Implications for flying fox conservation
Our study provides an opportunity to draw parallels for a comparison with another closer and less studied subspecies, and it offers insights important for the conservation of island flying foxes. Formosa fruit bats suffered a dramatic decline, starting over 30 years ago, from exploitation and habitat alteration and destruction, and remains extremely rare (Lin and Pei, 1999; Heaney et al. 2008; D.J. Lin, unpubl. data). The historical hunting episode on Lutao, lasting for 10-15 years, presumably arose from economic incentives, for most bats were snared and later exported (Lin and Pei, 1999), and coincided with significant trading during the same period in other Pacific islands (e.g., Guam and the Mariana Islands, Wiles and Payne 1986). Hunting has been officially banned and fruit bats are legally protected on Lutao, yet their future fate is far from certain due to other factors such as habitat alteration, lack of stable food availability, and possible human disturbance (Lin and Pei, 1999).
Unlike bats that inhibit Lutao (c. 17.3 km2 at low tide), Yaeyama fruit bats occur among islands of a total land area exceeding 550 km2. Typhoons frequent both areas, but have no apparent effects on flying foxes on larger islands, e.g., Iriomote (this study). Yet, remnant populations on small islands may still be vulnerable to disturbances, even by chance (Pierson et al., 1996). The resident density (c. 173.4/km2) and annual tourist numbers (> 300,000) on Lutao are 25-fold and one- or two-fold those on Iriomote (Statistics Bureau data, Japan; National Statistics data, Taiwan), and cause inevitably more intensive habitat alteration or destruction. Ota (1992) noted a rapid decline in bat colonies on Hateruma after plantings replaced native forests. Plantations may provide substitution, but over time bats may still suffer from nutrient deficiencies (Nelson et al., 2000), or need to travel farther for more foraging options, which will be increasingly more difficult for bats on isolated or small islands (Meyer and Kalko, 2008; Meyer et al., 2008), and poses additional threats.
Concerning the status of Ryukyu flying foxes, and Pacific Island flying foxes in general, Yaeyama fruit bats on Iriomote are a good learning case. Human attitudes toward bats are extremely important conservation aspects (Y.F. Lee, unpubl. data; McCallum and Hocking, 2005; Thiriet, 2005). Habitat preservation and restoration, preferably through efforts by the local communities (Entwistle, 2001), to recover native forests and suitable food plants (e.g., figs) need to be implemented. Tourism and development should be carefully evaluated and tightly regulated, particularly for critical and small islands, such as Lutao. It remains unclear whether the currently few bats on Lutao are returnees of dwindling colonies that left Lutao for refuges, remnants of a formerly larger population, or immigrants from elsewhere. Further studies should focus on dispersal patterns and population dynamics on multiple islands over the entire or most of the distribution area of this species to achieve a deeper understanding of the ecology of the species in support of improved and more effective conservation strategies.