Understanding how the spatial arrangement of habitats in a landscape affects biodiversity, and the resulting consequences for ecosystem services, is a continuing challenge for ecologists. Microcosms provide an opportunity to study landscape-scale processes on a smaller, more tractable scale. A microcosm of soil and leaf litter will be used to examine how the size and spatial arrangement of leaf litter influence the diversity of organisms contained within, and how observed differences in species diversity affects an important ecosystem service: leaf litter decomposition.

The results from this project will enable scientists and land managers to manage natural resources more effectively and efficiently, while conserving biodiversity. Conducting research on small, yet critical, soil organisms is challenging because they can be difficult, time consuming, or even impossible to identify visually. This project will use a state-of-the-art method of DNA analysis for rapid and accurate identification of the target organisms. The use and refinement of DNA technology is important for the field of community ecology, and science in general, since adoption of new methods based on the latest technology offers the opportunity to break new ground and to enable research in areas where data collection was previously not practical.

Project Report

Habitat loss is a major threat to biodiversity. On a landscape scale, habitat loss often results in a reduction in the mean size of habitat patches as well as an increase in the mean distance between patches (i.e. patches become smaller and more isolated). Because many species require relatively large areas of connected habitat, species loss often accompanies habitat loss in the landscape. The type of habitat in the intervening area (called matrix habitat), which surrounds focal habitat patches, can also have important effects on local diversity, but little is known about how the quality of matrix habitat can mediate the effects of patch size and isolation on biodiversity. There have been very few experimental studies that simultaneously examine the effects of both patch size and isolation on ecological communities and we know of no other study that also examines how matrix quality can mediate the effects of patch size and isolation on community structure. Interest in the effects of biodiversity on ecosystem function has resulted in a large body of literature, focused mainly on how increased diversity can enhance the productivity of plants. However, comparatively little is known about the effects of diversity on decomposition and nutrient cycling. Both the composition and diversity of decomposer species (e.g., microbes and microarthropods) can have important influences on decomposition rates, but a general pattern has not yet emerged. We used a microcosm system comprised of microbial and microarthropod communities inhabiting patches of pine and oak leaf litter on 1 m2 miniature landscapes to examine (1) how matrix quality mediates the effects of habitat size and isolation on local communities, and (2) how the resulting changes in community structure affect the rate of leaf litter decomposition. Each miniature landscape was comprised of four patches of oak litter (the focal habitat). Our experiment was a fully factorial design: patches of oak litter were either large or small, connected or isolated, and surrounded by an alternative habitat type of either pine litter or bare ground. We proposed to use a next-generation sequencing method (Illumina sequencing) to assess differences in diversity and species composition among treatments, however unresolved problems during sample preparation prevented successful sequencing. We therefore used a different molecular method, which provided sufficient data to answer our research questions. Differences in leaf litter decomposition among treatments were quantified by measuring leaf mass loss over time in small bags of leaf litter. With our study we found, as have others before us, that patch size and isolation are important for both the number of species and which particular species are present. However, we also found that the quality of the intervening matrix habitat can mediate the effects of patch size and isolation on communities. This has important consequences for the ecosystem function of leaf litter decomposition. When oak litter patches were surrounded by a matrix of pine litter habitat, as opposed to bare ground, the rate of oak litter decomposition was reduced. The reduction in decomposition rate cannot be attributed to differences in temperature or pH that may be associated with the pine litter habitat. The reduction in litter decomposition appears to result from differences in decomposer species composition. Species colonizing oak litter patches from pine litter patches may not be sufficiently adapted to local conditions or to processing oak leaf litter, therefore resulting in inefficient decomposition of leaf litter in that environment. In conclusion, we find that biodiversity is dependent on patch size and isolation, and that the quality of the intervening matrix habitat can mediate the effects of patch size and isolation on biodiversity. Moreover, the effects of landscape structure on biodiversity can translate to effects on important ecosystem processes, namely decomposition. This research integrates principles from multiple subfields in ecology, including microbial, community, landscape, and ecosystem ecology, while using the tools of molecular biologists and ecologists. We collaborated with another lab at FSU in order to complete the molecular analysis of microbial and microarthropod communities. Our collaborators use similar molecular methods to research very different questions in the fields of phylogenetics and speciation, and would not have otherwise investigated such questions of landscape structure on biodiversity and ecosystem function. Our project should help facilitate the development of new and efficient molecular methods of species identification for soil arthropods, which otherwise require an often prohibitive investment in time and expertise. Similar methods are commonly used to study patterns of microbial diversity, however our methods have rarely been used to study microarthropod diversity. The results of this research have been presented at a national conference (Ecological Society of America 2012) and to the Department of Biological Science at FSU. Results have been published in a PhD dissertation and are being written for publication in a peer-reviewed journal.

National Science Foundation (NSF)
Division of Environmental Biology (DEB)
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Maureen M. Kearney
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Florida State University
United States
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