Introduced species as moving targets: changes in body sizes of introduced lizards following experimental introductions and historical invasions

Abstract

Introduced species usually fail to establish, but when they succeed, may undergo character release and rapid evolutionary divergence in novel environments. We collected brown anoles (Anolis sagrei: Lacertilia: Iguanidae) from a single Florida population and released them onto two ecologically different dredge-spoil islands in central Florida (forested and non-forested) and measured differences in population growth, individual growth, body size, and condition over four years. The population on the non-forested island expanded twice as fast as the forested island population and reached a density of ca. 12,000 lizards ha⁻¹ and a biomass of ca. 43.3 kg ha⁻¹, among the largest values recorded for non-aggregated terrestrial vertebrates. First-year progeny grew larger than their surviving parents on both islands, indicating character release occurred in early stages of both invasions. However, in subsequent years, lizards became larger on the forested island, but smaller on the non-forested island. Body condition declined over time on both islands, but the effect was most dramatic on the non-forested island. Lizards on the forested island had the lowest survival rates and highest tail autotomy frequencies. These results were attributed to differences in abiotic and biotic conditions on the two islands. Brown anoles are generally larger on islands where they have been introduced than on their native Caribbean islands, and are much larger on mainlands than on islands, indicating character release occurred at larger geographic scales as well. Habitat influences the morphology of introduced species possessing the ability to rapidly adapt to local conditions, presenting invasive species managers with ‘moving targets’.