Miami heat: Urban heat islands influence the thermal suitability of habitats for ectotherms

Abstract

The urban heat island effect, where urban areas exhibit higher temperatures than less‐developed suburban and natural habitats, occurs in cities across the globe and is well understood from a physical perspective and at broad spatial scales. However, very little is known about how thermal variation caused by urbanization influences the ability of organisms to live in cities. Ectotherms are sensitive to environmental changes that affect thermal conditions, and therefore, increased urban temperatures may pose significant challenges to thermoregulation and alter temperature‐dependent activity. To evaluate whether these changes to the thermal environment affect the persistence and dispersal of ectothermic species in urban areas, we studied two species of Anolis lizards (Anolis cristatellus and Anolis sagrei) introduced to Miami‐Dade County, FL, USA, where they occur in both urban and natural habitats. We calculated canopy openness and measured operative temperature (Te), which estimates the distribution of body temperatures in a non‐thermoregulating population, in four urban and four natural sites. We also captured lizards throughout the day and recorded their internal body temperature (Tb). We found that urban areas had more open canopies and higher Te compared to natural habitats. Laboratory trials showed that A. cristatellus preferred lower temperatures than A. sagrei. Urban sites currently occupied by each species appear to lower thermoregulatory costs for both species, but only A. sagreihad field Tb that were more often within their preferred temperature range in urban habitats compared to natural areas. Furthermore, based on available Te within each species' preferred temperature range, urban sites with only A. sagrei appear less suitable for A. cristatellus, whereas natural sites with only A. cristatellus are less suitable for A. sagrei. These results highlight how the thermal properties of urban areas contribute to patterns of persistence and dispersal, particularly relevant for studying species invasions worldwide.

Enhanced sensitivity of the urban heat island effect to summer temperatures induced by urban expansion

“…A positive sensitivity of T-UHI indicates a higher UHI effect in a warming environment over an urbanized region, while an enhanced sensitivity resulted from urban expansion means a larger contribution of the UHI effect to the total warming. Those extra warmings aggravate the heat stress and harm the urban ecosystem and economies (Ma et al 2015, Estrada et al 2017, Battles and Kolbe 2019. In this situation, the city governments, such as Beijing, should pay more attention to the additive UHI effect and continued background temperature warming in urban planning.…”

Metropolitan lizards? Urbanization gradient and the density of lagartixas (Tropidurus hispidus) in a tropical city

“…Cities are warmer when compared with natural habitats (Ackley, Angilletta, DeNardo, Sullivan, & Wu, ; Grimm et al, ; Parris, ), and increased urban temperatures could have direct impact on lizards' fitness (Battles & Kolbe, ; Hall & Warner, ). Higher temperatures increase the body temperature of lizards, which could probably involve risk of overheating and increased thermoregulatory costs in the hotter urban environment (Battles & Kolbe, ; Kearney, Shine, & Porter, ). Moreover, extreme temperatures in urban environments increase egg mortality and might have negative impact on lizard development (Hall & Warner, ).…”

“…For instance, urbanization causes extreme structural habitat changes that affect locomotor performance and drive shifts in limb morphology and body size in some Anolis species (Battles, Irschick, & Kolbe, ; Kolbe, Battles, & Avilés‐Rodríguez, ; Marnocha, Pollinger, & Smith, ; Winchell, Maayan, Fredette, & Revell, ; Winchell, Reynolds, Prado‐Irwin, Puente‐Rolón, & Revell, ), which might favor niche expansion (Battles, Moniz, & Kolbe, ). The urban environment also tends be hotter, with wider variation in temperature that could affect development, survival, and persistence of Anolis in cities (e.g., Battles & Kolbe, ; Hall & Warner, ; Tiatragul, Hall, Pavlik, & Warner, ). Nevertheless, we still have gaps in our knowledge.…”

Ontogenetic scaling patterns of lizard skin surface structure as revealed by gel‐based stereo‐profilometry

“…Studying ontogenetic scaling patterns may yield valuable broad insights into trait adaptations, and may aid in identifying size‐related constraints within a species (Schmidt‐Nielsen, ). Here, we focused on the anole lizard species Anolis cristatellus , a focal lizard for diverse studies including thermal biology (Battles & Kolbe, ), behavioral ecology (Dufour et al. ; Gunderson et al.…”

“…Studying ontogenetic scaling patterns may yield valuable broad insights into trait adaptations, and may aid in identifying size-related constraints within a species (Schmidt-Nielsen, 1984). Here, we focused on the anole lizard species Anolis cristatellus, a focal lizard for diverse studies including thermal biology (Battles & Kolbe, 2018), behavioral ecology (Dufour et al 2018;Gunderson et al 2018a), invasion biology (Kolbe et al 2016;Kahrl & Cox, 2017), functional morphology (Kolbe, 2015;Winchell et al 2018) and evolutionary biology (Williams, 1972;Losos, 1990;Gunderson et al 2018b).…”