Abstract Urbanization significantly alters habitats for arboreal species, increasing the frequency of very smooth substrates by substituting artificial objects, such as metal poles and painted walls, for some trees. Because they experience these novel substrates more often, urban animals may use strategies to overcome challenges from substrate smoothness that animals from natural habitats do not. We assessed locomotor performance and two-dimensional hindlimb kinematics of two species of Anolis lizards (Anolis cristatellus and Anolis sagrei) from both urban and natural habitats in Miami, Florida. We ran lizards on six racetracks, crossing three substrates of increasing smoothness (rough bark, concrete blocks, and smooth, unpainted wood) with two inclinations (37° and vertical). We found that on vertical tracks with smooth substrates, lizards ran slower, took shorter strides and exhibited more contracted limb postures at the end of their stance than when running on the inclined track. Urban lizards, which are likely to be exposed more often to smooth substrates, did not adjust their movement to increase performance relative to lizards from natural habitats. This result, and the similarity of kinematic strategies between the two species, suggests the locomotor responses of lizards to substrate properties are highly conserved, which may be a mitigating factor that dampens or obviates the effects of natural selection on locomotor behaviour.
Abstract Species that occur in variable environments often exhibit morphological and behavioral traits that are specific to local habitats. Because the ability to move effectively is closely associated with structural habitat, locomotor traits may be particularly sensitive to fine‐scale habitat differences. A nolis lizards provide an excellent opportunity to study the relationship between locomotion and natural perch use in the field, as laboratory studies have demonstrated that lizards that use broader perches develop longer limbs and have higher sprint speeds. We examined A nolis carolinensis (the green anole) in three habitats in close proximity. Our goals were to determine whether habitat‐specific differences in hindlimb and toe morphologies occurred in a population in which perch size was variable but not manipulated, whether locomotor behaviors were associated with these morphologies, and whether habitat‐specific traits differed between the sexes. We found that while juveniles in the three habitats did not differ in limb or toe morphology, adult females using broader perches had relatively longer limbs than females using narrower perches. Females also differed in toe length across habitats, but not in relation to perch diameter. Males, in contrast, exhibited differing growth patterns (allometry) in these traits, and marginal differences in locomotor behavior. Together, these results suggest that sex‐specific responses in morphology and behavior, consistent with experimental observations of phenotypic plasticity, provide a mechanism for refining local habitat use.
Urbanization is accelerating worldwide and creates novel habitat conditions including increases in environmental temperature and changes in presence and abundance of predators, prey and parasites. For species that use urban habitats, these changes can have strong impacts on phenotypes. Anolis lizards commonly exploit urban habitats and, as ectotherms, are likely to experience pressures from these novel environments. Previous research shows that anoles may adapt to some aspects of urban habitats, but we lack an understanding of the breadth of traits that may shift in response to urbanization and how widespread these changes may be. To assess effects of urban habitat use on anole phenotypes, we measured morphology, thermal preference and parasitism in brown anoles (Anolis sagrei) and crested anoles (Anolis cristatellus) from urban and natural habitats within the Miami metropolitan area (FL, USA). In urban areas, individuals of both species were larger, but did not show any differences in preferred body temperatures. These results agree with other studies showing increased body size in anoles inhabiting urban areas, but the mechanisms underlying this pattern are unclear. Brown anoles experienced higher levels of parasite infection intensity in urban habitats, but crested anoles showed no differences between urban and natural sites. Increased infection intensity in urban brown anoles suggests that exploiting urban habitats may have costs and shows that urbanization can lead to species-specific changes in ecologically similar congeners. Understanding how urban habitats alter phenotypes of organisms that exploit these areas will be important in predicting costs of and adaptive responses to future urbanization.
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.
Abstract The structural habitat of terrestrial urban environments can differ drastically from environments less impacted by human activities. Whether or not urban species use anthropogenic structures, they are subject to novel selection pressures to effectively locomote. Urban environments are distinctly more open than non-urban habitats, they offer few refuges, and habitat space is patchy with clustered perches. Animals must either change their behaviour to use only natural substrates or contend with manufactured substrates. Arboreal species are particularly impacted because the anthropogenic structures with which they interact, even if infrequently, differ from trees in structural, material, and surface properties. The chapter explores potential adaptive responses to the spatial structure and properties of climbing substrates in urban environments relevant to terrestrial and climbing locomotion. For each, the authors first discuss differences between urban and non-urban terrestrial habitats relevant to locomotion. They then discuss how these differences influence behaviour and locomotor demands, providing a mechanism through which natural selection shapes morphology. Lastly, they discuss the morphological traits most likely to be impacted by these altered demands and predict how natural selection may affect these traits in urban environments based on biomechanical principles. As there have been very few studies investigating urban morphological adaptation related to locomotion, the chapter draws on trait–environment relationships in natural environments. The discussion provides a starting point for developing rigorous hypotheses about functionally relevant trait shifts in urban environments and future directions for investigating locomotor adaptations in urban species.
Summary As animals move through their environments, they encounter a variety of substrates, which have important effects on their locomotor performance. Habitat modification can alter the types of substrates available for locomotion. In particular, many types of artificial substrates have been added to urban areas, but effects of these novel surfaces on animal locomotion are little known. In this study, we assessed locomotor performance of two Anolis lizard species ( A. cristatellus and A. stratulus ) on substrates that varied in inclination and surface roughness. Rough substrates represented the tree trunks and branches typically used in natural forest habitats, whereas smooth, vertical substrates captured the qualities of artificial surfaces, such as posts and walls, available in human‐modified habitats. We then observed habitat use to test the habitat constraint hypothesis – that lizards should more frequently occupy portions of the habitat in which they perform better. Increased inclination and decreased surface roughness caused lizards to run slower. Both A. cristatellus and A. stratulus ran slowest on the smooth, vertical surface, and A. cristatellus often slipped and fell on this surface. In contrast to predictions, both species frequently used smooth, vertical substrates in the wild. Anolis cristatellus occupied artificial substrates 73% of the time in human‐modified habitats despite performing worse than A. stratulus on the smooth, vertical track. We therefore rejected the habitat constraint hypothesis for anoles in these human‐modified habitats. Despite overall poor performance on the smooth, vertical track, A. cristatellus had a significant morphology–performance relationship that supports the prediction that selection should favour smaller lizards with relatively longer limbs in human‐modified habitats. The smaller bodied A. stratulus performed better than A. cristatellus on smooth, vertical substrates and therefore may not be exposed to the same selective pressures. We contend that habitat modification by humans may alter morphology‐performance–habitat use relationships found in natural habitats. This may lead to changes in selective pressures for some species, which may influence their ability to occupy human‐modified habitats such as cities.
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