Assessing ecological communities in the wake of ongoing land use change in the Atlantic Forest and Pantanal of Brazil.

摘要

Globally, land use change (LUC) is responsible for 20% of anthropogenic CO2 emissions, widespread losses of ecosystem services and biodiversity, and erosion of ecosystem resilience to disturbance and climate change. In Brazil, vast tracts of tropical forest and other types of natural vegetation cover have been (and are being) replaced by crops and planted exotic (non-native) pasture, the latter for livestock rearing. I investigated how a range of ecological communities are being affected by ongoing LUC in two Neotropical biomes, the Atlantic Forest and Pantanal of Brazil. My objectives were to: (1) help understand the consequences of LUC, (2) provide baselines for current and future monitoring studies, and (3) help prioritize conservation actions.;The Atlantic Forest, which originally covered 1.5 million km2 of eastern Brazil, is a biodiversity hotspot with a range of tropical forest formations and a high proportion of endemic species. Five-hundred years of LUC, including coffee and sugarcane cultivation, timber extraction, wood charcoal production for industry, and urban development, shrank forested area to 11% of original coverage, creating a highly-fragmented landscape of mostly small (<100 ha) forest patches within an agriculturally-dominated matrix. In a fragmented region of inland seasonal forest, called the Planalto or interior Atlantic Forest, I investigated the state of headwater stream fish communities 80 years after much of the original vegetation was cleared for coffee plantations.;The Pantanal, which covers 150,500 km2 in central-western Brazil, southeastern Bolivia and northeastern Paraguay, is a highly-seasonal floodplain comprised of tropical forest, savanna, and wetland formations supporting large populations of fishes, waterbirds, and charismatic wildlife species. Since the late 1800s, LUC in the Pantanal has centered around extensive cattle ranching and more recently (since the 1960s) the expansion of grazing lands through conversions of native vegetation to planted exotic pasture. In the southern Pantanal, I investigated how cattle activity and ranching practices are affecting: (1) the macroinvertebrate and waterbird communities of enrichment-prone alkali soda lakes, and (2) the mammalian and avian forest communities that aggregate at fruiting trees.;Because historical records of biodiversity were lacking and focal species of conservation importance were largely unidentified in the study regions, community-level assessments were ideal starting points for evaluating the consequences of LUC. The assessments related abundance trends of multiple species to major environmental gradients, allowing me to characterize communities in relation to LUC and identify indicator species with strong responses to LUC. Analyses included ordinations that described species compositional trends along LUC gradients, univariate and multivariate comparisons of community composition between categories representing different levels of LUC, and indicator species analyses that identified species characteristic of particular LUC categories.;Despite the wide array of taxa and environments investigated, there were a number of common community-level responses to increasing intensity of LUC: (1) turnover and loss of species and guilds, (2) loss of environmental and biotic heterogeneity, (3) dominance by enrichment- and disturbance-tolerant species, (4) bottom-up trophic cascading, and in one case (5) an ecosystem regime shift. Applying results from the assessments of ecological communities and environments (Chapters 2--4, summarized below), I presented conservation priorities aimed at curbing impacts from LUC and maintaining biodiversity and ecosystem services. A key challenge will be convincing stakeholders, which are mostly private landowners, to change and improve their land use practices. To that end, successful approaches will need to balance environmental and economic sustainability. An effective conservation strategy will combine: (1) dissemination of basic research results demonstrating impacts from LUC, (2) additional research on sustainable management practices, (3) a landowner outreach program demonstrating the economic and long-term environmental benefits of adopting sustainable land use practices, and (4) an environmental education program that introduces sustainable practices to future landowners, land managers, and rural laborers. (Abstract shortened by UMI.).