Locomotor ecology of wild orangutans (Pongo pygmaeus abelii) in the Gunung Leuser Ecosystem, Sumatra, Indonesia: a multivariate analysis using log-linear modelling.

The large body mass and exclusively arboreal lifestyle of Sumatran orangutans identify them as a key species in understanding the dynamic between primates and their environment. Increased knowledge of primate locomotor ecology, coupled with recent developments in the standardization of positional mode classifications (Hunt et al. [1996] Primates 37:363-387), opened the way for sophisticated multivariate statistical approaches, clarifying complex associations between multiple influences on locomotion. In this study we present a log-linear modelling approach used to identify key associations between orangutan locomotion, canopy level, support use, and contextual behavior. Log-linear modelling is particularly appropriate because it is designed for categorical data, provides a systematic method for testing alternative hypotheses regarding interactions between variables, and allows interactions to be ranked numerically in terms of relative importance. Support diameter and type were found to have the strongest associations with locomotor repertoire, suggesting that orangutans have evolved distinct locomotor modes to solve a variety of complex habitat problems. However, height in the canopy and contextual behavior do not directly influence locomotion: instead, their effect is modified by support type and support diameter, respectively. Contrary to classic predictions, age-sex category has only limited influence on orangutan support use and locomotion, perhaps reflecting the presence of arboreal pathways which individuals of all age-sex categories follow. Effects are primarily related to a tendency for adult, parous females to adopt a more cautious approach to locomotion than adult males and immature subjects.

[1]  K. Hunt.  Body size effects on vertical climbing among chimpanzees , 1994, International Journal of Primatology.

[2]  Gn Gilbert,et al.  Modelling society: an introduction to loglinear analysis for social researchers , 1982, American Political Science Review.

[3]  J. Mackinnon.  The behaviour and ecology of wild orang-utans (Pongo pygmaeus) , 1974 .

[4]  A. Crook.  Determinants of the physiological colour patterns of juvenile parrotfish, Chlorurus sordidus , 1997, Animal Behaviour.

[5]  T. Grand.  2. Motion Economy Within the Canopy: Four Strategies for Mobility , 1984 .

[6]  M. Cartmill.  2 – Pads and Claws in Arboreal Locomotion , 1974 .

[7]  B. Tabachnick,et al.  Using Multivariate Statistics , 1983 .

[8]  J. Cant.  Positional behavior of female bornean orangutans (Pongo pygmaeus) , 1987, American journal of primatology.

[9]  Theodore Grand,et al.  A mechanical interpretation of terminal branch feeding , 1972 .

[10]  M. Remis,et al.  Effects of body size and social context on the arboreal activities of lowland gorillas in the Central African Republic. , 1995, American journal of physical anthropology.

[11]  S. Wich,et al.  Food Competition Between Wild Orangutans in Large Fig Trees , 1997, International Journal of Primatology.

[12]  R. Crompton.  3. Foraging, Habitat Structure, and Locomotion in Two Species of Galago , 1984 .

[13]  M. Dagosto.  Testing positional behavior of malagasy lemurs: a randomization approach. , 1994, American journal of physical anthropology.

[14]  Kevin D. Hunt,et al.  Standardized descriptions of primate locomotor and postural modes , 1996, Primates.

[15]  Peter Aerts,et al.  The biomechanical evolution of erect bipedality , 2003 .

[16]  M. Ruvolo.  Molecular evolutionary processes and conflicting gene trees: the hominoid case. , 1994, American journal of physical anthropology.

[17]  K. Hunt.  Social rank and body size as determinants of positional behavior inPan troglodytes , 1992, Primates.

[18]  K. Hunt.  Mechanical implications of chimpanzee positional behavior. , 1991, American journal of physical anthropology.

[19]  P. Rodman.  5. Foraging and Social Systems of Orangutans and Chimpanzees , 1984 .

[20]  D. Doran,et al.  Comparison of instantaneous and locomotor bout sampling methods: a case study of adult male chimpanzee locomotor behavior and substrate use. , 1992, American journal of physical anthropology.

[21]  H. Rijksen.  A field study on Sumatran orang utans (Pongo pygmaeus abelii Lesson 1827) : ecology, behaviour and conservation , 1978 .

[22]  J. Prost.  A Definitional System for the Classification of Primate Locomotion , 1965 .

[23]  R. Crompton,et al.  Locomotor ecology of Lepilemur edwardsi and Avahi occidentalis. , 1997, American journal of physical anthropology.

[24]  A. Agresti,et al.  Categorical Data Analysis , 1991, International Encyclopedia of Statistical Science.

[25]  C. R. Taylor,et al.  Running Up and Down Hills: Some Consequences of Size , 1972, Science.

[26]  S. Boinski.  The positional behavior and substrate use of squirrel monkeys: ecological implications , 1989 .

[27]  J. Cant.  Positional behavior and body size of arboreal primates: a theoretical framework for field studies and an illustration of its application. , 1992, American journal of physical anthropology.

[28]  J. Van Hooff,et al.  Age-sex class differences in the positional behaviour of the Sumatran orang-utan (Pongo pygmaeus abelii) in the Gunung Leuser National Park, Indonesia. , 1986, Folia primatologica; international journal of primatology.

[29]  J. Cant,et al.  Effects of sexual dimorphism in body size on feeding postural behavior of Sumatran orangutans (Pongo pygmaeus) , 1987 .

[30]  M. Cartmill.  Arboreal Adaptations and the Origin of the Order Primates , 1972 .

[31]  C. P. Schaik,et al.  Spatial variation in the structure and litterfall of a Sumatran rain forest , 1985 .

[32]  M. Cartmill,et al.  The lorisiform wrist joint and the evolution of "brachiating" adaptations in the hominoidea. , 1977, American journal of physical anthropology.