From Anoles to Indian Agamids to Australian Water Dragons to Western Fence Lizards, lizards from diverse branches of the squamate tree are proving themselves in urban environments. Add one more species to this growing list of urban lizards: Brazilian lagartixas, Tropidurus hispidus. In a recent paper, Antonio de Andrade examined the abundance and habitat use of this common Brazillian lizard in urban environments. Antonio hypothesized that high abundances of this common native lizard should facilitate their occurrence in urban habitats. Moreover, he hypothesized that these lizards would use anthropogenic substrates and attain higher densities in more urbanized environments.
Lagartixas of Paraiba, Brazil
Antonio quantified lizard abundance across a total of 47 transects in five districts of the city Joao Pessoa, which is the capital of the the state of Paraiba, Brazil and has a population of more than 800,000 people. The sampled areas included rural, peri-urban, and moderate and high-intensity urbanization, which ranged from less than 50% impervious surface coverage to more than 90%.
At each site Antonio sampled biotic and abiotic factors that he thought might influence lizard abundance. Along each transect he counted the total number of trees >10cm in diameter. Using 2x2m quadrats along his transects, he quantified impervious surface, herbaceous vegetation cover, potential shelters that could be used by lizards, and number of arthropods. He sampled each transect four times across multiple days and spanning the entire morning and afternoon active hours (like many urban lizards, lagartixas seem to be inactive at the hottest part of the day).
Urban lagartixas are more abundant
Antonio recorded a total of 234 lagartixas across all sites. He found a trend of increasing density with increasing urbanization, as predicted. Interestingly, although abundances increased from rural to peri-urban and medium urbanizations, they dropped again at the highest intensity urban sites where the number of lizards was equivalent to the rural sites. Additionally, although approximately 50% of lizards were observed the ground, they also frequently used anthropogenic structures. In fact, like many other urban lizard species, the lagartixas of Paraiba used anthropogenic substrates as perches more frequently than natural, vegetative, substrates.
More urbanized environments also differed in each of the environmental variables quantified. Urban habitats had more trees, more shelters, fewer arthropods, less herbaceous cover, and more impervious surface compared to rural sites. Of these, only number of shelters and number of trees were significantly and positively correlated with lizard abundance across sites.
Why so successful?
Overall, these data suggest that urbanization promotes higher abundances of this common Brazilian lizard. Yet the pattern of decreased abundance at highest disturbance levels (a trend not uncommon in other species) suggests that specific habitat features and quality of the habitat are most important in determining abundance, and not necessarily the degree of urbanization. Specifically, the presence of abundant shelters and trees appear to be key factors for the success of this species in urban habitats. These features may be crucial as refuges from predators, egg laying sites, and/or thermal shelters. Yet Antonio suggests that these lizards are not necessarily adapting to use a novel environment. Lagartixas may be so successful in urban environments because the abundant anthropogenic substrates resemble their ancestral hardscape habitat (i.e., rock outcrops and cliffs). In other words, they may be adapted to using this type of environment by virtue of its similarity to the ancestral habitat, and not because of contemporary selective pressures.
A model metropolitan lizard
Antonio’s work is a fantastic contribution to the growing body of literature documenting behavioral, ecological, morphological, and physiological shifts in urban lizards. As he points out in the manuscript (and a sentiment echoed by a recent paper on Sceloporus occidentalis), it is critical that we understand how different species are responding to urbanization to move towards a synthesis of urban evolutionary responses. Antonio makes a strong case for lagartixas as a model urban lizard. Much like anoles, which have become the model lizard system in urban environments to date, lagartixas clearly thrive in urban environments where they use anthropogenic habitat space. Couple that with a quick generation time, tolerance of tropical city temperatures, widespread abundance, and wide niche breadth and you have all the makings of a model metropolitan lizard.
Read the full manuscript here:
Featured image at top: Antonio de Andrade, Figure 1 from Andrade 2019.
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Very interesting! Great write up. Any insights into why the drop off at more dense urbanization? It would be very compelling to fully describe the mechanism constraining population size as urban land use intensifies
My guess would be that at the most urbanized sites they are lacking something crucial – a food resource or some habitat feature they rely on? This seems to be a common trend in a lot of urban species – moderate levels of urbanization have the highest abundances and biodiversity… I agree this would be fascinating to dig into!
Really interesting, and a cool model system. I really wish urban designers and housing developers would read these papers! Perhaps it can encourage greater consideration of design that includes structures resembling natural features?