If you have a truly outstanding memory or if you enjoy re-reading old AA articles, you might remember this post on how bolder lizards autotomized their tails more readily to compensate for risky behavior. As unlikely as it is, you might also remember me saying that this study solved one piece of the puzzle by explaining why the propensity of tail autotomy would vary within a population. Two years have since gone by, and I am glad to present to you, my fellow AA readers, another piece of the puzzle: how ecology might shape the variation in tail autotomy among populations.
Which aspects of ecology should we be looking at? Fortunately, the rich literature in tail autotomy helped us identify three main players: predation, food abundance and male-male fighting. Among these three ecological factors, the relevance of predation is the most straightforward: lizards will benefit from autotomizing more readily if predation pressure is high. On the other hand, the importance of food abundance lies in the fact that lizards need resources to grow the tails back, and the rate of regeneration depends on food abundance. Therefore, high food abundance will allow for faster regeneration and likely favors higher propensities for tail autotomy. The inclusion of male-male fighting as a key factor stems from the common observation that the tail is a common target for attack when males engage in territorial combats. In fact, quite a few studies have reported tail autotomy as a consequence of male-male fightings. As fights between males are rarely life-threatening (i.e. autotomy-worthy), tail autotomy under those circumstances would be undesirable. Consequently, environments in which male–male combat is common should favor lower autotomy propensities, with other things being equal.
To test these hypotheses, we first built a theoretical model in which we simultaneously varied predation, food abundance and the degree of male-male fighting and examined the propensity for tail autotomy that conferred the highest survival. Results from the model supported our hypotheses: higher predation and higher food abundance favored higher autotomy propensities, whereas higher intensities of male-male fighting favored the opposite. We then took one further step: we collected data on these three factors from five populations of side-blotched lizards (Uta stansburiana) in the western U.S. and used our model to explain the variation in the propensity for tail autotomy among those populations. It turned out that our model did a pretty good job, and we are confident that the variation in tail autotomy at the population level represents the outcome of ecological adaptations to predation, food abundance and male-male competition.
Are you wondering which of the three factors played the most important role in determining the propensity for tail autotomy (hint: it was NOT predation!)? Are you interested in more details about how we actually constructed the model? If so, you might want to give our recent paper a read:
CHI-YUN KUO and DUNCAN J. IRSCHICK. (2016). Ecology drives natural variation in an extreme antipredator trait: a cost-benefit analysis integrating modelling and field data. Functional Ecology 30: 953-963. doi: 10.1111/1365-2435.12593