Size and development of a proboscis monkey population (Nasalis larvatus) in Balikpapan Bay, Indonesia, in relation to habitat changes

Tadeáš Toulec

Disertační práce

Abstract:

This dissertation revolves around endangered proboscis monkeys (Nasalis larvatus), inhabiting coastal and flooded habitats, which are among the most threatened habitat types worldwide due to heavy anthropogenic pressure. We studied a large, yet relatively understudied proboscis monkey population in Balikpapan Bay, focusing on population size, structure, and development in a period from 2007 to 2022. Since habitat loss represents one of the most important threats to proboscis monkey survival, we assessed habitat size, its changes from 2000 to 2022, and the causes driving these land cover changes, threading separately two major components of proboscis monkey habitats - mangrove and secondary terrestrial non-mangrove forests. We subsequently addressed the Indonesian government’s decision to relocate the capital city to Balikpapan Bay and provided our recommendations for sustainable development towards proboscis monkeys. Proboscis monkey habitat decreased continuously throughout the period at a rather slow pace to a size of 195.10 km2 in 2022. Of the two habitat components, mangroves were lost in a disproportionally slower rate and also regenerated faster, compared to the non-mangrove part of the habitat, which had decreased to 63.26% of its original extent in 2022. Oil palm plantations were the most prominent deforestation driver of terrestrial non-mangroves in 2000 - 2007, but their influence reflected a whole-Indonesian trajectory of rapid increase peaking around 2007, followed by a continual decrease to virtual cessation. The threat of palm oil, however, remains present in Balikpapan Bay in the form of the processing sector. Industry became a major threat to proboscis monkey habitat after 2007, strengthening the position of Balikpapan City as a prominent industrial hub in Kalimantan. Although aquaculture was among the main drivers of mangrove deforestation worldwide in the 1980s - 1990s, it translated into Balikpapan Bay primarily at the beginning of the observed period and currently abandoned shrimp ponds started recently regrow with healthy mangroves. Forest fires, frequently induced by long-lasting droughts, which could burn down terrestrial forests, including proboscis monkey habitat, did not have a devastating effect on the periodically flooded mangroves in Balikpapan Bay. Based on periodical censusing of the whole-population segment, the Balikpapan Bay proboscis monkey population remained stable from 2007 to 2022, in response to slow and continual habitat changes. The stability of Balikpapan proboscis monkeys was confirmed in encountered groups, whereas group size slightly decreased, similarly to other localities. Proceeding deforestation also created a few local high-population density hotspots and habitat fragmentation split the whole population into six more-or-less isolated subpopulations. The whole-population census of Balikpapan Bay detected 359 groups, which resulted in an estimated population size of 3,907 individuals. Although approximately 37.08% of the local proboscis monkey population inhabited areas overlapping with the administration area of in-construction Nusantara Capital City, our results displayed that the rate of deforestation is highest just outside the limits of the proposed capital. The importance of this finding was confirmed by the incorporation of our recommendation into spatial planning and biodiversity master plan by the deputy for environment and natural resources at the Nusantara Capital City Authority. Finally, this dissertation also includes preliminary results on a population viability analysis for the local proboscis monkey population. Unlike the former published population viability analysis, which predicted a rapid decline of the population, our model described all subpopulations in Balikpapan Bay as stable under current conditions until at least 2072. Sensitivity testing identified parameters related to female reproduction and infant survival among the most influential in the model,

Abstract:

highlighting the need for studies on demography, with an emphasis on reproduction and infant sex ratio and survival rates. The most promising alternative scenario considering proboscis monkey survival included reforestation, which could take advantage of 45.33 km2 of potentially restorable habitat in the margins of Balikpapan Bay. Further fragmentation of the whole population would not threaten the majority of subpopulations with extinction unless hunting is introduced. Hunting was evaluated as a threat with the highest chance of extermination of the whole population. Prolongation of the moderate loss of habitat still resulted in a stable proboscis monkey population, therefore adherence of the Indonesian government to construct a “smart, green, beautiful, and sustainable city” with respect to the environment should be a principal conservation goal for forthcoming years.

Keywords

Proboscis monkey, population, mangroves, deforestation, population census, New Indonesian Capital city

Jazyk práce: angličtina

Datum vytvoření / odevzdání či podání práce: 21. 9. 2024

Obhajoba závěrečné práce

• Vedoucí: prof. RNDr. Vladimír Bejček, CSc.
• Oponent: Francisco Ceacero Herrador, Ph.D., doc., Ondřej Sedláček, externi, Barbora Kuběnová, externi

Česká zemědělská univerzita v Praze

Fakulta životního prostředí

Doktorský studijní program / obor:
Ekologie / Ekologie