碩士 / 國立臺灣大學 / 海洋研究所 / 90 / Fishes of Stegastes (Pomacentridae, Teleostei) occur widely on coral reefs. These fishes have a characteristic in common — they all hold permanent territories. To deny access to the resource or exclude others from specific areas, the territory owner will attack interspecific and/or intraspecific intruders actively or passively. In this study I used a population of the territorial dusky gregory, Stegastes nigricans, which occurred in the water inlet of the Third Nuclear Power Plant on the Kenting coast as materials and asked: what were determinants for the variation of the territory defense during intraspecific confrontation? I collected adult S. nigricans individuals by selective angling from the study area and used them as intruders to provoke aggressive behaviors of conspecific territory-owners. The results indicated that the owner’s maximum distance of attack (MDA) was in the range between 55 cm and 280 cm (147 cm in average). The MDA was not correlated with the body size of the territory holder. However, a negative correlation occurred between the MDA and the amount of algae in the owner’s territory. Similarly, the number of bite (NB) launched on a solitary conspecific near the territory was also negatively correlated with the amount of algae in the owner’s territory. When conspecifics intruded in pairs, the probability was significantly higher for the first attack to be launched on a neighbor than a non-neighbor. When a neighbor and a non-neighbor appeared simultaneously near the territory, the NB against the neighbor was also higher.
Results from 53 experimental removals of the territory owner showed that all the vacant territories were immediately taken over by conspecifics. Most of the occupiers were former owners of their nearest neighboring territories. After 24 hours, however, occupants of many of the territories changed again, and for most of the standing occupants the amounts of algae were found to be more in their new territories. When the removed territory-owners were released, 78% of them successfully returned to their earlier territories. Failures of return could be linked to either of the situation that the new territory occupants had obtained an extra amount of algae by the occupancy, or that the new occupants were among their previous nearest neighbors. The majority of the territories were built in aggregations. When an intrusion occurred to aggregated territories (territories between which the nearest distance was within 60 cm), the owner facing the intruder first would be the first to launch its attack. If the intruder kept approaching, defense would be reinforced by turns by owners from other territories. Besides, the MDA accompanied with the first defensive attack was the farthest. It became nearer and nearer from later defenders. It was also found that the first defender from aggregated territories in average would bite 56% more times in the first 5-min encounter than the owner of an isolated territory would do to the intruder. Intrusions might arrive from any direction. Each member of an aggregation of four was thus obligatory for only 1/2 — 1/4 of the total territory defense. Overall, members of aggregated territories were expected to have shared the benefit of group defense. When the juvenile (in the size of 5 cm TL) was involved in paired intrusions, the territory owner would choose to attack the juvenile first. The attack would go along with heavier bites. This findings applied to both aggregated territories and isolated territories, indicating that the territoriality of adults might have played an important role in mechanisms underlying for the recruitment of juveniles to the population.
| Identifer | oai:union.ndltd.org:TW/090NTU00279030 |
| Date | January 2002 |
| Creators | Cheng-Tse Ho, 何政擇 |
| Contributors | Rong-Quen Jan, Fuh-Kwo Shiah, 詹榮桂, 夏復國 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 68 |
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