INVADING TURTLES: Basking activities of Invasive Sliders (Trachemys scripta) in Lake Marburg, PA.

Kevin Carlson – Department of Biology, York College

INTRODUCTION

∙ Lake Marburg is located near Hanover in York County, PA and contains a number of aquatic turtle species. The species that are native to the lake are the painted turtle (Chrysemys picta) and the red-bellied turtle (Pseudemys rubriventris). The invasive sliders are the red-eared slider (Trachemys scripta elegans) and the yellow-bellied slider (Trachemys scripta).

∙ The introduction of invasive species affects both the structure and the functioning of ecosystems by altering processes such as energy flows through an ecosystem by displacing native species from their ecological niches (Herbold and Moyle 1986).

∙ Basking is common in aquatic turtles and is generally accepted to be a thermoregulatory behavior (Peterman and Ryan 2009). The active season is typically limited by environmental temperatures; basking can elongate the active season.

∙ Being able to emerge from hibernation earlier (spring: April) and abstain from hibernation later (fall: October) would give the sliders a competitive advantage. A longer active season for the sliders would allow the species to feed more and allow for the possibility to double-clutch in a single season.

∙ The time spent basking and basking-location selection are thus expected to obey optimality rules (Cadi and Joly 2003). Optimality is the idea that the organism will use specified internal or external variables to maximize its biological fitness. In this experiment the main basking optimality principles would be: 1) The depth of water to maintain safe escape response; 2) The greatest amount of sunlight the location receives throughout the day.

I conducted an observational experiment to determine whether or not the sliders within Marburg Lake are, as an invasive species, outcompeting the native turtle species based on their temperature tolerances and basking behaviors.

HYPOTHESIS

Ho: There will be no difference in temperature tolerance between the four species.

H1: Sliders have a wider temperature tolerance, giving them a complete advantage over the native species

DISCUSSION

∙A significant difference was observed between species in response to temperature. However, the difference was in the tolerance of painted turtles (more basking at higher temperatures and less at lower temperatures) not in the tolerance of invasive sliders.

∙ Larger turtles came out earlier in the spring – due to their smaller surface area per body – they had more potential to hold more heat.

∙ In the summer, larger turtles were found more likely to estivate or bask in the water (floating on vegetation) to avoid overheating.

∙ In the fall, observed many fewer turtles. This may be due to the water levels being significantly lower, limiting available basking locations. This was the opposite of our expected results.

AcknowledgmentsI would like to thank Dr. Nolan for her outstanding guidance and continuous support throughout the entire experiment as my mentor, this would have never gotten done without her. Also I would like to thank Dr. Thompson for being a positive instructor to help my poster and written lab come together. Finally, I would like to thank the Marburg Lake (Codorus Creek) staff for their trust and allowing me to perform my experiment at their park.

METHODS

RESULTS

Future Experiment(s)

In my experiment, it was observed that there was a lack of available basking locations for the turtles due to a significant drop in the lakes’ water level. It would be worth investigating the effects and impacts that less basking area has on all turtles and if it would be beneficial to the turtles’ basking habits to have basking platforms located in the deeper sections of the lake when water levels drop.

Average Temperature

May

June

July

August

Septe

mber

October

0

10

20

3020092010

Tem

per

atu

re (

C)

Figure 2. Average temperature recorded by the National Weather Service for the months of May through October in 2009 and 2010. Data shown are average values for the month.

Figure 1. Average temperature recorded while observing the turtles basking. Data shown are average values for the month ± SEM. A one-way ANOVA with a Tukey Posttest shows no difference between sampling times.

Native Species

Painted Turtle (Chrysemys picta)

Red-Bellied Turtle(Pseudemys rubriventris)

Works Cited

Cadi, A. A., & Joly, P. P. (2003). Competition for basking places between the endangered European pond turtle (Emys orbicularisgalloitalica) and the introduced red-eared slider (Trachemys scripta elegans). Canadian Journal of Zoology, 81(8), 1392-1398. Retrieved from EBSCOhost.

Herbold, B., and Moyle, B.P. 1986. Introduced species and vacant niches. Am. Nat. 128: 751–760.

Peterman, W. E., & Ryan, T. J. (2009). Basking Behavior of Emydid Turtles (Chysemys picta, Graptemys geographica, and Trachemys scripta) in an Urban Landscape. Northeastern Naturalist, 16(4), 629-636. Retrieved from EBSCOhost.

Invasive Species

Red-Eared Slider(Trachemys scripta elegans)

http://www.torontozoo.com/adoptapond/turtletally.asp?t=form

The three observational sites that turtles were studied at are circled: Dubs Cove, Chapel Cove and Sailboat Cove.

Sampling Schedule: Response to both low and high temperatures: April – emerge from hibernation July – response to high temperatures / estivate? October (mid-September to mid-November) - hibernation

Sampling: Observation of basking platforms (Leupold Spotting Scope) Recorded number of: Red-eared sliders

Yellow-bellied sliders

Red-bellied turtles

Painted turtles

Unknown turtles

Environmental characteristics: (Kestral Pocket Weather Tracker 4000) Temperature, Wind speed, Wind chill, Humidity, % Cloud cover, Wet bulb

Leupold Spotting ScopeKestral Pocket Weather

Tracker 4000 Turtle Basking Platform

http://www.spotters4less.com/ http://www.aceselectronics.co.uk/product.php?xProd=104

http://www.lakenormanwildlife.org/basking_platform_project.htm

Up close shot of turtle basking platforms at Chapel Cove.

Sample Site-Chapel Cove Sample Site-Dubs Cove

Photo taken from Victoria Kentner’s senior thesis poster

Figure 3. Turtles emerging from hibernation in April. Data shown are average values for the day ± SEM. A two-way ANOVA with a Bonferroni Posttest shows a significant difference between painted turtles and the remaining species on the 6th and 15th.*

Figure 4. Average number of turtles observed basking. Data shown are average values for the month ± SEM. A two-way ANOVA with a Bonferroni Posttest shows a significant difference both between species and over the course of the year.

Figure 5. Turtles hibernating in Fall. Data shown are average values for the day ± SEM. A two-way ANOVA with a Bonferroni Posttest shows a significant difference between painted turtles and the remaining species on the 2nd day (September 18th).

Figure 6. Average basking area available for turtles in spring and fall. Data shown are average values for the season ± SEM. A two-way ANOVA with a Bonferroni Posttest shows no difference between sampling times.

*

Yellow-Bellied Slider(Trachemys scripta)