Absence Of Predators Research Articles

The energetic cost of foraging explains growth anomalies in tadpoles exposed to predators.

Theoretical models predict that predator-induced phenotypes should have lower fitness in the absence of predators. Tadpoles frequently respond to invertebrate predators by reducing activity levels and changing their body proportions. While some studies have shown that induced defenses in tadpoles reduce growth rates, others have found no effect. The aim of this study was to measure the effects of predator presence on energy expenditure in tadpoles. Predator exposure lowered overall metabolic rate by 19%, while specific dynamic action due to food consumption increased resting metabolism by 11%. Control tadpoles moved significantly more (93.6 ± 3.9 cm/min) than predator-exposed animals (50.1 ± 7.5 cm/min), and swimming increased metabolic rate by up to 400% compared to stationary tadpoles, indicating that activity can be energetically expensive and can consume as much as 37% of assimilated energy. These findings suggest that the costs of reduced foraging are context dependent and may even be beneficial in environments where high-quality resources are closely spaced but detrimental when extensive movement is required to obtain optimal resources for growth.

The fear of unseen predators: ground squirrel tail flagging in the absence of snakes signals vigilance

Rather than fleeing from predators, many animals exhibit conspicuous displays that are thought to deter attacks by advertising quality (physical capabilities), or awareness of the predator. However, prey commonly exhibit the same antipredator display when predators are absent. Signaling in this context could either dishonestly indicate predator detection, or honestly indicate vigilance, but no study has tested these hypotheses experimentally. We tested the vigilance advertisement function of tail flagging, a signal given by California ground squirrels (Otospermophilus beecheyi) to rattlesnakes (Crotalus oreganus), by simulating snake strikes and quantifying strike avoidance behaviors in signaling and non-signaling squirrels. We removed the effect of snake presence on signaling by simulating strikes 1) in the presence of a rattlesnake, 2) with no snake present, or 3) in an area where squirrels had recently encountered a snake that was no longer present. Squirrels tail flagged most when interacting with a snake. Squirrels also signaled in areas of recent snake encounters, and in this context, they responded faster to simulated strikes and were more likely to leap vertically or horizontally away from the attack. Tail flagging rate was also related to squirrels’ body displacement time and flee modality. Squirrels rarely signaled or exhibited evasive leaping with no snake present. These results indicate that displays in the absence of predators can honestly signal vigilance, or the readiness to avoid an attack, even if predators are undetected. Such antipredator displays may be widespread as many species could benefit from advertising alertness when uncertain of the location of predators.

Evaluation of tree and shrub resources of the Eurasian beaver (Castor fiber L.) and changes in beaver foraging strategy after resources depletion

The results of comparative analysis of tree and shrub resources quantitative characteristics in the active and abandoned beaver habitats within the territory of the Tadenka River basin, Prioksko-Terrasny Nature Reserve, where beavers have been dwelling for more than 60 years, are presented. Using one-way ANOVA analysis with the settlement type (active or abandoned) as a factor, it was shown that long-term foraging by beaver leads to a decrease in the species richness of trees (P = 0.068). Different hypotheses of the impact produced by beaver selective foraging on various forest layers (overstorey and undestorey) are discussed. Factors promoting thinning and changes in the age structure of the overstorey and undestorey are considered. There were observed changes in the species composition, accompanied by an increase in the proportion of low preference and nonfood species. The conclusion is made that, if the foraging zone does not exceed 50 m at the beginning of habitat utilization, it extends up to 165 m in the absence of predators when the habitat is used repeatedly. This observation is confirmed by Fisher’s exact test (P = 0.005), Yates’ chisquared test (P = 0.002), and the likelihood ratio test (P = 0.0002). In the case of beavers recolonizing their abandoned habitats with unrecovered food resources in the Tadenka River basin, a distant zone within 50 to 165 m from the bank becomes the main zone for tree-shrub foraging.

When a little means a lot – slight daily cleaning is crucial for obligatory ant-tended aphids

Ant-aphid mutualism has been investigated by many authors but it is unknown if anti-predator protection provided by ants is the main benefit for aphids. The aim of our paper is to analyse the ant-aphid interactions in the absence of predators. Based on video recordings we distinguish ant behaviours in interactions with attended aphids and we present ant time-budget at different times of the day. We also test if an aphid colony can survive without ant attendance in an environment free from predators and we inquire how much ant attendance is needed to maintain an aphid colony in good condition. Our study shows that, despite the lack of predation pressure, aphids of the species Cinara tujafilina were not able to survive without ant attendance and the extinction was caused by the excessive honeydew that covered aphids and their surroundings. We also found that ants cleaning aphids was the most frequent and time-consuming activity in ant-aphid interactions. However, in general, ants interacted with aphids only for less than 5% of their total time-budget. Thus, despite the fact that cleaning seems to be crucial in aphid survival, surprisingly little ant effort is needed to maintain an aphid colony in good condition.

Artificial warming increases size at metamorphosis in plateau frogs (Rana kukunoris) in the presence of predators

Global warming may induce significant changes in species life history traits particularly in amphibians, which are characterized by complex and plastic life cycles. Because both warming and predators are often suggested to reduce size at metamorphosis in amphibians, we hypothesized that the size at metamorphosis was further reduced by experimental warming in the presence of predators. We conducted a factorial-designed experiment involving two factors and two levels (warmed vs. ambient, lethal predator absence vs. presence, resulting in four treatments) using Rana kukunoris tadpoles in the eastern Tibetan Plateau, and we examined its behavioral, growth, and developmental responses to warming in the presence and absence of predatory beetles (Agabus sp.) for 13 weeks. During the course of the experiment, a similar level of tadpole mortality due to the diving beetles was found between ambient and warmed treatments, but the warming effect on size at metamorphosis depended on whether the predators were present or absent. In the absence of predators, warming did not significantly increase tadpole growth but advanced the timing of metamorphosis, such that size at metamorphosis of forelimb emergence and tail resorption was much reduced in terms of body fresh weight. In the presence of predators, warming increased tadpole growth rate much more than the development rate (as reflected by duration of the tadpole stage), and therefore the size at metamorphosis was significantly increased. The significant effect of the interaction between predator and warming on the size at metamorphosis could be attributed to the tadpole response in the frequencies of feeding, resting, and swimming to the predator activity level, which was in turn increased by warming. We suggest that warming-induced changes in life history traits should be studied in relation to species interaction so as to accurately predict ecological response of amphibians to the future warmed world.

Control of periphyton standing crop in an Atlantic Forest stream: the relative roles of nutrients, grazers and predators

Summary Periphytic algae are an important source of energy fuelling stream food webs. Periphytic algal biomass can be controlled by bottom‐up and top‐down forces, but there are few studies that have investigated these effects simultaneously, especially in tropical streams, where periphyton can be a very important carbon source. Here, we investigated the bottom‐up effects of nutrients and the top‐down effects of grazers and predators in a coastal tropical stream in Brazil. We employed nutrient‐diffusing substrata to test for nutrient limitation, placed inside electric exclosures of different intensities, which prevented consumers from entering the electrified area. We used four types of substrata: one enriched with nitrogen alone (N), one with phosphorus alone (P), one with nitrogen + phosphorus (NP) and one control with no nutrients added (C). The electric exclosure had three treatments: high electricity that excluded both predators (Macrobrachium olfersi shrimps) and grazers (Baetidae mayflies), low electricity that excluded only shrimps, and a control treatment with no electricity where both shrimps and mayflies were allowed to enter. The limiting nutrient in the stream was nitrogen. Our results showed a greater magnitude of bottom‐up effects, with periphytic algae responding more strongly to nutrient addition than to grazers or predators. Top‐down control was not as strong, but periphytic algae responded negatively to grazers, especially in the absence of predators. This suggests that shrimps, either directly or indirectly, inhibit mayfly grazing activity. The response of periphytic algae to nutrients was stronger in the absence of grazers. Thus, top‐down effects, both directly and indirectly through a trophic cascade, can dampen the response to nitrogen addition, diminishing the degree of resource limitation.

Biocontrol in an impulsive predator–prey model

We study a model for biological pest control (or “biocontrol”) in which a pest population is controlled by a program of periodic releases of a fixed yield of predators that prey on the pest. Releases are represented as impulsive increases in the predator population. Between releases, predator-pest dynamics evolve according to a predator–prey model with some fairly general properties: the pest population grows logistically in the absence of predation; the predator functional response is either of Beddington–DeAngelis type or Holling type II; the predator per capita birth rate is bounded above by a constant multiple of the predator functional response; and the predator per capita death rate is allowed to be decreasing in the predator functional response and increasing in the predator population, though the special case in which it is constant is permitted too. We prove that, when the predator functional response is of Beddington–DeAngelis type and the predators are not sufficiently voracious, then the biocontrol program will fail to reduce the pest population below a particular economic threshold, regardless of the frequency or yield of the releases. We prove also that our model possesses a pest-eradication solution, which is both locally and globally stable provided that predators are sufficiently voracious and that releases occur sufficiently often. We establish, curiously, that the pest-eradication solution can be locally stable whilst not being globally stable, the upshot of which is that, if we delay a biocontrol response to a new pest invasion, then this can change the outcome of the response from pest eradication to pest persistence. Finally, we state a number of specific examples for our model, and, for one of these examples, we corroborate parts of our analysis by numerical simulations.

Protozoan predation is differentially affected by motility of enteric pathogens in water vs. sediments.

Survival of enteric bacteria in aquatic habitats varies depending upon species, strain, and environmental pressures, but the mechanisms governing their fate are poorly understood. Although predation by protozoa is a known, top-down control mechanism on bacterial populations, its influence on the survival of fecal-derived pathogens has not been systematically studied. We hypothesized that motility, a variable trait among pathogens, can influence predation rates and bacterial survival. We compared the survival of two motile pathogens of fecal origin by culturing Escherichia coli O157 and Salmonella enterica Typhimurium. Each species had a motile and non-motile counterpart and was cultured in outdoor microcosms with protozoan predators (Tetrahymena pyriformis) present or absent. Motility had a significant, positive effect on S. enterica levels in water and sediment in the presence or absence of predators. In contrast, motility had a significant negative effect on E. coli O157 levels in sediment, but did not affect water column levels. The presence/absence of protozoa consistently accounted for a greater proportion of the variability in bacterial levels (>95 %) than in bacterial motility (<4 %) in the water column. In sediments, however, motility was more important than predation for both bacteria. Calculations of total CFU/microcosm showed decreasing bacterial concentrations over time under all conditions except for S. enterica in the absence of predation, which increased ∼0.5-1.0 log over 5 days. These findings underscore the complexity of predicting the survival of enteric microorganisms in aquatic habitats, which has implications for the accuracy of risk assessment and modeling of water quality.

Insights into embryo defenses of the invasive apple snail Pomacea canaliculata: egg mass ingestion affects rat intestine morphology and growth.

BackgroundThe spread of the invasive snail Pomacea canaliculata is expanding the rat lungworm disease beyond its native range. Their toxic eggs have virtually no predators and unusual defenses including a neurotoxic lectin and a proteinase inhibitor, presumably advertised by a warning coloration. We explored the effect of egg perivitellin fluid (PVF) ingestion on the rat small intestine morphology and physiology.Methodology/Principal FindingsThrough a combination of biochemical, histochemical, histopathological, scanning electron microscopy, cell culture and feeding experiments, we analyzed intestinal morphology, growth rate, hemaglutinating activity, cytotoxicity and cell proliferation after oral administration of PVF to rats. PVF adversely affects small intestine metabolism and morphology and consequently the standard growth rate, presumably by lectin-like proteins, as suggested by PVF hemaglutinating activity and its cytotoxic effect on Caco-2 cell culture. Short-term effects of ingested PVF were studied in growing rats. PVF-supplemented diet induced the appearance of shorter and wider villi as well as fused villi. This was associated with changes in glycoconjugate expression, increased cell proliferation at crypt base, and hypertrophic mucosal growth. This resulted in a decreased absorptive surface after 3 days of treatment and a diminished rat growth rate that reverted to normal after the fourth day of treatment. Longer exposure to PVF induced a time-dependent lengthening of the small intestine while switching to a control diet restored intestine length and morphology after 4 days.Conclusions/SignificanceIngestion of PVF rapidly limits the ability of potential predators to absorb nutrients by inducing large, reversible changes in intestinal morphology and growth rate. The occurrence of toxins that affect intestinal morphology and absorption is a strategy against predation not recognized among animals before. Remarkably, this defense is rather similar to the toxic effect of plant antipredator strategies. This defense mechanism may explain the near absence of predators of apple snail eggs.

Opposite responses of body condition and fertility in adjacent moose populations

ABSTRACTMoose (Alces alces) populations exceed 3 individuals/km2 in some wildlife reserves and parks of northeastern Canada. Heavy browsing pressure at such densities is potentially altering the ecological integrity of forests with eventual negative consequences for moose. We hypothesized that regulation by resources would be limited by the capacity of female moose to modulate their reproductive strategies to maintain high fertility despite a decline in body condition. We observed a 20–33% decline in rump fat thickness in males and females, respectively, from the high density Matane Wildlife Reserve in Eastern Québec in October compared to an adjacent population. We also observed a lower mass of the peroneus group of muscles for males (−3%) and prime‐aged females (−8%) in the Matane Wildlife Reserve than in the adjacent population. Females from the Matane Wildlife Reserve population had a lower twinning ovulation rate (1 out of 20 vs. 7 out of 21 ovulating females in the adjacent population) but &gt;15% higher overall ovulation rate. Our results suggest that female moose can maintain high fertility despite a decline in body condition, by reducing their litter size at ovulation and conserving energy to increase the probability of annual reproduction. The adjustment of female reproductive strategies illustrates the plasticity of moose in response to decreasing habitat quality. We conclude that in the absence of specialist predators, equilibrium with forage is unlikely for large herbivores in the short or mid‐term. Active management of moose populations is likely required to maintain the ecological integrity of boreal forests. © 2014 The Wildlife Society.

Predation risk increases dispersal distance in prey.

Understanding the ecological factors that affect dispersal distances allows us to predict the consequences of dispersal. Although predator avoidance is an important cause of prey dispersal, its effects on dispersal distance have not been investigated. We used simple experimental setups to test dispersal distances of the ambulatory dispersing spider mite (Tetranychus kanzawai) in the presence or absence of a predator (Neoseiulus womersleyi). In the absence of predators, most spider mites settled in adjacent patches, whereas the majority of those dispersing in the presence of predators passed through adjacent patches and settled in distant ones. This is the first study to experimentally demonstrate that predators induce greater dispersal distance in prey.

Differences in predator composition alter the direction of structure‐mediated predation risk in macrophyte communities

Structural complexity strongly influences the outcome of predator–prey interactions in benthic marine communities affecting both prey concealment and predator hunting efficacy. How habitat structure interacts with species‐specific differences in predatory style and antipredatory strategies may therefore be critical in determining higher trophic functions. We examined the role of structural complexity in mediating predator–prey interactions across several macrophyte habitats along a gradient of structural complexity in three different bioregions: western Mediterranean Sea (WMS), eastern Indian Ocean (EIO) and northern Gulf of Mexico (NGM). Using sea urchins as model prey, we measured survival rates of small (juveniles) and medium (young adults) size classes in different habitat zones: within the macrophyte habitat, along the edge and in bare sandy spaces. At each site we also measured structural variables and predator abundance. Generalised linear models identified biomass and predatory fish abundance as the main determinants of predation intensity but the efficiency of predation was also influenced by urchin size class. Interestingly though, the direction of structure‐mediated effects on predation risk was markedly different between habitats and bioregions. In WMS and NGM, where predation by roving fish was relatively high, structure served as a critical prey refuge, particularly for juvenile urchins. In contrast, in EIO, where roving fish predation was low, predation was generally higher inside structurally complex environments where sea stars were responsible for much of the predation. Larger prey were generally less affected by predation in all habitats, probably due to the absence of large predators. Overall, our results indicate that, while the structural complexity of habitats is critical in mediating predator–prey interactions, the direction of this mediation is strongly influenced by differences in predator composition. Whether the regional pool of predators is dominated by visual roving species or chemotactic benthic predators may determine if structure dampens or enhances the influence of top–down control in marine macrophyte communities.

Effect of prey personality depends on predator species

The ability of prey to respond to predators is especially important in human-altered habitats, where prey are faced with changing predator regimes. A growing body of research has shown the important ecological impacts of intraspecific, individual differences in behavior, but few studies have shown direct fitness consequences of behavioral types in a predation context. We examined behavioral syndromes in the endemic Largespring mosquitofish (Gambusia geiseri) and how the behavioral type of individual G. geiseri affected their behavior and survival when exposed to 3 different species of predators. We measured latency to emerge from a container, time spent moving, and tank area used for individual G. geiseri in the presence and absence of predators. We then measured behavior and survival of these same individuals in one-on-one predation trials. We found that behavioral types and correlations between latency to emerge, time spent moving, and area used were consistent regardless of predator presence. Behavioral type did not predict survival of the predation trial. However, higher behavioral scores correlated with more escapes from predatory Fundulus grandis. We argue that this result indicates that active/exploratory fish have a greater ability than their conspecifics to escape this species, which is a novel predator. Our results illustrate the potential importance of considering individual differences in behavior in studying the impacts of introduced predator species.

When top-down becomes bottom up: behaviour of hyperdense howler monkeys (Alouatta seniculus) trapped on a 0.6 ha island.

Predators are a ubiquitous presence in most natural environments. Opportunities to contrast the behaviour of a species in the presence and absence of predators are thus rare. Here we report on the behaviour of howler monkey groups living under radically different conditions on two land-bridge islands in Lago Guri, Venezuela. One group of 6 adults inhabited a 190-ha island (Danto) where they were exposed to multiple potential predators. This group, the control, occupied a home range of 23 ha and contested access to food resources with neighbouring groups in typical fashion. The second group, containing 6 adults, was isolated on a remote, predator-free 0.6 ha islet (Iguana) offering limited food resources. Howlers living on the large island moved, fed and rested in a coherent group, frequently engaged in affiliative activities, rarely displayed agonistic behaviour and maintained intergroup spacing through howling. In contrast, the howlers on Iguana showed repulsion, as individuals spent most of their time spaced widely around the perimeter of the island. Iguana howlers rarely engaged in affiliative behaviour, often chased or fought with one another and were not observed to howl. These behaviors are interpreted as adjustments to the unrelenting deprivation associated with bottom-up limitation in a predator-free environment.

Meso-predators: A confounding variable in consumer exclusion studies

Large consumers are important in determining community structure and have been extensively researched. The impact of predation on hard-substrate marine invertebrate communities tends to be mixed. Numerous exclusion studies fail to incorporate appropriate procedural controls or account for meso-predators. An experimental exclusion study was performed to investigate the effects of large predators on the development of hard-substrate invertebrate assemblages, whilst simultaneously quantifying changes in the abundances of meso-predators. Settlement plates were deployed subtidally and were either caged (to exclude large predators), placed in cage controls or left exposed to predation. Assemblages were collected and censused after 9, 14 and 19weeks. The overall structure of the communities differed due to predation, and this effect was consistent through time. Encrusting bryozoans and hydroids occupied more space on exposed surfaces. Amphipod tube cover was greater in caged treatments, with the magnitude of the difference increasing through time, whilst solitary ascidian cover was greater on caged treatments in week 19 only. Meso-predators varied in their responses to large predators, with whelks more abundant in the absence of predators, whereas flatworm abundance was greater where predators were present. Our study demonstrated that strong effects of predators on particular taxa was able to alter the overall community composition, with the cascading effects of large predators on meso-predator abundances potentially contributing to this outcome.

Do omnivorous shrimp influence mayfly nymph life history traits in a tropical island stream?

Interspecific interactions can play an important role in determining habitat selection and resource use between competing species. We examined interactions between an omnivorous shrimp and a grazing mayfly, two co-dominant taxa found in Puerto Rican headwater streams, to assess how predator presence may influence mayfly resource use and instantaneous growth in a tropical rainforest ecosystem. We conducted a series of behavioral and growth experiments to determine the effects of the freshwater shrimp, Xiphocaris elongata, on the growth rate and resource selection of mayfly nymphs in the family Leptophlebiidae. For resource choice assessments, we conducted a series of five day laboratory experiments where mayflies were given access to two resource substrate choices (cobble vs. leaves) in the presence or absence of shrimp. To assess for the effects of shrimp on mayfly fitness, we measured mayfly growth in laboratory aquaria after five days using four treatments (cobble, leaves, cobble + leaves, no resource) in the presence or absence of shrimp. In resource choice experiments, mayflies showed preference for cobble over leaf substrata (p < 0.05) regardless of the presence of shrimps, however, the preference for cobble was significantly greater when shrimp were present in the leaf habitat. In growth experiments, there were no statistical differences in mayfly growth in the presence or absence of shrimp (p = 0.07). However, we measured increased mayfly nymph growth in the absence of predators and when both cobble and leaves were available. Our results suggest that interspecific interactions between these taxa could potentially influence organic matter resource dynamics (e.g., leaf litter processing and export) in Puerto Rican streams.

Alternative responses to predation in two headwater stream minnows is reflected in their contrasting diel activity patterns.

Animals exhibit diel periodicity in their activity in part to meet energy requirements whilst evading predation. A competing hypothesis suggests that partitioning of diel activities is less important because animals capitalise on opportunity. To test these hypotheses we examined the diel activity patterns for two cyprinid minnows, chubbyhead barb Barbus anoplus and the Eastern Cape redfin minnow Pseudobarbus afer that both occur within headwater streams in the Eastern Cape, South Africa. Chubbyhead barbs exhibited consistent nocturnal activity based on both field and laboratory observations. Due to the absence of fish predators within its habitat, its nocturnal behaviour suggests a response to the cost associated with diurnal activity, such as predation risk by diving and wading birds. In contrast, redfin minnows showed high diurnal activity and a shoaling behaviour in the wild, whereas, in the laboratory, they showed high refuge use during the diel cycle. Despite their preference for refuge in the laboratory, they were diurnally active, a behaviour that was consistent with observations in the wild. The diurnal activity of this species suggests a response to the cost associated with nocturnal activity. Such a cost could be inferred from the presence of the longfin eel, a native predator that was active at night, whereas the daytime shoaling behaviour suggests an anti-predator mechanism to diurnal visual predators. The implications of these findings relate to the impacts associated with the potential invasions by non-native piscivores that occur in the mainstem sections. Diurnal activity patterns for redfin minnows, that are IUCN-listed as endangered, may, in part, explain their susceptibility to high predation by visual non-native piscivores, such as bass and trout. In contrast, the nocturnal habits of chubbyhead barbs suggest a probable pre-adaptation to visual predation. The likelihood of invasion by nocturnally-active sharptooth catfish Clarias gariepinus, however, may compromise this prior advantage.

Seasonal Variation in the Fate of Seeds under Contrasting Logging Regimes

Seed predators and dispersers may drive the speed and structure of forest regeneration in natural ecosystems. Rodents and ants prey upon and disperse seeds, yet empirical studies on the magnitude of these effects are lacking. Here, we examined the role of ants and rodents on seed predation in 4 plant species in a successional gradient on a tropical rainforest island. We found that (1) seeds are mostly consumed rather than dispersed; (2) rates of seed predation vary by habitat, season, and species; (3) seed size, shape, and hardness do not affect the probability of being depredated. Rodents were responsible for 70% of seed predation and were negligible (0.14%) seed dispersers, whereas ants were responsible for only 2% of seed predation and for no dispersal. We detected seasonal and habitat effects on seed loss, with higher seed predation occurring during the wet season and in old-growth forests. In the absence of predators regulating seed-consumer populations, the densities of these resilient animals explode to the detriment of natural regeneration and may reduce diversity and carrying capacity for consumers and eventually lead to ecological meltdown.

How large are the extinct giant insular rodents? New body mass estimations from teeth and bones

The island rule entails a modification of the body size of insular mammals, a character related with numerous biological and ecological variables. From the Miocene to human colonization (Holocene), Mediterranean and Canary Islands were unaltered natural ecosystems, with paleofaunas formed with endemic giant rodents among other mammals. Our aim is to create methods to estimate the body masses of fossil island rodents and address the nature of ecological pressures driving the island rule. We created regression equations based on extant rodent data and used these to estimate the body masses of the extinct species. Our results show strong correlations between teeth, cranial and postcranial measurements and body mass, except for the length of the long bones, the transversal diameter of the distal tibia and the anteroposterior diameter of the proximal tibia, where the equations were less reliable. The use of equations obtained from a more homogeneous group (suborder and family) is preferable when analyzing the area of the first molar. The new regressions were applied to estimate the body masses of some Mediterranean and Canarian fossil rodents (Canariomys, C. bravoi 1.5 kg and C. tamarani 1 kg; Hypnomys, H. morpheus 230 g and H. onicensis 200 g; and Muscardinus cyclopeus 100 g). Our results indicate that under absence of predation, resource availability (island area) is the key factor that determines the size of the Canariomys sp. However, under presence of specialized predators (birds of prey), body size evolution is less pronounced (Hypnomys sp.).

Morphological divergence driven by predation environment within and between species of Brachyrhaphis fishes.

Natural selection often results in profound differences in body shape among populations from divergent selective environments. Predation is a well-studied driver of divergence, with predators having a strong effect on the evolution of prey body shape, especially for traits related to escape behavior. Comparative studies, both at the population level and between species, show that the presence or absence of predators can alter prey morphology. Although this pattern is well documented in various species or population pairs, few studies have tested for similar patterns of body shape evolution at multiple stages of divergence within a taxonomic group. Here, we examine morphological divergence associated with predation environment in the livebearing fish genus Brachyrhaphis. We compare differences in body shape between populations of B. rhabdophora from different predation environments to differences in body shape between B. roseni and B. terrabensis (sister species) from predator and predator free habitats, respectively. We found that in each lineage, shape differed between predation environments, consistent with the hypothesis that locomotor function is optimized for either steady swimming (predator free) or escape behavior (predator). Although differences in body shape were greatest between B. roseni and B. terrabensis, we found that much of the total morphological diversification between these species had already been achieved within B. rhabdophora (29% in females and 47% in males). Interestingly, at both levels of divergence we found that early in ontogenetic development, females differed in shape between predation environments; however, as females matured, their body shapes converged on a similar phenotype, likely due to the constraints of pregnancy. Finally, we found that body shape varies with body size in a similar way, regardless of predation environment, in each lineage. Our findings are important because they provide evidence that the same source of selection can drive similar phenotypic divergence independently at multiple divergence levels.