Chapter 15 Biodiversity and Conservation Biology
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Up until the past 200 years, tigers roamed widely across the Asian conti- nent, but people have driven these cats from most of their historic range, 1 and today tigers are exceedingly rare and are creeping toward extinction.
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~ The subspecies known as the Siberian (or Amur) tiger are the largest cats'
in the world, with males reaching 800 lbs and 12 feet long.
Siberian tigers find their last refuge in the temperate forests and taiga of
1 the remote Sikhote-Alin Mountains of the Russian Far East.
jFor thousands of years the Siberian tiger coexisted with the native people, and it was uncommon for indigenous people of the region to kill a tiger.
, The Russians who moved into the region in the early to mid-20th century i hunted the tiger for sport and hides, and some Russians killed as many as ]10 tigers in a single hunt.
Poachers killed tigers to sell their body parts for traditional medicine and aphrodisiacs to Asian countries, and road building, logging, and agricul- ture fragmented the tiger's habitat and provided easy access for hunters. The tiger population had dipped to 20-30 animals when international conservation groups launched a Russian-American effort, the Siberian Tiger Project, which studies and protects the tiger and educates people about tigers.
Due to various conservation efforts, today the Siberian tiger population -' numbers 150-450 individuals, and 500 more survive in zoos around the
/ world.
Our Planet of Life
Growing human population and resource consumption are putting great pressure on the tIora and fauna of the planet, from tigers to tiger beetles. Earth's diversity of life makes our planet unique in the universe, but we
have already begun losing the very thing that makes our planet so special. Biodiversity is the sum total of all organisms in an area, and includes di- versity of species, their genes, populations, and communities.
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What is biodiversity?
Dr. Edward O. Wilson defines biodiversity as the variety of organisms at
all levels, from genetic variants in the same species through genera, fami- lies, and ecosystems;
The UN Environment Programme (UNEP) defines biodiversity simply as
"the variety of life in all its forms, levels, and combinations."
Although there are multitudinous definitions of biodiversity, it is clear that biodiversity is not simply a count of species, but a multifaceted concept.
Biodiversity encompasses several levels of life's organization
The easiest and most commonly used definition of biodiversity is species
diversity.
Species Diversity Species diversity is expressed in terms of the number of species in the world or in a particular region.
A species is a population or group of populations whose members share certain unique characteristics and can freely breed with one another and produce fertile offspring.
Speciation, the generation of new species, adds to species diversity, whereas extinction decreases species diversity.
Biodiversity exists in subspecies, populations of a species that occur in different geographic areas and differ from one another in at least some characteristics.
Subspecies occur where divergence has not proceeded all the way to
speciation.
Genetic Diversity Genetic diversity encompasses the differences in DNA composition among individuals within a given species.
As a species becomes adapted to the local environment, its genetic diver- sity may decrease, because-as long as environmental conditions remain the same-the species survives better.
However, species with more genetic diversity have better chances of per-
sisting, because their built-in variation allows them to cope with environ- mental change.
Species with little genetic diversity are vulnerable to environmental change or diseases for which they are not genetically prepared.
Species with low genetic diversity may also suffer the effects of inbreed-
ing, whereby genetically similar individuals mate and produce weak or de- fective offspring. . :
Scientists are concerned over low genetic diversity in species with low
population sizes, including cheetahs, bison, and elephant seals.
Ecosystem diversity Biodiversity at this level includes groupings of
organisms, their interactions with one another, and their relationships with their abiotic environment.
Ecosystem diversity refers to the number and variety of ecosystems in an
area; community diversity refers to the number and variety of community types; and habitat diversity refers to the number and variety of habitats.
Landscape diversity refers to the variety and geographic arrangement of . habitats, communities, or ecosystems over a wide area, including the sizes, shapes, and interconnectedness of patches.
Measuring biodiversity is not easy
Species diversity is a good gauge for overall biodiversity when comparing different areas, but we still are profoundly ignorant of the number of species that exist.
Scientists have identified approximately 1.75 million species, but there may actually be about 14 million species.
Insects account for more than half of all species in the world, and about 40% of all insects are beetles.
There are several reasons why we don't know the exact number of species on Earth.
Some areas of Earth, such as the ocean depths, hydrothermal vents, and the tree canopies and soils of tropical forests, have not yet been completely explored.
Many species are tiny and easily overlooked, such as bacteria, roundworms, and soil-dwelling arthropods.
Finally, one species can turn out to be two or more once biologists look more closely, which happens even with large species such as trees, birds, and whales.
In 2000, the All Species Foundation was created "to discover and describe all living organisms on Earth within one human generation, and to
make this information available to everyone everywhere" and is backed by 100 collaborating scientists.
You may be able to help measure biodiversity near where you live
Today, more and more locally based efforts are springing up to measure biodiversity in small, commonplace areas.
In a "bioblitz," taxonomists a?d interested citizens team up and race to
thoroughly survey every species they can find within 24 hours in a state park or a city.
Bioblitzes promote public awareness of biodiversity as well as obtain accu- rate species counts, yet they can also result in the discovery of new species.
Global biodiversity is not distributed evenly
Species are not distributed across the planet evenly, and scientists have tried to explain the distribution of biodiversity.
One group may have only one or a few species, while another group, such as the family that contains daisies, ragweed, and sunflowers, may have thousands of species.
Adaptive radiation occurs when an ancestral species gives rise to many species that fill different niches, and each species adapts to its niche by natural selection.
Species richness also varies according to biome, and tends to increase as one approaches the equator, so that tropical dryforests and rainforests support more species than do tundra and deserts.
1 ms panern or vanauon wlm laUtuae, me laUtuamal graOlent, IS probably . due to increased plant productivity and climate stability at tropical latitudes. Stable climates, with similar daily temperatures and rainfall, allow species to co-exist and fill specialized niches.
Polar and temperate regions may have fewer species because glaciation could have forced species to move toward more tropical latitudes.
Biodiversity Loss and Species Extinction
Humans are causing the loss of all levels of biodiversity through the ex- tinction of species.
Extinction occurs when the last member of a species dies, and the species ceases to exist, while extirpation is the extinction of a particular popula- tion from a given area (but not the entire species globally).
Extinction is "natural"
Scientists estimate that roughly 99% of all species that have ever lived are already extinct.
Before humans, most extinctions occurred one by one; this background
rate of extinction caused one species of bird (or mammal) to became ex- tinct every 500-1,000 years.
Earth has experienced five previous mass extinction episodes
Extinction rates have surpassed this background rate during five mass ex- tinction events during Earth's history; each event took more than 20% of life's families and at least half its species.
The most severe episode was that at the end of the Permian period (248 million years ago), when 90% of all species vanished.
! The most well-known episode was at the end of the Cretaceous period, 65 million years ago, when an asteroid impact killed off the dinosaurs.
i The modern era, called the Quaternary period, may see the extinction of
more than half of all species, but today's ongoing mass extinction is dif- ferent in two primary respects: first, humans are causing it, and second, humans will suffer as a result of it.
Humans set the sixth mass extinction in motion years ago
1 There are many instances of human-induced species extinction over the
past few hundred years, including those of the dodo, passenger pigeon, Carolina parakeet, great auk, and Labrador duck; several more species,
like the whooping crane, California condor, and Kirtland's warbler, teeter on the brink of extinction.
J Human-caused extinction is nothing new: Thousands of years ago, waves
of extinctions occurred wherever people colonized new areas, from Hawaii to Australia.
Current extinction rates are much higher than normal
As our population and resource consumption strain habitats and wildlife, species are lost at a faster pace.
The world's leading scientists report th~t current global extinction rates . are more than 1,000 times greater than they would be without human de- struction of habitat.
More than 30,000 plant and animal species face extinction; mammals are becoming extinct 40 times faster than ever before and 45% of Earth's
forests, 50% of its mangrove ecosystems, and 10% of its coral reefs have been destroyed.
The World Conservation Union's (IUCN) Red List, a list of species facing unusually high risks of extinction, reported that 24% of mammal species and 12% of bird species are threatened with extinction.
From 1996 to 2002 the total number of threatened vertebrate animals
climbed by 6%, and the actual numbers of species extinct and threatened are greater than the known numbers.
The major causes of species loss spell "HIPPO"
HIPPO denotes the five primary causes of species decline and extinction:
Habitat alteration, Invasive species, Pollution, Population, and Overexploita- tion.
The most prevalent and powerful of these five causes is habitat alteration. Habitat alteration: Nearly every human activity-including farming,
grazing, deforestation, urban sprawl, and global climate change-alters the habitat of organisms.
Any change, including degradation or destruction, of a habitat is likely to make the habitat less suitable for organisms because they are adapted to the original habitat.
Human-induced habitat change may benefit species like starlings, house
sparrows, pigeons, and gray squirrels that do well in urban environments because they are weedy, cosmopolitan species that are in little danger of disappearing.
Habitat alteration is the primary source of population declines for 83% of threatened mammals and 85% of threatened birds.
Invasive species: The introduction of invasive species to new environ- ments has also pushed native species toward extinction.
Accidental introductions include marine organisms in the ballast water of ships, escaped pets, or the weed seeds that stick to our socks when we travel.
Humans who intentionally introduced species to new places for food, or for economic or aesthetic reasons, were usually unaware of the ecological consequences that could result.
If organisms in a new area are released from the limiting factors of their native parasites, predators, or competition, they can increase rapidly and displace native species.
Invasive species also cause billions of dollars in economic damage each year.
Island species are especially vulnerable to invasive species, because they
have been isolated for so long that they have not evolved the defenses to resist invaders.
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Pollution Air pollution can degrade forest ecosystems; water pollution . can affect fish and amphibians; and agricultural runoff can harm terres- trial and aquatic species.
Although pollution is a substantial threat, it is less significant than the
public thinks, and is less of a threat than are habitat alteration, invasive species, or human population growth
Population growth The increasing human population intensifies every environmental problem and poses an indirect threat to other species through each of the other components of the HIPPO dilemma.
Along with the increasing resource consumption, human population
growth is the ultimate reason behind many of the threats to biodiversity. Overexploitation This term refers to two different things: overharvesting of species from the wild and overconsumption of resources by people.
For some species, hunting by humans poses a threat of extinction (e.g.,
the Siberian tiger) because the species is large, few in number, long-lived, and raises few young-a classic K-strategist.
Many other K-strategist animals, such as whales, gorillas, and sharks, are killed each year.
Sometimes causes of biodiversity loss are difficult to determine
, The reasons for a species' decline can be multifaceted, complex, and hard to determine.
For example, frogs, toads, and salamanders worldwide are decreasing and several species have gone extinct due to a wide array of factors, including chemical contamination, disease transmission, habitat loss, ozone deple- tion, and climate change.
Benefits of Biodiversity
Biodiversity is being lost at all scales, but many people question whether extinction of species is important.
There are a number of concrete reasons for preserving biodiversity, show- ing how biodiversity directly or indirectly supports the long-term sustain- ability of human society.
In addition, many people feel that there are ethical and aesthetic dimen- sions to biodiversity preservation that cannot be ignored.
Biodiversity provides valuable ecosystem services free of charge
The valuable processes that intact ecosystems provide free of <;harge are
known as ecosystem services, including cleaning air and buffeting aquatic systems against flooding and drought.
Native races of crops can provide insurance against disease and drought,
while abundant wildlife can attract tourists and boost economies of devel- oping nations.
Biodiversity maintains free ecosystem services by: providing food, fuel, and building materials, purifying and detoxifying areas, moderating
droughts, winds, and climate, renewing soils, pollinating plants, control- ling pests, and maintaining genetic diversity.