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Sexual dimorphism and age-related differences are sources that contribute to morphologic and physiologic variation within animal populations. Measurement of animal performance may indicate whether this variation is functionally relevant. Our study aimed to experimentally test this statement in a captive population of House Sparrows (Passer domesticus (L., 1758)) by examining age- and sex-related differences in escape response and its relationship to several morphological (tarsus, wing, tail lengths, and body mass) and physiological traits (cell-mediated immunity, natural antibodies, complement activity, hematocrit, and stress response). Escape response from a predator is considered a good variable to measure animal performance, because natural selection clearly favours individuals that avoid predators successfully. Our experimental design also aimed to standardize possible confounding factors affecting escape behaviour under natural conditions. We exposed sparrows to short episodes of high predation risk by simulating the attack of a predator and assumed that the capture order of individuals was related to their escape capacity. The optimal strategy was the immediate escape response for all individuals. We found that first-year males were the best escapers. In support of the hypothesis, juvenile males gathered a better optimum of several morphological and physiological characters that related to capture order. Le dimorphisme sexuel et les differences reliees a l'age sont des sources qui contribuent a la variation morphologique et physiologique au sein des populations animales. La mesure de la performance animale peut indiquer si cette variation est fonctionnellement pertinente. Notre etude vise a teste experimentalement cet enoncee dans une population en captivite de moineaux domestiques (Passer domesticus (L., 1758)) en examinant les differences sexuelles et reliees a l'age dans la reaction de fuite et ses relations a plusieurs traits morphologiques (longueurs du tarse, de l'aile et de la queue, masse corporelle) et physiologiques (immunite cellulaire, anticorps naturels, activite du systeme complementaire, heematocrite, reponse au stress). La reaction de fuite en presence d'un predateur est consideree comme un bonne variable pour mesurer la performance animale, parce que la selection naturelle favorise nettement les individus qui reussissent a eeviter leurs predateurs. Notre plan d'experience cherche aussi a standardiser les facteurs confondants qui affectent le comportement de fuite dans les conditions naturelles. Nous avons expose des moineaux a de courts episodes de risque eleve; de predation en simulant l'attaque d'un predateur et avons presume que l'ordre de capture des individus est relie a leur capacite; de fuite. La strategie optimale chez tous les individus etait la reaction immediate de fuite. Ce sont les males dans leur premiere annee qui fuient avec le plus de succes. Les jeunes males possedent aussi de facon optimale un meilleur ensemble de plusieurs caracte;ristiques morphologiques et physiologiques relieees a l'ordre de capture, ce qui appuie l'hypothese. [Traduit par la Redaction], Introduction Because natural selection favours individuals that avoid predators successfully, predation is considered one of the most important selection pressures in shaping prey behaviour. In fact, numerous studies demonstrated that [...]

Abstract--Knowing where pinnipeds forage is vital to managing and protecting their populations, and for assessing potential interactions with fisheries. We assessed the spatial relationship between the seasonal distribution of Pacific [...]

Nest defense represents a parental strategy to maximize fitness by enhancing prospects of offspring survival. We used a taxidermic mount of a nest predator to measure nest defense of Eastern Kingbirds (Tyrannus tyrannus) at Malheur National Wildlife Refuge in southeastern Oregon in 2003 and 2004 to test the hypotheses that intensity of nest defense (1) was individually repeatable, (2) differed between males and females, and (3) predicted nest success. We also predicted that (4) intensity of defense would increase with age and number of young, but decline over the breeding season. Intensity of nest defense was significantly repeatable for male kingbirds. Male response was twice as strong as female response during incubation and the nestling period, but nest success was independent of defense scores of males and females. Simple paired comparisons suggested female responses did not change between incubation and the nestling period, whereas males tended to defend nestlings more vigorously than eggs. Multivariate analyses demonstrated strong individual differences were the main source of variation in nest defense. Intensity of nest defense by males and females increased with age of young, declined seasonally, but was not related to number of young. Kingbird nest defense is a repeatable behavior that differs between males and females and, as predicted by parental investment theory, nests of the greatest value (older young and earlier broods) were defended most aggressively., Parental defense of young is a fundamental aspect of behavior common to most vertebrates (Clutton-Brock 1991); attempts to explain why intensity of defense varies both among and within species have [...]

Abstract: Many antipredator behaviors are mediated by the ability of prey to recognize chemical cues from predators. Adult amphibians mainly use vision to detect predators, but the ability to detect [...]

Theoretical ecology is largely founded on the principle of mass action, in which uncoordinated populations of predators and prey move in a random and well-mixed fashion across a featureless landscape. [...]

ABSTRACT. On Ellesmere Island in 2006, arctic wolves (Canis lupus arctos) were observed making a two-pronged approach to a herd of muskoxen (Ovibos moschatus) and, on another occasion, ambushing muskoxen. [...]

Abstract: Purple sea urchins (Strongylocentrotus purpuratus (Stimpson, 1857)) are abundant grazing invertebrates that can have a major impact on the rocky intertidal community. Predators can control the urchin population and [...]

Abstract: Time activity budgets in the family Anatidae are available for the wintering and breeding periods. We present the first flyway-level study of foraging time in a long-distance migrant, the [...]

ABSTRACT. We report on the interspecific killing of an arctic fox (Alopex lagopus) by a red fox (Vulpes vulpes) in the Prudhoe Bay Oilfield, Alaska, an event that was captured [...]

Abstract: The risk-disturbance hypothesis proposes that organisms respond to generalized threat stimuli; therefore, human disturbances that elicit these behaviours will cause individuals to behave similarly to avoid a natural predator. [...]

Abstract: If there are differences in predation risk among the offspring within a clutch, parents should allocate less resources to the offspring facing higher risk. Predation risk, and thus offspring [...]

Abstract: We modeled the impact of puma (Puma concolor (L., 1771)) predation on the decline and recovery of mule deer (Odocoileus hemionus (Rafinesque, 1817)) in southern Idaho based on estimates [...]

ABSTRACT We studied the effectiveness of acoustic deterrents in limiting predation on Louisiana oyster leases by black drum Pogonias cromis. Three acoustic deterrents were used: (1) natural or synthesized alarm [...]

Abstract: Arthropods in several orders use traps to capture prey. Such trap-building predators expend most of their foraging energy prior to any prey contact. Nevertheless, relative investments in trap construction [...]

Abstract: Headfirst ingestion of prey is a common adaptive behavioral trait in gape-limited predators that swallow large prey whole. To ascertain this tendency during anurophagy, prey handling and direction of [...]

Abstract: Animals may compensate for increased predation risk by changing the behaviours that make them vulnerable. In this study, we compared the singing and perching behaviours of northern cardinals (Cardinalis [...]

Abstract: Water molds are widespread in aquatic environments and are important causes of mortality in amphibian and fish eggs. We tested the ability of two species of North American anurans [...]

Abstract: Approach distance (flight initiation distance) and escape methods depend on predation risk. I studied escape methods and effects of risk factors (temperature, perch height and orientation, conspicuousness) on approach [...]

INTRODUCTION The genus Gladicosa was erected in 1986 by Allen Brady to encompass 5 nearctic species of medium to large wolf spiders based upon similarity of genitalic characters and dorsal [...]

Abstract: We assessed the role of habitat structure in the outcome of predation by measuring how aquatic vegetation influences predation rates of water bugs (Belostoma oxyurum (Dufour, 1863), Hemiptera, Belostomatidae) [...]

In 1999, we compared foraging success rates (captures/rain) and foraging behaviors of Wood Storks (Mycteria americana) at tidal (Georgia) and non-tidal freshwater (South Carolina) foraging sites. Foraging success rates were 30 times greater at the tidal site, but storks foraging in tidal areas only fed at low tide, which limited their foraging time at that site. On-site behaviors indicated the window of prey availability. Storks at the tidal site engaged almost exclusively in foraging behaviors, whereas storks at the non-tidal site devoted more time to other, non-foraging behaviors (e.g., preening, resting). The greater foraging success rate associated with the tidal site suggests that salt marsh/tidal creek habitats are high-quality foraging areas. Received 21 December 2004, accepted 6 September 2005., Wading birds use a diversity of behaviors to acquire prey. Wood Storks (Mycteria americana) feed mostly by tactilocation, literally bumping into their prey with partially open bills and capturing prey [...]

ABSTRACT The prey and size-class preferences of four marine epibenthic predators was examined in a laboratory study by determining the mortality rates of four commercial bivalve species in 4-d trials [...]

ABSTRACT.--We document the first cases of cattle behaving as avian predators, removing nestlings and eggs from three active ground nests in continuously grazed pastures in southwestern Wisconsin, 2000-2001. Cows removed [...]

The influence of predation risk on microhabitat selection in male adult deer mice (Peromyscus maniculatus) was examined using an enclosure experiment. The relative amount of time spent by the deer mice on coniferous leaf litter, hardwood leaf litter and logs was measured. Mice preferred dry coniferous litter over dry hardwood litter, but had no preference when both litter types were wet. Deer mice traveled more along logs placed on hardwood litter than on coniferous litter. Nocturnal mammalian and avian predators of deer mice often use sound to locate their prey, and mice rustling in hardwood leaf litter should be more easily detected. Therefore, deer mice restrict their movements to routes that reduce the risk of auditory detection by predators., INTRODUCTION Some animals assess the risk of predation under different circumstances and incorporate this information into their behavioral decisions (Lima and Dill, 1990). On bright nights, nocturnal small mammals restrict [...]

The chicks of the Wattled Jacana (Jacana jacana) exhibited an unusual predator escape behavior in the floodplains of Venezuela. When approached by a human, chicks dove and remained completely immobile while entirely submerged with just the beak protruding vertically above the water line. Since breathing should continue while hiding, we reasoned that it would be advantageous for the bird to have the nostrils placed in a forward position along the bill to facilitate breathing while submerged. To examine this expectation we compared the relative position of the nostrils of the Wattled Jacana with those of species belonging to phylogenetically related Scolopacidae. In accordance with expectations, Wattled Jacanas have nostrils that are placed significantly more forward along the bill than all species of Scolopacidae measured. Nostril placement in species belonging to other phylogenetically related families, Thinocoridae, Pedionomidae, and Rostratulide is also basal as in Scolopacidae. Forward placement of nostrils seems to be a derived character in jacanas. The 'snorkeling' behavior of Wattled Jacana chicks is a behaviorally elaborate predator escape mechanism, seemingly accompanied by anatomical adaptations., Predation is often the major mortality factor of young birds and is therefore an important selective force shaping the behavior of young birds and their parents (Rickleffs 1969, Martin 1992). [...]

After photographic observations in the field and laboratory tests indicated that small rodents might be significant predators on small eggs, we conducted a field study in central Massachusetts to compare predation of House Sparrow (Passer domesticus) eggs in artificial nests near to (5-15 m) and far from (100-120 m) forest edges and between ground and shrub nests. As in earlier studies in managed northeastern forest landscapes that used larger quail eggs, predation rates on small eggs in nests at the forest edge did not differ (P > 0.05) from those in the forest interior for either ground nests (edge = 0.80 vs interior = 0.90) or shrub nests (edge = 0.38 vs interior = 0.28) after 12 days of exposure. However, predation rates on eggs in ground nests were significantly higher (P < 0.001) than in shrub nests at both the edge and interior. There were no significant (P > 0.05) differences in the frequency of capture of the 6 most common small mammal species between forest edge and interior. Logistic regression analyses indicated a highly significant (P < 0.001) nest placement effect but very little location or small mammal effect. Predation of small eggs by small-mouthed ground predators such as white-footed mice (Peromyscus leucopus) has not been documented as a major factor in egg predation studies, but use of appropriately-sized eggs and quantification of predator species presence and abundance seems essential to future studies., Previously published evidence for elevated nest predation rates at forest edges in the northeastern U.S. is not consistent. For example, in Maine, predation rates were higher for artificial nests placed [...]

A 4.5 kg/mol peptide released by an amoeban predator, Amoeba proteus, induced defensive behavioral changes in ciliates of the genus Euplotes. The interspecific signaling molecule named 'A-factor' was present in amoebae culture medium at a concentration of 0.01 [µgram] peptide/L, corresponding to 2 x [10.sup.-12] mol/L. Amoebae released [approximately]3 x [10.sup.5] molecules of A-factor per individual per hour. Prey ciliates added to solutions containing A-factor exhibited predator-avoidance behavior after a few hours. The discovery of a second function for this peptide-kairomone indicated why the predator betrays its presence to the prey and thereby unintentionally protects it. Inhibition of phagocytosis by particle-bound kairomone revealed that it also functions as a self-recognition signal in the predator. Phagocytosis of particles by amoebae depended on the amount of A-factor on the particle surface and decreased in linear correlation to the logarithm of peptide amount. Self-recognition prevents a mutual consumption of amoebae, leading to increased survival of these asexually reproducing organisms. The importance of self-recognition apparently outweighs the disadvantages of defense induction, since only few prey species of the omnivorous predator respond in this manner. Key words: behavioral changes; chemical ecology; chemical induction; defense; kairomone; phenotypic plasticity; predation; Protozoa; self recognition., INTRODUCTION Development of inducible defenses allows many prey organisms to reduce costs, or to respond more specifically to various size-selective predators (Dodson 1984, Riessen 1984, Lively 1986a, Havel and Dodson [...]

In this paper I seek an explanation for the low level of seed predation recorded for many plant species adapted for ant dispersal by examining the mechanical defense properties of seeds. Mechanical defense of 115 plant species, in the form of seed strength, was measured using two techniques, a Universal Force Tester and pressure applied with forceps. Most species tested had relatively strong seeds (>20 N), though a significant minority had relatively weak seeds. Preliminary findings of contrasts across independent phylogenetic divergences suggest there was no consistent tendency for seed strength to be greater in species adapted for ant dispersal compared to their relatives that are not. In seed removal assays performed in the field, weaker seeds were more likely to be removed than stronger seeds, whether elaiosomes were present or not. Weaker seeds were also more likely to be eaten than stronger seeds. In laboratory seed predation assays, strong seeds were rarely eaten by two common seed-removing ant species (Rhytidoponera metallica and Pheidole sp. 4). In contrast, species with relatively weak seeds experienced much higher levels of seed predation, up to 100%. In conclusion, the majority of species adapted for ant dispersal produce relatively strong seeds, and this may explain the low level of predation recorded for these species. Key words: mechanical defense; Pheidole sp. 4; predation, of seeds; Rhytidoponera metallica; seed dispersal by ants; seed removal: seed strength., INTRODUCTION Seeds are one of the most vulnerable stages in the life cycle of a plant. Predators can inflict heavy losses on a seed crop (Janzen 1971, Crawley 1992); therefore, [...]

Predatory behaviors of bobcats (Lynx rufus) that preyed on 39 radio-instrumented white-tailed deer (Odocoileus virginanus) in the Everglades during a 3-yr study, 1 April 1989-31 March 1992, are described and compared with those of other felids. Bobcats killed 33 fawns and six adults by administering ≥ one bite to the neck and throat region. The maximum prey:predator weight ratio was 8:1. Twelve (31%) of 39 kills were dragged 2-10 m to concealment cover before being eaten. Twelve (71%) of 17 carcasses that were not dragged from the kill site exhibited a characteristic death form in that the head on each was twisted backwards (throat dorsal) and positioned diagonally under the shoulder. Feeding was initiated on large muscle masses, predominantly on the hindquarters. Bobcats eviscerated 29 (83%) of 35 carcasses, severed ≥ one fore- or hind-limbs from 18 (55%) of 33 kills, and plucked hair from 13 (33%) of 39 carcasses. Bobcats partially or completely covered 17 (52%) of 33 carcasses with plant litter. Thus, bobcats preying on deer in the Everglades displayed notable differences in eviscerating, feeding, and covering behaviors., INTRODUCTION Throughout their range, bobcats (Lynx rufus) prey on small to medium-sized species, principally rodents and lagomorphs (Fritts and Sealander, 1978; Kitchings and Story, 1979; Fox and Fox, 1982; Litvaitis [...]

Predation often has important effects on prey populations and evolution of prey traits (Sih et al. 1985; Sih 1987; Vermeij 1987; Lima and Dill 1990). Recent reviews suggest that for [...]

Theoretical models for the evolution of inducible anti-predator defenses predict that there should be fitness costs associated with the defense, otherwise it should be permanent. Thus, in the absence of predators and with limited resources, defended individuals are expected to be outcompeted by individuals lacking the costly defense. Crucian carp, Carassius carassius, increase in body depth in response to chemical stimuli from piscivorous fish, and the deeper body constitutes a morphological defense against gape-limited piscivores. Here, we have performed a field experiment investigating effects of population density on the relative competitive performance of shallow-bodied and deep-bodied crucian carp. We assigned groups of six individually marked fish (the 'focal' individuals) of either morph into enclosures with either low or high crucian carp density, and monitored changes in body mass, length, and body depth of these fish for 4 mo. In addition, we determined sex, and final liver and gonadal mass, of all focal fish. At high population density, there was a reduction in food resources (zooplankters), which resulted in reduced gonad mass, reduced gonadosomatic indices, and reduced growth in fish of both morphs. Unexpectedly, the relative allocation to livers was higher at high density. There was no difference in body mass gain between morphs at the low density, whereas at the high density shallow-bodied fish gained twice as much body mass as deep-bodied fish. Hence, when predators were absent and food resources were limited, deep-bodied individuals suffered a substantial cost when competing with shallow-bodied conspecifics. This study verifies the theoretical prediction that an inducible defense results in fitness costs in the absence of predators. Further, as we found no measurable disadvantage of the deep-bodied morphology at high food availability but a strong disadvantage under intense competition for food, our results also demonstrate the importance of relating defense costs to levels of intraspecific competition. Key words: antipredator; body size; Carassius carassius; competition; cost; density dependence; field-enclosure experiment; fish; inducible defense; phenotypic plasticity; resource allocation; Sweden., INTRODUCTION Predation is an important selective force in most habitats. Through direct, lethal effects, predators may have profound effects on abundance and size structure of prey populations and on species [...]

We examined ways in which American Crows (Corvus brachyrhynchos) foraging in an urban environment balance the conflicting demands of finding food and avoiding predators. As individual vigilance (i.e., scanning) decreased, time devoted to foraging increased. Significant predictors of vigilance varied with location and included time of day, temperature, food availability, distance to nearest source of disturbance, cover distance, and size of foraging group. Group size and, secondarily, distance from cover accounted for most of the variability in vigilance. Crows were more vigilant in areas of high human disturbance than in areas of low human disturbance., Vigilance (used interchangeably with scanning) and foraging are mutually exclusive behaviors - a bird cannot simultaneously scan its environment for predators while feeding. Those individuals that successfully balance the tradeoffs [...]

We quantified predation on artificial nests in Iowa roadsides and examined the relationships between nest predation and characteristics of roadsides. Transects consisting of 10 nests (five in the foreslope and five the in backslope) were set up in 136 roadsides in six watersheds in south-central Iowa. Most roadsides had herbaceous vegetation with fences (67%); fewer were wooded (18%) or had herbaceous vegetation without fences (15%). Most roads were gravel (80%), and most roadsides were adjacent to row crops (63%). Average total nest predation per transect was 23% (SE = 2), ranging from 0 to 100%. Nest predation was categorized into one of three outcomes: disappearance of eggs without disturbance to the nest bowl (39%), disappearance of eggs with disturbance to the nest bowl (17%), and broken or crushed egg shell fragments in or near the nest bowl (44%). Wooded roadsides and herbaceous roadsides with fences had significantly greater nest predation than herbaceous roadsides without fences for disappearance of eggs without disturbance to the nest bowl. Backslopes had significantly greater nest predation than foreslopes for all outcome categories except the disappearance of eggs with disturbance to the nest bowl. Wooded roadsides and herbaceous roadsides with fences along the backslope may provide cover and travel corridors for mammalian predators or elevated perches for avian predators., Nest predation is an important cause of mortality for many bird species (Ricklefs 1969, Martin 1988), especially in grassland ecosystems where predators have responded positively to human disturbance and landscape [...]

It has been hypothesized that foraging tactics and ability of Bald Eagles (Haliaeetus leucocephalus) are influenced by age, phenotype, and prey availability. We studied the influence of eagle age class and prey availability of kokanee salmon (Oncorhynchus nerka) on foraging behavior of Bald Eagles during autumns of 1983 and 1984 at Glacier National Park, Montana. The relative use of foraging tactics differed among four age classes of eagles during both years. Stooping was the most successful tactic and was most frequently used by older birds. The relative use of stooping increased with age and the use of ground piracy tended to decrease with age. The relative use of different foraging tactics also reflected changing prey availability. During 1983, when lower numbers of salmon precluded accumulation of carcasses, eagles rarely used ground tactics (i.e., scavenging and ground piracy). In 1984, when salmon carcasses accumulated in large numbers, all age classes used ground tactics, which became the predominant foraging method of younger eagles. Our results support the hypotheses that the ability to obtain food increases with age and that eagles forage by methods for which their age class is most suited based on morphology (e.g., size and wing loading) and experience., During the autumns of 1983 and 1984 we assessed the influences of age and prey availability on foraging methods and prey capture success of Bald Eagles in Glacier National Park [...]

I present a model which at the same time evaluates optimal diel vertical migration (DVM) and optimal allocation patterns to growth or reproduction in the cladoceran Daphnia magna. The combined policies that maximize the intrinsic rate of increase r are found using the Perron Frobenius Theorem and dynamic programming. The model attempts to incorporate two traditions in aquatic behavioral ecology within the same model framework: variations in vertical migrations (short time behavior) and age or size at maturity (life history models). The predictions from the model are compared with observations from an experiment in thermally stratified flow-through tubes containing various concentrations of fish exudates. The model is able to reproduce many of the observations of both DVM and allocation, though there are some interesting deviations. I look at theoretical behavior and life history consequences of various size dependencies in mortality. Finally, I do a comparative analysis of two fitness measures, the intrinsic rate of increase r, and the net lifetime reproduction, [R.sub.0], where it turns out that the use of r makes predictions in better agreement with the observations. Key words: Daphnia magna; diel vertical migration; dynamic programming; fitness; intermediate allocation; life history; optimal behavior; population dynamics., INTRODUCTION The diel vertical migrations (DVM)and life histories (like age or size at maturity) of many marine and freshwater organisms have been shown to depend on the density and type [...]

Many of the venomous New World coral snakes (Micrurus and Micruroides) have a distinctive pattern of red, black, and yellow rings (Campbell and Lamar 1989; Savage and Slowinski 1992), which [...]

This investigation examines the role of trait-mediated indirect interactions in a simple aquatic food web. We conducted the experiments in cattle watering tanks in order to establish whether competitive and predator-prey interactions between two species are affected by other species in the system; i.e., are pairwise interaction strengths affected by the background species assemblage? We examined the survival and growth response of small bullfrog (Rana catesbeiana) and small green frog (Rana clamitans) tadpoles in the presence and absence of a competitor (large bullfrogs), the lethal presence of the larval odonate predator Tramea lacerata, and the nonlethal (caged) presence of the larval odonate predators Anax junius and Anax longipes. We demonstrate that large bullfrog competitors and caged Anax affect traits (foraging activity level) of small bullfrog and small green frog tadpoles and that these changes in traits, in turn, affect interactions of the small tadpole species with each other and with the other species. In particular, the following four trait-mediated indirect interactions were evident: (1) Presence of large bullfrog competitors increased the predation rate of Tramea on small green frogs and small bullfrogs. (2) Presence of nonlethal Anax reduced the predation rate of Tramea on small green frogs. (3) Presence of nonlethal Anax increased the competitive advantage of bullfrogs over green frogs. (4) Presence of nonlethal Anax facilitated midge invasion of the experimental units. The proposed mechanisms (changes in small tadpole activity) involved in these trait-mediated indirect interactions were supported by observational data on tadpole activity and resource levels in the experimental units, and in laboratory experiments examining tadpole activity responses to predators. The occurrence of strong trait-mediated indirect interactions in this simple food web underscores the potential importance of such interactions in animal communities. Key words: Anax; anuran larvae; behavioral induction; Chironomus; higher order interactions; odonate predator; predation risk; Rana; trait-mediated indirect interaction; Tramea., INTRODUCTION It has long been recognized that species in ecological communities interact indirectly with other species through the food web (for reviews see Schoener 1993, Menge 1994, Wootton 1994a). These [...]

The acanthocephalan parasite Pomphorhynchus laevis is transmitted by crustaceans such as Gammarus pulex to its paratenic or final hosts, fish. The conspicuous orange-yellow parasite is visible through the transparent cuticle of G. pulex. Infected gammarids are significantly less photophobic than uninfected ones. When hungry three-spined sticklebacks (Gasterosteus aculeatus), one of the hosts of this parasite, were offered equal numbers of uninfected and infected prey, G. pulex infected with P. laevis were eaten significantly more often. We tested experimentally whether parasite color and parasite-induced changes in host behavior affected the predation rate of G. pulex. Color effects were tested with uninfected G. pulex by painting an orange spot on their cuticle that simulated infection. Behavioral effects were tested with infected G. pulex by covering the place through which the orange parasite was visible with inconspicuous brown paint. We showed for the first time that both parasite color and changed intermediate host behavior promote the transmission of P. laevis to its next host. The evolution of orange parasite color, and why sticklebacks do not avoid infected prey, are discussed. Key words: behavioral changes; coloration; Gammarus pulex; Gasterosteus aculeatus; intermediate host; parasite transmission; Pomphorhynchus laevis; predation risk., INTRODUCTION Parasites with a complex life cycle involving several hosts are faced with problems of transmission from one host to the next. There is a wealth of solutions to this [...]

A 5-yr field study examined the ways in which prey abundance can influence the reproductive rates of predators. Water pythons (Liasis fuscus) on the Adelaide River floodplain in tropical Australia prey almost exclusively on dusky rats (Rattus colletti). Rat numbers varied dramatically among years of the study. Feeding rates of pythons were highest when rats were abundant, and the snakes were in good condition (mass relative to body length) at these times. The proportion of adult female pythons that reproduced in a given year was also tightly linked to rat abundances. However, reproductive output per litter (offspring size, and fecundity relative to maternal body size) was unaffected by prey availability, perhaps because of high fecundity-independent costs of reproduction. Instead, female pythons reproducing in 'good' years were in better condition after oviposition. These data support an energy-limitation model for snake reproduction, whereby prey availability determines predator reproductive output, but the relationship between the two variables is complex. The degree to which prey availability influences feeding rates of pythons and the degree to which feeding rates influence body condition depend crucially on snake body size (due to size-related shifts in foraging abilities and metabolic costs). Thus, a given prey abundance translates into different energy reserves for different-sized predators. Also, females delay reproduction until they can gain enough energy for a large clutch of eggs, and reproductive output per litter does not then increase with additional energy availability. Such nonlinearities in predator responses to prey availability may be widespread. Key words: costs of reproduction; energy limitation; Liasis fuscus; predation; Rattus colletti; reptile; Pythonidae; snake., INTRODUCTION Rates of reproduction vary enormously from time to time and from place to place. Even within a single population, females may vary considerably in the number and size of [...]

Identification of nest predators is critical for mitigation of nest predation. We critically examined the traditional belief that predators can be identified solely by the appearance and disposition of nest remains. During 2668 h of radio-tracking striped skunks (Mephitis mephitis), we observed depredation of 34 waterfowl nests. Natural (n = 18) and simulated (n = 16) waterfowl nests were partially depredated in 61% and 69% of initial encounters, respectively. Within a 24-h period, skunks returned to six of 21 partially depredated nests. Moreover, >30% of simulated nests discovered by skunks during our observations had been previously depredated. We conclude that variable patterns and temporal dynamics in the appearance of depredated nests preclude researchers from identifying predators solely on the basis of nest remains., INTRODUCTION Nest predation is the most important factor affecting the populations of many passerine (Ricklefs, 1969; Wilcove, 1985) and waterfowl species (Klett et al., 1988). Identification of nest predators is [...]

Noncyclic populations of microtine rodents may be limited within a relatively constant range of densities by generalist predators with a prey base sufficiently diverse to sustain them when rodents are scarce (generalist predator hypothesis). Collared lemmings (Dicrostonyx kilangmiutak) at Pearce Point, Northwest Territories, Canada, are noncyclic and limited to fairly constant low densities in summer by predation, principally by red fox and Rough-legged Hawks. We tested four predictions of the generalist predator hypothesis as a possible explanation for relatively constant lemming densities: (1) predators do not show strong numerical responses to lemming density; (2) the proportion of lemming biomass in predator diets declines with declining lemming abundance, compensated for by increased consumption of alternative prey; (3) predators show a type-III functional response to lemming density; and (4) at low densities, predation on lemmings ceases. The first prediction was not satisfied by the principal predators: at very low lemming densities, Rough-legged Hawks did not settle, and breeding success of red foxes and hawks was limited by lemming abundance. However, a number of generalist predators (Golden Eagle, grizzly bear, arctic ground squirrel, Peregrine Falcon, and Gyrfalcon) did not respond numerically to the lowest lemming densities. The second prediction was partly supported: all predators consumed lemmings at a lower rate as lemming densities declined. However, Rough-legged Hawks were not able to compensate fully for the declining consumption by increasing their use of alternative prey, and red foxes were able to do so in one of three years. Regarding the third prediction, foxes showed some evidence of a type-III functional response but hawks did not. As for the fourth prediction, most predators still consumed lemmings at very low densities; lemmings lacked a secure refuge. The Pearce Point system differs from those where microtine dynamics are relatively constant and nonirruptive because of persistent predation by generalists. In terms of biomass, lemmings are the principal prey for their dominant predators. These predators (the semigeneralist red fox and the specialist Rough-legged Hawk) rely on lemmings to breed, but drive them to densities too low to sustain breeding by these same predators in the subsequent spring. In this regard, the system is similar to one driven by specialists. In some winters, however, populations recover because lemmings breed under the snow and most summer predators are absent. As a result, lemming densities in spring are often high enough for specialists and semigeneralists to initiate breeding. When winter breeding and survival fail to allow population growth, hawks and foxes may fail to breed and then leave the system. Even so, summer generalists still persist and continue to consume lemmings, curtailing potential irruptive growth. In this regard, the system is similar to one where prey are relatively constant because of generalists. Community dynamics at Pearce Point can best be understood as a combination of three dominant processes. Summer predation by specialists and semigeneralists results in destabilizing declines. Winter breeding, coupled with good survival, can lead to destabilizing growth. However, this growth is curtailed in the following summer by either destabilizing specialist predation or the stabilizing influence of generalist predation. When lemmings are scarce, the semigeneralist red fox and some generalist predators rely on arctic ground squirrels as their primary prey or their principal alternative prey. The ground squirrel appears to be the critical species maintaining this relatively diverse arctic tundra predator community and the relatively constant lemming densities., Keywords: arctic ground squirrel; collared lemming; Dicrostonyx kilangmiutak; generalist predator; predator diets; prey refuge; red fox; Rough-legged Hawk; semigeneralist predator; specialist predator. INTRODUCTION Many microtine rodent populations do not exhibit [...]

Three experiments were conducted on antipredator behaviors of newly metamorphosed green frogs (Rana clamitans) and northern leopard frogs (R. pilpiens) in the presence of a common predator, the eastern garter snake (Thamnophis s. sirtalis). Both species engaged in distinctive antipredator behaviors, i.e., crouching and ceasing to move, in the presence of active snakes. These behaviors rendered frogs less likely to be captured. Green frogs were contacted by snakes more frequently than were leopard frogs, but capture rates of individuals that had been contacted were not different between species. Green frogs allowed snakes to approach more closely, and they jumped more frequently upon initial escape, than leopard frogs. Morphological measurements showed that there were no specific differences in snout-vent length, or in snout-vent length/leg length ratios, but that the average leap distance was greater for leopard frogs compared to green frogs. The results supported the hypothesis that leopard frogs use distance from the predator in terrestrial habitats more effectively than do green frogs to avoid predation, which agreed generally with some descriptive field results reported elsewhere., INTRODUCTION Anurans possess a variety of physical, chemical and behavioral defenses against predators. Cryptic coloration and behaviors and toxic skin secretions are evident in toads (Bufonidae: Hayes 1989; Heinen 1994a, [...]

Predation risk influences differentially the foraging decisions of rodent species with different morphologies (body size and locomotion type). Explanations for different foraging patterns have been derived largely from the behavior of heteromyid rodents, and there is a lack of information regarding the behavior of other rodent groups with different morphologies. Nevertheless, the explanations are thought to be applicable to other groups. In order to study the generality of hypotheses about the effect of morphology on foraging ecology, I investigated the foraging decisions of Chilean sigmodontine rodents (Muridae) in the laboratory, experimentally manipulating nocturnal illumination (a surrogate of predation risk) and food distribution. Three coexisting rodent species from the Chilean matorral were compared: two quadrupeds, one with large body size (Phyllotis darwini) and another with small body size (Abrothrix olivaceus), and one small species with bipedal escape behavior (Oligoryzomys longicaudatus). The species did not differ in patch utilization and food consumption in response to different food distributions. However, there was an overall significant effect of illumination on food consumption. When illumination was higher, A. olivaceus and P. darwin; increased food transportation to the refuge and decreased patch consumption and total food consumption. They also increased significantly the number of trips between food patch and refuge. P. darwini showed the most cautious foraging behavior. O. longicaudatus was insensitive to different conditions of illumination. It is argued that a large body size and quadrupedal locomotion seem to confer higher sensitivity to nocturnal illumination. Bipedality may confer less vulnerability to predation, and quadrupedal species show facultative central-place foraging, diminishing a possible greater vulnerability to potential risk. Former explanations for different foraging behaviors under the risk of predation may not be as general as previously assumed. This study emphasizes the need to consider the particular features of the system under investigation. Key words: bipedal locomotion; body size; central-place foraging; Chilean matorral; locomotion; patch utilization; predation risk; quadrupedal; sigmodontine rodents., INTRODUCTION Foraging behavior and habitat selection are multivariate phenomena that are influenced by intrinsic characteristics of the consumers as well as extrinsic factors of the environment. The foraging ecology and [...]

Predatory behavior of captive prairie rattlesnakes (Crotalus viridis) was observed when artificial rock burrows were and were not present in terraria. Euthanized mice were suspended from tongs in front of the snakes, each of which immediately struck and released these prey. The rodent was placed 30-35 cm from the snake. We measured latency to retrieve the envenomated carcass and to swallow the carcass once it was retrieved. Retrieval was faster in snakes living in terraria containing cover than in snakes without cover. Swallowing time did not differ between the conditions. Burrows were used not only as refugia during inactive periods, but also as centers of activity during predatory episodes., Zoo herpetologists commonly include cover in the cages of snakes, particularly those taxa considered to be nervous and prone to exhibiting defensive behaviors (e.g., various elapids; Kauffeld, 1969; Radcliffe & [...]

Parasites that are transmitted from prey to predator are often associated with altered prey behavior. Although many concur that behavior modification is a parasite strategy that facilitates transmission by making parasitized prey easier for predators to capture, there is little evidence from field experiments. We observed that conspicuous behaviors exhibited by killifish (Fundulus parvipinnis) were associated with parasitism by larval trematodes. A field experiment indicated that parasitized fish were substantially more susceptible to predation by final host birds. These results support the behavior-modification hypothesis and emphasize the importance of parasites for predator-prey interactions. Key words: behavior-modification hypothesis; bird predation; differential predation; effects of parasites on host behavior; Euhaplorchis californiensis; field experiment; Fundulus; killifish; meta-cercariae; parasites; trematode., INTRODUCTION Parasites are frequently associated with odd host behaviors such as unusual levels of activity, increased conspicuousness, disorientation, and altered responses to stimuli (Holmes and Bethel 1972). For the many [...]

We examined the effects of predatory and competitive interactions among three owl species on reproductive success and population composition of these raptors both experimentally and observationally. Eagle Owls (Bubo bubo, body mass ≅2700 g), Ural Owls (Strix uralensis, 900 g), and Tengmalm's Owls (Aegolius funereus, 130 g) coexist in Fennoscandia and feed mainly on small rodents. Predation may play an important role in interactions among these owl species, because Eagle Owls and Ural Owls can kill Tengmalm's Owls but cannot enter the small entrance hole of Tengmalm's Owl nest boxes. We asked (i) whether predation risk and interspecific competition due to Eagle Owls and Ural Owls reduced breeding density and fitness of Tengmalm's Owls, and (ii) whether these interactions increased intraspecific competition for safe nesting sites among Tengmalm's Owls. We manipulated breeding densities of potentially competing owls by erecting nest boxes, the control being boxes in areas where breeding attempts of competing owl species were absent. Control nest boxes in areas with no Eagle Owl and Ural Owl territories, and nest boxes within Eagle Owl territories, were used by breeding Tengmalm's Owls more than nest boxes within Ural Owl territories. Most breeding attempts of Tengmalm's Owls near Ural Owls failed during the courtship period. The observational data revealed that breeding frequency of Tengmalm's Owls was reduced and the mean start of egg laying was delayed by 11 d within 2 km of Ural Owl nests. In addition, male Tengmalm's Owls at these nests were younger and paired more often with short-winged (i.e., young and generally subdominant) females than when farther away from Ural Owl nests. Our results suggest that inexperienced male Tengmalm's Owls are forced to establish their territories in the vicinity of Ural Owls where they often paired with subdominant females. The areas near Ural Owl nests are suboptimal habitats for Tengmalm's Owls, whereas those near Eagle Owls are not. We conclude that predatory and competitive interactions from Ural Owls decrease the breeding population size of Tengmalm's Owls by reducing the suitable habitats. This is the first experimental demonstration that such interactions may decrease fitness of raptors. Key words: Eagle Owl; exploitative competition; field experiment; Finland; fitness consequences; habitat selection; interference competition; intraspecific competition; predation risk; Tengmalm's Owl; Ural Owl., INTRODUCTION Several studies have shown the importance of interspecific competition in both terrestrial and aquatic ecosystems, especially at higher trophic levels (see, e.g., Hairston et al. 1960, Menge and Sutherland [...]

Species evolve in response to the abiotic and biotic interactions they experience in a community, and so studying the adaptation of species in a community context is a necessary component for understanding the development of community structure. Previous studies have suggested that Enallagma damselflies (Odonata: Coenagrionidae) invaded aquatic habitats with large dragonflies as the top predators at least twice, and large changes in morphological structures (e.g., caudal lamellae and abdomen), which should increase swimming speed, are associated with these invasions. This is significant because these species swim away from attacking predators, whereas species in the ancestral habitat (habitats with fish as the top predators) do not swim from attacking predators. We quantified swimming speed over a large ontogenetic size range for larvae of seven Enallagma species, two in dragonfly lakes and five in fish lakes. Results of analysis of covariance and a modification of Felsenstein's method of evolutionary contrasts indicate that a large evolutionary increase in the slope of the ontogenetic relationship between swimming speed and [log.sub.e](body length) is associated with invasions into dragonfly lakes, and this shift results in larvae of dragonfly-lake species being faster swimmers, especially in larger size classes, than larvae of fish-lake species. We also present experimental results demonstrating that damselflies with larger lamellae are faster swimmers and have higher survival when exposed to dragonfly predation. The results of this study indicate that the change in selective environment associated with habitat shifts into dragonfly lakes promoted adaptations for increased swimming speed in Enallagma lineages. The potential ramifications of this adaptation for community structure are discussed. Key words: adaptation; Enallagma; Odonata; phylogenetic reconstruction; predation; predator avoidance; swimming performance., INTRODUCTION Species interactions influence community structure on both ecological and evolutionary time scales. On ecological time scales, species interactions influence which species can coexist and what population dynamics coexisting species [...]

This study examined the responses of ground-foraging ants to larval ant lions (Neuroptera: Myrmeleontidae). In central Oklahoma, these sit-and-wait arthropod predators are restricted by abiotic factors to sheltered cliff bases. A high-density ant lion zone forms an effective 'minefield' of predation for local ant assemblages. The density of ant-nest entrances and the number of pitfall-trap captures of ant foragers were significantly lower in the ant lion zone than in the adjacent forest or grassland. Differences in ant abundance could not be attributed to differences in thermal microhabitat within and outside the ant lion zone. Over a 24-h period, ants foraged continuously at tuna-fish baits placed on the forest floor, but never utilized baits placed within the ant lion zone. Field behavioral tests with individual ant foragers confirmed that the risk of predation from ant lions was high for common ant species in the assemblage. Among species, predation risk was negatively correlated with worker body mass. Manipulative field experiments tested whether ants use biotic or abiotic cues to avoid ant lion aggregations. Ants foraged readily at baits on the forest floor and baits placed in the center of experimental sand patches, but they avoided baits placed in sand patches that contained ant lions. Ant foraging was also substantially lower in patches from which ant lions had been removed 3 h prior to the start of the experiment. Ant foraging was slightly reduced in patches with artificial ant lion pits that had never contained predators. These experiments suggest that ants use biotic cues associated with the presence or recent presence of predators. Previous studies have not implicated predation as an important factor structuring ant communities. This study suggests that predators can have important community-wide impacts on the distribution, abundance, and behavior of ground-foraging ants. Key words: abundance; ant; ant lion; behavior; community; distribution; foraging; predation; rarefaction., INTRODUCTION There is considerable evidence that the presence of a predator can influence prey populations, even in the absence of direct predation (Sih 1987, Lima and Dill 1990). These indirect [...]

According to life history theory, adult mortality during the breeding season may have an important influence on the evolution of several aspects of breeding ecology in birds, yet few studies have tried to quantify such mortality. We studied disappearance of Pied Flycatchers (Ficedula hypoleuca) during four breeding seasons in a woodland area in Norway provided with nest boxes. The main cause of disappearance was probably predation by the European Sparrowhawk (Accipiter nisus). Disappearance was nonsignificantly higher in females (10% per season, n = 305) than in males (7% per season, n = 269). Female disappearance peaked during egg-laying (0.53% per day), but was also high during the nest-building (0.42% per day) and nestling (0.36% per day) stages. It was low during incubation (0.05% per day), probably because less time was spent outside the nest. Low risk of predation during incubation may help to explain why female body mass remains high during this stage of breeding but drops soon after hatching. Females with selected flight feathers experimentally removed to simulate molt suffered a much higher disappearance per season (24%, n = 109) than did control females (10%, n = 305). This may help to explain why breeding and molt usually are temporally segregated activities in birds. Variation in female body mass and size (wing length, tarsus length), age, previous breeding experience, mating date, laying date, clutch size, and mating status could not account for the variation found in female disappearance. Disappearance was lower in males than in females during the nest-building period, despite the more conspicuous plumage color of males. This may be explained by the fact that only the female builds the nest. We suggest that risk of predation is an important constraint on sexual selection of male plumage color in species in which males take part in nest building. Key words: adult predation; body mass; Ficedula hypoleuca; molt; physiological stress; sexual dimorphism., INTRODUCTION In birds, one or both of the parents may sometimes disappear from an apparently successful nesting attempt. This may be for several reasons. For instance, they may desert the [...]