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Lab AbstractsLauren PintorEcological Society of America, Montreal Canada 2005. Density versus per capita impacts of an introduced crayfish on stream communities. Pintor, L. and A. Sih. University of California, Davis, CA. Invasive species often devastate native communities and ecosystems through the invader's ability to attain high densities. Increased densities often lead to larger effects on a community often despite a reduced impact per individual. In northern California streams, the exotic signal crayfish, Pacifasticus leniusculus, has large negative impacts on native communities. However, the degree of their impact differs from stream to stream. We conducted a mesocosm experiment measuring the density and per capita impacts of signal crayfish populations collected from low and high density sites on a typical stream prey community (snails, benthic invertebrates and algae). Additionally, we evaluated the behavioral mechanisms underlying differing impacts between signal crayfish populations. Results indicate that signal crayfish significantly reduce prey densities and that impacts are significantly higher at high crayfish densities. However, behavioral observations suggest high densities also shift behavior (increased aggression and foraging rate) possibly leading to an increase in per capita effects. This synergistic effect (of density and behavior) may in part explain the devastating effects to native communities often found at high density crayfish sites, and also provide insight to mechanisms of invasion in general. Ecological Society of America, Portland OR 2004. Variation in aggression level influences behaviors underlying impacts of an invasive crayfish. Pintor, L. and A. Sih. University of California, Davis, CA. Although understanding the behavioral mechanisms underlying species interactions has provided powerful insights for community ecology, studies of interactions between invasive species and invaded communities have rarely focused on underlying behaviors. Interestingly, the invasion process itself can cause alterations in behavior that can, in turn, influence the impact of an invasive species. Comparing native and introduced populations of an invasive species can help identify whether behavioral traits contributing to invasion success are inherent or change as a result of the invasion process. We focused on the introduced signal crayfish, Pacifasticus leniusculus, which is having negative impacts on stream communities in northern California. In particular, signal crayfish have been identified as the primary cause of the decline of an endangered endemic crayfish. High levels of aggression have been observed to contribute to the ability of signal crayfish to outcompete endemic crayfish. A recent behavioral syndrome hypothesis posits that aggression may carry over to influence other behaviors, such as foraging and anti-predator behavior. We conducted foraging trials to determine whether variation in aggression carries over to influence foraging behavior. Results indicate that introduced populations of signal crayfish show significantly higher feeding rates than native populations. In the presence of a non-lethal predator, introduced populations of signal crayfish showed higher levels of activity and used refuge less than native populations. Although higher activity levels may make signal crayfish more vulnerable to predators, higher feeding rates may lead to higher growth rates enabling signal crayfish to gain a size advantage over other crayfish competitors. Ecological Society of America, Tuscon AZ 2002.Interpopulation variation in behavior and growth
underlying geographic differences in species interactions of an introduced
crayfish. Comparing native and introduced populations of an invasive species can provide insights into its invasion success. Differences in behavioral interactions can represent shifts in behavior following invasion that may have contributed to invasion success. Alternatively, variation may be due to differences in the species present in each range. Studies of the invasive rusty crayfish (Orconectes rusticus) have described this invader as competitively superior to resident species resulting in the displacement of resident crayfish. However, within its native range, O. rusticus is sympatric with other crayfish species and the community appears stable. In used a 2x2 factorial design to compare the interactions of native (Kentucky) and introduced (Illinois) populations of O. rusticus (OR) each when competing with Orconectes propinquus (OP) (native to IL) and Orconectes cristavarius (OC) (native to KY). When comparing with native congeners (OC) introduced OR had significantly higher recruitment than native OR in baiting experiments and were less often in refuge. These differences in behavior translated to higher growth rates for introduced OR then native OR. In contrast, when interacting with OP, there were no significant differences between native and introduced OR in recruitment or refuge use. Although there were no behavioral differences between populations, invaders (OR) had significantly higher growth rates than native OR. Results suggest that species replacement is due to a combination of population differences, along with differences in the species it interacts with. Ecological Society of America, Montreal Canada 2005. Pesticide-induced behavioral shifts differentially alter tadpole survivorship in the presence of a crayfish predator. Kerby, J., Sih, A. Pesticide exposure is often correlated with amphibian declines, particularly in California, despite the fact that levels detected in the environment are typically well below lethal concentrations. This study examines the impacts of a sub-lethal level (50 ug/L) of the pesticide carbaryl on two species of frogs, the Pacific tree frog (Hyla regilla) and the foothill yellow legged frog (Rana boylii) in the presence of a crayfish predator (Pacifasticus leniusculus). In the absence of pesticide, predation on tadpoles was similar. The presence of pesticide had a significantly larger impact on R. boylii anti-predatory behaviors. In the presence of both pesticide and a predator, R. boylii tadpoles suffered a significantly greater mortality. The differential behavioral responses between tadpole species (increase vs. decrease in refuge use) exposed to sub-lethal levels of pesticides and the resulting differences in survivorship when combined with a predator may provide insight on explaining mechanisms for some amphibian population declines. Ecological Society of America, Portland OR 2004. Differences in behavioral responses to sub-lethal pesticide concentrations in amphibians and a potential predator. Kerby, J., Sih, A. Sub-lethal effects of contaminants have become an increasing focus for research investigating the causes of amphibian declines. This study examines differences in behavioral responses in two species of larval frogs, the Pacific tree frog (Hyla regilla) and the foothill yellow legged frog (Rana boylii) when exposed separately to four different commonly used pesticides (atrazine, carbaryl, chlorpyrifos, and diazinon) at four different concentrations (0, 50, 500, and 5000 ug/L). Significant differences in behavioral responses (activity level, refuge use, position) occur between the two species for some pesticides but not others. R. boylii consistently exhibited behavioral shifts at lower concentrations of pesticides when compared to H. regilla. We also evaluated behavioral responses of H. regilla tadpoles in the presence of a predator, the western mosquitofish (Gambusia affinis) when both were simultaneously exposed to diazinon at four concentrations (solvent control, 0, 5000, and 10,000 ug/L). In this interaction, pesticide-exposed predators significantly reduced activity and predation rates on H. regilla. Exposure to pesticide alone had no significant direct effect on tadpoles. However, tadpoles exposed to both predator and pesticide significantly increased activity and reduced refuge use when compared to treatments with predators only. These differential responses between both predators and competitors when exposed to different sub-lethal levels of pesticides likely have large impacts on community dynamics and may provide insights on explaining some amphibian population declines. Society of Environmental Toxicology and Chemistry, Portland OR 2004. Behavioral shifts in amphibian larvae due to pesticide exposure. Kerby, J. An increasing shift in research on causes for amphibian decline has focused on the role of sub-lethal effects of contaminants. This study examines differences in behavioral responses in two species of larval frogs, the Pacific tree frog (Hyla regilla) and the foothill yellow legged frog (Rana boylii) when exposed separately to four different commonly used pesticides: atrazine, carbaryl, chlorpyrifos, and diazinon at four different concentrations (0, 50, 500, and 5000 g/L). I measured known ecologically important tadpole anti-predator behaviors (activity level and refuge use). Significant differences in behavioral responses occur between the two species for some pesticides but not others. Chlorpyrifos and carbaryl exposed tadpoles significantly reduce activity in both species similarly. In examining refuge use, H. regilla increased refuge use in response to all four pesticides while R. boylii decreased refuge use. In ecological studies, similar magnitude alterations of behavior on tadpoles result in significant differences on population survival rates. The differential responses between competitors (increase vs. decrease in refuge use) exposed to sub-lethal levels of pesticides may impact community dynamics and potentially can provide insights on explaining some amphibian population declines. Ecological Society of America, Savannah GA 2003.Factors limiting spread of the crayfish, Procambarus
clarkii, in Santa Monica Mountain streams. Invasive species are a major threat to stream ecosystems; however, research has seldom identified successful ways of prohibiting their spread. We surveyed 32 stream sections in the Santa Monica Mountains of southern California for two consecutive years to determine the distribution of the invasive crayfish, Procambarus clarkii. Surveys indicated that streams with large obstructions (waterfalls, culverts, artificial structures) often did not have crayfish present upstream of these obstructions. A mark recapture study indicated that P. clarkii displayed significantly more downstream than upstream movement when observed in three successive stream pools. Obstructions significantly reduced movement of crayfish between pools when compared to stream sections without any obstructions. The distribution of crayfish in streams and mark-recapture data thus suggest that crayfish mainly spread downstream from a point of colonization and are restricted in their movement to adjacent upstream sections by the presence of both natural and artificial obstructions. Society of Environmental Toxicology and Chemistry, Austin TX 2003.Diazinon altered predator-prey interactions between
a fish and two amphibians. We examined the effects of sub-lethal levels of the insecticide
Diazinon on interactions between a predatory fish and two amphibians.
Two 48- h experiments were performed in tubs containing one of four Diazinon
concentrations (0, 0.5, 1.0 mg/L and a methanol solvent control) and Western
mosquitofish (Gambusia affinis) with either Pacific treefrog tadpoles
(Hyla regilla) or Tiger salamander larvae (Ambystoma tigrinum). In the
absence of fish, pesticide treatments did not directly affect the behavior
or survival of tadpoles. However, in the presence of fish, tadpoles exposed
to pesticide treatments were more active and experienced greater survival
than those exposed to non-pesticide treatments. Higher tadpole activity
and survival is attributed to Diazinon significantly decreasing Biennial Fish Behavior Meetings (EEEF), 2006; American Society of Ichthyologists and Herpetologists (ASIH), 2006 Water
clarity and predator avoidance in reef fish. Human activities on land have multiple negative impacts on reef communities. Most attention has focused on the effects of excessive sediment on the health of hermatypic corals. We investigated the possible impacts of altered water clarity on reef fishes in the field at Cabo Blanco, Costa Rica. We measured the tendency of a prey species, the flag cabrilla Epinephelus labriformis, to engage in predator avoidance behavior across a gradient of underwater visibility. We presented a known, frightening stimulus, the "face of death", to cabrilla of different sizes and measured initial reaction and flight as the frightening image was moved closer to the prey species. We found that cabrilla reacted sooner to (at a greater distance from) the frightening image when water clarity was reduced. Younger fish were more sensitive than larger fish, reacting at a greater distance when water clarity was poorer. These results suggest that anthropogenic degradation of reef environments such as increased sediment inputs could impose costs on reef fishes in terms of lost energy and activity time. Ecological Society of America, Portland OR 2004.Effects of predator identity and habitat characteristics on prey’s perception of and response to risk. Ajie, B.C., Benard, M.F., Sih, A. University of California, Davis, CA, USA. Empirical studies of induced defenses have traditionally focused on responses to a single predator in one environment. As a result, relatively little is yet known about 1) prey responses to different predators; 2) the importance of the physical habitat or prey habitat use in the context of induced defenses; 3) and the degree to which prey functionally integrate and interchange the multiple modes of plasticity. Yet, these complexities are critical to our understanding of both how induced defenses evolve and what role they play in structuring natural populations because they more realistically reflect the context in which each of these processes occur. We address these issues in this study by quantifying several behavioral and morphological responses of tadpole prey in response to two functionally distinct predators (salamander larvae: Ambystoma tigrinum and predaceous diving beetle larvae: Dytiscus sp.) in two environmental contexts; a simple, ‘no chioce’ habitat and a heterogeneous, ‘chioce’ habitat where prey could choose between simple and complex microhabitats. We observed that tadpoles employed different degrees and strategies of defense in the simple versus heterogeneous habitat treatments, and that the effect of heterogeneity on induced defenses was predator-specific. The adaptive value of induced defenses was assessed in a series lethal predation assays. Interestingly, we found no evidence of a survival trade-off between phenotypes induced by alternative predators. This result along with the predator and habitat-specific strategies of tadpoles are discussed in light of the foraging tactics and habitat preferences of the predators. Society for the Study of Evolution, Annual Meeting, Champaign, IL 2002 Behavioral Degradation under Mutation Accumulation. Ajie, B.C., Estes, S.E., Lynch, M., Phillips, P.C. Spontaneous
mutations play a fundamental role in the maintenance of genetic variation
in natural populations, the nature of inbreeding depression, the evolution
of sexual reproduction, and the conservation of endangered species. Using
long-term mutation accumulation lines of the nematode Caenorhabditis elegans,
we estimate the rate and magnitude of mutational effects for a suite of
behaviors characterizing individual chemosensory responses to a repellant
stimulus. In accordance with evidence that the vast majority of mutations
are deleterious, we find that behavioral responses degrade over time as
a result of spontaneous mutation accumulation. The rate of mutation for
behavioral traits is roughly of the same order or slightly smaller than
those previously estimated for reproductive traits and the average size
of the mutational effects is also comparable. These results have important
implications for the maintenance of genetic variation for behavior in
natural populations as well as for expectations for behavioral change
within endangered species and captive populations.
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