|Biodiversity and Conservation|
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Cataloging and Discovering Species
Number of Species on Earth
Geographical Patterns of Species Richness
Importance of Distribution Patterns
Sparsely Distributed Species
Conservation Hot Spots
BIODIVERSITY IN THE UNITED STATES
BIODIVERSITY IN CALIFORNIA
THE CONVENTION ON BIOLOGICAL DIVERSITY
In order to monitor and conserve biological diversity, it is important to have ways of measuring it and documenting the levels of diversity in different parts of the world. We have to consider diversity at different levels. There is diversity between:
Subspecies are anatomically distinct from one another, but still able to interbreed under natural conditions. The White Rhino is an example we have already mentioned - it has northern and southern subspecies, each with their own conservation problems.
The anatomical differences between subspecies indicate that they are distinct genetic entities. They might often represent early stages in the creation of new species. For these reasons they are eligible for listing and protection under the Endangered Species Act, in the same way that species are protected.
The most useful level is the species, because most scientists agree on what constitutes a species. A commonly accepted definition is "a population whose members are able to interbreed freely under natural conditions". The phrase "under natural conditions" is important, because closely related species can often hybridize with one another under unnatural conditions (e.g. captivity). Even tigers and lions can interbreed in captivity, but there is no record of it having happened in nature (partly because they live in different habitats). An interesting example is the red wolf which some authorities consider a separate species, some a subspecies of gray wolf, and some a hybrid between the coyote and the gray wolf.
Notice that this definition says nothing about the commonly used criterion that species are usually anatomically different, or different in appearance, from each other. Anatomical differences are, in fact, usually the main basis for identifying and naming new species. Read about speciation - the process by which new species are formed.
Cataloging the biodiversity on Earth is a huge team effort. The The Tree of Life the All-species Foundation and the All-species Inventory are efforts to use the World Wide Web to coordinate the efforts of hundreds of biologists to classify and describe species.
The ultimate measure of biodiversity is the total number of species in existence. Surprisingly, biologists do not agree on this number, even to the nearest order of magnitude. There are about 1.8 million described and named species of organisms. Over half of described species are insects from temperate zones, but the real number of species of insects is very uncertain.
New Major Groups. Occasionally radically new forms are found:
For many years biologists divided life forms into:
A third major group of organisms, called Archaea, consisting of about 500 species, was discovered in 1977. They went undiscovered for so long because they look very much like bacteria, and they are very difficult to culture in the lab. They were first discovered in the most extreme environments on Earth - the hottest, coldest, and highest pressure environments, in high salt and alkaline environments, etc., so they are sometimes called "extremophiles". But now scientists are finding that they are very abundant in the open ocean as well, especially around Antarctica. In fact, they are so abundant that they are estimated to make up about 30% of the biomass on Earth.
A novel type of animal (less than 1mm long) was found living on the mouth parts of lobsters (Funch and Kristensen, 1995). It is totally unlike any known type of animal, both in its anatomy and its very complex life cycle. It defines a new phylum (Cycliophora) of animals. Examples of the other 35 phyla of animals are annelids (worms), arthropods (insects, spiders, crustaceans), echinoderms (sea urchins and starfish), mollusks (snails, clams), and chordates (including all the vertebrates).
New Species. About 10,000 new species are found every year, and most of these are insects and other inconspicuous animals. Usually new species are related to known ones and therefore fit into already-known groups of species such as families. Even in well-known groups such as birds and mammals, new species are still being discovered, at the rate of about 1-5 birds and 1-5 mammals per year (mainly in the tropics). Some recent examples are:
New videos taken by remote-controlled submersibles show some amazing and huge squid that are different from all known families.
The coelacanth. This very primitive fish with fleshy fins was known only from 80-million year old fossils until in 1938 one showed up in a fish market on an island near Madagascar. History repeated itself in 1998 when another one was found, again in a fish market but this time in Indonesia suggesting the existence of another population in the deep sea, thousands of miles from the first one. Apparently these fish live in caves on the sides of underwater volcanoes. Read Samantha Weinberg's fascinating account of the discovery! (click on the book)
Sometimes species thought to be extinct are rediscovered - for example the three-inch long, nocturnal, hairy-eared dwarf lemur rediscovered in 1989 in Madagascar after being missing since 1964.
Even entirely new ecosystems are still being discovered. In the last few decades new groups of organisms have been found living in the following environments:
Until a few years ago, the total number of species on earth was estimated at between 1.4 and 6 million. These estimates were obtained as follows:
For the more conspicuous birds and mammals, the number of species is known quite accurately, both for tropical species as well as temperate ones. It is estimated that at least 98% of birds have been discovered. For birds there are 2-3 times as many tropical species as temperate ones. For other organisms most of the named species (1.4 million) are from temperate countries. If we assume that the same factor applies to other organisms as to birds, then there are 2-3 times this many tropical species (2.8-4.2 million, giving an estimated total species of 4.2-5.6 million.
A dramatic upward revision of these estimates to 30 million came about as a result of work by Erwin on tropical beetles. Erwin used an insecticidal fog, generated by a machine hoisted high in the tree canopy, to knock down the canopy insects. Because they are so inaccessible, there had been few systematic studies of tropical canopy insects. Erwin collected the arthropods from 19 trees of a certain species (Luehea seemannii) in Panama over three seasons. The sample included 1,100 species of beetles!
To use this information to estimate the total species number, we need to know what fraction of these are host-specific (i.e. found only on this species of tree). The estimates (really guesses) are in the table. From this, Erwin estimated that 160 beetle species are host tree-specific.
Beetles represent about 40% of all known arthropod species; therefore Erwin estimated 160 x 100/40 = 400 arthropod species per tree species. Next, he estimated that the canopy is roughly twice as species-rich as the forest floor, and is composed mainly of different species. Therefore, including the forest floor brings the total to 600 arthropod species per tree species.
The estimated total number of species of tropical trees is 50,000. Therefore, the total number of tropical arthropod species is estimated as 600 x 50,000 = 30 million.
Each step of Erwin's argument is questionable. For example:
A more reliable estimate comes from work on tropical bugs (hemipterans) on the island of Sulawesi, Indonesia by Hodkinson and Casson (1991). They sampled bugs over a one-year period using several sampling methods at several sites including a variety of host plants. They found that the rate of accumulation of previously unrecorded species "slowed to a trickle" at the end of the study period, indicating that they had identified a substantial fraction of the species in that area. They found a total of 1690 species of which only 37.5% were previously described. Total of described species of hemipterans is 78,656. Therefore, a simple estimate for the real total is 78,656 x 100/37.5 = 209,749 (Hodkinson and Casson's calculation is a little more complex and difficult to understand). Hemipterans represent about 10% of all described insect species; therefore, the estimate for the total number of insect species is about 2.1 million, giving an estimate for the total species number of about 5 million - consistent with earlier estimates.
The best way to preserve biodiversity is, of course, by protecting the habitats of as many species as possible. Since we cannot protect everything, how do we decide which areas should receive the highest priority?
One way of assigning priorities would be to select the regions with the greatest number of species. For most well-studied groups of organisms, species richness increases from the poles to the equator.
The same geographical pattern is seen in the marine environment. For example, on Australia's Great Barrier Reef, the number of genera of coral is less than 10 at the southern end but more than 50 at the northern end. The number of sea squirt species is 103 in the arctic but 629 in the tropics. Even deep sea species diversity is higher in the tropics than at the poles.
The reason for the species richness of the tropics is not known, but the following ideas have been proposed:
There are, of course, local patterns superimposed on this global tendency, with some areas being especially rich in certain groups of species. The Philippines, Indonesia, New Guinea and the Solomon Islands are rich in many different types of organisms including corals.
In other places the wildlife is very abundant although the number of species may not break any records. An example is the Southern Ocean surrounding the Antarctic continent, which supports one of the most productive ecosystems on Earth. The Antarctic Circumpolar Current brings nutrient-rich water to the surface, supporting abundant growth of phytoplankton. The phytoplankton provides food for shrimp-like krill, and the krill provides food for huge populations of fish, birds, seals and whales.
The science of biogeography is the study of the geographic distribution of organisms. It was started by Alfred Russell Wallace, the co-originator with Charles Darwin of the theory of evolution. One of its principles is that the earth can be divided into six or eight biogeographic realms - the Nearctic, Palearctic, Ethiopian, Australian, Oriental, and Neotropical, in which the organisms present tend to be quite distinct from those of other realms. For example, the Australian realm is distinctive because of the large number of marsupials that have evolved during its long isolation. It has seven endemic families of mammals, as well as four of birds and 12 of flowering plants. Other systems have been drawn up for the marine environment.
Each biogeographic realm is subdivided into provinces, which reflect different types of environment within the realm. There are 227 provinces altogether.
Much more detailed classifications are possible, and in fact essential for conservation purposes. The World Wildlife fund and National Geographic Society recently mapped 867 terrestrial ecoregions of the world. Each is distinguished by its ecological features, climate, and animal and plant communities.
An example of fine-scale ecological diversity is provided by a small local canyon called Buck Gully, which contains nine different habitat types defined by their plant communities: chaparral, grassland, riparian, Venturan-Diegan coastal sage scrub, California buckwheat scrub, sagebrush scrub, mixed sage scrub, southern cactus scrub, and sagebrush-grassland scrub, each containing different collections of species and each worth preserving. The Nature Conservancy has identified over 3000 plant communities. A good target would be to preserve enough of each type of community to ensure its survival and that of all the species that live in it or depend on it (for example, migratory species).
Obviously rare organisms are more prone to extinction than common ones. However, the pattern of distribution is also important.
At one extreme are species which are restricted to one very small area, although they may be very abundant at that location (local endemics). The silversword plant grows only in the crater of Haleakala on Maui but there are some 47,000 individuals at that site. The Devil's Hole pupfish is restricted to a single desert spring in Nevada.
Locally endemic species tend to occur where the geography provides isolated patches such as mountains, islands, peninsulas, certain soil types or patches of forests surrounded by lava flows. Remote oceanic islands such as Hawaii and Ascension have the world's most distinctive floras. 91% of the 956 plants native to the Hawaiian Islands are endemic to those islands. The Hawaiian Islands are the most remote islands on earth, being at least 2,000 miles from the nearest major land mass in any direction. 80% of the 8,000 vascular plant species of Madagascar are endemic. 90% of the 9,000 flowering plants of Papua New Guinea and 76% of New Caledonia's 3,250 vascular plants are endemic. By contrast, regions that are not geographically isolated have lower proportions of endemic species - for example, only 1% of West Germany's species are endemic.
Locally endemic species can be saved by protecting a small area, but they are very susceptible to extinction due to over-exploitation and habitat loss. This is why many of the well-known extinctions are of species endemic to islands - notably the Dodo, the best-known example of extinction, which was endemic to the island of Mauritius. About half of the known animal extinctions in the last 400 years, and at least 90 percent of the bird extinctions, were of island dwellers (see Chapter 12).
Marine organisms tend to be much more widely distributed than terrestrial species because they encounter fewer physical barriers. Many marine species, including snails, crabs, sharks and fish, are found throughout the tropics. Most species found on Australia's Great Barrier Reef are also found in other parts of the Indo-West Pacific.
There are, however, certain oceanic regions that have a high proportion of locally endemic species. The Mediterranean Sea has a fairly narrow connection to the Atlantic Ocean and this isolation has allowed the evolution of numerous endemic species in the Mediterranean. Consequently 14% of the 362 species in the Mediterranean are found nowhere else. Similarly, the Red Sea has 15% endemic fish species, and the Gulf of California has 17%. Fish that are restricted to shallow waters can also show a high frequency of endemism around isolated oceanic islands. For example 30 to 40% of the fish species at Easter Island are locally endemic.
At the opposite extreme to local endemics are sparsely distributed species, which occur over very large geographical regions but are not very abundant anywhere. Top predators - animal species near the end of the food chain such as large cats, wolves, bears, sharks and eagles - tend to be relatively scarce but widely distributed. Saving these species in the wild is very difficult and expensive, even a small population requiring protection of a large area or of smaller areas connected by wildlife corridors. For example, the tiger's home range is 8-24 square miles. Top predators have also been targets for hunters and have been unpopular with farmers because they sometimes attack livestock or even people. The Grizzly Bear (subspecies of Brown Bear) is the symbol of California but was hunted to extinction in this state.
Migratory species present challenging problems because they often require habitats along and at each end of their migration routes. Many songbirds in North America are threatened by habitat loss in Central and South America as modernization of coffee plantations leaves less natural habitat than older methods, and as North American forests become fragmented.
Recent research shows that sea turtles migrate along well-defined corridors in the ocean. It might be necessary to provide protection of these migration routes as well as the nesting beaches in order to effectively conserve these species. Many of the world's most important feeding and nesting sites are along the coast of West Africa, and six species that depend on those sites are declining rapidly due to poaching for meat, eggs and shell.
The Convention on Migratory Species (CMS) was established to address the special political problems associated with conserving migratory species, many of which are in steep decline. The Convention uses a similar listing system to other conventions, in which the most endangered species are on "Appendix I" and species for which the threat is less imminent are on "Appendix II". At the September 2002 meeting some of the notable new listings on Appendix I were the Bactrian Camel (down to less than 1000 individuals), the Great White Shark and three species of whale.
The high levels of endemism in certain areas of the world, coupled with imminent threats from habitat loss in many of these areas, has led to the designation, by World Conservation Union (IUCN) and Conservation International, of "hot spots" for preservation. Coastal California is one of these regions. Other regions are the Atlantic coast of Brazil, Madagascar, and the Indo-west Pacific.
U.S. biodiversity in jeopardy, study shows
Two important facts about California:
The high biological significance of Southern California was also highlighted in a recent study of the geographic distribution of endangered species in the U.S. (Dobson et al., Science 275; 550). The maps show the number of listed species in each county for several groups of organisms. For plants especially, Southern California turns out to be a "hot spot" of threatened biodiversity. The other hot spots are Hawaii, the southeastern coastal states, and southern Appalachia. As expected, in most cases, hot spots occur where the ranges of many endemic species overlap with intensive urbanization and agriculture.
The predicted population growth means there will inevitably be increasing pressure on our natural resources in the coming decades. California has an urgent need to establish programs for cataloguing and preserving biodiversity. Fortunately the state is taking this task fairly seriously. In fact, a recent survey by the organization Defenders of Wildlife concluded that California has the nation's best biodiversity policies and programs. This was mainly in response to the development of Natural Communities Conservation Planning (see later lecture) and partly to the establishment of the the California Biodiversity Council, whose role is to "develop guiding principles and policies, design a statewide strategy to conserve biological diversity, and coordinate implementation of this strategy through regional and local institutions".
The California Resources Agency is responsible for the conservation, enhancement, and management of California's natural and cultural resources, including land, water, wildlife, parks, minerals, and historic sites. One of their programs is the California Environmental Resources Evaluation System (CERES), an information system designed to "facilitate access to a variety of electronic data describing California's rich and diverse environments".
In California, the California Department of Fish and Game (DFG) has the responsibility for identifying the most significant natural areas in the State.
Significant Natural Areas are those sites which meet at least one of the following criteria.
1.Areas supporting extremely rare species or
2.Areas supporting associations or concentrations of rare species or communities;
3.Areas exhibiting representative examples of common or rare communities;
4.Areas of high species-richness or habitat-richness.
The DFG has also produced an on-line map of habitat types in California. They also have an active program of documenting California's wildlife and endangered species. Visit their California Wildlife Habitat Relationships page.
The Convention on Biological Diversity (CBD) was signed by over 150 governments at the 1992 Earth Summit in Rio de Janeiro, and became effective as international law in December 1993. It is the first international agreement committing governments to comprehensive protection of the Earth's biological resources. As of April, 2001, 180 countries and the European Union had ratified the agreement, but the United States has not done so, mainly due to the efforts of a group of senators who felt that the treaty required giving "half of America back to the wolves to save the earth".
The CBD has three overall goals:
By signing the CBD, participating governments agree to carry out various measures to conserve biodiversity. The measures include (among other things):
The CBD has also published a useful Global Biodiversity Outlook.
The CBD also includes agreements for using biological diversity. And governments must provide for "fair sharing" of the benefits derived from genetic resources (i.e. compensation for its use or transfer of technology derived from genetic resources).
The requirements of the CBD are being met in this country by the Biological Resources Division of the U.S. Geological Survey (formerly the National Biological Service), established in 1993. Its operating mission is "to work with others to provide the scientific understanding and technologies needed to support the sound management and conservation of the nation's biological resources." It sponsors a variety of national scientific research programs as well as a national information infrastructure program. It has the following Strategic Science Plan:
BIOLOGICAL RESOURCES DIVISION STRATEGIC SCIENCE PLAN September 3, 1996
A National Biological Survey for the United States? from the Australian Nature Conservation Agency, provides an interesting perspective on how science should contribute to conservation rather than just collect information.
The U.S. Geological Service has developed a method for digitized mapping of many parameters important for conservation, including the distribution of plant communities and of vertebrate animals, and the geographic pattern of land use. This method is called GAP analysis, because it was designed to identify gaps in the system of protected land areas, where insufficient protection was being provided for endangered and other species. It certainly can perform this function (see example in slide show). However, the technology can also be used for many other purposes where geographic comparisons are important, such as monitoring changes in species distribution caused by climate change; for mapping levels of contaminants so they can be compared with changes in species distribution; for tracking the spread of exotic species and of urbanization and their consequences for species distribution, and so on.
Seas Yield a Bounty of Species by David Malakoff