Modeling population viability of local proboscis monkey Nasalis larvatus populations: conservation implications

Abstract

Population viability analysis (PVA) is a predictive procedure that uses different modeling approaches to estimate species vulnerability to extinction. Using the stochastic modeling software VORTEX, we assessed the status of proboscis monkeys Nasalis larvatus in 3 fully or partially protected areas in Borneo, 1 in the Malaysian state of Sabah and 2 in the Indonesian provinces of Kalimantan. Species-specific life-history parameters were used when possible, and missing parameters were taken from other populations or species. We tested the sensitivity of final predicted population size to 20% variation around the possibly inaccurate parameter estimates. The model we used predicts that in the absence of any management, the Malaysian population will remain fairly stable, whilst the 2 Indonesian populations will decrease by more than half, the smallest going effectively extinct in 30 yr. We investigated whether management strategies, such as reforestation, corridors to reconnect sub-populations, harvesting, reduction of deforestation and controlling fires, might help forestall population extirpation at each site. Fire had the greatest impact on the Indonesian populations, although hunting is also likely to play an important role. Remedial action to reduce the frequency and extent of fires, perhaps by regulated land clearing for agriculture, should slow proboscis monkey population decline and provide more time to collect the data necessary to evaluate other management decisions. As information regarding mortality, the effect of fire, and hunting rates on proboscis monkeys is limited, further research should concentrate on these areas to improve PVAs for this species.

Behavior and group movement of proboscis monkey’s (Nasalis larvatus Wurmb.) in Samboja, East Kalimantan

“…adalah primata endemik Borneo yang dilindungi dan masuk dalam kategori terancam punah (Meijaard et al, 2008). Ancaman terbesar terhadap populasi bekantan adalah terkait dengan kualitas dan kuantitas habitatnya yang semakin menurun baik habitat yang berada di wilayah Indonesia (Atmoko et al, 2007;Atmoko et al, 2011;Stark et al, 2012;Feilen & Marshall, 2014), maupun di Malaysia (Boonratana, 2013;Sha et al, 2008). Hal tersebut berbeda dengan habitat bekantan di Brunei Darusalam yang kondisinya relatif lebih baik, karena negara tersebut kaya akan minyak bumi sehingga secara umum tekanan terhadap hutan rendah (Nijman, 2015).…”

Use and Selection of Sleeping Sites by Proboscis Monkeys, Nasalis larvatus, along the Kinabatangan River, Sabah, Malaysia

“…As other Asian colobines, they form stable one-male social groups -consisting of a single adult male, several females and their offspring -and all-male groups -composed of males of different ages [Yeager, 1990;Murai, 2006]. Proboscis monkeys are restricted to coastal mangrove, swamp and riverine forests [Meijaard and Nijman, 2000;Sha et al, 2008;Stark et al, 2012]. They generally forage inland and return to the riverbank in late afternoon to rest and spend the night along the river's edge .…”

Modelling Population Viability of Three Independent Javan Gibbon (Hylobates moloch) Populations on Java, Indonesia

“…PVA models are not intended to determine an absolute risk of extinction, rather they are best used to help identify aspects of the system for which more data are needed, help direct funding to priority populations where it can be used efficiently and appropriately (e.g., policy decisions, habitat management, and conservation planning), and, overall, to offer insight into which current and potential management/mitigation strategies are likely to have the greatest positive effect on species' long-term survival [Shaffer et al, 2002;Drechsler and Burgman, 2004;Stark et al, 2012].…”

“…PVA has been a widespread tool in species conservation for the past 30 years, helping to provide assessments of species population trajectories and viability [Coulson et al, 2001;Reed et al, 2002], projections of the impacts of potential changes to habitat or direct threats to populations [Coulson et al, 2001;Nilsson, 2003], assessments of the relative efficacy of proposed management actions [Nilsson, 2003], and predictions for population growth under management practices or habitat limitations [Boyce, 1992;Reed et al, 2002;Stark et al, 2012]. PVA models are not intended to determine an absolute risk of extinction, rather they are best used to help identify aspects of the system for which more data are needed, help direct funding to priority populations where it can be used efficiently and appropriately (e.g., policy decisions, habitat management, and conservation planning), and, overall, to offer insight into which current and potential management/mitigation strategies are likely to have the greatest positive effect on species' long-term survival [Shaffer et al, 2002;Drechsler and Burgman, 2004;Stark et al, 2012].…”

“…The model uses mathematical simulations to estimate extinction probabilities of wildlife populations subject to different deterministic forces and stochastic events [Soule, 1985;Stark et al, 2012;Marshall et al, 2009]. When paired with empirical data from the field, PVA models can identify several factors that make a species more susceptible to extinction processes and can help to guide conservation management and funding [Sodhi et al, 2010;Marshall et al, 2013].…”