Plant-microbe interactions in tropical and subtropical ecosystems.

Microbes regulate many dimensions of plant performance with multiscale implications for plant fitness, competition, coexistence, and ecosystem functioning. Yet, this fascinating and diverse arena of study has been limited to a few thematic areas, ecosystems, and regions. In particular, despite growing evidence that microbes may be critical players in the dynamics of plant communities in tropical and subtropical ecosystems, these regions remain poorly represented in studies of plant-microbe interactions.

Consequences of Local Conspecific Density Effects for Plant Diversity and Community Dynamics.

Conspecific density dependence (CDD) in plant populations is widespread, most likely caused by local-scale biotic interactions, and has potentially important implications for biodiversity, community composition, and ecosystem processes. However, progress in this important area of ecology has been hindered by differing viewpoints on CDD across subfields in ecology, lack of synthesis across CDD-related frameworks, and misunderstandings about how empirical measurements of local CDD fit within the context of broader ecological theories on community assembly and diversity maintenance. Here, we propose a conceptual synthesis of local-scale CDD and its causes, including species-specific antagonistic and mutualistic interactions.

Anatomical traits explain drought response of seedlings from wet tropical forests.

Water availability regulates plant community dynamics but the drought response of seedlings remains poorly known, despite their vulnerability, especially for the Asian tropics. In particular, discerning how functional traits of seedlings mediate drought response can aid generalizable predictions of tree responses to global environmental change. We assessed interspecific variation in drought response explained by above- and below-ground seedling traits.

Climate and forest loss interactively restructure trait composition across a human-modified landscape.

Traits determine species response to climate conditions and the match between phenotypes and climate mediates spatial variation in species composition. These trait-climate linkages can be disrupted in human-modified landscapes. Human land use creates forest fragments where dispersal limitation or edge effects exclude species that may otherwise suit a given macroclimate.

Environment shapes the spatial organization of tree diversity in fragmented forests across a human-modified landscape.

Biodiversity patterns are shaped by the combination of dispersal, environment, and stochasticity, but how the influence of these drivers changes in fragmented habitats remains poorly understood. We examined patterns and relationships among total (γ) and site-level (α) diversity, and site-to-site variation in composition (β-diversity) of tree communities in structurally contiguous and fragmented tropical rainforests within a human-modified landscape in India's Western Ghats. First, for the entire landscape, we assessed the extent to which habitat type (fragment or contiguous forest), space and environment explained variation in α-diversity and composition.

Edge effects alter the role of fungi and insects in mediating functional composition and diversity of seedling recruits in a fragmented tropical forest.

Background And Aims: In fragmented forests, proximity to forest edges can favour the establishment of resource-acquisitive species over more resource-conservative species. During seedling recruitment, resource-acquisitive species may benefit from either higher light availability or weaker top-down effects of natural enemies. The relative importance of light and enemies for recruitment has seldom been examined with respect to edge effects.

Edge effects reduce α-diversity but not β-diversity during community assembly in a human-modified tropical forest.

Edge effects can alter the spatial organization of diversity in fragmented habitats. For tropical forests, however, there has been large variation in the strength and direction of such effects reported by different studies. For long-lived organisms like trees, one reason for inconsistent patterns might be due to most studies having examined patterns of diversity and compositional variation in older life stages that bear the legacy of a forest past.

Environment and past land use together predict functional diversity in a temperate forest.

Environment and human land use both shape forest composition. Abiotic conditions sift tree species from a regional pool via functional traits that influence species' suitability to the local environment. In addition, human land use can modify species distributions and change functional diversity of forests.

Influence of soil pathogens on early regeneration success of tropical trees varies between forest edge and interior.

Soil fungi are key mediators of negative density-dependent mortality in seeds and seedlings, and the ability to withstand pathogens in the shaded understory of closed-canopy forests could reinforce light gradient partitioning by tree species. For four species of tropical rainforest trees-two shade-tolerant and two shade-intolerant-we conducted a field experiment to examine the interactive effects of fungal pathogens, light, and seed density on germination and early seedling establishment. In a fully factorial design, seeds were sown into 1 m plots containing soil collected from underneath conspecific adult trees, with plots assigned to forest edge (high light) or shaded understory, high or low density, and fungicide or no fungicide application.

Testing predictions of the Janzen-Connell hypothesis: a meta-analysis of experimental evidence for distance- and density-dependent seed and seedling survival.

The Janzen-Connell hypothesis proposes that specialist natural enemies, such as herbivores and pathogens, maintain diversity in plant communities by reducing survival rates of conspecific seeds and seedlings located close to reproductive adults or in areas of high conspecific density. Variation in the strength of distance- and density-dependent effects is hypothesized to explain variation in plant species richness along climatic gradients, with effects predicted to be stronger in the tropics than the temperate zone and in wetter habitats compared to drier habitats.We conducted a comprehensive literature search to identify peer-reviewed experimental studies published in the 40+ years since the hypothesis was first proposed.

The response of the frugivorous lion-tailed macaque (Macaca silenus) to a period of fruit scarcity.

Tropical rainforests show seasonal fluctuations in the abundance of fruits resulting in periods of resource scarcity for frugivores. We examined the response of an obligate frugivore, the lion-tailed macaque (LTM) (Macaca silenus), to a period of fruit scarcity in a rainforest in the Western Ghats, India. We estimated the abundance and distribution of fruit resources from food tree densities obtained from 348 point centered quadrats, and fruit availability from phenological monitoring of 195 trees of 15 reported major food species.