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¡SOBRE México!: Student Opportunities for Biological Research in Mexico

¡SOBRE México!

Investigating How Animals Cope with Intense Seasonality in the Tropical Dry Forest

Dr. Daniel Beck and Dr. Andres Garcia Aguayo
Vertebrate evolution and adaptations to strong seasonality
Field of Research: 
Herpetology / Ecology
Estación de Biología, Chamela

Intense seasonality defines dry tropical forest and is a major driver of evolution. Yet little is known about how vertebrates respond to the striking differences in habitat structure and resource availability that occur between the dry and wet seasons.

 Estación de Biología, Chamela (EBCH) harbors 19 species of amphibians, 10 of which are endemic. Since 2010, Dr. Garcia and his students have been surveying amphibians along 6 km of ephemeral streams within EBCh.  So far, thousands of adult individuals and several thousand tadpoles of 14 species, 10 genera and four families have been observed during summer surveys. CWU students can participate in projects monitoring the timing of emergence, recording species diversity of amphibians as the summer rains begin in July, and exploring how emerging amphibians use water resources. Students can also work on acoustic surveys planned for the coming years to explore the hypothesis that anurans segregate among breeding pools when calling, that the timing of emergence varies among species, and that specific pool features are associated with breeding amphibians.  Students may also work with Dr. Garcia to use sound equipment to record amphibian calls in an effort to develop acoustic surveys for biodiversity appraisal at the Chamela field station.   These efforts will be focused at 25 ponds Dr. Garcia is monitoring for associations between physical variables (pond size, duration, temperature, substrate, insolation) and amphibian presence in concert with the cuencas (watershed) project at EBCh.

Students may also pursue projects with Dr. Garcia investigating the ecology of representative reptile species of the SDTF of western Mexico: Wood turtles (Rhinoclemmys rubida and R. pulcherrima), the Mexican beaded lizard (Heloderma horridum), the Spiny–tailed iguana (Ctenosaura pectinata), and the Mexican West coast rattlesnake (Crotalus basiliscus). These taxa were selected because they are endemic, are listed as species of concern by either the IUCN (i.e. Rhinoclemmys, Heloderma), or Mexican Red List (Ctenosaura), and most aspects of their ecology are still poorly known.  These projects address hypotheses that activity and microhabitat use are more constrained during the dry season due to reduced water resources, but that these ectotherms are able to regulate body temperatures with more precision during the dry season, where a broader range of thermal options exist. Students will outfit up to 12 individuals/species with temperature sensing dataloggers and radiotransmitters, and then monitor their movements, microhabitat use, and body temperatures from the late dry season through the early wet season. Dr. Garcia and his students from UNAM will continue to monitor radio-equipped animals after the CWU team leaves in early August. Knowledge of the autecology of these reptile species will not only provide insight into how ectotherms thrive in the wake of strong seasonality, but will provide crucial information for the long-term management of these and other threatened species.

Response to seasonality in ground-dwelling lizards -- This project will test hypotheses relating to how the assemblage of ground-dwelling lizard species respond to changes in temperature and microhabitat structure between the dry and wet seasons.  During the dry season deciduous trees drop their leaves, more sunlight penetrates through the forest canopy and leaf litter accumulates, creating a mosaic of thermal habitats for ground dwelling animals. When the rains arrive in July, the forest canopy rapidly closes as trees grow leaves, creating a more homogenous thermal landscape.  We will join Dr. Garcia-Aguayo in testing hypotheses related to how these changes in microhabitat structure within the forest translate to changes in occurrence and timing of activity of lizards within a 7-species assemblage of ground-dwelling insectivorous lizards. We will use existing pitfall trap arrays to sample lizards along transects that cross two major habitat types: Arroyo Forest and Upland Forest. Relative abundance of lizards sampled from different microhabitat types (arroyo vs upland forest) will be assessed and compared between the dry and wet seasons. We will use i-button dataloggers to measure the thermal diversity of microenvironments within those habitat types, and determine how environmental temperatures available to lizards change from dry to wet season. We will use a GLM in R to test the hypothesis that lizards broaden their use of microhabitats during the wet season.

Examples of specific projects include:

  • Summer amphibian diversity census: monitor timing of emergence and record species diversity of anurans as summer rains begin in July.
  • Record amphibian calls and develop acoustic surveys for biodiversity appraisal at the study site.
  • Investigate ecological response of ground-dwelling lizard species to rapid and profound transition from dry to wet season.
  • Analyze thermal diversity of microenvironments available to ectotherms and how they change as the wet season begins. 
  • Investigate ectoparasites (mites, ticks) of tropical dry forest lizards.
  • Investigate autecology (habitat use, activity patterns and thermal biology) of focal species of concern in the tropical deciduous forest (e.g. turtles, lizards, snakes).
  • Characterize habitat variation in fruiting phenology of trees used by dry forest birds
  • How do habitat use and vocalizations by chachalacas (and other SDTF endemic birds) change during transition from dry to wet seasons?
  • How do nesting resources for primary and secondary cavity-nesters vary across the landscape?

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