Search

The pattern of prey distribution can profoundly affect the foraging behavior and success of a predator. In pelagic marine ecosystems, where prey is often patchily distributed, predators must be able to adapt quickly to changes in the spatial patterning of prey. Antarctic fur seals feed primarily on krill, which is patchily distributed. When combined with information about swimming speed on the surface, the time taken for a fur seal to locate a new patch after leaving an old one is an indication of the distance between patches. The frequency distribution of intervals between bouts of foraging showed that fur seals foraged at two spatial distributions: (1) a fine-scale (median distance 0.18-0.27 km) represented by short (5 min) travel durations. In a study lasting 5 yr, the distributions of travel durations between bouts of feeding changed between years. These changes suggested that the structure and/or the spatial distribution of krill swarms varied between years. The behavior of fur seals suggested that there was overall clumping of prey at the fine-scale, but there was a more even spacing of prey patches at the meso-scale level. Only in 1 yr of the study (1990/1991) were there indications that fur seals had difficulty in finding enough food. Fur seal behavior suggested that there was no reduction in the number of prey patches available in that year but that prey patches were of poorer quality. The study showed how predator behavior can provide valuable information about the functional relationship between prey dispersion and predator performance. Key words: foraging; marine; pinniped; predator; scale., INTRODUCTION The way in which predators search their environment for prey and the rules they use to determine how long they should spend in a specific location have received considerable [...]

Although seasonal migrations of large predatory mammals that follow migrating prey are well documented, no equivalent phenomenon has been described previously in terrestrial reptiles. We surveyed and radio-tracked water pythons (Liasis fuscus) in Fogg Dam and its adjacent floodplain in the wet-dry tropics of northern Australia to document patterns of movement, with particular emphasis on the ways in which the snakes exploit their major prey species, the dusky rat (Rattus colletti). The distribution and abundance of these rodents vary seasonally. During the dry season the rats live in soil crevices in the floodplain, but wet-season flooding forces them to higher ground, primarily to natural levee banks. Python and rat abundances on the floodplain adjacent to Fogg Dam were significantly correlated through time: both reached a maximum during the dry season, and fell dramatically during the wet season. Activity of pythons was centered around Fogg Dam during the dry season, but all of the radio-tracked snakes moved away from this area during the wet season. Most pythons migrated to the vicinity of levee banks on the floodplain up to 12 km away from their dry-season range. By migrating seasonally, water pythons can efficiently utilize a migratory prey species that would otherwise be unavailable for much of the year. Key words: Australia; foraging; home range; predator-prey; rodent; seasonality; snake; weather., INTRODUCTION Many species of animals show consistent seasonal migratory movements, but the actual stimulus for migration varies considerably. One pattern reported for large mammalian predators involves seasonal migrations to track [...]

Early life stages are often particularly vulnerable to predation (e.g., Howe and Smallwood 1982). Consequently, predators have a strong effect on the timing and allocation of resources to reproduction (e.g., [...]

Predation at seven colonies that varied in size from 10 to hundreds of breeding pairs of Adelie (Pygoscelis adeliae) and Gentoo (P. papua) penguins was observed from a blind at King George Island, Antarctic Peninsula, from 21 Dec. 1993 to 3 Feb. 1994. We observed the colonies for 96 h to record foraging by Brown Skuas (Catharacta lonnbergi), Kelp Gulls (Larus dominicanus), and Giant Petrels (Macronectes giganteus) during the early chick through creche phase of the penguin breeding cycle. Activity rates by predators varied little with time of day or time of season for skuas and petrels. Kelp Gulls, however, showed significant variation in rates with time of season. Total activity and search rates were significantly higher for each predator species at larger versus smaller colonies. In addition, attempted predation and predation by skuas on penguin chicks were significantly higher, and from 4.1-7.9x more frequent, at colony edges rather than the center. Larger colonies probably receive greater attention by predators because of the larger number of prey, and by their greater circumference and edge area. Low breeding success by penguins in small colonies appeared to be partially attributed to predation losses, although predation rates were low. Penguin reproductive success may be significantly influenced by colony size and by the number and kinds of predators attending them. Received 8 Sept. 1994, accepted 15 Nov. 1994., Predation at breeding colonies has received a great deal of attention by ornithologists interested in the evolution and adaptive significance of coloniality (e.g., Wittenberger and Hunt 1985, Kharitonov and Siegel-Causey [...]

Marine larvae are consumed by a wide variety of generalist fishes and particle-feeding invertebrates, but larvae of any particular species probably constitute a small and variable portion of the diet for these consumers. Because virtually all consumers can ingest small quantities of noxious compounds with minimal detrimental effects, it is uncertain that toxic chemicals in larvae could be consumed in quantities sufficient to select for predator recognition and avoidance. Despite this, chemically defended larvae do occur. We show that, at low doses, secondary metabolites (the didemnins) from adults and larvae of the Caribbean tunicate Trididemnum solidum induced vomiting in fish, resulting in rapid learned aversion to the didemnin-defended food, The particle-feeding anemone Aiptasia pallida did not learn to avoid the chemically defended food. When anemones ingested the chemical equivalent of 15 larvae/d, representing Key words: chemical defense; fitness; larvae; learning; physiological effects; predator-prey interactions; reproduction; secondary metabolites., INTRODUCTION The advantages of chemically repelling consumers are obvious and have been studied extensively in both marine and terrestrial communities (see reviews in Paul 1992 and Rosenthal and Berenbaum 1992, [...]

I combined long-term (10 yr) descriptive and short-term experimental studies in a headwater stream in northern Minnesota to assess: (1) the effect of annual variation in stream discharge and spatial proximity of beaver (Castor canadensis) ponds on lotic fish abundance and (2) the subsequent influence of discharge and fish predation on lotic invertebrate colonization. Considerable annual variation in fish density occurred in the stream over the 10-yr period, particularly in pool habitats. Increased fish density was associated with increased stream discharge and creation of beaver ponds downstream from the study site. Weir traps used to monitor directional (upstream vs. downstream) fish movement during the last 4 yr of the study indicated annual changes in fish density were associated with the amount of fish dispersal occurring along the stream segment. Downstream fish movement, out of an upstream beaver pond occurred primarily during periods of elevated stream discharge. Upstream movement, out of a downstream beaver pond, occurred over a broader range of discharge conditions. A controlled, 'split-stream,' experiment examining the effect of very low vs. elevated discharge on upstream fish movement indicated, however, that upstream movement of fish out of beaver ponds was also reduced by very low discharge conditions. Movement data for individual fish species revealed considerable variation among the taxa in the tendency for downstream vs. upstream movement, due to variation in the morphology of upstream vs. downstream beaver ponds and its subsequent effect on the composition of fish dispersing from these source areas. Most fish movement occurred over relatively brief time periods, suggesting life history and developmental processes were critical in influencing the timing of dispersal. Size structure of fishes captured in the stream indicated predominantly older age classes (>age I) of fish were dispersing along the stream. However, based on the occurrence of age 0 individuals only 1 of 12 species, the creek chub (Semotilus atromaculatus), routinely reproduced in the stream. Experiments conducted in an artificial stream located below one of the beaver ponds indicated discharge and fish predation have potentially strong and interactive effects on invertebrate colonization in stream ecosystems. Differences in colonization of riffles and pools under low vs. elevated discharge and fish vs. no-fish treatments suggested, however, that the interactive effect of these factors on invertebrate colonization was variable over even small spatial scales. Elevated discharge increased invertebrate colonization in riffles but decreased invertebrate colonization in pools. Contrary to intuitive expectations, fish predation reduced invertebrate colonization more under elevated than low discharge conditions, particularly in pool habitats. Taken together, these results suggest: (1) beaver ponds act as reproductive 'sources' for fish on the landscape, while adjacent stream environments act as potential reproductive 'sinks,' (2) large-scale spatial relationships between beaver ponds and streams, along with the influence of discharge on the permeability of the boundaries between these habitats, are critical in controlling fish dispersal between ponds and streams and the subsequent abundance and composition of fish in lotic ecosystems, and (3) fish predation and discharge have potentially cascading effects on invertebrate colonization in lotic ecosystems. Key words: beaver ponds; boundary processes; Castor canadensis; colonization; fish assemblages; fish dispersal; invertebrates; landscape ecology; lotic ecosystems; Minnesota; predator-prey interactions; stream discharge; trophic-level interactions., INTRODUCTION Many aquatic vertebrates exhibit complex life cycles, with various life history stages using widely separated habitats (Sale 1978, 1979, Wilbur 1980, Werner and Gilliam 1984). Future empirical and theoretical [...]

We report the predation of Black Swan (Cygnus atratus) eggs and cygnets by adult Purple Swamphens (Porphyrio porphyrio), a mostly-herbivorous species of rail, in Melbourne, Victoria, Australia., The Purple Swamphen (Porphyrio porphyrio) is a large rail (males: 1,050 g; females: 850 g) whose range encompasses southern Africa, southern Asia, Papua New Guinea, Australia, and New Zealand (Marchant [...]

ABSTRACT. We describe the apparent predation of a polar bear (Ursus maritimus) cub by wolves (Canis lupus) on the sea ice just off the northwest coast of Banks Island, Northwest [...]

I observed a Western Scrub-Jay (Aphelocoma californica) consume a Golden-cheeked Warbler (Dendroica chrysoparia) nestling and a Brown headed Cowbird (Molothrus ater) nestling in northwestern Travis County, Texas, in May 1995. During a 4.5-hr period after brood destruction, warbler adults repeatedly brought insects to the depredated nest, and during each visit they appeared to search for the nestlings in the nest area and adjacent trees while carrying the insects. When the jay subsequently returned to the nest to take an unhatched egg, the female warbler perfomed a distraction display. My observations indicate that, in some cases, parental feeding behavior and nest defense can continue for a short time after brood loss. Received 27 March 2002, accepted 28 May 2004., The Golden-cheeked Warbler (Dendroica chrysoparia) is an endangered species that breeds only in mature oak (Ouercus spp.)-Ashe juniper (Juniperus ashei) forests or woodlands in central Texas. Nest predation is an [...]

The arthropod-flushing behavior of above-ground swarming army ants (tribe Ecitonini) provides Neotropical birds with a unique food resource. The extent to which birds exploit this resource varies geographically, because of the variable swarming behavior of different army ant species and their distributions. During the winter, Neotropical-Nearctic migrant birds may have greater opportunity at higher latitude army ant swarms because of a lack of dominant, obligate ant-following resident birds. Here we report observations of migrant birds foraging at a northern high tropical latitude, high elevation army ant (Labidus praedator) swarm., The extent to which different groups of birds exploit the prey-flushing behavior of army ant (Eciton burchelli or Labidus praedator) swarms in the Neotropics varies with latitude. Bird species that [...]

Northern Arizona winters vary within and between years with occasional heavy snows (up to 0.6 m) and extreme cold (overnight lows -18 to -29 ° C) interspersed with dry periods, [...]

Herbivores, especially specialists, must adapt to characteristics of their host to survive and reproduce successfully (Hardin and Tallamy 1992). If offspring survival among different hosts varies, natural selection should lead [...]

On 28 July 1991 at 08:08 EST at the Archbold Tropical Research Center, Springfield Field Station (15 ° 21[minutes]N, 61 ° 23[minutes]W), Dominica, West Indies, we saw a Gray Flycatcher [...]

Nest predation is the most important factor reducing breeding success of many birds, sometimes by [approximately equal] 50% (Ricklefs 1969, Arcese and Smith 1988, Martin and Roper 1988, McCleery and [...]

ANDREW RISTVEY [1] STEVE REBACH [*] Department of Natural Sciences, University of Maryland Eastern Shore, Princess Anne, Maryland 21853 Abstract. The rock crab, Cancer irroratus Say, uses chemically mediated learning [...]

We examined the responsiveness of adult gray rat snakes to avian prey in enclosures that simulated natural habitat conditions. Subjects searched for arboreal nest contents in the presence or absence of a bird model flown so as to simulate avian provisioning behavior. In the absence of the model, gray rat snake latency to capture prey was over 92 % greater than when searching for nest contents with the model. Snakes responded to model flight by turning their heads in the direction of its movement. We conclude that gray rat snakes perceive relatively distant visual cues from prey, and that nest provisioning (activity localized around a nest) may facilitate snakes correctly choosing to ascend trees that contain active nests and ignoring those that do not., INTRODUCTION Snakes are usually alerted to the presence of their prey by either chemosensory or visual stimuli. In particular, snakes detecting volatile prey chemicals will usually respond with increased tongue-flicking [...]

We observed a Northern Fulmar (Fulmarus glacialis) prey upon a live Common Murre (Uria aalge) off Cape Spear, Newfoundland, Canada on 4 November 2007. Active predation of Northern Fulmars on other seabirds has not previously been reported., Northern Fulmars (Fulmarus glacialis) are widespread throughout the northern Atlantic and Pacific oceans and populations have increased in Atlantic Canada (Stenhouse and Montevecchi 1999). The diet of Northern Fulmars includes [...]

Grey Herons (Ardea cinerea) typically prey upon fish and other aquatic organisms with occasional reports of predating small birds. I report observations of one or more Grey Herons predating on Aldabra White-throated Rails (Dryolimnas cuvieri aldabranus) on Picard Island (Aldabra Atoll, Seychelles). Grey Herons were observed on two occasions having caught rails and, on another occasion, a heron was observed ambushing and pursuing rails with no success. Heron(s) were not observed ingesting the rails, as they flew or ran off with their prey, but it is likely the rails were consumed. These are the first observations of any form of predation on the Aldabra White-throated Rail, which is one of the largest recorded avian prey of the Grey Heron., The Grey Heron (Ardea cinerea), widespread throughout the Seychelles, is one of the few waders that breed on Aldabra Atoll (9° 24' S, 46° 20' E) (Feare and Watson 1984). [...]

Eating is a necessity of animal life. So you might expect that individuals would do everything possible to maximize their food intake. An example, often invoked, is that lions live [...]

An adult Harpy Eagle (Harpia harpyja) attacked and killed an infant collared peccary (Pecari tajacu) at a site in eastern Amazonia. The eagle appeared to have been prevented from removing its prey immediately by surviving members of the peccary herd. Circumstantial evidence suggests that a set of specific factors, including the abundance of peccaries at the site and forest structure, may have facilitated the attack. Received 21 March 2002, accepted 30 August 2002., The world's largest raptor, the Harpy Eagle (Harpia harpyja) is known to prey on a variety of small--to medium-sized Neotropical rainforest mammals. Prey items typically are arboreal, primarily primates (Platyrrhini) [...]

We report predation of a Common Loon (Gavia immer) chick by an adult Bald Eagle (Haliaeetus leucocephalus) in northern Wisconsin., Common Loon (Gavia immer) chicks may be vulnerable to aerial and underwater predators, including Bald Eagle (Haliaeetus leucocephalus), Common Raven (Corvus corax), Herring Gull (Larus argentatus), snapping turtle (Chelydra serpentina), [...]

The Piping Plover (Charadrius melodus) is endemic to North America and breeds locally on the Great Plains, Great Lakes region, and upper Atlantic Coast (Haig 1992). By 1900 this species [...]

A Tephritid Fly Mimics the Territorial Displays of Its Jumping Spider Predators MOST FORMS OF MIMICRY, SUCHas cryptic coloration or Batesian and Mullerian systems, confer protection against a wide array [...]

Most plants (1) and some asexually reproducing invertebrates (2) respond to attack by consumers with production and mobilization of inducible defenses. Inducible defenses are produced only in response to stimuli [...]

We conducted a series of laboratory and field experiments to determine the effects of variation in plant quality and prey species on the survival, dispersal, and population size of a common, omnivorous insect. We also tested the hypothesis that plant feeding allows omnivorous 'predators' to survive periods when prey are scarce. In addition, we compared the response of omnivores and strict predators to variation in plants and prey. We found that variation in plant parts (pods and leaves) and prey species (moth eggs and aphids) affected the survival, dispersal, and population size of big-eyed bugs, Geocoris punctipes, in Maryland lima beans. The survival of big-eyed bugs fed moth eggs was high and unaffected by the availability of lima bean pods or leaves as supplemental food. The survival of big-eyed bugs fed aphids, however, was relatively low and dramatically improved by the availability of pods. Big-eyed bugs fed only pods developed normally through the first and second instar, but development was arrested in the third instar. Only bugs fed high quality prey or mixtures of low quality prey and high quality plant food developed beyond the third instar. Plant feeding, especially pod feeding, allowed big-eyed bug nymphs to survive prey-free periods, but plant feeding was not as important for adult survival when prey were unavailable. The dispersal of adult big-eyed bugs from lima bean plants with pods was significantly lower than the dispersal of big-eyed bugs from plants without pods. The presence of aphids on lima bean plants also reduced the dispersal of big-eyed bugs. Unexpectedly, the presence of moth eggs, high quality prey as measured by big-eyed bug survival in previous experiments, did not reduce the dispersal of big-eyed bugs. Populations of big-eyed bugs were larger in plots of beans with pods than in plots of pod-free beans. Furthermore, the most important predictor of the density of big-eyed bugs was the number of pods per plant. Populations of other omnivorous insects (minute pirate bugs, damsel bugs, and ladybird beetles) were also larger in plots of beans with pods than in plots of pod-free beans. However, other omnivores responded to changes in the numbers of flowers per plant and not to changes in the number of pods per plant or potential prey. Conversely, the most important predictor of the density of strict, non-plant-feeding predators was the density of potential prey (herbivores). Our results indicate that omnivory provides ecological flexibility for big-eyed bugs. Feeding at more than one trophic level furnishes big-eyed bugs with complimentary resources that allow these omnivores to survive when resources at one trophic level are of low quality (e.g., aphids) or when resources at one trophic level are totally unavailable (e.g., prey). Furthermore, the dynamics of omnivorous insects such as big-eyed bugs are intimately associated with variation in their host plants and not with changes in the density of their prey. Omnivorous insects appear to track resources at the lowest trophic level at which they feed, in this case plants, and not resources farther up the food chain (e.g., prey). Key words: Acyrthosiphum pisum; big-eyed bugs; corn earworm; Geocoris punctipes; Helicoverpa zea; lima beans; omnivory; pea aphids; Phaseolus lunatus; plant quality; population persistence; prey quality., INTRODUCTION There is a growing awareness among ecologists that trophic interactions involving omnivores, animals that feed at more than one trophic level, are more prevalent in nature than previously supposed [...]

Inducible defenses are found in both terrestrial and aquatic organisms and appear to be a common defensive strategy of both sessile and mobile species. Here we report the presence of previously undescribed inducible defenses in marine mussels, a dominant member of temperate rocky intertidal communities. In the Gulf of Maine, estuarine shorelines with low water flow are characterized by high crab predation on the common blue mussel, Mytilus edulis, compared to nearby shorelines with high water flow. Mussels at these high predation sites had thicker shells, relatively more shell mass, and were more tightly attached to the substrate than mussels at low predation sites. Field and laboratory experiments were used to test whether the between-site differences in these traits were the result of phenotypic plasticity. Mussels outplanted to high predation sites produced more byssal threads and attached more firmly to the substrate than did mussels outplanted to low predation sites. In the laboratory, thicker shells were induced by waterborne cues from both the common predator, Carcinus maenus, and damaged conspecifics, and these thicker shells were mechanically stronger than thinner, noninduced ones. Our results contribute to growing evidence that inducible defenses are a pervasive feature of intertidal assemblages. In addition to the bivalve example presented here, gastropods, barnacles, bryozoans, and seaweeds are also known to have inducible defenses. Phenotypic plasticity for defensive traits has likely evolved repeatedly in intertidal organisms and appears to play a major role in the dynamics of rocky intertidal communities. Key words: Carcinus maenus; hydrodynamics; inducible defense; Mytilus edulis; phenotypic plasticity; predation; predator-prey interactions; rocky intertidal zone; waterborne cues., INTRODUCTION Inducible defenses (phenotypically plastic traits that increase resistance to predators or competitors) are known in many organisms from both aquatic and terrestrial habitats (e.g., protozoans (Wicklow 1988), bryozoans (Harvell [...]

Why do so many aquatic organisms, including zooplankton, undertake vertical migrations of tens to hundreds of meters between deep, darker waters during the day and surface waters at night? The [...]

On the Advantage of Being Different BIRDS have long been the subject of study among ecologists, specifically relating to the factors that influence how communities are assembled. And within this [...]