Some people believe that other nonindigenous species, such as the green crab in waters near Martha's Vineyard, detract from the integrity of the environment. Regardless of these examples of beneficial effects of introduced nonindigenous species, the adverse effects of nonindigenous species on endemics have resulted in their being one of the leading causes of global extinctions Nott and others ; Pimm and others According to Norse , the other causes are overexploitation, physical alteration of habitat including habitat destruction and degradation , pollution, and global atmospheric changes.
In many discussions, biodiversity refers to "a diversity of landscapes". We consider a region that contains both grassland and forest to be more diverse than one that contains only grassland. It is the mixture of ponderosa pine savannas, grasslands, wetlands, and riparian woodlands that gives Boulder, Colorado, its diverse environment see the Boulder case study in chapter 3. Camp Pendleton has not only a large number of threatened and endangered species, but also a diversity of marine, estuarine, riparian, and terrestrial "habitat types" see the Camp Pendleton case study in chapter 1.
Costa Rica see the case study this chapter has many more life zones than an area of comparable size for example, West Virginia in eastern North America. Terms like grassland and forest denote different associations of species. Grassland and forest edge have high between-area diversity. Boundaries between associations often correspond to obvious physical differences in the environment and differences in ecological processes, such as nutrient cycling.
The use of landscape terms to describe biodiversity raises three questions for managers to deal with:. The term association of species is deliberately vague. Ecologists apply it to areas with the sets of species they contain that range from a few square meters to continents. On the largest scale, we refer to tundra, coniferous forest, deciduous forest, grassland, savanna, desert, tropical rain forest and so on. Ecologists call these major regions biomes.
On smaller scales, Noss and Peters classify and identify the endangered "ecosystems" of the United States. By ecosystem they mean distinct assemblages of plants and animals. For example, naming an ecosystem "Florida scrub" is a statement of the likelihood that we will find a set of plant and animals widely across this ecosystem. In addition, the species typically will be different from those in other ecosystems. On an even smaller scale, we have finer divisions of environments variously called habitats, associations, communities, and biotopes.
When sufficient data are available, formal statistical procedures enable a manager to recognize a biome, landscape, ecosystem, habitat, biotope, or other ecological association. The procedures group smaller areas into larger divisions according to the principle that species are similar within and different between those divisions Hengeveld ; Pielou For most of the cases, the recog-. In the s, C. Merriam, one of the great natural historians of the West, characterized the biodiversity of northern Arizona and mapped it into seven ''life zones'' on the basis of altitudinal bands of temperature and the appearance of the vegetation.
Merriam's classification preceded formal vegetation surveys and statistical analyses. Nonetheless, his classification retains its utility as a broad guide to where to find plants and animals and where the boundaries between their distributions will likely lie. On a much finer scale, the conspicuous zonation of intertidal rocky shores provided the initial motivation for studying near-shore marine ecosystems Gilsen Grassland and forest clearly do more than refer to the similarity of species within and the differences between associations.
A grassland, like any other environment, has its own typical set of ecological processes, and these might be different qualitatively and quantitatively from those in the nearby forest. The plants in grasslands, for example, might be adapted to frequent fires; indeed, without fires, trees might invade and forest take over. In contrast, the dominant ecological processes in a lake might be related to the nature of the nutrient effects inputs from surrounding areas.
Sometimes the threats to biodiversity are the human impacts on natural ecosystem processes, such as changes in the hydrology and fire regimes of the Everglades see the case study in chapter 3. Biodiversity on the landscape scale involves more than the mosaics that differ in composition such as forest versus grassland. It also includes the connections and dynamics between and among patches and their implications for the functioning of ecosystems Turner and Gardner Connections can occur through the flow of water, energy, materials, or organisms. For example, water moves through upland to riparian and wetland areas and then to streams, carrying with it dissolved nutrients.
The accumulation of water in wetland or riparian areas leads to soil saturation, decomposition by anaerobic pathways, dominance by different plant and microbial species, and substantial effects on the chemistry of streams. Nitrogen fertilizer that is leached from upland agricultural systems can be taken up and retained by riparian plants or denitrified to nitrogen gas in soils Hedin and others ; Peterjohn and Correll , In either case, the maintenance of landscape diversity controls the overall exchange of nutrients between terrestrial and aquatic ecosystems.
On a coarser scale, the seasonal movement of migratory birds between tropical and temperate ecosystems connects these otherwise independent biomes see Everglades case study, chapter 3. This flow of organisms requires that managers in each region consider the dynamics of the other region in their analyses. By its very nature, biotic exchange over long distances implies a lack of independence.
Each species has a unique history. Species are the result of evolution descent with modification Darwin or "accumulated history" Salthe , Species contain the history of the lineage that they represent, just as humans carry the history of their ancestors. The concept of lineage is central to the imagery of evolution. Equally central is the notion of relationship: some lineages are more closely related than others, in the sense that they shared an ancestor more recently.
Systematists now have well worked-out concepts of affinity, methods, and techniques for assessing degree of phylogenetic relationship and for reconstructing pieces of the history of life on Earth. Some taxa are of special interest because of their evolutionary relationships. For us, the chimpanzees, gorillas, and orangutans have special value as "kin". In the Galapagos, Darwin's finches are closely related species that serve as a living example of evolutionary diversification in action. Their special value stems from what the studies of them have contributed to intellectual history. Hawaiian honeycreepers are even more deeply differentiated, and they show a varied adaptation that makes them a special object of study.
On another scale, closely related beetles remind us that South America and Africa were once the supercontinent Gondwana; their common heritage is evident despite about million years of geographic separation Pitman and others Other taxa gain special value not as a result of their close evolutionary relationships but because they are distantly related to other groups. In the tree of life branches have different lengths. Long branches represent early divergences now lacking close relatives. Some well-known examples are the platypus and echidnas of Australia.
The sole living representatives of the monotremes, a long-branch taxon that is the sister-group of all other living mammals. A sister group is the closest genealogical relative of a given taxon, exclusive of the ancestral species of both taxa Wiley The mountain beaver of the Pacific Northwest is a long-branch taxon. It is the sister-group of all the family Sciuridae the squirrels and relatives or perhaps even of all rodents the largest of the mammalian orders and might date back 40 million years as a separate lineage.
Often several or many long-branch taxa occur in the same region Morrone and others Biologists believe that regions with long-branch taxa have a high probability of including additional, as yet unknown or unstudied, taxa. Thus, regions where long-branch taxa occur have special significance as biodiversity-conservation areas. The forest region of the Pacific Northwest harbors the tailed frog the single species of the endemic family Ascaphidae, about million years old and the sister group of all other roughly 4, species of frogs , the torrent salamanders an endemic family of four species, distantly related to all other salamander taxa , the Pacific giant salamanders the endemic family Dicamptodontidae, the sister group of the well-known ambystomatid salamanders , and a number of insects.
The torrent salamanders house a long-branch. The redwood and sequoia trees are sister species that form a long-branch taxon. They are distantly related to the dawn redwood of China, which is extinct in the wild but was preserved in Chinese monasteries and is itself a long-branch taxon. Biologists assess the importance of conserving biodiversity in various ways. Some are based on conserving species, others on maintaining community or ecosystem functions. From the perspective of the field of biological systematics, species do not all have equal value when it comes to biodiversity maintenance and conservation.
Several approaches have been used to assign such value. One can use a generalized hierarchical approach, working along a genealogical to phylogenetic continuum from genetically distinct sister populations to groups at various taxonomic levels. Populations of a species that vary geographically in degree of genetic distinctiveness would have greater value than populations of a species that are genetically more uniform.
Similarly, with respect to a given protected species, a related species that is more distinct genetically would have greater value than one that is only slightly different. That kind of ranking can be used in a phylogenetic ranking of taxa; species that are phylogenetically increasingly remote would have increasing value because the goal is to maintain the greatest amount of biological diversity. The method can be made precise when sufficient information on relationships is available Faith With such a scheme, long-branch taxa have the greatest value.
That scheme can be combined with habitat, community, ecosystem, and geographic bioregion approaches. A habitat or region that has several long-branch taxa is more valuable for biodiversity maintenance than one that has none or only one. In contrast, one might choose to focus on a region that is relatively poor in long-branch taxa because many factors go into valuation, and pragmatic concerns or special interest in a species might force decision-making. When this happens, it is wise policy to identify a rationale underlying the decision.
Another consideration in biodiversity maintenance is the geographic distribution of a species. In general, species that are widely distributed require less attention than species that are narrowly distributed, although that widely distributed species that have low population density might be of more concern than an endemic that is well protected and in good demographic condition. The components of biodiversity are hierarchical and intricately linked. For example, the genetic variability within a species is related to their continued adaptation and evolution in the face of biological, physical, and chemical changes.
A variety of species in an ecosystem might increase productivity and stability. The pattern of ecosystems on the landscape influences energy flow, nutrient. The value of agricultural or forest productivity is undeniable, but its intrinsic relationship to soil microbial processes, hydrological and atmospheric cycles, pollinators, and pest predators is largely unknown and unappreciated by most sectors of society.
Chapter 3 discusses the values of biological components in detail. Given that funds for conservation are limited, how should they best be allocated to ensure the most efficient conservation of biological diversity?
That question confronts decision-makers in institutions as varied as government departments responsible for protected areas and nongovernment organizations, such as The Nature Conservancy. Typically, the answer involves setting priorities for habitat or ecosystem conservation; and this, in turn, requires assigning relative values to the areas under consideration for protection. Although ultimate decisions of which habitats or ecosystems will be protected might be influenced by considerations of the cost of protecting various sites or assessments of the likely threat to a site in the absence of protection, the initial ranking of sites should be based on biological criteria.
No approach to priority-setting can serve all biodiversity-conservation objectives. For example, one logical goal of conservation would be to conserve both the greatest diversity of species and the greatest diversity of natural habitats. Consider two hypothetical ecosystems, one with 1, endemic species and one with If sufficient money were available to protect two 1,hectare sites, where should they be. Locating both in the species-rich site would protect far more species but would sacrifice the protection of unique habitats.
Placing one conservation site in each ecosystem would protect the diversity of ecosystems but with a tremendous loss of species diversity. There is no scientifically based means of comparing the value of a "unit" of habitat protection with a "unit" of species protection, so there is no single solution to the problem.
The Nature Conservancy's method for ranking "elements of natural diversity" is the best-known example of a valuation approach that is based primarily on the rarity of and threat to species and biological communities. The conservancy obtains information about the known or estimated numbers of subpopulations, the estimated numbers of individuals, the narrowness of ranges and habitats, trends in population and habitat, threats, and fragility, and then it assigns a rank of 1—5 with 1 representing extreme vulnerability Johnson It then focuses its habitat-acquisition efforts on areas that have more rare and imperiled species.
In addition, a variety of quantitative tools permit a population's status or viability to be assessed or a habitat's ecological importance to be determined. Box classifies and lists some of these techniques as a quick guide for a manager seeking widely available literature relevant to some local and pressing situation. The union later conducted a series of systematic regional reviews to identify gaps in protected-area coverage, with emphasis on ensuring representative coverage of protected areas. Other international efforts, such as the UNESCO Man and the Biosphere Program, also have chosen to emphasize representative coverage of protected areas in their conservation priority-setting.
By the late s, about 15 of some biogeographic provinces still had no protected areas, and 30 had five or fewer areas that encompassed less than 1, km 2 Reid and Miller Bedward and others ; Forey and others ; Gaston ; Groombridge ; Johnson ; Myers , , ; Prendergast and others ; Reid ; Wilson A number of priority-setting systems focus on the protection of areas that are particularly rich in species or that have many endemics.
For example, Myers identified 10 "hot spots" that deserved conservation emphasis—tropical forest areas with high species richness and relatively high endemism that also faced exceptional degrees of threat from human activities. The list was expanded to include eight additional regions—four in the humid tropics and four in Mediterranean-type habitats Myers Myers estimates the number of plant species in a region and the percentage of those species that are endemic, evaluates the threat of habitat loss for the region, and then ranks highest regions with large numbers of threatened endemics on relatively small areas.
Birdlife International has followed a similar approach, identifying regions that have relatively high numbers of bird species with restricted ranges less than 50, km 2. In all, "endemic bird areas" have been identified and are being emphasized as a focus for conservation action Johnson The preceding sections have focused on the varied definitions of biodiversity, how it is related to landscape-scale patterns, its genetic basis, and its evolutionary origin and significance.
Those descriptive accounts identify what biodiversity is; they do not address how it is maintained or influenced by specific interactions or what the role of species—individually or collectively—might be in ecosystem functioning. These are developed more fully in chapter 3. The role of ecological interactions in influencing whether species can coexist locally has been recognized at least since the time of Darwin , who showed that a clipped grassy plot harbored more species than an undisturbed one. Since then, an extensive literature has developed the theme that various interactions can influence the genetic structure and morphological appearance of local populations Tollrian and Harvell , the probability of species coexistence Paine , and the biological structure and function of entire freshwater assemblages Brooks and Dodson ; Carpenter and Kitchell ; Werner Probably all known taxa, ranging from pathogens to especially humans, are involved in this interactive natural world.
The dynamic relationships and their immediate and long-term consequences obviously influence the determination and evaluation of species diversity patterns. The locally resident species also affect considerations of ecosystem function. For instance, these are increasingly factored into conservation priority-setting, particularly with regard to the protection of water quality.
Many countries have forest policies that require the protection of forested buffers along rivers and streams to reduce siltation and protect the rivers from changes in water temperature. In some cases, protected areas have been estab-. The management implications of changes on local species composition and therefore probably richness and of its capacity to alter ecosystem function are developed in chapter 3 in the Everglades case study and the section Ecosystem Services , and in chapter 6 in the Lake Washington case study.
Nature is complex and highly interactive: management decisions increasingly consider the totality of the biological matrix; no species lives in isolation, and changes in one are certain to affect the ecological and evolutionary continuity and the performance of others and of the assemblage in which they are imbedded. Because biodiversity is such a broad concept, methods for its quantification are necessarily broad. In this chapter, we have attempted to define the components of biodiversity and to describe some of the ways to measure them. In the following chapters, case studies illustrate management decisions driven by various concepts of what biodiversity is or does.
For instance, aesthetic considerations were influential in the preservation of open spaces in Boulder, CO chapter 3 , whereas water quality issues motivated the restoration of Lake Washington chapter 6. The Everglades case study describes a major federal project in which biodiversity itself and habitat restoration were the primary considerations chapter 3. Given such variation in mission, managers must consider both the maintenance of viable local populations of species of interest and the maintenance of biodiversity on larger scales, which is essential for the functioning of ecosystems.
This chapter has addressed the many components of biodiversity that managers need to consider; the next chapter extends our understanding of how people value the components of biodiversity. Throughout the report, case studies illustrate management decisions that were based on the varied biodiversity components.
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Loss of these species would make growing crops requiring pollination impossible, increasing dependence on other crops. Finally, humans compete for their food with crop pests, most of which are insects. Pesticides control these competitors; however, pesticides are costly and lose their effectiveness over time as pest populations adapt. They also lead to collateral damage by killing non-pest species and risking the health of consumers and agricultural workers.
Ecologists believe that the bulk of the work in removing pests is actually done by predators and parasites of those pests, but the impact has not been well studied. A review found that in 74 percent of studies that looked for an effect of landscape complexity on natural enemies of pests, the greater the complexity, the greater the effect of pest-suppressing organisms. An experimental study found that introducing multiple enemies of pea aphids an important alfalfa pest increased the yield of alfalfa significantly.
This study shows the importance of landscape diversity via the question of whether a diversity of pests is more effective at control than one single pest; the results showed this to be the case. Loss of diversity in pest enemies will inevitably make it more difficult and costly to grow food. In addition to growing crops and raising animals for food, humans obtain food resources from wild populations, primarily fish populations. For approximately 1 billion people, aquatic resources provide the main source of animal protein.
But since , global fish production has declined. Despite considerable effort, few fisheries on the planet are managed for sustainability. Fishery extinctions rarely lead to complete extinction of the harvested species, but rather to a radical restructuring of the marine ecosystem in which a dominant species is so over-harvested that it becomes a minor player, ecologically. In addition to humans losing the food source, these alterations affect many other species in ways that are difficult or impossible to predict.
The collapse of fisheries has dramatic and long-lasting effects on local populations that work in the fishery. In addition, the loss of an inexpensive protein source to populations that cannot afford to replace it will increase the cost of living and limit societies in other ways. In general, the fish taken from fisheries have shifted to smaller species as larger species are fished to extinction. The ultimate outcome could clearly be the loss of aquatic systems as food sources.
Finally, it has been argued that humans benefit psychologically from living in a biodiverse world. A chief proponent of this idea is entomologist E.
He argues that human evolutionary history has adapted us to live in a natural environment and that built environments generate stressors that affect human health and well-being. There is considerable research into the psychological regenerative benefits of natural landscapes that suggests the hypothesis may hold some truth. In addition, there is a moral argument that humans have a responsibility to inflict as little harm as possible on other species. The core threat to biodiversity on the planet, and therefore a threat to human welfare, is the combination of human population growth and resource exploitation.
The human population requires resources to survive and grow, and those resources are being removed unsustainably from the environment. The three greatest proximate threats to biodiversity are habitat loss, overharvesting, and introduction of exotic species. The first two of these are a direct result of human population growth and resource use. The third results from increased mobility and trade. A fourth major cause of extinction, anthropogenic climate change, has not yet had a large impact, but it is predicted to become significant during this century.
Environmental issues, such as toxic pollution, have specific targeted effects on species, but they are not generally seen as threats at the magnitude of the others. Atmospheric carbon dioxide levels fluctuate in a cyclical manner. Humans rely on technology to modify their environment and replace certain functions that were once performed by the natural ecosystem. Other species cannot do this. Elimination of their ecosystem—whether it is a forest, a desert, a grassland, a freshwater estuarine, or a marine environment—will kill the individuals in the species.
Remove the entire habitat within the range of a species and, unless they are one of the few species that do well in human-built environments, the species will become extinct. Human destruction of habitats accelerated in the latter half of the twentieth century. The neighboring island of Borneo, home to the other species of orangutan, has lost a similar area of forest. Forest loss continues in protected areas of Borneo. The orangutan in Borneo is listed as endangered by the International Union for Conservation of Nature IUCN , but it is simply the most visible of thousands of species that will not survive the disappearance of the forests of Borneo.
Palm oil is used in many products including food products, cosmetics, and biodiesel in Europe. A five-year estimate of global forest cover loss for the years — was 3. In the humid tropics where forest loss is primarily from timber extraction, , km 2 was lost out of a global total of 11,, km 2 or 2. In the tropics, these losses certainly also represent the extinction of species because of high levels of endemism.
These animals are examples of the exceptional biodiversity of c the islands of Sumatra and Borneo. Other species include the b Sumatran tiger Panthera tigris sumatrae and the d Sumatran elephant Elephas maximus sumatranus , both critically endangered species. Lian Pin Koh. Most consumers do not imagine that the home improvement products they buy might be contributing to habitat loss and species extinctions. Yet the market for illegally harvested tropical timber is huge, and the wood products often find themselves in building supply stores in the United States.
Most of the illegal products are imported from countries that act as intermediaries and are not the originators of the wood. How is it possible to determine if a wood product, such as flooring, was harvested sustainably or even legally? The Forest Stewardship Council FSC certifies sustainably harvested forest products, therefore, looking for their certification on flooring and other hardwood products is one way to ensure that the wood has not been taken illegally from a tropical forest.
While there are other industry-backed certifications other than the FSC, these are unreliable due to lack of independence from the industry. Another approach is to buy domestic wood species. While it would be great if there was a list of legal versus illegal wood products, it is not that simple. Logging and forest management laws vary from country to country; what is illegal in one country may be legal in another.
Where and how a product is harvested and whether the forest from which it comes is being maintained sustainably all factor into whether a wood product will be certified by the FSC. It is always a good idea to ask questions about where a wood product came from and how the supplier knows that it was harvested legally. Habitat destruction can affect ecosystems other than forests. Rivers and streams are important ecosystems and are frequently modified through land development and from damming or water removal.
Damming of rivers affects the water flow and access to all parts of a river. Differing flow regimes can reduce or eliminate populations that are adapted to these changes in flow patterns. For example, an estimated 91percent of river lengths in the United States have been developed: they have modifications like dams, to create energy or store water; levees, to prevent flooding; or dredging or rerouting, to create land that is more suitable for human development.
Many fish species in the United States, especially rare species or species with restricted distributions, have seen declines caused by river damming and habitat loss. Research has confirmed that species of amphibians that must carry out parts of their life cycles in both aquatic and terrestrial habitats have a greater chance of suffering population declines and extinction because of the increased likelihood that one of their habitats or access between them will be lost. Overharvesting is a serious threat to many species, but particularly to aquatic species. There are many examples of regulated commercial fisheries monitored by fisheries scientists that have nevertheless collapsed.
The western Atlantic cod fishery is the most spectacular recent collapse. While it was a hugely productive fishery for years, the introduction of modern factory trawlers in the s and the pressure on the fishery led to it becoming unsustainable. The causes of fishery collapse are both economic and political in nature. Common resources are subject to an economic pressure known as the tragedy of the commons in which essentially no fisher has a motivation to exercise restraint in harvesting a fishery when it is not owned by that fisher. The natural outcome of harvests of resources held in common is their overexploitation.
While large fisheries are regulated to attempt to avoid this pressure, it still exists in the background. This overexploitation is exacerbated when access to the fishery is open and unregulated and when technology gives fishers the ability to overfish. In a few fisheries, the biological growth of the resource is less than the potential growth of the profits made from fishing if that time and money were invested elsewhere. In these cases—whales are an example—economic forces will always drive toward fishing the population to extinction. For the most part, fishery extinction is not equivalent to biological extinction—the last fish of a species is rarely fished out of the ocean.
At the same time, fishery extinction is still harmful to fish species and their ecosystems. There are some instances in which true extinction is a possibility. Whales have slow-growing populations and are at risk of complete extinction through hunting. There are some species of sharks with restricted distributions that are at risk of extinction. The groupers are another population of generally slow-growing fishes that, in the Caribbean, includes a number of species that are at risk of extinction from overfishing.
Coral reefs are extremely diverse marine ecosystems that face peril from several processes. Most home marine aquaria are stocked with wild-caught organisms, not cultured organisms. Although no species is known to have been driven extinct by the pet trade in marine species, there are studies showing that populations of some species have declined in response to harvesting, indicating that the harvest is not sustainable at those levels. There are concerns about the effect of the pet trade on some terrestrial species such as turtles, amphibians, birds, plants, and even the orangutan.
Bush meat is the generic term used for wild animals killed for food.
Hunting is practiced throughout the world, but hunting practices, particularly in equatorial Africa and parts of Asia, are believed to threaten several species with extinction. Traditionally, bush meat in Africa was hunted to feed families directly; however, recent commercialization of the practice now has bush meat available in grocery stores, which has increased harvest rates to the level of unsustainability. Additionally, human population growth has increased the need for protein foods that are not being met from agriculture.
Species threatened by the bush meat trade are mostly mammals including many primates living in the Congo basin. Exotic species are species that have been intentionally or unintentionally introduced by humans into an ecosystem in which they did not evolve. Such introductions likely occur frequently as natural phenomena. For example, Kudzu Pueraria lobata , which is native to Japan, was introduced in the United States in It was later planted for soil conservation.
Problematically, it grows too well in the southeastern United States—up to a foot a day. It is now a pest species and covers over 7 million acres in the southeastern United States. If an introduced species is able to survive in its new habitat, that introduction is now reflected in the observed range of the species. Most exotic species introductions probably fail because of the low number of individuals introduced or poor adaptation to the ecosystem they enter. Some species, however, possess preadaptations that can make them especially successful in a new ecosystem.
These exotic species often undergo dramatic population increases in their new habitat and reset the ecological conditions in the new environment, threatening the species that exist there. For this reason, exotic species are also called invasive species. Exotic species can threaten other species through competition for resources, predation, or disease.
The brown tree snake, Boiga irregularis , is an exotic species that has caused numerous extinctions on the island of Guam since its accidental introduction in Lakes and islands are particularly vulnerable to extinction threats from introduced species. In Lake Victoria, as mentioned earlier, the intentional introduction of the Nile perch was largely responsible for the extinction of about species of cichlids. Several other species are still threatened.
The brown tree snake is adept at exploiting human transportation as a means to migrate; one was even found on an aircraft arriving in Corpus Christi, Texas. Constant vigilance on the part of airport, military, and commercial aircraft personnel is required to prevent the snake from moving from Guam to other islands in the Pacific, especially Hawaii. Islands do not make up a large area of land on the globe, but they do contain a disproportionate number of endemic species because of their isolation from mainland ancestors.
This Limosa Harlequin Frog Atelopus limosus , an endangered species from Panama, died from a fungal disease called chytridiomycosis. The red lesions are symptomatic of the disease. There is evidence that the fungus is native to Africa and may have been spread throughout the world by transport of a commonly used laboratory and pet species: the African clawed toad Xenopus laevis. It may well be that biologists themselves are responsible for spreading this disease worldwide. The North American bullfrog, Rana catesbeiana , which has also been widely introduced as a food animal but which easily escapes captivity, survives most infections of Batrachochytrium dendrobatidis and can act as a reservoir for the disease.
The disease has decimated bat populations and threatens extinction of species already listed as endangered: the Indiana bat, Myotis sodalis , and potentially the Virginia big-eared bat, Corynorhinus townsendii virginianus. How the fungus was introduced is unclear, but one logical presumption would be that recreational cavers unintentionally brought the fungus on clothes or equipment from Europe. This little brown bat in Greeley Mine, Vermont, March 26, , was found to have white-nose syndrome. Despite considerable effort, knowledge of the species that inhabit the planet is limited.
A recent estimate suggests that the eukaryote species for which science has names, about 1. Estimates of numbers of prokaryotic species are largely guesses, but biologists agree that science has only begun to catalog their diversity. Even with what is known, there is no central repository of names or samples of the described species; therefore, there is no way to be sure that the 1. It is a best guess based on the opinions of experts in different taxonomic groups. Given that Earth is losing species at an accelerating pace, science is very much in the place it was with the Lake Victoria cichlids: knowing little about what is being lost.
There are various initiatives to catalog described species in accessible ways, and the internet is facilitating that effort. Nevertheless, it has been pointed out that at the current rate of species description, which according to the State of Observed Species Report is 17, to 20, new species per year, it will take close to years to finish describing life on this planet. Naming and counting species may seem an unimportant pursuit given the other needs of humanity, but it is not simply an accounting.
It allows biologists to find and recognize the species after the initial discovery, and allows them to follow up on questions about its biology. In addition, the unique characteristics of each species make it potentially valuable to humans or other species on which humans depend.
Understanding these characteristics is the value of finding and naming species. In , British environmentalist Norman Myers developed a conservation concept to identify areas rich in species and at significant risk for species loss: biodiversity hotspots. Biodiversity hotspots are geographical areas that contain high numbers of endemic species. The purpose of the concept was to identify important locations on the planet for conservation efforts, a kind of conservation triage.
By protecting hotspots, governments are able to protect a larger number of species. The original criteria for a hotspot included the presence of or more endemic plant species and 70 percent of the area disturbed by human activity. Conservation International has identified 34 biodiversity hotspots, which cover only 2. Preserving biodiversity is an extraordinary challenge that must be met by greater understanding of biodiversity itself, changes in human behavior and beliefs, and various preservation strategies.
DNA barcoding is one molecular genetic method, which takes advantage of rapid evolution in a mitochondrial gene present in eukaryotes, excepting the plants, to identify species using the sequence of portions of the gene. Plants may be barcoded using a combination of chloroplast genes. Rapid mass sequencing machines make the molecular genetics portion of the work relatively inexpensive and quick. Computer resources store and make available the large volumes of data.
Projects are currently underway to use DNA barcoding to catalog museum specimens, which have already been named and studied, as well as testing the method on less studied groups. As of mid , close to , named species had been barcoded. Early studies suggest there are significant numbers of undescribed species that looked too much like sibling species to previously be recognized as different.
These now can be identified with DNA barcoding. Numerous computer databases now provide information about named species and a framework for adding new species. However, as already noted, at the present rate of description of new species, it will take close to years before the complete catalog of life is known.
Many, perhaps most, species on the planet do not have that much time. There is also the problem of understanding which species known to science are threatened and to what degree they are threatened. The Red List is supported by scientific research. In , the list contained 61, species, all with supporting documentation.
Legislation throughout the world has been enacted to protect species. The legislation includes international treaties as well as national and state laws. The treaty is limited in its reach because it only deals with international movement of organisms or their parts. The illegal trade in organisms and their parts is probably a market in the hundreds of millions of dollars. Within many countries there are laws that protect endangered species and regulate hunting and fishing. Species at risk are listed by the Act; the U.
The Act, and others like it in other countries, is a useful tool, but it suffers because it is often difficult to get a species listed, or to get an effective management plan in place once it is listed. Additionally, species may be controversially taken off the list without necessarily having had a change in their situation. More fundamentally, the approach to protecting individual species rather than entire ecosystems is both inefficient and focuses efforts on a few highly visible and often charismatic species, perhaps at the expense of other species that go unprotected.
At the same time, the Act has a critical habitat provision outlined in the recovery mechanism that may benefit species other than the one targeted for management. The Act now lists over protected species. It makes it illegal to disturb or kill the protected species or distribute their parts much of the hunting of birds in the past was for their feathers. The international response to global warming has been mixed. The Kyoto Protocol, an international agreement that came out of the United Nations Framework Convention on Climate Change that committed countries to reducing greenhouse gas emissions by , was ratified by some countries, but spurned by others.
Two important countries in terms of their potential impact that did not ratify the Kyoto Protocol were the United States and China. Some goals for reduction in greenhouse gasses were met and exceeded by individual countries, but worldwide, the effort to limit greenhouse gas production is not succeeding. The intended replacement for the Kyoto Protocol has not materialized because governments cannot agree on timelines and benchmarks. Meanwhile, climate scientists predict the resulting costs to human societies and biodiversity will be high.
As already mentioned, the private non-profit sector plays a large role in the conservation effort both in North America and around the world. The Nature Conservancy takes a novel approach. It purchases land and protects it in an attempt to set up preserves for ecosystems. Ultimately, human behavior will change when human values change. At present, the growing urbanization of the human population is a force that poses challenges to the valuing of biodiversity.
Establishment of wildlife and ecosystem preserves is one of the key tools in conservation efforts. A preserve is an area of land set aside with varying degrees of protection for the organisms that exist within the boundaries of the preserve. Preserves can be effective in the short term for protecting both species and ecosystems, but they face challenges that scientists are still exploring to strengthen their viability as long-term solutions.
Due to the way protected lands are allocated they tend to contain less economically valuable resources rather than being set aside specifically for the species or ecosystems at risk and the way biodiversity is distributed, determining a target percentage of land or marine habitat that should be protected to maintain biodiversity levels is challenging. This area is greater than previous goals; however, it only represents 9 out of 14 recognized major biomes. Research has shown that 12 percent of all species live only outside preserves; these percentages are much higher when only threatened species and high quality preserves are considered.
For example, high quality preserves include only about 50 percent of threatened amphibian species. The conclusion must be that either the percentage of area protected must increase, or the percentage of high quality preserves must increase, or preserves must be targeted with greater attention to biodiversity protection. Researchers argue that more attention to the latter solution is required.
There has been extensive research into optimal preserve designs for maintaining biodiversity. The fundamental principle behind much of the research has been the seminal theoretical work of Robert H. MacArthur and Edward O. Wilson published in on island biogeography. The fundamental conclusion was that biodiversity on an island was a function of the origin of species through migration, speciation, and extinction on that island. Islands farther from a mainland are harder to get to, so migration is lower and the equilibrium number of species is lower.
Within island populations, evidence suggests that the number of species gradually increases to a level similar to the numbers on the mainland from which the species is suspected to have migrated. In addition, smaller islands are harder to find, so their immigration rates for new species are lower. Smaller islands are also less geographically diverse so there are fewer niches to promote speciation. And finally, smaller islands support smaller populations, so the probability of extinction is higher.
As islands get larger, the number of species accelerates, although the effect of island area on species numbers is not a direct correlation. For a species to persist in a preserve, the preserve must be large enough. The critical size depends, in part, on the home range that is characteristic of the species. A preserve for wolves, which range hundreds of kilometers, must be much larger than a preserve for butterflies, which might range within ten kilometers during its lifetime. But larger preserves have more core area of optimal habitat for individual species, they have more niches to support more species, and they attract more species because they can be found and reached more easily.
Preserves perform better when there are buffer zones around them of suboptimal habitat. The buffer allows organisms to exit the boundaries of the preserve without immediate negative consequences from predation or lack of resources. One large preserve is better than the same area of several smaller preserves because there is more core habitat unaffected by edges. All of these factors are taken into consideration when planning the nature of a preserve before the land is set aside. In addition to the physical, biological, and ecological specifications of a preserve, there are a variety of policy, legislative, and enforcement specifications related to uses of the preserve for functions other than protection of species.
These can include anything from timber extraction, mineral extraction, regulated hunting, human habitation, and nondestructive human recreation. Many of these policy decisions are made based on political pressures rather than conservation considerations. In some cases, wildlife protection policies have been so strict that subsistence-living indigenous populations have been forced from ancestral lands that fell within a preserve.
In other cases, even if a preserve is designed to protect wildlife, if the protections are not or cannot be enforced, the preserve status will have little meaning in the face of illegal poaching and timber extraction. This is a widespread problem with preserves in areas of the tropics. Some of the limitations on preserves as conservation tools are evident from the discussion of preserve design. Political and economic pressures typically make preserves smaller, never larger, so setting aside areas that are large enough is difficult.
If the area set aside is sufficiently large, there may not be sufficient area to create a buffer around the preserve. In this case, an area on the outer edges of the preserve inevitably becomes a riskier suboptimal habitat for the species in the preserve. Enforcement of protections is also a significant issue in countries without the resources or political will to prevent poaching and illegal resource extraction. Climate change will create inevitable problems with the location of preserves. The species within them will migrate to higher latitudes as the habitat of the preserve becomes less favorable.
Scientists are planning for the effects of global warming on future preserves and striving to predict the need for new preserves to accommodate anticipated changes to habitats; however, the end effectiveness is tenuous since these efforts are prediction based. Finally, an argument can be made that conservation preserves reinforce the cultural perception that humans are separate from nature, can exist outside of it, and can only operate in ways that do damage to biodiversity.
Creating preserves reduces the pressure on human activities outside the preserves to be sustainable and non-damaging to biodiversity. Ultimately, the political, economic, and human demographic pressures will degrade and reduce the size of conservation preserves if the activities outside them are not altered to be less damaging to biodiversity.
Habitat restoration holds considerable promise as a mechanism for restoring and maintaining biodiversity. Of course once a species has become extinct, its restoration is impossible. However, restoration can improve the biodiversity of degraded ecosystems. Reintroducing wolves, a top predator, to Yellowstone National Park in led to dramatic changes in the ecosystem that increased biodiversity.
Reducing elk populations has allowed revegetation of riparian areas, which has increased the diversity of species in that habitat. Decreasing the coyote population has increased the populations of species that were previously suppressed by this predator. The number of species of carrion eaters has increased because of the predatory activities of the wolves.
In this habitat, the wolf is a keystone species, meaning a species that is instrumental in maintaining diversity in an ecosystem. Removing a keystone species from an ecological community may cause a collapse in diversity. The results from the Yellowstone experiment suggest that restoring a keystone species can have the effect of restoring biodiversity in the community. Ecologists have argued for the identification of keystone species where possible and for focusing protection efforts on those species; likewise, it also makes sense to attempt to return them to their ecosystem if they have been removed.
The reintroduction of wolves into Yellowstone National Park in led to a change in the grazing behavior of b elk. To avoid predation, the elk no longer grazed exposed stream and riverbeds, such as c the Lamar Riverbed in Yellowstone. This allowed willow and cottonwood seedlings to grow. The seedlings decreased erosion and provided shading to the creek, which improved fish habitat. A new colony of d beaver may also have benefited from the habitat change.
Other large-scale restoration experiments underway involve dam removal. In the United States, since the mids, many aging dams are being considered for removal rather than replacement because of shifting beliefs about the ecological value of free-flowing rivers and because many dams no longer provide the benefit and functions that they did when they were first built. The measured benefits of dam removal include restoration of naturally fluctuating water levels the purpose of dams is frequently to reduce variation in river flows , which leads to increased fish diversity and improved water quality.
In the Pacific Northwest, dam removal projects are expected to increase populations of salmon, which is considered a keystone species because it transports key nutrients to inland ecosystems during its annual spawning migrations. In other regions such as the Atlantic coast, dam removal has allowed the return of spawning anadromous fish species species that are born in fresh water, live most of their lives in salt water, and return to fresh water to spawn. Some of the largest dam removal projects have yet to occur or have happened too recently for the consequences to be measured. The large-scale ecological experiments that these removal projects constitute will provide valuable data for other dam projects slated either for removal or construction.
Zoos have sought to play a role in conservation efforts both through captive breeding programs and education. The transformation of the missions of zoos from collection and exhibition facilities to organizations that are dedicated to conservation is ongoing. In general, it has been recognized that, except in some specific targeted cases, captive breeding programs for endangered species are inefficient and often prone to failure when the species are reintroduced to the wild. Zoo facilities are far too limited to contemplate captive breeding programs for the numbers of species that are now at risk.
Education is another potential positive impact of zoos on conservation efforts, particularly given the global trend to urbanization and the consequent reduction in contacts between people and wildlife. Biodiversity exists at multiple levels of organization and is measured in different ways depending on the goals of those taking the measurements. These measurements include numbers of species, genetic diversity, chemical diversity, and ecosystem diversity. The number of described species is estimated to be 1. Estimates for the total number of species on Earth vary but are on the order of 10 million.
Biodiversity is negatively correlated with latitude for most taxa, meaning that biodiversity is higher in the tropics. The mechanism for this pattern is not known with certainty, but several plausible hypotheses have been advanced. Five mass extinctions with losses of more than 50 percent of extant species are observable in the fossil record. Biodiversity recovery times after mass extinctions vary, but have been up to 30 million years. Recent extinctions are recorded in written history and are the basis for one method of estimating contemporary extinction rates.
The other method uses measures of habitat loss and species-area relationships. Estimates of contemporary extinction rates vary, but some rates are as high as times the background rate, as determined from the fossil record, and are predicted to rise. Humans use many compounds that were first discovered or derived from living organisms as medicines: secondary plant compounds, animal toxins, and antibiotics produced by bacteria and fungi.
More medicines are expected to be discovered in nature. Loss of biodiversity will impact the number of pharmaceuticals available to humans. Crop diversity is a requirement for food security, and it is being lost. Ecosystems provide ecosystem services that support human agriculture: pollination, nutrient cycling, pest control, and soil development and maintenance.
Loss of biodiversity threatens these ecosystem services and risks making food production more expensive or impossible. Wild food sources are mainly aquatic, but few are being managed for sustainability. Biodiversity may provide important psychological benefits to humans.
Additionally, there are moral arguments for the maintenance of biodiversity. The core threats to biodiversity are human population growth and unsustainable resource use. To date, the most significant causes of extinctions are habitat loss, introduction of exotic species, and overharvesting. Climate change is predicted to be a significant cause of extinctions in the coming century. Habitat loss occurs through deforestation, damming of rivers, and other activities. Overharvesting is a threat particularly to aquatic species, while the taking of bush meat in the humid tropics threatens many species in Asia, Africa, and the Americas.
Exotic species have been the cause of a number of extinctions and are especially damaging to islands and lakes. Climate change is forcing range changes that may lead to extinction. It is also affecting adaptations to the timing of resource availability that negatively affects species in seasonal environments. The impacts of climate change are greatest in the arctic. Global warming will also raise sea levels, eliminating some islands and reducing the area of all others. There is also a legislative framework for biodiversity protection. International treaties such as CITES regulate the transportation of endangered species across international borders.
Legislation within individual countries protecting species and agreements on global warming have had limited success; there is at present no international agreement on targets for greenhouse gas emissions.