Robert Bagchi

• PhD
• Professor (Assistant) at University of Connecticut

Pathogenic interactions between fungi and plants facilitate plant species coexistence and tropical rainforest diversity. Such interactions, however, may be affected by forest fragmentation as fungi are susceptible to anthropogenic disturbance. To examine how fragmentation affects fungus-induced seed and seedling mortality, we sowed seeds of six pla...

1. Rapid climate change is generating an urgent need to understand how organisms respond to environmental variation. Understanding these responses at an organismal level requires environmental data at finer spatial and temporal scales than is available from global datasets. Current measurement technologies force a trade‐off between collecting data...

In fragmented forests, tree diversity declines near edges but the ecological processes underlying this loss of diversity remain poorly understood. Theory predicts that top-down regulation of seedling recruitment by insect herbivores and fungal pathogens contributes to maintaining tree diversity in forests, but it is unknown whether proximity to for...

Deforestation and biodiversity loss in agroecosystems are generally the result of rational choices, not of a lack of awareness or knowledge. Despite both scientific evidence and traditional knowledge that supports the value of diverse production systems for ecosystem services and resilience, a trend of agroecosystem intensification is apparent acro...

Background/Question/Methods Species with broader environmental tolerances are expected to be more widely distributed than specialist species, leading to the prediction of a positive correlation between niche breadth and geographic range size. This relationship is often evaluated based on data derived from the broad-scale geographic distributions of...

Aim Species with broader environmental tolerances are expected to be more widely distributed than specialist species, implying a positive correlation between niche breadth and geographic range size. When this relationship is evaluated using data derived from broad‐scale geographic distributions of species, spatial autocorrelation of species distrib...

Reduced ecological specialization is an emerging, general pattern of ecological networks in fragmented landscapes. In plant–herbivore interactions, reductions in dietary specialization of herbivore communities are consistently associated with fragmented landscapes, but the causes remain poorly understood. We propose several hypothetical bottom–up a...

1.Declines of large vertebrates in tropical forests may reduce dispersal of tree species that rely on them, and the resulting undispersed seedlings might suffer increased distance- and density- dependent mortality. Consequently, extirpation of large vertebrates may alter the composition and spatial structure of plant communities and impair ecosyste...

The ability of species to shift their distributions in response to climate change may be impeded by lack of suitable climate or habitat between species’ current and future ranges. We examined the potential for climate and forest cover to limit the movement of bird species among sites of biodiversity importance in the Albertine Rift, East Africa, a...

We measured the terminal velocity of helicopter-like fruit from the Dipterocarpaceae family and present a model predicting the terminal velocities for all dipterocarp species in the Malesiana region. A ballistic model of seed dispersal using the observed terminal velocities predicted dispersal distances of 17–77 m under normal atmospheric condition...

Seed dispersal governs the distribution of plant propagules in the landscape and hence forms the template on which density-dependent processes act. Dispersal is therefore a vital component of many species coexistence and forest dynamics models and is of applied value in understanding forest regeneration. Research on the processes that facilitate fo...

Data S1. Generating dispersal kernels and calculation of approximate P-values

Table S1. Parameter estimates from the bootstrapped LMM model fitting IWL, maximum wind speed and their interaction to log-transformed fruit dispersal distance using the “new species” approach for unidentified dipterocarps.

Data S2. R script of the analysis performed.

Table S2. Median and 95% C.I. percentile dispersal distances predicted using the “new species” approach for dipterocarp species with IWLs 1 to 50 and wind speeds 1 to 10 m/s.

Figure S1. Simulated dispersal kernels of S. seminis, S. smithiana and S. argentifolia at maximum wind speed 1 and 5 m/sec (dashed and full lines respectively) with associated 95% confidence bands.

Many ecological questions could gain insight from linking variation in spatial structure to explanatory variables. Although methods that make these links have been developed in the statistical literature, they have been used rarely in ecology. We present an approach that considers point patterns from different sources (e.g. multiple plots or specie...

Niche diversification is prominent among the mechanisms proposed to explain tropical rain forest tree diversity, with many studies focusing on trade-offs among shade tolerance and growth. Less obvious is the impact of occasional, ephemeral and often minor disturbances on tree seedling survival. We propose that differential tolerances to soil waterl...

Background/Question/Methods Pathogenic fungi account for significant mortality in tropical seedling communities and their host-specific interactions can influence plant community dynamics through negative feedbacks. The long-standing Janzen-Connell hypothesis suggests that specialized pests such as insects and pathogens maintain high plant divers...

Tropical forests are important reservoirs of biodiversity, but the processes that maintain this diversity remain poorly understood. The Janzen-Connell hypothesis suggests that specialized natural enemies such as insect herbivores and fungal pathogens maintain high diversity by elevating mortality when plant species occur at high density (negative d...

The value of local ecological knowledge (LEK) to conservation is increasingly recognised, but LEK is being rapidly lost as indigenous livelihoods change. Biodiversity loss is also a driver of the loss of LEK, but quantitative study is lacking. In our study landscape in SW China, a large proportion of species have been extirpated. Hence, we were int...

The coexistence of plant species in species-rich tropical forests can be promoted by specialised enemies acting in a negatively density-dependent manner. While survival of tropical tree seedlings is often negatively density-dependent, the causes have rarely been identified. We tested whether insects and plant pathogens cause density-dependent seedl...

We forecasted potential impacts of climate change on the ability of a network of key sites for bird conservation (Important Bird Areas; IBAs) to provide suitable climate for 370 bird species of current conservation concern in two Asian biodiversity hotspots: the Eastern Himalaya and Lower Mekong. Comparable studies have largely not accounted for un...

Forests are of major importance to human society, contributing several crucial ecosystem services. Biodiversity is suggested to positively influence multiple services but evidence from natural systems at scales relevant to management is scarce. Here, across a scale of 400,000 km(2), we report that tree species richness in production forests shows p...

Supplementary Figures S1-S3 and Supplementary Tables S1-S6

Most general circulation models predict that most tropical forests will experience lower and less frequent rainfall in future as a result of climate change, which may reduce the capacity of fungal pathogens to drive density-dependent tree mortality. This is potentially significant because fungal pathogens are thought to play a key role in promoting...

The responses of plants to shade and foliar herbivory jointly affect growth rates and community assembly. We grew 600 seedlings of ten species of the economically important Dipterocarpaceae in experimental gradients of shading (0.3–47.0% of full sunlight) and defoliation (0, 25%, 50% or 75% of leaf area removed). We assessed stem diameters initiall...

Much of the forest remaining in South East Asia has been selectively logged. The processes promoting species coexistence may be the key to the recovery and maintenance of diversity in these forests. One such process is the Janzen-Connell mechanism, where specialized natural enemies such as seed predators maintain diversity by inhibiting regeneratio...

Understanding how plant species coexist in tropical rainforests is one of the biggest challenges in community ecology. One prominent hypothesis suggests that rare species are at an advantage because trees have lower survival in areas of high conspecific density due to increased attack by natural enemies, a process known as negative density dependen...

Background/Question/Methods Fungi are important plant pathogens at key life history stages of recruitment, and can influence plant community structure through negative feedbacks. Much is known of the identities and specificity of pathogens in agriculture and forest management systems. An increasing body of literature shows fungal pathogens to be...

Ecology Letters (2010) The Janzen-Connell hypothesis is a leading explanation for plant-species diversity in tropical forests. It suggests that specialized natural enemies decrease offspring survival at high densities beneath parents, giving locally rarer species an advantage. This mechanism, in its original form, assumes that density dependence is...

Insurance effects of biodiversity can stabilize the functioning of multispecies ecosystems against environmental variability when differential species’ responses lead to asynchronous population dynamics. When responses are not perfectly positively correlated, declines in some populations are compensated by increases in others, smoothing variability...

Effect of predators of different body size (None, Small, All) on seed survival at two experimentally manipulated seed densities (low = 2 or high = 24 seeds/m2). Results are shown as mean and standard error (logit scale). The effects are reported as the value for the control (None) and the differences (in italics) between control and the other treat...

Tree specific response to con/hetero-specific seed survival. Percentage of mean seed survival in exclosures that allowed vertebrate predators of the specified size classes either close (conspecific) or away (heterospecific) from maternal tree. Results are shown as means ± s.e.m. back transformed from the generalized linear mixed-effects model analy...

Effect of predators of different body size (None, Small, All) on con/hetero-specific seed survival. Results are shown as mean and standard error (logit scale). The effects are reported as the value for the control and the differences (in italics) between control and the other treatments. (0.04 MB DOC)

Tree specific response to seed survival at high vs low experimental seed density. Percentage of mean seed survival in exclosures that allowed vertebrate predators of the specified size classes at the high and the low experimental seed density treatment. Results are shown as means ± s.e.m. back transformed from the generalized linear mixed-effects m...

Fiddler crab (arrowhead) halfway in its hole with the strings and seeds going into the hole. Photo credit: Yann Hautier. (0.26 MB JPG)

The Janzen-Connell hypothesis proposes that seed and seedling enemies play a major role in maintaining high levels of tree diversity in tropical forests. However, human disturbance may alter guilds of seed predators including their body size distribution. These changes have the potential to affect seedling survival in logged forest and may alter fo...

Insurance effects of biodiversity can stabilize the functioning of multispecies ecosystems against environmental variability when differential species' responses lead to asynchronous population dynamics. When responses are not perfectly positively correlated, declines in some populations are compensated by increases in others, smoothing variability...

One important hypothesis to explain tree-species coexistence in tropical forests suggests that increased attack by natural enemies near conspecific trees gives locally rare species a competitive advantage. Host ranges of natural enemies generally encompass several closely related plant taxa suggesting that seedlings should also do poorly around adu...

Background/Question/Methods The rapid loss of biodiversity from natural communities has motivated much research investigating how this loss impacts the provision of ecosystem services. The majority of these studies have concentrated on individual ecosystem functions, and have, for the most part, identified a positive, but decelerating, relationshi...

Biodiversity loss can affect ecosystem functions and services. Individual ecosystem functions generally show a positive asymptotic relationship with increasing biodiversity, suggesting that some species are redundant. However, ecosystems are managed and conserved for multiple functions, which may require greater biodiversity. Here we present an ana...

Biodiversity loss can affect ecosystem functions and services. Individual ecosystem functions generally show a positive asymptotic relationship with increasing biodiversity, suggesting that some species are redundant. However, ecosystems are managed and conserved for multiple functions, which may require greater biodiversity. Here we present an ana...

On an upland moor dominated by pioneer Calluna vulgaris and with an understorey of mosses and lichens, experimental plots were treated with factorial combinations of nitrogen (N) at +0 and +20 kg N ha−1 yr−1, and phosphorus (P) at +0 and +5 kg P ha−1 yr−1. Over the 4-year duration of the experiment, the cover of the Calluna canopy increased in dens...

The extent to which plant communities are determined by resource availability is a central theme in ecosystem science, but patterns of small-scale variation in resource availability are poorly known. Studies of carbon (C) and nutrient cycling provide insights into factors limiting tree growth and forest productivity. To investigate rates of tropica...

Seed predators are considered important in the evolution of mast fruiting. Mast events in turn provide an abundant food resource for consumers, but only for a limited period of time. In this study seed removal experiments, feeding trials and small mammal trapping were used to determine the potential of forest rats (Muridae) as predators and dispers...