When we first went to the Red Island to begin our respective studies of ring-tailed lemur ecology (nearly twenty years ago), we were both struck by the sheer wild-ness of Madagascar. A land of great contrasts, one could travel the major highway that bisects the continent, and go from devastated vistas directly linked to human-induced changes, to intact forests where one could encounter a fantastic array of organisms. At that time there were only a handful of researchers who had met the challenges of fieldwork there, but over the past fifteen years there has been a virtual renaissance of studies focusing on Madagascar's unique plants and animals (see volumes by Kappeler and Ganzhorn, 1993; Rakotosamimanana et al., 1999; Goodman and Benstead, 2003; Jolly et al., 2006).

The lemurs of Madagascar remain the primate ambassadors of adaptive radiation. True to Darwin, they exhibit a wonderful example of the interplay between geographic isolation and speciation. Having evolved in complete isolation from other primates—lemur evolution dates back to the Eocene epoch (55-37 million years ago) and possibly even earlier (Martin, 1972, 2000; Mittermeier et al., 1994; Yoder et al., 2003)—the amazing variety of lemurs that we know today arose from either one or several separate waves of migration (see Yoder et al., 2003; Tattersall, 2004; Karanth et al., 2005; Tattersall, this volume). Once they arrived on Madagascar, these ancestral forms spread geographically into numerous niches to become a remarkable array of lemur species. As of this writing (2006) there are between 49 and 63 extant lemur species, depending upon which taxonomic source is consulted (Groves, 2001; Jungers et al., 2002; Moreira, 2005; Mittermeier et al., 2006), but there are also at least 16 species of subfossil lemurs, most of which have only gone extinct within the last 2000 years (see, for example, Karanth et al., 2005; Godfrey et al., this volume). Furthermore, there are new lemur taxa still being discovered. Given such a wealth of species, both living and extinct, it is not surprising that Madagascar attracts researchers from all over the world.

Madagascar's lemurs are also enterprising primates. From both a climatic and a geographical perspective, Madagascar has provided numerous challenges to its inhabitants. Lemurs make a living in a variety of habitats, from exotic spiny forests to seasonal dry forests, diminishing rain forests, limestone forests, and even high-altitude terrain, eking out an existence in habitats with poor soils, low and very seasonal plant productivity, and often unpredictable and sometimes devastating climates (Wright, 1999). Like their fellow island hoppers in Australia, this has resulted In a diverse and unusual number of traits, Including female dominance, sexual monomorphism, seasonal fat storage, and strict seasonal breeding (Jolly, 1984; Wright, 1999 and this volume; Curtis, this volume, Fietz and Dausmann, this volume).

With such a wealth of lemur research during the last fifteen years, the major purpose of this volume is to provide a single source for information from many of these new studies. This volume brings together information on newly studied taxa as well as summaries from long-term data on well-known lemur species from a number of sites. Information found in this volume provides us with answers to questions concerning life-history traits, adaptations to extreme seasonality, and natural disasters. It also brings up new information on the ecology and adaptations of the recently extinct subfossil lemurs, which has emerged from both new excavations and technological advances in primate paleontology. From these collected readings we hope to provide new insight into the study of lemur origins, and the ecology and adaptation of both extant and recently extinct species. In a larger context, the information contained in this book will expand our knowledge of primate ecology and allow us further insight into mammalian adaptations to unusual and often harsh environmental conditions that arise from both natural and anthropogenic factors.

We begin literally at the beginning, with Tattersall's (Chapter 1) overview of lemur evolution based on recent fossil, molecular, and ecological evidence. One of the biggest questions regarding lemur evolution is how did lemur ancestors arrive in Madagascar? Current evidence indicates that all of Madagascar's extant and extinct terrestrial mammalian species arrived via an overwater route that may have included ephemeral land bridges or "steppingstones" formed by geological forces in the seafloor. We move from prehistory to history in the chapter by Jolly and Sussman (Chapter 2), where we are introduced to the world of lemur studies in a lively recounting of the history of lemur research in Madagascar and a look at future prospects for conservation in Madagascar. Godfrey et al. (Chapter 3) then enliven the fossil record by using skeletal evidence from the extinct lemurs to suggest possible patterns of their social behavior, biology, and life history.

Given the unique phylogenetic status of the Malagasy lemurs, understanding their basic as well as unusual adaptations is key. Cuozzo and Yamashita (Chapter 4) provide an in-depth overview of what we currently understand regarding lemur dentition. Putting this discussion in a strongly ecological context, they discuss how the external environment leaves an imprint on lemur dentitions, either through adaptations to the physical requirements of specific environments or through environmental effects during the lifetime of the animal. Fietz and Dausmann (Chapter 5) discuss one of the most unusual primate adaptations to Madagascar's marked seasonal climate changes, that of hibernation in Cheirogaleus medius. The authors contrast the mechanisms of hibernation in this species, a tropical hibernator, with those of temperate climate hibernators in terms of physiological changes in body mass, internal temperature, and energy efficiency. They explain this unusual behavioral pattern as a response to low ambient temperature as well as food and water shortages during the cool, dry season in western Madagascar.

Freed (Chapter 6) notes that in most communities, different species of diurnal lemurs barely tolerate, displace, or chase one another; yet amicable polyspecific associations are common among members of crowned lemurs and Sanford's lemurs. He then explores these patterns and discusses why such an unusual association occurs.

Several lemur species have been described as cathemeral, and Curtis presents information on cueing mechanisms, adaptive significance, and the evolution of this unusual activity pattern in Eulemur, Hapalemur, and Varecia (Chapter 7). Hypotheses related to the development of cathemerality, which involve such variables as differences in canopy cover, predator avoidance, and offsetting food competition, are presented, as Curtis stresses that there is no single explanation for the evolution of cathemerality. Sterling and McCreless (Chapter 8) discuss the behavior and adaptations of Madagascar's most unusual-looking lemur, indeed one of the most unique primates, the aye-aye. The ecology and biology of this primate are likewise unique and in nearly every aspect, this species stands outside what is even the norm for lemurs.

During the past 15 years a wealth of new lemur studies have greatly enhanced our understanding of lemur taxonomy and ecology, making distinctive connections between ecological factors and patterns of social organization and behavior. Johnson (Chapter 9) presents an overview of the taxonomy and behavioral ecology of the brown lemur complex (Eulemur fulvus spp.), and explains recent taxonomic changes and genetic differences between species and subspecies. He clarifies the question of hybrids, subspecies, and species differentiation, and highlights ecological distinctions in this geographically widespread array of lemurs. Radespiel (Chapter 10) provides us with comparative information on both intra-and interspecific differences in mouse lemurs (Microcebus) covering ecological, physiological, reproductive, and social variables, some of these correlating with Madagascar's marked climatic seasonality. Radespiel also posits a model for ancestral mouse lemur social organization and sociality, which may in fact reflect the ancestral lemur, or even the ancestral primate condition. The way in which climate and environmental variables have likely shaped social organization and sociality are addressed in Overdorff and Tecot's chapter on red-bellied lemurs (Chapter 11). They discuss how ecological pressures in the habitat of Eulemur rubriventer, and resource defense by both sexes, may have led to the evolution of pair bonding in this species. Gould (Chapter 12) provides an in-depth update of what is currently known of the ring-tailed lemur's geographic distribution, variation in habitat and population density, diet and feeding ecology, and life-history variables, illustrating the remarkable adaptability of this species. Gould stresses that future research in non-gallery forest habitats is needed in order for us to fully comprehend this highly adaptable lemur. Vasey (Chapter 13) synthesizes both theoretical and empirical studies, and using her extensive fieldwork on wild Varecia rubra, the red ruffed lemur, she tests a number of hypotheses that link large body size to particular foraging and social patterns and reproductive costs.

Recent studies of the behavioral ecology of many lemur species have provided us with a much clearer picture of their diversity, and their behavioral and morphological adaptations. Irwin (Chapter 14) provides a summary of the ecology and behavior of the beautiful eastern sifakas. These species have only recently been studied in any depth, and Irwin summarizes what is currently known, revealing a striking level of variability in terms of home range, diet, and social structure. Thalmann (Chapter 15) provides important new information on aspects of behavior and ecology of two sympatric nocturnal lemurs, Avahi occidentalis and Lepilemur edwardsi. He notes striking differences in their feeding ecology, activity, and behavioral patterns, highlighting alternative solutions to similar ecological stresses experienced by the two lemur species. Powzyk and Mowry (Chapter 16) focus on ecological research on the indri (Indri indri) at three sites in different decades: Mantadia and Betampona in the 1990s and 2000, and Analamazaotra in the 1970s. They discuss distinctions between indri and other lemur species with respect to gut and dental anatomy, and point out intraspecific differences in diet between habitats and study sites. In light of Indri indri being the largest prosimian folivore, Powzyk and Mowry suggest that they be considered "energetic minimizers" and that their unique territorial calls may have evolved because calling requires less energy than scent-marking given their large home ranges. Tan (Chapter 17) presents an overview of Hapalemur ecology, with a focus on the unusual diet of this genus, the only primates to specialize on bamboo. She touches on new research focusing on physical properties of Hapalemur food items, and masticatory adaptations that have evolved in the genus to allow for the processing of bamboo. Tan also points out that we know little about the ability of Hapalemur to cope with and avoid cyanide in their bamboo intake, and she suggests directions for future research in this area.

Madagascar is a place of changes. We know that in many respects the particular patterns of Madagascar's climate play a critical role in understanding lemur adaptations. Anthropogenic change is also a part of Madagascar's landscape and lemurs have long faced additional stresses from human-induced changes. Many of the authors address how lemurs respond to such stressors. For example, a serious drought in 1991-1992 affected Lemur catta populations at both Berenty and Beza Mahafaly research sites, and Gould (Chapter 12) discusses how these populations recovered within a few years. Godfrey, Jungers, and Schwartz (Chapter 3) address how human impact through habitat destruction, introduction of domestic animals, and direct hunting led to the extinction of the giant lemurs, while Irwin (Chapter 14) highlights important conservation issues for the endangered eastern sifakas, for example, noting that in his own study on Propithecus diadema, fragmented habitats may alter diet composition in ways that may have both serious reproductive and social (i.e., competitive) effects. Cuozzo and Yamashita (Chapter 4) report that dental health may be compromised when lemurs begin to include foods of human origin.

Natural disasters and climate extremes are part of the climatic unpredictability of Madagascar, as discussed by Wright (Chapter 18). She notes that the Malagasy lemurs have a number of biological and behavioral responses to periods of food scarcity that may be responses to such unpredictability. Droughts and cyclones can seriously affect already fragile lemur populations, and likely have for thousands or millions of years. In this context Ratsimbazafy (Chapter 19) discusses the feeding and foraging strategies employed by a group of Varecia variegata edito-rium (black-and-white ruffed lemurs) at the Manombo rainforest site after a devastating cyclone hit southeastern Madagascar in 1997. Even though half of their preferred food trees were killed, many Varecia at this site survived and remained highly frugivorous, which Ratsimbazafy attributes to their use of two exotic plant species. He stresses that such diet flexibility prevented subsequent starvation in these lemurs after the cyclone hit. Monitoring health and understanding disease transmission in wild lemur populations is also critical with respect to future conservation efforts. Junge and Sauther (Chapter 20) explain how the relatively recent arrival of humans and domestic animals in Madagascar has had an important impact on pathogen transmission in lemur populations, and how introduced diseases can have serious detrimental effects on endemic lemur populations residing both in remote regions as well as in habitats undergoing rapid anthropogenic change.

Many populations of Madagascar's lemurs are threatened by anthropogenic and climatic factors, despite the fact that all lemur species are listed in the Convention on International Trade in Endangered Species (CITES). In just the past decade, several new species have been discovered (see for example Kappeler et al., 2005; Thalmann and Geissmann, 2005) bringing the number of extant species and subspecies to far more than previously thought.

The 2005 IUCN Red List assessment considers that 63% of today's lemur species are threatened with extinction, and 11 of these are considered Critically Endangered (Mittermeier et al., 2006). Anthropogenic effects such as habitat destruction (primarily for cattle grazing and crops), charcoal production, and hunting are still major threats to lemur population survival. A mere 3% of Madagascar's area is actually protected (Mittermeier et al., 2006), but Madagascar's president, Marc Ravalomanana, announced in 2003 that he plans to triple the amount of protected land in the next 5 years (Mittermeier et al., 2006; and see Jolly and Sussman, this volume, for a more detailed explanation). Hopefully this plan will be successful, and will allow for far greater protection for Madagascar's unique fauna and flora.

It is important that lemur conservation and scientific research go hand in hand, as one has a crucial influence on the other. New research conducted on well-known species as well as on newly discovered species, or species and populations for which little was previously known, can aid conservation strategies and programs, as such studies can clarify or contribute to diverse issues such as genetics, disease ecology, habitat change, hormone ecology, life-history and population ecology. Morphological and paleontological studies can also help us to understand the evolutionary history and adaptation of the lemurs, and give us greater perspective on past and present environments, and the multitude of ways that extinct and extant lemurs have coped with and adapted to the unique habitats found on the Red Island. In this volume, we present some of the recent and insightful research conducted on these topics, and at the same time, we look forward to an even further blossoming of future research on the remarkable lemurs of Madagascar.

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