Travis J. Ryan

Movement and habitat use of two aquatic turtles (Graptemys geographica and Trachemys scripta) in an urban landscape

Our study focuses on the spatial ecology and seasonal habitat use of two aquatic turtles in order to understand the manner in which upland habitat use by humans shapes the aquatic activity, movement, and habitat selection of these species in an urban setting. We used radiotelemetry to follow 15 female Graptemys geographica (common map turtle) and each of ten male and female Trachemys scripta (red-eared slider) living in a man-made canal within a highly urbanized region of Indianapolis, IN, USA. During the active season (between May and September) of 2002, we located 33 of the 35 individuals a total of 934 times and determined the total range of activity, mean movement, and daily movement for each individuals. We also analyzed turtle locations relative to the upland habitat types (commercial, residential, river, road, woodlot, and open) surrounding the canal and determined that the turtles spent a disproportionate amount of time in woodland and commercial habitats and avoided the road-associated portions of the canal. We also located 21 of the turtles during hibernation (February 2003), and determined that an even greater proportion of individuals hibernated in woodland-bordered portions of the canal. Our results clearly indicate that turtle habitat selection is influenced by human activities; sound conservation and management of turtle populations in urban habitats will require the incorporation of spatial ecology and habitat use data.

Basking behavior of emydid turtles (Chysemys picta, Graptemys geographica, and Trachemys scripta) in an urban landscape.

Abstract Basking is common in emydid turtles and is generally accepted to be a thermoregulatory behavior. In 2004, we quantified and described the basking behavior of turtles in the Central Canal of Indianapolis. This canal system flows through an urban landscape that is dominated by fragmented woodlots, residential areas, and commercial areas. We observed that basking turtles exhibited variable basking behavior, with spatial and temporal shifts in basking behavior from east-facing banks in the morning to west-facing banks in the afternoon. Turtles in the Central Canal are subject to frequent disturbance, which altered basking behavior. Many turtles forewent aerial basking on emergent substrates for aquatic basking on vegetation mats, which maintained warmer and more consistent temperatures than either emergent substrates or the surrounding water. Living in an intensively managed urban habitat, turtles in the Central Canal are susceptible to frequent anthropogenic perturbations, and future management should consider the life history and ecology of urban turtle populations

Hydroperiod and Metamorphosis in Small-mouthed Salamanders (Ambystoma texanum)

Abstract Ambystoma texanum (Small-mouthed Salamander) breeds primarily in temporary wetlands, and while natural history studies have suggested a minimum larval period of about 2 mo, it is not clear how hydroperiod (the length of time that a temporary wetland holds water) influences populations. I conducted a mesocosm experiment to investigate the effects of hydroperiod on the completion of metamorphosis, as well as age and size at metamorphosis. I used hydroperiods of 50, 75, and 100 d, and a non-drying treatment as a control. Survival to the end of each hydroperiod was consistent among all groups, but no individuals completed metamorphosis in the 50-d treatment. The proportion of individuals completing metamorphosis increased with longer hydroperiods, as did the age at metamorphosis. The size at metamorphosis, however, was not affected by the length of the hydroperiod. My results show that a minimum hydroperiod of 2.5 mo is necessary for populations of Small-mouthed Salamander. Maintenance of natural hydroperiods in wetlands under the threat of development is a critical consideration for the long-term persistence of Small-mouthed Salamander populations.

Movement and habitat use of the snapping turtle in an urban landscape

In order to effectively manage urban habitats, it is important to incorporate the spatial ecology and habitat use of the species utilizing them. Our previous studies have shown that the distribution of upland habitats surrounding a highly urbanized wetland habitat, the Central Canal (Indianapolis, IN, USA) influences the distribution of map turtles (Graptemys geographica) and red-eared sliders (Trachemys scripta) during both the active season and hibernation. In this study we detail the movements and habitat use of another prominent member of the Central Canal turtle assemblage, the common snapping turtle, Chelydra serpentina. We find the same major upland habitat associations for C. serpentina as for G. geographica and T. scripta, despite major differences in their activity (e.g., C. serpentina do not regularly engage in aerial basking). These results reinforce the importance of recognizing the connection between aquatic and surrounding terrestrial habitats, especially in urban ecosystems.

Influence of Light Quality and Quantity on Heterophylly in the Aquatic Plant Nymphaea odorata subsp. tuberosa (Nymphaeaceae)

Abstract Heterophylly, the production of different leaf forms on the same plant, is a widespread phenomenon in terrestrial and aquatic plants and provides an opportunity to study how sessile organisms sense and respond to changes in environmental factors. Nymphaea odorata subsp. tuberosa (American White Water Lily) produces 2 distinct leaf forms: a floating surface leaf and an aerial form in which the lamina is held above the water. Previous research suggests that changes in the light environment may be a critical determinant of heterophylly in Nymphaea. In this study, we tested the hypothesis that changes in light quantity and light quality stimulate the production of aerial leaf forms in water lilies. Specifically, shade cloth was used to reduce light intensity (quantity), and varying plant densities were used to increase leaf cover (affecting light quality) in artificial ponds. Aerial leaf production was not stimulated by reduction in light quantity alone but was when leaf cover exceeded 30–40%. We suggest that as the surface of a pond becomes covered with a canopy of leaves, American White Water Lily responds with the production of aerial leaves that rise above the surface of the water to gain access to light. Interestingly, water lilies exhibit an atypical shade response in that aerial leaves have short, thick petioles that allow them to rise above the surface of the water, rather than displaying the elongated phenotype associated with etiolation, which is the typical shade response of other flowering plants.