Invasive Lizards

You are a herpetologist interested in biological invasions in urban habiats. The brown anole Anolis sagrei is invasive to Southern Florida, where it now competes with the native green anole Anolis carolinensis. Males of both species fight over territory in their now shared habitat. The males aggressively signal using a series of pushups to display their physical condition to other males. Males that perform more pushups are deemed more aggressive than males who perform fewer pushups You are wondering whether the invasive brown anoles are better space competitors than the native green anoles, and whether space competition in these species is linked to their aggressive behaviour. To test this, you transported wild-captured individuals of both species to the lab. You administered three rounds of an aggression assay, in which the lizard was presented with a mirror and recorded. Males perceive their reflection to be an intruder, and engage in pushup display behaviour. You recorded the number of pushups performed in each of three separate trials, then calculated an ‘average aggression’ level for each lizard. You then placed one native A. carolinensis and one invasive A. sagrei into an arena and recorded the area of space they occupied over the course of three days (cm3) in a variable called ‘space use’, as a measure of their ability to compete for space.

Analyze this dataset to see whether species ID or aggression level has an effect on space competition ability.

1. Run the following chunk of code, unedited, to simulate this dataset

2. Using the lm() command, create and analyze a statistical model that tests for the effect of species, aggression, and their interaction on square-root-transformed space use.
   • Give a verbal inferential statement for each effect in this model

3. Using ggplot, produce a plot with a histogram of the average aggression level for both green anoles and brown anoles on a single panel. Colour the green anole distribution green, and the brown anole distribution brown. Make the colours transparent so that overlap is visible.

4. In base R plotting, Create a boxplot comparing space use occupied by green versus brown anoles. Again colour the green anole boxplot green, and the brown anole boxplot brown.

5. In ggplot, create a scatterplot of space use as a function of average aggression. Add a colour factor, so that the dots are coloured according to their species label (green for green anoles, brown for brown anoles).
   • Overlay a lm-based line of fit for each species, as well as a measure of estimated error for those lines of fit.
   • Position your legend such that it appears in a convenient blank spot on the figure panel

Files to download:

To download, right-click and press “Save File As” or “Download Linked File”

1. invasivelizards.csv

Laboratory and Institution or PI

Unpublished work – PhD Candidate Brendan McEwen

References and Further Reading

Farrell, W. J., & Wilczynski, W. (2006). Aggressive experience alters place preference in green anole lizards, Anolis carolinensis. Animal Behaviour, 71(5), 1155-1164.

Rodríguez, C., Fusani, L., Raboisson, G., Hödl, W., Ringler, E., & Canoine, V. (2022). Androgen responsiveness to simulated territorial intrusions in Allobates femoralis males: evidence supporting the challenge hypothesis in a territorial frog. General and comparative endocrinology, 326, 114046.