Article
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

Escape behaviour is a common antipredator strategy of lizards. Here, we studied the effect of several variables predicted to have a potential effect on escape behaviour of lizards. Specifically, we measured the effects of starting distance (SD), distance to cover, sex–age and the observer’s head orientation on flight initiation distance (FID) in the common agama Agama agama. Agamas were approached in urban localities in Limbe city, Cameroon, where they were habituated to the presence of humans. We found no association between FID and SD, but individuals closer to potential cover had shorter FID than individuals farther from a refuge. Juveniles escaped later than adults, but no significant differences were found in the FID between adult males and females. Head direction of the approaching observer had no effect on FID. This is, to the best of our knowledge, the first study investigating factors affecting FID in common agamas, extending our knowledge on risk-related behaviour in lizards of Old World tropics.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

ResearchGate has not been able to resolve any citations for this publication.
Article
Full-text available
Animals often evaluate the degree of risk posed by a predator and respond accordingly. Since many predators orient their eyes towards prey while attacking, predator gaze and directness of approach could serve as conspicuous indicators of risk to prey. The ability to perceive these cues and discriminate between high and low predation risk should benefit prey species through both higher survival and decreased energy expenditure. We experimentally examined whether Indian rock lizards (Psammophilus dorsalis) can perceive these two indicators of predation risk by measuring the variation in their fleeing behaviour in response to type of gaze and approach by a human predator. Overall, we found that the gaze and approach of the predator influenced flight initiation distance, which also varied with attributes of the prey (i.e. size/sex and tail-raise behaviour). Flight initiation distance (FID) was 43 percent longer during direct approaches with direct gaze compared with tangential approaches with averted gaze. In further, exploratory, analyses, we found that FID was 23 percent shorter for adult male lizards than for female or young male (FYM) lizards. In addition, FYM lizards that showed a tail-raise display during approach had a 71 percent longer FID than those that did not. Our results suggest that multiple factors influence the decision to flee in animals. Further studies are needed to test the generality of these factors and to investigate the proximate mechanisms underlying flight decisions.
Article
Full-text available
Predation has long been implicated as a major selective force in the evolution of several morphological and behavioral characteristics of animals. The importance of predation during evolutionary time is clear, but growing evidence suggests that animals also have the ability to assess and behaviorally influence their risk of being preyed upon in ecological time (i.e., during their lifetime). We develop an abstraction of the predation process in which several components of predation risk are identified. A review of the literature indicates that an animal's ability to assess and behaviorally control one or more of these components strongly influences decision making in feeding animals, as well as in animals deciding when and how to escape predators, when and how to be social, or even, for fishes, when and how to breathe air. This review also reveals that such decision making reflects apparent trade-offs between the risk of predation and the benefits to be gained from engaging in a given activity. Despite this body of evidence, several areas in the study of animal behavior have received little or no attention from a predation perspective. We identify several such areas, the most important of which is that dealing with animal reproduction. Much work also remains regarding the precise nature of the risk of predation and how it is actually perceived by animals, and the extent to which they can behaviorally control their risk of predation. Mathematical models will likely play a major role in future work, and we suggest that modelers strive to consider the potential complexity in behavioral responses to predation risk. Overall, since virtually every animal is potential prey for others, research that seriously considers the influence of predation risk will provide significant insight into the nature of animal behavior.
Article
Full-text available
Publisher Summary The chapter describes a simple economic model that predicts in a qualitative way on how costs (lost feeding opportunity and risk) interact to produce an optimal flight distance from approaching predators. Animals often defer the decision to flee from an approaching predator and continue with their ongoing activities. The view is that, a profitable approach to the problem of why such decisions are deferred, and how they are eventually made, is to view the process as an economic, one in which the relative costs of fleeing and staying change as a predator approaches. It is suggested that the economic approach will prove useful in analyzing many aspects of predator-prey interactions.
Article
Full-text available
The present study investigates relationships among size, shape and speed in the Australian agamid lizard Amphibolurus nuchalis. Maximal running speed, body mass, snout-vent length, tail length, fore- and hind limb spans and thigh muscle mass were measured in 68 field-fresh individuals spanning the entire ontogenetic size range (1.3 48 g). Relative lengths of both foreand hind limbs decrease with increasing body mass (= negative allometry), whereas relative tail length and thigh muscle mass increase with body mass (= positive allometry). Repeatable and significant differences in maximal running speed exist among individuals. Maximal running speed scales as (body mass)0.161, and 59% of the variation in maximal speed was related to body mass. Based on the results of the present and previous studies, data on scaling of body proportions alone appear inadequate to infer scaling relationships of functional characters such as top speed. Surprisingly, individual variation in maximal speed is not related to individual variation in shape (relative limb, tail and body lengths). These components of overall shape are not independent; individuals tended to have either relatively long or relatively short limbs, tails and bodies for their body mass. Even the significant difference in multivariate shape between adult males and females has no measurable consequences for maximal speed. Speeds of field-fresh animals did not vary on a seasonal basis, and eight weeks of captivity had no effect on maximal running speeds. Gravid females and long-term (obese) captive lizards were both approximately 12% slower than field-fresh lizards.
Article
Full-text available
The amount of risk animals perceive in a given circumstance (i.e. their degree of 'fear') is a difficult motivational state to study. While many studies have used flight initiation distance as a proxy for fearfulness and examined the factors influencing the decision to flee, there is no general understanding of the relative importance of these factors. By identifying factors with large effect sizes, we can determine whether anti-predator strategies reduce fear, and we gain a unique perspective on the coevolution of predator and anti-predator behaviour. Based on an extensive review and formal meta-analysis, we found that predator traits that were associated with greater risk (speed, size, directness of approach), increased prey distance to refuge and experience with predators consistently amplified the perception of risk (in terms of flight initiation distance). While fish tolerated closer approach when in larger schools, other taxa had greater flight initiation distances when in larger groups. The presence of armoured and cryptic morphologies decreased perception of risk, but body temperature in lizards had no robust effect on flight initiation distance. We find that selection generally acts on prey to be sensitive to predator behaviour, as well as on prey to modify their behaviour and morphology.
Article
I tested biomechanical predictions that morphological proportions (snout-vent length, forelimb length, hindlimb length, tail length, and mass) and maximal sprinting and jumping ability have evolved concordantly among 15 species of Anolis lizards from Jamaica and Puerto Rico. Based on a phylogenetic hypothesis for these species, the ancestor reconstruction and contrast approaches were used to test hypotheses that variables coevolved. Evolutionary change in all morphological and performance variables scales positively with evolution of body size (represented by snout-vent length); size evolution accounts for greater than 50% of the variance in sprinting and jumping evolution. With the effect of the evolution of body size removed, increases in hindlimb length are associated with increases in sprinting and jumping capability. When further variables are removed, evolution in forelimb and tail length exhibits a negative relationship with evolution of both performance measures. The success of the biomechanical predictions indicates that the assumption that evolution in other variables (e.g., muscle mass and composition) did not affect performance evolution is probably correct; evolution of the morphological variables accounts for approximately 80% of the evolutionary change in performance ability. In this case, however, such assumptions are clade-specific; extrapolation to taxa outside the clade is thus unwarranted. The results have implications concerning ecomorphological evolution. The observed relationship between forelimb and tail length and ecology probably is a spurious result of the correlation between these variables and hindlimb length. Further, because the evolution of jumping and sprinting ability are closely linked, the ability to adapt to certain microhabitats may be limited.
Article
Systematic reviews and meta-analyses often examine data from diverse taxa to identify general patterns of effect sizes. Meta-analyses that focus on identifying generalisations in a single taxon are also valuable because species in a taxon are more likely to share similar unique constraints. We conducted a comprehensive phylogenetic meta-analysis of flight initiation distance in lizards. Flight initiation distance (FID) is a common metric used to quantify risk-taking and has previously been shown to reflect adaptive decision-making. The past decade has seen an explosion of studies focused on quantifying FID in lizards, and, because lizards occur in a wide range of habitats, are ecologically diverse, and are typically smaller and differ physiologically from the better studied mammals and birds, they are worthy of detailed examination. We found that variables that reflect the costs or benefits of flight (being engaged in social interactions, having food available) as well as certain predator effects (predator size and approach speed) had large effects on FID in the directions predicted by optimal escape theory. Variables that were associated with morphology (with the exception of crypsis) and physiology had relatively small effects, whereas habitat selection factors typically had moderate to large effect sizes. Lizards, like other taxa, are very sensitive to the costs of flight.
Article
Antipredator behavior and risk assessment of many species are affected by the presence of humans and their activities. Previous studies have largely been conducted on birds and mammals and relatively less is known about human impacts on reptiles. We used flight initiation distance (FID) as a measure of risk assessment in inland blue-tailed skinks (Emoia impar) and tested the direct and indirect effects of humans on risk assessment. We first examined the effects of varying levels and types of human disturbance and activity on skink FID. We found that skinks flushed at significantly longer distances in areas with the least human activity. We then tested the degree to which skinks are able to discriminate different numbers of humans by comparing FID across three different types of approaches. Skinks did not significantly differentiate between a single approacher and a single approacher coming from a group of two other people, but did flush at greater distances when approached by three people simultaneously. Although skinks are not directly harvested or harassed by humans, they have refined human discrimination abilities. Overall, skinks habituate to a variety of human activities and perceive a larger threat when the number of human approachers is greater.
Article
Escape theory predicts flight initiation distance (FID), distance between predator and prey when escape begins, for factors affecting costs of fleeing and not fleeing. Starting distance (SD), distance between predator and prey when approach begins, appears to affect FIE) for so,e species and risk levels, but not others. I predicted that in an active forager under low risk FID would appear to increase as SD increases due to (1) inclusion of SDs shorter than optimal FID and (2) spontaneous movements not motivated by escape. I predicted that FID and SD are unrelated at low risk when SDs shorter than optimal FID and spontaneous movements are excluded. When I approached the lizard Aspidoscelis exsanguis, an active forager, all predictions were confirmed. Effects of short SD and spontaneous movement might account for relationships between FID and SD in some birds and lizards. Nevertheless, as a predator approaches, costs of monitoring may increase, as may assessed risk and risk-averse errors due to shorter available assessment time. Risk-aversion might account for restriction of the relationship between FID and SD to high risk levels in an ambushing lizard species, for which spontaneous movements are far less frequent than for active foragers such as A. exsanguis. Although FID and SD are unrelated in A. exsanguis, SD and the related alert distance can provide valuable insights into risk assessment in other taxa having escape movements distinct from other movements. Present findings emphasize the importance of distinguishing between escape and other movements that may be initiated during approaches. A previously untested prediction of escape theory is that escape begins immediately when a prey detects an approaching predator closer than optimal FID, leading to the prediction of a slope of 1.0 between FID and SD. This prediction was confirmed for SDs less than 1.5 m.
Article
We compared the escape behaviour of juvenile and adult Psammodromus algirus lizards, by using data of escape performance in the laboratory and field observations of escape behaviour. We specifically examined whether a differential escape response is a constraint of body size, or whether juveniles behave differently in order to maximize their escape possibilities taking into account their size-related speed limitations. In the laboratory, juvenile lizards were slower than adult lizards, and escaped during less time and to shorter distances, even when removing the effect of body size. In the field, juveniles allowed closer approaches and after a short flight usually did not hide immediately, but did so after successive short runs if the attack persists. Approach distance of juveniles was not affected by habitat, but initial and total flight distances were shorter in covered microhabitats. There was no significant effect of environmental temperature on approach and initial flight distances of juveniles. However, the total flight distances were significantly correlated with air temperatures.
Article
Escape behaviour often differs between sexes, reproductive states and ages. Escape theory predicts that flight initiation distance (FID = predator-prey distance when escape begins) increases as predation risk and fitness increase, and decreases as cost of escaping increases. Similar predictions hold for distance fled and refuge entry, suggesting that age and sex differences in escape behaviour may occur when risk, fitness, and opportunity costs differ. I studied such differences in two lizard species and reviewed relevant literature on escape by lizards. In Sceloporus virgatus no difference occurred between sexes or female reproductive states in FID, distance fled, distance from refuge, or probability of entering refuge. In S. jarrovii juveniles had shorter FID and distance fled than adults; juveniles were closer than females to refuge, but this did not affect FID or distance fled. Juveniles were more likely than adults to be on rocks and use them as refuges. The literature review showed that sexual dimorphism in FID occurs in about 1/5 of species (male FID usually > female FID), but distance fled differed between sexes in only 1 of 21 species. Juveniles had shorter FID than adults in all of five species; the relationship between age and distance fled was highly variable. Reasons for patterns of age/sex differences are discussed. Because age and sex differences in these factors and escape strategy can alter multiple components affecting optimality, sometimes in opposite ways, these factors and escape strategy must be known to predict effects of age, sex and reproductive state on escape.
Article
Examined the ability of basking black iguanas ( Ctenosaura similis) to discriminate risk from a person walking directly toward them vs one walking tangentially by them when the person looked either directly at them or away from them. All iguanas were tested near the Organization for Tropical Studies Palo Verde, Costa Rica field station or the refuge hacienda, where they were habituated to the presence of humans. The animals responded most quickly to a direct approach with a direct gaze, followed by a direct approach with an averted gaze and a tangential approach with a direct gaze, and least quickly to a tangential approach with an averted gaze. Behavioral responses were not related to body size but were intercorrelated. These results demonstrate that iguanas can use both body orientation and gaze direction to assess the threat of an approaching predator. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Article
Flight initiation distance in relation to substratum type, sex, reproductive status and tail condition was studied in two lacertid lizards with contrasting habits: the ground-dwelling common lizard Zootoca vivipara and the rupicolous Horvath's rock lizard Iberolacerta horvathi. These species were studied in sympatric populations in a mountain area in North-Eastern Italy, Tarvisio Forest. Mean escape distance was significantly higher in I. horvathi than in Z. vivipara. In both species there were significant differences between sexes, with males escaping at longer distances than females but there were no significant differences between adults and subadults. In both species there were no differences in escape distance of females in different reproductive states. In Z. vivipara specimens with broken tails escaped at a shorter distance than individuals with intact tails. Substratum type had a significant effect on escape distance in both species. How close should an animal allow a poten-tial predator to approach before fleeing to a refuge? This is a crucial question for the sur-vival of most animal population, but it has been only rarely tested on vertebrate species up to now (e.g. Kramer and Bonenfant, 1997; Martín and López, 2000a, b). Antipredatory behaviour is essential, especially in those animal species which are basal or intermediate in a trophic chain. Lizards are among the most widely pre-dated organisms in the temperate zone ecosys-tems, being preyed upon by a variety of preda-tors including birds of prey, carnivorous mam-mals, snakes, etc. (e.g., see Agrimi and Luiselli, 1994; Martín and López, 1996). Indeed, there is a great wealth of studies investigating the es-1 -Agenzia Regionale per i Parchi (ARP), Regione Lazio,
Article
Flight initiation distance (FID), or the distance between a prey animal and an approaching intruder when the prey initiates its escape, is an important factor in wildlife management. We conducted a study on individually identified yellow-bellied marmots (Marmota flaviventris) to test 3 key assumptions of FID research: (1) differences in individual responses are small enough so as not to confound results; (2) pseudoreplication may bias results; and (3) habituation and sensitization can be studied without knowledge of individuals. We found that individual identity was not a significant predictor of FID. Furthermore, a moderate degree of pseudoreplication did not significantly affect the results of most analyses. However, individuals differed greatly in their rates of habituation, such that habituation was apparent only when individual identity was known and could not be detected without knowledge of individuals. If our marmot results can be generalized to other species, they suggest that researchers need not be concerned about individual identity when studying variables largely dependent on environmental factors, but that identification of individuals is important for studies of properties of individuals, such as habituation.
Article
When approached by humans, virtually all species flee, but we lack an understanding of the factors that influence flight response among species. Understanding this variation may allow us to understand how ‘fear’ structures communities, as well as to predict which species are likely to coexist with humans. I used flight initiation distance (FID) as a comparative metric of wariness and examined the relative importance of life history and natural history traits in explaining variation in FID in 150 species of birds. In a series of comparative analyses, I used independent contrasts to control for phylogenetic similarity and regressed continuous life history traits against flight initiation distance. Body size had a large and significant effect in explaining variation in flightiness: larger species initiated flight at greater distances than smaller species. After controlling for variation explained by body size, there was a nonsignificant positive relation between the age of first reproduction and FID. There were no relations between FID and clutch size, number of days spent feeding young, longevity, or habitat density. I used concentrated changes tests to look for evidence of coevolution between flightiness and dichotomous traits. Flightiness evolved multiple times and some clades were flightier than others. Flightiness was more likely to evolve in omnivorous/carnivorous species and in cooperatively breeding species. These results suggest that body size and age of first reproduction are important in explaining variation in disturbance tolerance in birds, and that species that capture live prey and those that are highly social are relatively wary. The results suggest a novel mechanism of how anthropogenic disturbance may contribute to extinction.
Article
Several aspects of escape behavior are predictable by escape theory based on expected costs due to predation risk and escaping. Although the function of pursuit-deterrent signaling is to dissuade predators from attack, relatively little is known about relationships between specific components of escape and the signaling behavior. I studied effects of the risk factor distance from refuge on flight initiation distance, distance fled, probability of entering refuge, and the distance between predator (an approaching human) and prey when pursuit-deterrent display begins (display distance) in the Cuban curly-tailed lizard (Leiocephalus carinatus). I also investigated whether starting distance (distance between predator and prey when approach begins) affects escape behaviors. As predicted by escape theory, flight initiation distance and distance fled were greater and refuge entry was less probable at greater distance from refuge, indicating that qualitative predictions of escape theory apply to pursuit deterrent signalers. Starting distance did not affect escape behaviors, presumably because it did not affect perceived risk, but might do so at a faster approach speed. Display distance and flight initiation distance were identical in the data set analyzed, but individuals sometimes perform tail displays prior to fleeing. Interspecific variation in the timing of pursuit-deterrent displays is discussed, as are possible reasons for observed differences in the effect of starting distance.
Article
To understand how selection acts on performance capacity, the ecological role of the performance trait being measured must be determined. Knowing if and when an animal uses maximal performance capacity may give insight into what specific selective pressures may be acting on performance, because individuals are expected to use close to maximal capacity only in contexts important to survival or reproductive success. Furthermore, if an ecological context is important, poor performers are expected to compensate behaviorally. To understand the relative roles of natural and sexual selection on maximal sprint speed capacity we measured maximal sprint speed of collared lizards (Crotaphytus collaris) in the laboratory and field-realized sprint speed for the same individuals in three different contexts (foraging, escaping a predator, and responding to a rival intruder). Females used closer to maximal speed while escaping predators than in the other contexts. Adult males, on the other hand, used closer to maximal speed while responding to an unfamiliar male intruder tethered within their territory. Sprint speeds during foraging attempts were far below maximal capacity for all lizards. Yearlings appeared to compensate for having lower absolute maximal capacity by using a greater percentage of their maximal capacity while foraging and escaping predators than did adults of either sex. We also found evidence for compensation within age and sex classes, where slower individuals used a greater percentage of their maximal capacity than faster individuals. However, this was true only while foraging and escaping predators and not while responding to a rival. Collared lizards appeared to choose microhabitats near refugia such that maximal speed was not necessary to escape predators. Although natural selection for predator avoidance cannot be ruled out as a selective force acting on locomotor performance in collared lizards, intrasexual selection for territory maintenance may be more important for territorial males.
Article
1. Size relationships are central in structuring trophic linkages within food webs, leading to suggestions that the dietary niche of smaller carnivores is nested within that of larger species. However, past analyses have not taken into account the differing selection shown by carnivores for specific size ranges of prey, nor the extent to which the greater carcass mass of larger prey outweighs the greater numerical representation of smaller prey species in the predator diet. Furthermore, the top-down impact that predation has on prey abundance cannot be assessed simply in terms of the number of predator species involved. 2. Records of found carcasses and cause of death assembled over 46 years in the Kruger National Park, South Africa, corrected for under-recording of smaller species, enabled a definitive assessment of size relationships between large mammalian carnivores and their ungulate prey. Five carnivore species were considered, including lion (Panthera leo), leopard (Panthera pardus), cheetah (Acinonyx jubatus), African wild dog (Lycaon pictus) and spotted hyena (Crocuta crocuta), and 22 herbivore prey species larger than 10 kg in adult body mass. 3. These carnivores selectively favoured prey species approximately half to twice their mass, within a total prey size range from an order of magnitude below to an order of magnitude above the body mass of the predator. The three smallest carnivores, i.e. leopard, cheetah and wild dog, showed high similarity in prey species favoured. Despite overlap in prey size range, each carnivore showed a distinct dietary preference. 4. Almost all mortality was through the agency of a predator for ungulate species up to the size of a giraffe (800-1200 kg). Ungulates larger than twice the mass of the predator contributed substantially to the dietary intake of lions, despite the low proportional mortality inflicted by predation on these species. Only for megaherbivores substantially exceeding 1000 kg in adult body mass did predation become a negligible cause of mortality. 5. Hence, the relative size of predators and prey had a pervasive structuring influence on biomass fluxes within this large-mammal food web. Nevertheless, the large carnivore assemblage was dominated overwhelmingly by the largest predator, which contributed the major share of animals killed across a wide size range.
ModEvA: model evaluation and analysis. R package, version 1
  • A M Barbosa
  • J Brown
  • A Jiménez-Valverde
  • R Real
Barbosa, A.M., Brown, J., Jiménez-Valverde, A., Real, R. (2014): ModEvA: model evaluation and analysis. R package, version 1.3. https://www.r-project.org.
Final revision received
  • Luca Luiselli
Submitted: October 21, 2018. Final revision received: December 10, 2018. Accepted: December 12, 2018. Associate Editor: Luca Luiselli.