby seeds, or fruits containing them, are dispersed through the activities of animals. Rodents are one group of mammals that commonly prey on seeds (granivores) and play a critical, often destructive, role in primary dispersal and the dynamics of plant communities. In North America, geomyid, heteromyid and some sciurid rodents have specialized cheek pouches for transporting seeds from plant source to larder, where they are often eliminated from the pool of plant propagules by consumption. These seed-laden rodents are commonly consumed by snakes as they forage, but unlike raptors, coyotes, bobcats, and other endothermic predators which eat rodents and are known or implicated to be secondary seed dispersers, the role of snakes in seed dispersal remains unexplored. Here, using museum-preserved specimens, we show that in nature three desert-dwelling rattlesnake species consumed heteromyids with seeds in their cheek pouches. By examining the entire gut we discovered, furthermore, that secondarily ingested seeds can germinate in rattlesnake colons. In terms of secondary dispersal, rattlesnakes are best described as diplochorous. Because seed rescue and secondary dispersal in snakes has yet to be investigated, and because numerous other snake species consume granivorous and frugivorous birds and mammals, our observations offer direction for further empirical studies of this unusual but potentially important channel for seed dispersal.

Jellyfish and other gelata as food for four penguin species – insights from predator‐borne videos

Jellyfish and other pelagic gelatinous organisms (“gelata”) are increasingly perceived as an important component of marine food webs but remain poorly understood. Their importance as prey in the oceans is extremely difficult to quantify due in part to methodological challenges in verifying predation on gelatinous structures. Miniaturized animal‐borne video data loggers now enable feeding events to be monitored from a predator's perspective. We gathered a substantial video dataset (over 350 hours of exploitable footage) from 106 individuals spanning four species of non‐gelatinous‐specialist predators (penguins), across regions of the southern oceans (areas south of 30°S). We documented nearly 200 cases of targeted attacks on carnivorous gelata by all four species, at all seven studied localities. Our findings emphasize that gelatinous organisms actually represent a widespread but currently under‐represented trophic link across the southern oceans, even for endothermic predators, which have high energetic demands. The use of modern technological tools, such as animal‐borne video data loggers, will help to correctly identify the ecological niche of gelata.

Post-release survival, movement, and habitat use of school shark Galeorhinus galeus in the Great Australian Bight, southern Australia

Bycatch of marine mammals in the gillnet sector of the Southern and Eastern Scalefish and Shark Fishery in the Great Australian Bight prompted managers to assess the use of demersal automatic longlines as an alternative method to target gummy shark (Mustelus antarcticus). The school shark (Galeorhinus galeus) is a migratory species that is occasionally taken as bycatch when targeting gummy shark, and the stock is currently managed under a rebuilding strategy. We used pop-up satellite archival tags (PSAT) to investigate the survival, movements, and habitat use of mature female school shark (147–170cm total length) following capture and release from demersal automatic longlines. Satellite telemetry data indicated lively school sharks survived the capture, on-board handling, tagging and release processes. Tracked school sharks mostly moved offshore and across the continental shelf in south to south-easterly directions. Depth habitat use reflected semi-pelagic behavioural traits and a preference for lower mixed layer depths of 50–100m where water temperatures were 15–21°C. Two PSATs provided data that we interpreted as indicative of tag and/or tagged shark ingestion, and tag regurgitation by endothermic predators. This study also identified an area where neonate and large, mature female school sharks were observed together during the Austral summer. Findings of this study are crucial to informing current fisheries management, stock recovery and bycatch mitigation strategies off southern Australia.

Winter sheltering by juvenile brown trout (Salmo trutta) – effects of stream wood and an instream ectothermic predator

Summary In boreal streams, juvenile salmonids spend substantial amounts of time sheltering in the streambed and in stream wood, presumably as a means of protection against the physical environment and from terrestrial endothermic predators. Relatively little is known about sheltering by salmonids in response to instream ectothermic predators. We tested the effects of burbot (Lota lota) on the winter sheltering behaviour of PIT‐tagged 0+ brown trout (Salmo trutta) in daylight and darkness. Sheltering in the streambed by trout was studied in the presence and absence of fine wood bundles. We found that the use of streambed and fine wood was lower in darkness than in daylight. Availability of fine wood significantly decreased sheltering in the streambed, and this effect was more pronounced in daylight than in darkness. The presence of a burbot significantly decreased sheltering in the streambed, had no effect on use of fine wood and resulted in a higher number of exposed trout. Our results indicate that juvenile brown trout decrease streambed sheltering in response to a burrowing, ectothermic predator.

The importance of plant cover and predation in shaping a desert community

The classical paradigm describe desert communities as being controlled by abiotic conditions and therefore it was assumed that predation had a limited role in the determination of desert community structure and that only one effective trophic level was expected. In the Negev desert, the desert isopod (Hemilepistus raeumuri) is common in the less productive habitats but almost absent from the more productive wadis. In the present study we tested whether predation by ectothermic predators has a role in controlling isopod populations in wadis. We hypothesized that plant cover provides a refuge for these predators from secondary endothermic predators. We addressed this hypothesis by comparing isopod survivorship with and without predation exclusion, and with and without plant cover removal. Isopods protected from predation had a sustainable population whereas unprotected isopods had an unsustainable sink population. Removal of plant cover did not affect the survivorship of predator-protected isopods, however it did increase the survivorship and reduced predation pressure when not protected from predators, for at least four years. Hence, we conclude that predation controls isopod population and causes an unsustainable sink population in wadis. We have shown that plant cover mediates predation and that some habitats in the desert have an effective third trophic level, suggesting that energy is not the major limiting factor in determining the length of food chains.

Geometric factors influencing the diet of vertebrate predators in marine and terrestrial environments.

Predator–prey relationships are vital to ecosystem function and there is a need for greater predictive understanding of these interactions. We develop a geometric foraging model predicting minimum prey size scaling in marine and terrestrial vertebrate predators taking into account habitat dimensionality and biological traits. Our model predicts positive predator–prey size relationships on land but negative relationships in the sea. To test the model, we compiled data on diets of 794 predators (mammals, snakes, sharks and rays). Consistent with predictions, both terrestrial endotherm and ectotherm predators have significantly positive predator–prey size relationships. Marine predators, however, exhibit greater variation. Some of the largest predators specialise on small invertebrates while others are large vertebrate specialists. Prey–predator mass ratios were generally higher for ectothermic than endothermic predators, although dietary patterns were similar. Model-based simulations of predator–prey relationships were consistent with observed relationships, suggesting that our approach provides insights into both trends and diversity in predator–prey interactions.

Effects of ice cover on the diel behaviour and ventilation rate of juvenile brown trout

Summary Winter ice conditions in boreal streams are highly variable, and behavioural responses by fish to river ice may affect overwinter survival rates. One type of ice, surface ice, stabilises water temperatures, reduces instream light levels and may provide overhead cover. Because surface ice is believed to afford protection against endothermic predators, we predicted that metabolic costs associated with vigilance would be lower under surface ice than in areas lacking surface ice. This potentially favourable effect of ice cover was tested by observing ventilation rates of juvenile brown trout (Salmo trutta) in a laboratory stream at dawn, during the day and at night in the presence and absence of real, light‐permeable surface ice. Further, we offered trout drifting prey during daylight to test whether ice cover increased daytime foraging activity. Ice cover reduced ventilation rates during the day, but not at night or dawn. Moreover, fish made more daytime foraging attempts in the presence of ice cover than in its absence. We suggest that the most plausible explanation for these results is that fish experience a reduced perceived predation risk under surface ice.

The role of thermal contrast in infrared-based defensive targeting by the copperhead, Agkistrodon contortrix

The facial pit organs of the copperhead are the end organs of a complex infrared-imaging system that allows accurate and precise strikes on potential prey. Anecdotal and recent experimental observations show that pit vipers can use their infrared-imaging systems to discriminate between cool and warm features in the environment. We tested the hypothesis that the infrared-imaging system is a thermal contrast detector and determined whether behavioural responses of copperheads differ with contrast type. We found that blindfolded copperheads responded behaviourally towards both warm objects moving against cool backgrounds and cool objects moving against warm backgrounds. Responses towards the former were more robust than those towards the latter. Furthermore, oscillating warm targets generated rhythmic following behaviour in-phase with target motion, while oscillating cool targets generated rhythmic behavioural movement in antiphase to target motion. The results show that the infrared-imaging system of pit vipers operates on the basis of thermal contrast, but the differences in behavioural responses with respect to contrast type indicate that pit vipers preferentially target the warm aspect of thermal differentials. Our results also demonstrate that the infrared-imaging system allows defensive targeting of potential endothermic predators.

Going deep: common murres dive into frigid water for aggregated, persistent and slow-moving capelin

Owing to the necessity of delivering food to offspring at colonies, breeding seabirds are highly constrained in their foraging options. To minimize constraints imposed by central-place foraging and to optimize foraging behavior, many species exhibit flexible foraging tactics. Here we document the behavioral flexibility of pursuit-diving common murres Uria aalge when foraging on female capelin Mallotus villosus in the northwest Atlantic. Quite unexpectedly, being visual foragers, we found that common murres dived throughout the day and night. Twenty-one percent of recorded dives (n = 272 of 1,308 dives) were deep (≥50 m; maximum depth = 152 m, maximum duration = 212 s), bringing murres into sub-0°C water in the Cold Intermediate Layer (CIL; 40–180 m) of the Labrador Current. Deep dives occurred almost exclusively during the day when murres would have encountered spatially predictable aggregations of capelin between 100 and 150 m in the water column. Temperatures within the CIL shaped trophic interactions and involved trade-offs for both predators and prey. Sub-0°C temperatures limit a fish’s ability to escape from endothermic predators by reducing burst/escape speeds and also lengthening the time needed to recover from burst-type activity. Thus, while deep diving may be energetically costly, it likely increases certainty of prey capture. Decreased murre foraging efficiency at night (indicated by an increase in the number of dives per bout) reflects both lower light conditions and changing prey behavior, as capelin migrate to warmer surface waters at night where their potential to escape from avian predators could increase.

Endothermy, ectothermy and the global structure of marine vertebrate communities

Birds and mammals are the leading marine predators at high latitudes, while sharks and other large fish occupy top positions in tropical waters. The present study proposes that temperature- dependent predation success (TPS) explains global patterns of marine vertebrate community struc- ture. Burst speed increases with temperature in ectotherms but is independent of temperature in endotherms. If capture success depends on relative swimming speeds of predator and prey, ecto- thermic prey will be more vulnerable to attack by endothermic predators at low temperatures. Conversely, high temperatures should enhance the ability of ectothermic predators to prey on endotherms. Pursuit-diving seabirds (penguins, auks and some cormorants) and pinnipeds (seals and sea lions) are ubiquitous in ocean waters with summer surface temperatures cooler than the mid- teens to low 20s (°C) but are virtually absent in warmer regions. We suggest that the near-absence of these animals at low latitudes is due to TPS, as warm water increases the difficulty of capturing fish prey and increases vulnerability to predation by large ectothermic and partially endothermic sharks. Pursuit-diving birds and pinnipeds are virtually absent from warm temperate and tropical waters, even where primary productivity and fisheries data suggest that food supplies are ample. This indi- cates that the low productivity that prevails in much of the tropical zone cannot explain the world- wide distributional patterns of pursuit-diving birds and pinnipeds. Endothermy in marine communi- ties increases with cooler temperatures and with animal size. Pursuit-diving birds and pinnipeds are sensitive to temperature limits and may suffer important range contractions as oceans warm.

Physiology of Intermittent Feeding: Integrating Responses of Vertebrates to Nutritional Deficit and Excess

Food intakes of wild animals may not match their requirements for nutrients and energy but may vary between periods of nutritional excess (hyperphagia) and nutritional deficit (hypophagia) at timescales that vary from days to months. We present a simple model of feeding patterns and requirements of vertebrates. Frequent fasts and high intakes are typical of endothermic predators and migratory birds, whereas slow cycles and long deficits typify feeding patterns of ectothermic predators and ungulates in seasonal environments. We propose that hyperphagia is constrained by the ability to increase processes of digestion, absorption, intermediary metabolism, net deposition in tissue, and excretion to match loads of digesta and metabolites. Hyperphagia on high-quality diets is limited by the clearance of metabolites, whereas digestive tract capacity and flow limit consumption of low-quality diets. Of all digestive strategies, small omnivores with simple digestive systems may be the most tolerant of frequent hyperphagia. Tolerance of hypophagia favors large endogenous stores or low mass-specific rates of metabolism and reproductive output. Large animals may be most able to sustain reproduction during prolonged deficits in seasonal environments. Responses to excessive and deficient intakes of food are constrained by the length of the feeding cycle. Animals adapted to short feeding cycles may be best suited to unpredictable food supplies but at the energetic cost of maintaining spare capacity for digestion and absorption. Predictions of the response to food disruption are best evaluated in the context of body size, nutritional physiology, and life history of the species and the time for internal response.

Energetics and food requirements of the female snake Phillodryas chamissonis during the breeding season.

1.The energetic performance and food requirements of female Phillodryas chamissonis was determined during its breeding season at different ambient temperatures. 2. If the long tailed snake is active for 24 weeks, 25 to 32 30-g rodents are required for reproduction and maintenance. This is slightly more than one rodent per week. 3. The energy cost of reproduction (38 to 48% of total metabolism) is close to the values reported for fish (35% of metabolizable energy). 4. Due to their low metabolic rates, the theoretical predation pressure (on a prey biomass basis) exerted by the snakes should be 2 to 2.5% of that expected for endothermic predators of similar body size.