Landscape Biodiversity

Biodiversity, the variety of biological life, is hierarchically organized at different scales, from the molecular and genetic levels to populations, ecosystems, and landscapes. Research on landscape biodiversity studies how the interaction between the distribution of biotic factors and human land use shapes the distribution of biodiversity at landscape scales. Landscape ecology emphasizes the connection between spatial pattern and ecological process. Thus, landscapes are viewed as heterogeneous compositions of many smaller units, typically ecosystems. The type, quality, relative proportion, and spatial distribution of these ecosystems determine the flows of energy, material, and species through the landscape and thus affect the spatial distribution of biodiversity. Abiotic factors such as soils, topography, and climate further interact with and constrain the biological interactions between organisms, resulting in complex spatial patterns of species distribution in a landscape. These spatial patterns in turn influence the distribution of abiotic and biotic resources within the landscape. Thus, landscape biodiversity studies tend to focus on the relationships between pattern (spatial patterns of species distribution) and process (processes of species survival, persistence, growth, and dispersal).

A landscape perspective becomes especially critical for biodiversity management as human impacts on biodiversity increase, since the consequences of human modifications in land use and land cover (such as habitat fragmentation) manifest themselves most severely at the landscape scale yet are often ignored by local ecological [Page 1702]studies. Landscape biodiversity research therefore typically focuses on spatial and temporal scales that are much larger and longer than those addressed in traditional studies of ecology, providing an organizing framework that is useful for land managers and conservation science. For instance, a landscape framework is often used while planning the location of protected areas and parks, such that a park is not created in isolation but is often surrounded by a buffer area of limited human use to improve spatial connectivity and reduce the impacts of habitat fragmentation. Theories of island biogeography, vegetation gradient analysis, and metapopulation dynamics have been influential in landscape biodiversity planning, with conservation biologists striving to protect and restore large, connected landscapes for the survival of rare and endangered species.

Indices of species diversity can be computed at a range of scales, from the local to the landscape level. Alpha diversity refers to the diversity of species at a particular location, while beta diversity describes the turnover in species between two locations. Gamma diversity integrates information from alpha and beta diversity studies to describe the levels of species diversity at larger, landscape scales. The composition and structure of landscapes critically influences gamma diversity, and in-depth understanding of this relationship is critical for biodiversity planning at the landscape scale. The composition of a landscape refers to the number, variety, and relative proportion of the components of a landscape—ecosystems, habitats, and ecological communities. The structure of a landscape is described by the geometry of these components—their size, shape, connectivity, and context—which affects the distribution of specific species to different extents. For instance, area-sensitive species such as large carnivores have requirements for large, unfragmented habitats; edge-sensitive species tend to avoid edges where there are sharp atmospheric gradients and increases in human presence; while dispersal-sensitive species are affected when connectivity between habitats is affected. Thus, other things being equal, patches of greater area constitute better habitat for area-sensitive species. Habitat shape is also critical, as patches of the same size that are more indented or linear have a greater edge, consequently harboring a greater proportion of edge-generalist species while being avoided by edge-sensitive species. Connectivity between patches affects metapopulation dynamics and determines the overall probability that a species will persist on a landscape. Context is also critical; for instance, an orchard in the midst of a forest is more likely to harbor edge-sensitive forest birds than if it were located in the center of a city.

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