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PubMed2005

Coots Fulica atra reduce their vigilance under increased competition.

Birds frequently interrupt feeding to scan their surrounding environment. Usually an inverse correlation between scan rate and flock size exists. The 'many-eyes' hypothesis suggests that more eyes are able to detect a predator earlier. Due to the 'dilution-effect' animals in larger groups experience 'safety in numbers', while the 'scramble competition' hypothesis suggests that individuals reduce their vigilance in larger groups since they compete for a limited amount of scarce resources. Here, I induced competition in natural coot populations. Coots preferred feeding on grass and were occasionally fed by passers-by at the study sites. However, this resource was scarce and coots experienced additional food as a very limited resource. I sampled coots prior and after an experimental treatment with an additional food supply. Correlations between vigilance rate (number of scans during 1 min of foraging), nearest neighbor distance and flock size existed before the experimental treatment but afterwards the correlation between vigilance and nearest neighbor distance faded. I found a significantly lower vigilance rate and nearest neighbor distance after inducing competition. This study provided experimental evidence for the 'scramble competition' hypothesis namely that individuals in groups lowered their vigilance when faced with competition for a limited amount of food resources given similar flock sizes.

Animals↗
PubMed2006

Juvenile stress induces a predisposition to either anxiety or depressive-like symptoms following stress in adulthood.

Epidemiological studies indicate that childhood trauma is predominantly associated with later emergence of several stress-related psychopathologies. While most 'early-stress' animal models focus on pre-weaning exposure, we examined the consequences of exposure to stress during the early pre-pubertal period, "juvenile stress", on adulthood stress responses. Following two different juvenile stress protocols, predator scent or short-term variable stress, we examined adulthood stress responses using the elevated plus-maze and startle response or exploration and avoidance learning. Employing Cut-off Behavioral Criteria analyses of clustering symptoms on the rats' altered stress responses discriminated between different patterns of maladaptive behaviors. Exposure to either juvenile stress protocols resulted in lasting alteration of stress responses with the majority of rats exhibiting anxiety-like behaviors, while the remaining third displayed depressive-like behaviors. The results suggest that the presented "Juvenile stress" model may be relevant to the reported predisposition to develop both anxiety and depression following childhood trauma.

Acoustic Stimulation↗
PubMed2006

Instabilities in spatially extended predator-prey systems: spatio-temporal patterns in the neighborhood of Turing-Hopf bifurcations.

We investigate the emergence of spatio-temporal patterns in ecological systems. In particular, we study a generalized predator-prey system on a spatial domain. On this domain diffusion is considered as the principal process of motion. We derive the conditions for Hopf and Turing instabilities without specifying the predator-prey functional responses and discuss their biological implications. Furthermore, we identify the codimension-2 Turing-Hopf bifurcation and the codimension-3 Turing-Takens-Bogdanov bifurcation. These bifurcations give rise to complex pattern formation processes in their neighborhood. Our theoretical findings are illustrated with a specific model. In simulations a large variety of different types of long-term behavior, including homogenous distributions, stationary spatial patterns and complex spatio-temporal patterns, are observed.

Animals↗
PubMed2005

Intermittent exposure to reduced oxygen levels affects prey size selection and consumption in swimming crab Thalamita danae Stimpson.

Portunid crabs Thalamita danae (carapace width: 46-56 mm) were exposed to low oxygen level (4.0 mg O2 l(-1)) and hypoxia (1.5 mg O2 l(-1)) for 6 h each day with three size classes (large: 15.0-19.9 mm, medium: 10.0-14.9 mm, small: 5.0-9.9 mm) of mussels Brachidontes variabilis offered as food. Consumption rate, prey size preference, and prey handling including breaking time, handling time, eating time and prey value, were studied during the time the crabs were exposed to reduced oxygen levels and results were compared with the crabs maintained at high oxygen level (8.0 mg O2 l(-1)) throughout the experiment. Consumption of mussels from all size classes was significantly higher at high oxygen level than at reduced oxygen levels. No mussel size preference was observed for crabs exposed to 4.0 or 8.0 mg O2 l(-1) but those crabs exposed to 1.5 mg O2 l(-1) preferred medium mussels. Both breaking time and handling time increased with mussel size but did not vary with oxygen level. Prey value of each mussel consumed (mg dry wt eaten crab(-1) s(-1)) was calculated by dividing the estimated dry weight of the mussel by the observed handling time. Mean prey value varied significantly with mussel size, with values obtained for large mussels being higher than small mussels at 4.0 and 8.0 mg O2 l(-1); the effect of oxygen level, however, was insignificant. In view of portunid crabs as major predators of mussels, results may help explain dominance of mussels in eutrophic harbours in Hong Kong.

Analysis of Variance↗
PubMed2006

Prey capture behavior and kinematics of the Atlantic cownose ray, Rhinoptera bonasus.

The structurally reinforced jaws of the cownose ray, Rhinoptera bonasus testify to this species' durophagous diet of mollusks, but seem ill-suited to the behaviors necessary for excavating such prey. This study explores this discordance by investigating the prey excavation and capture kinematics of R. bonasus. Based on the basal suction feeding mechanism in this group of fishes, we hypothesized a hydraulic method of excavation. As expected, prey capture kinematics of R. bonasus show marked differences relative to other elasmobranchs, relating to prey excavation and use of the cephalic lobes (modified anterior pectoral fin extensions unique to derived myliobatiform rays). Prey are excavated by repeated opening and closing of the jaws to fluidize surrounding sand. The food item is then enclosed laterally by the depressed cephalic lobes, which transport it toward the mouth for ingestion by inertial suction. Unlike in most sharks, upper jaw protrusion and mandibular depression are simultaneous. During food capture, the ray's spiracle, mouth, and gill slit movements are timed such that water enters only the mouth (e.g., the spiracle closes prior to prey capture and reopens immediately following). Indigestible parts are then hydraulically winnowed from edible prey portions, by mouth movements similar to those used in excavation, and ejected through the mouth. The unique sensory/manipulatory capabilities of the cephalic lobes, as well as the cownose ray's hydraulic excavation/winnowing behaviors and suction feeding, make this species an effective benthic predator, despite its epibenthic lifestyle.

Analysis of Variance↗
PubMed2004

Daphnicle dynamics based on kinetic theory: an analogue-modelling of swarming and behaviour of daphnia.

Attempts are presented of an analogue modelling of Daphnia responses to various influences and stimuli, as distribution of food and of predators. An aim of the study is to examine to what extent a statistical-mechanical approach may be useful as a tool in modelling of Daphnia swarms behaviour. In the modelling we follow a line close to test particle studies in physical sciences. A generalized kinetic equation of what we shall call daphnicles is derived. The modelling incorporates individual characteristics of daphnicles, as position, velocity, degree of food saturation and responses daphnicles have to outside influences. Each daphnicle we assume responds to some stimuli in ordered ways and to others in stochastic ways, and the degree or strength of reactions depends on the density of all daphnicles, the density of food available, the saturation level of daphnicles and the threat level in the environment, or background, the daphnicles are living on. Some fluid equations of daphnicle swarms are subsequently derived from the basic equation, and solutions are given of the model-equations, including a food distribution equation, in some particular cases that show peculiarities in reactions of daphnicles to food, degree of saturation and to threat, when these are acting alone, and in combination. The modelling results may be compared to results of laboratory experiments of Daphnia behaviour that soon will be performed.

Animals↗
PubMed1991

Feline aggression. Classification, diagnosis, and treatment.

Types of aggressive behavior commonly recognized in cats include intermale, territorial, fear/defensive, play, predation, and redirected. Diagnosis is made on the basis of signalment data, the pattern of aggressive postures displayed by the aggressive cat, and the circumstances in which the aggressive behavior occurred. Treatment varies with the type of aggressive behavior but may include neutering, desensitization and counter-conditioning techniques, punishment, drug therapy, and management changes.

Aggression↗
PubMed1997

Rebels with a cause.

Female mate choice is often for males bearing exaggerated sexual characters. A new experiment with guppies reveals they also prefer males that risk their lives inspecting predators.

Animals↗
PubMed2000

Does prey matter? Geographic variation in antipredator responses of hatchlings of a Japanese natricine snake (Rhabdophis tigrinus).

Rhabdophis tigrinus, which typically forages on toads, has unusual nuchal glands on its dorsal neck region containing secretions chemically comparable to cardiac steroids found in toads. R. tigrinus also has several peculiar antipredator displays involving the neck region. If the nuchal gland secretions of R. tigrinus are derived from toads obtained as prey, populations of R. tigrinus that have not eaten toads over an evolutionary time scale would be expected to lose antipredator displays related to the nuchal glands. We found that laboratory-hatched R. tigrinus from a small toad-free island exhibited displays related to nuchal glands less frequently and flight responses more frequently than hatchling snakes from areas sympatric with toads. These results are consistent with the hypothesis of the dietary origin of the nuchal gland secretions and also support the genetic origin of the behavioral differences between the populations.

Animals↗
PubMed2002

Snake circumvents constraints on prey size.

For animals who are unable to take bites out of their food, the size of the food item that can be consumed is constrained by the maximal size of the mouth opening (gape)--snakes are an example of gape-limited predators and they usually swallow their prey whole. Here we describe unique feeding behaviours in two closely related species of snake, which circumvent their gape limitation by removing and consuming pieces from newly moulted crabs that are too large to be swallowed intact. This evolutionary innovation is surprising, as the needle-like teeth and highly mobile bones that facilitate the capture and engulfment of large, whole prey by snakes are ill-suited both to cutting and to generating large bite forces.

Animals↗
PubMed2006

A mechanism for diversity in warning signals: conspicuousness versus toxicity in poison frogs.

Many animals advertise their chemical defense to predators with conspicuous coloration and unpalatability, but little is known about the information in these signal elements. To effectively avoid predation, is it more advantageous to invest in increased conspicuousness or greater noxiousness, or to allocate equally to both signal modalities? Using natural variation among poison frog species measured with spectral reflectance and toxicity assays, we tested the relative importance of warning signal components with predator-learning and avoidance experiments. We demonstrate that closely related species use alternative strategies: increasing either conspicuousness or toxicity affords equivalent avoidance by predators and provides protection to nontoxic mimic species. These equally effective predator avoidance tactics demonstrate different aposematic solutions for two potentially costly signal components, providing a mechanism for natural diversity in warning signals.

Animals↗