Do Hurricanes Rock Lizards Harder in the City?

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.