Urbanization is Shortening the Legs of Western Fence Lizards

Western fence lizards (Sceloporus occidentalis) are a common sight across the western United States. The ability of western fence lizards to rapidly adapt to different environments makes them an interesting subject for studying the effects of geography on climbing behaviors and habitat use. These lizards thrive in diverse landscapes, from coastal areas to mountainous regions, urban settings to suburban backyards.

Natural Habitats and Climbing Preferences

Western fence lizards are often found in forests, grasslands, and chaparral regions. In those natural landscapes, the western fence lizard is morphologically adapted to climbing on surfaces such as rocks and tree bark. In forests, they frequently can be seen climbing tree trunks and branches.

The limbs, toes, and claws of the western fence lizard are adapted to both gripping and moving quickly across these different surfaces and slopes.

Urban and suburban adaptations of the western fence lizard

Urbanization has significantly altered the landscapes these lizards inhabit. Research has shown that urban and suburban populations of western fence lizards use a mix of human-made and natural surfaces. These lizards are often seen basking on concrete walls, metal fences, and other artificial surfaces that absorb and retain heat, providing the warmth they need for their ectothermic (cold-blooded) bodies.

How has the urban landscape affected western fence lizards?

A team of researchers from UCLA’s Department of Ecology and Evolutionary Biology, wanted to analyze morphological differences in western fence lizards across a range of both natural and manmade environments. The study looked at lizard populations across four sites in Los Angeles County, representing a range of natural versus urban environments. Researchers measured limb and toe lengths, scale counts, and microhabitat use to understand how urbanization affects these lizards’ physical traits and behaviors.

These researchers found two main physical adaptations among lizards living in the built environment compared to natural environments. The morphological evolution is due to differences in predators, reduced vegetation, altered water availability, and new structures like buildings and roads. The changes in lizard morphology caused by living in a manmade environment are referred to as human-induced rapid environmental change (HIREC).

Urban surfaces have shortened the limbs of western fence lizards

The study found that lizards from urban areas often have shorter limbs and toes, which may be an adaptation to the smoother, more uniform surfaces found in cities. These adaptations allow them to maintain a better grip and navigate their urban habitats more efficiently.

Influence of the urban heat island effect on western fence lizards

Urban surfaces, particularly concrete and asphalt, contribute to the urban heat island (UHI) effect, where cities become significantly warmer than surrounding rural areas. This temperature increase can influence lizard behavior and physiology in several ways. Lizards are ectothermic (cold-blooded), meaning their body temperature is regulated by external environmental temperatures. Warmer urban temperatures can extend the active periods for lizards, allowing them to forage and reproduce for longer periods.

However, increased urban temperatures can create thermal stress, particularly during the hottest parts of the day. Urban lizards may need to adjust their activity patterns, seeking shade or cooler surfaces to avoid overheating. The reduced vegetation in urban areas can exacerbate this issue, limiting the availability of natural cooling spots.

The comparatively warmer temperatures in urban areas not only affects lizard behavior but also their physical traits, such as scalation. This same UCLA study found that urban lizards tend to have fewer and larger dorsal scales. This trait is believed to be an adaptation to the urban heat island effect, where cities are warmer than surrounding rural areas.

Larger scales help reduce water loss through evaporation, enabling these lizards to conserve moisture in hotter urban climates. Fewer scales can also mean thicker, more protective layers, helping lizards retain moisture in warmer conditions.

Expanding research on the adaptation of wildlife to urbanization

This research highlighted the impact of manmade structures on the behavior, morphology, and physiology of western fence lizards. Human-altered environments can rapidly influence the evolution of some wildlife species in a process known as human-induced rapid environmental change (HIREC).

Reference

Putman, B. J., Gasca, M., Blumstein, D. T., & Pauly, G. B. (2019). Downsizing for downtown: limb lengths, toe lengths, and scale counts decrease with urbanization in western fence lizards (Sceloporus occidentalis). Urban Ecosystems, 22(6), 1071-1081. DOI: 10.1007/s11252-019-00889-z

Fonte : National Geographic