Locating emergent trees in a tropical rainforest using data from an Unmanned Aerial Vehicle (UAV)

Emergent trees, which are taller than surrounding trees with exposed crowns, provide crucial services to several rainforest species especially to endangered primates such as gibbons and siamangs (Hylobatidae). Hylobatids show a preference for emergent trees as sleeping sites and for vocal displays, however, they are under threat from both habitat modifications and the impacts of climate change. Traditional plot-based ground surveys have limitations in detecting and mapping emergent trees across a landscape, especially in dense tropical forests. In this study, a method is developed to detect emergent trees in a tropical rainforest in Sumatra, Indonesia, using a photogrammetric point cloud derived from RGB images collected using an Unmanned Aerial Vehicle (UAV). If a treetop, identified as a local maximum in a Digital Surface Model generated from the point cloud, was higher than the surrounding treetops (Trees_EM), and its crown was exposed above its neighbours (Trees_SL; assessed using slope and circularity measures), it was identified as an emergent tree, which might therefore be selected preferentially as a sleeping tree by hylobatids. A total of 54 out of 63 trees were classified as emergent by the developed algorithm and in the field. The algorithm is based on relative height rather than canopy height (due to a lack of terrain data in photogrammetric point clouds in a rainforest environment), which makes it equally applicable to photogrammetric and airborne laser scanning point cloud data

Consistent patterns of common species across tropical tree communities

Trees structure the Earth’s most biodiverse ecosystem, tropical forests. The vast number of tree species presents a formidable challenge to understanding these forests, including their response to environmental change, as very little is known about most tropical tree species. A focus on the common species may circumvent this challenge. Here we investigate abundance patterns of common tree species using inventory data on 1,003,805 trees with trunk diameters of at least 10 cm across 1,568 locations1,2,3,4,5,6 in closed-canopy, structurally intact old-growth tropical forests in Africa, Amazonia and Southeast Asia. We estimate that 2.2%, 2.2% and 2.3% of species comprise 50% of the tropical trees in these regions, respectively. Extrapolating across all closed-canopy tropical forests, we estimate that just 1,053 species comprise half of Earth’s 800 billion tropical trees with trunk diameters of at least 10 cm. Despite differing biogeographic, climatic and anthropogenic histories7, we find notably consistent patterns of common species and species abundance distributions across the continents. This suggests that fundamental mechanisms of tree community assembly may apply to all tropical forests. Resampling analyses show that the most common species are likely to belong to a manageable list of known species, enabling targeted efforts to understand their ecology. Although they do not detract from the importance of rare species, our results open new opportunities to understand the world’s most diverse forests, including modelling their response to environmental change, by focusing on the common species that constitute the majority of their trees

Frugivory in sun bears (Helarctos malayanus) is linked to El Niño-related fluctuations in fruiting phenology, East Kalimantan, Indonesia

Sun bear (Helarctos malayanus) frugivory and fruiting phenology was investigated in a lowland dipterocarp forest in East Kalimantan, Indonesia. Two mast fruiting events, both coinciding with El Niño/Southern Oscillation events, occurred 4 years apart, resulting in large fluctuations in fruit availability. Sun bear fruit availability decreased from 13 trees ha-1 fruiting month-1 during the mast fruiting to 1.6 trees ha-1 fruiting month-1 during the intermast period. Almost 100% of sun bear diet consisted of fruit during mast fruiting period, whereas sun bear diet was predominantly insectivorous during intermast periods. The majority of sun bear fruit trees displayed 'mast-fruiting' and 'supra-annual' fruiting patterns, indicating sporadic productivity. Sun bears fed on 115 fruit species covering 54 genera and 30 families, with Ficus (Moraceae) being the main fallback fruit. The families Moraceae, Burseraceae, and Myrtaceae contributed more than 50% to the sun bear fruit diet. Sun bear fruit feeding observations were unevenly distributed over forest types with more observations in high-dry forest type despite fewer fruiting events, possibly due to a side-effect of high insect abundance that causes bears to use these areas more intensively. The possible evolutionary pathways of sun bears in relation to the Sundaic environment are discussed

Geographic variation in Thomas Langur (Presbytes thomasi) loud calls

Geographic variation in primate vocalizations has been described at two levels. First, at the level of acoustic variation within the same call type between populations and, second, at the level of presence or absence of certain call types in different populations. Acoustic variation is of interest because there are several factors that can explain this variation, such as gene flow, ecological factors and population density. Here we focus on the first level in a Southeast Asian primate, the Thomas langur. We recorded male loud calls in four populations that differed in their geographic distances from each other and had varying geographic barriers in between them, such as rivers and mountain ranges. The presence of these barriers leads to expectations of loud call variation under the gene flow model, which are examined here. We conducted a principal components analysis to condense the number of acoustic variables. With a subsequent discriminant function analysis on the six principal component scores, we found that the percentage of loud calls that were correctly assigned to a population was relatively high (50.0–76.2%) when three randomly selected loud calls from each male were used. Using the discriminant functions from this analysis to predict population membership of the remainder of the loud calls yielded lower, but still relatively high correct assignment percentages (26.2–66.7%). Analyses to examine the influence of barriers on similarities between populations confirm our expectations. We discuss that differences in loud calls are probably most parsimoniously explained by gene flow (or the lack thereof) between the populations and that future studies of genetic differences are crucial to test this hypothesis

Geographic variation in Thomas Langur (Presbytes thomasi) loud calls

Geographic variation in primate vocalizations has been described at two levels. First, at the level of acoustic variation within the same call type between populations and, second, at the level of presence or absence of certain call types in different populations. Acoustic variation is of interest because there are several factors that can explain this variation, such as gene flow, ecological factors and population density. Here we focus on the first level in a Southeast Asian primate, the Thomas langur. We recorded male loud calls in four populations that differed in their geographic distances from each other and had varying geographic barriers in between them, such as rivers and mountain ranges. The presence of these barriers leads to expectations of loud call variation under the gene flow model, which are examined here. We conducted a principal components analysis to condense the number of acoustic variables. With a subsequent discriminant function analysis on the six principal component scores, we found that the percentage of loud calls that were correctly assigned to a population was relatively high (50.0–76.2%) when three randomly selected loud calls from each male were used. Using the discriminant functions from this analysis to predict population membership of the remainder of the loud calls yielded lower, but still relatively high correct assignment percentages (26.2–66.7%). Analyses to examine the influence of barriers on similarities between populations confirm our expectations. We discuss that differences in loud calls are probably most parsimoniously explained by gene flow (or the lack thereof) between the populations and that future studies of genetic differences are crucial to test this hypothesis

Vocal fold control beyond the species-specific repertoire in an orang-utan

Vocal fold control was critical to the evolution of spoken language, much as it today allows us to learn vowel systems. It has, however, never been demonstrated directly in a non-human primate, leading to the suggestion that it evolved in the human lineage after divergence from great apes. Here, we provide the first evidence for real-time, dynamic and interactive vocal fold control in a great ape during an imitation “do-as-I-do” game with a human demonstrator. Notably, the orang- utan subject skilfully produced “wookies” – an idiosyncratic vocalization exhibiting a unique spectral profile among the orang-utan vocal repertoire. The subject instantaneously matched human-produced wookies as they were randomly modulated in pitch, adjusting his voice frequency up or down when the human demonstrator did so, readily generating distinct low vs. high frequency sub-variants. These sub-variants were significantly different from spontaneous ones (not produced in matching trials). Results indicate a latent capacity for vocal fold exercise in a great ape (i) in real-time, (ii) up and down the frequency spectrum, (iii) across a register range beyond the species-repertoire and, (iv) in a co-operative turn-taking social setup. Such ancestral capacity likely provided the neuro-behavioural basis of the more fine-tuned vocal fold control that is a human hallmark