Prey animals often respond to predators by reducing activity levels. Th is can produce a trait-me... more Prey animals often respond to predators by reducing activity levels. Th is can produce a trait-mediated indirect interaction (TMII) between predators and prey resources, whereby reduced foraging by prey in the presence of a predator causes an increase in prey resources. TMIIs play important roles in structuring communities, and it is important to understand factors that determine their strength. One such infl uence may be behavioural variation in the prey species, with indirect eff ects of predators being stronger within populations that are more responsive to the presence of a predator. We tested 1) whether the behavioural responsiveness of populations of wood frog tadpoles to predator cues was related to the predation risk in their native ponds, and 2) whether more responsive tadpoles yielded stronger TMIIs. To do this, we 1) measured the activity of tadpoles from 18 populations in mesocosms with and without caged predators, and 2) measured changes in the biomass of periphyton (the tadpoles ' diet) between predator treatments for each population. We found that tadpoles from higher predation risk ponds reduced their time outside refuges more in the presence of predators and tended to move less when visible, suggesting possible local adaptation to predation regimes. Th ough the presence of predators generally resulted in higher periphyton biomass -a TMII -there was no evidence that the strength of this TMII was aff ected by variation in tadpole behaviour. Foraging activity and general activity may be decoupled to some extent, enabling high predation riskadapted tadpoles to limit the fi tness costs of reduced foraging when predators are present.
Locating and following animals using tracking devices is a method commonly used on many taxa, fro... more Locating and following animals using tracking devices is a method commonly used on many taxa, from mammals (Chamberlain and Leopold, 2000; Daniels et al., 2001; Long, 2001) to insects (Roland et al., 1996; Carreck et al., 1999; Kutsch, 1999; Capaldi et al., 2000). Animals are tracked to study aspects of their home range (Li et al., 2000; Rodrigues and Monterio, 2000), movement patterns (Matthews and Pope, 1999; Rodrigues and Monterio, 2000), daily and seasonal activities (Lamoureux and Madison, 1999; Chamberlain and ...
In many studies, it is necessary for researchers to mark individual animals for later identificat... more In many studies, it is necessary for researchers to mark individual animals for later identification. It is often assumed in the interpretation of these studies that marks have no effects on the biology of the animals. This assumption is insufficiently tested, and, when it is, coarse assessments of negative effects are often used, such as survival and growth under simplified laboratory conditions. We examined the consequences of a common larval amphibian marking technique (staining with methylene blue) for wood frog tadpole behavior and survival in an ecologically realistic scenario (predation). We measured a number of tadpole behavioral variables, under baseline conditions and in the presence of olfactory cues of a predator, for marked and unmarked tadpoles. We then exposed pairs of tadpoles (one marked and one unmarked) to one of two predators and tested for the effects of marking on the susceptibility of tadpoles to predation. We found that marking suppressed the increase in movement rate that typically occurred in (unmarked) tadpoles in the presence of predator cues. Marked tadpoles were significantly more likely to be captured by predators, an effect that could not be attributed to this difference in movement rate. These results raise concern about the use of this staining method and highlight the need for studies involving marked animals to thoroughly address any relevant effects the marks may have on the biology of the subjects.
The introduction of non-native species is becoming increasingly common. Understanding the impact ... more The introduction of non-native species is becoming increasingly common. Understanding the impact of invaders on native populations is critical for effective management. Red imported fire ants (Solenopsis invicta Buren, 1972) were introduced to the USA in the 1930s. They will attack, and can kill, native fence lizards (Sceloporus undulatus (Bosc and Daudin in Sonnini and Latreille, 1801)), which co-occur with these ants across much of their invasive range. I determined whether fence lizards minimize encounters with S. invicta by altering their habitat use following invasion or avoiding cues of the presence of these fire ants. I recorded the habitat use of fence lizards and S. invicta mounds across four sites with different histories of invasion, and quantified lizard avoidance of S. invicta scent. I found that lizards do not alter their habitat use following S. invicta invasion, nor do they spatially avoid their mounds. Fence lizards do avoid S. invicta scent, but this was only evident in naĂ¯ve or recently invaded populations. The lack of avoidance of S. invicta by fence lizards could be explained by the high prevalence of these fire ants, making them difficult to avoid, and adaptive shifts in the escape behaviour and morphology of these lizards following invasion that permit them to survive fire ant attack.
Animals typically exhibit adaptive behaviors that reduce their risk of predation. The term 'boldn... more Animals typically exhibit adaptive behaviors that reduce their risk of predation. The term 'boldness' describes individual variation in the propensity to exhibit risk-reducing behavior and is the subject of much research attention. Predators should select against boldness, and this has been supported by empirical studies and behavioral ecology theory. We tested whether a standardized assay of three boldness-associated behaviors in wood frog (Lithobates sylvaticus) tadpoles predicted survival when faced with a predator. Tadpole behavior was assayed in an open field and then tadpoles were placed, in pairs, in an enclosure with a predator (newt or larval dragonfly). Survival did not depend on differences in measured boldness, and this result held when we accounted for interactions between different boldness behaviors and between behavior and size or predator identity. The absence of selection by predators against bolder tadpoles is counterintuitive and inconsistent with our understanding of the behavioral ecology of these animals. Two possible explanations are offered for this result. First, selection against boldness may be minimized by other phenotypic traits, such as escape ability. Alternatively, the potential lack of consistency between standardized boldness assays and natural encounters with predators may limit our capacity to study the evolution of boldness, cautioning against this approach. These results highlight the complexities of the relationships between behavioral traits and fitness and the challenges associated with their study.
Antipredator mechanisms employed by animals are obviously beneficial if they increase survival, b... more Antipredator mechanisms employed by animals are obviously beneficial if they increase survival, but their use may be costly and decrease fitness. Fitness costs of antipredator mechanisms may, in turn, be defrayed by behavioural compensation. We used lizards as a model to measure behavioural fitness costs of the antipredator mechanism, autotomy, as they commonly lose their tails when attacked by predators. In addition, we examined whether male skinks, Carlia jarnoldae (Scincidae), behaviourally compensate for tail loss by comparing the behaviour of tailed and tailless males in experimental enclosures, either alone, with a conspecific male or female, or with a predator. Tailless males experience several costs of autotomy including reduced energy stores, and loss of autotomy as a defence. We identified an additional cost of tail loss: reduced mating success. However, this species did not behaviourally compensate these costs. Instead, characteristics of the ecology of C. jarnoldae may minimize the costs of autotomy. This species experiences an extended breeding season, which means that they experience reduced mating success for only 20% of this breeding season. Additionally, the presence of inguinal fat stores which supply energy in addition to stores in the tail reduce energetic costs.
It may seem as if behaviour is so plastic that it would not foster the establishment of a genetic... more It may seem as if behaviour is so plastic that it would not foster the establishment of a genetically determined trait, but under some circumstances, it can greatly influence whether a novel trait, such as a new morphology, spreads in a population. If the behaviours associated with the trait's function already exist, a new variant finds a ready foothold, and selection can act accordingly. Behaviours that are particularly likely to foster novel traits include those that play a role in life history, such as antipredator behaviour, sexual signalling and foraging. Examples of behaviour facilitating novel trait establishment include the spread of a silent mutant in male Pacific field crickets, Teleogryllus oceanicus, and the propensity of juvenile fence lizards to show antipredator behaviours towards attacking fire ants, providing a selective opportunity for the evolution of longer limbs. The genetic or physiological mechanisms behind a behaviour can also influence its establishment; for example, learning may generate selection in favour of conspicuous novel traits faster, and for a wider range of traits, than genetically based sensory biases. Just as changes in behavioural traits over evolutionary time may expose populations of individuals to new adaptive zones, behavioural variation within a population may increase the diversity of environments to which individuals are exposed. Ă“
An ethogram for male rainbow skinks, Carlia jarnoldae (mean snout-to-vent length 44 mm), was deri... more An ethogram for male rainbow skinks, Carlia jarnoldae (mean snout-to-vent length 44 mm), was derived from observations of captive individuals in large, semi-natural field enclosures during the summer. Males were observed in one of four treatments: solitary, socially with a male conspecific, socially with a female conspecific, or with a model of an avian predator. We identified 32 different types of behaviour, including postures and simple movements. Six of the behaviours (dorsolateral orientation, head bob, letisimulation, slow motion, throat ...
Human-generated noise has profoundly changed natural soundscapes in aquatic and terrestrial ecosy... more Human-generated noise has profoundly changed natural soundscapes in aquatic and terrestrial ecosystems, imposing novel pressures on ecological processes. Despite interest in identifying the ecological consequences of these altered soundscapes, little is known about the sublethal impacts on wildlife population health and individual fitness. We present evidence that noise induces a physiological stress response in an amphibian and impairs mate attraction in the natural environment. Traffic noise increased levels of a stress-relevant glucocorticoid hormone (corticosterone) in female wood frogs (Lithobates sylvaticus) and impaired female travel towards a male breeding chorus in the field, providing insight into the sublethal consequences of acoustic habitat loss. Given that prolonged elevated levels of corticosterone can have deleterious consequences on survival and reproduction and that impaired mate attraction can impact population persistence, our results suggest a novel pathway by which human activities may be imposing population-level impacts on globally declining amphibians.
Humans use a large variety of chemicals in their everyday lives, including many of which are know... more Humans use a large variety of chemicals in their everyday lives, including many of which are known or suspected endocrine disrupting compounds (EDCs). These chemicals are in pharmaceuticals and personal care products (PPCPs) and agrochemicals, such as pesticides. The land-application of human and animal wastes and pesticides to agricultural fields introduces EDCs into the environment, which then become mobilized during rainfall events and may impact nearby receiving water bodies. These EDCs have the potential to cause endocrine disruption in amphibians that develop in impacted vernal ponds. In October 2013, we collected baseline water samples from seven vernal ponds in Centre County, Pennsylvania. Two of the vernal ponds were in natural forested landscapes, three were impacted by wastewater effluent irrigation, one was in a catchment receiving dairy manure applications, and one was near agricultural areas with unknown application practices. Water samples were analyzed for nutrients (nitrogen, phosphorus, and carbon), hormones (natural and synthetic), semi-volatile organic compounds, including pesticides, and pH. Our preliminary data showed a wide range of Total Kjeldahl Nitrogen concentrations (1.3 -132 mg-N/L) across the seven ponds, total phosphorus values from 0.4 -5.1 mg-P/L, and pH values between 5.5 and 6.8. One of the ponds affected by wastewater effluent irrigation had detectable levels of 17β-estradiol and estrone. These preliminary results suggest that further research is needed to better understand how anthropogenic activities impact the presence of EDCs in vernal ponds and how their presence may impact developing amphibians.
Prolonged elevations of glucocorticoids due to long-duration (chronic) stress can suppress immune... more Prolonged elevations of glucocorticoids due to long-duration (chronic) stress can suppress immune function. It is unclear, however, how natural stressors that result in repeated short-duration (acute) stress, such as frequent agonistic social encounters or predator attacks, fit into our current understanding of the immune consequences of stress. Since these types of stressors may activate the immune system due to increased risk of injury, immune suppression may be reduced at sites where individuals are repeatedly exposed to potentially damaging stressors. We tested whether repeated acute elevation of corticosterone (CORT, a glucocorticoid) suppresses immune function in eastern fence lizards (Sceloporus undulatus), and whether this effect varies between lizards from high-stress (high baseline CORT, invaded by predatory fire ants) and low-stress (low baseline CORT, uninvaded) sites. Lizards treated daily with exogenous CORT showed higher hemagglutination of novel proteins by their pla...
Individual organisms encounter regular changes in the environment throughout their lifetime, resu... more Individual organisms encounter regular changes in the environment throughout their lifetime, resulting in fluctuations in phenotypic optima. Consequently, many species have evolved phenotypic flexibility to adjust to these seasonal changes. The ability of an ...
The spatial and temporal distribution of individuals of different phenotypic traits (sex, body si... more The spatial and temporal distribution of individuals of different phenotypic traits (sex, body size, body condition, etc.) within a population reflect many factors, including mating systems and environmental heterogeneity. For example, species that exhibit territorial defence often exhibit overdispersion of the territorial sex across the landscape ; harem-based systems involve aggregations of several females plus single large males ; and lek systems are associated with phenotype-structured aggregations of males . Thus, we expect to see correlations between the mating system of a population and the temporal and spatial patterns of distribution of individuals of different phenotypic traits within that population.
Animals must balance the conflicting needs to forage and avoid predation. The optimal balance of ... more Animals must balance the conflicting needs to forage and avoid predation. The optimal balance of risk and reward should depend on the individual's state, particularly hunger status. Satiated individuals are hypothesized to react more strongly to risk than hungry individuals, for which the necessity for food overrides perceived danger. We tested this in wood frog (Lithobates sylvaticus) tadpoles by comparing the response of fasted and fed tadpoles to injured conspecifics (alarm cue) and uninjured conspecifics (control). Food restriction significantly affected the activity levels of tadpoles and the impact of injured conspecific cues on activity. Fed tadpoles responded little to these cues, tending to decrease activity. Hungry tadpoles were more active overall and responded to injured conspecific cues by increasing activity. We propose that hungry tadpoles increase their activity in response to an injured conspecific because, in addition to indicating danger, this cue represents a nutrient source for this opportunistically cannibalistic species, and hungry tadpoles should thus adopt risky behavior to acquire this valuable resource. Differences in hunger may therefore explain variation among studies of tadpole responses to injured conspecifics. Future studies in aquatic organisms should consider the role of hunger status when assessing antipredator behavior.
Prey animals often respond to predators by reducing activity levels. Th is can produce a trait-me... more Prey animals often respond to predators by reducing activity levels. Th is can produce a trait-mediated indirect interaction (TMII) between predators and prey resources, whereby reduced foraging by prey in the presence of a predator causes an increase in prey resources. TMIIs play important roles in structuring communities, and it is important to understand factors that determine their strength. One such infl uence may be behavioural variation in the prey species, with indirect eff ects of predators being stronger within populations that are more responsive to the presence of a predator. We tested 1) whether the behavioural responsiveness of populations of wood frog tadpoles to predator cues was related to the predation risk in their native ponds, and 2) whether more responsive tadpoles yielded stronger TMIIs. To do this, we 1) measured the activity of tadpoles from 18 populations in mesocosms with and without caged predators, and 2) measured changes in the biomass of periphyton (the tadpoles ' diet) between predator treatments for each population. We found that tadpoles from higher predation risk ponds reduced their time outside refuges more in the presence of predators and tended to move less when visible, suggesting possible local adaptation to predation regimes. Th ough the presence of predators generally resulted in higher periphyton biomass -a TMII -there was no evidence that the strength of this TMII was aff ected by variation in tadpole behaviour. Foraging activity and general activity may be decoupled to some extent, enabling high predation riskadapted tadpoles to limit the fi tness costs of reduced foraging when predators are present.
Locating and following animals using tracking devices is a method commonly used on many taxa, fro... more Locating and following animals using tracking devices is a method commonly used on many taxa, from mammals (Chamberlain and Leopold, 2000; Daniels et al., 2001; Long, 2001) to insects (Roland et al., 1996; Carreck et al., 1999; Kutsch, 1999; Capaldi et al., 2000). Animals are tracked to study aspects of their home range (Li et al., 2000; Rodrigues and Monterio, 2000), movement patterns (Matthews and Pope, 1999; Rodrigues and Monterio, 2000), daily and seasonal activities (Lamoureux and Madison, 1999; Chamberlain and ...
In many studies, it is necessary for researchers to mark individual animals for later identificat... more In many studies, it is necessary for researchers to mark individual animals for later identification. It is often assumed in the interpretation of these studies that marks have no effects on the biology of the animals. This assumption is insufficiently tested, and, when it is, coarse assessments of negative effects are often used, such as survival and growth under simplified laboratory conditions. We examined the consequences of a common larval amphibian marking technique (staining with methylene blue) for wood frog tadpole behavior and survival in an ecologically realistic scenario (predation). We measured a number of tadpole behavioral variables, under baseline conditions and in the presence of olfactory cues of a predator, for marked and unmarked tadpoles. We then exposed pairs of tadpoles (one marked and one unmarked) to one of two predators and tested for the effects of marking on the susceptibility of tadpoles to predation. We found that marking suppressed the increase in movement rate that typically occurred in (unmarked) tadpoles in the presence of predator cues. Marked tadpoles were significantly more likely to be captured by predators, an effect that could not be attributed to this difference in movement rate. These results raise concern about the use of this staining method and highlight the need for studies involving marked animals to thoroughly address any relevant effects the marks may have on the biology of the subjects.
The introduction of non-native species is becoming increasingly common. Understanding the impact ... more The introduction of non-native species is becoming increasingly common. Understanding the impact of invaders on native populations is critical for effective management. Red imported fire ants (Solenopsis invicta Buren, 1972) were introduced to the USA in the 1930s. They will attack, and can kill, native fence lizards (Sceloporus undulatus (Bosc and Daudin in Sonnini and Latreille, 1801)), which co-occur with these ants across much of their invasive range. I determined whether fence lizards minimize encounters with S. invicta by altering their habitat use following invasion or avoiding cues of the presence of these fire ants. I recorded the habitat use of fence lizards and S. invicta mounds across four sites with different histories of invasion, and quantified lizard avoidance of S. invicta scent. I found that lizards do not alter their habitat use following S. invicta invasion, nor do they spatially avoid their mounds. Fence lizards do avoid S. invicta scent, but this was only evident in naĂ¯ve or recently invaded populations. The lack of avoidance of S. invicta by fence lizards could be explained by the high prevalence of these fire ants, making them difficult to avoid, and adaptive shifts in the escape behaviour and morphology of these lizards following invasion that permit them to survive fire ant attack.
Animals typically exhibit adaptive behaviors that reduce their risk of predation. The term 'boldn... more Animals typically exhibit adaptive behaviors that reduce their risk of predation. The term 'boldness' describes individual variation in the propensity to exhibit risk-reducing behavior and is the subject of much research attention. Predators should select against boldness, and this has been supported by empirical studies and behavioral ecology theory. We tested whether a standardized assay of three boldness-associated behaviors in wood frog (Lithobates sylvaticus) tadpoles predicted survival when faced with a predator. Tadpole behavior was assayed in an open field and then tadpoles were placed, in pairs, in an enclosure with a predator (newt or larval dragonfly). Survival did not depend on differences in measured boldness, and this result held when we accounted for interactions between different boldness behaviors and between behavior and size or predator identity. The absence of selection by predators against bolder tadpoles is counterintuitive and inconsistent with our understanding of the behavioral ecology of these animals. Two possible explanations are offered for this result. First, selection against boldness may be minimized by other phenotypic traits, such as escape ability. Alternatively, the potential lack of consistency between standardized boldness assays and natural encounters with predators may limit our capacity to study the evolution of boldness, cautioning against this approach. These results highlight the complexities of the relationships between behavioral traits and fitness and the challenges associated with their study.
Antipredator mechanisms employed by animals are obviously beneficial if they increase survival, b... more Antipredator mechanisms employed by animals are obviously beneficial if they increase survival, but their use may be costly and decrease fitness. Fitness costs of antipredator mechanisms may, in turn, be defrayed by behavioural compensation. We used lizards as a model to measure behavioural fitness costs of the antipredator mechanism, autotomy, as they commonly lose their tails when attacked by predators. In addition, we examined whether male skinks, Carlia jarnoldae (Scincidae), behaviourally compensate for tail loss by comparing the behaviour of tailed and tailless males in experimental enclosures, either alone, with a conspecific male or female, or with a predator. Tailless males experience several costs of autotomy including reduced energy stores, and loss of autotomy as a defence. We identified an additional cost of tail loss: reduced mating success. However, this species did not behaviourally compensate these costs. Instead, characteristics of the ecology of C. jarnoldae may minimize the costs of autotomy. This species experiences an extended breeding season, which means that they experience reduced mating success for only 20% of this breeding season. Additionally, the presence of inguinal fat stores which supply energy in addition to stores in the tail reduce energetic costs.
It may seem as if behaviour is so plastic that it would not foster the establishment of a genetic... more It may seem as if behaviour is so plastic that it would not foster the establishment of a genetically determined trait, but under some circumstances, it can greatly influence whether a novel trait, such as a new morphology, spreads in a population. If the behaviours associated with the trait's function already exist, a new variant finds a ready foothold, and selection can act accordingly. Behaviours that are particularly likely to foster novel traits include those that play a role in life history, such as antipredator behaviour, sexual signalling and foraging. Examples of behaviour facilitating novel trait establishment include the spread of a silent mutant in male Pacific field crickets, Teleogryllus oceanicus, and the propensity of juvenile fence lizards to show antipredator behaviours towards attacking fire ants, providing a selective opportunity for the evolution of longer limbs. The genetic or physiological mechanisms behind a behaviour can also influence its establishment; for example, learning may generate selection in favour of conspicuous novel traits faster, and for a wider range of traits, than genetically based sensory biases. Just as changes in behavioural traits over evolutionary time may expose populations of individuals to new adaptive zones, behavioural variation within a population may increase the diversity of environments to which individuals are exposed. Ă“
An ethogram for male rainbow skinks, Carlia jarnoldae (mean snout-to-vent length 44 mm), was deri... more An ethogram for male rainbow skinks, Carlia jarnoldae (mean snout-to-vent length 44 mm), was derived from observations of captive individuals in large, semi-natural field enclosures during the summer. Males were observed in one of four treatments: solitary, socially with a male conspecific, socially with a female conspecific, or with a model of an avian predator. We identified 32 different types of behaviour, including postures and simple movements. Six of the behaviours (dorsolateral orientation, head bob, letisimulation, slow motion, throat ...
Human-generated noise has profoundly changed natural soundscapes in aquatic and terrestrial ecosy... more Human-generated noise has profoundly changed natural soundscapes in aquatic and terrestrial ecosystems, imposing novel pressures on ecological processes. Despite interest in identifying the ecological consequences of these altered soundscapes, little is known about the sublethal impacts on wildlife population health and individual fitness. We present evidence that noise induces a physiological stress response in an amphibian and impairs mate attraction in the natural environment. Traffic noise increased levels of a stress-relevant glucocorticoid hormone (corticosterone) in female wood frogs (Lithobates sylvaticus) and impaired female travel towards a male breeding chorus in the field, providing insight into the sublethal consequences of acoustic habitat loss. Given that prolonged elevated levels of corticosterone can have deleterious consequences on survival and reproduction and that impaired mate attraction can impact population persistence, our results suggest a novel pathway by which human activities may be imposing population-level impacts on globally declining amphibians.
Humans use a large variety of chemicals in their everyday lives, including many of which are know... more Humans use a large variety of chemicals in their everyday lives, including many of which are known or suspected endocrine disrupting compounds (EDCs). These chemicals are in pharmaceuticals and personal care products (PPCPs) and agrochemicals, such as pesticides. The land-application of human and animal wastes and pesticides to agricultural fields introduces EDCs into the environment, which then become mobilized during rainfall events and may impact nearby receiving water bodies. These EDCs have the potential to cause endocrine disruption in amphibians that develop in impacted vernal ponds. In October 2013, we collected baseline water samples from seven vernal ponds in Centre County, Pennsylvania. Two of the vernal ponds were in natural forested landscapes, three were impacted by wastewater effluent irrigation, one was in a catchment receiving dairy manure applications, and one was near agricultural areas with unknown application practices. Water samples were analyzed for nutrients (nitrogen, phosphorus, and carbon), hormones (natural and synthetic), semi-volatile organic compounds, including pesticides, and pH. Our preliminary data showed a wide range of Total Kjeldahl Nitrogen concentrations (1.3 -132 mg-N/L) across the seven ponds, total phosphorus values from 0.4 -5.1 mg-P/L, and pH values between 5.5 and 6.8. One of the ponds affected by wastewater effluent irrigation had detectable levels of 17β-estradiol and estrone. These preliminary results suggest that further research is needed to better understand how anthropogenic activities impact the presence of EDCs in vernal ponds and how their presence may impact developing amphibians.
Prolonged elevations of glucocorticoids due to long-duration (chronic) stress can suppress immune... more Prolonged elevations of glucocorticoids due to long-duration (chronic) stress can suppress immune function. It is unclear, however, how natural stressors that result in repeated short-duration (acute) stress, such as frequent agonistic social encounters or predator attacks, fit into our current understanding of the immune consequences of stress. Since these types of stressors may activate the immune system due to increased risk of injury, immune suppression may be reduced at sites where individuals are repeatedly exposed to potentially damaging stressors. We tested whether repeated acute elevation of corticosterone (CORT, a glucocorticoid) suppresses immune function in eastern fence lizards (Sceloporus undulatus), and whether this effect varies between lizards from high-stress (high baseline CORT, invaded by predatory fire ants) and low-stress (low baseline CORT, uninvaded) sites. Lizards treated daily with exogenous CORT showed higher hemagglutination of novel proteins by their pla...
Individual organisms encounter regular changes in the environment throughout their lifetime, resu... more Individual organisms encounter regular changes in the environment throughout their lifetime, resulting in fluctuations in phenotypic optima. Consequently, many species have evolved phenotypic flexibility to adjust to these seasonal changes. The ability of an ...
The spatial and temporal distribution of individuals of different phenotypic traits (sex, body si... more The spatial and temporal distribution of individuals of different phenotypic traits (sex, body size, body condition, etc.) within a population reflect many factors, including mating systems and environmental heterogeneity. For example, species that exhibit territorial defence often exhibit overdispersion of the territorial sex across the landscape ; harem-based systems involve aggregations of several females plus single large males ; and lek systems are associated with phenotype-structured aggregations of males . Thus, we expect to see correlations between the mating system of a population and the temporal and spatial patterns of distribution of individuals of different phenotypic traits within that population.
Animals must balance the conflicting needs to forage and avoid predation. The optimal balance of ... more Animals must balance the conflicting needs to forage and avoid predation. The optimal balance of risk and reward should depend on the individual's state, particularly hunger status. Satiated individuals are hypothesized to react more strongly to risk than hungry individuals, for which the necessity for food overrides perceived danger. We tested this in wood frog (Lithobates sylvaticus) tadpoles by comparing the response of fasted and fed tadpoles to injured conspecifics (alarm cue) and uninjured conspecifics (control). Food restriction significantly affected the activity levels of tadpoles and the impact of injured conspecific cues on activity. Fed tadpoles responded little to these cues, tending to decrease activity. Hungry tadpoles were more active overall and responded to injured conspecific cues by increasing activity. We propose that hungry tadpoles increase their activity in response to an injured conspecific because, in addition to indicating danger, this cue represents a nutrient source for this opportunistically cannibalistic species, and hungry tadpoles should thus adopt risky behavior to acquire this valuable resource. Differences in hunger may therefore explain variation among studies of tadpole responses to injured conspecifics. Future studies in aquatic organisms should consider the role of hunger status when assessing antipredator behavior.
Uploads
Papers by T. Langkilde