Author: Kevin Aviles-Rodriguez

This blog post was also featured in the blog Life in the City

The Puerto Rican Crested Anole (Anolis cristatellus)

Hurricanes are powerful storms that shape ecosystems by removing or displacing individuals. Additionally, hurricanes can change habitats due to tree mortality, damage and/or landslides. Ecosystem changes caused by hurricanes can impact species diversity. For example, following Hurricane Hugo, some insects thrived due to higher abundances of new young leaves as the canopy regenerated. On the other hand, canopy openness led to warmer and drier forest conditions which negatively affected other species. While we have several examples of how hurricanes impact species in forest environments, virtually nothing is known about how hurricanes affect urban species..

Hurricane in the city:

Cities can be quite different than non-urban ecosystems resulting in diverging ecological and evolutionary trajectories. Often, green spaces are highly cultivated which directly affects which species are able to exploit city environments. In this study, my co-authors and I evaluated the urban exploiter Anolis cristatellus to contrast population density and species composition in the months following Hurricane Maria.

Relative gust speed in knots of Hurricane Maria in the municipalities of Puerto Rico. Brighter colors show regions that experience the strongest winds. The letters correspond to the location of paired urban and forest sites. Pictures show the sites four months after the storm.

Anole populations after the storm:

Hurricane Maria was a powerful category 5 storm that made landfall in Puerto Rico in 2017 near the southeastern region of the island. As such, eastern locales experienced stronger winds in contrast to more western regions. We began our study four months after the hurricane and visited sites again eleven and sixteen months after the storm. The main takeaway we found was that irrespective of when we visited, forest sites had nearly double the number of lizards as urban sites. Sites in the east had the lowest population numbers at four months after the hurricane and showed nearly a doubling in population size between four and eleven months afterward. We presumed that this is due to higher mortality at these sites since they experience stronger winds associated with the hurricane.

Estimated lizard density per hectare. Forest sites are shown in green and urban sites in blue. Sites in San Juan had the lowest population density four months after the hurricane and showed population growth in the following months.

City humans as ecosystem engineers

An unexpected finding of this study was documenting how new plant growth following the hurricane facilitated the colonization of a bush specialist anole ecomorph at one of our sites. Four months after the hurricane, the forest floor consisted of leaf litter and downed trees and tree branches. However, both eleven and sixteen months afterward, new plants had established exploiting access to light resulting from the open canopies. Access to shrubs and young plants provided the preferred habitat of the grass-bush ecomorph Anolis krugi, a species that was not previously seen within that forest plot. In contrast, urban environments remained relatively unchanged. All of the downed branches and trees were quickly removed. Thus, while forest habitats and the ecosystems they support appear to be altered dramatically by hurricanes, human intervention maintained urban habitats near constant conditions during the extent of our study. Future studies might consider how human intervention in urban habitats affects ecosystems and the species they support.

Read the study

Avilés-Rodríguez, K.J., De León, L.F. & Revell, L.J. Population density of the tropical lizard Anolis cristatellus in urban and forested habitats after a major hurricane. Tropical Ecology (2022).

Featured Image: Anolis cristatellus (K. Avilés-Rodríguez)

Concrete Escape: Increased Wariness of Anoles when Escaping from Cement Walls

By Kevin Aviles-Rodriguez

On April 16, 2019

In New Research

A. cristatellus copulating on metal

A. evermanni dewlaping on wall

A. cristatellus riding the dolphin

A. cristatellus dewlaping on metal

Fig. 1. Anoles perched on various manmade surfaces

Lizards in the city are everywhere! Often you see them on buildings, statues, benches and other objects (Fig 1). These manmade structures are very different from natural substrates and thus might affect their locomotor ability and escape responses. This observation led me to develop questions around how lizards respond to incoming threats when using these artificial structures. I am very grateful that I got to “get my feet wet” tackling some of these questions during my master’s degree as a member of the Kolbe Lab in the University of Rhode Island.

In our recent paper, we contrasted the escape response of Anolis cristatellus in forests versus cities, and within the latter, between lizards perched on natural versus manmade surfaces. We selected this question because we believed that the heterogeneity of habitat structure in the city might influence the decision-making of flight responses. When a predator approaches, an animal should flee when the costs of staying outweigh the energetic costs of fleeing. Consequently, we hypothesized that the cost of flight varies when the animal is perched on smooth surfaces. However, we expected that city lizards should have reduced flight responses largely influenced by habituation to humans.

The bad habits of habituation

One of the major hurdles involved designing our project to separate the component of behavioral adjustments to humans versus structural habitat differences when contrasting escape responses. The literature often has used the concept of habituation as a discussion point when contrasting flight responses of habitats that differ in human activity. Only a few studies have attempted to quantify how human activity might influence escape responses. We explored this concept by sampling lizards perched on trees at edges of a forest trail or sidewalk that were frequently visited by pedestrians and cyclers. Lizards perched closest to the trail or sidewalk should be more exposed to human activity and respond with reduced flight initiation distance. We found that forest lizards perched at the edge of the trail had shorter flight initiation distances (Fig. 2). Lizards perched 4m away from the trail had longer flight responses. In contrast, city lizards sampled at trees along a sidewalk showed no difference in flight response with increasing distance from the sidewalk. With this, we were able to show how habituation influenced escape responses, possibly driven by the degree lizards were able to see human activity. At 4m from the forest trail, we had very limited visibility of the trail. In contrast, in the sidewalk at 8m away from the sidewalk, we could see the sidewalk, the road and the sidewalk at the other side of the road. However, more work specifically directed to tackle the concept of habituation is needed to understand its role in facilitating the successful colonization of urban habitats.

Fig. 2. Log flight initiation distance of lizards sampled with increasing distance away from a trail in the forest or a sidewalk in the city.

The wall

City lizards were abundantly using cement and metal structures. For this reason, we compared escape responses of forest lizards on trees to city lizards on cement, metal and trees. Most of the cement structures were large buildings, whereas metal often included fence posts and light fixtures. Both metal and cement are smoother than bark and greatly reduce stability during locomotion. When lizards run vertically on smooth surfaces, they are more likely to slip and fall. We hypothesized that such locomotor constraints should increase the cost of flight and thus lizards on manmade surfaces should have longer flight initiation distances. We found that forest lizards had the longest flight initiation distance (Fig 3). Surprisingly, we found that there was no difference in flight response between city lizards perched on trees and those on metal posts. Metal perches were often cylindrical and lizards could circle around the perch, breaking away from the line of sight. In contrast, cement walls were often long and required lizards to either slowly move up and out of reach or sprint longer distances to circle towards the next connecting wall. The ability to quickly hide with a short burst of movement decreased the cost of flight on metal posts.

Fig. 3. Flight initiation distance of forest anoles perch on trees and urban anoles perched on trees, metal posts and cement walls.

Escape in the city

We found that even though sprinting performance is lower on artificial perches, lizards often perch on these surfaces. It’s likely that behavioral modulation plays a role in increasing their success in evaluating predation risk when using these perches. If I were to continue this study, I would track individual lizards to contrast their response when perching on the various natural and man-made surfaces. Additionally, multiple tests on marked individuals would allow for a more appropriate test of habituation across these populations.

Evolution 2017: Integrating Ecological, Antagonistic and Reproductive Character Displacement

By Kevin Aviles-Rodriguez

On June 30, 2017

In New Research

The arrival of an outsider that overlaps in resource use and habitat with local species can lead to intense competition between the two. A result of this competition can be character displacement, where traits of the species (one or both) change in sympatric populations (where the co-occur), but not in allopatric populations. Claire Dufour (Post-Doctoral researcher at Harvard University) presented her work on character displacement for two anole species on the island of Dominica: the native Anolis oculatus and the introduced Anolis cristatellus. Her objective was to integrate ecological, antagonistic and reproductive character displacement. Specifically, she tested whether competition between these new island-mates leads to changes in habitat use, morphology, and display behavior.

Location of populations of the introduced A. cristatellus with the sampled area, Calibishie inset

Claire compared allopatric populations of the two species with sympatric populations in the northern area of the island in Calibishie, where Anolis cristatellus has been present for two years. She found that in sympatry, both morphological and behavioral shifts have occurred. In sympatry, Anolis oculatus perched higher and had shorter limbs. She also found differences in display behavior, which she tested with an anole robot programmed to dewlap and do push-ups. This experiment showed that in sympatry, Anolis cristatellus dewlapped less, but Anolis oculatus does not alter its display behavior. Future work will test for reproductive character displacement and contrast populations where Anolis cristatellus has been present for a longer time span.

JMIH 2016: Herp League Graduate Student Award Winner: Urban Habitat Partitioning by Two Common Species of Puerto Rican Anolis

By Kevin Aviles-Rodriguez

On July 9, 2016

In All Posts

Kristin Winchell, my fellow lab mate at the Revell lab, presented her work on the habitat use of two urban dwellers in Puerto Rico. Past studies have shown that Anolis cristatellus and Anolis stratulus vary in abundances and use different portions of the natural habitat. As early as 1964, Rand showed that A. stratulus was less abundant and perched higher on trees in forest habitat. However, we know very little about whether these patterns are maintained in urban areas where species have access to novel manmade structures. To address this, Kristin evaluated the habitat use of these two species across seven urban replicates and contrasted it to the available habitat. She found that urban A. stratulus uses more isolated perches with greater vegetative canopy and perches at higher portions of the habitat. Anolis cristatellus uses perches that are less isolated, shaded mostly by manmade canopy (i.e. buildings and houses) and at lower heights. When examining these patterns in a multidimensional space, she showed that A. cristatellus has expanded its urban niche through the use of manmade structures, while A. stratulus uses a subset of the natural portion of the habitat that A. cristatellus also uses.

Her research shows that these two urban dwellers interact with the novel portions of the habitat differently. Anolis cristellus has expanded its niche towards manmade structures which has implications for adaptation to enhance stability and locomotion when using these structures as shown in some of her previous work (Winchell, et al, 2016). Anolis stratulus uses the less available remnants of the natural habitat which may have implication for conservation if they become sparser as urbanization expands.

JMIH 2016: Comparative Phylogeography of Three Widespread Anolis species across the Puerto Rico Bank

By Kevin Aviles-Rodriguez

On July 9, 2016

In All Posts

Alexandra Herrera presented on using genetic population structure to understand how geographical processes have shaped genetic isolation of three widespread Anolis species on the Puerto Rican Bank. Geographical processes are an important event in shaping current populations and can lead to interesting patterns of diversification. However, these processes may not necessarily affect species similarly. In this study, Alexandra used a combination of nuclear genes and one mitochondrial gene to examine the population structure of these three anoles.

Evidence strongly suggests that populations of Anolis pulchellus were separated into two major clades through the formation of mountains. These two clades are made up of one cluster from south Puerto Rico and a cluster that includes both Northeast Puerto Rico and the Virgin Islands.

The diversification of the other two species corresponds with tectonic and sea level changes. For Anolis stratulus, divergence between populations in PR, Culebra, Vieques and the Virgins Islands occurred at the end of the Pliocene after the formation of the Virgin Passage. These populations formed five clusters east PR, south PR, Virgin Islands, Vieques-Culebra and Peter-Norman islands.

For Anolis cristatellus the divergence between east PR and south PR with the Virgin Islands was estimated around the late Miocene-Pliocene transition when the Mona and Virgin Island passages formed. These populations formed 4 clusters east PR, south PR, Virgin Islands and Carrot Rock-Peter-Culebra-Piñeiro.

This research shows that each species had a different diversification pattern and that they all occurred around the middle of late Pleistocene. Furthermore, geographical processes may affect species differently, leading to various patterns of population structures.

Land Hermit Crabs Congregate on Anoles’ Sleeping Perches

By Kevin Aviles-Rodriguez

On August 5, 2015

In All Posts

Recently I was on Long Island alongside Graham and his team capturing Anolis sagrei. For our last night survey, we collected female lizards from a beach scrub habitat in McKanns (23.38831, -75.1408). During such a survey, we used headlamps to search for sleeping lizards perched on branches and leaves. At other sites we frequently found lizards on vegetation along the trails. At McKanns, land hermit crabs (Coenobita spp.) were congregated in high numbers on such vegetation. We seldom found lizards perching on plants where hermit crabs congregated.

Land hermit crabs (Coenobita spp.) active at night. Photo by Alberto Puente

Most lizards perched further away from the trail on the broad leaves of Cocoloba uvifera where hermit crabs were seen less abundantly. Perhaps due to their large numbers and the fact that they were active at night, land hermit crabs might be occupying perches that would otherwise be used by Anolis sagrei.