Conservation Biology

One of the critical challenges in conservation biology is to develop quantitative methods for evaluating the fate of populations that are threatened by human activities (Soulé 1987). Predicting population responses to various perturbations, such as habitat destruction, harvest, or supplementation via reintroduction, requires some practical analyses of population viability. These “population viability analyses” (PVAs) have come into increasing usage, and every indication is that their importance will rise in the future. A recent National Research Council panel convened to evaluate the Endangered Species Act vigorously recommended even greater reliance on viability models (NRC 1996), as have many other groups of biologists seeking to improve management of endangered and rare species (e.g., Carroll et al. 1996; Mangel et al. 1996; Ruggiero, Hayward, and Squires 1995; Schemske et al. 1994).

The ability to predict extinction risks is crucial to answering several recurring questions involving the conservation of plant species. Is a given reserve large enough to support a viable population? Is active intervention necessary to rescue a declining population (e.g., Burgman and Lamont 1992)? Should a small, unprotected population be ignored because it is doomed to extinction? Unfortunately, there are usually insufficient empirical data to answer these questions. One approach in the face of scarce data is the application of viability assessments based on stochastic population modeling. In this chapter, I explore stochastic viability models as a tool for gaining insight into which management regimes might best enhance population viability.

The consequences of habitat fragmentation are widely discussed in the conservation literature, usually with an emphasis on metapopulation dynamics and landscape ecology. Spatial aspects of fragmentation typically receive the greatest attention; in particular, how the size and shape of habitat patches and the distance between patches affect resident species. Relatively little notice has been given to the most obvious and direct effect of fragmentation: the physical changes that accompany the division of continuous habitat into fragments. In terrestrial systems, physical change is first expressed in the increase of perimeter to area ratio for each habitat patch. This change initiates a sequence of related physical changes that can profoundly influence resident flora and fauna. A comparable sequence of events follows fragmentation in aquatic systems. Field research is just beginning to provide links between patterns of fragmentation and the mechanisms that may lead to biotic changes. My aim in this chapter is to highlight the non-spatial effects of fragmentation. I limit my discussion to two types of ecosystems: forests and rivers. The first section considers the direct abiotic impacts of fragmentation on remnant habitat patches, often referred to as “edge effects” in the literature, and illustrates how these physical factors affect various organisms. In the second section I address the indirect effects of fragmentation, the biotic effects we can expect as a secondary consequence of the direct effects of fragmentation. I center many of my examples on recent research in an attempt to keep pace with the burgeoning conservation literature.

Many endangered plant species have been reduced to so few populations and such low numbers that timely collection and storage of seed has become imperative. If donor populations become extinct or seriously depleted, then off-site, or ex situ, samples can be used to reintroduce or augment populations in the wild. The strategic value of an ex situ component for plant conservation has been articulated by Falk (1987, 1990, 1992), who also helped establish the Center for Plant Conservation (CPC). The CPC is a national network of botanic gardens and arboreta that is attempting to assemble a genetically representative collection of our nation’s most rare and endangered plants while it is still possible to do so.

Until recently, conservation biology as a science has largely been a land-locked endeavor, in spite of decades of managed harvest in the sea. Fortunately, scientists and policymakers are beginning to heed warning signs, manifest most dramatically as extinctions of marine organisms in recent historical time (including the Caribbean monk seal, Stellar’s sea cow, a number of marine bird species, and several gastropods; Carlton 1993b; Vermeij 1993). Although global extinction rates in the ocean may be lower than those in terrestrial communities, there is an alarmingly long list of marine species for whom precipitous declines have been well documented (Estes, Duggins, and Rathbun 1989; Upton 1992; Norse 1993; Clark 1994). As biologists examine threats to marine biodiversity, it is becoming clear that conservation in the marine environment presents special challenges distinct from our experience in more traditional terrestrial conservation. Increased communication among terrestrial and marine conservation scientists will improve the prospects of all species through a better understanding of the successes and failures of conservation approaches in both environments.

The fossil record of the earth shows that faunal and floral extinctions increased dramatically during certain periods. These “paleo” upheavals like those at the end of Permian and Cretaceous have long provided the punctuations that geologists and paleontologists use to divide the geological periods. A challenging question in conservation science is whether the processes affecting extinction rates today are helpful in interpreting extinction in the past and, conversely, whether prehistoric extinctions are useful for understanding recent extinctions.

In the five years since we first reviewed the status of the world’s fishes (Moyle and Leidy 1992), there has been an explosion of new information on the conservation of aquatic organisms and their ecosystems. Notwithstanding this surge of interest, many aquatic ecosystems remain poorly understood because conservation biology remains primarily focused on the loss of biotic diversity in terrestrial environments. Loss of diversity in aquatic environments has received comChapautively little attention, even though the physical, chemical, and biological degradation of aquatic environments is widely recognized as a major problem, usually in the context of the spread of human disease, loss of fisheries, or degraded water quality for drinking, irrigation, or recreation. Yet aquatic habitats support an extraordinary array of species, many of which are being lost as their habitats deteriorate.

The vast majority of the world’s species are insects (at least 80%; Mawdsley and Stork 1995). Their importance is overwhelming by almost any measure. For example, insects and other arthropods contribute substantially to standing biomass; 1,000 kg/ha is an estimate for the United States (Pimentel et al. 1980). In most terrestrial and freshwater ecosystems they play critical roles as prey, predators, herbivores and pollinators (Free 1970; Debach and Rosen 1991; Kellert 1993; Lloyd and Barrett 1996). Indeed, in one of the first issues of the Society for Conservation Biology’s journal, E.O. Wilson (1987) called insects “the little things that run the world.” Because they comprise the majority of the earth’s biodiversity, insects should be considered pivotal in conservation efforts (Kim 1993). Unfortunately, an alarmingly small percent of our conservation literature focusses on insect issues. For example, in 1993, 1994 and 1995, the journals Ecological Applications, Conservation Biology, and Biological Conservation published 1,070 articles with only 62 related to insect issues and still fewer related to conservation of declining insect populations. Thus, only 6% of our conservation literature is aimed at 80% of our planet’s biodiversity. This neglect of insect conservation cannot be justified on the basis of insects not being endangered. In Britain where the biodiversity is relatively well-documented, approximately 22,500 insect species occur; 43 insects are believed to have gone extinct between 1900 and 1987 (Hambler and Speight 1996). The number of insect species believed extinct in Britain is over eight times that of number of extinct vertebrates, and over three times that of flowering plants (Hambler and Speight 1996).

Conservation biology has emerged as an important scientific discipline in Australia, reflected by the appearance of the new journal Pacific Conservation Biology, and the publication of a number of recent symposium volumes (e.g., Saunders et al. 1987, 1990, 1993, 1995; Saunders and Hobbs 1992; Moritz and Kikkawa 1994; Bradstock et al. 1995; Hopper et al. 1996). My purpose here is to provide an overview of current Australian plant conservation practice and the scientific knowledge that has delivered tangible outcomes. The emphasis on plants is deliberate because some exciting insights have recently unfolded.

Modern conservation biology had its origins in the management of game species and later of rare species, focusing attention on understanding the biological origins and causes of population decline, rarity, and endangerment. But while anthropogenic global change has resulted in the decline of some species, others have thrived and proliferated, accompanied by sometimes dramatic impacts on both single populations and whole ecosystems (Office of Technology Assessment 1993). Although some have long recognized invasive, non-native species as a force capable of irreversibly transforming the natural world (Elton 1958; Baker 1965), these scientists were in large part acting in isolation from those doing traditional conservation biology. In fact, even recent books on conservation biology often include only a cursory treatment, if any, of the problem of nonnative species (e.g., Soulé 1986; Fiedler and Jain 1992; Given 1994; Jordan 1995).

Although the Hawaiian Islands exhibit a rich diversity of birds, with especially high rates of endemism, the avian diversity is only a small fraction of what the archipelago once supported. In fact, it is estimated that over two thirds of Hawaii’s forest bird species have gone extinct since human contact (Freed, Conant, and Fleisher 1987; Jacobi and Atkinson 1994). Few faunas on Earth and no other island avifauna have experienced as many recent extinctions or include as many endangered species. In total, 21 of the 59 historically known species and subspecies of Hawaiian birds have gone extinct in the last 150 years and most of those remaining are threatened (Pyle 1990). Interestingly, it is not only contact with “modern” western Europeans that caused extinctions, but as fossils suggest, it is also contact with Polynesians that began 15 centuries ago (Olsen and James 1982). Current threats to Hawaiian birds are especially acute (Table 12.1), and we risk losing perhaps the most celebrated example of adaptive radiation in any vertebrate, the Hawaiian honeycreepers, finches in the subfamily Drepanidinae (Freed, Conant, and Fleisher 1987). Honeycreepers are believed to be derived from a single colonization event (Johnson, Martin, and Ralph 1989) and are exceedingly diverse in morphology, coloration, and habits (Figure 12.1). In addition to the honeycreepers, threatened forest species from three other passerine families occur in the archipelago: the Melaphagidae (honeyeaters), Corvidae (crows), and Muscicapidae (old world flycatchers and solitaires).

Historical debates about environmental degradation on oceanic islands acted as crucibles for the evolution of modern conservation thought (Grove 1995). These largely colonial debates recognized the link between forest loss and watershed decline and the possibility that habitat loss can result in species loss. Currently, oceanic islands are manifesting very high levels of extinction that demand urgent and innovative approaches to conservation. The Chapaudigms established for continental areas, based primarily on the establishment of protected areas, are not sufficient to ensure the survival of the highly modified biotas and ecologies of many oceanic islands. On such islands the habitats prior to human colonization are largely destroyed, the original ecological processes lost or diverted, and the populations of endemic taxa severely reduced and fragmented. To salvage endemic species and their ecologies, habitat conservation needs to be matched with intensive species management and habitat restoration.

Conservation biology cannot be concerned solely with preserving what remains. With many habitat types reduced to as little as 1% (e.g., tallgrass prairie east of the Mississippi River, USA) or even 0.1% (e.g., Central Valley riparian forest, California, USA) of their original area (see references in Noss et al. 1995), protecting what is left often represents “too little, too late.” Even habitat types that remain relatively common often occur in isolated patches that are too small for long-term conservation of viable populations of all organisms, particularly those of large carnivores and ungulates (Schonewald-Cox 1983). For these reasons, effective preservation of biodiversity may require investment in ecological restoration to increase the size as well as the connectivity of available habitat (Jordan et al. 1988). Restoration will be especially vital for restoring native diversity to many of the world’s most fertile and productive communities, where habitat destruction resulting from human activities has been concentrated (Janzen 1988).

Biodiversity is of special interest in California, a state with a great number of species, a large proportion of endemics, and many taxa in jeopardy. Because major developments have occurred along the Pacific Ocean, coastal habitats have been particularly affected. It is no surprise, therefore, that ten of California’s 94 endangered and threatened animal species are ones with coastal wetland affinities (Dept. of Fish and Game 1989); in southern California, these include the light-footed clapper rail (Rallus longirostris levipes), the California least tern (Sterna antillarum browni), and Belding’s Savannah sparrow (Passerculus sandwichensis beldingi). Of the 298 coastal species considered rare by the California Native Plant Society, 17 (6%) occur in coastal wetlands.

Economics is about choice. In a world where resources are finite relative to the demands that human beings make on them, choice is unavoidable. We cannot have everything. Choosing is the same as “trading off,” balancing the net gains from one course of action against an alternative action. The action of conserving biological diversity is not immune from this problem of making choices, although, as we shall see, some conservation literature appears to deny the choice, while some of it argues that the choice is there but that the tradeoff in favor of diversity destruction is unacceptable biological diversity is somehow “special.” If choice is inevitable, if we cannot retain all the diversity that there is, how should such choices be made? What should be conserved and where? Few problems in economics are more complex than making choices in the context of biodiversity and no economist would argue that the problem is resolved. Nonetheless, economics offers some insights into biodiversity conservation policy and these are worth exploring.

Patagonia, at the southern tip of South America (Figure 17.1), is a region of over one million km² shared by Chile and Argentina, endowed with some of the wildest landscapes in the world. Although remote and sparsely populated, Patagonian ecosystems are not pristine—most of them have been significantly disturbed by human activities. As is the case with much of Latin America, Patagonia is experiencing a push for economic development that is imposing ever increasing strains on natural resources.

The amount of land that is abandoned or severely degraded is large and increasing, with especially profound implicatons for conservation in the tropics. In particular, approximately one-half of the area of tropical forest lost each year expands the base of productive agriculture, whereas the other half simply replaces agricultural land that is worn out and abandoned (Houghton 1994). Consequently, if tropical agriculture were sustainable, the “...total agricultural area could continue to grow at current rates while, at the same time, rates of deforestation could be reduced by approximately 50%” (Houghton 1994, p. 311). Clearly, for the tropics at least, sustainable agriculture is a necessary precondition for the conservation of biodiversity (see also Hoffman and Carroll 1995).

Conservation of threatened and endangered species depends upon understanding the contribution of migration and local demography to population change. Unfortunately, studies of species at risk tend to be plagued by logistic problems, including limited access to populations, small sample sizes, and restrictions prohibiting manipulative experimentation. Thus, even the most basic demographic data (e.g., birth and death rates) — and certainly data regarding migration — can be difficult to acquire. Technological advances such as radio telemetry and geographic positioning systems have improved somewhat our ability to pursue field demography (i.e., McKelvey et al. 1993; Lahaye et al. 1994), but in general studies that employ such technology remain extremely expensive and logistically difficult. In contrast, recent technological advances in molecular population genetics have greatly reduced the cost and simultaneously increased the ease of field genetic studies. For example, the recent development of the polymerase chain reaction (PCR) allows amplification of DNA from tiny skin biopsies, individual hairs, or even scat. These non-intrusive sampling methods mean we can obtain genetic data on highly endangered species without sacrificing a single individual. In addition, easy-to-use computer packages are readily available to translate genetic data from individuals into assessments of population genetic structure (i.e., BIOSYS by Swofford and Selander 1981; GDA by Lewis and Zaykin 1996). Most importantly, the analysis of genetic structure does not require tracking the fate of individuals, or even capturing individuals more than once.

Conservation biology as a scientific discipline is dominated by natural history and population biology. However, there are several challenges and questions in conservation biology that can be elegantly addressed with new techniques from endocrinology. The major change in endocrinology that makes this possible is the development of field techniques that allow us to probe an animal’s hormonal status while the animal ranges free in the wild (Wingfield and Farner 1976). Clearly hormones are as crucial an attribute to an animal as are its body size, general health, and reproductive rates. In fact, from one perspective, hormones might be the most fundamental measure of an animal’s likely success. After all, it is hormones that largely control reproduction and coordinate the physiological responses necessary for survival in a stressful environment. Thus, endocrinology offers us a window to better understand the factors impairing a species’ demographic vitality, and it may even offer us early-warning signals of a risk before survivorship or reproductive rates plummet. In this chapter we sketch the recent advances in endocrinology that have the greatest potential as tools in the service of conservation biology. Before turning to case studies that document the role that endocrinology can play in conservation, we briefly review some pertinent aspects of vertebrate endocrine systems.

A major environmental concern of this century is the impact of human activity on the Earth’s climate, with prospects of major biological upheaval. The combined effects of deforestation and release of chemicals to the environment are likely to dramatically modify global temperature, and wind and rain patterns within the next century (Schneider 1989; Wetherald, 1991). However, most conservation biology proceeds without reference to climate shifts. This may be because the major threats to biodiversity (e.g., habitat destruction) occur quite independently of climate. Unfortunately, however, many of our solutions to biodiversity threats, such as the creation of national parks and reserves, are designed on the assumption that the climate will stay as it currently is. In this chapter I review the commonly accepted scenarios for climate change, sketch some research regarding impact on different organisms, and focus on two issues: how might climate change threaten the persistence of species and what surprises might await us as a result of climate change.

Every reader will find some favorite topic in conservation biology missing from this book. Where is the discussion of biodiversity and its function, for example? Why isn’t there a chapter on ecosystem management, because we all know that single-species conservation is passé? Why is there no explicit discussion of mapping biodiversity? or of remote sensing in conservation? Those are all real gaps, and we want to use these final remarks to suggest where else the reader might turn to build a firm and complete understanding of conservation biology in the frontlines of both practice and research these days.