If lemurs as a guild are adapted to rely on the timing of the phenology of fruits in order for lactation and weaning to succeed, what are the long-term effects should the climate parameters change causing the fruiting patterns to change? It is important to note that many of the fleshy-fruit plant species used by lemurs are also hardwood species favored by selective loggers in undisturbed forest (Wright et al., 2005b). These same species are eliminated first from fragments (Dehgan et al., 2000; Dehgan, 2003; Irwin, 2005). While loss of key fruit trees may not drive lemurs into extinction immediately, it may adversely affect reproductive success years after logging (Arrigo-Nelson and Wright, 2004a,b; Pochron et al., 2004; Dunham et al., 2005). Female body mass and successful reproduction are linked and there is strong evidence that females in selectively logged, fragmented as well as in cyclone-disturbed forest (Ratsimbazafy, 2002; Irwin, 2005; Arrigo-Nelson, 2006) weigh less than in undisturbed forest. This kind of "energetic debt" can affect reproduction decades after the logging has ceased. Ultimate survival of populations may be at risk even though the forest cover is present.
Although we know that there has been a dramatic desiccation of western and highland regions in the past thousand years (Gade, 1996; Simons, 1997; Godfrey et al., 1997), there are indications that deforestation and fragmentation of forests are presently continuing to produce a drier climate in Madagascar (Madagascar Weather Bureau, 1960-2005). Although drought is known to be a natural phenomenon, especially in the south of Madagascar (Gould et al., 1999), droughts may be becoming more frequent. Southern Madagascar underwent a severe drought in 1990-1991 (Sauther, 1998; Gould et al., 1999, 2003; Jolly, 2004). The impact on lemur populations in the spiny desert was dramatic. For example, the population of Lemur catta at Beza Mahafaly dropped from 85 individuals in early 1991 to 51 in 1994, with 21% of adult females, 80% of infants, and 57% of juveniles dying during the 6 months of drought (Gould et al., 1999). Ten years later the population had recovered to be 61 adult individuals, far below the 1991 figure of 85 adults (Gould et al., 2003). Additional droughts in 1997 and 2005 have been recorded. There is some indication that tooth morphology in recent generations may be evolving to cope with this drier environment (Cuozzo and Sauther, in press). If droughts continue to occur with greater frequency, there will be less opportunity for lemur populations to recover.
Recently, a study of Milne-Edward's sifakas has shown that dry years can even have an effect on lemur reproduction in a rainforest (King et al., 2005). The surprising result showed that older females (14% of the population) with worn teeth lost infants if the months of early lactation had low rainfall. It is hypothesized that the elder females cannot shear the leaves, which are more fibrous in dry months, to obtain moisture and nutrition necessary for successful lactation. This study showed how even a slight decrease in rainfall can have an impact on lemur populations.
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