Meredith L. Bastian

An estimate of the number of tropical tree species

Significance People are fascinated by the amazing diversity of tropical forests and will be surprised to learn that robust estimates of the number of tropical tree species are lacking. We show that there are at least 40,000, but possibly more than 53,000, tree species in the tropics, in contrast to only 124 across temperate Europe. Almost all tropical tree species are restricted to their respective continents, and the Indo-Pacific region appears to be as species-rich as tropical America, with each of these two regions being almost five times as rich in tree species as African tropical forests. Our study shows that most tree species are extremely rare, meaning that they may be under serious risk of extinction at current deforestation rates. The high species richness of tropical forests has long been recognized, yet there remains substantial uncertainty regarding the actual number of tropical tree species. Using a pantropical tree inventory database from closed canopy forests, consisting of 657,630 trees belonging to 11,371 species, we use a fitted value of Fisher’s alpha and an approximate pantropical stem total to estimate the minimum number of tropical forest tree species to fall between ∼40,000 and ∼53,000, i.e., at the high end of previous estimates. Contrary to common assumption, the Indo-Pacific region was found to be as species-rich as the Neotropics, with both regions having a minimum of ∼19,000–25,000 tree species. Continental Africa is relatively depauperate with a minimum of ∼4,500–6,000 tree species. Very few species are shared among the African, American, and the Indo-Pacific regions. We provide a methodological framework for estimating species richness in trees that may help refine species richness estimates of tree-dependent taxa.

Effects of Pleistocene glaciations and rivers on the population structure of Bornean orangutans (Pongo pygmaeus)

Sundaland, a tropical hotspot of biodiversity comprising Borneo and Sumatra among other islands, the Malay Peninsula, and a shallow sea, has been subject to dramatic environmental processes. Thus, it presents an ideal opportunity to investigate the role of environmental mechanisms in shaping species distribution and diversity. We investigated the population structure and underlying mechanisms of an insular endemic, the Bornean orangutan (Pongo pygmaeus). Phylogenetic reconstructions based on mtDNA sequences from 211 wild orangutans covering the entire range of the species indicate an unexpectedly recent common ancestor of Bornean orangutans 176 ka (95% highest posterior density, 72–322 ka), pointing to a Pleistocene refugium. High mtDNA differentiation among populations and rare haplotype sharing is consistent with a pattern of strong female philopatry. This is corroborated by isolation by distance tests, which show a significant correlation between mtDNA divergence and distance and a strong effect of rivers as barriers for female movement. Both frequency-based and Bayesian clustering analyses using as many as 25 nuclear microsatellite loci revealed a significant separation among all populations, as well as a small degree of male-mediated gene flow. This study highlights the unique effects of environmental and biological features on the evolutionary history of Bornean orangutans, a highly endangered species particularly vulnerable to future climate and anthropogenic change as an insular endemic.

Soils on exposed Sunda Shelf shaped biogeographic patterns in the equatorial forests of Southeast Asia

The marked biogeographic difference between western (Malay Peninsula and Sumatra) and eastern (Borneo) Sundaland is surprising given the long time that these areas have formed a single landmass. A dispersal barrier in the form of a dry savanna corridor during glacial maxima has been proposed to explain this disparity. However, the short duration of these dry savanna conditions make it an unlikely sole cause for the biogeographic pattern. An additional explanation might be related to the coarse sandy soils of central Sundaland. To test these two nonexclusive hypotheses, we performed a floristic cluster analysis based on 111 tree inventories from Peninsular Malaysia, Sumatra, and Borneo. We then identified the indicator genera for clusters that crossed the central Sundaland biogeographic boundary and those that did not cross and tested whether drought and coarse-soil tolerance of the indicator genera differed between them. We found 11 terminal floristic clusters, 10 occurring in Borneo, 5 in Sumatra, and 3 in Peninsular Malaysia. Indicator taxa of clusters that occurred across Sundaland had significantly higher coarse-soil tolerance than did those from clusters that occurred east or west of central Sundaland. For drought tolerance, no such pattern was detected. These results strongly suggest that exposed sandy sea-bed soils acted as a dispersal barrier in central Sundaland. However, we could not confirm the presence of a savanna corridor. This finding makes it clear that proposed biogeographic explanations for plant and animal distributions within Sundaland, including possible migration routes for early humans, need to be reevaluated.

Diet Traditions in Wild Orangutans

This study explores diet differences between two populations of wild Bornean orangutans (Pongo pygmaeus wurmbii) to assess whether a signal of social learning can be detected in the observed patterns. The populations live in close proximity and in similar habitats but are separated by a river barrier that is impassable to orangutans in the study region. We found a 60% between-site difference in diet at the level of plant food items (plant species-organ combinations). We also found that individuals at the same site were more likely to eat the same food items than expected by chance. These results suggest the presence of diet (food selection) traditions. Detailed tests of three predictions of three models of diet acquisition allowed us to reject a model based on exclusive social learning but could not clearly distinguish between the remaining two models: one positing individual exploration and learning of food item selection and the other one positing preferential social learning followed by individual fine tuning. We know that maturing orangutans acquire their initial diet through social learning and then supplement it by years of low-level, individual sampling. We, therefore, conclude that the preferential social learning model produces the best fit to the geographic patterns observed in this study. However, the very same taxa that socially acquire their diets as infants and show evidence for innovation-based traditions in the wild paradoxically may have diets that are not easily distinguished from those acquired exclusively through individual learning.

Call cultures in orang-utans?

Background Several studies suggested great ape cultures, arguing that human cumulative culture presumably evolved from such a foundation. These focused on conspicuous behaviours, and showed rich geographic variation, which could not be attributed to known ecological or genetic differences. Although geographic variation within call types (accents) has previously been reported for orang-utans and other primate species, we examine geographic variation in the presence/absence of discrete call types (dialects). Because orang-utans have been shown to have geographic variation that is not completely explicable by genetic or ecological factors we hypothesized that this will be similar in the call domain and predict that discrete call type variation between populations will be found. Methodology/Principal Findings We examined long-term behavioural data from five orang-utan populations and collected fecal samples for genetic analyses. We show that there is geographic variation in the presence of discrete types of calls. In exactly the same behavioural context (nest building and infant retrieval), individuals in different wild populations customarily emit either qualitatively different calls or calls in some but not in others. By comparing patterns in call-type and genetic similarity, we suggest that the observed variation is not likely to be explained by genetic or ecological differences. Conclusion/Significance These results are consistent with the potential presence of ‘call cultures’ and suggest that wild orang-utans possess the ability to invent arbitrary calls, which spread through social learning. These findings differ substantially from those that have been reported for primates before. First, the results reported here are on dialect and not on accent. Second, this study presents cases of production learning whereas most primate studies on vocal learning were cases of contextual learning. We conclude with speculating on how these findings might assist in bridging the gap between vocal communication in non-human primates and human speech.

Paternal Care in Propithecus verreauxi coquereli

Alloparental behavior is documented for several anthropoid primates, but few researchers have investigated the extent or variability of such behavior in prosimians. We report results from a study of male-infant interactions in 2 groups of Coquerel’s sifaka (Propithecus verreauxi coquereli) at the Duke University Primate Center (DUPC). Both groups contained 1 adult pair, 2 juveniles, and a newborn. The adult males exhibited paternal behavior toward their offspring in the form of grooming and holding the infant, though males differed in the amount of time they spent engaged in these activities. Group differences in the proximity maintained between the infants’ parents suggest that the relationship between adult males and females may help account for the variation. The presence of juveniles appeared to diminish paternal behavior in the group exhibiting a higher overall rate of male-infant interaction.

Maximum ingested food size in captive anthropoids.

OBJECTIVES Maximum ingested food size (Vb ) is an empirically tested performance variable that can shed light on feeding energetics and adaptation in the masticatory system. Until now, this variable had been tested in strepsirrhines alone among primates. Here, we present the first data on Vb in a broad sample of anthropoid primates and describe scaling patterns. MATERIALS AND METHODS Vb data on anthropoids were collected under captive conditions at the Philadelphia Zoo and compared with published data on strepsirrhines. Data on Vb were scaled against individual body mass and were compared with experimentally determined toughness and stiffness values for the test foods. RESULTS Unlike in strepsirrhines, where essentially Vb scales isometrically with body mass, Vb in anthropoids scales with negative allometry. There is a significant effect of food material properties on Vb , although bite size in anthropoids varies less based on food properties than in strepsirrhines. Large folivorous strepsirrhines follow the anthropoid trend in bite size scaling, but large frugivorous ones take especially large bites. DISCUSSION Negative scaling of bite size in the anthropoids sampled could be due to reduced adaptation for gape. Some early anthropoids likely evolved adaptations for maximizing mechanical advantage and fatigue resistance in the chewing muscles, resulting in reduced gape. This might have channeled them toward smaller bites of more-resistant foods and away from taking large bites. This might also be the case for some folivorous strepsirrhines.

Innovative behaviors in wild Bornean orangutans revealed by targeted population comparison

The aim of this study was to assess whether geographic variation in wild orangutan behavior reflected the presence of innovations or merely variation induced by genetic or environmental differences. We improved upon previous attempts to answer this question in three complementary ways. First, to minimize the possible effects of differences in genetic composition or the physical, biological and social environment, we compared a population of Bornean orangutans (Pongo pygmaeus wurmbii) at a new site (Sungai Lading) with that of an established site (Tuanan). These two populations were physically separated but showed high genetic similarity and occupied very similar habitats, leaving different innovation histories as the only plausible source of significant differences in their behavioral repertoires, if these were found. Second, we used identical observation methods and overlapping observers at both sites, deliberately attempting to record the full behavioral repertoire. Third, we introduced statistical techniques to reduce the likelihood of false absences. The results showed several behavior patterns unique to the new site, as well as the absence of several patterns observed at the established site, most of them satisfying the criteria previously proposed for recognizing innovations. We, thus, confirm that orangutans produce behavioral innovations, and conclude that the geographic method for identifying innovations in wild populations is a valid, albeit conservative, approach that can complement other techniques. Finally, the results also strongly support a cultural interpretation of geographic variation in orangutan behavior.

On the concept of animal innovation and the challenge of studying innovation in the wild

The commentaries have both drawn out the implications of, and challenged, our definition and operationalization of innovation. In this response, we reply to these concerns, discuss the differences between our operationalization and the preexisting operationalization if innovation, and make suggestions for the advancement of the challenging and exciting field of animal innovation.