Declining orangutan encounter rates from Wallace to the present suggest the species was once more abundant.

<h4>Background</h4>Bornean orangutans (Pongo pygmaeus) currently occur at low densities and seeing a wild one is a rare event. Compared to present low encounter rates of orangutans, it is striking how many orangutan each day historic collectors like Alfred Russel Wallace were able to sho...

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Autores principales:	Erik Meijaard, Alan Welsh, Marc Ancrenaz, Serge Wich, Vincent Nijman, Andrew J Marshall
Formato:	article
Lenguaje:	EN
Publicado:	Public Library of Science (PLoS) 2010
Materias:	Medicine R Science Q
Acceso en línea:	https://doaj.org/article/633292ba41654df7a60c4dac724e3296
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spelling	oai:doaj.org-article:633292ba41654df7a60c4dac724e32962021-11-18T06:36:11ZDeclining orangutan encounter rates from Wallace to the present suggest the species was once more abundant.1932-620310.1371/journal.pone.0012042https://doaj.org/article/633292ba41654df7a60c4dac724e32962010-08-01T00:00:00Zhttps://www.ncbi.nlm.nih.gov/pmc/articles/pmid/20711451/pdf/?tool=EBIhttps://doaj.org/toc/1932-6203<h4>Background</h4>Bornean orangutans (Pongo pygmaeus) currently occur at low densities and seeing a wild one is a rare event. Compared to present low encounter rates of orangutans, it is striking how many orangutan each day historic collectors like Alfred Russel Wallace were able to shoot continuously over weeks or even months. Does that indicate that some 150 years ago encounter rates with orangutans, or their densities, were higher than now?<h4>Methodology/principal findings</h4>We test this hypothesis by quantifying encounter rates obtained from hunting accounts, museum collections, and recent field studies, and analysing whether there is a declining trend over time. Logistic regression analyses of our data support such a decline on Borneo between the mid-19th century and the present. Even when controlled for variation in the size of survey and hunting teams and the durations of expeditions, mean daily encounter rates appear to have declined about 6-fold in areas with little or no forest disturbance.<h4>Conclusions/significance</h4>This finding has potential consequences for our understanding of orangutans, because it suggests that Bornean orangutans once occurred at higher densities. We explore potential explanations-habitat loss and degradation, hunting, and disease-and conclude that hunting fits the observed patterns best. This suggests that hunting has been underestimated as a key causal factor of orangutan density and distribution, and that species population declines have been more severe than previously estimated based on habitat loss only. Our findings may require us to rethink the biology of orangutans, with much of our ecological understanding possibly being based on field studies of animals living at lower densities than they did historically. Our approach of quantifying species encounter rates from historic data demonstrates that this method can yield valuable information about the ecology and population density of species in the past, providing new insight into species' conservation needs.Erik MeijaardAlan WelshMarc AncrenazSerge WichVincent NijmanAndrew J MarshallPublic Library of Science (PLoS)articleMedicineRScienceQENPLoS ONE, Vol 5, Iss 8, p e12042 (2010)
institution	DOAJ
collection	DOAJ
language	EN
topic	Medicine R Science Q
spellingShingle	Medicine R Science Q Erik Meijaard Alan Welsh Marc Ancrenaz Serge Wich Vincent Nijman Andrew J Marshall Declining orangutan encounter rates from Wallace to the present suggest the species was once more abundant.
description	<h4>Background</h4>Bornean orangutans (Pongo pygmaeus) currently occur at low densities and seeing a wild one is a rare event. Compared to present low encounter rates of orangutans, it is striking how many orangutan each day historic collectors like Alfred Russel Wallace were able to shoot continuously over weeks or even months. Does that indicate that some 150 years ago encounter rates with orangutans, or their densities, were higher than now?<h4>Methodology/principal findings</h4>We test this hypothesis by quantifying encounter rates obtained from hunting accounts, museum collections, and recent field studies, and analysing whether there is a declining trend over time. Logistic regression analyses of our data support such a decline on Borneo between the mid-19th century and the present. Even when controlled for variation in the size of survey and hunting teams and the durations of expeditions, mean daily encounter rates appear to have declined about 6-fold in areas with little or no forest disturbance.<h4>Conclusions/significance</h4>This finding has potential consequences for our understanding of orangutans, because it suggests that Bornean orangutans once occurred at higher densities. We explore potential explanations-habitat loss and degradation, hunting, and disease-and conclude that hunting fits the observed patterns best. This suggests that hunting has been underestimated as a key causal factor of orangutan density and distribution, and that species population declines have been more severe than previously estimated based on habitat loss only. Our findings may require us to rethink the biology of orangutans, with much of our ecological understanding possibly being based on field studies of animals living at lower densities than they did historically. Our approach of quantifying species encounter rates from historic data demonstrates that this method can yield valuable information about the ecology and population density of species in the past, providing new insight into species' conservation needs.
format	article
author	Erik Meijaard Alan Welsh Marc Ancrenaz Serge Wich Vincent Nijman Andrew J Marshall
author_facet	Erik Meijaard Alan Welsh Marc Ancrenaz Serge Wich Vincent Nijman Andrew J Marshall
author_sort	Erik Meijaard
title	Declining orangutan encounter rates from Wallace to the present suggest the species was once more abundant.
title_short	Declining orangutan encounter rates from Wallace to the present suggest the species was once more abundant.
title_full	Declining orangutan encounter rates from Wallace to the present suggest the species was once more abundant.
title_fullStr	Declining orangutan encounter rates from Wallace to the present suggest the species was once more abundant.
title_full_unstemmed	Declining orangutan encounter rates from Wallace to the present suggest the species was once more abundant.
title_sort	declining orangutan encounter rates from wallace to the present suggest the species was once more abundant.
publisher	Public Library of Science (PLoS)
publishDate	2010
url	https://doaj.org/article/633292ba41654df7a60c4dac724e3296
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Declining orangutan encounter rates from Wallace to the present suggest the species was once more abundant.

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