273 research outputs found
Forest observational studies in India: Past developments and considerations for the future
No full textLong term forest research sites in India, going by different names including Linear Tree Increment Plots, Linear Increment Plots, Linear Sample Plots and Permanent Preservation Plots, cover diverse plant communities and environmental conditions. Presently, some of these long-term observational studies are functional, some are disturbed and others have almost been lost. The accumulated data will become increasingly important in the context of environmental modelling and climate change, especially if the plots and data can be maintained and/or revived. This contribution presents the history and current state of forest research plots in India, including details of locations and re-measurements. We provide a brief introduction of the National Forest Inventory (NFI), Preservation Plots in natural forests, the 50-ha Mudumalai Forest Dynamics Plot as part of the Centre for Tropical Forest Science and Smithsonian Institution Global Earth Observatories network (CTFS-SIGEO), and research plots established in plantations for tree growth studies and modelling. We also present some methodological details including assessment and analysis for two types of observational studies, the Tree Count Plots (TCP) and Tree Re-measurement Plots (TRP). Arguments are presented in favour of enumeration and analysis methods which are consistent with current approaches in forest ecological research. (c) 2013 Elsevier B.V. All rights reserved
Elephants on the Move: Implications for Human–Elephant Interactions
No full textAsian elephants often traverse large areas to gather food and water. However, the environment in which they live is dynamic (changing with the seasons). Some of these changes in the environment, however, are accelerated due to human-induced factors. To survive and persist in fragmented, human-dominated landscapes, especially in the Anthropocene, elephants often need to modify their behaviour. Some of these modifications may be short-term adaptations that include altering their time-activity budgets in response to changing local ecological and anthropogenic settings, while others could be long-term shifts in home ranges in response to large-scale changes in land use and global climatic events. In this chapter, using empirical data, the authors assess the behavioural adaptability of elephants, as determined by their innate biological variables, such as age, sex and grouping patterns at the population level. They also discuss the impacts of global climatic changes on the behaviour and distribution of Asian elephants, as evidenced through studies conducted on these aspects. They discuss how elephants, in general, avoid areas of high human use. In addition, their recent studies suggest that elephants may be altering their social systems and forming all-male groups-a novel social unit in Asian elephants-in highly human-dominated landscapes in order to persist and at times successfully exploit resources. The issues highlighted in this chapter may be significant for the future management of human-elephant conflict and the conservation of Asian elephants, as most management strategies do not take into account variability in elephant behaviour or impending climate change in implementation
Stress Physiology of Free-ranging Asian Elephants (Elephas maximus) : Influence of Ecological and Anthropogenic Stressors
No full textVarious ecological and human-induced disturbances play an important role in defining the health of an animal. To cope up with such threats or challenges to its homeostasis, an animal responds by secreting stress hormones (glucocorticoids) to mobilize the energy. In general, glucocorticoids help animals to cope up with the ‘stressors’. Prolonged exposure to any ‘stressors’ may lead to an elevation in the levels of glucocorticoids, thereby leading to reproductive inhibition, immune system suppression, neuronal death and impaired cognitive function and hence, threatening the survival and fitness of an animal. However, the long-term effects of environmental or anthropogenic disturbances on the fitness and survival are difficult to analyze in a slow reproducing, long-lived species such as elephants.
Spread over 3% of India’s geographical area, India shelters around 28,000 to 30,000 Asian elephants (Elephas maximus; Bist, 2002; Santiapillai and Sukumar, 2006). Protected areas in India are estimated to form 22% of elephant habitat; while the rest of the elephant habitats extend outside the protected areas (Lenin and Sukumar, 2011) making them vulnerable to human-induced threats. Consequently, there are increased incidences of human-elephant conflicts leading to crop and property depredation and human-elephant mortality. Most of the studies, in context of such conflicts, highlight the temporal, spatial scales of conflicts majorly focusing on mitigation measures. None of the studies so far have elucidated how escalating human-elephant conflicts would influence the physiological health of Asian elephants.
This study, hence, focused on addressing the proximate causation of the stress-response in free-ranging Asian elephants of the Bandipur National Park, the Nagarahole National Park and Hassan district of Karnataka, using a non-invasive technique for measuring faecal glucocorticoid metabolites (fGCM). There are several factors which could act as possible stressors to the physiological state of an elephant, but depending upon the feasibility and time limitations of conducting the study, we selected those factors which we thought are essential to address the proximate causation of stress-response in Asian elephants. Being the first detailed study to explore the stress-response in free-ranging Asian elephants, this study attempted to understand the influence of some of the fundamental ecological (seasonality, group size, and body condition) and human-induced stressors.
The main body of the dissertation is divided into six chapters. The first and the last chapters discuss the general introduction and conclusion while the rest four chapters highlight the main four objectives of the study. The main objectives of the thesis were:
1. The first objective of this thesis was to validate and standardize some of the crucial parts of protocols to avoid any technique-based bias while interpreting the levels of faecal glucocorticoid metabolites. Under the first objective, the influences of some of the fundamental intrinsic and extrinsic factors on the fGCM levels were also assessed.
2. The second objective was to assess the association between body condition, seasonality and stress response.
3. Having assessed the relationship between body condition and stress-status, the third objective focused on the influence of socio-ecological correlates such as group size, lactational status and the presence of adult females in a herd on the stress status of female adult elephants.
4. With above three objectives majorly highlighting the influence of ecological factors, the fourth objective was to assess the influence of anthropogenic factors on stress-response of free-ranging elephants under which we compared the stress-response between crop-raiding in human-dominated and nonraiding elephants in forested habitats.
The study was conducted during dry season (February to May) and wet season (August to
December) of 2013 and 2015. The dissertation is organized in the following way:
Chapter 1:
General Introduction
The first chapter provides a general introduction about stress response and its physiological pathway. It also discusses the importance of non-invasive technique used in our study. It highlights the significance of this study based on the available literature on both African and Asian elephants.
Chapter 2:
General validation and standardization of field techniques and assays; influence of intrinsic and extrinsic factors on faecal glucocorticoid metabolites
This chapter is divided into two parts. The first part deals with general validation and standardization of field techniques and the second part assesses the influence of fundamental intrinsic and extrinsic factors. Being the first study on stress-response of free-ranging Asian elephants, influence of various field-based techniques and variations were studied to facilitate the reliable interpretation of fGCM levels. We first conducted the experiments to standardize the field protocol and the laboratory protocol. Under the field protocol, we found that there was no within sample variation (as observed in many other species) in fGCM levels from thoroughly mixed faecal samples and samples from the center of the same dung bolus. The time of collection of samples had a significant influence, suggesting that the concentration of fGCM remains stable until 6-9 hours. Influence of storage of lyophilized samples suggested that the concentrations of fGCM levels decline if exposed to moisture. Under the laboratory protocol, A group specific 11-oxoetiocholanolone EIA, used for analyzing fGCM levels (μg/g), was modified to enhance the repeatability, accuracy and precision. EIA was analytically validated in every hormonal analysis by calculating the inter- and intra-assay coefficients of variation, specificity and parallelism. In the second part, we assessed the influence of age, sex and season on fGCM levels and found there was no age-wise variation and sex-wise variation. Season-wise variation was significant only in female elephants. We discuss the potential physiological reasons behind such variation. These findings suggest that aspects such as time of collection, proper storage of samples and the influence of extrinsic stresses (seasonality) should be considered for reliable and unbiased interpretation of fGCM levels.
Chapter 3:
Assessment of season-dependent body condition scores in relation to faecal glucocorticoid metabolites in free-ranging Asian elephants.
(Published in Conservation Physiology; Pokharel et al., 2017; doi:10.1093/conphys/cox039)
We studied seasonal and annual changes in visual body condition scores (BCS), and assessed how these scores were related to levels of fGCM levels in free-ranging Asian elephants in the seasonally dry tropical forests of the Mysore and Nilgiri Elephant Reserves in southern India. We assessed the animals’ BCS visually on a scale of 1 to 5; where 1 represents a very thin and 5 represents a very fat elephant. To understand the influence of seasonality on BCS, we sampled the population during dry and wet seasons of 2013 and 2015 while, for annual changes in BCS, we sampled nine free-ranging adult females from different family groups that had been repeatedly sighted over seven years. To evaluate the influence of body condition on fGCM, we measured the fGCM levels from fresh fecal samples collected from the body-condition scored animals. Effect of age and season on BCS in relation to fGCM was also studied. We found that the BCS was related with season, i.e. individuals with low BCS were more frequent during the dry season as compared to the wet season and fGCM levels were negatively associated with BCS. To be precise, concentrations of fGCM were highest in individuals with the lowest BCS (BCS-1) and then significantly declined till BCS-3. fGCM levels were almost comparable for BCS 3, 4 and 5. This pattern was more conspicuous in female than in male elephants. We discussed the possible reasons behind such relationship between fGCM and BCS. The findings from this chapter suggest that season-dependent BCS, hence, reflect the stress status as measured by fGCM, especially in female Asian elephants and could be used as an important non-invasive approach to monitor the physiological health of free-ranging elephant populations. This is the first study to compare the body condition scores and stress-response in free-ranging elephants.
Chapter 4:
Influence of ecological and physiological correlates on stress physiology of free-ranging female Asian elephants.
We investigated the influence of herd size (HS), lactational status and number of adult females present in a herd on adrenocortical function in free-ranging adult female Asian elephants by measuring their fecal glucocorticoid metabolites (fGCM) levels. We found that there was a negative association between herd size and fGCM levels when only HS and fGCM were compared. Lactating females showed higher fGCM than that observed in non-lactating females, which might reflect the nutritional stress on mother and anti-predatory challenges against the calves. Herds with only one adult female had higher fGCM levels than herds with more than one adult female which could be because of social challenges. The poor association between herd size and fGCM when all predictor variables were combined elucidate that group size may not necessarily influence the adreno-cortical function. However, the numbers of adult females present in a herd and their lactational status has a significant role in defining the stress-response in free-ranging adult female Asian elephants. This study is the first study to document the influence of lactational status with the stress-response in free-ranging elephants.
Chapter 5:
How physiologically costlier it is to be a crop-raider in a human-dominated landscape? Diet quality as a possible ‘pacifier’ against stress.
We studied the stress-response in crop-raiding elephants in a human-dominated landscape and non-raiding elephants in the protected forested areas. While raiding agricultural crops, elephants face various associated threats such as retaliation by humans, human-induced disturbances and stress of raiding which could enhance the energetic costs, ultimately elevating their stress levels. We hypothesized that crop-raiders (in human-dominated landscape; Hassan district of Karnataka, India) will exhibit higher faecal glucocorticoid metabolite (a proxy of stress-response; fGCM) levels as compared to the nonraiders (in forested areas; Bandipur and Nagarahole National Parks). Contrary to our hypothesis, fGCM levels were found to be higher in both nonraiding female and male elephants than female and male crop-raiders. To assess the influence of benefits obtained from crop-raiding as one of the possible factors for the lower fGCM in crop-raiders, the difference in vegetation between human-dominated landscape and forested areas were further analyzed by using a remotely sensed NDVI (Normalized Differential Vegetation Index) and was ground-truthed by measuring the quality of diet (C:N ratio through fecal samples). Interestingly, the NDVI values were higher at the human-dominated and the C:N ratio was lower (higher Nitrogen content) in faecal samples of crop-raiding elephants (both in females and in males) than the nonraiders in the forested areas. Positive correlation was observed between C:N ratio and fGCM levels. These findings suggest that crop-raiding comes with the benefits of easy access to good quality of diet which may help in reducing the stress-response in elephants while being in the human-dominated landscapes, provided there is a low intensity of human disturbance. This is the first study to document and compare the stress-status of crop-raiding Asian elephants with elephants in their natural habitats using NDVI and C:N ratio.
Chapter 6:
Conclusion
In conclusion, the work presented in this dissertation provides an overview of how ecological and anthropogenic factors could influence the physiological health of free-ranging Asian elephants. This dissertation focused on providing detailed insights about the stress-response in free-ranging Asian elephants. The objectives have been achieved by assessing the relationship between ecological stressors such as seasonality, body condition, herd size, lactational status, a presence of individuals in a herd and anthropogenic stressors such as
human-induced threats or crop-raiding using well-validated and standardized laboratory and field protocols. This study provides valuable insights into the physiological health or stress-response being synergistically influenced by various ecological, social and anthropogenic factors in free-ranging Asian elephants. Findings obtained from this study could help in addressing the issues related to the management of free-ranging elephant populations
Barriers and prospects of India’s conditional cash transfer program to promote institutional delivery care : a qualitative analysis of the supply-side perspectives
No full textBackground Under the National Health Mission (NHM) of India, Janani Suraksha Yojana (JSY) offers conditional cash transfer and support services to pregnant women to use institutional delivery care facilities. This study aims to understand community health workers’ (ASHAs) and program officials’ perceptions regarding barriers to and prospects for the uptake of facilities offered under the JSY. Methods Fifty in-depth interviews of a purposively selected sample of ASHAs (n = 12), members of Village Health and Sanitation Committees (n = 11), and officials at different tiers of healthcare facilities (n = 27) were conducted in three Indian states. The data were analyzed thematically using ATLAS.ti software. Results Although the JSY has triggered considerable advancement on the Indian maternal and child health front, there are several barriers to be resolved pertaining to i) delivering quality care at health-facility; ii) linkages between home and health-facility; and iii) the community/household context. At the facility level, respondents cited an inability to treat birth complications as a barrier to JSY uptake, resulting in referrals to other (mostly private) facilities. Despite increased investment in health infrastructure under the program, shortages in emergency obstetric-care facilities, specialists and staff, essential drugs, diagnostics, and necessary equipment persisted. Weaker linkages between various vertical (standalone) elements of maternal and primary healthcare programs, and nearly uniform resource allocation to all facilities irrespective of caseloads and actual need also constrained the provision of quality healthcare. Barriers affecting the linkages between home and facility arose mainly due to the mismatch between the multiple demands and the availability of transport facilities, especially in emergency situations. Regarding community/household context, several socio-cultural issues such as resistance towards the ASHA’s efforts of counselling, particularly from elderly family members, often adversely affected people’s decision to seek healthcare. Conclusion Adequate interventions at the community level, capacity building for healthcare providers, and measures to address underlying structural and systemic barriers are needed to improve the uptake of institutional maternal healthcare
sj-docx-1-hol-10.1177_09596836211066592 – Supplemental material for Paleovegetation dynamics in an alternative stable states landscape in the montane Western Ghats, India
No full textSupplemental material, sj-docx-1-hol-10.1177_09596836211066592 for Paleovegetation dynamics in an alternative stable states landscape in the montane Western Ghats, India by Prabhakaran Ramya Bala, Sarath Pullyottum Kavil, Ichiro Tayasu, Chikage Yoshimizu, Kaustubh Thirumalai, Krishnan Sajeev and Raman Sukumar in The Holocene</p
R Markdown code to convert bird point count data to ebird bulk upload CSV file
No full textThe .Rmd file contains the R code (script in R Markdown format) used for converting bird point count data and locations from the following dataset to prepare a CSV file in the eBird record format for bulk upload of the data to the eBird citizen science portal (https://www.ebird.org/):
Raman TRS et al. 2022. Data on bird communities and vegetation in relation to altitude and habitat alteration in the Kalakad - Mundanthurai Tiger Reserve, Tamil Nadu, India , Dryad, Dataset, https://doi.org/10.5061/dryad.41ns1rngj
The .html file contains the knit version of the same R markdown code.The dataset contains data on bird communities and habitat collected between 1997 and 1999 from Kalakad Mundanthurai Tiger Reserve, Tamil Nadu, India, related to the following two publications:
Raman, T. R. S., Joshi, N. V. & Sukumar, R. 2005. Tropical rainforest bird community structure in relation to altitude, tree species composition, and null models in the Western Ghats, India. Journal of the Bombay Natural History Society 102: 145-157. https://archive.org/details/journalofbomb10222005bomb/page/145/mode/2up
Raman, T. R. S. & Sukumar, R. 2002. Responses of tropical rainforest birds to abandoned plantations, edges, and logged forest in the Western Ghats, India. Animal Conservation 5: 201-216. http://dx.doi.org/10.1017/S136794300200225
Eco-Hydrology of a Seasonally Dry Tropical Forest : Tree Growth, Belowground Water Dynamics and Drought-Vulnerability
No full textTropical forests are storehouses of more thanhalf of the world‘s biodiversity and play a key role in global carbon, water and energy cycles. However, as a consequence of rapid anthropogenic climate change, biodiversity and climate functions of these forests are under a threat. Climate is changing not only in mean state but its variability is increasing, with extreme events such as droughts, heat waves and storms also rising. Water is fundamental to plants‘ existence, and in the tropics, is a key determinant of plant species‘richness, composition, growth and survival. There is thus an increasing interest in understanding how changing rainfall may cause functional changes in forests or change their species composition. Therefore, the overarching goal of thisdissertation was to understand the impact of water variability on tropical forest tree growth and vulnerability to drought.Forest tree growth along spatial and temporal rainfall gradientsObservational studies that measure whole forest tree growth along spatial or temporal gradients of rainfall are the most common way of formulating forest growth response curves to water availability, when manipulative experiments are cost-prohibitive or impractical (fire or large mammal disturbance). In the tropics, since very few species show anatomically distinct tree rings, estimating tree growth from trunk diameter is the standard practice to obtain growth patterns across species. However, this method—of equating woody growth to diameter change--is susceptible to bias from water-induced stem flexing. In the absence of bias correction, temporal variability in growth is likely to be overestimated and incorrectly attributed to fluctuations in resource availability, especially in forests with high seasonal and inter-annual variability in water. This problem has been largely ignored in the absence of any corrective measure and due to under-appreciation of the magnitude of error. While diameter re-censuses in permanent sampling plots (PSPs) have been most commonly done at 3-5 year scale (using a graduate tape), increasingly they are done at seasonal and annual scales (using band dendrometers) to closely match variation in rainfall, the scales at which hydrostatic bias may be greater in magnitude relative to woody growth. Besides, along a spatial rainfall gradient, inter-annual variability in water may vary, causing systematic differences in the hydrostatic bias for forests along the gradient. Therefore, one broad objective of this thesis was to evaluate the problem of hydrostatic bias in whole forest growth-rainfall relationship at annual and supra-annual scales, for temporal as well as spatial rainfall gradients and propose and test a novel corrective solution.Further, it also examines if growth-diameter relationship vary along the spatial gradient, which it may arise due to differences in light environments and/or disturbance history and species composition.
The missing link of Eco-hydrology Differential responses of tree species in terms of growth and survival to variation in water that they can access, the proximate cause is likely shaped through their life-history strategies, the ultimate cause. However, we neither know the depths at which the diverse tree species in a forest draw water from and its dynamics, nor variation in water at those depths vis-à-vis rainfall patterns—for lack of appropriate methods. This has been a key missing link in understanding how water shapes trees‘ life-history strategies, their demographic trade-offs and co-existence, and also our predictive ability to determine species-specific responses to changing rainfall patterns, especially droughts. Since droughts are highly stochastic events and trees‘ responses to their drought ―experiences‖ may be revealed at decadal scales, long-term evaluations are key. Therefore, the second broad objective of this thesis was to develop a framework to determine trees’ water uptake depths, variation in water availability at those depths and trees’ demographic responses over multiple decades. From this, to understand how belowground hydrology shapes drought-vulnerability, demographic trade-offs and coexistence of forest tree species. This thesis titled—Eco-Hydrology of a Seasonally Dry Tropical Forest: Tree Growth, Belowground Water Dynamics and Drought-Vulnerability—is organized as follows: Chapter 1 lays down an introduction to the thesis, followed by a description of the study site and datasets used in the thesis in Chapter 2. This thesis uses a variety of methods and multiple datasets, all of which are from the protected Seasonally Dry Tropical Forests of the Western Ghats in southern India in the Mudumalai and Bandipur National Parks. It is then followed by three data chapters: Chapter 3 describes the seasonal fluctuations in a five year long (1980-1985) tree diameter time series (using dendrometers) of a Seasonally Dry Tropical Forest in Bandipur National Park to illustrate the issue of hydrostatic stem-flexing. It investigates the possibility that band dendrometers may themselves underestimate stem shrinkage at diurnal or seasonal scale. It also evaluates if there could be a best season and time of the day for undertaking forest diameter censuses that can minimize hydrostatic bias. Chapter 4(published in Forest Ecology and Management)measures the hydrostatic bias in a sample of trees in a 50 ha PSP of a Seasonally Dry Tropical Forest in Mudumalai National Park, and proposes a novel way to correct this bias at the whole community level in the 20 year long 4-year interval growth time series. Chapter 5 (in review with Environmental Research Letters) investigates and presents two new confounding factors in growth-rainfall relationships along a spatial rainfall gradient: hydrostatic bias and size-dependency in growth rates. For this it evaluates forest tree growth estimates in seven 1-ha PSPs (~800 trees, 3-year annual time series 9using dendrometers) along a 1000 mm rainfall gradient spanning a mesic savanna-moist forest transition in Mudumalai National Park. Using the period for which seasonal diameter time series was available (2 yrs), it evaluates if the extent of seasonal fluctuations systematically vary along the gradient—most likely due to hydrostatic stem flexing. It also describes the presence of an anomalous size-diameter relationship in the mesic savanna from a large plots (50 ha PSP, diameter records using graduated tape). These observations are then used to draw insights for ―space for time‖ substitution modeling. Chapter 6 (in prep for Nature Plants) analyses belowground water environments of trees over two decades (1992-2012), a period that includes a prolonged and intense drought, in the 50 ha PSP of a Seasonally Dry Tropical Forest in Mudumalai. It uses a locally parametarised dynamic hydrological model in which site rainfall is also a forcing variable. It then develops a novel dynamic growth model and inversely estimates water uptake depths for adult trees of all common species (include ~9000 trees) in the PSP from their above-ground growth patterns over two decades vis-à-vis belowground water availability at multiple depths. It then examines if species‘ water uptake depth obtained thus is a predictor of their drought-driven mortality. Finally, this is used to evaluate the hydrological niche partitioning tree species operate under and how that drives their water uptake strategies, demographic trade-offs, and drought-vulnerability. Summarizes the thesis and suggests future direction
Structure and Dynamics of a Tropical Dry Forest Plant Community
No full textThis thesis is spurred by the overarching question “why is a plant where it is in space and time?”, which, when asked in different global communities over the last century or so, has contributed to the development of general theories of plant community ecology and has provided information relevant to understanding, managing, and predicting the future of those communities. The question is asked in the context of a seasonally dry tropical forest (SDTF) plant community in southern India, based on long-term research conducted in a permanent 50-ha sampling plot. We employ a layered approach to answering this question, wherein we deconstruct the structure and dynamics of the plant community by first establishing the spatial structure of soils, topography and lithology in the plot. Next we assess how this spatial structure, together with temporal variation in precipitation, affects plant abundances in space and time. Next we break up abundance variation into the components of recruitment, mortality and stem radial growth and assess how these respond to variation in environmental factors such as precipitation, temperature, soils, topography and fire, and biotic neighborhoods.
In Chapter 2, we examine the roles of lithology, topography, vegetation and fire in generating local-scale (<1 km2) soil spatial variability in the 50-ha plot. For this, we mapped soil (available nutrients, Al, total C, pH, moisture and texture in the top 10cm), rock outcrops, topography, all native woody plants ≥1 cm diameter at breast height (DBH), and spatial variation in fire frequency (times burnt during the 17 years preceding soil sampling) in a permanent 50-ha plot. Unlike classic catenas, lower elevation soils had lesser moisture, plant-available Ca, Cu, Mn, Mg, Zn, B, clay and total C. The distribution of plant-available Ca, Cu, Mn and Mg appeared to largely be determined by the whole-rock chemical composition differences between amphibolites and hornblende-biotite gneisses. Amphibolites were associated with summit positions, while gneisses dominated lower elevations, an observation that concurs with other studies in the region which suggest that hillslope-scale topography has been shaped by differential weathering of lithologies. This “inverse catena” pattern is possibly reinforced by topography due to nutrient leaching and clay depletion in the drainage area. Neither NO3--N nor NH4+-N was explained by the basal area of trees belonging to Fabaceae, a family associated with N-fixing species, and no long-term effects of fire on soil parameters were detected. A strong SW-NE trending P pattern remained unexplained by any of the factors considered. Local-scale lithological variation is an important first-order control over soil variability at the hillslope scale in this SDTF, by both direct influence on nutrient stocks and indirect influence via control of local relief.
The extent to which interspecific niche differences structure plant communities is highly debated, with extreme viewpoints ranging from fine-scaled niche partitioning, where every species in the community is specialized to a distinct niche, to neutrality, where species have no niche or fitness differences. However, there exists a default position wherein niches of species in a community are determined by their evolutionary and biogeographic histories, irrespective of other species within the community. According to this viewpoint, a broad range of pair-wise niche overlaps – from completely overlapping to completely distinct – are expected in any community without the need to invoke interspecific interactions.
In Chapter 3, we develop a method that can test for both habitat associations and niche differences along an arbitrary number of spatial and temporal niche dimensions and apply it to a 24-year data set of the eight dominant woody-plant species (representing 84% and 76% of total community abundance and basal area, respectively) from the 50-ha plot, using edaphic, topographic and precipitation variables as niche axes.
Species separated into two broad groups in niche space – one consisting of three canopy species and the other of a canopy species and four understory species – along axes that corresponded mainly to variation in soil P, Al and a topographic index of wetness (the second and fourth principal components (PCs) of soil and topographic variables). All three species from the former group and one understorey species from the latter group showed evidence of niche specialization along the same axes. Based on the landscape-scale distributions, local-scale habitat associations, and traits of the constituent species, we suggest that species in the former group have a more resource-conservative strategy compared to those in the latter group. Species within groups tended to have significantly greater niche overlap than expected by chance. Community-wide niche overlap in spatial and temporal niche axes was never smaller than expected by chance. Species-habitat associations were neither necessary nor sufficient preconditions for niche differences to be present.
Our results suggest that this tropical dry-forest community consists of several tree species with broadly overlapping niches, and where significant niche differences do exist, they are not readily interpretable as evidence for niche differentiation. We argue, based on a survey of the literature, that many of the observed niche differences in tropical forests are more parsimoniously viewed as autecological differences between species that exist independently of interspecific interactions.
In Chapter 4, we study the dynamics of the plant community in relation to environmental factors and biotic neighborhoods. We assess resources (precipitation, soil nutrients), environmental conditions (temperature), microhabitat conditions (topography), disturbances (fire) and conspecific and heterospecific
plant neighborhoods to identify which of these best predicted mortality, recruitment and growth over a 24-yr study period. We fitted regression trees with recruitment, mortality or growth as the response variable and environmental and biotic neighborhood variables as predictors, with tree selection performed by a cross validation technique that accounted for the spatial and temporal autocorrelation present in the data.
Niche specialists or species with abundances skewed towards particular habitats did not necessarily grow faster, recruit more or die less on “preferred” habitats. On the whole, spatial environmental factors were selected into models less frequently than either temporal environmental or neighborhood factors, and their effect sizes were also smaller. The first and second PCs of soil and topographic variables were selected into more models than the remaining PCs.
While there was some evidence of conspecific negative density dependence, particularly on suppressing growth, density-dependent effects were on the whole weaker than temporal environmental factors and also decayed rapidly with distance. Positive density-dependence was prevalent, possibly resulting from dispersal limitation and facilitation. In some cases, initial increases in neighborhood density had positive effects that turned negative when densities further increased, suggesting non-linear responses.
Precipitation increases largely had a positive, and minimum and maximum temperatures increases a negative, effect on recruitment, growth and survival, although responses were species-specific and, sometimes, non-linear. By far, the strongest and most consistent effects amongst all factors considered were that of fire, with recent fires having a strong and unidirectional, negative effect on all species for which fire was selected into a model.
From a theoretical standpoint, there is limited support for the neutral perspective, given the strong and species-specific responses to spatial and temporal environmental variation and the presence of niche specificity at the local scale. Despite the evidence supporting the existence of niche specialization, it seems unlikely that this community is strongly stabilized by the presence of systematic niche differences. The net evidence on the structure and dynamics of this community point to what may be considered a null hypothesis, that is, species are responding individualistically – and independently of each other – to fluctuations in the environmental. It is hoped these results will provide information relevant to understanding, managing, and predicting the future of this ecosystem and contribute towards the development of general theories of plant community ecology.Ministry of Environment, Forests and Climate Change, the Department of Science and Technology, the Department of Biotechnolog
The Nation and its citizens: Tales of Bondage and Belonging
No full textThe Nation and Its Citizens: Tales of Bondage and Belonging is about nationalism as a uniquely modern political doctrine, shaped by the lived experience of citizens. Nationalism has changed in its appeal through history, as have its manifestations. Getting to know these may be part of the challenge of negotiating the ongoing turmoil, both internal and external to the nation.
In addressing these issues, this book offers several propositions on how the construct of ‘identity’ is crafted, with all its power to influence modern politics. It then explores how well India’s practice of republican democracy has lived up to the competing dynamics of identity and equality.
As India celebrates 75 years of Independence, author Sukumar Muralidharan takes the readers on a journey into how the sense of fellow-feeling and mutual dependence of the nation are consolidated, and under what circumstances these could fray. The Nation and Its Citizens offers many fresh perspectives in understanding India’s unique political trajectory
And yet it shrinks: a novel method for correcting bias in forest tree growth estimates caused by water-induced fluctuations
No full textAccuracy in tree woody growth estimates is important to global carbon budget estimation and climate-change science. Tree growth in permanent sampling plots (PSPs) is commonly estimated by measuring stem diameter changes, but this method is susceptible to bias resulting from water-induced reversible stem shrinkage. In the absence of bias correction, temporal variability in growth is likely to be overestimated and incorrectly attributed to fluctuations in resource availability, especially in forests with high seasonal and inter-annual variability in water. We propose and test a novel approach for estimating and correcting this bias at the community level. In a 50-ha PSP from a seasonally dry tropical forest in southern India, where tape measurements have been taken every four years from 1988 to 2012, for nine trees we estimated bias due to reversible stem shrinkage as the difference between woody growth measured using tree rings and that estimated from tape. We tested if the bias estimated from these trees could be used as a proxy to correct bias in tape-based growth estimates at the PSP scale. We observed significant shrinkage-related bias in the growth estimates of the nine trees in some censuses. This bias was strongly linearly related to tape-based growth estimates at the level of the PSP, and could be used as a proxy. After bias was corrected, the temporal variance in growth rates of the PSP decreased, while the effect of exceptionally dry or wet periods was retained, indicating that at least a part of the temporal variability arose from reversible shrinkage-related bias. We also suggest that the efficacy of the bias correction could be improved by measuring the proxy on trees that belong to different size classes and census timing, but not necessarily to different species. Our approach allows for reanalysis - and possible reinterpretation of temporal trends in tree growth, above ground biomass change, or carbon fluxes in forests, and their relationships with resource availability in the context of climate change
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