Introduction

The understanding of the size, shape, overlap, and constraints of geographic ranges of organisms forms one important foundation of the very active field of biogeography, and is tightly connected to the understanding of evolutionary processes that give rise to the diverse distribution patterns that can be found today throughout all terrestrial and aquatic biomes (Cox and Moore, 2010; Lomolino et al., 2010). Madagascar is well known for its hypervariable environments (Dewar and Richard, 2007) and its extraordinary diversity in fauna and flora, most of which evolved endemically during the long period of isolation of Madagascar from other landmasses (Yoder et al., 1996; Poux et al., 2005; Crottini et al., 2012; Samonds et al., 2012). Some meta-analyses and reviews have recently aimed to investigate the evolutionary processes that led to the endemic radiations in Malagasy vertebrates and emphasized the role of climatic factors and physical barriers as drivers of allopatric speciation (e.g., Goodman and Ganzhorn, 2004; Yoder and Nowak, 2006; Wilmé et al., 2006; Pearson and Raxworthy, 2009; Vences et al., 2009). In particular, the role of large rivers and mountain ranges in disrupting gene flow and thereby leading to the evolution of local and regional endemics has been emphasized for various vertebrate clades (e.g., Wilmé & Goodman, 2003; Olson et al., 2004; Wilmé et al., 2006; Olivieri et al., 2007; Townsend et al., 2009). It should be mentioned that many geographic range sizes of Malagasy lemurs are only inferred from a rather small amount of point location data rather than known from extensive survey work which is known to limit the power of testing biogeographic hypotheses (Gaston, 1994). Nevertheless, none of the available biogeographic models for Madagascar can explain why some phylogenetic lineages contain closely related species with quite variable geographic range sizes. Mouse lemurs (Microcebus spp.) form one such lineage among lemurs and it shall be explored in this chapter whether ecological and behavioral traits may explain the existence of such divergent distribution patterns within a single genus.

Mouse lemurs comprise a total of 21 described species (Mittermeier et al., 2010; Radespiel et al., 2012; Rasoloarison et al., 2013) and can be found in all forest habitats of the island.