Geographical distribution pattern and interisland movements of Orii's flying fox in Okinawa Islands, the Ryukyu Archipelago, Japan

Abstract

The study of mobile animals such as flying foxes in insular habitats involves clarifying the population status on each island and determining the factors affecting movement patterns among the islands in their distributional range. We visited 25 of the Okinawa Islands and documented the number of Orii's flying foxes Pteropus dasymallus inopinatus from August 2005 to May 2006. We also conducted a monthly road census on the main island (Okinawa-jima Island) and six adjacent islands from June 2006 to January 2007 and counted the number of fruit-bearing trees of the bats' four main food plants. The results of classification and regression tree analysis suggested that distance from the main island was a primary factor in determining the distribution pattern and population size of this flying fox, whereas island area, number of plant species, and food availability did not directly affect population size. The number of flying foxes on each island tended to decrease with an increase in distance from the main island; no flying foxes existed on islands [30 km away from the main island. On the other hand, the results of the monthly census showed that the population size on each island fluctuated seasonally. Individuals may move between islands in response to seasonal changes in food availability. In conclusion, the distribution and abundance of Orii's flying foxes in the Okinawa Islands may be determined by the rate of immigration/emigration, depending on each island's distance from the main island. Seasonal changes in food availability may act as a trigger for interisland movement, but that movement may be restricted by island connectivity.

Biogeographical Survey Identifies Consistent Alternative Physiological Optima and a Minor Role for Environmental Drivers in Maintaining a Polymorphism

“…As expected, several of these parameters were strongly correlated and may therefore not be included together in one regression model, because of multi-collinearity problems [84] . To make an a priori selection among the explanatory variables and meanwhile avoiding problems with multi-collinearity, we used two independent methods which have been proven to be successful in the past: classification and regression trees (CART) [85] – [87] and partial least squares regressions (PLS) [88] , [89] . CART explains variation of a single response variable by repeatedly splitting the data with the best predictive variables into more homogeneous groups.…”

Population genetic structure of the insular Ryukyu flying fox Pteropus dasymallus

“…According to Nakamoto et al. (2011), Yaeyama flying foxes have been presumed to be dispersing eastward across the sea to a new insular habitat approximately 50 km away (from Tarama‐jima to Miyako‐jima). The flying fox population on Yonaguni‐jima or the neighboring islands may also expand westward to Gueishan Island with the help of wind, forming a widely distributed and diverse population.…”

“…In 2004, an additional small population of the Formosan flying fox was recorded for the first time on Gueishan Island (Turtle Island), 9.7 km off the northeastern coast of Taiwan, and some individuals have occasionally been found on the main island of Taiwan since 2006 (Wu, 2010), although the origin of these populations is unclear. Other indirect evidence of movements across water comes from the population census of Orii's flying foxes (Nakamoto et al, 2011) and from inferred gene flow from the Yaeyama flying fox (Taki et al, 2020).…”

“…A third scenario is that active dispersal was driven by population expansion of the Yaeyama flying fox population.Yonaguni-jima of Japan, the westernmost margin of the distribution of the Yaeyama flying fox, is 110 km from Gueishan Island. According toNakamoto et al (2011), Yaeyama flying foxes have been presumed to be dispersing eastward across the sea to a new insular habitat approximately 50 km away (from Tarama-jima to Miyako-jima). The flying fox population on Yonaguni-jima or the neighboring islands may also expand westward to Gueishan Island with the help of wind, forming a widely distributed and diverse population.…”

Dietary Plasticity in the Ryukyu Flying Fox on a Subtropical Island at the Northern Range Limit ofPteropus

“…The seasonal density of P. dasymallus is not correlated with the number of seasonal available plant species, but is positively correlated with the number of seasonal available trees with fruits (Nakamoto et al, 2007b). In addition, the density of P. dasymallus in a given island is correlated with the total food abundance (summing the weighted scores of the abundance of each food plant) in each island (Nakamoto et al, 2011a). So, the declines in the observed numbers of flying foxes in winter suggest that the winter season is a period of food shortage.…”