Attempting to develop a predictive framework to better understand patterns of species distributions and community assembly is an important goal of ecology. Here we document the distributions of three species of non-native Anolis lizards over the past century on the oceanic island of Bermuda, and specifically, we develop hypotheses to explain range dynamics and community assembly patterns following introductions. To do this, we conducted species’ presence-absence surveys and estimates of relative abundance at 114 sites across contiguous Bermuda and several outlying islands. Since interspecific interactions are considered a dominant feature in the structure and organization of Anolis communities, we conducted interspecific behavioral trials to test the relative strengths of agonistic relationships between species. These data provided the basis for creating a hypothesis-driven framework to explain observed distribution patterns.
Results/Conclusions
After initial introduction in the early 20th century, the Jamaican anole (A. grahami), quickly spread across the island and remains distributed across its entirety at present. Of the two more recent arrivals – both introduced independently to different locations in the 1940s – the Antiguan anole (A. leachi), the largest and most behaviourally dominant species, has almost doubled its distribution in the past 25 years and is now found across much of the island. Conversely, the most behaviorally submissive species, the Barbadian anole (A. extremus), has halted its range expansion near an A. leachi contact zone. Communities with all three species exist, but an asymmetric relationship is observed in which these communities only exist in regions where A. leachi has successfully dispersed into areas outside of its former range. Mixed communities have not been formed through the dispersal of A. extremus into the distribution of A. leachi. This study highlights how priority effects can asymmetrically affect range dynamics and therefore lead to the formation of different communities despite the same founding species’ pool. Priority effects may provide a demographic advantage such that i) biotic resistance may inhibit another species from joining a community, or ii) species may persist in a community despite apparent competitive weakness.