Tag: Territoriality

SICB 2020: Acute Interactions between Green and Brown Anoles

Jordan Bush giving her talk on the interaction between green and brown anoles at SICB 2020

Green and brown anole interacting within Jordan’s enclosures.

As brown anoles (Anolis sagrei) become more and more abundant, many people (trained and citizen scientists alike) are intrigued with exactly how the native green anole (A. carolinensis) will respond. Newspaper articles still report on these interspecific interactions, and some recent research has shown the brown anoles can be quite mean to the native green. Thankfully, it seems that the green anole may simply be moving higher into the canopy and aren’t being merely driven to extinction by the invading brown. However, we do not yet understand the nuances of how green anoles respond when brown anoles first arrive to a new location, and that’s where Jordan Bush, a sixth year PhD student in Dan Simberloff’s lab at the University of Tennessee, Knoxville, comes in.

To understand how green anoles immediately react to the novel presence of brown anoles, Jordan built 5 x 5 x 5m enclosures in which she placed 6 female and 6 male green anoles. These animals then set up territories and became acclimated to their new living space. Jordan quantified baseline behavior and territory sizes (in 3D!!!) for each individual in an enclosure.

Example 3D territories

After 10 days, Jordan introduced brown anoles in these enclosures, either two females and two males or four females and four males to investigate the effects of density, and quantified behavioral and territorial changes in the green anole. Being the careful researcher that she is, she also introduced the same number of green anoles to other enclosures so that she could show that any changes in behavior were not simply due to more animals being present. After 10 days of interacting with the brown anole, Jordan found no change in activity level, home range volume, or perch height, suggesting that, at least within an acute time frame, the green anole can handle its own against the brown anole.

‘Whoops’! Anolis bicaorum Falls during Dewlap Display!

While performing population research of Anolis (Norops) bicaorum at Kanahau Utila Research & Conservation Facility, we stumbled upon two males in close proximity initiating a territorial dispute. With the intention of documenting this behavior, we began to record the interaction.

In all honesty, the confrontation was a little shorter than any of us expected…  It may well be one of my funniest fieldwork memories to date (despite watching it on repeat, I still can’t help but chuckle at this anole’s misfortune!) . To detail, upon the first exchange of dewlap extensions, the responding male slipped and fell clumsily from the trunk; meanwhile, his contender (who was in the process of displaying) looked on, apparently baffled at the sudden disappearance of his rival.

It appears the falling males mistake arose owing to a combination of two factors. The simple explanation is that this male lost his footing on the steep vertical trunk (which formed the battleground on this occasion), but indeed it’s rare to see an anole make such an error of judgement;  the lamellae on their feet afford them excellent grip on many substrates.   The second explanation owes to the fact males are completely intolerant of one another.  We noted that when engaging in territorial disputes, males of A. bicaorum become entirely absorbed in their confrontation, possessed by their territorial natures and relentless in their efforts to dissuade and expel contenders from their patch.  Often, competing individuals become so preoccupied that hey no longer perceive apparent dangers (e.g., the closely observing biologists).  Perhaps the haphazard approach of males in territorial engagement leaves them prone to the occasional miscalculation.

If you are curious to learn more about Anolis (Norops) bicaorum (a threatened species endemic to Isla de Utila, Honduras),  the most recent research by Brown et al. (2017) at Kanahau URCF resulted in published records on their geographic distribution, natural history, ecology and interactions with sympatric anoles. 

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