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.
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.
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.
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.