Competing through eating: lessons from a lizard

Post by Isabel Damas

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 (termed interference competition), or they can indirectly out-compete rivals by consuming more resources (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 good refuge. Photo by Isabel Damas Moreira.

Interestingly, other studies have document 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 behavior of the native species. Our study highlights the potential importance of behavior as a key trait that helps explain the success of invasive species.

Here is the abstract:

Biological invasions are a contemporary global threat because invasive species can have substantial negative economic and ecological impacts. Invasive species can out-compete native species through two main mechanisms: interference competition (direct, negative interactions like aggression) and / or exploitative competition (indirect, negative interactions resulting from species using the same, limited resources like food). The invasive Italian wall lizard (Podarcis siculus) was introduced into Lisbon, Portugal, 20 years ago, and is believed to be locally displacing the native green Iberian wall lizard (Podarcis virescens). We experimentally tested for competition between these two lizard species by establishing heterospecific (one pair of each species) and conspecific (two pairs of the same species; control) treatments in enclosures containing a high- and a low-quality refuge. Lizards were fed from food dishes every other day. We tested if species showed interference (aggressive behavior, stealing food and shelter exclusion) or exploitative competition (tolerance between species but differences in food consumption efficiency). We found evidence for exploitative competition: the invasive species arrived first at food stations, consumed more food and gained more weight than the native species. We suggest that exploitative competition may, in part, explain the observed displacement of P. virescens from contact areas with the invasive P. siculus . Deciphering the competitive mechanisms between invasive and native species is vital for understanding the invasion process.

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. DOI: 10.1007 / s00265-020-02893-2

Dispatches from the field: following the Sulawesi Forest Turtle

Note, this field work formed the basis for Angela’s Masters thesis.

By Angela Simms

I wasn’t sure what to expect on the first night searching for the Sulawesi Forest Turtle. As little as 30 minutes into the stream walk, our local guide spots a large male perched on the edge of the clear shallow . . . → Read More: Dispatches from the field: following the Sulawesi Forest Turtle

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Dr. Birgit Szabo talking about . . . → Read More: Dr. Birgit Szabo talks lizard smarts!

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As children we have much to learn after we are born. We learn to walk, to talk, to develop our social skills, and when we start school we learn how to read, write and do maths.

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The paper, . . . → Read More: Australian Geographic features frilled lizard work!

Hot off the press! An invasive lizard species can learn from other species

Check out our new paper on social learning in the Italian wall lizard, Podarcis sicula. This work formed part of Isabel Damas’ PhD thesis, and it was a huge effort! The question of what makes an invasive species successful compared to other species, that may fail to gain a foothold in a new location, . . . → Read More: Hot off the press! An invasive lizard species can learn from other species

What tree skinks know about change: A story in colour and shape

Note from Martin Whiting: This blog posts details a chapter of Birgit Szabo’s PhD recently published in Animal Behaviour and represents an enormous amount of work. Birgit did a 9-month cognition experiment, which could be the longest lizard cognition experiment thus far conducted. (Let us know if it isn’t!) The work is in collaboration . . . → Read More: What tree skinks know about change: A story in colour and shape

Come on a tour of The Lizard Lab

This is a behind-the-scenes video tour of the lab. We will show you our research facilities, some of our study animals, and our lizard enclosures. This video was entirely put together by Cooper Van De Wal. Cooper is a student at Macquarie and volunteers in the lab. He also has his own, highly successful . . . → Read More: Come on a tour of The Lizard Lab

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By: Fonti Kar & Julia Riley

“Never study an animal that is smarter than you” – Dr Martin Whiting

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