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PubMed2006

Aggregation, defence and warning signals: the evolutionary relationship.

In a seminal contribution, Fisher argued how distastefulness could incrementally evolve in a prey species that was distributed in family groups. Many defended prey species occur in aggregations, but did aggregation facilitate the evolution of defence as Fisher proposed or did the possession of a defence allow individuals to enjoy the benefits of group living? Contemporary theory suggests that it can work both ways: pre-existing defences can make the evolution of gregariousness easier, but gregariousness can also aid the evolution of defence and warning signals. Unfortunately, the key phylogenetic analyses to elucidate the ordering of events have been hampered by the relative rarity of gregarious species, which in itself indicates that aggregation is not a pre-requisite for defence. Like the underlying theory, experimental studies have not given a definitive answer to the relative timing of the evolution of defence and aggregation, except to demonstrate that both orderings are possible. Conspicuous signals are unlikely to have evolved in the absence of a defence and aggregated undefended prey are likely to be vulnerable to predation in the absence of satiation effects. It therefore seems most likely that defence generally preceded the evolution of both aggregation and signalling, but alternative routes may well be possible.

Animals↗
PubMed2005

Dynamics of social balance on networks.

We study the evolution of social networks that contain both friendly and unfriendly pairwise links between individual nodes. The network is endowed with dynamics in which the sense of a link in an imbalanced triad--a triangular loop with one or three unfriendly links--is reversed to make the triad balanced. With this dynamics, an infinite network undergoes a dynamic phase transition from a steady state to "paradise"--all links are friendly--as the propensity p for friendly links in an update event passes through 1/2 . A finite network always falls into a socially balanced absorbing state where no imbalanced triads remain. If the additional constraint that the number of imbalanced triads in the network not increase in an update is imposed, then the network quickly reaches a balanced final state.

Adaptation, Physiological↗
PubMed2003

Rapid growth results in increased susceptibility to predation in Menidia menidia.

Several recent studies have demonstrated that rapid growth early in life leads to decreased physiological performance. Nearly all involved experiments over short time periods (<1 day) to control for potentially confounding effects of size. This approach, however, neglects the benefits an individual accrues by growing. The net effect of growth can only be evaluated over a longer interval in which rapidly growing individuals are allowed the time required to attain the expected benefits of large size. We used two populations of Menidia menidia with disparate intrinsic growth rates to address this issue. We compared growth and survivorship among populations subject to predation in mesocosms under ambient light and temperature conditions for a period of up to 30 days to address two questions: Do the growth rates of fish in these populations respond differently to the presence of predators? Is the previously demonstrated survival cost of growth counterbalanced by the benefits of increased size? We found that growth was insensitive to predation risk: neither population appeared to modify growth rates in response to predation levels. Moreover, the fast-growing population suffered significantly higher mortality throughout the trials despite being 40% larger than the slow-growing population at the experiment's end. These results confirm that the costs of rapid growth extend over prolonged intervals and are not ameliorated merely by the attainment of large size.

Animals↗
PubMed2006

Intraguild indirect effects through trophic cascades between stream-dwelling fishes.

1. To examine the strength and role of indirect effects through trophic cascades by omnivorous fish on algal biomass in streams, we introduced one of four fish species (ayu Plecoglossus altivelis altivelis, pike gudgeon Pseudogobio esocinus esocinus, Japanese dace Tribolodon hakonensis and pale chub Zacco platypus) in experimental pools. We also investigated the indirect effects of gudgeon, dace and chub on the growth of ayu. 2. We chose the four fish species across a continuum of omnivory. Ayu fed mainly on benthic algae, and gudgeon predominantly on invertebrates. Dace and chub fed on both algae and invertebrates, but dace preyed on invertebrates more than chub. 3. The presence of gudgeon, dace and chub reduced the number of algal-feeding invertebrates and increased the algal biomass through trophic cascades. Consequently, ayu growth rate over the experimental period in pools with one of the three fish species was 25.9-44.1 times greater than the growth rate in pools with only ayu. 4. The positive indirect effect on ayu growth was large for gudgeon and dace and small for chub, whereas the addition of ayu reduced ayu growth considerably due to intraspecific competition. 5. The relative intensity of indirect effects on ayu growth through trophic cascades was predictable from the food overlap between ayu and the other fishes. However, the similar strength of indirect effects by gudgeon and dace that fed differently on algae and invertebrates suggests that feeding behaviour, prey preference and trait-mediated indirect interactions were also important in the prediction.

Animals↗
PubMed2006

Ecological mechanisms favouring behavioural diversification in the absence of morphological diversification: a theoretical examination using brook charr (Salvelinus fontinalis).

1. Behavioural diversification is thought to be an important initial step in the origin of resource polymorphisms. We developed a model for young brook charr (Salvelinus fontinalis Mitchill) to examine four mechanisms that could generate a U-shaped relationship between growth rate (fitness) and the proportion of time spent moving that would favour alternative foraging tactics in the absence of obvious differences in body size and shape. 2. Recently emerged brook charr of similar size and shape inhabit still-water pools along the sides of streams. Some individuals tend to sit and wait for crustacean prey at the pool substrate near the bank, while others tend to search actively for insect prey at the pool surface away from the bank. 3. The ecological mechanisms modelled were (i) the relationship between the rate of prey capture and the proportion of time spent moving is curvilinear, such that net rate of energy gain is maximized at two different levels of activity; (ii) switching between foraging locations and, hence, tactics involves lost opportunity and travel costs; (iii) switching between prey types and, hence, tactics involves a learning cost; and (iv) foraging success is status-dependent with individuals switching between tactics having a lower status than those specializing at a tactic. 4. Singly, no mechanism predicted the U-shaped relationship between growth rate and the proportion of time spent moving. Together, a U-shaped relationship was obtained, indicating that the behavioural diversification and diversifying selection observed in the field may be a consequence of multiple, subtle mechanisms.

Animals↗
PubMed1992

Modelling the effect of feeding-related mortality on the feeding strategy of tsetse (Diptera: Glossinidae).

Free-living haematophagous insects risk death through host grooming responses or through increased susceptibility to predation whenever they take a bloodmeal. In this paper we investigate the effects of these risks on the feeding strategy of tsetse. A model is presented that allows for death of tsetse by starvation if they do not succeed in feeding within a fixed time (set at 6 days in the first instance) and for mortality specifically associated with feeding. In addition there is background mortality that applies to all flies at all times. The model is used to compute the individual life-time fertility (number of female puparia per female) as a function of the probability of obtaining a meal (indicated by field data to be very high, usually > 0.85 per day) and the day on which flies start to search for a meal. We suggest that the feeding strategy that would be selected for is that which allows the maximum reproductive output. The model shows that this strategy involves making no attempts to feed for 3-4 days after the previous meal and then attempting to feed with the greatest possible probability until a meal is obtained. The predicted feeding interval, obtained independently of any trapping data, agrees closely with all previous estimates from field studies using a variety of methods. Preliminary results from a laboratory experiment reveal an increased risk of predation of recently fed as compared with hungry tsetse. The lower the actual feeding mortality the more frequently will flies be able to feed should conditions so demand. It is adaptive, however, for tsetse to delay attempting to feed for as long as they can, which is made possible by the near certainty of locating and feeding on a host within 1 day, using their sophisticated sensory systems.

Animals↗
PubMed2006

Effect of family support on the success of translocated black-tailed prairie dogs.

Translocation has become a widely used conservation tool but remains only marginally successful. High mortality is often attributed to predation, but for highly social species, founder group composition may also play a critical role in postrelease survival. I compared the fitness of black-tailed prairie dogs translocated with or without their family groups. Animals in the family translocated groups were individually marked and observed until coterie membership was determined. Nonfamily translocated animals were trapped without regard to family membership. I measured fitness by retrapping all marked animals remaining at release sites in the summer following release. Family translocated animals were five times more likely to survive and had significantly higher reproductive success than those translocated without families. Predation was an important impediment of translocation success, but family translocation significantly reduced the success of predators on newly established prairie dog colonies. Postrelease survival was also affected by the timing of release, but appeared to be more important for juveniles than adults. These results demonstrate the importance of considering familiarity when translocations are required. More broadly, these results illustrate the value of applying animal behavior to conservation efforts and suggest that other species dependent on social interactions for survival and reproduction may benefit substantially from the maintenance of social groups during translocations.

Age Factors↗
PubMed1994

Sensorimotor model of bat echolocation and prey capture.

A model of the bat sensorimotor system is developed using acoustics, signal processing, and control theory to illustrate the fundamental issues in accomplishing prey capture with echolocation. This model indicates that successful nonpredictive tracking of an ideal prey can be accomplished with a very simple system. Circular apertures approximate the mouth and ears for deriving acoustic beam patterns, using the big brown bat Eptesicus fuscus as a model. Fundamental and overtone frequency components in the emissions allow two simultaneous acoustic beams to be defined. A pair of nonlinear, time-variable, sampled-data controllers alter the bat's heading by applying yaw and pitch heading corrections. The yaw correction attempts to position the prey in the midsagittal plane by nulling the interaural intensity difference of the fundamental component. The pitch correction compares the intensities of the overtone and fundamental components and acts to null their difference. By initiating pitch correction when the overtone intensity first exceeds that of the fundamental, the ambiguity problem is solved and the prey is directed to the capture region. Simulations of passive prey capture indicate that the capture probability decreases as the prey speed increases. Both quick and sluggish prey are considered, with sluggish prey found to be caught with slightly better efficiency. The magnitude of the prey's lateral motion just prior to capture is observed to be an important factor determining capture. The presence of a blind stage is considered, during which the interference of the emission with the echo is assumed to disrupt any sonar information. The presence of such a blind stage is found to have negligible effect on capture efficiency.

Acoustics↗
PubMed2005

Allometry of alarm calls: black-capped chickadees encode information about predator size.

Many animals produce alarm signals when they detect a potential predator, but we still know little about the information contained in these signals. Using presentations of 15 species of live predators, we show that acoustic features of the mobbing calls of black-capped chickadees (Poecile atricapilla) vary with the size of the predator. Companion playback experiments revealed that chickadees detect this information and that the intensity of mobbing behavior is related to the size and threat of the potential predator. This study demonstrates an unsuspected level of complexity and sophistication in avian alarm calls.

Animals↗
PubMed1991

Behavioral and physiological consequences of unilateral ablation of the nucleus isthmi in the leopard frog.

Unilateral lesions of the nucleus isthmi result in a scotoma to visually presented prey and threat stimuli in the contralateral monocular visual field. There is a correlation between the size of the scotoma and the amount of n. isthmi ablated. Following the lesion, there is a regression of the scotoma in the nasal part of the visual field which then stabilizes. Upon longer behavioral examination, the animals can be divided into two classes: (1) animals in which the scotoma remains relatively stable in size for up to two years, and (2) animals which recover from the scotoma. In the latter group, there tends to be damage to both the n. isthmi and the posterodorsal tegmental nucleus which lies mediocaudal to the n. isthmi. Electrophysiological recording from positions within the area of the optic tectum representing the scotoma reveal an average threefold increase in the size of the multiunit receptive fields compared to mirror image positions in the contralateral optic tectum.

Animals↗
PubMed1990

Correlation between histological and behavioral measures of visual acuity in a zooplanktivorous fish, the white crappie (Pomoxis annularis).

Estimates of visual acuity in a pelagic freshwater zooplanktivorous fish, the white crappie (Pomoxis annularis, Centrarchidae), were made using a behavioral measure, the maximum observed prey pursuit distance (MxPD), and a histological measure, the density of cone cells in the retina. The greatest number of pursuits occurs in the 0-30 degrees wedge of the visual field; 87% of all pursuits occur in the first 40 degrees. The longest pursuits (200 mm) also occur in this area and generally get shorter from 0 to 180 degrees (from forward-directed) in the visual field. Consistent with the behavioral results, the largest number of cone photoreceptors (13,000/mm2) is found in the far temporal retina along the eye's horizontal meridian. Cone cell densities in the corresponding region of the nasal retina are approximately half this value. The number of cones decreases dorsally and ventrally from the horizontal meridian. Although the absolute values of visual acuity calculated from cone cell topography (i.e. MxPDs of 500 mm) are 2-3 times greater than those observed behaviorally (i.e. MxPDs of 200 mm), the trends in visual acuity across the visual field obtained from both measures are consistent. We suggest that overestimates of visual acuity obtained from cone cell counts alone result from this measure's not accounting for, among other properties of the nervous system, cone cell convergence onto ganglion cells and higher brain centers. Behavioral measures of visual acuity are, therefore, likely to yield a more accurate estimate of an animal's visual abilities.

Animals↗
PubMed1997

Feeding behaviour and predation of a bat by Saimiri sciureus in a semi-natural Amazonian environment.

A free-ranging group of Saimiri sciureus was studied in a semi-natural forest habitat in eastern Amazonia, where behaviour patterns were broadly similar to those recorded for the species in the wild. According to focal-animal samples, the monkeys spent the vast majority of their time foraging and feeding, in particular for arthropod prey, which contributed almost half of identified food items. The predation of a small-bodied bat was also observed, although the study animals did not appear to forage systematically for chiropterans in the manner recorded for Saimiri oerstedi.

Animals↗
PubMed1996

Ethological and experimental approaches to behavior analysis: implications for ecotoxicology.

Laboratory research in toxicology has progressed far beyond reliance on measures of mortality to make use of sophisticated behavioral preparations that can evaluate the consequences of sublethal toxicant exposure. In contrast, field studies have not evolved as rapidly. Approaches developed by experimental psychologists and ethologists provide powerful and complementary methodologies to the study of environmental pollutants and behavior. Observational data collection techniques can easily be used to broaden the number of questions addressed regarding sublethal exposure to toxic agents in both field and laboratory environments. This paper provides a background in such techniques, including construction of ethograms and observational methodologies, and the use of laboratory analogues to naturally occurring activities such as social behavior, predation, and foraging. Combining ethological and experimental approaches in behavior analysis can result in a more comprehensive evaluation of the effects of environmental contaminants on behavior.

Animals↗
PubMed2001

Geographic variation in antisnake tactics: the evolution of scent-mediated behavior in a lizard.

We used modern comparative methods to examine the evolution of scent-mediated antisnake behavior in the rock-dwelling velvet gecko (Oedura lesueurii). The selective agent is a snake species (broad-headed snake, Hoplocephalius bungaroides) that feeds primarily on velvet geckos by remaining sedentary in rock crevices for days or weeks, waiting to ambush lizards. The past and present distribution of this predator is well documented because of its threatened conservation status. We used this information to sample lizards from three populations distributed with snakes (sympatric) and three populations that appear never to have been distributed with snakes (allopatric) in each of two widespread but geographically distinct genetic groups of velvet gecko (as determined using allozyme electrophoresis). Wild-caught immature geckos from sympatric populations showed higher tongue-flick rates and stronger shifts in locomotion (increased duration of crawling and remaining stationary while pressed against the rock) toward snake-scented rocks than did lizards from allopatric populations. However, predation environment did not significantly affect a lizard's tendency to display other typical antisnake tactics such as tail waving or fleeing. These results were highly repeatable across the two sampled genetic groups of velvet gecko, despite demonstrable genetic divergence between groups. Experiments with hatchling lizards that had no experience with predators indicate that qualitative components of antisnake behaviors are probably inherited. The method of phylogenetically independent contrasts strongly suggests that the presence or absence of snakes has driven the evolution of behavior in velvet geckos. Collectively, these results provide support for an often suggested but speculative expectation that prey can adapt to predation pressure on a local scale.

Animals↗
PubMedDate not supplied

Haematophagy and cleptohaematophagy of clerada apicicornis (Hemiptera: lygaeidae), a potential biological control agent of rhodnius prolixus (Hemiptera: reduviidae).

Because of its ability to prey on Triatominae in rural houses, Clerada apicicornis has been suggested as a potential biological control agent of Rhodnius prolixus. It has also been suggested as a potential vector of mammalian trypanosomes such as Trypanosoma cruzi, because of its ability to take blood directly from mammals. To help resolve these conflicting ideas, we assessed the haematophagic behaviour of C. apicicornis by carrying out feeding trials on laboratory animals. Cleptohaematophagic behaviour was also assessed by allowing C. apicicornis to feed on R. prolixus previously engorged with avian blood. The low proportion of blood meals taken directly from laboratory animals indicates a facultative haematophagy in this species, whereas a greater proportion of nymphs and adults were able to obtain vertebrate blood by predation on engorged R. prolixus. The results suggest that C. apicicornis is unlikely to be effective as a biological control agent, but is also unlikely to have a significant role in the transmission of vertebrate pathogens.

Animals↗
PubMed1978

Vulnerability of bot fly (Cuterebra) infected Peromyscus maniculatus to shorttail weasel predation in the laboratory.

In the laboratory, Peromyscus bearing a single Cuterebra larva are no more vulnerable to weasel predation than are uninfected control mice, and may be taken less often under certain conditions. Mice bearing two or more larvae appear to be more vulnerable than either controls or singly infected mice. Their increased vulnerability probably results from their failure to use arboreal pathways. Decreased activity may be responsible for the relative advantage of singly infected mice. Previous reports of higher survivorship among mice with a single bot parasite than among uninfected mice, and of lower survivorship among multiply infected mice, may result in part from differential predation rates.

Animals↗
PubMed2005

[Roles of olfaction and vision in orientation behavior of adult Campylomma chinensis Schuh (Hemiptera: Miridae) toward Lantana plants (Verbanaceae)].

Investigations were carried out on the orientation behavior of adult Campylomma chinensis Schuh (Hemiptera: Miridae) toward plant hosts Lantana camara, L. caniara cv. 'Flava', and L. montevidensis (Spreng. ) Briq. (Verbanaceae). Surveys on three Lantana plants showed that the distribution of C. chinensis in inflorescences was not related to floral color (partial correlation coefficient was 0.240, P = 0. 147, n = 40), but to the number of Thrips hawiiensis Morgan (partial correlation coefficient was 0.512, P < 0.0001, n = 40) and the flowers per inflorescence (partial correlation coefficient was 0.451, P < 0.0001, n = 40). In a colour preference experiment, no adult C. chinensis attracted to six different colour plates in longan field. The testing results of four-armed olfactometer indicated that adult C. chinensis had a significantly higher preference for L. camara. It was concluded that olfactory stimuli played an important role in searching for plant hosts of C. chinensis. Solid phase microextraction (SPME) and GC-MS were employed to analyze the volatiles compounds of Lantana, and seven same chemical constituents were detected from the volatiles of three Lantana plants inflorescence.

Animals↗