Development of foraging skills in two orangutan populations: needing to learn or needing to grow?

Abstract

BackgroundOrangutans have one of the slowest-paced life histories of all mammals. Whereas life-history theory suggests that the time to reach adulthood is constrained by the time needed to reach adult body size, the needing-to-learn hypothesis instead suggests that it is limited by the time needed to acquire adult-level skills.To test between these two hypotheses, we compared the development of foraging skills and growth trajectories of immature wild orangutans in two populations: at Tuanan (Pongo pygmaeus wurmbii), Borneo, and Suaq Balimbing (Pongo abelii), Sumatra. We collected behavioral data on diet repertoire, feeding rates and ranging competence during focal follows, and estimated growth through non-invasive laser photogrammetry.ResultsWe found that adult-like diet repertoires are attained around the age of weaning and that female immatures increase their repertoire size faster than their male peers. Adult-level feeding rates of easy techniques are reached just after weaning, but several years later for more difficult techniques, albeit always before adulthood (i.e. age at first reproduction). Independent immatures had faster feeding rates for easy to process items than their mothers, with male immatures achieving faster feeding rates earlier in development relative to females. Sumatran immatures reach adult-level feeding rates 2–3 years later than their Bornean peers, in line with their higher dietary complexity and later weaning. The range-use competence of independently ranging and weaned immatures is similar to that of adult females. Body size measurements showed, immatures grow until female age of first reproduction.ConclusionsIn conclusion, unlike in humans, orangutan foraging skills are in place prior to reproduction. Growth trajectories suggest that energetic constraints, rather than skills, best explain the length of immaturity. However, skill competence for dietary independence is reached later where the adult niche is more complex, which is consistent with the relatively later weaning age with increasing brain size found generally in primates, and apes in particular.Electronic supplementary materialThe online version of this article (doi:10.1186/s12983-016-0178-5) contains supplementary material, which is available to authorized users.

Body growth and life history in wild mountain gorillas (Gorilla beringei beringei) from Volcanoes National Park, Rwanda

“…Our ability to test this hypothesis is currently limited by the scarcity of comparable data from other wild great ape populations. Schuppli et al (; Figure 4a,b) found that wild female orangutans reach maximum arm length at 12.5–15.0 years of age, which is in broad agreement with mountain gorillas. However, with this and other notable exceptions (chimpanzee body mass: Machanda et al, ; Pusey et al, ), body size growth in known‐aged great apes is best documented from captive environments (e.g., Leigh, ).…”

“…Continued longitudinal study of body size growth in Virunga mountain gorillas, coupled with investigations of how milestones of physical, behavioral and reproductive milestones covary among individuals in this and other wild gorilla populations (e.g., as reported recently in chimpanzees; Thompson et al, ), are necessary to better understand the influence of social and ecological environments and changing demographics on developmental life history within the genus Gorilla . This work will also contribute to a growing database on the physical ontogeny of other great ape taxa in natural settings (Pusey et al, ; Machanda et al, ; Schuppli et al, ), enabling future comparative studies.…”

“…Available data suggest that female western chimpanzees from Taï Forest cease linear skeletal growth by 12.5–16.5 years of age, which overlaps with age at first birth (Boesch & Boesch‐Achermann, ; Zihlman, Bolter, & Boesch, 2007). However, until we have comparable data across wild populations (Machanda et al, ; Schuppli et al, ), this limits our ability to understand how great ape mothers may vary in prioritizing resources towards their own growth versus reproduction.…”

“…Long‐term data accumulating across great ape study sites is demonstrating considerable diversity in life history characteristics within and among species (Breuer et al, ; Robbins et al, ; Stoinski, Perdue, Breuer, & Hof, ), and in other factors such as habitat use, daily travel distance, feeding ecology, arboreality and energy intake rate, which are relevant to understanding life history strategies (e.g., Doran et al, ; Leigh & Blomquist, ; Masi, Cipolletta, & Robbins, ; Rogers et al, ; Wich et al, ; van Noordwijk & van Schaik, ; Wright et al, ). However, quantitative studies of the physical growth and development of known‐aged great apes have been overwhelmingly derived from captive environments or less well documented museum collections (e.g., Shea, ; Taylor, ), with notable exceptions [e.g., orangutan arm length (Schuppli et al, ); chimpanzee body weight, linear dimensions, brain size and tooth emergence (e.g., Machanda et al, ; Neubauer, Gunz, Schwarz, Hublin, & Boesch, ; Pusey, Oehlert, Williams, & Goodall, ; Smith & Boesch, ; Smith et al, ; Zihlman, Bolter, & Boesch, ); western gorilla body length (Breuer et al, ); mountain gorilla brain size and dental development (McFarlin et al, ; Kralick et al, 2017)]. As captive environments differ significantly from natural settings, systematic investigations of factors influencing variation in postnatal ontogeny in the wild are critical for a comprehensive understanding of socio‐ecological influences on ape life history and a more salient comparative framework for understanding human life history evolution.…”

Correction to: development of foraging skills in two orangutan populations: needing to learn or needing to grow?

“…Upon publication of this article [1] it was noticed corrections were not carried out correctly and subsequently figure placement and some figure citations were incorrect. The original article has now been updated to reflect the correct figure placement and their respective citations within the text and the publisher apologizes for any inconvenience caused.…”