Lydia Beaudrot

Primate communities are structured more by dispersal limitation than by niches

1. A major goal in community ecology is to identify mechanisms that govern the assembly and maintenance of ecological communities. Current models of metacommunity dynamics differ chiefly in the relative emphasis placed on dispersal limitation and niche differentiation as causal mechanisms structuring ecological communities. Herein we investigate the relative roles of these two mechanisms in structuring primate communities in Africa, South America, Madagascar and Borneo. 2. We hypothesized that if dispersal limitation is important in structuring communities, then community similarity should depend on geographical proximity even after controlling for ecological similarity. Conversely, if communities are assembled primarily through niche processes, then community similarity should be determined by ecological similarity regardless of geographical proximity. 3. We performed Mantel and partial Mantel tests to investigate correlations among primate community similarity, ecological distance and geographical distance. Results showed significant and strongly negative relationships between diurnal primate community similarity and both ecological similarity and geographical distance in Madagascar, but significant and stronger negative relationships between community similarity and geographical distance in African, South American and Bornean metacommunities. 4. We conclude that dispersal limitation is an important determinant of primate community structure and may play a stronger role in shaping the structure of some terrestrial vertebrate communities than niche differentiation. These patterns are consistent with neutral theory. We recommend tests of functional equivalence to determine the extent to which neutral theory may explain primate community composition.

Responses of Primates and Other Frugivorous Vertebrates to Plant Resource Variability over Space and Time at Gunung Palung National Park

Identifying patterns of primate diversity and abundance over space and time provides a window into the ecological processes that influence species distributions and community composition. Long-term studies of primate communities across multiple habitat types at small spatial scales are rare, yet can improve our understanding of habitat and resource use. Within primate community ecology, there has been recent interest in studying primate species in the context of the broader faunal communities of which they are a part because interactions with ecologically similar but distantly related species may influence habitat use. We present the results of a 64-mo study of 10 vertebrate frugivore species with highly overlapping diets inhabiting seven distinct forest types at the Cabang Panti Research Station, West Kalimantan, Indonesia. We used survey transects and phenology plots to measure variation in vertebrate population densities (four primate, three hornbill, two squirrel, and one pig species) and fruit resources over space and time. We found little evidence of habitat partitioning or specialization. Densities of all 10 frugivore species, however, varied spatially, due largely to elevation and forest structure. Ordination analyses demonstrated that forest types differed in their structure, floristic composition, plant phenology, and frugivore communities. We also documented substantial temporal variation in orangutan densities, reflecting movements over large spatial scales. The densities of other mammalian and avian frugivores, particularly other primates, varied comparatively little over time. Our results demonstrate the importance of forest structure for determining frugivore community structure and highlight the importance of lowland forest types for the conservation of tropical frugivores.

Co-occurrence patterns of Bornean vertebrates suggest competitive exclusion is strongest among distantly related species

Assessing the importance of deterministic processes in structuring ecological communities is a central focus of community ecology. Typically, community ecologists study a single taxonomic group, which precludes detection of potentially important biotic interactions between distantly related species, and inherently assumes competition is strongest between closely related species. We examined distribution patterns of vertebrate species across the island of Borneo in Southeast Asia to assess the extent to which inter-specific competition may have shaped ecological communities on the island and whether the intensity of inter-specific competition in present-day communities varies as a function of evolutionary relatedness. We investigated the relative extent of competition within and between species of primates, birds, bats and squirrels using species presence–absence and attribute data compiled for 21 forested sites across Borneo. We calculated for each species pair the checkerboard unit value (CU), a statistic that is often interpreted as indicating the importance of interspecific competition. The percentage of species pairs with significant CUs was lowest in within-taxon comparisons. Moreover, for invertebrate-eating species the percentage of significantly checkerboarded species pairs was highest in comparisons between primates and other taxa, particularly birds and squirrels. Our results are consistent with the interpretation that competitive interactions between distantly related species may have shaped the distribution of species and thus the composition of Bornean vertebrate communities. This research highlights the importance of taking into account the broad mammalian and avian communities in which species occur for understanding the factors that structure biodiversity.

Climate and species richness predict the phylogenetic structure of African mammal communities

We have little knowledge of how climatic variation (and by proxy, habitat variation) influences the phylogenetic structure of tropical communities. Here, we quantified the phylogenetic structure of mammal communities in Africa to investigate how community structure varies with respect to climate and species richness variation across the continent. In addition, we investigated how phylogenetic patterns vary across carnivores, primates, and ungulates. We predicted that climate would differentially affect the structure of communities from different clades due to between-clade biological variation. We examined 203 communities using two metrics, the net relatedness (NRI) and nearest taxon (NTI) indices. We used simultaneous autoregressive models to predict community phylogenetic structure from climate variables and species richness. We found that most individual communities exhibited a phylogenetic structure consistent with a null model, but both climate and species richness significantly predicted variation in community phylogenetic metrics. Using NTI, species rich communities were composed of more distantly related taxa for all mammal communities, as well as for communities of carnivorans or ungulates. Temperature seasonality predicted the phylogenetic structure of mammal, carnivoran, and ungulate communities, and annual rainfall predicted primate community structure. Additional climate variables related to temperature and rainfall also predicted the phylogenetic structure of ungulate communities. We suggest that both past interspecific competition and habitat filtering have shaped variation in tropical mammal communities. The significant effect of climatic factors on community structure has important implications for the diversity of mammal communities given current models of future climate change.

Do epigeal termite mounds increase the diversity of plant habitats in a tropical rain forest in peninsular Malaysia

The extent to which environmental heterogeneity can account for tree species coexistence in diverse ecosystems, such as tropical rainforests, is hotly debated, although the importance of spatial variability in contributing to species co-existence is well recognized. Termites contribute to the micro-topographical and nutrient spatial heterogeneity of tropical forests. We therefore investigated whether epigeal termite mounds could contribute to the coexistence of plant species within a 50 ha plot at Pasoh Forest Reserve, Malaysia. Overall, stem density was significantly higher on mounds than in their immediate surroundings, but tree species diversity was significantly lower. Canonical correspondence analysis showed that location on or off mounds significantly influenced species distribution when stems were characterized by basal area. Like studies of termite mounds in other ecosystems, our results suggest that epigeal termite mounds provide a specific microhabitat for the enhanced growth and survival of certain species in these species-rich tropical forests. However, the extent to which epigeal termite mounds facilitate species coexistence warrants further investigation.

The Influences of Species Richness and Climate on the Phylogenetic Structure of African Haplorhine and Strepsirrhine Primate Communities

Many factors contribute to the structure of primate communities, including historical processes, interspecific competition, and climate. Here, we quantify the phylogenetic structure of individual primate communities to evaluate these factors relative to a null model. Then, we examine the effects of species richness and local climate on variation in community phylogenetic structure. We analyze 71 haplorhine and 29 strepsirrhine communities in Africa and quantify their net relatedness (NRI) and nearest taxon (NTI) indices. Significantly low, i.e., phylogenetically even, NRI and NTI values are indicative of interspecific competition in the past, resulting in closely related species not being found in the same community. In contrast, significantly high, i.e., phylogenetically clustered, NRI and NTI values suggest that closely related species have similar ecological requirements, resulting in closely related species occupying the same community. In a second set of analyses, we used simultaneous autoregressive models to examine if species richness, rainfall, and temperature predict variation in community phylogenetic structure. Most individual communities exhibited phylogenetically random species assemblages. However, significantly structured haplorhine communities were even whereas strepsirrhine communities were clustered. Species richness significantly predicted variation in haplorhine phylogenetic structure, whereas abiotic factors significantly predicted variation in strepsirrhine phylogenetic structure. We suggest that past interspecific competition and habitat filtering have affected a relatively small proportion of African primate communities, but that past interspecific competition has more strongly influenced haplorhine communities whereas environmental conditions have more strongly influenced strepsirrhine communities. Our study illustrates the utility of phylogenetic metrics and spatially explicit models for understanding primate communities.

Strong influence of palaeoclimate on the structure of modern African mammal communities.

Ecological research often assumes that species are adapted to their current climatic environments. However, climate fluctuations over geologic timescales have influenced species dispersal and extinction, which in turn may affect community structure. Modern community structure is likely to be the product of both palaeoclimate and modern climate, with the relative degrees of influence of past and present climates unknown. Here, we assessed the influence of climate at different time periods on the phylogenetic and functional trait structure of 203 African mammal communities. We found that the climate of the mid-Holocene (approx. 6000 years ago) and Last Glacial Maximum (approx. 22 000 years ago) were frequently better predictors of community structure than modern climate for mammals overall, carnivorans and ungulates. Primate communities were more strongly influenced by modern climate than palaeoclimate. Overall, community structure of African mammals appears to be related to the ecological flexibility of the groups considered here and the regions of continental Africa that they occupy. Our results indicate that the future redistribution, expansion and contraction of particular biomes due to human activity, such as climate and land-use change, will differentially affect mammal groups that vary in their sensitivity to environmental change.

Why male orangutans do not kill infants

Infanticide is widespread among mammals, is particularly common in primates, and has been shown to be an adaptive male strategy under certain conditions. Although no infanticides in wild orangutans have been reported to date, several authors have suggested that infanticide has been an important selection pressure influencing orangutan behavior and the evolution of orangutan social systems. In this paper, we critically assess this suggestion. We begin by investigating whether wild orangutans have been studied for a sufficiently long period that we might reasonably expect to have detected infanticide if it occurs. We consider whether orangutan females exhibit counterstrategies typically employed by other mammalian females. We also assess the hypothesis that orangutan females form special bonds with particular “protector males” to guard against infanticide. Lastly, we discuss socioecological reasons why orangutan males may not benefit from infanticide. We conclude that there is limited evidence for female counterstrategies and little support for the protector male hypothesis. Aspects of orangutan paternity certainty, lactational amenorrhea, and ranging behavior may explain why infanticide is not a strategy regularly employed by orangutan males on Sumatra or Borneo.

African Primate Assemblages Exhibit a Latitudinal Gradient in Dispersal Limitation

Recent studies have demonstrated that dispersal limitation, which refers to the limited ability of individuals to reach distant geographic areas, is an important influence on the species that are found in primate assemblages. In this study, we investigate the relative influences of dispersal limitation and environmental filtering in 131 African primate assemblages in 9 biogeographic regions throughout sub-Saharan Africa. Specifically, we evaluate the dispersal-ecological specialization hypothesis, which posits that there are trade-offs between dispersal ability and ecological specialization that are influenced by climatic variation along latitudinal gradients. The hypothesis predicts that species in assemblages near the equator, where climatic conditions are more stable, will exhibit stronger dispersal limitation and greater ecological specialization than species within assemblages located further from the equator, where climate is more variable. In contrast, assemblages located at higher latitudes are expected to be influenced more strongly by environmental filtering than dispersal limitation. We used hierarchical cluster analysis to identify regions, conducted partial Mantel tests to evaluate the contributions of dispersal limitation and environmental filtering in each region, and evaluated predictors of those contributions with linear regression. In all regions, dispersal limitation was a stronger predictor of community similarity than was environmental filtering, yet the strength of dispersal limitation varied. Dispersal limitation was greatest at low latitudes and declined with increasing absolute latitude. Thus, primate assemblages exhibited a significant latitudinal gradient in dispersal limitation, but not in environmental filtering. These results support aspects of the dispersal-ecological specialization hypothesis and call for future mechanistic studies to address this broad-scale pattern.

Dietary diversity, feeding selectivity, and responses to fruit scarcity of two sympatric Bornean primates (Hylobates albibarbis and Presbytis rubicunda rubida)

Effectively characterizing primate diets is fundamental to understanding primate behavior, ecology and morphology. Examining temporal variation in a species’ diet, as well as comparing the responses of different species to variation in resource availability, can enhance understanding of the evolution of morphology and socioecology. In this study, we use feeding data collected over five years to describe the diets of two sympatric Southeast Asian primate species of similar body size: white-bearded gibbons (Hylobates albibarbis) and red leaf monkeys (Presbytis rubicunda rubida), in Gunung Palung National Park, West Kalimantan, Indonesia. Long-term data sets are especially important for characterizing primate diets in Southeast Asia, where the forests exhibit supra-annual mast fruiting events. We found that gibbons were mainly frugivorous, with fruit and figs comprising 70% of their 145 independent feeding observations, whereas leaf monkeys ate a substantial amount of seeds (26%), fruits and figs (26.5%) and leaves (30%, n = 219 independent feeding observations). Leaf monkeys consumed a higher number of plant genera, and this was due mostly to the non-frugivorous portion of their diet. To investigate resource selection by these primates we utilized two different approaches: the Manly Selectivity Ratio, which did not take into account temporal variation of resource availability, and a model selection framework which did incorporate temporal variation. Both species selected figs (Ficus) more than predicted based on their availability under the Manly Selectivity Ratio. Model selection allowed us to determine how these primates alter the proportion of leaves, flowers, seeds, figs and fruit in their diets in response to variation in fruit availability. When fruits were scarce, both gibbons and leaf monkeys incorporated more leaves and figs into their diets, indicating that these two food classes are fallback foods for these primates. We discuss how different measures of resource selection can provide seemingly contradictory results, and emphasize the importance of long term studies that combine independent feeding observations with rigorous assessment of temporal variation in resource availability when modelling feeding selectivity.