Losing Leaf Litter Lizards

The phrase “climate change” typically conjures up images of melting ice caps and starving polar bears in the North Pole. Few people think of the tropics being affected by climate change. Yet in the tropics, many species have evolved living in a relatively stable climate, so changes by even a few degrees in temperature or a few weeks in timing of rain can drastically affect them.

Meredith Swartwout purs rainwater into a rainforest plot at La Selva Biological Station.

Meredith Swartwout pours rainwater into a rainforest plot at La Selva Biological Station.

Meredith Swartwout, a doctoral student in the Department of Biological Sciences, traveled this summer to the Organization for Tropical Studies’ La Selva Biological Station in the lowland tropical forest of Costa Rica to study how changes in precipitation are influencing the habitat of organisms that live in leaf litter on the forest floor, and how it is affecting small lizards such as the leaf litter lizard (seen in the image above).

“The past few decades have seen dramatic declines in leaf litter lizard abundances at La Selva Biological Station,” Meredith said. “Climate change, through rises in temperature and rainfall, has been implicated as a leading factor behind these declines. Most inhabitants of leaf litter are tiny, ranging from microscopic bacteria and miniscule mites, to lizards and salamanders that are several inches long. Small lizards, such as the leaf litter anole, are both vulnerable to climate change and are an important component of the leaf litter food web, consuming a wide range of invertebrates and themselves being eaten by ants and large spiders.”

Meredith focused on changes in the influence of leaf litter depth and rainfall frequency on invertebrates such as thief ants, which are important predators of lizard eggs. She also investigated whether ants detect prey faster in plots with more frequent rainfall and deeper leaf litter.

Her field experiment involved controlling litter depth by removing litter from some rainforest plots and adding it to others, as well as supplementing rainfall. Every morning for three weeks she poured rainwater onto each of her water-addition plots. To obtain snapshots of invertebrate communities in the plots, she took leaf litter and put it in a Berlese Funnel, a device that uses light and heat to drive invertebrates out of the litter and into a container for collection. Meredith attracted predatory ants by setting out tuna bait stations, and recorded how quickly the ants could locate and consume the baits on different plots.

Ant bait station full of small red ants after being left out for 12 hours.

Ant bait station full of small red ants after being left out for 12 hours.

“I’m still processing my invertebrate samples, but my preliminary data suggests interesting trends that could help explain the role of precipitation and litter depth in shaping invertebrate communities,” she said.

Meredith’s research is funded by a National Science Foundation Graduate Research Fellowship, which provides $34,000 a year and can be renewed for up to three years. The highly competitive awards are made to support students in science, technology, engineering, and mathematics and recognize academic excellence and the potential contribution that each student will make to his or her field and to society at large.




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