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At least 1,513 records · Page 84Linked to original sources
PubMed1987

A possible mechanism for binocular depth judgements in anurans.

Two experiments were performed to analyze how anurans (Bufo marinus) use binocular cues to gauge the distance of their prey. In the first, bilateral lesions of the nucleus isthmi eliminated the major source of input from the ipsilateral eye to the tectum. These lesions did not disrupt the animals' ability to use binocular cues to judge distance, suggesting that frogs and toads may not employ binocular disparity-selective cells to assess prey distance. They may instead use a scheme more overtly akin to triangulation, with each tectum providing an output signal encoding the angular position of the prey with respect to the contralateral eye and with distance extracted from the difference between these tectal outputs. In the second experiment, prisms imposed large (13.5 degrees) vertical disparities between the two eyes' images. The toads continued to use binocular cues. The added vertical disparities, like added horizontal ones, caused toads to undershoot their prey. Thus the binocular system must tolerate such vertical disparities and fail to distinguish them from horizontal ones.

Animals↗
PubMed1987

Equilibria in systems of interacting structured populations.

The existence of a stable positive equilibrium density for a community of k interacting structured species is studied as a bifurcation problem. Under the assumption that a subcommunity of k-1 species has a positive equilibrium and under only very mild restrictions on the density dependent vital growth rates, it is shown that a global continuum of equilibria for the full community bifurcates from the subcommunity equilibrium at a unique critical value of a certain inherent birth modulus for the kth species. Local stability is shown to depend upon the direction of bifurcation. The direction of bifurcation is studied in more detail for the case when vital per unity birth and death rates depend on population density through positive linear functionals of density and for the important case of two interacting species. Some examples involving competition, predation and epidemics are given.

Animals↗
PubMed1989

Predator-prey populations with parasitic infection.

A predator-prey model, where both species are subjected to parasitism, is developed and analyzed. For the case where there is coexistence of the predator with the uninfected prey, an epidemic threshold theorem is proved. It is shown that in the case where the uninfected predator cannot survive only on uninfected prey, the parasitization could lead to persistence of the predator provided a certain threshold of transmission is surpassed.

Animals↗
PubMed1985

A model of the neural mechanisms responsible for pattern recognition and stimulus specific habituation in toads.

A neural model of the mechanisms possibly responsible for stimulus-specific habituation in toads is proposed. The model follows the hypothesis that prey-predator recognition is performed by command units as a result of retina-tectum-pretectum interaction. The model allow us to study the possible coding that the nervous system of toads uses for different prey stimuli, the neural mechanisms of habituation and dishabituation, and the dynamic changes that the command units may have during these processes. The model proposes specific hypothesis and experiments to clarify the nature of these processes and to test the validity of the command unit hypothesis.

Animals↗
PubMed1976

Behaviour of Dictyostelium discoideum amoebae and Escherichia coli grown together in chemostat culture.

When Dictyostelium discoideum amoebae and Escherichia coli were grown together in chemostat culture damped oscillations in the population densities of the organisms occurred followed by a sudden increase in bacterial numbers and a concommitant decrease in the number of amoebae. After the system had come to equilibrium altering the dilution rate resulted in a monotonic change in the experimental variables to new steady state levels. A square wave increase in the concentration of limiting nutrient in the feed medium during the oscillatory phase of culture produced a sinusoidal response indistinguishable from that prior to the perturbation. The results are more complicated than those predicted by simple models of microbial predator-prey dynamics although they correspond most nearly to models which incorporate saturation kinetics.

Animals↗
PubMed1983

Primary lateral line response to water surface waves in the topminnow Aplocheilus lineatus (Pisces, Cyprinodontidae).

1. The function of supraorbital organ II/2 of the head lateral line system of the surface feeding fish Aplocheilus lineatus is characterized here by the lateral line nerve response evoked by biologically relevant surface wave trains. 2. A single organ is particularly sensitive to the high frequency, low amplitude cycles at the beginning of a click evoked wave train. By using gated sinusoidal signals it was shown that the following mechanisms are responsible: a. a strong phasic component superimposed on the tonic response component, b. high sensitivity of the organ in the frequency range between 70 and 120 Hz (corresponding to the frequency range of the first cycles of a prey evoked wave), c. the organ is responsive to the acceleration component of wave stimulation (b approximately f2). 4. As the time structure of a surface wave is encoded in a corresponding discharge pattern in the lateral line nerve it is probable that the time structure ('stimulus pattern') of a signal is used by A. lineatus to estimate the distance to its source.

Animals↗
PubMed1988

Frogs use retinal elevation as a cue to distance.

We have investigated the role that retinal elevation plays in a frog's (Rana pipiens) estimate of prey distance. We dissociated retinal elevation from other depth cues by artificially increasing the height of the frogs' eyes above the ground. Frogs then snapped short of their prey in their ventral visual field as if their estimate of distance were determined primarily by the retinal elevation of the image of the prey. The data suggest that the frog assumes its eyes to be about 3 cm above the ground. Other cues modify depth judgements when targets are close to this assumed ground-plane.

Animals↗
PubMed1988

Crocodiles don't focus underwater.

Crocodilians are amphibious reptiles which hunt prey both on land and in water. Previous refractive and anatomical studies have suggested that their eyes can focus objects in air and that their ability to refocus the eye underwater may be limited. Examination of the plane of focus of six species of crocodilians both in air and underwater has revealed that they are generally well focused in air for distant targets and severely defocused underwater. These results suggest that sensory systems other than vision must play an important role in prey capture underwater.

Accommodation, Ocular↗
PubMed1987

Coding of sinusoidally amplitude modulated acoustic stimuli in the inferior colliculus of the rufous horseshoe bat, Rhinolophus rouxi.

Single neuron responses to sinusoidally amplitude modulated (SAM) signals were studied in the inferior colliculus of the horseshoe bat, Rhinolophus rouxi. 57% of the neurons responded to SAM stimuli with periodical discharges synchronized to the modulation cycle. The proportion of cells driven by amplitude modulated signals was independent of the best frequency of the neurons. Best modulation frequencies were at or below 100 Hz in about 70% of the neurons. Synchronized activity could be elicited by modulation frequencies up to 400 Hz. Best SAM responses were observed at stimulus intensities 10 dB above threshold. Generally the BMF of a neuron did not change with intensity. The BMF decreased with decreasing modulation depth of the amplitude modulation. A trend for a topographical organization of neurons according to best modulation frequencies was detected. The results did not reveal any significant specialization of the bat's auditory system for coding of amplitude modulations as compared to other mammals.

Animals↗
PubMed1991

Behavioral comparisons of the Tsukuba emotional strains of rats (Rattus norvegicus) in three types of novel situations.

Tsukuba High- and Low-Emotional rats (THE and TLE), Wistar-Imamichi/Iar rats (control group for the Tsukuba Emotional rats), and F344/DuCrj rats were tested in three types of novel situations: the open field, a runway devised as a type of open field with a shelter, and an I-maze devised as a narrow runway with shelters and covers to remove rats' freezing behavior against predatory attack. The TLE was the most active, and the THE the least active in the three tests. While the F344 was inactive in the runway and the I-maze, this strain was as active as the Wistar-Imamichi in the open field. While the THE and F344 defecated frequently, the TLE never defecated.

Animals↗
PubMed1989

Distribution of some anystid mites (Acari: Anystidae) in Australia and Indonesia and their role as possible predators of the cattle tick, Boophilus microplus (Acari: Ixodidae).

The geographic and habitat distributions of Anystis baccarum, A. jabanica, A. salicinus, and A. sp. B Walzia australica Womersley and Chaussieria warregense in Australia and parts of Indonesia are presented. Laboratory trials showed that A. baccarum will feed upon the larvae of the cattle tick Boophilus microplus, whilst A. jabanica also showed some predatory potential. Walzia australica and C. warregense had no effect on survival of tick larvae.

Animals↗
PubMed1991

Predation of free-living engorged female Rhipicephalus appendiculatus.

In experiments done over a period of 1 1/2 years using engorged female Rhipicephalus appendiculatus tethered in a grass plot, 42% predation was observed in long grass (40-60 cm), and 36% in short grass (6-10 cm). Deaths due to environmental factors were 4.8% and 6.8% in long and short grass, respectively. Six groups of animals were confirmed to be predators of the ticks, namely: ants, spiders, rodents, birds, lizards and shrews. The implications of these results in making tick population models, and the possibility of using predators in integrated tick-control packages are discussed.

Animals↗
PubMed1991

Predators of the tick Amblyomma variegatum (Acari: Ixodidae) in Guadeloupe, French West Indies.

Some vertebrate species in Guadeloupe are predators of free or parasitic stages of Amblyomma variegatum (Fabricius). Among birds, 1.9% of the 421 identified animals found in the stomachs of grackles (Quiscalus lugubris), 1.6% of the 364 animals found in the stomachs of free-ranging chickens, and 0.3% of the 4642 animals found in the stomach of cattle egrets (Bubulcus ibis) were A. variegatum ticks. The most efficient predator of ticks was the tropical fire ant, Solenopsis geminata, which was observed to only attack engorged stages of ticks. An average of 8% of the 564 individual ticks or batch of ticks released on the ground, mainly in a grass environment, were attacked by this ant species. Mice (Mus musculus) and mongooses (Herpestes auropunctatus) feed on engorged nymphs and female ticks. None of the 15 strains of entomophagous nematodes, genera Steinernema and Heterorhabditis, experimentally put in contact with engorged larvae and nymphs were able to parasitize them. In the laboratory, the insects Megaselia scalaris (Diptera) and Tineola sp. (Lepidoptera) were occasionally found to feed on engorged and unfed ticks, respectively.

Animals↗