Cost-benefit models of escape behaviour predict that flight initiation distance (FID, predator-prey distance when the prey starts to flee from an approaching predator) increases as the cost of not ...fleeing (risk) increases. This prediction has been verified for many risk factors and prey species. The same predictions may apply to other aspects of escape, but testing has been much less extensive. For the lizards Callisaurus draconoides and Sceloporus magister, we tested several such predictions and examined the effect of a previously unstudied risk factor, recent movement by prey. Starting distance (predator-prey distance when approach begins) was unrelated to FID in C. draconoides, as in previously studied ambush foragers. Because movement increases probability of being detected, we predicted that FID would be greater for prey that had moved immediately before being approached than those that had been immobile. FID and distance fled (DF) were longer for lizards that had moved recently. In C. draconoides DF and probability of entering refuge were greater for the second of two approaches, as predicted from greater threat posed by a persistent predator. Callisaurus draconoides had shorter FID and shorter DF, and fewer entered refuge where lizards were habituated than unhabituated to human presence. In S. magister FID increased as distance to refuge increased, FID and DF were longer for fast than slow approaches; probability of fleeing and FID were larger for direct than indirect approach. Effects of these risk factors on FID are consistent across studies, but approach speed has affected DF in only half of studies, perhaps due to constraints by refuge entry and variable distance to refuge. Similarities in effects of risk factors across escape variables, types of predator-prey encounters, and latency to emerge from refuge suggest that similar risk assessment mechanism are used for all variables and settings.
Abstract
Escape studies often focus on one variable, but tactics and refuge use vary with microhabitats, exposure, distance to refuge, and temperature. We studied these effects and effects of ...microhabitats and risk factors (distance from refuge, temperature) on flight initiation distance (FID, distance between predator and prey when escape begins) and distance fled (DF) in the lizard Sceloporus virgatus. FID increased as distance to refuge increased and temperature decreased. DF increased as FID increased, supporting the hypothesis that individual differences in boldness are consistent among encounter phases. Refuges were rock crevices, trees, logs, and grass clumps. Interhabitat differences in FID and DF matched those in distance to refuge. FID was longer for lizards on rocks and ground than trees due to proximity to and use of refuge. Lizards on trees rarely changed microhabitats, moving to the far side and unpredictably up or down. Lizards on slopes fled long distances up slopes. Most lizards on rocks entered crevices or switched microhabitats. Lizards on ground usually changed microhabitats. Optimal escape theory accurately predicted effects of risk on FID, but initial microhabitats and final microhabitats and refuges affected tactics, FID and DF. DF was affected by risk, being longer when lizards remained visible.
We examined how herbivore distribution and density, neighboring plant density and species composition, and individual plant morphology all influence the risk that individual arctic lupines (Lupinus ...arcticus) will be browsed by arctic ground squirrels (Spermophilus parryii plesius). Risk of being browsed was significantly influenced by the number of resident ground squirrels but not by overall squirrel density at a site.
AbstractTo determine aspects of escape strategy by the Carolina grasshopper, Dissosteira carolina, and applicability of models of escape behavior applied primarily to vertebrates, I conducted three ...field experiments by simulating an approaching predator. Escape theory predicts that flight initiation distance (distance from predator when escape begins) and distance fled increase as predation risk increases. Some aspects of escape are not predicted, and theory does not identify escape strategies including several components. I examined effects of risk factors (predator approach speed, directness of approach, and repeated approach) on flight initiation distance, distance fled, and the initial direction of escape. Flight initiation distance and distance fled were predicted to increase with approach speed. Because predators approaching directly may bypass prey without detecting it, probability of fleeing and flight initiation distance were predicted to increase with directness of approach. Because a persistent predator poses greater threat, flight initiation distance and distance fled were predicted to be greater for the second of two successive approaches. All findings were consistent with predictions of the Ydenberg & Dill (1986) model, suggesting that risk assessment and escape decisions by visually oriented insects may be similar to those of vertebrates. Although escape directly away from the predator might be expected to minimize risk, most grasshoppers escaped by flying at nearly right angles to the approach path. Lateral escape may be part of an escape strategy in which dark wing colour during flight rapidly disappears upon landing. With sudden change in colour and movement, the grasshopper becomes cryptic and difficult to relocate. Lateral escape may increase difficulty of maintaining visual contact with the grasshopper until it lands. It also avoids need for further escape from a predator that continues in its initial direction.
Female Eumeces laticeps experience a substantial decrease in running speed (ca. 25%) and an even greater loss of endurance (slightly over 50%) while gravid. Because some widely foraging lizards, ...including E. laticeps, rely primarily on running to escape predators, the decreases in speed and stamina may contribute to an increased risk of predation. However, observations suggest that gravid females become less active or conspicuous on the surface. Ambush foraging lizards rely relatively more on crypsis associated with immobility to avoid predation and thus can have greater average relative clutch mass (RCM) than active foragers. Behavioral compensation for locomotor impairment by becoming less active or conspicuous may allow some species the advantages inherent in both high relative clutch mass when gravid and the increased energetic profitability of active foraging when not gravid. As females gain weight during the breeding season, they may forage actively until the risk due to increasing locomotor impairment becomes too great and then change defensive strategy to greater reliance on crypsis. Without such a shift, widely foraging squamate reptiles may be less able than ambush foragers to exploit life-historical strategies demanding high current investment in reproduction.
Despite recent interest in refuge use, refuge characteristics and their relationships to refuge‐associated antipredatory defences have been relatively neglected. These topics were studied ...experimentally in the Cape girdled lizard, Cordylus cordylus. Lizards used crevices in novel situations under uncertain risk and when confronted by a human simulated predator. They preferred narrow crevices opening on only one side at ground level and orientated horizontally. Narrowness restricts access by predators, reduces detectability to a small visual angle and permits use of crevice‐specific defences, making the lizards difficult to dislodge. Limiting openings to one side decreases detectability by reducing light, limits attacks to one direction and permits further withdrawal from any opening. Crevices at ground level confer greater distance from and reduced visibility to an overhead predator. Horizontal orientation may reduce visibility to an overhead predator, but the preference could be an artefact of the greater ease of entering horizontal crevices. Pheromonal labelling of crevices by conspecific males did not influence short‐term crevice choices by males. Within crevices, C. cordylus pressed their dorsal surfaces against crevice roofs, pushing upward with their legs. They also positioned their tails to block access by predators to their bodies. We discuss these and related crevice‐associated defences in other animals.
In gekkonoid lizards, a few species of actively foraging eublepharids have been shown to identify prey chemicals by tongue-flicking and a few ambush foragers have been shown not to do so. Gekkonids ...in the omnivorous genus Rhacodactylus identify both plant and animal food by lingually sampling chemical cues. We conducted experiments with several species of geckos to provide further evidence on the evolutionary association between active foraging and lingually mediated prey chemical discrimination, to begin examination of the relationship between plant diet and chemosensory response to plant foods, and examine the utility of palatable plant chemicals as a pungency control for studies of insectivores. Chemosensory discriminations were investigated by observing tongue-flicking and biting responses to cotton swabs bearing animal prey chemicals, palatable plant chemicals, and control substances. The eublepharids Goniourosaurus luii and Eublepharis macularius both responded strongly to cricket chemicals, but not to control stimuli, whereas the gekkonids Gekko gecko and Uroplatus were unresponsive to all cues. These data support and extend the evidence for correlated evolution between prey chemical discrimination and foraging mode. They provide support of limited scope for the hypotheses that insectivorous geckos do not respond to plant chemicals and that such responses evolve with inclusion of plants in the diet. The lack of any strong response to plant chemicals by insectivores indicates the potential usefulness of plant chemical as pungency controls. Vomerolfactory discriminations are usually indicated by tongue-flicking, but several G. luii bit swabs bearing cricket chemicals without first tongue-flicking. This suggests that those individuals may have identified prey by olfaction, corroborating evidence for two other species of geckos.
In 2013, in response to an epidemic of ash dieback disease in England the previous year, we launched a Facebook-based game called Fraxinus to enable non-scientists to contribute to genomics studies ...of the pathogen that causes the disease and the ash trees that are devastated by it. Over a period of 51 weeks players were able to match computational alignments of genetic sequences in 78% of cases, and to improve them in 15% of cases. We also found that most players were only transiently interested in the game, and that the majority of the work done was performed by a small group of dedicated players. Based on our experiences we have built a linear model for the length of time that contributors are likely to donate to a crowd-sourced citizen science project. This model could serve a guide for the design and implementation of future crowd-sourced citizen science initiatives.
We conducted experimental tests of the responses to food chemicals presented on cotton swabs or ceramic tiles by tuataras and insectivorous species from several families of iguanian lizards. ...Tuataras, which are primarily carnivorous, never tongue flicked but frequently bit cotton balls bearing prey surface chemicals, suggesting that they may be able to detect airborne prey chemicals via olfaction. None of the lizards tested, the agamids Chamaeleo pardalis and Acanthosaura crucigera, the polychrotids Anolis smallwoodi and Chamaeleolis chamaeleonides, the phrynosomatids Sceloporus variabilis and Uta stansburiana, and the crotaphytid Crotaphytus collaris, exhibited any differential responses among prey chemicals, chemicals from palatable plants, and pungency control or odorless control stimuli. The findings buttress previous work that has shown a lack of prey chemical discrimination in ambush foragers, including all sampled iguanian insectivores. Given that all tested omnivores and herbivores respond strongly to plant chemicals, they are also consistent with the hypothesis that discriminatory lingual and biting responses to plant chemicals occur only in species having diets with a large plant component. Correlated evolution between herbivory and plant chemical discrimination remains to be established. For unknown reasons, Sceloporus variabilis tongue flicked less frequently in tile tests with romaine lettuce stimuli than with cricket and banana stimuli.
Male and female Cordylus cordylus can discriminate between tiles labeled by their own pheromones and tiles labeled by individuals of the same sex, as shown by elevated tongue-flick rates in which the ...tongue contacts only air above the tiles labeled by other individuals and tongue-flicks in which the tongue contacts the tiles themselves. Potential pheromone sources for these discriminations are the femoral glands, cloacal glands, generation glands, ventral skin, and excretory products. Although studied in few species, pheromonal discriminations between self and other individuals, familiar and unfamiliar individuals, and kin and unrelated individuals appear to be broadly distributed in lizards, occurring in Iguania and in both Gekkonoidea and Scincomorpha within Scleroglossa. Both sexes of C. cordylus defend territories against both sexes. An ability to distinguish pheromones of other individuals of the same sex from self-produced pheromones would allow detection of intruders, but pheromonal discriminations among individuals would be more useful. Adaptive functions of pheromonal discriminations for residents and nonresidents and discriminatory abilities required are discussed. Tongue-flicks touching labeled tiles differed between experimental conditions, suggesting vomerolfactory discrimination, but the interpretation of a similar difference for tongue-flicks that contacted no substrate is problematical. Such air tongue-flicks might indicate sampling of volatile molecules for delivery to the vomeronasal organs. Experiments are needed to conclusively determine the sensory bases of the discriminations and the role of air tongue-flicks.PUBLICATION ABSTRACT
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