Canadian Journal of Zoology
Escape Behavior of Side -Blotched Lizards in Response to Model Predators
Journal: Canadian Journal of Zoology
Manuscript ID cjz-2016-0255.R3
Manuscript Type: Article
Date Submitted by the Author: 02-Apr-2017
Complete List of Authors: Wagner, E.A.; University of Wisconsin Stevens Point, Biology Zani, Peter; University of Wisconsin-Stevens Point, Department of Biology; Draft antipredator behavior, geographic variation, predator-dependent escape Keyword: response, common side-blotched lizards, Uta stansburiana, latitude
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Escape Behavior of Side-Blotched Lizards in Response
to Model Predators
E.A. Wagner and P.A. Zani
Draft
E.A. Wagner and P.A. Zani. Department of Biology, University of Wisconsin-
Stevens Point, Stevens Point, WI 54481, USA.
Corresponding author: P.A. Zani ([email protected]).
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Escape Behavior of Side-Blotched Lizards in Response to Model Predators
E.A. Wagner and P.A. Zani
Abstract: Few field studies have tested for geographic variation in escape behavior and even fewer have examined responses of prey to multiple predators despite most prey occurring in multipredator environments. We performed 458 escape trials on common side-blotched lizards (Uta stansburiana Baird and Girard, 1852) from 10 populations that differed in predator abundances. We quantified escape behavior of side-blotched lizards when approached with one of two model predators: a lizard ( Crotaphytus bicinctores
Smith and Tanner, 1972) or a snake ( Coluber mormon Fitch, 1981). Our results suggest that the escape responses of side-blotchedDraft lizards (flight initiation distance, distance fled, refuge entry) do not differ when approached by either a model predatory lizard or snake.
Nor do the escape responses of individual side-blotched lizards differ in relation to the abundances of predatory lizards or snakes in the local environment. Rather, only the directness of fleeing toward a refuge differed based on model predator type with side- blotched lizards fleeing more directly toward a refuge in response to a model lizard.
These findings suggest that side-blotched lizards tend to use a more generalized escape response to approaching predators.
Key words: antipredator behavior, geographic variation, latitude, predator- dependent escape response, Uta stansburiana, common side-blotched lizards
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Introduction
To evade predators, prey must develop and use relevant escape strategies. A prey
species is likely to maximize its time spent foraging or attracting mates when its escape
responses are tailored to counter particular predation strategies or in particular predation
environments. For example, Trinidadian guppies (Poecilia reticulata Peters, 1859) forage
less in the presence of a high-risk predator, freshwater prawns (Macrobrachium
crenulatum Holthuis, 1950), but forage for longer periods of time in the presence of a
low-risk predator, pike cichlids (Crenicichla alta Eigenmann, 1912)(Magurran 1999). In
some instances, predator-specific escapeDraft responses can be antagonistic. A particular
escape tactic for one predator (e.g., seeking refuge) may increase the risk of attack from
another predator (e.g., one foraging for prey in a refuge). For example, wall lizards
(Podarcis muralis Laurenti, 1768) fleeing from avian predators often use rock crevices
that may also contain predatory snakes (Amo et al. 2005). In populations that contain
predators, such as smooth snakes (Coronella austriaca Laurenti, 1768), wall lizards
spend more time detecting the chemosensory cues released by snakes, leading to a
decrease of refuge entries by the lizards (Amo et al. 2005). Taken together, such findings
suggest that the use of contextualized responses may enhance the escape behavior of a
prey species, especially when predators differ in their foraging strategies. Yet relatively
little research has focused on the contextual responses of prey to different predators or to
different predator environments (e.g., Sherbrooke 2008; Staudinger et al. 2011; for
review see Lima and Dill 1990).
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In environments containing multiple types of predators, behavioral variation is compounded as prey may have evolved predator-specific responses for each predator that they encounter (Ydenberg and Dill 1986; Lima and Bednekoff 1999; Blumstein 2006).
Moreover, predator-specific responses often differ amongst populations occurring in disparate regions due to behavioral plasticity or to the evolution of escape behavior
(Schall and Pianka 1980; Foster 1999; Magurran 1999). Predator-specific responses have been shown to vary geographically in multipredator environments for prey species such as fish (Magurran 1999), reptiles (Brock et al. 2014), mammals (Coss et al. 1993), and birds (Díaz et al. 2013). These results suggest certain environmental conditions that vary across geographic regions can favorDraft prey species with locally-adapted anti-predator responses (e.g., Foster 1999). However, many previous studies of predator-prey interactions have only focused on one-prey-one-predator scenarios in single-predator environments (Lima and Dill 1990; Ilany and Eilam 2007; Stankowich and Coss 2007) even though many prey species coexist with a variety of predators across their geographic distribution (but see Díaz et al. 2013, 2015; Samia et al. 2015). Thus, the role of context during the escape response of prey is relatively unknown for predator-prey systems occurring in multipredator environments (but see Lima 1992; Blumstein et al. 2004;
Blumstein and Daniel 2005; Díaz et al. 2013).
The logic of the economics of escape behavior ( sensu Ydenberg and Dill 1986) extended across a geographic scale predicts that the behavior of a prey species should be optimized in each different predation environment. Moreover, geographic variation in escape behavior should be caused by different predator regimes to maintain predator-
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specific responses that counteract the foraging tactics of each suite of predators. Thus,
escape behavior is likely to vary in relation to latitude or variables that correlate with
latitude, such as predator abundances (e.g., Díaz et al. 2013, 2015; Samia et al. 2015).
Likewise, escape behavior is also predicted to be related to predator type (e.g., Blumstein
2006; Sherbrooke 2008; Staudinger et al. 2011). The goals of the present study are to
clarify (i) whether the escape behavior of prey species varies geographically and (ii )
whether any such variation differs based on model predator type as well as local predator
abundances.
To test these ideas, we examined variation among populations in the anti- predatory behavior of a widespread Draftprey species (common side-blotched lizards, Uta stansburiana Baird and Girard, 1852) related to two different predator types (other
predatory lizards or snakes) by quantifying several aspects of escape behavior (flight
initiation distance [FID], distance fled [DF], refuge angle [RA], and refuge entry [RE]).
We hypothesize that when assessed among environments, the escape responses of side-
blotched lizards will differ in such a way so as to minimize risk in each population (Table
1). Namely, altered risk related to changes in predator abundances and the presence or
absence of certain predator types should lead to concomitant changes in wariness. Thus,
we predict that escape responses of side-blotched lizards are predator-specific in each
population. Alternatively, the absence of variation across diverse predator regimes may
be evidence of conserved or generalized behavioral responses in prey species.
Study System
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To investigate context-dependent escape behavior, we examined populations of side-blotched lizards, which are small (adult snout-vent length [SVL] = 40-55 mm) phrynosomatid lizards common throughout the western United States and Mexico. Side- blotched lizards are a common prey item for many predatory lizards and snakes (Wilson
1991). However, the suite of co-occurring predators varies geographically (Tinkle 1967;
Nussbaum et al. 1983) and the predator diversity and distribution across northern Nevada and the Pacific Northwest changes markedly (Wilson 1991).
All locations where Uta are known to occur also occur within geographic range of multiple predatory snakes such as yellow-bellied racers ( Coluber mormon ), gopher snakes ( Pituophis catenifer )(Blainville,Draft 1835), and Pacific rattlesnakes ( Crotalus oreganus Holbrook, 1840), yet the relative abundances of these predators can be noticeably different at different sites. Like snakes, populations of predatory lizards also differ geographically in their relative abundances. The predatory lizards in northern
Nevada and the Pacific Northwest include Great-Basin collared lizards ( Crotaphytus bicinctores ), long-nosed leopard lizards ( Gambelia wislizenii )(Baird and Girard, 1852), desert spiny lizards ( Sceloporus magister Hallowell, 1854), tiger whiptail lizards
(Aspidoscelis tigris )(Baird and Girard, 1852), and zebra-tailed lizards ( Callisaurus draconoides Blainville, 1835). The distributions of predatory lizards are generally limited to the more southern portions of the distribution of Uta . As latitude increases from central
Nevada, the suite of predatory lizards decreases from five species at ~40°N and lower
(those listed above; see Fig. 1) to three species between 40–42.5°N (C. bicinctores , G. wislizenii , A. tigris ) to only one species between 42.5–43°N (either G. wislizenii or A.
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tigris ), with no predatory lizards commonly occurring north ~43°N (see Nussbaum et al.
1983; Bula et al. 2014). Thus some populations of Uta coexist with multiple predators of
multiple types (both predatory lizards and snakes) while other populations coexist with
less abundant predators as well as fewer species or types of predators. This pattern of
natural geographic variation in predation environment leads to the intriguing possibility
of predator-specific escape responses of Uta .
The differences in prey-capture and -subjugation strategies of lizards and snakes
allow us to predict that prey populations that are sympatric with both types of predators
will maintain and use a greater array of escape tactics when approached by either a lizard or a snake predator. However, prey Draftpopulations sympatric with only predatory snake may use ( i) snake-specific escape behavior in response to either predator, ( ii ) lizard- or snake-
specific escape behavior in response to their respective predators, or ( iii ) snake-specific
responses to a snake predator, but lack an appropriate response to a lizard predator due to
relaxed selection in the absence of predatory lizards. Along with these predictions, the
geographically separated study sites used in this study allow us to predict that prey
populations will exhibit spatial variation in escape tactics due to the specific selective
pressures of predation at each site.
Materials and methods
Study Sites
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All sites (named as in Bula et al. 2014) occupied typical sage-steppe (Frenchman
Coulee [FC], Wrights Point [WP], Summer Lake [SL], Coleman Hills [CH], Trout Creek
[TC], Long Draw [LD]), salt scrub (Lovelock [LV], Walker Lake [WL]), or juniper woodland (Horse Ridge [HR], Hampton Buttes [HB]) habitat and ranged across the southern Columbia Plateau of Washington State and Northern Great Basin Desert of
Nevada and Oregon. The 10 sites included in this study (Fig. 1) are described elsewhere in more detail (see Bula et al. 2014).
Estimation of Predator Abundances Each study site was characterizedDraft by a unique composition of predator richness and abundance. We used measurement of predator abundances as a surrogate for predation pressure at each site because direct observation of actual predation events is rare (Tinkle 1967; Nussbaum et al. 1983). We began by using information from previous researchers (e.g., Wilson 1991) and our own field sightings from previous years (Bula et al. 2014) to compile a list of predators. However, certain predators (notably mammals) or species that prey on inactive animals (e.g., night snakes [ Hypsiglena Cope, 1860]) were excluded from our list as these predators are less likely to affect the escape behavior of active side-blotched lizards. Because we were unable to determine actual predation probability directly, we recorded the number of predators observed / researcher / km travelled (termed “predator abundances”)(Table 2), which is similar to methods used previously (e.g., Pianka 1970; Calsbeek and Sinervo 2002). As part of this estimation, 2-4 researchers conducted censuses of suitable habitat by walking transects separated by 5 m
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in a systematic, non-overlapping fashion and recorded the types and numbers of all
predators observed. Censuses were constrained to occur during favorable conditions and
to be at least 30-min long covering at least 1 km, but were not otherwise standardized.
Handheld GPS was used to determine the distance covered by the observers each day.
During these censuses we attempted to count each individual only once and to search an
area only once during each observation period. We then calculated the average predators
observed / person / km as an estimate of predator abundances. Data for predator
abundances were collected in the same year as the escape-behavior trials.
Model Predators Draft To test Uta escape responses in the field, we created two model predators
approximating the morphological characteristics of representative predator groups. A 13-
cm long (SVL) rubber lizard was painted using Testors brand model enamel paints to
match a Great Basin collared lizard ( Crotaphytus bicinctores )(Fig. 2a). Similarly, a 1.1-m
long rubber snake was painted to match a yellow-bellied racer ( Coluber mormon )(Fig.
2b) and shaped into a typical periscope-hunting position. These life-sized models were
separately affixed via 1-m long, 3-mm thick wires to 1-m long metal golf-club shafts (~2
cm diameter). When extended at arm’s length the distance between the snout of the
model and the operator’s feet was over 2 m (Fig. 2c) and was sufficient to evoke a typical
escape response (see Zani et al. 2009) without apparent awareness by the subject of the
model operator. Both lizard and snake models were presented to side-blotched lizards at
all sites. Yellow-bellied racers were sympatric with Uta at all study sites, though were not
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observed at two sites during our study (HR and HB). Great-Basin collared lizards, on the other hand, were only sympatric with Uta at the four southern-most sites (WL, LV, LD, and TC; see Fig. 1). Another predatory lizard (long-nosed leopard lizards) commonly occurred at two other study sites that lacked collared lizards (SL and CH; see Table 2).
Escape Behavior Data Collection
Data on escape behavior were collected in three separate years: 2010 (FC, HR,
WP, SL, LD, LV), 2013 (HB, CH, WL), and 2015 (TC). In each year, data were collected from 6 June to 14 July (Julian days 157-195) on days of favorable weather (sunny and warm). All data were collected betweenDraft 08:00 and 18:00, starting about 1 h after the first Uta was sighted each day to ensure that lizards were near their thermoregulatory set point. In each case, a lizard was only included in the study if it was deemed undisturbed at the start of the trial as determined by movements of less than 0.25 m between first observation and trial initiation. In most instances lizards were first located from >5 m away and the lizard gave no sign of reacting to the researchers.
Upon locating a potential subject, care was taken not to move rapidly or alert the subject to our presence while 1-2 additional observers would position themselves to within no closer than 5 m of the subject while trying to remain unseen (by using natural cover objects as blinds). This allowed us to observe the likely escape routes (see Fig. 2d), but not affect the escape behavior of the subjects. Upon achieving their observation posts, observers would remain motionless while observing the subject through binoculars. The subject was immediately approached by a model operator starting from a distance > 5 m
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within 3-5 min of initial detection by us. If a subject moved during the time it took to
position the observers that trial was abandoned. The model operator used a practiced
approach with a slow, but steady speed of approximately 0.5 m/s. At the outset of the
approach the pole supporting the model predator was extended at arm’s length and the
model was held as close to the ground as terrain and vegetation allowed (usually a height
of ~ 6-8 cm)(Fig. 2c), but keeping the model within sight of the subject. The model
operator proceeded directly toward each subject until an identifiable escape response by
the subject. In each case, a subject was only included in the study if it maintained focus
on the model predator’s approach and not the model operator, which could be determined by the angle at which lizards held orDraft turned their heads. Because of the proximity of the model relative to the operator (Fig. 2c), nearly every subject focused its attention solely
on the model and gave no indication of being aware of any of the observers, including the
model operator.
When the subject finished its response to the model, we would mark the path
taken by the subject by placing colored plastic poker chips at the location of the model at
the initiation of the escape response, at the initial location of the subject, along the escape
path taken by the subject, and at the final resting place of the subject. An escape was
considered terminated when the subject stopped more than momentarily; brief pauses of
<1 sec. were disregarded except to note changes in escape direction. A subject that
entered a crevice or bush from which a predator could not likely extract it (subjectively
determined by us) was considered to have entered a refuge. The actual model predator
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used during each trial alternated between the lizard and snake models. The approach direction of the model was randomly predetermined using Microsoft Excel.
Upon completion of a trial we measured linear distances using a flexible tape (for lengths < 5 m) or surveyor’s wheel (for > 5 m). These distances, which follow the terminology of Cooper and Blumstein (2015) included (i) flight initiation distance (FID, shortest distance between model predator and subject at initial escape response), and (ii) distance fled (DF, distance along the escape path from the initial perch to where the subject stopped permanently).
In addition to escape distances, we measured escape direction of subjects (measured using a handheld compass)Draft in two ways: ( i) escape angle (EA; absolute value of difference between subject's escape angle and predator's approach angle) and ( ii ) refuge angle (RA; absolute value of difference between subject’s escape angle and nearest refuge direction). However, EA was only used to calculate RA and not analyzed on its own because we had no clear expectation that escape angle would vary geographically or with predator type. Escape directions were plotted as population averages on an axial scale of 0-180° for clarity. We also scored refuge entry (RE) for each subject that entered a potential refuge (again, subjectively determined by us).
Regardless of whether or not a subject actually entered the refuge, we identified the nearest refuge as a rock crevice or bush where subjects could enter, but predatory lizards or snakes could not. Finally, we measured cover density (number of shrubs greater than
20-cm diameter within 5 m of initial perch) for use as a variable in statistical analyses.
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Data Analysis
For statistical analyses we initially considered latitude of population origin, model
predator type (lizard, snake), and estimates of predation environment (abundances of
predatory lizards and snakes) as independent variables in analyses of measures of escape
behavior (FID, DF, RA, RE). In addition, because cover density may both covary with
predation environment as well as affect escape behavior (Martín and López 1995; Cooper
2003; Pietrek et al. 2009), we considered brush cover density as a covariate. We began by
performing correlations among these variables (latitude, model type, predator
abundances, and cover density) as a test of multicollinearity and excluded factors showing significant inter-relationships.Draft Next, we tested for the appropriateness of analysis of covariance (ANCOVA) by including cover density as a covariate in analyses.
To do this, we first tested for homogeneity of regression coefficients, a requirement of
ANCOVA, as outlined by Pedhazur (1982: 497). We performed change-in-R2 tests by
calculating the relevant R2 values and then testing the increment in proportion of variance
explained by the covariate and independent variables. If ANCOVA was deemed
inappropriate we instead performed multiple regressions that included cover density as an
independent variable. For directional data, we used angular-linear correlations as outlined
by Zar (1999). We tested for relationships between the independent variables and refuge
angle (escape angle relative to refuge direction). Finally, for refuge entry (RE), we used
logistic regression to test for statistical effects of the independent variables.
Linear and proportional variables are reported as mean ± 1 S.E.M. However, for
computational reasons directional variables are reported as mean ± 95% confidence
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interval (see Zar 1999). All statistical tests were performed using JMP 10.0 (SAS, Cary,
NC, 2012), with the exception of change-in-R2 tests and angular-linear correlations, which were computed in Microsoft Excel. Due to the large number of statistical tests, we applied the principle of a Bonferroni correction and only consider P < 0.001 to be statistically significant, but report P > 0.001 and < 0.05 as marginally insignificant.
Results
We measured the predator abundancesDraft from 10 different populations of side- blotched lizards over 75 sampling periods (7.5 ± 1.85 periods; range = 3-23; Table 2).
Concurrent with measurement of predator abundances, we performed 458 escape trials and measured local cover density for side-blotched lizards from these same 10 populations with 45.8 ± 3.13 trials / population (range = 31-60; Table 3). These trials were evenly split between trials using a model lizard (23.4 ± 1.51 trials / population) or model snake (22.4 ± 1.65 trials / population).
Preliminary correlational results among independent variables indicated potential multicollinearity between latitude and cover density ( F1,455 = 33.78, P < 0.001) as well as between latitude and predatory lizard abundance ( F1,8 = 15.72, P = 0.004), but not predatory snakes ( F1,8 = 0.03, P = 0.861). Thus, to avoid confounding results, we excluded latitude from further analyses and performed analyses with model type, predator abundance, and cover density as independent variables. Furthermore, in all cases
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ANCOVA was deemed inappropriate due to heterogeneous regression coefficients (P's <
0.05). Therefore, we analyzed escape behavior using full-factorial multiple regression
(FID, DF) or logistic regression (RE).
Flight Initiation Distance (FID)
Side-blotched lizard allowed a model predator to get to within 0.34 ± 0.020 m
before escaping (range = 0.0-3.36 m). The difference in FID between the model lizard
(0.34 ± 0.022 m; 0.06-3.30 m) and snake (0.35 ± 0.033; 0.00-3.36 m) was only 0.01 m.
Even though FID values were found to be extremely short, they are consistent with FID values of Uta when approached by observersDraft without models (unpublished data; Zani et al. 2009). Multiple regression in which model predator type, lizard and snake
abundances, and local cover density (as well as all interactions) were included as
independent variables indicated that the full model was marginally able to predict
2 variation in FID ( F15,441 = 1.81, P = 0.032, R = 0.058). Post-hoc effect tests revealed that
the main effects of predatory lizard and snake abundances as well as their interactions
with cover density, but not model predator type, were related to variation in FID (Table
4).
Distance fled (DF)
Side-blotched lizard ran 1.29 ± 0.089 m upon escaping (range = 0.02-18.8 m) on
average. The difference in DF between the model lizard (0.87 ± 0.059 m; 0.06-5.05 m)
and snake (1.74 ± 0.167; 0.02-18.8 m) was 0.87 m. Multiple regression in which model
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predator type, lizard and snake abundances, and local cover density (as well as all interactions) were included as independent variables indicated that significant variation in
2 DF could be explained by these predictors (F15,441 = 5.65, P < 0.001, R = 0.159).
However, post-hoc effect tests revealed no clear explanation for variation in DF; only two interactions involving the abundances of lizards and snakes were even marginally insignificant (Table 4).
Refuge Angle (RA)
Side-blotched lizards ran 112.3 ± 6.06° (avg. ± 95% C.I.) relative to the approaching predator model (range Draft= 0-180° with 0° indicating approach of model predator; Fig. 3a). The difference in escape angle between the model lizard (113.7 ±
8.79°; 0-180°) and snake (110.9 ± 8.41; 0-180°) was only 3°. Relative to the nearest refuge, side-blotched lizard ran 74.5 ± 7.02° (range = 0-180° with 0° indicating direction of nearest refuge; Fig. 3b). The difference in refuge angle between the model lizard (66.0
± 9.94°; 0-180°) and snake (83.5 ± 9.63°; 0-180°) was 18°. Angular-linear correlation indicated that RA was significantly correlated with model type ( n = 458, Χ2 = 11.97, d.f.
= 1, P < 0.001, Fig. 3b), such that side-blotched lizards fled more directly toward a refuge
(0°) when approached by a model lizard compared to a snake. However, RA of individuals were marginally insignificant when compared to the abundances of predatory lizards ( n = 458, Χ2 = 5.28, d.f.= 1, P = 0.021) or snakes ( n = 458, Χ2 = 4.03, d.f. =1, P =
0.045) and not correlated with local cover density ( n = 423, Χ2 = 3.44, d.f. = 1, P =
0.064).
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Refuge Entry (RE)
Of the 458 trials, side-blotched lizards entered a refuge in 112 (24.5%) of those
trials. The difference in refuge entry between trials using model lizards (29.9%) or snakes
(18.8%) was 11%. Logistic regression in which model predator type, lizard and snake
abundances, and local cover density (as well as all interactions) were included as
independent variables indicate that significant variation in RE could be explained by
these predictors ( Χ2 = 59.97, d.f. = 15, P < 0.001). However, post-hoc effect tests again
revealed no clear explanation for variation in RE; only the main effect of predatory lizard abundance was even marginally insignificantDraft (Table 4).
Discussion
Optimal escape theory predicts that flight initiation distance should be correlated
with predation pressure (Ydenberg and Dill 1986). As such, FID has been generally
empirically correlated with predation pressure in numerous taxa (Díaz et al. 2013; Samia
et al. 2013; Williams et al. 2014), including in lizards (Diego-Rasilla 2003; Cooper and
Pérez-Mellado 2012; Brock et al. 2014; Samia et al. 2016). Although we found that FID
was marginally predictable among individual side-blotched lizards, both predatory lizard
and snake abundances, not model predator type, were primarily responsible for this
relationship (Table 4). Thus we were able to demonstrate that FID varies geographically
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in side-blotched lizards and is related to predation environment (lizard and snake abundances). However, we failed to support the hypothesis that side-blotched lizards contextualize their escape behavior based on model predator type. The lack of association between model predator type and FID may be due to Uta using a generalized anti- predator behavior to encompass a wide range of predator types (Crowder et al. 1997;
Krause and Ruxton 2002). Flight initiation distance as an escape response might not vary amongst types of terrestrial predators approaching because Uta may not differentiate their response until the escape movement has begun. Rather, treating any object approaching along the ground equally as a threat may be the generalized response of side-blotched lizards to an approach. Alternatively,Draft we cannot reject the possibility that subjects did not view our model predators as a threat considering that the foraging behavior of both collared lizards and racers relies on ambush (e.g., Cooper et al. 2001; Herzog and
Burghardt 1974; Husak and Ackland 2003).
Despite the fact that side-blotched lizards do not react any differently to the initial approach of either the model lizard or snake, when side-blotched lizards did initiate a response, their escape behavior in terms of distance fled was explainable by a statistical model containing predator type, predator abundances, and cover density. Yet no single factor in this model clearly explained distance fled despite observed trends based on the model predator type; Uta tended to run farther from the snake model than from the lizard model. Thus, once again, we fail to support the idea that side-blotched lizards contextualize their response to different predators. This result is contrary to previous reports of lizard antipredator behavior in response to different types of predators (e.g.,
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Sherbrooke 2007; Cooper 2008). For example, horned lizards ( Phrynosoma Wiegmann,
1828) exhibit predator-specific responses to rattlesnakes ( Crotalus ) vs. whipsnakes
(Masticophis Baird and Girard, 1853)(Sherbrooke 2007) by contextualizing their escape
response based on the subjugation strategy of the predator. In the present study the
interactions between predatory lizard and snake abundances were marginally
insignificant at explaining distance fled (Table 4). Thus we failed to demonstrate clear
differences in escape response based on predator abundances as well, which further
suggests a lack of contextualized response to predation environment by side-blotched
lizards. Again, this finding is contrary to previous reports of differences in the escape response of lizards, specifically in distanceDraft fled (e.g., Cooper 2009; Cooper et al. 2009a). Unlike FID or DF, refuge angle showed contextualized response to model lizard
or snake predators. Side-blotched lizards ran more directly toward the nearest refuge
when escaping from the lizard model than from the snake model. In other words, after
initiating a response the directional escape behavior of Uta is consistent with optimal
escape theory in that they differ for each predator type (Ydenberg and Dill 1986). One
explanation for this finding is that the anti-predator responses of Uta are attributable to
the distinct performance capacities of the different predator types. Uta sprint speeds have
been estimated at 2.6 m/s on average (Bonine and Garland 1999), but Uta are unlikely to
be fast enough to escape commonly encountered predatory lizards, such as Crotaphytus
(avg. sprint speed = 4.6 m/s), Gambelia (4.1 m/s), or Aspidoscelis spp. (3.5-6.2
m/s)(Bonine and Garland 1999). Predatory snakes, such as Coluber , have aerobic and
anaerobic thresholds consistent with a lifestyle that demands relatively short bursts of
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speed coupled with potential endurance (Ruben 1976). Yet data on locomotor performance suggest that Uta are likely able to escape Coluber , which have sprint speeds of only 1.5 m/s on average (Walton et al. 1990). Thus, more directly fleeing toward a refuge when approached by a collared lizard likely minimizes potential predation risk for side-blotched lizards, while fleeing less directly toward a refuge when approached by a slower moving racer may not substantially increase risk. However, this risk minimization depending on predator is only marginally affected by predator abundances in the local environment. Nor do model predator type or predator abundances appear to effect refuge entry (Table 4). Both of these escape responses involving refuges are consistent with a more generalized anti-predator behaviorDraft by Uta . Despite the interest in antipredator behavior of animals, including lizards, relatively little research has focused on the role of predation risk itself on escape behavior, especially among multiple populations. For example, in their recent review on the FID of lizards, Samia et al. (2016) did not include aspects population variation in risk among the numerous factors affecting escape behavior, primarily because such studies are few making generalizations difficult (see also Cooper et al. 2009 a, 2009 b; Cooper and Pérez-Mellado 2012). Diego-Rasilla (2003) reported that European wall lizards
(Podarcis muralis ) from populations with higher predation pressure were more likely to run sooner (greater flight initiation distance) and to use refuges (refuge entry) than lizards from lower risk environments, but not more likely to run longer distances (distance fled) when they did escape. We failed to find clear support that side-blotched lizards contextualize their responses to either model predator type or depending on local predator
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abundances. The only evidence for differences in escape behavior we could detect
involved the directness of fleeing toward a refuge in response to model lizard predators.
Rather, our main conclusion by comparing multiple lizard populations that differ in terms
of observed predator abundances is that side-blotched lizards appear to use more
generalized anti-predator responses to multiple types of predators.
Acknowledgements
We thank: Tree Tops-IslandDraft Ranch for access to Wrights Point and Sheldon NWR
for access to Long Draw; K. Flanery for field facility hospitality; L. Flynn, N. Clarke, S.
Manka, P. Bula, C. Olson A. Sewart for help collecting data; D. Ganskopp and R.
Anderson for helpful discussions regarding this research; R. Huey for suggesting the size
and metabolic scaling of predator abundance. This research was conducted with the
permission of the Oregon Department of Fish and Wildlife, the Nevada Division of
Wildlife, and the Washington Department of Fish and Wildlife as well as the Institutional
and Animal Care Committees of Gonzaga University and University of Wisconsin-
Stevens Point.
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Table 1. Predicted response of side-blotched-lizard, Uta stansburiana , escape behavior to
increasing latitude as well as to different predator types or predator abundances.
Escape trait Relationship to:
Latitude Predatory lizards Predatory snakes
Flight initiation distance Reduced Increased Reduced
Distance fled Reduced Reduced Increased
Refuge angle Less toward refuge More toward refuge Less toward refuge
Refuge entry Reduced Increased Reduced
The predicted escape response is theDraft same for side-blotched lizards presented with different model predator types or in environments with higher abundances of that
predator, and so are not distinguished here.
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Table 2. Mean ± S.E.M. (min.-max.) abundance of predators of side-blotched lizards, Uta stansburiana , measured as n observed / person / km at each of 10 sites (listed from north-to-south; see Fig. 1).
Site Observation Predatory Predatory
periods lizard abundance snake abundance
FC 3 0 0.06 ± 0.030 (0.00-0.10)
HR 4 0 0
HB 6 0 0
WP 23 0 0.82 ± 0.175 (0.00-3.60) SL 8 0.89 ± 0.127Draft (0.40-1.15) 0.02 ± 0.019 (0.00-0.15) CH 10 0.70 ± 0.245 (0.02-2.40) 0.11 ± 0.053 (0.00-0.17)
TC 4 1.67 ± 0.474 (0.95-3.07) 0.10 ± 0.038 (0.00-0.18)
LD 5 0.51 ± 0.267 (0.02-1.39) 0.14 ± 0.037 (0.08-0.29)
LV 7 1.39 ± 0.479 (0.00-2.93) 0.01 ± 0.008 (0.00-0.06)
WL 5 4.04 ± 1.768 (0.19-7.00) 0.10 ± 0.070 (0.00-0.40)
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Table 3. Mean ± 1 S.E.M. (linear trait) or ± 95% confidence intervals (directional trait)(min.–max.) for cover density, flight
initiation distance (FID), distance fled (DF), escape angle (EA), refuge angle (RA), and refuge entry (RE) for 10 side-blotched-
lizard, Uta stansburiana , populations (listed from north-to-south; see Fig. 1) when approached by model lizard (L) or snake
(S). N is sample size.
Latitude Site Model N Cover density Flight initiation Distance fled Escape angle Refuge angle Refuge
(°N) type (brush/m 2) distance (m) (m) (°) (°) entry (%) 47.04 FC L 21 0.77 ± 0.083 0.57Draft ± 0.158 1.32 ± 0.284 135 ± 17.3 53 ± 46.1 33.3 (0.14-1.63) (0.09-3.3) (0.16-4.6) (25-175) (0-175)
S 22 0.80 ± 0.072 0.51 ± 0.133 1.82 ± 0.564 128 ± 16.4 87 ± 51.6 31.8
(0.25-1.56) (0.09-2.48) (0.13-10.5) (50-170) (0-170)
46.97 HR L 19 0.38 ± 0.031 0.36 ± 0.058 0.60 ± 0.107 138 ± 17.8 75 ± 43.7 47.4
(0.11-0.75) (0.06-0.93) (0.1-1.43) (75-175) (0-155)
S 18 0.41 ± 0.034 0.34 ± 0.143 0.55 ± 0.170 134 ± 13.9 60 ± 41.5 11.1
(0.11-0.76) (0.0-2.65) (0.02-2.67) (65-175) (0-170)
43.78 HB L 29 0.51 ± 0.061 0.29 ± 0.033 0.80 ± 0.145 92 ± 26.1 70 ± 25.4 48.3
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(0.16-1.48) (0.14-0.94) (0.06-3.11) (0-170) (0-170)
S 29 0.51 ± 0.049 0.23 ± 0.045 0.46 ± 0.120 86 ± 18.3 105 ± 28.3 31.0
(0.12-1.16) (0.0-1.3) (0.08-3.39) (10-170) (5-180)
43.44 WP L 27 0.14 ± 0.032 0.26 ± 0.028 1.18 ± 0.203 144 ± 16.3 61 ± 34.3 3.8
(0.0-0.64) (0.09-0.69) (0.11-3.5) (35-180) (0-175)
S 24 0.21 ± 0.035 0.28 ± 0.122 3.60 ± 0.894 124 ± 26.2 99 ± 28.6 (5- 4.3 (0.0-0.45) Draft(0.0-3.04) (0.1-18.8) (5-180) 180) 42.78 SL L 16 0.33 ± 0.064 0.47 ± 0.169 0.57 ± 0.102 119 ± 24.0 78 ± 66.1 37.5
(0.0-0.69) (0.13-2.96) (0.07-1.67) (45-170) (0-180)
S 15 0.33 ± 0.060 0.59 ± 0.215 1.88 ± 0.462 139 ± 30.0 71 ± 36.5 13.3
(0.0-0.66) (0.1-3.36) (0.3-6.5) (30-180) (5-180)
42.75 CH L 30 0.77 ± 0.028 0.25 ± 0.031 0.88 ± 0.149 99 ± 30.64 61 ± 34.3 20.0
(0.48-0.12) (0.09-0.83) (0.14-2.96) (10-180) (0-175)
S 30 0.77 ± 0.040 0.30 ± 0.063 1.64 ± 0.418 101 ± 32.3 95 ± 22.4 23.3
(0.32-1.24) (0.04-1.55) (0.08-11.5) (5-180) (10-175)
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42.16 TC L 20 0.36 ± 0.021 0.32 ± 0.035 1.15 ± 0.297 97 ± 40.2 40 ± 22.6 50.0
(0.20-0.55) (0.12-0.65) (0.25-5.05) (15-180) (0-165)
S 20 0.32 ± 0.028 0.27 ± 0.036 2.72 ± 0.651 101 ± 63 67 ± 23.8 30.0
(0.15-0.60) (0.11-0.75) (0.09-8.58) (5-180) (5-155)
42.00 LD L 23 0.42 ± 0.035 0.26 ± 0.030 0.50 ± 0.063 112 ± 24.9 78 ± 20.8 30.4
(0.15-0.73) (0.09-0.62) (0.14-1.15) (10-180) (0-160) S 21 0.43 ± 0.046 0.34Draft ± 0.090 1.28 ± 0.375 113 ± 18.1 93 ± 28.4 28.6 (0.15-0.81) (0.07-1.53) (0.02-7.2) (25-175) (0-180)
40.22 LV L 21 0.33 ± 0.047 0.31 ± 0.056 0.78 ± 0.202 133 ± 24.1 26 ± 27.9 47.6
(0.0-0.69) (0.07-0.97) (0.07-3.9) (45-175) (0-165)
S 17 0.26 ± 0.048 0.46 ± 0.131 1.97 ± 0.379 121 ± 21.1 62 ± 53.0 11.8
(0.0-0.65) (0.0-2.1) (0.16-6.08) (30-180) (0-180)
38.75 WL L 28 0.44 ± 0.034 0.37 ± 0.043 0.85 ± 0.146 62 ± 25.4 87 ± 28.3 0.0
(0.12-1.04) (0.12-1.24) (0.15-3.5) (0-160) (0-175)
S 28 0.43 ± 0.032 0.31 ± 0.089 1.68 ± 0.450 77 ± 28.4 74 ± 25.4 0.0
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(0.12-0.76) (0.07-2.0) (0.11-8.1) (0-180) (10-170)
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Table 4. Effects of model predators, predator abundance (lizards and snakes), and cover
density on flight initiation distance (FID), distance fled (DF), and refuge entry (RE) for
458 side-blotched lizards, Uta stansburiana . Data presented are F- or Χ2-values from
full-factorial multiple regressions (FID and DF) or logistic regression (RE), respectively.
For multiple regressions d.f. = 1 and 441, while for logistic regression d.f. = 15. Only
independent variables with P-values <0.05 are included for clarity.
Effect Flight initiation Distance Refuge
distance fled entry
Model predator type
Predatory lizard abundance Draft 12.03*** 6.05*
Predatory snake abundance 14.81***
Cover density
Model type X Predatory lizards 4.52*
Model type X Predatory snakes 4.13*
Model type X Cover density
Predatory lizards X Predatory snakes 14.47*** 5.07*
Predatory lizards X Cover density 6.02*
Predatory snakes X Cover density 11.63***
Model X Lizards X Snakes 5.06* 5.51*
Model X Lizards X Cover
Model X Snakes X Cover
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Lizards X Snakes X Cover 12.76***
Model X Lizards X Snakes X Cover
Due to the large number of comparisons, only independent variables with P<0.001 are considered significant. * P<0.05; ** P<0.01; *** P<0.001.
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Figure Legends
Fig. 1. Map showing study sites in Washington, Oregon, and Nevada. Abbreviations
correspond to previously published localities (see Bula et al. 2014). Gray shading
indicates approximate range of northern side-blotched lizards, Uta stansburiana , based
on data from herpnet.org. Inset is map of the United States with study area indicated by
dashed box.
Fig. 2. (a) Photo of Great-Basin collared lizard ( Crotaphytus bicinctores ) from Long
Draw (LD) compared to painted model (top). (b) Photo of yellow-bellied racer ( Coluber mormon ) from Wrights point (WP) Draftcompared to painted model (top). (c) Lateral view showing distance between lizard on rock and researcher holding model snake mounted to
a pole (mounted model lizard shown for comparison). (d) Overhead view showing
positioning of approach and two observers beyond 5 m radius (solid circle) from subject,
but within line of sight (dashed lines).
Fig. 3. Escape directions of side-blotched lizards, Uta stansburiana , when approached by
a model lizard (filled) or snake (open). In both cases subjects start at center of circle and
escape directions are shown as population averages ( n = 10) rather than as individuals ( n
= 458) for clarity. (a) Escape angle is flee direction for each site relative to predator’s
approach (absolute value of difference between subject’s escape angle and predator’s
approach angle) with predator standardized as approaching from 0°. (b) Refuge angle is
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flee direction for each site relative to nearest refuge (absolute value of difference between subject’s escape angle and refuge direction) with refuge standardized as occurring at 0°.
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= 100 km FC Washington
HR 44°N HB Idaho WP
CH Draft 43°N SL Oregon LD TC 42°N California Nevada 41°N
LV 40°N
WL 39°N
38°N
124°W 122°W 120°W 118°W 116°W 114°W
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A) B)
Draft
C) D) 5 m
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Model 180° Lizard Snake
Away Toward from refuge predator
Draft Escape 0° Refuge angle angle
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