Balanced Ecosystems Depend on the Top-Down Effects Driven by Apex Predators

Trail camera image of coyotes in an urban park in Nashville, Tennessee

Predators create a phenomenon known to ecologists as the Landscape of Fear. This is a top-down effect that influences the behavior and movements of prey animals.

The Landscape of Fear is a multidimensional phenomenon that occurs in both time and space. In the figure above a herd of zebra have adjusted their behavior to mitigate predation risk from lions. During the day the lions are not as active, the zebra are more free to forage in the open. At night their activity changes because the lions are more active and the moon is full giving the lions an advantage in the open. The zebra have moved into cover to mitigate predation risk to avoid light from the full moon.

To investigate this in the neotropics, I will be studying mammals in the Brazilian Pantanal under the guidance of Dr. Malu Jorge. My first field season is quickly approaching during the summer of 2025. Check back for more updates!

Past Research

Foraging Behavior In Bats

My current research is taking place on Fort Campbell Military Installation along the border of Kentucky and Tennessee just Northwest of Clarksville, TN. As a part of the Haase Lab at Austin Peay State University, my project is being overseen and advised by Dr. Catherine Haase. I am currently studying the effects of perceived increased predator presence on the foraging behavior of local species.

Leah Crowley walks past a threatened tricolor bat during a cave survey

Predation has direct and indirect effects..

Not only do predators directly affect populations by taking individuals for consumption, but they can affect their behavior in ways that can be detrimental. Fear may cause them to change their foraging behavior by foraging less or abandoning fruitful sites for subpar sites to mitigate predation risk. This can have a negative effect on overall populations, but we don’t have a good grasp on how bats respond to predators. This is the study of fear driven ecology.

The food chain is divided into what ecologists refer to as trophic levels. These levels are divided by each organism’s role in the food web, starting at the bottom level which are the autotrophs. Autotrophs are organisms that photosynthesize. At the top are tertiary or quaternary consumers that eat everything below their level.

Knowing all we can about factors influencing bat populations will be vital to their conservation, including predation.

To test the the temporal and spatial changes bats may make to mitigate predation risk we designed an experiment which will manipulate the natural environment of bats by increasing the perception that predators may be present. We accomplished this through broadcasting pre-recorded calls of nocturnal predators and using predator decoys as visual cues. Each site was sampled for two weeks, week one as control, week two as treatment.

Update

FIELD SEASON ENDED, 10/06/2023….

Over the summer I sampled 10 sites on Ft Campbell, KY, and ended up with over 250,000 data points. After running the raw data through analytic software, over 45,000 data points were identified as bats. In May 2024 I defended my thesis and submitted it to the Graduate School of APSU. The manuscript is currently being revised for publication.

Plot at APSU Farm: Several plots were laid out for each site, pictured above is one that had been treated with a predator decoy and a sound box, that would broadcast predator calls at specific times.

*Handling bats can be dangerous. Do not try this at home! All research is conducted under the proper federal and state permits, and approved under IACUC 23.008 from Austin Peay State University. Members of the lab have been properly trained and immunized to handle chiroptera species.