areas of particular importance to restoration biology Restoration Biology: that offer potentially unique opportunities to couple basic research with the practical needs of restoration- ists. The five research areas are: (1) the influence of A Population Biology numbers of individuals and genetic variation in the initial population on population colonization, estab- lishment, growth, and evolutionary potential; (2) the Perspective role of local adaptation and life history traits in the success of restored populations; (3) the influence of Arlee M. Montalvo1,10,11 the spatial arrangement of landscape elements on 2 metapopulation dynamics and population processes Susan L. Williams such as migration; (4) the effects of genetic drift, gene Kevin J. Rice3 flow, and selection on population persistence within 4 an often accelerated, successional time frame; and (5) Stephen L. Buchmann the influence of interspecific interactions on popula- Coleen Cory5 tion dynamics and community development. We also 6 provide a sample of practical problems faced by prac- Steven N. Handel titioners, each of which encompasses one or more of Gary P. Nabhan7 the research areas discussed, and that may be solved by addressing fundamental research questions. Richard Primack8 9 Robert H. Robichaux Introduction ur understanding of the ecological mechanisms Abstract O underlying successful habitat restoration is not keeping pace with the societal needs for restoration. An A major goal of population biologists involved in res- improved understanding of the processes involved in a toration work is to restore populations to a level that successful restoration can be gained if we learn from will allow them to persist over the long term within a the “field experiment” that underlies every restoration dynamic landscape and include the ability to undergo project. However, because of the expense of restoration adaptive evolutionary change. We discuss five research and its often mandated practice, biologists cannot wait to learn the specific responses of every species within every different restoration site. Instead, we need inno- 1U.S.D.A. Forest Service, Pacific Southwest Research Station, vative research to develop a general template that will 4955 Canyon Crest Drive, Riverside, CA 92507, U.S.A. help us to manage ongoing projects and provide guid- 2Department of Biology, San Diego State University, San Diego, ance for the design of future restoration efforts. As a CA 92182-0057, U.S.A. step toward addressing this problem, this paper sum- 3Department of Agronomy and Range Science and the Center marizes the results of discussions of the Population Bi- for Population Biology, University of California, Davis, CA ology Group during the Restoration Ecology Workshop 95616, U.S.A. of the National Science Foundation. 4U.S.D.A. Agricultural Research Service, Carl Hayden Bee Re- The long-term viability and credibility of the practice search Center, 2000 East Allen Rd., Tucson, AZ 65719, U.S.A. 5Nature Conservancy of Hawaii, 1116 Smith St., Suite 201, of restoration depends on an understanding of the basic Honolulu, HI 96817, U.S.A. biological and ecological processes that operate at a site 6Department of Biology, Nelson Lab, Rutgers University, P.O. under restoration. Restoration projects span a contin- Box 1059, Piscataway, NJ 08855-1095, U.S.A. uum, from augmentation of populations of single spe- 7The Arizona-Sonora Desert Museum, Tucson, AZ 85743- cies within relatively intact ecosystems to the building 8919, U.S.A. of ecosystems from bare ground. This continuum can 8Department of Biology, Boston University, 5 Cummington provide valuable opportunities for comparing the suc- St., Boston, MA 02215, U.S.A. cess of restored populations under different sets of initial 9 Department of Ecology and Evolutionary Biology, University conditions. However, ultimate goals vary widely, as do of Arizona, Tucson, AZ 85721, U.S.A. the criteria used in judging whether a restoration is suc- 10The order of the three primary authors was assigned ran- cessful (Hobbs & Norton 1996; White & Walker 1997). domly. The remaining authors are arranged alphabetically. 11Corresponding author. The discipline of population biology provides one perspective on what might be considered a successful © 1997 Society for Ecological Restoration restoration. Population biology is a marriage of popula- DECEMBER 1997 Restoration Ecology Vol. 5 No. 4, pp. 277–290 277 Population Biology and Restoration tion ecology and population genetics. The field of pop- Third, research conducted within restorations is likely ulation ecology examines birth, growth, reproduction, to involve organisms that are not the conventional “mod- and death within populations and seeks to identify the els” for testing ecological and evolutionary theory. The factors that influence the success and distribution of practical necessity of manipulation of a wider array of populations. Population genetics seeks to understand organisms should help, in the long run, to increase our how the genetic composition of populations changes understanding of the robustness of theoretical predic- over time, and what factors influence the change. The tions, as well as providing a broader appreciation of integration of the theoretical and empirical aspects of biodiversity. For example, despite the longstanding in- these disciplines promotes our understanding of the terest in the evolutionary biology of colonizing species processes involved in causing evolutionary change, es- (Baker & Stebbins 1965; Parsons 1983; Barrett & Hus- pecially adaptive change (Harper 1977; Solbrig 1980). band 1989; Rejmánek 1996), there has been surprisingly As was so aptly stated by Dobzhansky (1973), “nothing little direct testing of hypotheses about colonizing abili- in biology makes sense except in the light of evolution.” ties in the field or the genetic consequences of coloniza- In essence, the conceptual framework of population bi- tion. By its very nature, restoration is characterized by ology originates from the theory of organic evolution. colonization processes. This conceptual framework forms the basis of a popula- Finally, successful restorations provide case histories tion biologist’s viewpoint that restoration is ultimately of populations that have persisted despite suboptimal successful when populations are restored to a level that edaphic conditions, herbivore pressures, lack of mutu- allows them to persist as dynamic parts of a metapopu- alists, and invasion by non-native species. These case lation over the long term within a changing landscape. histories, and the potential to design restorations as ex- Restored populations must possess attributes necessary periments (Pavlik et al. 1993), provide a challenging op- for reproduction, growth, migration, and adaptive evolu- portunity for the biologist who wishes to understand tionary change. population processes within the realistic context of en- Restoration provides special research opportunities vironmental variation, multispecies interactions, and for population biology. Although there is a wealth of successional change. Because restorations often occur population genetic and demographic theory, there is an on degraded or virtually unpopulated sites, research empirical gap in testing such theory with species cho- conducted in such sites is relevant to understanding the sen for reasons other than their experimental tractabil- factors that influence colonization, growth, and distri- ity (i.e., model systems). Research in restorations pro- bution of populations within a complex ecological vides a way to close this empirical gap. We see four arena. Such empirical data are needed for basic tests of major research opportunities for population biologists population biology theory. Furthermore, understand- who use restorations for research. First, restorations are ing the responses of populations to extreme ecological fundamentally a manipulation of biota in the field conditions typified by many restorations will help iden- within habitats already degraded. Restorations thus tify the boundary conditions important for population provide a sanction for population biologists to conduct growth, persistence, adaptation, and interactions. Restora- field experiments, sometimes over large spatial scales, tion research should afford a rich payoff for understand- that are otherwise unthinkable for fear of resulting ef- ing fundamental evolutionary and ecological theory. fects on natural populations and communities. For exam- During the National Science Foundation (NSF) Work- ple, the demographic and genetic attributes of popula- shop, we grappled with our charge of identifying re- tions can be manipulated to examine how these factors search gaps that could be uniquely addressed in a resto- influence population growth, or extinction, or both. ration context and also include the definitive components Second, restored communities are also often character- of quality restoration research. This is, in part, because ized by very dynamic temporal change resulting from we kept uncovering population biology research that is colonization events and succession. A common restora- needed by practitioners to carry out economically feasi- tion goal is to either accelerate or freeze the process of ble, successful restorations. Other than special opportu- ecological succession. Some species and populations will nities discussed above, there really is no reason why a be established deliberately by the restoration while oth- population biologist would submit