Judul: Tumpang Tindih Habitat antara Presbytis sumatrana dan Trachypithecus cristatus di Area Tambang Emas Martabe, Tapanuli Selatan
Abstrak: Habitat overlap frequently occurs when species share resource preferences. This overlap can lead to interspecific competition, particularly when resources are limited. In this study, we examined the habitat overlap and potential competition between the endangered and endemic Presbytis sumatrana and the vulnerable Trachypithecus cristatus, both of which inhabit the same forest areas adjacent to industrial zones in Batang Toru, South Tapanuli. Data collection was conducted using scan and ad libitum sampling methods. The results indicated that the home ranges of both species overlapped by more than 50%. Both P. sumatrana and T. cristatus predominantly occupied the same canopy height of 6-20 m, classified as stratum A. Although 15 of the 31 food species were utilised by both species, the Pianka index, which measures dietary overlap, did not indicate a significant overlap. P. sumatrana primarily consumed fruits, whereas T. cristatus mostly fed on leaves. While clear evidence of interspecific competition was not observed, langur species frequently used man-made substrates and exhibited a high tolerance for human presence. These results suggest that forest enrichment is critical for future conservation efforts to ensure continued coexistence., Tumpang-tindih habitat terjadi ketika spesies memiliki kemiripan preferensi sumberdaya sehingga menempati area yang sama. Hal ini dapat berujung pada kompetisi antarspesies, terutama ketika sumberdaya tersebut terbatas. Pada studi ini, tumpang-tindih habitat dan potensi terjadinya kompetisi diukur pada Presbytis sumatrana, salah satu spesies endemik terancam punah, dan Trachypithecus cristatus, spesies terkategori rawan, yang menempati satu hutan yang juga bersisian dengan area industri di Batang Toru, Tapanuli Selatan. Pengambilan data menggunakan metode scan sampling dan ad libitum. Hasil penelitian menunjukkan bahwa lebih dari 50% habitat kedua spesies tumpang-tindih. P. sumatrana dan T. cristatus juga menggunakan ketinggian kanopi pohon 6-20 m, yang terkategori sebagai strata A. Meskipun 15 dari 31 spesies pohon pakan digunakan keduanya, Pianka indeks, yang mengukur tumpang-tindih pakan, tidak menunjukkan nilai signifikan. P. sumatrana paling sering mengonsumsi buah sedangkan T. cristatus paling sering memakan daun. Meskipun kompetisi antarspesies tidak teramati, kedua spesies seringkali menggunakan substrat buatan dan menoleransi kehadiran manusia. Hasil-hasil ini mengindikasikan pentingnya pengayaan hutan untuk konservasi di masa depan demi koeksistensi berkelanjutan mereka.
Keyword: Batang Toru, Diet, Industrial Area, Interspecific competition, Niche

Judul: Biodiversitas Hewan di Hutan Dataran Rendah Batang Toru, Tapanuli Selatan, Indonesia
Abstrak: Tropical rainforests are home to a wide variety of flora and fauna on earth. Batang Toru Forest (North Sumatra, Indonesia) is known for its robust wild biodiversity. This study inventoried the biodiversity of amphibians, reptiles, and mammals in the South Tapanuli area of forest, located in the lowland with an altitude of 110-347 meter above sea level (masl). This study aimed to determine the diversity of three classes of animals in four study areas adjacent to a mining area. The method used was purposive sampling. The data were analysed with diversity, evenness, and dominance indices. As many as 29 amphibians, 23 reptiles, and 16 mammals' species were recorded. The diversity of species was found highest in the study area of I for amphibians and reptiles. The study area of III was high for mammals. There are five species listed as threatened by IUCN, nine species listed by CITES appendix, and six species protected by the Indonesian government. It can be concluded that the study areas were in sustainable condition, indicated by variegated amphibians, reptiles, and mammal species of different ecological functions., Hutan hujan tropis adalah rumah bagi beragam flora dan fauna di bumi. Hutan Batang Toru (Sumatera Utara, Indonesia) dikenal dengan keanekaragaman hayati yang kuat. Studi ini menginventarisasi keanekaragaman hayati amfibi, reptil, dan mamalia di kawasan hutan Tapanuli Selatan yang terletak di dataran rendah dengan ketinggian 110-347 meter di atas permukaan laut (mdpl). Studi ini bertujuan untuk mengetahui keanekaragaman tiga kelas satwa di empat area studi yang berdampingan dengan area pertambangan. Metode yang digunakan adalah purposive sampling. Data dianalisis dengan indeks keanekaragaman, kemerataan, dan dominansi. Tercatat sebanyak 29 spesies amfibi, 23 reptil, dan 16 mamalia ditemukan. Keanekaragaman spesies tertinggi ditemukan di area studi I untuk amfibi dan reptil, serta area studi III untuk mamalia. Ada lima spesies yang dikategorikan terancam oleh IUCN, sembilan spesies terdaftar dalam apendiks CITES, dan enam spesies dilindungi oleh pemerintah Indonesia. Dapat disimpulkan bahwa area studi berada dalam kondisi lestari, ditandai dengan keanekaragaman spesies amfibi, reptil, dan mamalia dengan berbagai fungsi ekologi berbeda.
Keyword: Ecological Function, Fauna, Mining Area, Rainforests, Threatened

Judul: Hamiltonian formulation for linear waves motion in two layers fluid
Abstrak: The surface wave could be considered as a wave that separates two fluids, namely water and air. Based on this assumption, it is introduced the interfacial wave, a wave between two layers of fluid with different density. The formulation of interfacial waves motion begins with deriving the base equation of irrotational ideal fluid. Furthermore, according to irrotational fluid assumption, the base equation can be stated in velocity potential. In this derivation, the fluids domain is assumed to be restricted by rigid lid boundary conditions, both at the upper and lower limit. Therefore, the interfacial waves motion can be explained in a hamiltonian formulation. In the hamiltonian formulation, total energy is defined as the sum of kinetic and potential energy. The hamiltonian system is obtained from reduction of kinetic energy by using the Dirichlet Neumann Operator. The resulted kinetic energy equation is nonlinear. Therefore, this form is linearized by first part of the Taylor expansion. This linearization gives a dispersion relation of linear wave. Based on this dispersion relation, the phase speed of the linear wave depends on the density ratio of the two layers fluid.
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