Evolution, 57(3), 2003, pp. 574±585

EVOLUTION OF PREY BEHAVIOR IN RESPONSE TO CHANGES IN PREDATION REGIME: IN FISH AND LAKES

R. STOKS,1,2 M. A. MCPEEK,1,3 AND J. L. MITCHELL1,4 1Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire 03755 2Laboratory of Aquatic Ecology, University of Leuven, Ch. De Beriotstraat 32, B-3000 Leuven, Belgium E-mail: [email protected]

Abstract. In a large behavioral experiment we reconstructed the evolution of behavioral responses to predators to explore how interactions with predators have shaped the evolution of their prey's behavior. All damsel¯y species reduced both movement and feeding in the presence of coexisting predators. Some Enallagma species inhabit water bodies with both ®sh and dragon¯ies, and these species responded to the presence of both predators, whereas other Enallagma species inhabit water bodies that have only large dragon¯ies as predators, and these species only responded to the presence of dragon¯ies. Lineages that shifted to live with large dragon¯ies showed no evolution in behaviors expressed in the presence of dragon¯ies, but they evolved greater movement in the absence of predators and greater movement and feeding in the presence of ®sh. These results suggest that Enallagma species have evo- lutionarily lost the ability to recognize ®sh as a predator. Because species coexisting with only dragon¯y predators have also evolved the ability to escape attacking dragon¯y predators by swimming, the decreased predation risk associated with foraging appears to have shifted the balance of the foraging/predation risk trade-off to allow increased activity in the absence of mortality threats to evolve in these lineages. Our results suggest that evolution in response to changes in predation regime may have greater consequences for characters expressed in the absence of mortality threats because of how the balance between the con¯icting demands of growth and predation risk are altered.

Key words. Antipredator behavior, damsel¯y, evolutionary loss, foraging, predator-prey interactions, trade-off.

Received July 8, 2002. Accepted October 21, 2002.

Prey have developed a bewildering array of defenses to 2000; Diehl et al. 2000; Relyea 2000; Schmitz and Suttle avoid, deter, or escape predators (reviewed in Edmunds 1974; 2001). Endler 1986). However, many of these defenses come at costs We know that predators impose selection on the antipred- to other ®tness components such as growth and reproduction ator behaviors of their prey (Brodie 1992; Watkins 1996; (Werner and Gilliam 1984; Sih 1987, Lima 1998). One aspect Cousyn et al. 2001; Juliano and Gravel 2002; but see Van of the phenotype in which such a trade-off is readily apparent Buskirk et al. 1997), and that many of these behaviors possess is in behavioral responses to predators. Theory predicts that heritable variation (Breden et al. 1987; Riechert and Hedrick prey should generally reduce their activity in environments 1990; Brodie 1992, 1993; Magurran et al. 1992; De Meester where the risk of predation is greater, and should reduce 1996; Storfer and Sih 1998; Cousyn et al. 2001, O'Steen et activity even further when a predator threat is imminent (e.g., al. 2002; but see Watkins 2001). Thus, the potential for adap- when a prey is within the detection ®eld of a predator) (Endler tive evolution is present in many populations and species. 1986; Abrams 1991; Werner and Anholt 1993). Activity of Our understanding of the role that predation plays in the the prey modulates this trade-off, because greater activity evolution of prey phenotypes is incomplete, however, be- results in greater foraging returns to the prey but also results cause it is based on studies scattered across disparate taxa in more exposure to and a greater likelihood of detection by and phenotypes. Only rarely has the evolution of antipredator the predator. traits been examined in a group of prey species for which Many taxa respond behaviorally to predators. Con- predator-prey relations are well characterized and phyloge- sistent with theoretical predictions, prey generally reduce netic relationships are well established so that the direction their activity (e.g., spending more time in refuges [Sih 1992; of character change can be inferred. One notable exception Eklov and Persson 1996], moving less frequently or more is the work of Richardson (2001a,b), who studied 14 frog slowly [Kohler and McPeek 1989; McPeek 1990a; Peckarsky species from three families. Richardson found no consistent 1996; Anholt et al. 2000; Relyea 2000, 2001; Richardson differences in activity among species that coexist with dif- 2001a]) and consequently reduce their foraging efforts when ferent predators. However, the change in activity in response presented with predation threats. This reduced foraging often to different predators appeared to be evolutionarily con- leads to reduced growth and development (Skelly and Werner strained. The evolution of activity level in the presence of 1990; Skelly 1992; Peckarsky et al. 1993; Relyea and Werner various predators was positively correlated across species, 1999; Relyea 2000; Johansson et al. 2001) and may affect suggesting that the behavioral response to one predator may the dynamics of ecological communities (McPeek 1990b, not evolve independently of the behavioral response to an- 1998; Werner and Anholt 1996; Peacor and Werner 1997, other (Richardson 2001a). Using evolutionary contrasts anal- yses (Felsenstein 1985, 1988) at an intraspeci®c level, Downes and Adams (2001) also found that the presence or 3 Corresponding author. E-mail: [email protected]. 4 Present Address: Department of Biological Sciences, University absence of snakes had driven the evolution of antipredator of Michigan, Ann Arbor, Michigan 48109; E-mail: jmitchez@ behavior in a gecko. Sih et al. (2000) concluded that the umich.edu. ineffective antipredator behavior of a salamander species that 574 ᭧ 2003 The Society for the Study of Evolution. All rights reserved. EVOLUTION OF PREY BEHAVIOR 575

TABLE 1. Summary of source populations for larvae of the ten Enallagma species included in this study. N identi®es the total sample size for each species; equal numbers of replicates were performed for the three treatments for each species. The habitat af®nities of species are identi®ed by F, ®sh lakes; and D, Dragon¯y lakes. The last two columns identify which author observed replicates on a given species and the year in which those replicates were performed.

Species N Source population Habitat Observer Year E. annexum 24 Sylvester Pond, Norwich, VT D RS 2001 E. aspersum 24 KBS Pond Laboratory, Hickory Corners, MI D MM 1988 E. boreale 24 Ferson Road Marsh, Hanover Center, NH D JM 1994 E. geminatum 15 Palmatier Lake, Hastings, MI F MM 1988 E. hageni 24 Little Salem Pond, Derby, VT F RS 2001 E. ebrium 24 McDaniel's Marsh, En®eld, NH F RS 2001 E. vernale 24 McDaniel's Marsh, En®eld, NH F JM 1994 E. divagans 24 Lee's Pond, Moultonborough, NH F RS 2001 E. signatum 24 Little Salem Pond, Derby, VT F RS 2001 E. vesperum 24 Palmatier Lake, Hastings, MI F MM 1988 coexists with ®sh could partly be explained by its recent itat shifts from a predation regime with ®sh and small, rel- divergence from a sister species that does not live with ®sh. atively inactive dragon¯ies to a predation regime without ®sh In this paper, we present a phenotypic and evolutionary but with large, active dragon¯ies. To test these hypotheses, analysis of behavioral responses to predators for ten species we reconstruct the evolution of these behavioral traits on the of Enallagma damsel¯ies (Hexapoda: ). These con- phylogeny of the Enallagma using evolutionary contrasts stitute two ecological groups of species that inhabit the per- analysis (Felsenstein 1985, 1988; McPeek 1995b). Evolu- manent ponds and lakes of eastern North America (Johnson tionary contrasts provide an ideal methodology for testing and Crowley 1980; McPeek 1990b, 1998). One group of En- such hypotheses because they encapsulate both direction and allagma species occurs as larvae only in ponds and lakes with rate of character evolution in one metric (Felsenstein 1985, ®sh, the top predator in this environment; whereas the re- 1988). Behavioral characters that evolved in response to this maining Enallagma species occur as larvae only in ponds and change in selective environment should show: (1) consistent lakes without ®sh but with large dragon¯ies (e.g., Anax, Aesh- directions of change in both lineages that shifted into drag- na, and Tramea species) as the top predator (hereafter, we on¯y lakes, and (2) substantially accelerated rates of evo- refer to these two ecological groups as ®sh-lake Enallagma lution along the branches of the phylogeny on which the and dragon¯y-lake Enallagma, respectively). These two eco- habitat shifts are hypothesized to have occurred relative to logical groups of species segregate between the two lake rates of character change on the rest of the phylogeny types because they are differentially vulnerable to ®sh and (McPeek 1995a,b). The evolution of greater activity and feed- dragon¯ies (McPeek 1990a,b). Previous phenotypic analyses ing in situations in which these species apparently perceive of behavior for two species in each of these two groups show no imminent danger would suggest that behavioral evolution that dragon¯y-lake Enallagma are active in the absence of in this group has been shaped primarily by changes in the predators, respond only to the presence of dragon¯ies by balance of the con¯icting demands of the growth/predation decreasing their activity, and swim away from attacking pred- risk trade-off. ators, which is a very successful evasive tactic against drag- on¯ies but not against ®sh (Pierce et al. 1985; McPeek MATERIALS AND METHODS 1990a). In contrast, ®sh-lake Enallagma are less active than dragon¯y-lake Enallagma in the absence of predators, re- Phenotypic Differences in Behavior spond to the presence of both ®sh and dragon¯ies by de- Study species and maintenance of larvae creasing their activity (a set of smaller and less active drag- on¯y species also coexist with ®sh [Morin 1984a,b; McPeek Throughout this study we closely followed the methods 1990b, 1998]), and perform no evasive actions when attacked used by McPeek (1990a). We included larvae of ten Enal- by a predator (Pierce et al. 1985; McPeek 1990a). Fish lakes lagma species in this study: three dragon¯y lake Enallagma are the ancestral habitat for Enallagma, and the dragon¯y- species (E. annexum, E. aspersum, and E. boreale) and seven lake species are the result of at least two ®sh-lake lineages ®sh lake Enallagma species (E. geminatum, E. hageni, E. recently invading and adapting to live with these large drag- ebrium, E. vernale, E. divagans, E. signatum, and E. ves- on¯y predators that dominate ®shless ponds and lakes perum). Data were collected over 11 years by the three au- (McPeek and Brown 2000; Brown et al. 2000). Previous func- thors. Table 1 gives the source populations, sample sizes, tional and comparative analyses have shown that part of this years when trials on each species were performed, and which adaptation involved phenotypic changes to increase swim- author observed the trials. We acknowledge that ideally all ming speed in order to increase the likelihood of evading an species should have been tested in a randomized sequence attacking dragon¯y (McPeek 1995a,b, 1999, 2000; McPeek by the same observer. However, because each of us observed et al. 1996). at least one dragon¯y-lake Enallagma species and one ®sh- The objective of the present paper is to test whether the lake Enallagma species in a randomized sequence (Table 1) behavioral differences between the two Enallagma groups can and the striking similarity of behaviors among Enallagma be attributed to adaptive evolution associated with these hab- species within the same ecological group irrespective of the 576 R. STOKS ET AL. observer (see results: Fig. 2), it is highly unlikely that our during replicates. Fiberglass window screening covered the results are biased by an observer/year effect. Moreover, we bottoms of both compartments to provide footing for odo- were unable to detect an observer effect when comparing nates, but no other structure was included in either com- observations on E. boreale/E.cyathigerum done by M. A. partment. In laboratory feeding trials, predator feeding biases McPeek in 1988 with those done by J. L. Mitchell in 1994 among species under these conditions are indistinguishable (for each individual behavior, all P Ͼ 0.20 for differences from those when natural macrophyte densities are added to between observers). containers for structure (McPeek 1990b). Also, larvae held We have excluded data for E. boreale and E. cyathigerum in the laboratory under similar conditions display growth collected by McPeek in 1988 that were included in the pre- rates that are nearly identical to those in natural populations vious report (McPeek 1990a). These two species are nearly (McPeek et al. 2001). impossible to distinguish as larvae, and the ones used by All replicates were performed in three identical containers. McPeek in 1988 were a mixture of the two species (McPeek Before performing replicates for a species, each container 1990a). We also now refer to E. cyathigerum as E. annexum, was randomly assigned to a predator treatment (i.e., all rep- because recent genetic analysis shows that the North Amer- licates of a predator treatment for a species were done in the ican and Eurasian taxa previously described both as E. cy- same container). We intentionally confounded any potential athigerum are actually very distantly related in the phylogeny container effects with predator treatment effects to minimize of the Enallagma (Stoks et al., unpubl. ms.). We therefore the potential carryover of any chemical residues left by the will use the speci®c epithet annexum to identify the North predators in a container. Also, water was replaced each day. American species (Hagen 1861). We are con®dent that the For all behavioral assays, each container (irrespective of the larvae observed by Mitchell in 1994 were all E. boreale, predator treatment) was placed in the same position in the because only this species was found as adults (which are laboratory to minimize any potential laboratory positioning easily identi®ed to species) ovipositing the previous summer effects among containers (hence treatments). Because the in the pond where the larvae were obtained. The same is true containers were identical in construction and all were placed for E. annexum observed by Stoks in 2001. in the same position in the laboratory when used, confounding For each species, a large stock of larvae were collected effects that would systematically bias larval behavior should from the source lake and larvae were housed individually in be negligible. 20 ml vials containing pond water and wooden dowels (3 The three treatments were constructed by placing either mm diameter) for perches. Each larva was fed Daphnia pulex (1) no predators, (2) three ®nal-instar Anax junius larvae (Cladocera: Daphnidae) ad libitum every two days and main- (Odonata: Aeshnidae), or (3) one Lepomis sun®sh in the pred- tained in an incubator at 20±21ЊC on a 14:10 L:D photoperiod ator compartment. Bluegill sun®sh (L. macrochirus) were until they were used in trials. For species observed by McPeek used in the 1988 trials and pumpkinseed sun®sh (L. gibbosus) in 1988 and Mitchell in 1994, larvae were only included in were used in the 1994 and 2001 trials. Anax dragon¯ies are trials after they had molted into the ®nal instar in the labo- a common predator of damsel¯ies in ®shless ponds and lakes ratory. For species observed by Stoks in 2001, both larvae (McPeek 1990b, 1998; Werner and McPeek 1994). Both blue- that molted in the laboratory into the ®nal instar and larvae gill and pumpkinseed sun®shes are major littoral predators that were ®nal instars when collected in the ®eld were in- in lakes with ®sh (Brown and Ball 1942; Cooper et al. 1971; cluded. We found no difference in behavior within a species Osenberg et al. 1988; Werner and McPeek 1994), and they for larvae handled in these two ways. impose similar levels of mortality and show similar feeding biases among these damsel¯ies (McPeek and Stoks, unpubl. Behavioral assays data). Predators were fed natural prey every two days after the last replicate on that day was ®nished. The same set of We observed the behavior of solitary larvae of each species 1±2 ®sh and 3±5 Anax were used as predators in all relevant under three experimental treatments: in the presence of (1) replicates of all Enallagma species tested by an observer. no predators, (2) dragon¯y larvae, or (3) ®sh. Each treatment That way we minimized the possibility that differences in was performed in one of three identical rectangular Plexiglas antipredator behavior among Enallagma species were due to containers (34.5 cm long ϫ 24.0 cm wide ϫ 12.5 cm deep). differences in predator behavior. Again, the striking simi- Each container was divided into two compartments. A 10.0 larity in behavior among Enallagma species of the same eco- cm ϫ 10.5 cm inner compartment was enclosed against the logical group tested by different observers (and different sets middle of one wall with three Plexiglas sides. Damsel¯y lar- of ®sh and dragon¯y predators; see results, Fig. 2) strongly vae and their Daphnia prey were placed in this compartment argues against any biases caused by differences among in- during replicates (hereafter referred to as the damsel¯y com- dividual predators. partment). Predators were placed in the larger outer com- All replicates consisted of continuous 30-min behavioral partment (predator compartment) surrounding the damsel¯y observations of the damsel¯y larvae. Replicates were done compartment on three sides. A 2 cm ϫ 2 cm hole, covered between 1000 and 1730 h with water at room temperature with 0.5 mm Nitex screen, in one of the dividing walls al- (20±23ЊC), which is well within the range of temperatures lowed movement of water between these two compartments. that larvae experience in nature over much of their larval This container design allowed the damsel¯y larvae to detect period (M. A. McPeek, pers. obs.). Containers were ®lled to the presence of predators in the outer compartment by sight, a depth of 8.5 cm two hours before the start of the ®rst assay olfaction, and mechanoreception, but prevented the predators on that day. Then one ®nal-instar larva Anax or one Lepomis from consuming the damsel¯y larvae or the Daphnia prey sun®sh was placed in each of the damsel¯y and predator EVOLUTION OF PREY BEHAVIOR 577 compartment of the respective predator treatment containers. ORIENTÐthe number of orientations of the head or body The predators where left in the damsel¯y compartments until towards prey; ADVNUMÐthe number of walking advances the replicates for that day began, and were then removed. towards prey; STRIKEMISSÐthe number of unsuccessful The predator treatments were then established in the respec- strikes at prey; and CAPTUREÐthe number of prey captures. tive containers. Each replicate began with 25 Daphnia pulex The third variable set contains one variable (ABDNUM) in the damsel¯y compartment. Generally, ®ve to seven Daph- quantifying the number of abdominal bends, a conspicuous nia were killed during a replicate, and they were not replaced behavioral display for which the function is currently ques- as eaten because of the disturbance involved. The 30-min tionable (Baker 1981; Richardson and Anholt 1996). In the observation period began when a single damsel¯y larva was previous analysis, each set focused most heavily on a dif- introduced and reached the bottom of the damsel¯y com- ferent principal component, indicating that these sets describe partment. Larvae usually became responsive to prey within largely independent features of behavior in these species. We a few seconds of reaching the bottom of the container. Larvae then applied the same analyses to each set of variables. This were randomly assigned to treatments. approach to the data analysis resulted in easily interpretable A laptop computer was used to record the behaviors of results that are consistent with the previous analysis. damsel¯y larvae. The complete set of behavioral variables We applied multivariate analyses of variance to the move- recorded in this study are described in McPeek (1990a). ment and feeding sets and analogous univariate methods to Walking was de®ned as a change in position on the substrate the number of abdominal bends to test a priori hypotheses when a larva moved its legs. Swimming was de®ned as a about the differences among the two ecological groups (i.e., larva leaving the bottom substrate and moving through the dragon¯y-lake Enallagma, ®sh-lake Enallagma), and re- chamber by swinging its abdomen and caudal lamellae. In sponses to the presence of predators within each group. One the abdominal bend display, a larva bends its abdomen general model cannot be constructed to simultaneously test through an arc from side to side while standing on the bottom hypotheses about group differences and predator treatment (Baker 1981). Orienting toward prey was de®ned as a larva differences. Consequently, we have taken a two-step ap- turning its head or body toward a Daphnia without changing proach to the analysis. The ®rst step was to test for group its position on the substrate. Advancing toward prey was differences without regard to predator treatments in a mul- de®ned as a walk to chase a Daphnia. We separately scored tivariate nested analysis of variance (MN-ANOVA), with unsuccessful strikes and successful strikes (called captures) group and species nested within group as independent vari- at prey. It is important to note that there is no necessary ables in the model. Species nested within group was used as sequence to any of the behaviors we recorded, example, lar- the error variance for group. To test for group differences vae routinely struck at prey without ®rst orienting towards between dragon¯y-lake versus ®sh-lake Enallagma, we con- them. In other words, the occurrence of one behavior was structed a linear orthogonal contrast with the species nested not conditional upon another behavior. In this paper we an- within group term as the error variance for each (Sokal and alyzed only a subset of these variables. Our choice of vari- Rohlf 1995). We examined the characteristic equations from ables to include in this analysis was based on their importance the multivariate analyses of variance and performed univar- to discriminating species and responses to predators in the iate analyses employing the same model to examine which previous analysis (McPeek 1990a). variables were responsible for signi®cant results (Morrison 1990). Statistical analyses In the second step of the analysis, we examined responses to the presence of predators for each species group separately, In a previous analysis of a subset of these data (McPeek because we had a priori expectations that each would group 1990a), principal components were ®rst extracted from the respond differently (McPeek 1990a). As above, the same original data to reduce the dimensionality of the data set to model was applied to each set of variables. We constructed a few summary variables. The resulting principal component a multivariate analysis of variance model (MANOVA) with scores were then analyzed to determine species differences species, predator treatment, and the species ϫ predator in- and treatment responses. When this same analysis was ap- teraction term as independent factors. We consider species a plied to the present dataset containing ten species, the re- random effect and predator a ®xed effect, and so the species sulting principal components had no simple interpretations ϫ predator interaction was used as the error variance estimate (even after rotations), as in the ®rst study. We, therefore, in all signi®cance tests of the predator treatment main effect have taken a different approach to the analysis. and contrasts among predator treatments (Sokal and Rohlf We ®rst reduced the number of variables in the analysis 1995). Because we had a priori expectations that the two by including only those variables that loaded heavily on prin- species groups would differ in their responses to the predator cipal components in the ®rst study and that were important treatments, the set of linear, orthogonal contrasts used to test to the interpretation of the results (McPeek 1990a). We re- for differences among predator treatments differed between tained eight variables that naturally group into three sets. The the groups. In the analysis reported by McPeek (1990a), drag- ®rst variable set contains three variables describing move- on¯y-lake Enallagma responded signi®cantly only to the ment and activity (Movement Set): WALKNUMÐthe number presence of dragon¯y larvae, so we tested the contrast set of walks performed during a trial; WALKMEANÐthe mean for (1) dragon¯ies present versus (predators absent ϩ ®sh duration of individual walks (in seconds); and INACTIVEÐ present), and (2) predators absent versus ®sh present. In con- the duration of the longest motionless period (in minutes). trast, ®sh lake Enallagma responded to the presence of both The second set contains four variables describing feeding: ®sh and dragon¯ies, and therefore we tested the contrast set 578 R. STOKS ET AL.

FIG. 1. The phylogenetic hypothesis for the 11 species included in this study. This phylogenetic hypothesis is derived from the analysis of Brown et al. (2000) based on 815 bp of mtDNA sequence and 51 morphological characters. The two dashed branches identify branches along which habitat shifts of lineages from ®sh lakes to dragon¯y lakes are hypothesized to have occurred. The habitat af®nities of species are identi®ed by F, ®sh lakes; D, dragon¯y lakes. Numbers on the braches are branch lengths derived using maximum likelihood methods assuming the HKY model of nucleotide substitutions (see Brown et al. 2000). for (1) predator absent versus (dragon¯ies present ϩ ®sh pothesis derived by Brown et al. (2000) for the North Amer- present), and (2) dragon¯ies present versus ®sh present. ican Enallagma. Branch lengths were derived using maxi- Again, we examined the characteristic equations from the mum-likelihood methods assuming the HKY model (Hasa- multivariate analyses of variance and performed univariate gawa et al. 1985) of nucleotide substitutions on the nucleotide analyses employing the same model to examine which var- sequence data for 815 bp of sequence from the mitochondrial iables were responsible for signi®cant results (Morrison cytochrome oxidase I and II genes and the intervening tRNA 1990). (Brown et al. 2000). Species were then pruned from the tree until only those included in this study remained (Fig. 1). The Evolution of Antipredator Behavior systematics study could not resolve the clade containing E. We employed evolutionary contrasts analysis (Felsenstein boreale, E. annexum, E. ebrium, E. hageni, and E. vernale. 1985, 1988; Martins and Garland 1991; McPeek 1995b) to This clade explosively radiated very recently (Brown et al. test whether the present behavioral differences between the 2000; McPeek and Brown 2000; Turgeon and McPeek 2002), dragon¯y-lake and ®sh-lake Enallagma were the result of and so we consider this a ``hard'' polytomy (Purvis and Gar- adaptive evolution associated with recent habitat shifts of land 1993). We resolved this clade for analysis by ®rst plac- formerly ®sh-lake lineages into the dragon¯y lake habitat (for ing E. boreale and E. annexum together so that only one similar analyses of other characters, see also McPeek habitat shift is assumed in this clade. We then arbitrarily 1995a,b, 1997, 1999, 2000; McPeek et al. 1996; McPeek and resolved the remaining splits among species included in this Brown 2000; Brown et al. 2000). Evolutionary contrasts or- study, and assigned branch lengths of 0.0 to all these arbi- thogonally partition the evolutionary change in a character trarily resolved branches (Purvis and Garland 1993). We tried to estimate the direction and rate of character change across many resolutions within this clade and all gave qualitatively a phylogeny (Felsenstein 1985, 1988; McPeek 1995b). Al- identical results. though most analyses construct all evolutionary contrasts us- For each species we calculated the mean of each behavioral ing pairs of branches, alternative orthogonal partitions that variable in each predator treatment (e.g., each species has isolate character change on single branches can be made three values for WALKNUM, one for each predator treat- (McPeek 1995b). We employed this alternative partitioning ment). We take these means to represent the behavior of the technique to estimate character change along the two branch- species in the presence of each predator. We then applied a es of the Enallagma phylogeny on which the shift in habitat modi®cation of Felsenstein's (1985, 1988) method of evo- from ®sh lakes to dragon¯y lakes are hypothesized to have lutionary contrasts to isolate evolutionary changes on the occurred. By comparing evolutionary contrasts values for single branches of the phylogeny on which habitat shifts from these two single branches to the rest of the evolutionary con- ®sh to dragon¯y lakes are hypothesized to have occurred trasts, we are testing whether the direction of character (McPeek 1995b): the external branch leading to E. aspersum change associated with these two habitat shifts is consistent and the branch leading to the immediate ancestor of E. bo- and whether the rate of evolution is signi®cantly accelerated reale and E. annexum (Fig. 1). over the rate of character change that occurs within habitats. We applied this methodology to calculate a set of stan- To perform these analyses we used the phylogenetic hy- dardized evolutionary contrasts for each behavior in each EVOLUTION OF PREY BEHAVIOR 579 predator treatment. As stated in the introduction, the test of Behavioral responses toward predators character change consistent with adaptive evolution involves The two ecological groups of damsel¯ies showed funda- both directional and rate components. For the two single mentally different patterns of behavioral response to the pres- branches along which habitat shifts are hypothesized to have ence of dragon¯y and ®sh predators. occurred, we subtracted the phenotypic value for the ®sh- Overall MANOVAs showed that dragon¯y-lake Enallagma lake ancestral taxon from the derived dragon¯y-lake taxon, responded behaviorally only to the presence of dragon¯ies so that an increase in the character as a result of the habitat (Fig. 2). Dragon¯y-lake Enallagma walked less frequently shift would result in a positive contrast value. We then com- and were inactive for a much longer period of time in the pared these two single branch contrast values to the remaining presence of dragon¯ies than when no predators or ®sh were evolutionary contrasts that quantify the rate of character present (contrast comparing dragon¯y treatment to the no change within the two habitats. The direction of subtraction predator and ®sh present treatments: overall MANOVA F was arbitrary for contrasts describing character change within 3,2 ϭ 49.80, P Ͻ 0.02; WALKNUM F ϭ 9.82, P Ͻ 0.04; habitats. This comparison simultaneously tests whether the 1,4 INACTIVE F ϭ 26.43, P Ͻ 0.01), but their movement did direction of change in the two branches with habitat shift is 1,4 not differ between the no predator and ®sh treatments (con- consistent (i.e., if their direction of change is not consistent, trasts for overall MANOVA and the three individual move- their average will be near zero) and whether the rate of evo- ment variables with P Ͼ 0.30). Their performance of the lutionary change in a character is signi®cantly higher when abdominal bend behavior did not differ among the predator habitat shifts are hypothesized to have occurred as compared treatments (F ϭ 0.35, P Ͼ 0.72). Dragon¯y-lake Enallagma to the rate of change within the habitats (i.e., are the two 2,4 also oriented toward prey less, and struck at and captured habitat shift values outliers when compared to character fewer prey in the presence of dragon¯ies as compared to the change within habitats). We performed multivariate ANO- other two predator treatments (contrasts for all feeding var- VAs (equivalent to Hotelling's multivariate T2 test [Morrison iables with P Ͻ 0.05, but the overall MANOVA test for this 1990]) on the movement and feeding variable set within each contrast was not signi®cant, F ϭ 10.09, P Ͼ 0.23, because predator treatment, and a univariate t-test (Sokal and Rohlf 4,1 of the small number of denominator degrees of freedom), but 1995) on the number of abdominal bends for each predator their feeding behavior in the no predator and ®sh treatments treatment. did not differ (contrasts for all feeding variables with P Ͼ All statistical analyses were performed in SAS version 8.0 0.25). (SAS Institute 1990). Fish-lake Enallagma responded to the presence of both dragon¯ies and ®sh by decreasing their movement and feed- RESULTS ing (Fig. 2: MANOVAs for overall predator treatment dif- Phenotypic Differences in Behavior ferences in movement F6,20 ϭ 4.10, P Ͻ 0.01; feeding F8,18 ϭ 9.80, P Ͻ 0.001). Fish-lake Enallagma walked less fre- Overall group differences in behavior quently and were inactive for longer in the presence of the predators as compared to the no predator treatment (contrast Behaviors characterizing movement differed greatly comparing no predator treatment to the two predator treat- among the two Enallagma groups (Fig. 2a±c: MN-ANOVA ments: WALKNUM F ϭ 23.93, P Ͻ 0.001; INACTIVE for overall group effect F ϭ 8.80, P Ͻ 0.02). The two 1,12 3,6 F ϭ 22.89, P Ͻ 0.001), but they did not alter the duration Enallagma groups did not differ overall in the frequency of 1,12 of their movements (all these contrasts with P Ͼ 0.15). Fish- movements (WALKNUM F ϭ 4.33, P Ͼ 0.071), but the 1,8 lake Enallagma did not alter their performance of abdominal ®sh-lake Enallagma had a much longer mean duration of bends across the predator treatments (F ϭ 0.35, P Ͼ 0.70). walks than the dragon¯y-lake Enallagma (WALKMEAN F 2,12 1,8 Fish-lake Enallagma also greatly reduced their feeding and ϭ 8.16, P Ͻ 0.03). Our observations indicate that this dif- responsiveness to prey in the presence of both dragon¯ies ference in mean duration of walks re¯ects the fact that ®sh- and ®sh (contrasts comparing the no predator treatment to lake Enallagma move much more slowly than dragon¯y-lake the two predator treatments all with P Ͻ 0.001). None of Enallagma. Although we did not measure distances, dam- these variables differed between the dragon¯y and ®sh treat- sel¯ies in this study typically moved about 1±3 cm with each ments for the ®sh-lake Enallagma (all contrasts P Ͼ 0.05). walk, and mean duration of walks re¯ects the average time each species takes to move this distance. The two groups did Evolution of Antipredator Behavior not differ in the longest inactive period during trials (IN- ACTIVE F1,8 ϭ 1.46, P Ͼ 0.26). Enallagma lineages that recently invaded the dragon¯y- The groups also differed overall in their performance of lake habitat from ®sh lakes evolved large changes in all as- the abdominal bend behavior (Fig. 2d: F1,8 ϭ 15.53, P Ͻ pects of their behavior that were quanti®ed in this study (Fig. 0.01). Dragon¯y-lake Enallagma routinely performed this be- 3). The evolutionary contrasts analyses indicated that behav- havior, sometimes for extended periods of time, whereas ®sh- ioral aspects of movement in both the absence of predators lake Enallagma species performed the behavior much less and the presence of ®sh evolved in association with the hab- frequently on average, and three ®sh-lake Enallagma never itat shifts (MANOVA for No Predators F3,6 ϭ 4.98, P Ͻ performed this behavior (Fig. 2d). 0.05; Fish F3,6 ϭ 5.29, P Ͻ 0.05), but movement in the The results of the MN-ANOVA indicated that the two presence of dragon¯ies did not change signi®cantly (F3,6 ϭ groups did not differ overall in their feeding behavior (Fig. 4.08, P Ͼ 0.05). These responses were primarily caused by 2e±h: F4,3 ϭ 1.67, P Ͼ 0.29). the evolution of an increased number of walks and decreased 580 R. STOKS ET AL.

FIG. 2. The eight behavioral variables for the 10 species included in this study. Enallagma species found as larvae only in dragon¯y lakes are identi®ed by white bars. Enallagma species found as larvae only in ®sh lakes are identi®ed by gray bars. Means ϩ 1SEare shown for each species in the No Predator (N), Dragon¯ies Present (D) and Fish Present (F) treatments. Dragon¯y-lake species are more active in the absence of predators than the ®sh-lake species, and respond only to the presence of dragon¯ies. Fish-lake species respond to the presence of both dragon¯ies and ®sh. EVOLUTION OF PREY BEHAVIOR 581

FIG. 3. Evolutionary contrasts for the eight behavioral variables measured in the three predator treatments. Each bar shows the mean (Ϯ 1 SE) of the evolutionary contrasts for either evolutionary change within habitats (gray bars) or evolutionary change associated with habitat shifts (white bars) in one of the predator treatments. Panels (a) and (d) show results for the No Predator treatment, panels (b) and (e) for the Dragon¯ies Present treatment, and panels (c) and (f) for the Fish Present treatment. WALKNUM and WALKMN are the number and duration of walks, respectively. INACTIVE is the longest inactive period. ABDNUM is the number of abdominal bends. ORIENT and ADVNUM are the number of orientations and advances toward prey, respectively. STIKEMISS and CAPTURE are the number of unsuccessful and successful strikes at prey, respectively. The statistical signi®cance of MANOVA tests for the variable sets are identi®ed in each panel (*P Ͻ 0.05; **P Ͻ 0.01). Evolutionary contrasts associated with habitat shifts are signi®cantly larger than contrasts for change within habitats for the movement set in the absence of predators, the movement set in the presence of ®sh, and the feeding set in the presence of ®sh. These results indicate that dragon¯y-lake lineages evolved to be more active when no predators or ®sh are nearby. duration of walks in the absence of predators and in the For the feeding variable set, signi®cant evolution associ- presence of ®sh, and less inactivity in the presence of ®sh ated with habitat shifts was only apparent in the presence of (Fig. 3a,c). ®sh (MANOVA in the ®sh treatment F4,5 ϭ 6.59, P Ͻ 0.04), Signi®cant evolutionary increases were also apparent for with all four variables showing signi®cant evolutionary in- abdominal bends in all three predator treatments (Fig. 3a±c: creases in the presence of ®sh (Fig. 3f). all t-tests with P Ͻ 0.01). Very few correlations among the evolutionary contrasts 582 R. STOKS ET AL. for the behavioral variables in different treatments were sig- to minimize the likelihood of being detected by the predator. ni®cant when considered separately and none were signi®cant If these lineages had evolved to decrease their susceptibility when signi®cance levels were corrected for multiple tests to the large dragon¯y predators found in ®shless lakes, we (e.g., Bonferroni or Dunn-SÏidaÂk corrections). Thus, behav- would expect the evolutionary contrasts analyses to show the ioral responses to the different predators and different be- evolution of decreases in movement and/or feeding in the havioral components appeared to have evolved largely in- dragon¯y treatment of the behavior experiment. However, no dependently in this clade. behavioral variable in the dragon¯y treatment showed sig- ni®cant change associated with habitat shifts (Fig. 3b,e). Be- DISCUSSION cause dragon¯ies are potential mortality threats in both ®sh and dragon¯y lakes, it is not surprising that species from Among natural ponds and lakes in eastern North America, both lake types would decrease their movement and respon- Enallagma species segregate as larvae among ponds domi- siveness to prey to similar degrees in the presence of threat- nated by ®sh predators and ponds dominated by large drag- ening dragon¯ies. on¯y predators (Johnson and Crowley 1980; McPeek 1990b, The dragon¯y-lake Enallagma lineages appear to have lost 1998). These differences in habitat distribution are caused the ability to identify ®sh as potential predators. The move- primarily by differences in species' abilities to avoid ®sh and ment and responsiveness to prey by dragon¯y-lake Enallag- dragon¯y predators (McPeek 1998). The results of the present ma were not different between the no predator and ®sh treat- analysis con®rm the differences among ®sh-lake and drag- ments (Fig. 2), and all variables showed signi®cant evolu- on¯y-lake Enallagma groups seen in previous analyses, tionary changes associated with habitat shifts in the ®sh treat- which included many fewer species (cf. Pierce et al. 1985; ment (Fig. 3c,f). Abdominal bends also increased in these McPeek 1990a). All ten Enallagma species responded to the lineages, but the functional signi®cance of abdominal bend- presence of predator types with which they coexist by de- ing remains unclear, although it may be related to more ef- creasing their frequency of walking (Fig. 2a), and conse- ®cient processing of ingested food (Richardson and Anholt quently increasing the length of their longest continuous in- 1995; Richardson and Baker 1996). Odonate larvae appear active period (Fig. 2c). These results are consistent with pre- to use speci®c cues that allow them to discriminate among vious studies of species in this genus (Pierce et al. 1985; different types of predators (e.g., ®sh vs. dragon¯ies: Hooper Jeffries 1990; McPeek 1990a; Steiner et al. 2000). All ten 2001), but dragon¯y-lake Enallagma did not respond to the Enallagma species also responded to predators by reducing available cues emitted by ®sh in this experiment. their feeding and responsiveness to prey (Fig. 2e±h: see also Loss of response to cues from ®sh could be either the Pierce et al. 1985; McPeek 1990a; Steiner et al. 2000). These evolutionary loss of an innate response or the lack of suf®- responses to the presence of predators may be interpreted as cient conditioning to ®sh as predators in the ®shless, drag- adaptive predator avoidance behavior. Predators are much on¯y-lake environment. Enallagma boreale larvae from west- more likely to strike at damsel¯y larvae when they are mov- ern North American populations have been shown to decrease ing than when they remain motionless (Baker et al. 1999; movement and feeding in response to chemical cues from Elkin and Baker 2000); movement attracts the attention of ®sh predators (northern pike, Esox lucius) that have been fed predators and thus increases the rate at which prey are de- damsel¯ies, and to learn to associate cues from pike with tected by predators (e.g., Jakobsson et al. 1995). Also, dam- these chemical cues from injured damsel¯ies (Chivers et al. sel¯y larvae with higher foraging rates have higher mortality 1996; Wisenden et al. 1997). The dragon¯y-lake larvae we rates from ®sh predation (Stoks and Johansson 2000). used in these experiments were completely naive of ®sh when Based on a phylogenetic hypothesis derived from mtDNA included in experiments, and thus they would not have de- sequences and morphological data, the ®sh-lake environment veloped any of these learned responses to ®sh. However, our appears to have been the ancestral lake type for the Enal- ®eld experiences in eastern North America also suggest that lagma, and the extant dragon¯y-lake species arose from at although damsel¯ies may be able to learn that ®sh are po- least two very recent shifts of lineages into the dragon¯y- tential predators, these learning responses are not adequate lake habitat (Brown et al. 2000; McPeek and Brown 2000). to prevent their extirpation from water bodies when ®sh are Functional and comparative phenotypic studies have shown introduced. For example, we have witnessed the rapid extir- that morphological and biochemical evolution to increase pation of all three dragon¯y-lake Enallagma species included swimming speed and thus increase the likelihood of evading in this study (including E. boreale) from numerous water an attacking dragon¯y was a major component of the ad- bodies after the introduction of Lepomis species (M. A. aptation associated with these habitat shifts (McPeek McPeek, pers. obs.; D. M. Johnson, pers. comm.), and ®sh 1995a,b, 1997, 1999, 2000; McPeek et al. 1996). The present introductions in general are known to decimate the diversity analysis identi®es evolutionary changes in behavior that were of many vertebrate and invertebrate taxa that are adapted to associated with these habitat shifts. However, unlike the be- living in ®shless waters (Knapp et al. 2001). These species havioral shift to using swimming as an evasive tactic against may be capable of learning to alter their behavior to some attacking predators and the associated morphological and bio- degree in response to the threats that novel predators pose, chemical changes to increase swimming speed, the evolu- but whatever learning does occur is not adequate to permit tionary changes identi®ed in this study would not directly them to coexist with the ®sh found in eastern North America. affect larval survival under dragon¯y predation. When the Similar erosion of antipredator recognition in populations or threat of predation is imminent but before an attack has be- species after the relaxation of a selective force associated gun, prey should decrease their activity as much as possible with the change in the predation regime are documented in EVOLUTION OF PREY BEHAVIOR 583 several (Berger 1999; Berger et al. 2001; O'Steen et work for the long-term evolution of predator avoidance and al. 2002; reviewed in Coss 1999, including also counterex- food acquisition. amples where prey retained predator recognition abilities for thousands of years after predation as a selective force has ACKNOWLEDGMENTS been relaxed). This evolutionary loss now may prevent these We would like to thank C. L. McPeek for providing ®sh naive prey species from coexisting with the predators that to us. Comments by T. Watkins, B. Crespi, and two anon- were syntopic with the prey's ancestors. ymous reviewers on previous drafts greatly improved the Not only did Enallagma lineages that shifted into drag- manuscript. This work was supported by a Research Expe- on¯y-lakes lose the ability to recognize ®sh as potential pred- riences for Undergraduates supplement from the National ators, they also evolved to move more frequently and more Science Foundation to JLM, grants from the National Science quickly in the absence of predators (Fig. 2a,b). We hypoth- Foundation to MAMcP, and grants from the Fund for Sci- esize that this change in movement in the absence of predators enti®c Research-Flanders (FWO-Flanders) and the Belgian was coupled with the evolutionary shift from remaining cryp- American Educational Foundation to RS. tic to using swimming to avoid attacking predators. The re- sponse of most ®sh-lake Enallagma larvae to an attacking LITERATURE CITED predator is to remain motionless until actually captured, whereas dragon¯y-lake Enallagma swim away from attacking Abrams, P. A. 1991. Life-history and the relationship between food availability and foraging effort. Ecology 72:1242±1252. predators (Pierce et al. 1985; McPeek 1990a). Damsel¯y lar- Anholt, B. R., E. E. Werner, and D. K. Skelly. 2000. Effect of food vae are not capable of evading a ®sh by swimming (Stoks and predators on the activity of four larval ranid frogs. Ecology and De Block 2000), and thus remaining motionless until 81:3509±3521. captured is a successful strategy for ®sh-lake Enallagma. This Baker, R. L. 1981. Behavioral interactions and use of feeding areas by nymphs of resolutum (, Odonata) strategy places a premium on reducing detection by ®sh, and Oecologia 49:353±358. therefore slow and infrequent movements would seem to be Baker, R. L., C. M. Elkin, and H. A. Brennan. 1999. Aggressive the behavioral repertoire favored by phenotypic selection im- interactions and risk of ®sh predation for larval damsel¯ies. J. posed by ®sh predation. In contrast, because swimming away . Behav. 12:213±223. from an attacking dragon¯y is a successful evasive tactic, Berger, J. 1999. Antropogenic extinction of top carnivores and in- terspeci®c animal behaviour: implications of the rapid decou- being detected by dragon¯y predators is less important to pling of a web involving wolves, bears, moose, and ravens. Proc. ultimately evading predation (McPeek 1990b; Stoks and De R. Soc. Lond. B 266:2261±2267. Block 2000). Thus, selection imposed by dragon¯y predation Berger, J., J. E. Swenson, and I.-L. Persson. 2001. Recolonizing on activity when the prey perceive no dragon¯y in their im- carnivores and naõ¨ve prey: conservation lessons from Pleistocene extinctions. Science 291:1036±1039. mediate vicinity would be relaxed, and selection imposed by Breden, F., M. Scott, and E. Michel. 1987. Genetic differentiation other activities, namely foraging, may favor increased activ- for anti-predator behaviour in the Trinidad guppy, Poecilia re- ity in the absence of immediate dragon¯y threats (Werner ticulata. Anim. Behav. 35:618±620. and Anholt 1993). In other words, the evolution of swimming Brodie, E. D., 1992. Correlational selection for color pattern and as an evasive tactic against dragon¯y predators may have antipredator behavior in the garter snake Thamnophis ordinoides. Evolution 46:1284±1298. tipped the balance in the growth/predation risk trade-off to Brodie, E. D., 1993. Homogeneity of the genetic variance-covari- allow greater activity in the absence of immediate predator ance matrix for antipredator traits in two natural-populations of threats to evolve. This interpretation is consistent with the the garter snake Thamnophis ordinoides. Evolution 47:844±854. evolved behavioral changes we see, but further experiments Brown, C. J. D., and R. C. Ball. 1942. A ®sh population study of Third Sister Lake. Trans. Am. Fish. Soc. 72:177±186. are obviously needed to test this conjecture. Brown, J. M., M. A. McPeek and M.L. May. 2000. A phylogenetic Several ecological studies, mostly at an intrapopulation perspective on habitat shifts and diversity in the North American level, have shown predictable responses of prey under chang- Enallagma damsel¯ies. Syst. Biol. 49:697±712. ing levels of predation risk (reviewed in Lima and Dill 1990; Chivers, D. P., B. D. Wisenden, and R. J. F. Smith. 1996. Damsel¯y Lima 1998, see also Werner and Anholt 1993). Surprisingly, larvae learn to recognize predators from chemical cues in the predator's diet. Anim. Behav. 52:315±320. the primary behavioral changes we have identi®ed in the Cooper, E. L., C. C. Wagner, and G. E. Krantz. 1971. Bluegills Enallagma are changes in activity in the absence of predators, dominate production in a mixed population of ®shes. Ecology and not evolution in the presence of predators. The behavioral 52:280±290. evolution identi®ed in this study resulted in greater activity Coss, R. G. 1999. Effects of relaxed natural selection on the evo- lution of behavior. Pp. 180±208 in S. A. Foster, and J. A. Endler, in the absence of perceived predators (i.e., changes that would eds. Geographic variation in behavior: perspectives on evolu- shift the balance between predator susceptibility and foraging tionary mechanisms. Oxford Univ. Press, Oxford, U.K. in favor of feeding when larvae perceive no mortality threats). Cousyn, C., L. De Meester, J. K. Colbourne, L. Brendonck, D. This result presents evolutionary evidence illustrating the im- Verschuren, and F. Volckaert. 2001. Rapid, local adaptation of portance of the foraging/predation risk trade-off to the ®tness zooplankton behavior to changes in predation pressure in the absence of neutral genetic changes. Proc. Natl. Acad. Sci. USA of prey. Phylogenetic comparison of species that have 98:6256±6260. evolved under different selection regimes provide a powerful De Meester, L. 1996. Evolutionary potential and local genetic dif- tool to evaluate the evolution of a shift in the optimal balance ferentiation in a phenotypically plastic trait of a cyclical par- between foraging effort and predation risk. Comparisons with thenogen, Daphnia magna. Evolution 50:1293±1298. Diehl, S., S. D. Cooper, K. W. Kratz, R. M. Nisbet, S. K. Roll, S. other species groups with known relationship that underwent W. Wiseman, and T. M. Jenkins. 2000. Effects of multiple, pred- similar changes in predation regime are needed to evaluate ator-induced behaviors on short-term producer-grazer dynamics the generality of the predictive power of this trade-off frame- in open systems. Am. Nat. 156:293±313. 584 R. STOKS ET AL.

Downes, S. J., and M. Adams. 2001. Geographic variation in an- single branches of a phylogeny using evolutionary contrasts. tisnake tactics: the evolution of scent-mediated behavior in a Am. Nat. 145:686±703. lizard. Evolution 55:605±615. ÐÐÐ. 1997. Measuring phenotypic selection on adoptation: la- Edmunds, M. 1974. Defense in animlas: a survey of anti-predator mellae of damsel¯ies experiencing dragon¯y predation. Evo- defenses. Longman Press, London. lution 51:459±466. Eklov, P., and L. Persson. 1996. The response of prey to the risk ÐÐÐ. 1998. The consequences of changing the top predator in a of predation: proximate cues for refuging juvenile ®sh. Anim. food web: a comparative experimental approach. Ecol. Monogr. Behav. 51:105±115. 68:1±23. Elkin, C. M., and R. L. Baker. 2000. Lack of preference for low- ÐÐÐ. 1999. Biochemical evolution associated with antipredator predation-risk habitats in larval damsel¯ies explained by costs adaptation in damsel¯ies. Evolution 53:1835±1845. of intraspeci®c interactions. Anim. Behav. 60:511±521. ÐÐÐ. 2000. Predisposed to adapt? Clade-level differences in Endler, J. A. 1986. Defense against predators. Pp. 109±134 in M. characters affecting swimming performance in damsel¯ies. Evo- E. Feder and G. V. Lauder, eds. Predator-prey relationships. lution 54:2072±2080. Univ. of Chicago Press, Chicago, IL. McPeek, M. A., and J. M. Brown. 2000. Building a regional species Felsenstein, J. 1985. Phylogenies and the comparative method. Am. pool: diversi®cation of the Enallagma damsel¯ies in eastern Nat. 125:1±15. North American waters. Ecology 81:904±920. ÐÐÐ. 1988. Phylogenies and quantitative characters. Annu. Rev. McPeek, M. A., A. K. Schrot, and J. M. Brown. 1996. Adaptation Ecol. Syst. 19:445±471. to predators in a new community: Swimming performance and Hagen, H. A. 1861. Synopsis of the Neuroptera of North America, predator avoidance in damsel¯ies. Ecology 77:617±629. with a list of the South American species. Smithson. Misc. Col- McPeek, M. A., M. Grace, and J. M. L. Richardson. 2001. Physi- lect. 4:1±347. ological and behavioral responses to predators shape the growth/ Hasagawa, M., H. Kishino, and T. Yano. 1985. Dating of the human- predation risk trade-off in damsel¯ies. Ecology 82:1535±1545. ape splitring by a molecular clock of mitochondrial DNA. J. Morin, P. J. 1984a. Odonate guild composition: experiments with Mol. Evol. 21:160±174. colonization history and ®sh predation. Ecology 65:1866±1873. Hooper, K. R. 2001. Flexible antipredator behavior in a dragon¯y Morin, P. J. 1984b. The impact of ®sh exclusion on the abundance species that coexists with different predator types. Oikos 93: and species composition of larval odonates: results of short-term 470±476. experiments in a North Carolina farm pond. Ecology 65:53±60. Jakobsson, S., O. Brick, and C. Kullberg. 1995. Escalated ®ghting Morrison, D. F. 1990. Multivatiate statistical methods. 3rd ed. Mc- behavior incurs increased predation risk. Anim. Behav. 49: Graw-Hill, New York. 235±239. Osenberg, C. W., E. E. Werner, G. G. Mittelbach and D. J. Hall. Jeffries, M. 1990. Interspeci®c differences in movement and hunting 1988. Growth patterns in bluegill (Lepomis macrochirus) and success in damsel¯y larvae (Zygoptera: ): responses to pumpkinseed (L. gibbosus) sun®sh: environmental variation and prey availability and predation threat. Freshwater Biol. 23: the importance of ontogenetic niche shifts. Can. J. Fish. Aquat. Sci. 45:17±26. 191±196. O'Steen, S., A. J. Cullum, and A. F. Bennett. 2002. Rapid evolution Johansson, F., R. Stoks, L. Rowe, and M. De Block. 2001. Life of escape ability in Trinidadian guppies (Poecilia reticulata). history plasticity in a damsel¯y: effects of combined time and Evolution 56:776±784. biotic constraints. Ecology 82:1857±1869. Peacor, S. D., and E. E. Werner. 1997. Trait-mediated indirect in- Johnson, D. M., and P. H. Crowley. 1980. Habitat and seasonal teractions in a simple aquatic food web. Ecology 78:1146±1156. segregation among coexisting odonate larvae. Odonatologica 9: ÐÐÐ. 2000. Predator effects on an assemblage of consumers 297±308. through induced changes in consumer foraging behavior. Ecol- Juliano, S. A., and M. E. Gravel. 2002. Predation and the evolution ogy 81:1998±2010. of prey behavior: an experiment with tree hole mosquitos. Behav. Peckarsky, B. L. 1996. Alternative predator avoidance syndromes Ecol. 13:301±311. in stream-dwelling may¯ies. Ecology 77:1888±1905. Knapp, R. A., K. R. Matthews, and O. Sarnelle. 2001. Resistance Peckarsky, B. L., C. A. Cowan, M. A. Penton, and C. Anderson. and resilience of alpine lake fauna to ®sh introductions. Ecol. 1993. Sublethal consequences of predator-avoidance by stream- Monogr. 71:401±421. dwelling may¯y larvae to adult ®tness. Ecology 74:1836±1846. Kohler, S. L., and M. A. McPeek. 1989. Predation risk and the Pierce, C. L., P. H. Crowley, and D. M. Johnson. 1985. Behavior foraging behavior of competing stream insects. Ecology 70: and ecological interactions of larval Odonata. Ecology 66: 1811±1825. 1504±1512. Lima, S. L. 1998. Stress and decision making under the risk of Purvis, A., and T. Garland, Jr. 1993. Polytomies in comparative predation: recent developments from behavioral, reproductive, analyses of continuous characters. Syst. Biol. 42:569±575. and ecological perspectives. Adv. Study Behav. 27:215±290. Relyea, R. A. 2000. Trait-mediated indirect effects in larval an- Lima, S. L., and L. M. Dill. 1990. Behavioral decisions made under urans: Reversing competition with the threat of predation. Ecol- the risk of predation: a review and prospectus. Can. J. Zool. 68: ogy 81:2278±2289. 619±640. ÐÐÐ. 2001. Morphological and behavioral plasticity of larval Magurran, A. E., B. H. Seghers, G. R. Carvalho, and P. W. Shaw. anurans in response to different predators. Ecology 82:523±540. 1992. Behavioral consequences of an arti®cial introduction of Relyea, R. A., and E. E. Werner. 1999. Quantifying the relation guppies (Poecilia reticulata) in North Trinidad: evidence for the between predator-induced behavior and growth performance in evolution of antipredator behavior in the wild. Proc. R. Soc. larval anurans. Ecology 80:2117±2124. Lond. B 248:117±122. Richardson, J. M. L. 2001a. A comparative study of activity levels Martins, E. P., and T. Garland, Jr. 1991. Phylogenetic analyses of in larval anurans and response to the presence of different pred- the correlated evolution of continuous characters: a simulation ators. Behav. Ecol. 12:51±58. study. Evolution 45:534±557. ÐÐÐ. 2001b. The relative roles of adaptation and phylogeny in McPeek, M. A. 1990a. Behavioral differences between Enallagma determination of larval traits in diversifying anuran lineages. species (Odonata) in¯uencing differential vulnerability to pred- Am. Nat. 157:282±299. ators. Ecology 71:1714±1726. Richardson, J. M. L., and B. R. Anholt. 1995. Ontogenetic behaviour ÐÐÐ. 1990b. Determination of species composition in the En- changes in larvae of the damsel¯y verticalis (Odonata: allagma damsel¯y assemblages of permanent lakes. Ecology 71: Coenagrionidae). Ethology 101:308±334. 83±98. Richardson, J. M. L., and R. L. Baker. 1996. Function of abdomen ÐÐÐ. 1995a. Morphological evolution mediated by behavior in wave behavior in larval Ischnura verticalis (Odonata: Coena- the damsel¯ies of two communities. Evolution 49:749±769. grionidae). J. Ins. Behav. 9:183±195. ÐÐÐ. 1995b. Testing hypotheses about evolutionary change on Riechert, S. E., and A. Hedrick. 1990. Levels of predation and EVOLUTION OF PREY BEHAVIOR 585

genetically based anti-predator behavior in the spider, Agelen- foraging effort in damsel¯ies that differ in life cycle length. opsis aperta. Anim. Behav. 40:679±687. Oikos 91:559±567. SAS Institute, Inc. 1990. SAS/STAT User's Guide, Version 6, Storfer, A., and A. Sih. 1998. Gene ¯ow and ineffective antipredator Fourth Edition, Volume 2. Cary, North Carolina. behavior in a stream-breeding salamander. Evolution 52: Schmitz, O. J., and K. B. Suttle. 2001. Effects of top predator species 558±565. on direct and indirect interactions in a food web. Ecology 82: Turgeon, J., and M. A. McPeek. 2002. Phylogeographic analyses 2072±2081. of a recent radiation of Enallagma damsel¯ies (Odonata: Coen- Sih, A. 1987. Predators and prey lifestyles: an evolutionary and agrionidae). Mol. Ecol. 11:1989±2002. ecological overview. Pages 203±224 in W. C. Kerfoot and A. Van Buskirk, J., S. A. McCollum, and E. E. Werner. 1997. Natural Sih (eds.), Predation: direct and indirect impacts on aquatic com- selection for environmentally induced phenotypes in tadpoles. munities. University of New England Press, Hanover, New Evolution 51:1983±1992. Hampshire, USA. Watkins, T. B. 1996. Predator-mediated selection on burst swim- ÐÐÐ. 1992. Prey uncertainty and the balancing of antipredator ming performance in tadpoles of the Paci®c tree frog, Pseudacris and feeding needs. Am. Nat. 139:1052±1069. regilla. Physiol. Zool. 69:154±167. Sih, A., L. B. Kats, and E. F. Maurer. 2000. Does phylogenetic ÐÐÐ. 2001. A quantitative genetic test of adaptive decoupling inertia explain the evolution of ineffective antipredator behavior across metamorphosis for locomotor and life-history traits in the in a sun®sh-salamander system? Behav. Ecol. Sociobiol. 49: Paci®c tree frog, Hyla regilla. Evolution 55:1668±1677. 48±56. Werner, E. E., and B. R. Anholt. 1993. Ecological consequences Skelly, D. K. 1992. Field evidence for a cost of behavioral anti- of the trade-off between growth and mortality rates mediated by predator response in a larval amphibian. Ecology 73:704±708. foraging activity. Am. Nat. 142:242±272. Skelly, D. K., and E. E. Werner. 1990. Behavioral and life-historical ÐÐÐ. 1996. Predator-induced behavioral indirect effects in an- responses of larval american toads to an odonate predator. Ecol- uran larvae. Ecology 77:157±169. ogy 71:2313±2322. Werner, E. E., and J. F. Gilliam. 1984. The ontogenetic niche and Sokal, R. R., and F. J. Rohlf. 1995. Biometry: third edition. W. H. species interactions in size-structured populations. Annu. Rev. Freeman and Co., New York. Ecol. Syst. 15:393±425. Steiner, C., B. Siegert, S. Schulz, and F. Suhling. 2000. Habitat Werner, E. E., and M. A. McPeek. 1994. The roles of direct and selection in the larvae of two species of Zygoptera (Odonata): indirect effects on the distributions of two frog species along an biotic interactions and abiotic limitation. Hydrobiologia 427: environmental gradient. Ecology 75:1368±1382. 167±176. Wisenden, B. D., D. P. Chivers, and R. J. F. Smith. 1997. Learned recognition of predation risk by Enallagma damsel¯y larvae Stoks, R., and M. De Block. 2000. The in¯uence of predator species (Odonata, Zygoptera) on the basis of chemical cues. J. Chem. and prey age on the immediate survival value of antipredator Ecol. 23:137±151. behaviours in a damsel¯y. Arch. Hydrobiol. 147:417±430. Stoks, R., and F. Johansson. 2000. Trading off mortality risk against Corresponding Editor: B. Crespi