Karakteristik Patch Habitat dan Metapopulasi Bekantan (Nasalis larvatus) di Daerah Penyangga Taman Nasional Sebangau

Abstract

Bekantan merupakan primata endemik Kalimantan yang dilindungi pemerintah. Populasi bekantan terpecah menjadi sub-sub populasi akibat fragmentasi hutan hingga membentuk metapopulasi sehingga rentan terhadap kepunahan lokal. Daerah penyangga Taman Nasional Sebangau merupakan habitat bekantan yang terfragmentasi, berpotensi banyak gangguan. Tujuan penelitian ini adalah: 1) mengetahui kondisi dan karakteristik patch habitat bekantan; 2) mengetahui sebaran, jumlah populasi, variasi kelompok dan kelas umur bekantan; dan 3) mengetahui tipe metapopulasi, prospek kelestarian dan memperkirakan kepunahan lokal bekantan di daerah penyangga Taman Nasional Sebangau. Habitat bekantan daerah penyangga Taman Nasional Sebangau didominasi tipe patch berupa hutan riparian (42,37%), badan air dan danau (17,93%), rawa (16,71%), dan open area (14,36%). Bentuk geometri patch habitat tidak beraturan karena dipengaruhi oleh pemanfaatan lahan dan kejadian kebakaran hutan. Tumbuhan penyusun habitat bekantan sedikitnya 106 jenis pohon dalam 70 genus, dan 38 famili. Jenis vegetasi dengan kepentingan tinggi (INP) antara lain Cephalomappa beccariana, Elaeocarpus stipularis, Litsea accedens, Gluta velutina, Syzygium sp. 1, dan Shorea balangeran. Teridentifikasi 56 jenis pohon pakan bekantan, yaitu Cephalomappa beccariana, Artocarpus teysmannii, Gluta velutina, Syzygium sp., Lophopetalum javanicum, dan Sonneratia caseolaris. Pola sebaran bekantan menunjukkan pola mengelompok (Morisita index; Ip:0,54). Jumlah populasi bekantan daerah penyangga Taman Nasional Sebangau berkisar antara 1389-1736 individu dengan kepadatan populasi 8,01 individu/km², kepadatan kelompok 0,65 kelompok/km², serta nisbah kelamin 1:5,6. Jumlah kelompok yang dijumpai adalah 114 kelompok meliputi 109 one male units, tiga kelompok all mall units, dan dua soliter (jantan dewasa dan remaja). Berdasarakan kelas umur ditemukan jantan dewasa 8,62%, betina dewasa 48,19%, remaja 19,42%, anak 18,55%, dan bayi 5,22%. Terdapat delapan metapopulasi yang terbagi menjadi tiga tipe, yaitu patchy metapopulation (50%), classic metapopulation (37,5%), dan non-equilibrium metapopulation (12,5%). Berdasarkan semua skenario, empat metapopulasi patchy, yaitu Keruing, Muara Bulan, Tewang Perigi Timur, dan Mendawai Barat dapat bertahan lebih dari 80 tahun. Sebaliknya, metapopulasi classic (Asam Kumbang, Tewang Perigi Barat, dan Mendawai Timur) dan metapopulasi non-equilibrium (Landabung) memiliki risiko kepunahan yang beragam. Secara keseluruhan metapopulasi bekantan di Daerah Penyangga Taman Nasional Sebangau diperkirakan akan mengalami penurunan populasi sebesar 30,79% selama 80 tahun. Skenario pencegahan kebakaran hutan dan penegakan hukum memperlambat penurunan populasi 14,57%, sedangkan skenario pemulihan ekosistem diperkirakan akan meningkatkan populasi bekantan 23,41%.

The proboscis monkey (Nasalis larvatus) is a Borneo endemic species that is protected by the government. The population is divided into subpopulations due to forest fragmentations to form metapopulations, and highly vulnerable to local extinctions. The Sebangau National Park’s buffer zone is a proboscis monkey habitat that is fragmented and has the potential for many disturbances. The objectives of this study were: 1) to identify the conditions and the characteristics of the proboscis monkey patch habitat; 2) to analyze the distribution, population size, group variation, and sex ratio of proboscis monkeys; c) to figure out the type of metapopulation, population survival, and the threat that causes the local extinction of proboscis monkey in the buffer zone of Sebangau National Park. The proboscis monkey habitat in the buffer zone of Sebangau National Park is dominated by patch types such as riparian forests (42,37%), water bodies and lakes (17,93%), swamps (16,71%), and open areas (14,36%). The patch geometry is irregular and influenced by land use and forest fires. The vegetation of the proboscis monkey habitat consists of at least 106 tree species from 70 genera and 38 families. The vegetation with high importance value index (IVI) are Cephalomappa beccariana, Elaeocarpus stipularis, Litsea accedens, Gluta velutina, Syzygium sp. 1, and Shorea belangeran. Of all the species recorded, 56 tree species were identified as proboscis monkey diet, i.e., Cephalomappa beccariana, Artocarpus teysmannii, Gluta velutina, Syzygium sp., Lophopetalum javanicum, and Sonneratia caseolaris. The proboscis monkey distribution pattern was clustered (Morisita index; Ip=0.54). The number of proboscis monkeys ranges from 1389-1736 individuals, with a population density of 8.01 individuals/km², a group density of 0.65 groups/km², and a sex ratio of 1:5.6. We found 114 groups including 109 one male units, three all male units groups, and two solitary groups (adult males and juveniles). Based on age class, there were adult males (8.62%), adult females (48.19%), sub-adults (19.42%), juveniles (18.55%), and infants (5.22%). There were eight metapopulations which were divided into three types, i.e., patchy metapopulation (50.0%), classic metapopulation (37.5%), and non-equilibrium metapopulation (12.5%). Based on all scenarios, four patchy metapopulations, namely Keruing, Muara Bulan, East Tewang Perigi, and West Mendawai are expected to survive over 80 years. In contrast, the classic metapopulations (Asam Kumbang, West Tewang Perigi, and East Mendawai) and the non-equilibrium metapopulation (Landabung) have varying extinction risks. Overall, the metapopulation of proboscis monkeys in the buffer zone of Sebangau National Park is expected to experience a population decline by 30.79% over 80 years. The forest fire prevention and law enforcement scenario can slow the population decline by 14.57%. The ecosystem recovery scenario is predicted to increase the proboscis monkey population by 23.41%.