Competing through eating: lessons from a lizard

One way invasive species can have a major impact on ecosystems is by threatening native species, particularly through competition for resources. Animals typically use two strategies to out-compete their opponents: they can be directly aggressive (called interference competition), or they can indirectly out-compete rivals by consuming more resources (called exploitative competition).

Our new study published in the journal Behavioral Ecology and Sociobiology compared the behavior of two lizards living together – the invasive Italian Wall Lizard (Podarcis siculus) and the native Green Iberian Wall Lizard (Podarcis virescens) – to understand if and how they compete with one another. We conducted experiments with manipulated resources – in this case by providing a single nice warm basking spot and a bowl of delicious mealworms, to test for competition. We found that the invasive lizards do not aggressively out-compete the native lizard. In fact, the invasive lizard was friendly enough – frequently sharing shelters with the native species! Instead, the invasive lizard was quicker to the food bowl and gobbled up more mealworms, which is consistent with exploitative competition.

The Italian Wall Lizard and the Green Iberian Wall Lizard in the high-quality refuge.

Photo by Isabel Damas-Moreira.

Interestingly, other studies have documented that the Italian Wall Lizard can be aggressive to native lizards but, in our study, we did not find much evidence for aggressive encounters. Perhaps, this lizard behaves differently depending on local conditions. Given that fights are costly because you risk injury and sometimes death, it can make sense to avoid them and instead, focus on getting resources faster than your rivals.

This study suggests that the Italian Wall Lizard, as well as other invasive species, may be able to adjust how they compete depending on their environment, such as the amount of food and shelter availability and even the behaviour of the native species. Our study highlights the potential importance of behaviour as a key trait that helps explain the success of invasive species.

The graphical abstract for our paper! Created by Isabel Damas-Moreira.

To cite this article: Damas-Moreira I, Riley JL, Carretero MA, Harris DJ, Whiting MJ. (2020) Getting ahead: exploitative competition by an invasive lizard. Behavioral Ecology and Sociobiology, 74: 117.

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