Thermal Biology of the Mexican Spotted Wood Turtle in a Tropical Deciduous Forest

Student: Nicholas DeHollander

Mentor: Dan Beck

Abstract

As global temperatures have increased with climate change, hurricanes have become stronger in the tropics. In October of 2015, Hurricane Patricia, a massive, category 5 storm struck the tropical dry forest (TDF) of Chamela, Jalisco, a biosphere reserve in western Mexico where this study was done. The strong winds broke branches, toppled trees, and deposited considerable woody debris onto the forest floor, resulting in a more open forest canopy and increased surface temperatures. We investigated how the Mexican Spotted Wood Turtle (R. r. perixantha), an endemic terrestrial turtle in Mexico’s TDF, responded to the changes in forest temperatures brought about by this disturbance. We outfitted six turtles with continuous hourly temperature dataloggers during 12 weeks of the dry (March-June) and wet (August-October) seasons of 2019. We also sampled forest temperatures by placing temperature-logging copper models on exposed surfaces, and under woody debris, in microhabitats available to the turtles. Temperature data were retrieved on three males and one female for both seasons. Temperatures of dataloggers carried by the turtles during the dry season were significantly cooler and showed much greater variation (25.98°C ± 4.5; n=4), than during the wet season (28.08°C ± 2.6; n=4). Temperatures of data loggers (copper models) in the forest were higher (and less variable) during the wet season, suggesting that thermoregulation may be more challenging at that time because there are fewer temperature options for turtles. As forest temperatures increase due to climate change, turtles may have more difficulty finding adequate microhabitats in which to thermoregulate.

Presentation

20 thoughts on “Thermal Biology of the Mexican Spotted Wood Turtle in a Tropical Deciduous Forest”

  1. Holy cow, what terrific images — such a difference just three days after rain. Those plants are amazing, aren’t they. Oh, and turtles, choosing habitats. And woody debris. So dead plants are useful too. Hmmm… It is nice that you got to work with the local students. I liked the mural (it included plants). Thanks for the presentation Nick. You did a nice job. MP

  2. Excellent presentation. It’s interesting to see that the turtles preferred the shelter of woody debris after the hurricane. Did you come across any information about how long it takes for the woody debris to decompose in this environment, and thus how long this increase in the woody-debris shelter will be available to the turtles?

    1. Nicholas DeHollander

      What a great question! I have not found any information about how long the woody-debris will take to completely decompose but from my talks with Dr. Beck he has already begun to notice the forest understory opening up more since Hurricane Patricia. While I can’t give a timeline for decomposition because of the variety of factors involved, I speculate that the woody debris may take longer to decompose in the TDF than in Washington because of the long dry seasons. I suspect that before the woody debris decomposes we will see another large hurricane that deposits more given the trend of more frequent and intense storms.

  3. Nice job Nick! How did the temperatures vary with elevation? Do you think that turtles will try to move farther down in elevation to combat temperature changes over a longer span of time?

    1. Nicholas DeHollander

      Hey Lauren great question!
      From my project measuring forest temperatures in the spring I found that open surface temperatures varied the most based on elevation. This is because in the spring the forest canopy is thinner and more sunlight reaches the forest floor. However, woody debris temperatures remained fairly consistent regardless of elevation during the dry season. The turtles are almost never active during the dry season so as long as they have access to these cooler microhabitats in the uplands I don’t expect them to move farther down in elevation. During the wet season, temperatures are more consistent throughout the forest so elevation is not a viable option for the turtles to moderate their temperatures.

  4. Good job Nicholas! I was apart of the cohort in 2017 and it was so fun to watch this presentation. Your presentation was clear, interesting, and well done. I thought it was really interesting that there were fewer cool places that the turtles had access to in the rainy season; I would have expected the opposite. Thank you for sharing! I miss living in Mexico and at the field station! Good work.

    Stacey

  5. Hi Nicholas, great presentation it was very well presented and seems like a fun experiment to conduct. I was wondering if you think the turtle’s diet could have also impacted the locations the turtles decided to inhabit?

  6. Alexander Hilstad

    Hey Nicholas, great presentation! I was curious if you knew about the patterning of the turtles and how they might have served as a potential camouflage? Since the turtles were previously spending much of their time below leaf litter, I imagined that perhaps their patterning was meant to mimic the decaying brown leaves that might make up that leaf litter, and it made me wonder if now that they are increasingly moving to live below fallen woody debris if that might somehow alter their patterning in future generations.

  7. Question: Good work! Thermoregulation is so important for herps and increasing surface temperatures can be vary problematic. With it increasing during the wet season, do you think this would change their activity timing, i.e. between day and night?

  8. Hey Nick,
    Awesome presentation! It’s interesting to see how abiotic factors can influence the behavior of organisms within an ecosystem. If climate change makes finding adequate microhabitats more difficult for the turtles, where besides under leaf litter or woody debris do you think they would take to?

  9. I wonder if the shift in microhabitats has caused any effects on the diet of these turtles or if their diet has stayed consistent?

  10. That’s interesting that the Mexican Spotted Wood Turtle could go without water for 6 months. My question is how does it work? Does the system just shut down or still function normally? I really like your presentation, well organize and the transitions flow pretty smoothly

  11. Hi Nick,

    Great job on your presentation! What did you use to stick the loggers to the turtles? Do you think that they changed preference to woody debris because it was simply more available and they prefer slightly cooler temperatures?

  12. Hey Nicholas, Great presentation. This seems like it was an amazing experience for you. The only thing I wonder is where the turtles will go once their woody debris decompose, although this may be awhile, I still wonder how they will react once it is gone.

  13. Hi Nick, I appreciated the detail you gave in the microhabitats that the turtles choose to live. I think its very neat that they are able to find habitats that mirror what they were adapted to before a large natural disaster.

  14. hey Nick
    this was a great presentation i really enjoyed it. it seemed like a fun and interesting research trip. do you think that there was a change in predation of the turtles after the hurricane

  15. Jennifer Edwards

    How were the turtles outfitted with the temperature logger? Did you have to pierce their shell at all? Were they removed easily after the study?

  16. Tristan A Lashua

    Hey Nick, great presentation. It was very interesting to learn about the turtles and their preferred microhabitats with the varying temperatures. One question I have is did the gender of the turtle have any affect on the turtles temperature or preferred microhabitat?

Leave a Reply

Your email address will not be published. Required fields are marked *