Causes and Consequences of Variation in the Invasive Lizard, Anolis sagreiEPA Grant Number: U916175
Title: Causes and Consequences of Variation in the Invasive Lizard, Anolis sagrei
Investigators: Kolbe, Jason J.
Institution: Washington University
EPA Project Officer: Graham, Karen
Project Period: January 1, 2003 through January 1, 2006
Project Amount: $81,769
RFA: STAR Graduate Fellowships (2003) Recipients Lists
Research Category: Fellowship - Zoology , Academic Fellowships , Biology/Life Sciences
The objective of this research project is to test the following hypotheses concerning this problem:
1. Do populations of A. sagrei from introduced and native areas differ in their ecology, morphology, and behavior?
2. Does the population of origin or the new environment predict the pheno-types of introduced populations of A. sagrei?
Invasive species are second only to habitat destruction as the greatest threat to biodiversity (Wilson, 1992; Wilcove, 1998). Conservation strategies attempting to deal with invasive species often are hampered by a lack of knowledge of the invasion history and changes in the biology of invading organisms relative to their native range (Tsutsui, et al., 2001). A key question concerning the establishment of an invasive species in a new area is whether the invading species arrives preadapted to coexist with members of the new community or if competition upon arrival leads to rapid evolutionary change and subsequent coexistence (Losos, et al., 1993). Invasive species that are preadapted for coexistence in their new environment may have a greater impact on native fauna if sufficient differences in resource use do not exist; competition may result in the extinction of either the invader or one or more residents. Understanding the relative importance of these factors for invaders, and the patterns of genetic and phenotypic variation in both the native and introduced ranges of an invasive species, is essential for formulating management strategies in the introduced areas and assessing future risk of invasion in new areas.
The native range of A. sagrei includes Cuba, the Bahamas, Cayman Brac, Little Cayman, Swan Island, Jamaica, and the Caribbean coast of Mexico and Belize (Schwartz and Henderson, 1991). Introductions over the past 60 years have resulted in established A. sagrei populations in Hawaii, Texas, Louisiana, Grand Cayman, Taiwan, and, most notably, Florida (Lee, 1985; McKeown, 1996). Continued northerly expansion of populations from Florida into Georgia suggests that the A. sagrei invasion has not yet stabilized (Echternacht, et al., 1995; Campbell, 1996). Where it is invasive, negative effects of A. sagrei on native fauna are numerous and include competition-induced habitat shifts (Losos, et al., 1993), decreases in population density (Campbell, 1999; Echternacht, 1999), and intraguild predation (Gerber and Echternacht, 2000). Only 10 years after its introduction to Grand Cayman, A. sagrei occupied most of the island, occurred in very high densities in some areas, and displaced the native anole, Anolis conspersus, in some habitats. This introduction resulted in a shift in structural habitat and potentially influenced the life history and survival of this native lizard (Losos, et al., 1993). Evidence from experimental introductions of A. sagrei showed that introduced A. sagrei increased dramatically in density at the expense of native Anolis carolinensis (Campbell, 1999) and A. carolinensis persisted at lower densities and was more likely to go extinct when on islands with A. sagrei (Losos and Spiller, 1999). Furthermore, asymmetrical intraguild predation exists between introduced A. sagrei and native A. carolinensis from Florida and A. conspersus from Grand Cayman (Gerber and Echternacht, 2000). Adult A. sagrei are significantly more likely to eat juveniles from the two native species than the native species are to eat introduced juveniles. The predatory effects of A. sagrei on congeners are of particular concern because of the greater potential for predators to cause extinctions compared to the effect of competitors (Mooney & Cleland, 2001).
As introductions of invasive species continue, and A. sagrei continues to expand its range, many questions remain concerning the effect of invasive species on native fauna. Limited study of A. sagrei indicates highly detrimental effects of this invasive on native lizards. However, little is known about the causes of variation in ecology, morphology, and behavior of invasive species or the consequences of this variation for interactions with native species. Within its native range, A. sagrei is extremely variable in morphology, life history, and physiology (e.g., Lister, 1976; Lee, 1992) and is divided into locally endemic populations that may be unique species (J. Kolbe, unpublished data). This extreme phenotypic and genetic variability within its native range makes pinpointing the causes and consequences of invasive A. sagrei populations very difficult. Thus, any approach to determining why A. sagrei is invasive needs to connect patterns of variation between introduced and source populations, and is best accomplished by using an approach that incorporates the historical relationships among native and introduced populations. A historical approach will facilitate identification of the relative importance of ecological vs. evolutionary factors that lead to the coexistence of invasive A. sagrei in new communities. I propose an integrative approach combining molecular analysis of genetic variation within A. sagrei and comparative analyses of ecological, morphological, and behavioral trait variation between introduced and source populations. This information will serve as the basis for sound management decisions to mitigate the impact of invasive A. sagrei on native fauna, both in areas where A. sagrei currently is invasive and other areas where A. sagrei introductions are possible. Successful management will benefit from addressing the three problems described below.
Problem 1: Uncertainty concerning the relationships among populations and the origin of introduced populations of Anolis sagrei. Many anole species are highly geographically structured (Glor, et al., 2001) and my preliminary data suggest that A. sagrei consists of several genetically differentiated populations. However, the extent of genetic differentiation throughout the native range of A. sagrei as well as the origin of introduced populations of A. sagrei in the United States and worldwide are unclear. Evidence exists that introduced populations in Florida are from both Cuba and the Bahamas (Lee, 1985), but the relative contribution of these or other source populations is unknown. Identifying the number of populations contributing to the invasion and their geographic origin is critical for understanding the causes and consequences of variation in this invasive species. Establishing this historical perspective, that is, the relationships among A. sagrei populations, is a prerequisite for comparing variation in ecology, morphology, and behavior between introduced and native populations. This phylogenetic perspective will provide the context for comparative studies underlying the development of invasive species management plans. I propose to test the following hypotheses concerning this problem:
1. Are A. sagrei monophyletic (i.e., are all populations of A. sagrei more closely related to each other than any is to populations of another species)?
2. What is the extent of locally endemic (i.e., genetically differentiated) populations throughout the native range of A. sagrei?
3. Where did the introduced populations of A. sagrei originate?
Problem 2: Lack of understanding of the causes of variation in ecology, morphology, and behavior of Anolis sagrei. Patterns of ecomorphological variation among Anolis lizard species are well studied (Losos, 1990a,b); however, detailed studies of variation in ecology, morphology, and behavior at the population level are lacking. Anolis sagrei shows geographic variation in morphology, life history, and physiology (e.g., Lister, 1976; Lee, 1992), including parts of its introduced range (Lee, 1985, 1987). Whether patterns of variation in introduced populations represent their ancestral heritage or adaptation to the new environments in which introduced populations exist is uncertain. Experimental evidence indicates that morphology can evolve rapidly in A. sagrei populations experiencing new structural environments (Losos, et al., 1997), but also suggests that phenotypic plasticity in hindlimb length may contribute to variability among individuals and populations (Losos, et al., 2000). Both causes of variation suggest an important influence of new environments on A. sagrei populations either through natural selection or phenotypic plasticity. Conversely, phenotypic evolution of introduced populations may be constrained because of low genetic variation associated with small founder populations or developmental canalization. Sorting out the causes and patterns of variation among introduced and native populations will provide the ecological and evolutionary context for evaluating the consequences of variation for native fauna. Furthermore, invasive species management plans that incorporate knowledge of the causes and patterns of variation in introduced populations will increase their chances for success.
Problem 3: Uncertainty about the consequences of different source populations of Anolis sagrei and their effects on native fauna in introduced areas. The impact of an invasive species is measured by the extent of its negative interactions, such as predation or competition, with native fauna (Mooney and Cleland, 2001). Some of the negative effects of A. sagrei on native fauna include competition-induced habitat shifts, intraguild predation, and decreases in population density. The extent to which these interactions are novel for A. sagrei in introduced areas is unknown. Are A. sagrei interacting differently with fauna in introduced areas as compared to its interaction with species in its native community? Do A. sagrei eat lizards in Cuba and Bahamas or just in introduced parts of its range? Do A. sagrei affect abundance of other species in its native range? These questions directly relate to whether invading species arrive preadapted to coexist with members of the new community or if competition upon arrival leads to evolutionary change and subsequent coexistence, which is likely a crucial element in determining invasion success rates and the extent of detrimental effects on native fauna. Knowledge of both the causes and patterns of variation in introduced populations and the consequences of this variation for native fauna will enhance the success of management plans. I propose to test the following hypotheses concerning this problem:
1. Does variation in ecological, morphological, and behavioral traits influence the effects of invasive A. sagrei on native fauna?
2. Do different A. sagrei source populations result in differential effects on native fauna?
The goal of this research is to understand the causes and consequences of ecological, morphological, and behavioral variation in the invasive lizard, Anolis sagrei. I will accomplish this goal using molecular phylogenetics to reconstruct the invasion history of A. sagrei and comparative ecological studies to determine the causes of phenotypic variation in introduced A. sagrei populations and the consequences for native fauna.