Invasion Ecology and Control Feasibility of the Jackson Chameleon (Trioceros jacksonii xantholophus) in Hawai‘i

Abstract

Biological invasions provide opportunities to investigate micro-evolutionary change and the relative roles of key factors that lead to differentiation. Following introduction, release from native selective pressures and exposure to novel evolutionary forces can reduce morphological and physiological constraints and impose new ones, resulting in rapid micro-evolutionary changes. Studying ecosystem and geographic variation in invasive taxa on an ecological time scale can help provide conservation relevant information for management. I investigated ecological and evolutionary questions involving adaptation and ecomorphological variation and the roles of habitat characteristics on form, function and behavior of an invasive lizard in Hawaii. In Chapters 1 and 2 I evaluate substantial variation in head-size and horn-length among and within islands, and between native and introduced ranges. Larger heads are associated with low precipitation, and consumption and higher availability of hard prey, while longer horns are exhibited by chameleons in their native range and are associated with fight success and higher precipitation in the introduced range. Results may suggest rapid ecomorphological adaption to introduced microhabitats and release from natural selective pressures influencing sexually dimorphic characters in the native range. Chapter 3 examined predatory behavior in chameleons in response to prey size and type. Instead of the well-documented lingual prehension mechanism in Chamelaeonidae, a novel feeding mechanism is described, in association with both prey/predator size and prey type. Finally, for Chapter 4, I present the first proposed control strategy for T.j. Xantholophus in Hawaii. We tested a method based on an approach using acetaminophen deployed by resource managers to control the invasive brown tree snake on Guam. We determined minimum dosage necessary to cause >95% mortality in <48 hours. Additionally, I propose methods of field delivery, including use of introduced snail shells as a vessel for ingestion. Although there is a massive and increasing body of invasion ecology research, this study provides new insights into trait adaptation of invasive predators and how this information can help develop management strategies. In addition, this study presents a framework by which biological invasions can be used to examine evolutionary questions on an ecological rather than evolutionary time-scale.