Lizards in an Evolutionary Tree: Ecology and Adaptive Radiation of Anoles

8. Cradle to Grave: Anole Life History and Population Biology

135 8 CRADLE TO GRAVE Anole Life History and Population Biology Before tackling the question of how anole species interact (Chapter 11), and how such interactions might drive evolutionary change (Chapter 12), I need to discuss what makes anoles tick. That is, how do anoles interact with their environment? What happens during the course of an anole lifetime and why? These questions will be the focus of this and the next two chapters. The goal of this chapter is to review the basic aspects of anole population biology and life history, as well as to discuss the role of anoles in the ecosystem. In some sense, much of the information that I will discuss could be categorized as “natural history.” In recent years, natural history has not been given a lot of respect—some contend that it does not even qualify as a science. Quite the contrary, I would argue that natural history is not only based on the important scientific foundations of careful observation and inquiry, but that it is essential if we are to formulate meaningful hypotheses about an organism’s place in the environment. Moreover, to understand how species interact and evolve through time, knowledge of natural history is indispensable (Greene, 1994, 2005). Anoles have been intensively studied for more than 40 years, and we know more about anole natural history than we do for most types of organisms. Nonetheless, the amount of information we do not know is staggering. One clear message from this chapter is that many important aspects of anole biology are still little known. As subsequent chapters will illustrate, this lack of information impedes our ability to interpret broad scale patterns of anole ecology and evolutionary diversification. This chapter is meant to be a call to arms: there’s much to be discovered and no time like the present! losos_ch08.qxd 4/11/09 9:04 AM Page 135 The purpose of this chapter is to review the basic aspects of anole biology. In some cases, such as reproductive biology, anoles exhibit little variation (at least of which we are aware), and my goal is simply to report what anoles do.173 In other cases, such as diet, considerable diversity exists within and among anole species, and my goal is to explore this diversity and to explain its ecological and evolutionary significance. REPRODUCTION I’ll start at the beginning, with the way a young Anolis makes its way into the world. Anole courtship is a highly stereotyped business. Males perform a display in which they bob their heads and extend their dewlaps in a species-specific manner. The stereotypy of the head-bob cadence is important, as it appears to be a means for females to distinguish conspecifics from heterospecifics, a topic to which we will return in Chapter 14. Females respond by headbobbing or dewlapping (or both), and sometimes arch their neck to indicate receptivity. The male often bites the female on the neck and mounts on her back, swinging his tail around to the underside of the female’s tail and bringing their cloacae into close proximity. The male then everts one of his two intromittent organs, termed hemipenes and stored in the base of the tail (Fig. 8.1), and inserts it into the female’s 136 • A N O L E L I F E H I S T O R Y A N D P O P U L A T I O N B I O L O G Y F I G U R E 8.1 Photo of the everted hemipenes of a museum specimen of A. magnaphallus. As the name implies, this species’ hemipenes are larger than those of most anoles. Only one hemipenis is used at a time: males alternate their use. The hemipenis used depends on whether the male swings its tail over the left or right side of the female. Why some species, such as A. magnaphallus, have bilobed hemipenes is not known; the lobes function as a single intromittent organ, rather than being used separately. Photo courtesy of Steve Poe. 173. An important caveat is that most generalizations are based on data for relatively few species, most of which are usually West Indian. Even basic aspects of the biology of most of the 361 species of anoles are unknown. Who knows what surprises remain to be discovered? losos_ch08.qxd 4/11/09 9:04 AM Page 136 cloaca...