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10 - Toward an integrative theory on the origin of bat flight
- Edited by Gregg F. Gunnell, Duke University, North Carolina, Nancy B. Simmons, American Museum of Natural History, New York
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- Book:
- Evolutionary History of Bats
- Published online:
- 05 June 2012
- Print publication:
- 29 March 2012, pp 353-384
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Summary
In bats . . . we perhaps see traces of an apparatus originally constructed for gliding through the air rather than for flight.
Darwin (1859, p. 181)Introduction
It is easy to grasp why bats are so successful: a small nocturnal mammal in possession of powered flight can explore resources in a relatively low-risk environment at spatial scales orders of magnitude larger than that of non-volant mammals of comparable size. As an example, the median home range of the 8–11 g vespertilionid Chalinolobus tuberculatus can be as large as 1500 ha (O'Donnell, 2001); this is the average area used, for instance, by a 300 kg herbivore, the Wapiti (Cervus elaphus canadensis; Calder, 1996). Acquisition of powered flight represented an immediate advantage to the bat lineage. As attested by the fossil record, bats reached nearly worldwide distribution early in their evolution. By the Early Eocene, bats suddenly appear in all the major landmasses they inhabit today (Gunnell and Simmons, 2005; Tejedor et al., 2005; Eiting and Gunnell, 2009). This suggests that powered flight may have played a key role in the fast expansion of bats, thereby contributing to their spectacular diversification.
16 - Early evolution of body size in bats
- Edited by Gregg F. Gunnell, Duke University, North Carolina, Nancy B. Simmons, American Museum of Natural History, New York
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- Book:
- Evolutionary History of Bats
- Published online:
- 05 June 2012
- Print publication:
- 29 March 2012, pp 530-555
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Summary
Introduction
Size is the single most important factor affecting physiology, locomotion, ecology and behavior of mammals (MacNab, 2007 and citations therein). Understanding evolution of size is important in all organisms, but especially so in cases like bats which exhibit many energetically expensive behaviors (e.g., powered flight, echolocation, long-distance migration), as well as characteristics that represent extreme energy-saving mechanisms (e.g., torpor and hibernation). Most bat species are small: from data in Smith et al. (2004), the central tendency in size in extant bats, as estimated by the median value, is around 14 g (Figure 16.1). However, size in bats as a group spans three orders of magnitude, ranging from 2–3 g (e.g., Craseonycteris, Thyroptera, Furipterus, some vespertilionids; Smith et al., 2004) to a few species exceeding 1 kg (e.g., Acerodon jubatus, Pteropus vampyrus; Kunz and Pierson, 1994). This variation in size scales a number of fundamental traits in bats, including physiological features (e.g., basal metabolic rate; McNab and Bonaccorso, 2001; MacNab, 2003, Speakman and Thomas, 2003); aerodynamic performance (Norberg, 1986, 1990; Rayner, 1986; Watts et al., 2001); dimensions of limb bones and their biomechanical properties (Swartz, 1997, 1998; Swartz and Middleton, 2008); behaviors (e.g., extreme dietary habits like carnivory; Norberg and Fenton, 1988); echolocation call parameters (Jones, 1999); and most life-history traits (e.g., litter mass; Hayssen and Kunz, 1996). These traits likely have an important phylogenetic component of variation, as has been shown, for instance, for the relationship of basal metabolic rate to body mass (Cruz-Neto et al., 2001; cf. MacNab, 2007). Besides the many dependent variables responding to body mass in various ways, size is a fundamental trait that should be understood by itself as an evolving character in bat lineages.