Authors: A. Bak, H. Bliska | Location: El Campanario Biological Station (Osa Peninsula, Costa Rica)
Abstract: Measuring patterns of parasite distribution across host populations can help us understand host selection by parasites. To determine which host-specific factors influence the abundance and variation of ectoparasites across hosts, we observed the relationship between bat flies and bats. We studied the abundance and species of bat flies on three species of bats (Pteronotus parnellii, P. personatus, and P. gymnonotus: Chiroptera: Mormoopidae) on the Osa Peninsula, Costa Rica. We captured bats as they exited their roost and recorded bat species, sex, ratio of body weight to forearm length, reproductive status, and the number and species of parasites for each bat. Host species influenced parasite abundance; P. parnellii had significantly more parasites than P. personatus. Corrected weight, sex, and reproductive status of bats had no effect on parasite abundance. However, there was variation in bat fly species for bats of different species and reproductive status. Future studies could consider how social behavior and roost structure of these bats species may diverge and subsequently affect patterns of parasite abundance and variation.
Authors: A. Bak, F. Cullen, K. Griffee, J. Salvay | Location: Cuerici Biological Station (Cartago Province, Costa Rica)
Abstract: Organisms often face trade-offs in which the benefits of investing in a trait are weighed against its costs. Among plants, trade-offs may involve investing in growth or in defense. We examined secondary metabolites as one such defensive mechanism. Drimys granadensis, Curia (Family: Asteraceae), and Lycopodium thyoides are all found in Cuerici, Costa Rica, and are known for their medicinal qualities, which may arise from high levels or action of secondary metabolites. We measured herbivory among D. granadensis and Curia in both light and shade environments, and compared it to control plants without known medicinal qualities. Herbivory was significantly lower for D. granadensis than control plants, but there was no difference between Curia and control plants. We also measured the coagulant properties of Curia and the antibiotic properties of L. thyoides. While the coagulant abilities of Curia matched control plants, all plants tested performed better than pure blood and a blood/saliva mixture. For the antibiotic assay, treatments with L. thyoides showed the least bacterial growth for all inoculates except for the sterile control, strongly suggesting antibiotic properties of L. thyoides. These results shed light on why these plants are used medicinally in human populations.
Authors: A. Bak, H. Bliska, A. Wing | Location: Central Caribbean Marine Institute (Little Cayman, Cayman Islands)
Abstract: Determining organismal distribution in natural environments is vital for understanding what relative impacts organisms may have on the health and function of their ecological communities. In order to determine what ecological and anthropogenic factors affect the abundance and distribution of invertebrate grazers in marine ecosystems, we studied the abundances of two Caribbean sea urchins, Diadema antillarum and Echinometra lucunter, in the intertidal zone of Little Cayman. Because these urchins are grazing herbivores, we expected areas with higher urchin abundance to have lower abundances of turtle grass and macroalgae. We surveyed the abundance and distribution of urchins at two sites (one protected, one unprotected) in the coral reefs of Little Cayman along transects and used a quadrat to estimate percent cover of turtle grass and macroalgae on each transect. There was significantly higher urchin abundance of both species at the unprotected than the protected site. There was no relationship between urchin abundance and turtle grass cover, but increased algae cover correlated with decreased urchin abundance for both D. antillarum and E. lucunter. Future studies can better elucidate which anthropogenic and environmental factors determine the pattern of urchin abundance and how it is related to macroalgae growth.
Authors: A. Bak, K. Griffee, J. Salvay, A. Wing | Location: Palo Verde Research Station (Bagaces, Costa Rica)
Abstract: Living in social groups enriches the opportunity for social learning. The success of many organisms depends on their ability to observe and repeat the actions of others. Arboreal jumping is one such action that is prevalent among White-faced capuchins (Cebus imitator) and Mantled howler monkeys (Alouatta palliata). We studied jumping behavior in both species in Palo Verde National Park, Costa Rica, to evaluate if juvenile monkeys behave differently from larger, older monkeys in their group. We hypothesized that individual size would influence jumping distance and jump preparation time but found no relationship. We expected individuals would take less time to prepare for a jump that other individuals just completed but found that following individuals actually prepared for a bit longer. Social learning likely plays a role in monkey locomotion, but factors other than those examined in this present study may better elucidate its influence.
Authors: A. Bak, J. Park | Location: Smithsonian Tropical Research Institute (Barro Colorado Island, Panama)
Abstract: Predation is a strong selection force in nature and may pose special challenges to organisms with developmental metamorphosis. For example, frogs begin their life cycle as aquatic tadpoles that are prey to aquatic and terrestrial predators. As they mature, tadpoles develop limbs that are adapted for use on land. How do transitionary phenotypes affect the fitness of metamorphosing organisms? Escape behavior may be one indicator of differences in fitness between tadpoles and metamorphs that have begun growing limbs. We studied tadpole behavior in response to simulated predation. Our results suggest shorter swimming distances in metamorphs as evidence of inferior escape capacity. Metamorphs may be traveling shorter distances due to the inefficiencies of a transitionary life stage. Further studies should compare other factors contributing to predation risk of tadpoles and metamorphs. The results of such studies could shed light on how natural selection balances the potential benefits of having multiple life stages with the cost of metamorphosis.
Authors: A. Bak, H. Marr, C. Page, A. Wing | Location: Monteverde Biological Station (Monteverde, Costa Rica)
Abstract: The ideal free distribution predicts that foraging animals will partition themselves in proportion to the amount of resources present in various patches. This model can be evaluated through studies of how individuals allot foraging time among patches. We studied hummingbirds foraging on bottlebrush trees in Monteverde, Costa Rica. We measured feeding behavior and aggressive interactions in patches of varying inflorescence densities. The number and duration of hummingbird visits increased with inflorescence density and hummingbirds spent about the same amount of time at each inflorescence regardless of inflorescence density in a patch. We observed no relationship between inflorescence density and aggressive interactions. Future studies could further examine feeding behaviors and observe more bouts to draw conclusions about hummingbird interactions with conspecifics and floral resources.
Authors: A. Bak, H. Marr, C. Page, A. Wing | Location: Central Caribbean Marine Institute (Little Cayman, Cayman Islands)
Abstract: Tide pools, which are usually characteristic of a rocky intertidal zone, are ephemeral habitats that change constantly as a result of different tidal and weather conditions. The organisms that occupy them therefore face some of the most temporally variable environmental conditions of any marine habitat. This study asks how the abiotic conditions of tide pools change with distance from the waterline, and how these different abiotic factors influence the richness and diversity of species found in tide pools. To test our hypothesis that the abiotic factors of tide pools and therefore species richness and abundance change with their distance from the waterline, we collected data from two different intertidal locations on Little Cayman, assessing abiotic variables (temperature, salinity, dissolved oxygen, and pH) and surveying macroinvertebrate and fish abundance and diversity. Our results indicate that distance from waterline influences several abiotic factors, with temperature and pH increasing with distance from waterline at both sites, and salinity and dissolved oxygen decreasing with distance from waterline at one site. At one site, overall species richness decreased as the distance from waterline increased, with no significant relationship demonstrated at the other site. These results are interesting and unexpected, and future studies can expand upon these results to further elucidate the patterns we observed. This study and future ones like it have the potential to inform the fate of tidal pool ecosystems as sea levels rise and the oceans warm and acidify.