Interactions between all pairs of neighboring trees in 16 forests worldwide reveal details of unique ecological processes in each forest, and provide windows into their evolutionary histories.

When Darwin visited the Galapagos archipelago, he observed that, in spite of the islands' physical similarity, members of species that had dispersed to them recently were beginning to diverge from each other. He postulated that these divergences must have resulted primarily from interactions with sets of other species that had also diverged across these otherwise similar islands. By extrapolation, if Darwin is correct, such complex interactions must be driving species divergences across all ecosystems. However, many current general ecological theories that predict observed distributions of species in ecosystems do not take the details of between-species interactions into account. Here we quantify, in sixteen forest diversity plots (FDPs) worldwide, highly significant negative density-dependent (NDD) components of both conspecific and heterospecific between-tree interactions that affect the trees' distributions, growth, recruitment, and mortality. These interactions decline smoothly in significance with increasing physical distance between trees. They also tend to decline in significance with increasing phylogenetic distance between the trees, but each FDP exhibits its own unique pattern of exceptions to this overall decline. Unique patterns of between-species interactions in ecosystems, of the general type that Darwin postulated, are likely to have contributed to the exceptions. We test the power of our null-model method by using a deliberately modified data set, and show that the method easily identifies the modifications. We examine how some of the exceptions, at the Wind River (USA) FDP, reveal new details of a known allelopathic effect of one of the Wind River gymnosperm species. Finally, we explore how similar analyses can be used to investigate details of many types of interactions in these complex ecosystems, and can provide clues to the evolution of these interactions.

Living in small spaces: Forest fragment characterization and its use by Philippine tarsiers (Tarsius syrichta Linnaeus, 1758) in Mindanao Island, Philippines.

The Philippine tarsier (Tarsius syrichta) is a charismatic species that is threatened by illegal hunting and deforestation. Although they occur in forest and disturbed habitats, ecological information about them is still considerably lacking, which consequently hampers our ability to effectively protect tarsiers from further endangerment. Here, we characterized a 36-ha forest fragment in Mindanao Island where a population of tarsiers persist, and assessed the factors that could have influenced their distribution within the area. We sampled trees (> 1 cm DBH) within 10 × 10-m sampling plots (N = 54), which were established within 1-ha grids (N = 32) and locations where tarsiers were captured (N = 22). The habitat was characterized as a regenerating forest over limestone, with a generally homogeneous structure in terms of tree species richness, abundance, mean DBH, and height. In both sampling plots, we found an abundance of trees below 5 cm in DBH (> 50%) and between 2.6 and 5 m in height (> 40%), which, accordingly, the tarsiers appeared to prefer to use when foraging or sleeping. Lianas were among the most important features of the forest, possibly being a keystone structure in such habitats. Community assemblage, species richness, and mean height of trees, as well as distance to the forest edge, were found to be significant factors that influenced tarsier distribution in the fragment. Our study provides basic yet critical information on the habitat and ecology of Philippine tarsiers in Mindanao, and highlights the importance of forest fragments with rich flora diversity to the survival of the species.

Trees represent community composition of other plant life-forms, but not their diversity, abundance or responses to fragmentation.

Our understanding of the patterns of plant diversity in tropical forests and their responses to fragmentation are mostly based on tree surveys. But are these patterns and responses representative of other plant life-forms? We sampled trees, lianas, herbs, and ferns in a fragmented tropical forest landscape in South-west China. We compared community types generated by clustering presence-absence data for the non-tree life-forms with those generated for trees. We tested how well measures of tree diversity, density and composition, predicted cognate indices in other life-forms. We compared fragmentation responses, with respect to the three measures, of all four life-forms. Presence-absence data from all life-forms generated three community clusters, with only small differences between classifications, suggesting that tree data identified community types representative of all vascular plant life-forms. Tree species diversity and density indices poorly predicted cognate indices of lianas and ferns, but represented herbs well. However, the slopes of these relationships differed substantially between community types. All life-forms responded to fragmentation variables but their responses did not consistently match with responses of trees. Plot-level tree data can identify vegetation community types, but is poorly representative of the richness and density of other life-forms, and poorly represents forest fragmentation responses for the entire plant community.

Effects of forest fragmentation on nocturnal Asian birds: A case study from Xishuangbanna, China.

Owls have the potential to be keystone species for conservation in fragmented landscapes, as the absence of these predators could profoundly change community structure. Yet few studies have examined how whole communities of owls respond to fragmentation, especially in the tropics. When evaluating the effect of factors related to fragmentation, such as fragment area and distance to the edge, on these birds, it is also important in heterogeneous landscapes to ask how 'location factors' such as the topography, vegetation and soil of the fragment predict their persistence. In Xishuangbanna, southwest China, we established 43 transects (200 m×60 m) within 20 forest fragments to sample nocturnal birds, both visually and aurally. We used a multimodel inference approach to identify the factors that influence owl species richness, and generalized linear mixed models to predict the occurrence probabilities of each species. We found that fragmentation factors dominated location factors, with larger fragments having more species, and four of eight species were significantly more likely to occur in large fragments. Given the potential importance of these birds on regulating small mammal and other animal populations, and thus indirectly affecting seed dispersal, we suggest further protection of large fragments and programs to increase their connectivity to the remaining smaller fragments.