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Hokkaido University (北海道大学) / 博士 / 地球環境科学

Hokkaido University (北海道大学) / 博士 / 地球環境科学

Hokkaido University (北海道大学) / 博士 / 地球環境科学

Hokkaido University (北海道大学) / 博士 / 地球環境科学

Hokkaido University (北海道大学) / 博士 / 地球環境科学

Loggerhead sea turtles Caretta caretta nesting off coasts of Japan are known to travel an immense distance throughout their life, however much of their behavior in the open ocean is still not clear. Argos transmitters were attached to 30 turtles, which were either postnesting, headstarted, or bycaught, and their tracks were recorded spanning several months to over a year. Location data were low in quality with nearly 70% of the points having error radii that could not be estimated. As an initial step, the noisy data were smoothed under a systematic set of criteria to remove redundant information and obtain the most reasonable paths taken, controlling both location and average velocity. Smoothed turtle tracks were obtained for all individuals with average velocities no greater than 250 cm/s. Behavior was categorized into three groups; 1) remaining, 2) returning and 3) departing, among which significant differences were found in straight carapace lengths (SCLs), being largest for remaining turtles and smallest for departing turtles. Logistic regression estimated the pivotal range of SCL to be 725 to 783 mm dividing coastal (remaining and returning) and non-coastal (departing) turtles. Longitudinal distributions were clearly different between behaviors and also within the returning turtles being west of 135°E from May to July due to mating and nesting, which took place near the coast. During the same season, departing turtles were in regions as far as 170°E. In latitudinal distribution, all turtles were seasonally variable, being in latitudes higher than 30°N during warmer months. Behavioral differences were examined based on relative velocity of the turtle with respect to ocean current, where geostrophic current velocity was obtained from optimally interpolated satellite data (J-OFURO). Regression analysis was undergone comparing relative velocity to current velocity, along with other oceanographic parameters, such as sea surface temperature (SST) from AVHRR satellite data and nutrient concentrations from WOA01 climatological data. Turtle paths were divided into specific stages and comparisons were made between returning and departing turtles. In regions with strong Kuroshio currents, all turtles were drifted, however returning turtles were swimming in the opposite direction of the current more often than the departing turtles, which were reacting more to cooler SST. This indicates that returning turtles were unintentionally drifted into the direction of the strong currents. Frequently, turtles made roaming or circular movements in the open ocean, just off of the Kuroshio extension, possibly being drifted into circular currents or eddies, however in all cases, turtles confronted regions with plenty of prey during the roaming stage. After this stage, turtles either moved farther east to the Kuroshio extension bifurcation region, a “hotspot” for juvenile turtles, or changed their directions and headed back to nesting grounds. Deciding moments were characterized by a difference in current velocity magnitude and direction, which was mainly due to the turtles being at different latitudes, in which returning turtles were located south of the Kuroshio mainstream, being closer to cyclonic currents and nutrient-high cold rings, whereas departing turtles were closer to the center of the mainstream. When returning turtles initiated their long journeys back to the coast spanning several months, they headed southward into regions of relatively weaker currents and with a lower chance of finding prey. Initially, they were swimming more actively in the opposite direction of the current, but were less active as they headed south towards the end of their returning path. Hence, they seemed to have been extremely cautious concerning energy consumption, by swimming slower even in warmer SST, only swimming opposite of weak currents to head towards high silicate regions. They may have also been making frequent shallow dives in order to sense subsurface water temperatures as a cue to returning back to familiar waters near Japan. Departing turtles in the bifurcation region were continuously influenced by the currents and constantly headed towards prey abundant regions, remaining in this area until transmissions ended. It has been verified that ocean currents and other environmental factors influenced the horizontal movement and behavior of loggerhead sea turtles in the North Pacific at different stages of their tracks. Abrupt environmental changes causing SST increase, distributional change in plankton and intensification of the Kuroshio and its countercurrent could have an impact on their behavior, however the degree of the impact would depend on the adaptability of the turtles. These effects as well as those related to human activity are the determinant factors for their survival to endangerment. / Hokkaido University (北海道大学) / 博士 / 地球環境科学

A one-male group (BE-Group) of proboscis monkey Nasalis larvatus consisting of the α-male Bejita, six adult females and some immatures was chosen and focal male and females in BE-Group were followed for a total of 1,968 and 1,539 hours, respectively, along the Menanggul River (which is a tributary of the Kinabatangan River), Sabah, Malaysia, focusing on feeding and ranging behaviors from May 2005 to May 2006. In order to determine the availability and seasonal changes of plant species consumed by the focal monkeys, vegetation surveys were carried out in 2.15 ha along 16 200-500 m trails set up in the forest. In addition, sleeping sites of all the groups in the area were surveyed in the evenings of 6-22 days per month using a boat along the river side. The main results were: 1) Sleeping sites of BE-Group were distributed in a wide range of overlap with those of other groups, suggesting no territoriality between different groups on the riverside trees. BE-Group seemed to select their sleeping sites on riverside trees at narrow river locations to reduce the predation chance of clouded leopard and/or to raise the probability of successful river crossing by females (often with infants) and juveniles to escape from predators. 2) As there was no difference in time budget between individuals excluding the category others (grooming + copulation) which contributed very little, the data of all focal monkeys were pooled, and its resting, feeding, moving and others accounted for 76.4%, 19.5%, 3.5% and 0.5%, respectively. In the feeding time, young leaves, fruits, flowers, mature leaves and other food sources constituted 65.9%, 25.9%, 7.7%, 0.03% and 0.5%, respectively, indicating that the tendency of consuming young leaves was strong in terms of total food amount. However, monthly fruit production of plants positively correlated with monthly fruit-eating and feeding activity of proboscis monkeys, respectively, though young leaf production to young leaf-eating and flower production to flower-eating did not correlate with each other, respectively, and both young leaf and flower production did not correlate with feeding activity. These suggest that fruit production significantly affects the activity budget of proboscis monkeys. 3) In both the male and females, the ratio of feeding time was the highest at 15:00 - 17:00, i. e. shortly before sleeping. As proboscis monkeys require about 50 hours for processing leaves, they may feed on lots of foods in late afternoon to spend the night time not only for sleeping but also for digestion. 4) Total number of plant species consumed by focal monkeys was 188 (127 genera, 55 families). When the availability of each species was estimated from the vegetation survey in which 180 tree and vine species were described and monthly followed their phenology, the actual observed time for consuming them was significantly different from consumption time expected from availability in some species, suggesting that the proboscis monkey is the picky eater. For instance, Mallotus muticus, Ficus binnendijikii, Crudia reticulate, Lophopyxis maingayi and so on were positively preferred by proboscis monkeys. 5) The seven focal monkeys spent a total of 177.2 hours for fruit-eating, of which seed-eating constituted 97%, suggesting that the proboscis monkeys seemed to consume the fruits in favor of seeds. Whenever monkeys collected ripe fruits, they abandoned flesh and consumed only seeds. They fed extensively on the seeds of Mallotus muticus trees and Lophopyxis maingayi vines which were the most abundant plant species in the study area, although some dominant and predominant species were not consumed or showed negative food preference. Because the proboscis monkeys almost completely grind and digest the seeds of these abundant plant species, in this study site, they may limit too much increase of the predominant species and permit minor plant species to survive in the community. 6) Nonetheless, some seeds of Antidesma thawaitesianum, Nouclea subdita and Ficus spp. remained undigested in the feces of proboscis monkeys. The undigested seeds were small and relatively hard and were found in intact shape. Especially seeds of Ficus spp. were often found in feces when the proboscis monkeys often fed on its fruits, and Ficus species have been thought to be one of the most important plant species for a lot of wildlife. There is a possibility that proboscis monkeys may play the role of seed dispersal for a few plant species. 7) During 1,968 hours, the BE-Group moved within the range of 138.3 ha. The ranging of proboscis monkey was affected by the location of river crossing points and the availability of foods, in particular fruits. 8) The daily path length of BE-Group ranged from 220 m to 1,734 m (mean: 799 m) which was negatively correlated with fruit availability. The proboscis monkeys were apt to stay within a small range in fruit-abundant seasons. 9) BE-Group sometimes stayed within a limited area to frequently visit a particular tree which produced their favorite foods. Out of positively preferred trees or vines, Crudia reticulate, Cynometra ramiflora and Carallia brachiata could be such behavioral core trees. 10) Since the water level of the river had a statistically significant effect on the location of BE-Group’s sleeping site, when more than 3 m deep water covered the forest floor more than 1 km from both sides of the riverbank towards the inland in seasonal flood, the group slept inside the forest. It may be that the proboscis monkeys are not restricted to the riverbank, which has an uncluttered view for easily finding predators, because of reduced predation pressure by terrestrial animals during times when high water levels prevent predators from hunting. Thus, the feeding behavior of proboscis monkeys shows a high degree of fruit-eating (or seed-eating) in some seasons, and their extremely wide dietary diversity was demonstrated. Therefore, the ranging behaviors of proboscis monkeys were influenced by availability of fruits. The fruit-eating and fruit availability were one of the key factors to control the feeding and ranging behaviors of proboscis monkeys. In addition to those factors, ranging behaviors, including the sleeping sites selection of proboscis monkeys may be affected by predation pressure. In any case, the riverine forest of at least 800 m from the both river banks is evidently needed for the surviving of proboscis monkeys. / Hokkaido University (北海道大学) / 博士 / 地球環境科学

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(地球環境学) / 甲第15557号 / 地環博第66号 / 新制||地環||13(附属図書館) / 28035 / 京都大学大学院地球環境学舎地球環境学専攻 / (主査)教授 杉山 雅人, 教授 藤井 滋穂, 准教授 藤田 健一, 教授 藤原 建紀 / 学位規則第4条第1項該当

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(地球環境学) / 甲第15558号 / 地環博第67号 / 新制||地環||13(附属図書館) / 28036 / 京都大学大学院地球環境学舎地球環境学専攻 / (主査)准教授 ラジブ ショウ, 教授 松下 和夫, 教授 森本 幸裕 / 学位規則第4条第1項該当