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Fort Washington, MD, United States

Porter E.T.,Washington College | Mason R.P.,University of Connecticut | Sanford L.P.,University of Cambridge
Marine Ecology Progress Series | Year: 2010

To test the effect of sediment resuspension on the nutrient and ecosystem dynamics we performed a 4 wk experiment in three 1000 l shear-turbulence- resuspension-mesocosm (STURM) resuspension (R) tanks and three 1000 l non-resuspension (NR) tanks. All tanks contained defaunated muddy sediment and brackish estuarine water and had similar water-column turbulence intensities (̃1 cm s-1), energy dissipation rates (̃0.08 cm2 s-3), and tidal cycles (4 h mixing-on and 2 h mixingoff). However, while bottom shear velocity (stress) was low in the NR tanks, high instantaneous bottom shear produced resuspension in the R tanks during the mixing-on cycles. Tidal resuspension in the R tanks resulted in concentrations of 120 to 220 mg l-1 total suspended solids when mixing was on, decreasing to between 10 and 20 mg l-1 when mixing was off. Particulate nitrogen, phosphorus, and carbon concentrations, as well as dissolved inorganic nitrogen, nitrate + nitrite, and phosphate levels were higher in the R tanks. Phytoplankton biomass was also higher in the R tanks, though light was limiting. Tidal resuspension affected water-column algal and zooplankton community composition and induced significantly higher concentrations of brown tide Aureococcus anophagefferens. Microphytobenthos biomass was significantly higher in the NR tanks. Dissolved inorganic nitrogen sediment effluxes were similar in both tanks; however, polychaetes and amphipods developed in the NR, but not in the R tank sediments. Tidal resuspension shifted processes from the benthos to the water column. Regular tidal resuspension profoundly affected ecosystem structure and function, often through indirect pathways and linkages. © Inter-Research 2010. Source


Roth T.C.,Franklin And Marshall College | Krochmal A.R.,Washington College
Current Biology | Year: 2015

The severity of the environment often influences animal cognition [1-6], as does the rate of change within that environment [7-10]. Rapid alteration of habitat places limitations on basic resources such as energy, water, nesting sites, and refugia [8, 10]. How animals respond to these situations provides insight into the mechanisms of cognition and the role of behavior in adaptation [11-13]. We tested the hypothesis that learning plays a role in the navigation of the painted turtle (Chrysemys picta) within a model of environmental change. We radiotracked experienced and naive turtles at different developmental stages from two different populations as they sought out new habitats when their pond was destroyed. Our data suggest that the ability of turtles to navigate is facilitated in part by experience during a critical period. Resident adults repeatedly used specific routes with exceptional precision, while translocated adults failed to find water. Naive juveniles (1-3 years old) from both populations used the same paths taken by resident adults; the ability to follow paths was lost by age 4. We also used laboratory behavioral assays to examine the possible cues facilitating this precise navigation. Turtles responded to manipulation of the local ultraviolet environment, but not the olfactory environment. This is the first evidence to suggest that learning during a critical period may be important for how animals respond to changing environments. Our work emphasizes the need for the examination of learning in navigation and the breadth of critical learning periods across vertebrates. © 2015 Elsevier Ltd Source


Beasley C.R.,Washington College | Jason L.A.,DePaul University
American Journal of Community Psychology | Year: 2015

This study tested an affective events theory (AET) model in the Oxford House network of recovery homes. Residents’ congruence with their home (P–E fit) was hypothesized to directly influence behavior that supported the house and other residents—citizenship behavior. We further hypothesized P–E fit would be related to member intentions to leave, with attitudes toward the home mediating that relationship. To assess this, we administered a cross-sectional national survey to 296 residents of 83 randomly selected Oxford Houses. Although the AET model demonstrated good fit with the data, an alternative model fit better. This alternative model suggested an additional indirect relationship between P–E fit and citizenship mediated by attitudes. Results suggested affective experiences such as feeling like one fits with a community may influence engagement and disengagement. There appears to be a direct influence of fit on citizenship behavior and an indirect influence of fit through recovery home attitudes on both citizenship and intentions to leave the home. We conclude affective experiences could be important for community engagement and disengagement but AET may need to integrate cognitive dissonance theory. © 2015, Society for Community Research and Action. Source


Roth T.C.,Franklin And Marshall College | Krochmal A.R.,Washington College
Proceedings of the Royal Society B: Biological Sciences | Year: 2016

The ability to learn about the spatial environment plays an important role in navigation, migration, dispersal, and foraging. However, our understanding of both the role of cognition in the development of navigation strategies and the mechanisms underlying these strategies is limited. We tested the hypothesis that complex navigation is facilitated by spatial memory in a population of Chrysemys picta that navigate with extreme precision (+3.5 m) using specific routes that must be learned prior to age three.We used scopolamine, a muscarinic acetylcholine receptor antagonist, to manipulate the cognitive spatial abilities of free-living turtles during naturally occurring overland movements. Experienced adults treated with scopolamine diverted markedly from their precise navigation routes. Naive juveniles lacking experience (and memory) were not affected by scopolamine, and thereby served as controls for perceptual or non-spatial cognitive processes associated with navigation. Further, neither adult nor juvenile movement was affected by methylscopolamine, a form of scopolamine that does not cross the blood–brain barrier, a control for the peripheral effects of scopolamine. Together, these results are consistent with a role of spatial cognition in complex navigation and highlight a cellular mechanism that might underlie spatial cognition. Overall, our findings expand our understanding of the development of complex cognitive abilities of vertebrates and the neurological mechanisms of navigation. © 2016 The Author(s) Published by the Royal Society. All rights reserved. Source


Carr J.M.,Indiana State University | Carr J.M.,Washington College | Lima S.L.,Indiana State University
Oecologia | Year: 2014

Wintering birds can gain significant thermal benefits by foraging in direct sunlight. However, exposure to bright sunlight might make birds easier to detect by predators and may also cause visual glare that can reduce a bird's ability to monitor the environment. Thus, birds likely experience a trade-off between the thermal benefits and predation-related costs of foraging in direct sunlight. To examine this possible thermoregulation-predation trade-off, we monitored the behavior of mixed-species flocks of wintering emberizid sparrows foraging in alternating strips of sunlight and shade. On average, these sparrows routinely preferred to forage in the shade, despite midday air temperatures as much as 30 °C below their thermoneutral zone. This preference for shade was strongest at relatively high temperatures when the thermal benefits of foraging in sunlight were reduced, suggesting a thermoregulation-predation trade-off. Glare could be reduced if birds faced away from the sun while feeding in direct sunlight, but we found that foraging birds tended to face southward (the direction of the sun). We speculate that other factors, such as the likely direction of predator approach, may explain this southerly orientation, particularly if predators use solar glare to their advantage during an attack. This interpretation is supported by the fact that birds had the weakest southerly orientation on cloudy days. Wintering birds may generally avoid foraging in direct sunlight to minimize their risk of predation. However, given the thermal benefits of sunshine, such birds may benefit from foraging in habitats that provide a mosaic of sunlit and shaded microhabitats. © 2013 Springer-Verlag Berlin Heidelberg. Source

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