Islands of nature.

Your primary concern is biological diversity: in other words, to prevent as many native species as possible from becoming extinct.

Here's a hypothetical puzzle for you: It's the year 2000 and the U.S. Congress has been seized by a rare case of nonpartisan common sense. They've consolidated all the land conservation agencies into one. We'll call it the Department of Nature Reserves. You've been placed in charge of it (congratulations) and given the mission of preserving five percent of the nation's land mass. (That's about a twofold increase, incidentally, over what's currently protected in wilderness, national parks, and large state parks.)

Your primary concern is biological diversity: in other words, to prevent as many native species as possible from becoming extinct. It's a great job, but you soon find there's one fundamental question that's going to make your decisions very difficult: Will more species be saved by setting aside a small number of very large natural areas or by preserving a large number of tiny, disconnected ones?

That is a question being asked in a sub-discipline of ecology called island biogeography. As the phrase implies, it is the study of the ecology of islands. It has become, in addition, the study of the degree to which the ecology of protected lands may be analogous to that of islands as the habitat outside their boundaries becomes increasingly altered. Island biogeography may help solve our hypothetical puzzle.

The seminal event in this field was the publication, in 1967, of The Theory of Island Biogeography by Robert MacArthur and Edward O. Wilson. In that book, the authors reported two predictable principles of islands. The first is that larger islands support more species of animals than smaller ones. The second is that remote islands support fewer species than less remote islands. Over geologic time, islands experience both extinctions and colonizations. But based mainly on these two factors--size and remoteness--each island has a number of faunal species it will tend toward.

MacArthur and Wilson took the second principle, remoteness, and expanded it to include insularity--a form of remoteness not caused necessarily by distance but by anything that effectively tends to insulate the island from other lands. They also predicted that their theory would apply not just to islands but to isolated land-based habitats:

"Insularity is moreover a universal feature of biogeography. Many of the principles graphically displayed in the Galapagos Islands and other remote archipelagos apply in lesser or greater degree to all natural habitats" (MacArthur & Wilson, 1967, p. 3).

Around the same time, a scientist named Preston (1962a, 1962b) studied distributions of common and rare species in natural areas. One of his conclusions, simply put, was that many nature reserves were too small: "If what we have said is correct, it is not possible to preserve in a State or National Park, a complete replica on a small scale of the fauna and flora of a much larger area (1962b, p. 427)."

The late 1960s and 1970s witnessed a rapid growth in interest in island biogeography. Jared Diamond, researching bird diversity and equilibrium theory in the tropics, became concerned about the effects of rain forest destruction. Referring to attempts in New Guinea to save habitat samples, he wrote "If these plans succeed, the rain forests, instead of disappearing completely, will be broken into "islands" surrounded by a `sea' of open country in which forest species cannot live" (1972, p. 3203).

Continuing to apply island biogeography to conservation problems, Diamond (1975) offered a set of "design principles" for an ecologically sound park ("nature reserve") system. Among his principles were that large units will hold more species than small ones; that a unit close to another unit will hold more species than an isolated one; that a group of reserves adjacent to each other or clustered close together will hold more species than the same units isolated from each other; that a round unit will hold more species than a long, narrow one; and that corridors between fragmented habitats might alleviate the island effect (1975) (our emphasis). These "design principles" were supported, though phrased differently, nearly twenty years later in a paper by Fahrig and Merriam (1994) called "Conservation of Fragmented Populations."

An important contribution was made by Terborgh (1975), who also argued for corridors between reserves and pointed out the need for spacious wilderness complexes if large predators were to be saved. Similar conclusions were drawn by May (1975) in a paper called "Island Biogeography and the Design of Wildlife Reserves."

This line of thinking was challenged, however, in 1976, by Simberloff and Abele, who argued that May, Diamond and others were generalizing too broadly with insufficient evidence. A rather spirited debate ensued in certain journals, especially Science, for several years, the key question often being whether one large wilderness complex was preferable to several scattered smaller ones of equal total size ([eland big-' geography and conservation, 1976; Simberloff & Abele, 1976; Gilpin & Diamond, 1980; Higgs & Usher, 1980; Higgs, 1981). Central to that question was the role of habitat diversity: would it be better, given limited resources for conservation, to save one or two large chunks of relatively homogeneous habitat, or many small pieces of diverse ones? Another related question: To what degree is the species/ area correlation a function of the fact that the larger the island, the more habitats it's likely to contain?

None of these questions have yet been sufficiently answered. A long-term attempt is underway, though, in Brazil through a project originally called the Minimum Critical Size of Ecosystems Project. The designers of this project used a Brazilian law requiring that 50 percent of the forest on certain lands be saved when the rest is cleared for cattle ranches. The researchers were able to inventory species before cutting began and to arrange for the remaining fragments to be left in several prescribed sizes for comparison purposes. What they have found so far--not surprisingly, perhaps--supports both the "size per se" theory and the habitat diversity theory. The "size per se" theory was supported by losses of numerous species from the first two fragments studied, a one-hectare piece and a ten-hectare piece. Among the disappeared were large predators such as the jaguar, puma, and margay cat. Vanished prey species included pace, deer, and white-lipped peccary (Lovejoy et al., 1984).

From the same project, however, there emerged at least one dissenter to island biogeography. Barbara Zimmerman studied 39 Amazon frog species and concluded that the critical variable for frogs, at least, is not size but habitat quality (Zimmerman and Bierregaard, 1986). Island biogeography, she wrote, "has taught us little that can be of real value planning real reserves in real places".

And that may be true, especially given the practical difficulties of preserving large spaces. In the late 80s and 90s, ecologists have proposed other models, most of them more complex. But the "species/area correlation" continues to prove strong, and the isolation of habitat fragments continues to show up as a primary reason for the loss of species within them. For example, Soulec et al. (1988) conducted a thorough study of chaparral-dependent birds in the increasingly fragmented canyon habitat around San Diego, California. They found that virtually all the fragments were losing species. The ones that have lost the most species were the older, the smaller, and the more insulated. "...[I]t appears," they wrote, "that all the chaparral-requiring species will disappear in a century, even in the largest canyons" (p. 82). One of their recommendations was to connect the fragments with corridors of chaparral habitat.

An even more dramatic example comes from the other side of the continent. In metropolitan Boston, Drayton and Primack (1994) updated a census of plant species in a 162-acre conservation area known as Middlesex Fells West A census had also been taken a century earlier, in 1894. It was found that out of 422 original plant species, 155 were no longer there. Sixty-four new plants had moved in, but most were exotics--not native to the area. The researchers estimated a species decline of .36% per year, and observed that "many remaining native plant species have been reduced to one or a few small populations".

You could argue in this case that the species decline has less to do with island ecology than with plain old overuse. For the loss of species there "has coincided with an increase in human activity, including ground fires, a great number of trails and roads, thinning of the forest, and trampling of the vegetation" (p. 30). But all of these causes are themselves the result of a tiny remnant island simply being overwhelmed by an immense rapid rise of human activity.

Furthermore, similar studies in a variety of places have yielded similar results. For instance, Turner et al. (1996) re-inventoried a 10-acre fragment of tropical rain forest that had been preserved in the Singapore Boating Gardens since 1859. They found that 228 of 448 original species had disappeared. They concluded that such fragments might act as refuges for a time, but "on their own they will not provide a permanent guarantee of the conservation of tropical biodiversity".

The Newmark Warning

The most controversial work has been done recently by William Newmark, a zoologist at the University of California, San Diego. He initially studied large mammal extinctions and colonizations in 14 western national parks. Using sighting records, he reported that 29 species of large mammals had become extinct in those parks since the parks were established. Newmark also reported that in these parks, "the rate of extinction is inversely related to park area" (1995, p. 512). Newmark's final conclusion is worth reciting:

In the long term..., a net loss of species will most likely continue, particularly if habitat adjacent to the parks is extensively modified. Areas considerably larger than most parks in western North America will need to be managed if the historical mammal faunal assemblages within the parks are to be reestablished. (p. 521)

Keep in mind that Newark's study was based on observation records, which are considered far less than ideal by most zoologists and ecologists. At best, his work suggests that our parks may be acting like islands and begs for more research using more reliable data (Bogan et al., 1988).

And so, what's a land manager to do? In the past, our tendency has been to save large chunks of nature in remote areas where the scenery is most spectacular, and to supplement that with small fragments of "critical habitats" in places already quite developed. Island biogeography suggests we need a far less piecemeal approach. Most of our wilderness areas are still too small for the large carnivores--wolves, mountain lions, and grizzly bears specifically (Noss et al., 1996; Forbes & Theberge, 1996). The smaller reserves, if not too small, are almost certainly too isolated ("insularized") to do much ecological good.

One tangible thing that land managers on all levels can do is plan for more corridors between protected habitats to reduce their insularity from each other: to connect them. Nearly every study reviewed here recommends corridors. It is true that we do not know how wide and pristine such corridors should be for maximum benefit. Harrison (1992) suggests some minimum widths for certain target species but admits "there are little data" on how animals use corridors. But if we wait for perfect information, the job will never get done.

Two good models are available. In one, the state of Florida has adopted a plan to establish or enlarge core areas of habitat for cougar, black bear, and other native species and to develop a system of buffers and corridors to link the core habitats (Foreman, 1995). One early study suggests that Florida panthers are using highway underpasses to safely cross "Alligator Alley" and thus mitigate the bisection of their remaining habitat (Foster & Humphrey, 1995).

And in the northern Rockies, several groups, most notably the Greater Yellowstone Coalition and Alliance for the Wild Rockies, have helped write and introduce a novel piece of federal legislation. Known as the Northern Rockies Ecosystem Protection Act (of course: NREPA), this bill could, among other things, identify and protect essential corridors between wilderness areas. This would include finding ways to connect two major core habitats for wolves, grizzlies, and other species: the Yellowstone area and the Waterton-Glazier/Bob Marshall Wilderness complex (Foreman, 1995; Noss, 1992).

As mentioned, the Rockies project is just a bill in Congress right now. But, who knows, someday, Congress may have a rare case of brilliant common sense and pass it.

References

Bogan, M. A. (1988). The Importance of Biological Surveys in Managing Public Lands in the Western United States. Management of Amphibians, Reptiles, and Small Mammals in North America: Proceedings of the Symposium, July 19-21, 1988, Flagstaff, Arizona. Fort Collins, CO: U.S. Forest Service General Technical Report RM166), 254-261.

Diamond, J. M. (1972). Biographic Kinetics: Estimation of Relaxation Times for Avifaunas of Southwest Pacific Islands. Proceedings of the National Academy of Science, USA, 69, 3199-3203.

Diamond, J. M. (1975). The Island Dilemma: Lessons of Modern Biogeographic Studies for the Design of Natural Reserves. Biological Conservation, 7, 129-146.

Drayton, B., & Prinack, R. B. (1996). Plant Species Lost in an Isolated Conservation Area in Metropolitan Boston from 1894 to 1993. Conservation Biology, 10, 30-39.

Fahrig, L. & Merriam, G. (1994). Conservation of Fragmented Populations. Conservation Biology, 8, 50-59.

Forbes, G. J., & Theberge, J. B. (1996). Cross-Boundary Management of Algonquin Park Wolves. Conservation Biology, 10, 1091-1097.

Foreman, D. (1995, September). Missing Links. Sierra 80, 52-57, 96-98.

Foster, M. L., & Humphrey, S. R. (1995). Use of Highway Underpasses by Florida Panthers and Other Wildlife. Wildlife Society Bulletin, 23, 95-100.

Gilpin, M. E., and Diamond, J. M. (1980). Subdivision of Nature Reserves and the Maintenance of Species Diversity. Nature, 285, 567-568.

Harrison, R. L. (1992). Toward a Theory of Inter-Refuge Corridor Design. Conservation Biology, 6, 293-295.

Higgs, A. J., and Usher, M. B. (1980). Should Nature Reserves be Large or Small? Nature, 285, 568-569.

Higgs, A. J. (1981). Island Biogeography Theory and Nature Reserve Design. Journal of Biogeography, 8, 117-124.

Island Biogeography and Conservation: Strategy and Limitations (1976). Science, 193, 1027-1032.

Lovejoy, T. E., Rankin, J. M., Bierregaard, R. O. Jr., Brown, K. S. Jr., Emmons, L. H., & VanderVoort, M. E. (1984). Ecosystem Decay of Amazon Forest Remnants. In M. H. Nitecki (Ed.), Extinctions (pp. 295-325). Chicago: University of Chicago Press.

MacArthur, R., & Wilson, E. O. (1967). The Theory of Island Biogeography. Princeton: Princeton University Press.

May, R. M. (1975). Island Biogeography and the Design of Wildlife Preserves. Nature, 5497, 177-178.

Newmark, W. D. (1995). Extinction of Mammal Populations in Western North American National Parks. Conservation Biology, 9, 512-526.

Noss, R. F. (1992). The Wildlands Project: Land Conservation Strategy. Wild Earth (special issue), 10-25.

Noss, R. E, Quigley, H. B. Hornocker, M. G., Merrill, T., and Paquet, P. C. (1996). Conservation Biology and Carnivore Conservation in the Rocky Mountains. Conservation Biology, 10, 949-963.

Preston, F. W. (1962a). The Canonical Distribution of Commonness and Rarity: Part I. Ecology, 43, 185-215.

Preston, F. W. (1962b). The Canonical Distribution of Commonness and Rarity: Part II. Ecology, 43, 410-432.

Simberloff, D. S., & Abele, L. G. (1976). Island Biogeography Theory and Conservation Practice. Science, 191, 285-286.

Soulec, M. E., Bolger, D. T., Alberts, A. C., Wright, J., Sorice, & Hill, S. (1988). Reconstructed Dynamics of Rapid Extinctions of Chaparral Requiring Birds in Urban Habitat Islands. Conservation Biology, 2, 75-92.

Terborgh, J. (1975). Faunal Equilibria and the Design of Wildlife Preserves. In F. B. Golley & E. Medina (Eds.) Tropical Ecological Systems: Trends in Terrestrial and Aquatic Re search. New York: Springer-Verlag.

Turner, I. M., Chua, K. S., Ong, J. S. Y., Soong B. C., & Tan, T. W. (1996). A Century of Plant Species Loss from an Isolated Fragment of Lowland Tropical Rain Forest. Conservation Biology, 10, 1229-1244.

Zimmerman, B. L. & Bierregaard, R. O. (1986). Relevance of the Equilibrium Theory of Island Biogeography and Species-Area Relations to Conservation with a Case from Amazonia. Joumal of Biogeography, 13, 133-143.

RELATED ARTICLE: RESEARCH INTO ACTION: BIOGEOGRAPHY FOR MANAGEMENT

Research Into Action is published monthly by the society of Park and Recreation Educators, National Recreation and Park Association. As an accompaniment to "Research Update." its goal is to turn research findings into field action by highlighting management strategies. Founding editors are Dr. Ruth Russell and Dr. Daniel D. McLean, Department of Recreation and Park Administration, Indiana University 

Introduction

A sub-discipline of ecology called island biogeography is used in this month s Research Update to understand how to preserve more animal species in America's wilderness areas, national parks, and large state parks. As the phrase implies, island biogeography is the study of the degree to which the ecology of protected lands is analogous to that of islands as the habitat outside their boundaries becomes increasingly altered.

Impact of Research

Two principles about islands form the basis for the research reviewed 1.) Larger islands support more species of animals than smaller ones, and 2.) Remote islands support fewer species than less remote islands. Thus, questions about size and remoteness have become, over the past 30 years, the basis for numerous studies. That is, would it be better, given limited resources for conservation, to save one or two large chucks of relatively homogeneous habitat, or many small pieces of diverse ones? Also, to what degree is this species/area correlation a function of the fact that the larger the island, the more habitats it's likely to contain? Neither of these questions have been conclusively answered, yet the most provocative recent work is by Newmark who studied large mammal extinctions and colonizations in 14 western national parks. His conclusion was:

"In the long term..., a net loss of species will mostly likely continue, particularly if habitat adjacent to the parks is extensively modified. Areas considerably larger than most parks in western North America will need to be managed if the historical mammal faunal assemblages within the parks are to be reestablished".

How to Use This Research

And so, what's a land manager to do?

1.) Larger and less insulated areas must be preserved. Most of our wilderness areas are still too small for large carnivores (wolves, mountain lions, grizzly bears, etc.); and the smaller reserves are also too insularized to do much ecological good.

2.) Land managers on all levels can plan for more corridors between protected habitats to reduce their insularity from each other--to connect them:

For More Information

For additional reading on the conclusions from the Newmark study, see: Newmark, W.D. (1995). Extinction of Mammal Populations in Western North American National Parks. Conservation Biology 9:512-526.

Also, two good models of the recommendations made above are available. Florida has adopted a plan to enlarge core areas of habitat for cougar and black bear and to develop a system of buffers and corridors to link the core habitats. For more information, see: Foreman, D. (1995, September). Missing Links. Sierra 80:52-57 and 96-93.

In the northern Rockies, several groups have introduced federal legislation that could identify and protect essential corridors between wilderness areas. For specifics, see: Noss, R.F. (1992). The Wildlands Project: Land Conservation Strategy. Wild Earth. Special issue: 10-25.

James M. Glover is an associate professor of Recreation at Southern Illinois University at Carbondale. Joseph Dadey is a master's degree candidate in Recreation at Southern Illinois University at Carbondale. He also holds a bachelors degree in Zoology from Syracuse University 

Research Update is edited by Dr. Irma O'Dell of Southern Illinois University at Carbondale.