landscape ecology of small mammals || small mammal ecology: a landscape perspective

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1 Small Mammal Ecology: A Landscape Perspective GARY W. BARRETT AND JOHN D. PELES Emergence of the Landscape Paradigm The dictionary defines landscape as "an expanse of the scenery, usually ex- tensive, that may be seen by the eye as one view." Landscapes have been a construction of the visual perspective for centuries. For example, in one of the older shrines at Catal Hiiyiik (presently in the country of Turkey), a paint- ing was uncovered that has been interpreted as pure landscape (de la Croix and Tansley 1986). According to C-14 dating, it was painted soon after 6200 S.c. More recently, a special issue of Time magazine, entitled "American Vi- sions," illustrated numerous landscape paintings, including Thomas Moran's "The Grand Canyon of the Yellowstone" (1893-1901), the first American landscape by an American artist to be bought by the U.S. government and put on display in the Capitol (Hughes 1997). Landscapes have also been viewed as the subject matter in landscape de- sign for centuries in which gardens and natural scenery (i.e., the mosaic of natural, agricultural, and human-built systems) were established and man- aged for human creativity, enjoyment, and benefit. In an ecological context, a landscape has more recently been defined as "a heterogeneous land area composed of a cluster of interacting ecosystems that are repeated in a similar form throughout" (Forman and Godron 1986). The term landscape ecology arose from the European disciplines of regional geography and vegetation science and was first used in the late 1930s (Naveh and Lieberman 1984, Turner 1989). Diverse fields, such as economics, geography, and environmen- tal design, frequently refer to "the landscape" when describing, planning, or designing a particular space, vista, or region. Although landscape ecology became an active discipline in Europe after World War II, this field of study did not become firmly established in North America until the early 1980s. It was not until 1983, however, that the definition of and mission statement for landscape ecology were agreed upon, resulting in this field "anchoring its roots" in the United States. A workshop, funded by the NSF, was held at G. W. Barrett et al. (eds.), Landscape Ecology of Small Mammals © Springer Science+Business Media New York 1999

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Page 1: Landscape Ecology of Small Mammals || Small Mammal Ecology: A Landscape Perspective

1 Small Mammal Ecology: A Landscape Perspective

GARY W. BARRETT AND JOHN D. PELES

Emergence of the Landscape Paradigm

The dictionary defines landscape as "an expanse of the scenery, usually ex­tensive, that may be seen by the eye as one view." Landscapes have been a construction of the visual perspective for centuries. For example, in one of the older shrines at Catal Hiiyiik (presently in the country of Turkey), a paint­ing was uncovered that has been interpreted as pure landscape (de la Croix and Tansley 1986). According to C-14 dating, it was painted soon after 6200 S.c. More recently, a special issue of Time magazine, entitled "American Vi­sions," illustrated numerous landscape paintings, including Thomas Moran's "The Grand Canyon of the Yellowstone" (1893-1901), the first American landscape by an American artist to be bought by the U.S. government and put on display in the Capitol (Hughes 1997).

Landscapes have also been viewed as the subject matter in landscape de­sign for centuries in which gardens and natural scenery (i.e., the mosaic of natural, agricultural, and human-built systems) were established and man­aged for human creativity, enjoyment, and benefit. In an ecological context, a landscape has more recently been defined as "a heterogeneous land area composed of a cluster of interacting ecosystems that are repeated in a similar form throughout" (Forman and Godron 1986). The term landscape ecology arose from the European disciplines of regional geography and vegetation science and was first used in the late 1930s (Naveh and Lieberman 1984, Turner 1989). Diverse fields, such as economics, geography, and environmen­tal design, frequently refer to "the landscape" when describing, planning, or designing a particular space, vista, or region. Although landscape ecology became an active discipline in Europe after World War II, this field of study did not become firmly established in North America until the early 1980s.

It was not until 1983, however, that the definition of and mission statement for landscape ecology were agreed upon, resulting in this field "anchoring its roots" in the United States. A workshop, funded by the NSF, was held at

G. W. Barrett et al. (eds.), Landscape Ecology of Small Mammals© Springer Science+Business Media New York 1999

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Allerton Park, Piatt County, Illinois, during April 1983. A report entitled "Landscape Ecology: Directions and Approaches" summarized the workshop (Risser et al. 1984), and landscape ecology quickly became a new integrative field of study in the United States. This mission statement recommended that landscape ecology consider the development and dynamics of spatial hetero­geneity, spatial and temporal interactions and exchanges across heteroge­neous landscapes, influences of spatial heterogeneity on biotic and abiotic processes, and the management of spatial heterogeneity. Following this land­mark NSF workshop, landscape ecology quickly emerged as an integrative field of study and became established as an area of scientific research and education. In the United States, for example, the International Association for Landscape Ecology (US-IALE) was established and held the first annual sym­posium on Landscape Ecology at the University of Georgia January IS-17, 1986. The first issue of the journal Landscape Ecology was published in July 1987. It is of interest that 21 out of 261 articles published in Landscape Ecology (8%) have focused on the ecology of small mammals.

Levels-of-Organization Perspective

The landscape has increasingly been recognized as a component of the lev­els-of-organization concept (Forman and Godron 1981, Lidicker 1994, 1995, Barrett et al. 1997a). Ecologists initially focused more on the population, community, and ecosystem levels-of-organization. Ecologists came to recog­nize, however, that numerous processes, such as the transfer of materials and exchange of biota between ecosystems, occur at greater spatial scales. Ecolo­gists now recognize that emergent properties arise when the landscape is investigated as a whole. It is important that research conducted at the land­scape level of organization often permits an understanding of ecological mechanisms and processes that cannot be addressed at lower levels of organi­zation (Turner 1989, Wiens et al. 1993, Lidicker 1995). For example, pro­cesses, such as rates of dispersal, habitat connectivity, and the transfer of materials and exchange of biota (source-sink dynamics) between habitat types or ecosystem types are best understood from a landscape perspective. It has been suggested that landscape processes can perhaps best be understood based on the levels-of-organization concept (Barrett et al. 1997a).

Small Mammals as Model Organisms

Various vertebrate groups, such as birds (Opdam 1991, Wiens 1995, Tucker et al. 1997) and amphibians (Dickman 1987, Laan and Verboom 1990, Vas and Stumpel 1996) have been used to test hypotheses at the landscape scale. We feel, however, that small mammals are the ideal taxonomic group to serve as

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models for addressing questions at this scale. We make this argument for the following reasons:

1. We know detailed information regarding the biology and natural histo­ries of numerous species of small mammals, especially at the organismal, popUlation, and community levels of organization. We also know the roles and niches of member species functioning in old-field, grassland, and forest ecosystems.

2. We can mark (identify) small mammals and follow their lives and monitor their patterns of movement. We can determine their survivorship, repro­ductive success, size of home range, and trophic level dynamics at the community, ecosystem, and landscape levels. Live-trapping and radiote­lemetry studies have permitted insights regarding dispersal behavior and why a particular species predominantly selects a particular ecosystem or patch type. This is the kind of information ecologists need to understand how landscape patterns affect population and community dynamics of small mammals.

3. Because small mammals live in relatively small spatial areas, have short lives, typically disperse from their natal areas on reaching adulthood, and frequently exhibit behavioral response to seasonal changes, small mammal ecologists can gain new insights into processes such as rates of colonization, extinction, dispersal, and persistence. These data and in­formation are vital to gaining a better understanding of ecosystem and landscape processes and relationships.

In essence, we already know the many important details of the life histories of numerous species of small mammals. Because of the good work and sound research on the part of ecologists who study small mammals, it turns out that this knowledge base regarding how small mammals live their lives make them model subjects for the study of landscape-level processes. Because of this base of knowledge, it is now possible to move beyond description and into the experimental phase of science. With cleverly designed experiments, it is possible to answer questions and to test simple hypotheses, thereby gain­ing insights into how landscapes operate. The small mammal ecologists who contributed to this book are the first to ask these questions, and to design studies that are beginning to open this window of opportunity and under­standing.

Questions regarding population-level and community-level processes in small mammals were traditionally addressed from the perspective of indi­vidual habitat patches; however, the publication of the seminal paper en­titled "Spatial dynamics of field voles Microtus agrestis in heterogeneous landscapes," published in Oikos by L. Hansson of the Swedish University of Agricultural Sciences (Hansson 1977), led many mammalian ecologists to consider the importance of the surrounding landscape when investigating the

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relationship of ecological processes to population dynamics and survivor­ship in small mammals. Following the paper's publication the ecology of small mammals has increasingly been studied from a landscape perspective, especially during the 1990s. For example, landscape-level investigations in­volving small mammals have addressed questions such as the effects of land­scape elements (e.g., corridors) on dispersal behavior (e.g., Henderson et al. 1985, Merriam and Lanoue 1990, LaPolla and Barrett 1993, Lorenz and Barrett 1993) the effects of habitat fragmentation on species success and abundance (e.g., Robinson et al. 1992, Diffendorfer et al. 1995, Collins and Barrett 1997), or the role of patch quality (as well as shape or size) on small mammal popu­lation dynamics (e.g., Harper et al. 1993, Peles and Barrett 1996).

Much large-scale (temporal and spatial) theory had fortunately been de­veloped, and partially tested, which served as an underpinning infrastructure regarding investigations that focused on the role of small mammals at the landscape level. These "roots" for landscape ecology include island bioge­ography (MacArthur and Wilson, 1967), metapopulation theory (Levins 1969, 1970), hierarchy theory (Allen and Starr 1982), and patch dynamics (Pickett and Thompson 1978, Pickett and White 1985). Thus, the "time was ripe" as we entered the final decade of the twentieth century to establish a set of rigorous and robust experimental designs that focused on small mammals at the landscape scale.

Research Approaches

Typical of most emerging fields of science, the majority of studies in land­scape ecology have been descriptive in nature. These studies, however, have been important because they helped to develop new technologies (GIS, sys­tems modeling), to encourage new holistic approaches for addressing ques­tions at greater temporal and spatial scales (hierarchy theory, cybernetics), and to provide a more integrative understanding of the total environment by the public (Ahl and Allen 1996, Barrett et al. 1997a).

Although several books have been published that describe the emerging field oflandscape ecology (Naveh and Lieberman 1984, Forman and Godron 1986, Zonneveld and Forman 1990, Lidicker 1995), as well as an array of books that focus on select components of, or changes in, the landscape, such as ecotones (Risser et al. 1984), corridors (Saunders and Hobbs 1991), habitat fragmentation (Harris 1984), or analysis of heterogeneity (Turner and Gardner 1990), few books have focused on the need for and design of experimental approaches to landscape ecology. The reasons that so few replicated, experi­mental studies have been conducted at this level of organization are because of funding constraints (Lubchenco et al. 1991), the problems associated with pseudoreplication (Hurlbert 1984), and/or the difficulties typically encoun­tered with long-term, large-scale investigations (Likens 1989).

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A number of researchers have designed and conducted investigations to address questions regarding the ecology of small mammals at the landscape scale. These investigators have utilized small mammals as a model taxonomic group in which major questions have been addressed and tested to increase our understanding of landscape ecology. These investigations have illus­trated both how landscape patterns and processes have impacted small mam­mals functioning within these landscapes as well as how small mammals have, in turn, increased our understanding oflandscape structure and function (e.g., Ostfeld et al. 1997).

Small Mammals in Landscapes

Several books have been published in the area of small mammal ecology, including those that have focused on small mammal population dynamics (Golley et al. 1975), patterns of dispersal (Chepko-Sade and Halpin 1987, Stenseth and Lidicker 1992), and social behavior (Cockburn 1988). Lidicker (1995) was the first to begin a dialogue regarding the relationship of small mammals to landscape ecology. No attempt has been made, however, to pro­vide a comprehensive, experimental, landscape-level perspective regarding the ecology of small mammals at this scale, and how this increased knowl­edge has enhanced our understanding of landscape processes. That is the purpose of this book.

The focus of this book, therefore, is to describe experimental landscape approaches used to advance our understanding of small mammal ecology; to synthesize existing landscape theory regarding the role of small mammal ecology at these greater spatial scales; to challenge researchers to design new, integrative experimental studies within this new area of investigation; and to illustrate how small mammals represent a model group of organisms to advance our understanding of landscape structure and dynamics. To accom­plish this objective, a group of ecologists with expertise in the area of small mammal ecology was assembled at a workshop on April 25-26, 1997, at the Conference Center at the Savannah River Ecology Laboratory, Aiken, South Carolina, to help outline this book. It was decided after extensive discussion to outline this book into the following areas of knowledge: patterns of move­ment and habitat use (Chapters 2-5), population and community dynamics in heterogeneous landscapes (Chapters 6-9), ecological processes at habitat edges (Chapters 10-12), experimental designs and parameter estimators at the landscape level (Chapters 13-14), and a current synthesis (Chapter 15), including recommendations regarding future investigations and trans­disciplinary approaches.

The mechanisms, concepts, processes, and approaches described in this book naturally have great relevance to larger mammalian species; to advancing our theory and understanding in related fields of study such as conservation

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ecology, disturbance ecology, restoration ecology, and sustainable landscape management; and to challenge the next generation of ecologists, mammalo­gists, and resource managers to establish studies at meaningful scales, includ­ing the urgent need to recouple and better manage an integrated urban and agricultural landscape (Barrett et al. 1997b).

Whereas in the past small mammals served as a model group to advance our knowledge at the molecular and cellular (mainly in a laboratory setting) through the organismal and population levels of organization, we now en­courage researchers to consider small mammals as a model experimental group to advance our knowledge and understanding at the community, ecosystem, landscape, and global levels. Small mammals represent an excellent group of organisms to investigate transcending processes across all levels of organiza­tion (Barrett et al. 1997a). We argue that the landscape level provides the least understood, but most exciting, level of organization in which to address questions that will both increase our understanding of the ecology of small mammals and how small mammals can be used to advance our understanding of landscape patterns and processes. Accepting this challenge will greatly advance our understanding both in the areas of landscape ecology and small mammal ecology, and will also illustrate how mammalian species and metapopulations function in our increasingly fragmented landscape. Biodiversity (genetic, species, niche, and habitat diversity) of small mammals, for example, must be investigated and understood based on a perspective ranging from the molecular and organismal to the landscape and global levels of organization. Such knowledge and understanding is mandatory if we are to protect biodiversity, restore landscapes in a sustainable manner, and manage our biotic and abiotic resources in an integrative manner for future generations.

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