The Iriomote cat Prionailurus iriomotensis is a small felid found only on Iriomote Island (284 km²) of the Ryukyu Archipelago, Japan. This species is listed as an endangered species in IUCN Red list because of the small population size and the restricted distribution. Its population estimated at approximately 100 in 1994 had declined during last decade mainly due to the habitat reduction by developmental activities. Here we focused on population declines and habitat reductions of cats in two study sites; Ohtomi site has extremely changed in last decade by large-scale agricultural land reforms, while northern coastal site has been stable except recent road- expansion works. Habitat reductions were estimated using satellite remote sensing with eight scenes of LANDSAT TM data obtained between 1984 and 2000. The condition of vegetation covers were assessed based on Normalized Difference Vegetation Index (NDVI) using IDRISI. Natural forests maps of two sites in each period were created using NDVI images; the forest reductions and the status of development during past 17 years were estimated. According to the results, the forest reduction in Ohtomi site occurred particularly in 1992-1994 while large- scale agricultural land reforms were conducted. After then a trend toward reforestation had begun. Number of resident cats monitored by using photo gradually decreased with the forest reduction, and then the population density was still low even after the reforestation. In northern coastal site, number of resident cats was stable as the abundance of forest was unchangeable. It suggests that drastic change of environment has decreased carrying capacity of animal such as the Iriomote cat which requires wide range of habitat. And satellite remote sensing using LANDSAT TM is considered to be an effective method to monitor the extensive land covers during long-term period.

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It is essential to estimate and avoid the impacts of large structures on ecosystems from an early planning stage. Although detailed and long-termed data collection is desirable, conducting such intensive surveys at a number of locations during the initial stage of highway route selection is not realistic. Conventional ecological assessment methods essentially have positive values; however, a holistic point of view for biodiversity protection is currently missing. With these concerns in mind, we carried out research on the procedure to estimate the relative impacts of highway alternative routes on habitats as a general guide for initial route selections. The estimation procedure incorporated habitat dependency indices of species groups that were hypothetically established from landscape ecological studies. We conducted a case study along US highway 93 in the Flathead Reservation, Montana, U.S.A. to observe the resourcefulness of the results in relation to the sensitivity of the 2 parameters : the assigned habitat values and the road-effect width. The consistency in the rank of the routes indicated that the estimation method can potentially be used as a general guide for a highway planning. The effects of the sets of the habitat value numbers were to operate HDIs with the numbers of grid cells and to change the degree of agreement for a longer route. The general effect of the widths of road-effect zone was to increase or decrease the difference of the estimated habitat impacts of 2 routes. Narrower buffer zones created the greater difference. The use of landscape ecological species groups has the merit of the holistic approach of the procedure. The complementary use of the estimation procedure will enhance the conventional approach that relies on rarity, typicality and ecological rank of species. Further research with actual field data was necessary to examine the detailed characteristics of the habitat impact estimation procedure.

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