Spring 2006 Asa Gray Seminars
6 February, 2006
Hannah Cleary, Jennifer Warner, and Dr. Mary S. Rea
Dept. of Biology, Russell Sage College
“The Effects of Photoperiod on the Behavioral Patterns in Green Tree Frogs.”
My students and I have been studying the circadian behavior of American green treefrogs, Hyla cinerea. We have found that treefrogs entrained to 12L:12D cycles exhibit crepuscular behavior with most activity occurring during the dawn and dusk transition times. This activity is significantly suppressed in continuous light and continuous dark with a loss of rhythmicity during the first 24 hours. When given a pulse of light during the dark phase of a 12L:12D cycle frog activity was phase-advanced. Our preliminary studies measuring spectral sensitivity indicate that light levels at or near 6 Lux are too low to phase-advance frog activity.
13 February, 2006
Bottom-up and top-down control of a grazing ecosystem: drought and wolves in Yellowstone National Park.
Terrestrial ecosystems are regulated by (a) bottom-up effects that directly influence plants, then ascend up the food chain, and (b) top-down effects of predators that directly influence prey, then cascade down to lower trophic levels. In this talk I will review 17 years of research that has examined the effects of large herds of migratory ungulates, drought, and the introduction in 1995 of the gray wolf on grassland production and nutrient cycling in grasslands of Yellowstone National Park. Results indicate that all three factors have important and interacting effects on grassland processes.
6 March, 2006
Pennsylvania State University -
“Age-related Patterns of Reproductive Success in House Sparrows.”
A common life history pattern in several taxa is that reproductive success increases with age. We found a similar pattern in house sparrows (Passer domesticus), and tested one hypothesis concerning the potential mechanisms underlying the observed increase in offspring production with age. For most measures of reproductive success, older individuals performed better than yearlings. Older males and females began breeding earlier in a given season and fledged more young than their yearling counterparts. Individual males also fledged more young at two years of age than they did at one year of age, but individual females did not show consistent improvement from year one to two. A path analysis indicated that the effect of age was primarily through the timing of breeding and number of nesting attempts. A path analysis indicated that earlier breeding within a season was associated with more young fledged. For both males and females, age was negatively related to the date the first egg was laid earlier by older individuals in the nest. Neither male nor female age was directly related to the number of young fledged. Path analysis indicated that the effect of age was primarily through the timing of breeding and not on other aspects of fledging success such as hatching or survival from hatching to fledging. Increased reproductive success with age may arise from high quality individuals surviving to be older (selection hypothesis). Contrary to this hypothesis we found survival from one year of age to two years of age was negatively related to reproductive success. Additionally, individuals that survived to breed as two-year-olds did not differ in reproductive performance in their first year from those that did not survive to breed as two-year-olds.
20 March 2006
Dr. Michael L. McCormick
Assistant Professor of Biology, Hamilton College
The Contributions of Bacteria and Biogenic Magnetite to Carbon Tetrachloride Degradation in a Model Iron-Reducing System
It has long been recognized that both cell-mediated (biotic) and mineral-mediated (abiotic) reactions may participate in the reductive transformation of select contaminants in iron-reducing environments. Yet attempts to quantify the magnitude of these biotic and abiotic reactions are rare. For this reason, we often have little knowledge of the predominant agents responsible for contaminant degradation in these complex systems. In this work, the contributions of cell-mediated and mineral-mediated reactions to carbon tetrachloride (CT) transformation were studied in a model iron-reducing system. The results indicate that when cells and minerals are present together, CT transformation is due, almost entirely, to abiotic surface-mediated reactions. These findings suggest that reactive biogenic minerals could play a significant role in the natural attenuation of chlorinated solvents in iron-reducing environments. The research also suggests that a novel approach for remediating alkyl halides, and other groundwater contaminants, may be to engineer the formation of reactive biogenic minerals in-situ.
3 April 2006
Dr. Tom McCarthy
Assistant Professor of Biology, Utica College
"Exploring implications of the risk allocation hypothesis: sex and death"
This talk will examine how both mating and predator-prey interactions are influenced by variations in the temporal patterns of exposure to chemical cues that indicate the occurrence of previous predation events. Hundreds of studies have examined factors that influence the mating systems of many different types of organisms. Likewise, many studies have examined factors that influence predator-prey interactions. Furthermore, there are numerous studies that have integrated these fields and considered how predation risk influences the mating systems of prey species. A set of recent theory (the ‘risk allocation hypothesis’) predicts that animals always at risk of being killed (e.g. high predator density) will behave differently than animals that are rarely in danger (low predator density) when under similar conditions. For example, animals accustomed to predators should have less intense avoidance behaviors than naive animals when they perceive predation risk; conversely, animals accustomed to predators should have higher activity rates when no risk is perceived. Thus, current prey behavior should be influenced by the temporal patterns of predation risk that prey have experienced in the past. Several experimental studies have tested the predictions of this theory and found that prey behaviors can be influenced by temporal patterns of predation risk. I will discuss several experiments that are, directly or indirectly, relevant to the risk allocation hypothesis. I also propose a series of field and laboratory experiments that extend the predictions of the risk allocation hypothesis to consider mating behaviors of prey, foraging behaviors of predators, and the results of interactions between predators and prey.
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