Research

When Territorial Species Collide

When an invasive species is introduced to a new place, a large part of its success is determined by how it interacts with the species that already live there – can it eat native prey? avoid native predators? compete with native competitors? I am specifically interested in these behavioral interactions in a territorial context. What happens when a territorial native species is invaded by a closely related territorial invasive species, one who competes over the same resources and communicates with similar defensive behaviors?

I explore this question using anole lizards. For the past 50 years, the Cuban brown anole (Anolis sagrei) has been displacing the native green anole (A. carolinensis) throughout Florida. The mechanism behind the brown anole’s success is unclear, and little is known about if and how the two species interact with one another on a day-to-day basis. I want to know if the two species compete over territories, and how green anoles respond to having to share space with a new competitor.

In this study, I house captive populations of green anoles in large outdoor structures in Oak Ridge, Tennessee, and record their display behaviors and habitat use for several weeks. I then introduce brown anoles to the structures and re-measure the green anoles’ behaviors over the following several weeks, looking for differences between pre- and post-invasion behaviors. I also record the outcomes of territorial fights between the two species to determine if one species is competitively dominant over the other. Through this study, I hope to provides insights into how native species respond to novel competitors in a territorial context, and to explore the effects of combative vs passive interactions between native and invasive species.

 

Three Dimension Home Range Estimation

When studying animal spatial behaviors, it is often important to try to outline where an animal lives, to identify on a map which parts of the habitat they consider “theirs.” We do this by watching an animal’s movement for a period of time and then applying mathematical models to these points to estimate how the animal moved from point to point. This can give us a measure of an individual’s its overall range (called a home range) or the area that the animal considers exclusively theirs (called a territory).

Home ranges and territories are almost always estimated in two dimensions. While this makes sense for many terrestrial animals, these metrics lose information when animals occupy (and subdivide) three dimensional spaces, such as arboreal (tree-dwelling), marine, and flying animals.There have been a few studies that have used 3D territory metrics, however we do not know how accurate these metrics are or how different estimation metrics compare to each other.

I have developed R code to model 3D home ranges using two estimation techniques (minimum convex polygon and kernel density), and I am in the process of evaluating the accuracy of these 3D metrics using a statistical modeling approach. My goal is to understand how well these methods can reflect a known distribution, and if their accuracy changes depending on the 3D spatial landscape (i.e., if one is more accurate for arboreal species vs marine species). I plan to combine this analysis with a review of how researchers have used 3D home range metrics in the past.

 

Tyrannical spiders: When siblings don’t get along

The desert spider Agelenopsis aperta experiences two distinct social landscapes in its lifetime: an early gregarious stage where siblings live together on a maternal web, followed by a solitary adult stage. In this study, we sought to understand the early social interactions of juvenile A. aperta. Specifically, we wanted to determine if spiderlings are competitive, cooperative, or neutral towards their siblings in maternal webs and how survival, foraging behavior, and growth differ in juvenile populations of different sizes.

To do this, we created replicate populations of siblings (n =1, 2, 4, 8). We fed each individual every few days over a three-week period and recorded the behavior exhibited towards prey and fellow siblings for a 10-min period. We found that these spiderlings did not engage in cooperative prey capture; instead, they fought with their siblings over food and prevented each other from eating. We found that as our populations increased in size, we saw increasing differences in the survival and growth of dominant vs submissive spiderlings, with aggressive individuals stealing more and more food from timid ones. Overall, this study shows that juvenile A. aperta exhibit high levels of competition even in food rich environments and that the particular level of competition observed varies by individual personality.