L 8 Biodiversity

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BIODIVERSITY

Biodiversity is a combination of two words 'biological' and 'diversity'. Biodiversity refersto the number, variety and variability of all life forms on earth. These include millions of

plants, animals and micro-organisms, the genes they contain, and the intricate

ecosystems of which they are a part.

Why Is Biodiversity Important?

One important renewable resource is biological diversity, or biodiversity: the different

life-forms and life sustaining processes that can best survive the variety of conditions

currently.

Biodiversity may sound like an abstract concept, but in reality it touches almost every

aspect of our life. The earth has an enormous variety of plants and animals, both domesti-

cated and wild, as also a wide array of habitats and ecosystems. This diversity meets the

food, medicinal, clothing, shelter, spiritual as well as the recreational needs of millionsof people around the world. It also ensures that ecological functions such as the supply

of clean water, nutrient cycling and soil protection are maintained. In fact, biodiversityloss would mean a threat to the survival of the human race. Here are some reasons why

each one of us should be concerned about biodiversity and its loss.

Kinds of biodiversity include the following:

Genetic diversity (variety in the genetic makeup among individuals within a

species The diversity of genes within a species, passed down the generations isknown as genetic biodiversity. It is this type of diversity that gives rise to the

different varieties of rice, mangoes, etc).

Species diversity (variety among the species or distinct types of living organismsfound in different habitats of the planet)

Ecological diversity (variety of forests, deserts, grasslands, streams, lakes, oceans,

coral reefs, wetlands, and other biological communities))

Functional diversity (biological and chemical processes or functions such asenergy flow and matter cycling needed for the survival of species and biological

communities).

Microorganism diversity (Microbes include bacteria, viruses, protozoa, yeast, fungus,etc., and form a vital part of life on earth)

Ecosystem diversity (An ecosystem is a set of life forms e.g. plants, animals,

micro-organisms; interacting with one another and with non-living elements (soil,

air, water, minerals, etc.). Ecosystem diversity is, therefore, the diversity ofhabitats which include the different life forms within. The term also refers to the

variety of ecosystems found within a biogeographical or political boundary

(May also be called habitat diversity: the diversity of habitats in a given unitarea).

Domesticated diversity (When we think of biodiversity, we tend to think only ofwild plants and animals. But there is also considerable diversity among

domesticated plants and animals. Domesticated biodiversity may be the result of

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manipulation by humans, or of natural adaptations to different condit ions over

a period of time)

This rich variety of genes, species, biological communities, and life-sustaining biological

and chemical processes Gives us food, wood, fibers, energy, raw materials, industrial chemicals, and

medicines, all of which pour hundreds of billions of dollars into the world econ-omy each year.

Provides us with free recycling, purification, and natural pest control services.

Every species here today (1) contains genetic information that represents thousands to

millions of years of adaptation to the earth's changing environmental conditions and (2) is

the raw material for future adaptations. Loss of biodiversity (1) reduces the availability ofecosystem services and (2) decreases the ability of species, communities, and ecosystems

to adapt to changing environmental conditions. Biodiversity is nature's insurance policy

against disasters.

Some people also include human cultural diversity as part of the earth's biodiversity. The

variety of human cultures represents numerous social and technological solutions tochanging environmental conditions.

EVOLUTION AND BIODIVERSITY

We can summarize the 3.7-billion-year biological history of the earth in one sentence:

Organisms convert solar energy to food, chemicals cycle, and a variety of species with

different biological roles (niches) has evolved in response to changing environmentalconditions.

Each species here today represents a long chain of evolution, and each of thesespecies plays a unique ecological role in the earth's communities and ecosystems. These

species, communities, and ecosystems also are essential for future evolution as the earth

continues its long history of environmental change.

How was the earth's species evolved and what is the nature of their niches or biological

roles. This information is important for helping us (1) understand the effects of human

actions on wild species and (2) protect species-including the human species-frompremature extinction.

Evidence about the earth's early history comes from chemical analysis and measurementsof radioactive elements in primitive rocks and fossils. Chemists have also conducted

laboratory experiments showing how simple inorganic compounds in the earth's early

atmosphere might have reacted to produce amino acids, simple sugars, and other organicmolecules used as building blocks for the protein, complex carbohydrate, RNA, and

DNA molecules needed for life. From this diverse evidence scientists have hypothesized

that life on the earth developed in two phases over the past 4.7-4.8 billion years):

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Chemical evolution of the organic molecules, biopolymers, and systems of chemical

reactions needed to form the first protocells (taking about 1 billion years)

Biological evolution from single-celled prokaryotic bacteria, to single-celled eu-karyotic creatures, and then to multicellular organisms (taking about 3.7-3.8 billion years)

How Do We Know What Organisms Lived in the Past? Most of what we know of theearth's life history comes from fossils: mineralized or petrified replicas of skeletons,

bones, teeth, shells, leaves, and seeds, or impressions of such items. Such fossils (1) give

us physical evidence of organisms that lived long ago and (2) show us what their internalstructures looked like.

How did Life First Evolve?

About 3.2 billion years ago, the earth was a very hostile environment for life. Hot lavaspewed from its surface and beneath the sea, much of the land was dotted with boiling

hot springs, and the atmosphere was thick with steam and carbon dioxide. Over time, it is

believed that early protocells evolved into singlecelled, bacterialike prokaryotes having

the properties we describe as life. However, scientists hotly debate the details of how thismight have happened.

EVOLUTION

What Is Evolution? According to scientific evidence, the major driving force of

adaptation to changes in environmental conditions is biological evolution, orevolution:the change in a population's genetic makeup (gene pool) through successive generations.

Note thatpopulations, not individuals, evolve by becoming genetically different.

According to the theory of evolution, all species descended from earlier, ancestralspecies. This widely accepted scientific theory explains how life has changed over the

past 3.7 billion years and why life is so diverse today.

Biologists use the term microevolution to describe the small genetic changes that

occur in a population. The term macroevolution is used to describe longterm, large-scale

evolutionary changes through which (1) new species are formed from ancestral speciesand (2) other species are lost through extinction.

How Does Microevolution Work? The first step in evolution is the development of

genetic variability in a population. Recall that (1) genetic information in chromosomes iscontained in various sequences of chemical units (called nucleotides) in DNA molecules

and (2) genes found in chromosomes are segments of DNA coded for certain traits that

can be passed on to offspring.A population's gene pool is the set of all genes in the individuals of the population of

a species.Microevolutionis a change in a population's gene pool over time.

Genetic variability in a population originates through mutations: random changes in thestructure or number of DNA molecules in a cell.

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The process of natural selection occurs when some individuals of a population have

genetically based traits that increase their chances of survival and their ability to produce

offspring.

Some biologists have proposed that interactions between species also can result in

microevolution in each of their populations. According to this hypothesis, whenpopulations of two different species interact over a long time, changes in the gene pool of

one species can lead to changes in the gene pool of the other species. This process is

called coevolution.

Suppose that certain individuals in a population of carnivores (such as owls) become

better at hunting prey (such as mice). Because of genetic variation, certain individuals of

the prey have traits that allow them to escape or hide from their predators, and they passthese adaptive traits on to some of their offspring. However, a few individuals in the

predator population also may have traits (such as better eyesight or quicker reflexes) that

allow them to hunt the better-adapted prey successfully. They would then pass these traits

on to some of their offspring.Similarly, individual plants in a population may evolve defenses, such as camouflage,

thorns, or poisons, against efficient herbivores. In turn, some herbivores in the populationmay have genetic characteristics that enable them to overcome these defenses and

produce more offspring than those without such traits.

ECOLOGICAL NICHES

What Is an Ecological Niche? If asked what role a certain species such as an alligator

plays in an ecosystem, an ecologist would describe its ecological niche, or simply niche

(pronounced "nitch"), the species' way of life or functional role in an ecosystem. Aspecies' niche involves everything that affects its survival and reproduction. This includes

(1) its range of tolerance for various physical and chemical conditions, such as

temperature or water availability (2) the types and amounts of resources it uses, such asfood or nutrients and space, (3) how it interacts with other living and nonliving

components of the ecosystems in which it is found, and (4) the role it plays in the energy

flow and matter cycling in an ecosystem.

The ecological niche of a species is different from its habitat, or physical location, where

it lives. Ecologists often say that a niche is like a species' occupation, whereas habitat is

like its address.

A species' ecological niche represents the adaptations oradaptive traits that its members

have acquired through evolution. These traits enable its members to survive andreproduce more effectively under a given set of environmental conditions.

Understanding a species' niche is important because it can help us (1) prevent it frombecoming prematurely extinct and (2) assess the environmental changes we make in

terrestrial and aquatic systems. For example, how will the niches of various species be

changed by clearing a forest, plowing up a grassland, filling in a wetland, or dumping

pollutants into a lake or stream?

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What Is the Difference Between a Species' Fundamental Niche and Its Realized

Niche?

A species' fundamental niche is the full potential range of physical, chemical, and

biological conditions and resources it could theoretically use if there were no directcompetition from other species. But in a particular ecosystem, species often compete with

one another for one or more of the same resources. This means the niches of competing

species overlap.

To survive and avoid competition for the same resources, a species usually occupies only

part of its fundamental niche in a particular community or ecosystem-what ecologists call

its realized niche. By analogy, you may be capable of being president of a particularcompany (yourfundamental professional niche), but competition from others may mean

you may become only a vice president (yourrealized professional niche).

The niches of species can be used to broadly classify them asgeneralists or specialists.

Generalist species have broad niches. They can (1) live in many different places, (2) eata variety of foods, and (3) tolerate a wide range of environmental conditions. Flies,

cockroaches, mice, rats, whitetailed deer, raccoons, coyotes, copperheads, channel

catfish, and humans are generalist species.

Specialist species have narrow niches. They may be able to (1) live in only one type of

habitat, (2) use only one or a few types of food, or (3) tolerate only a narrow range of

climatic and other environmental conditions. This makes them more prone to extinctionwhen environmental conditions change. Examples of specialists are (1) tiger sala-

manders, which can breed only in fishless ponds so their larvae will not be eaten, (2) red-

cockaded woodpeckers, which carve nest holes almost exclusively in old (at least 75years) longleaf pines, (3) spotted owls, which need old-growth forests in the Pacific

Northwest for food and shelter, and (4) China's highly endangered giant pandas, which

feed almost exclusively on various types of bamboo.

Is it better to be a generalist than a specialist? It depends. When environmental

conditions are fairly constant, as in a tropical rain forest, specialists have an advantage

because they have fewer competitors. But under rapidly changing environmentalconditions, the generalist usually is better off than the specialist.

What Are Two Common Misconceptions About Evolution? Two commonmisconceptions about evolution are as follows:

"Survival of the fittest" means "survival of the strongest." To biologists, fitness is a

measure of reproductive success not strength. Thus the fittest individuals are those thatleave the most descendants.

Evolution involves some grand plan of nature in which species become progressively

more perfect. From a scientific standpoint, no plan or goal of perfection exists in the

evolutionary process. However, some people (creationists) believe there is a conflict

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between the scientific theory of evolution and their religious beliefs about how life was

created on the earth.

SPECIATION, EXTINCTION, AND BIODIVERSITY

How Do New Species Evolve?Under certain circumstances, natural selection can lead to an entirely new species. In this

process, called speciation, two species arise from one. So, Speciation is the evolution of

two species from one species because of divergent natural selection in response tochanges in environmental conditions. It usually takes thousands of years to take place.

The most common mechanism of speciation (especially among animals) takes place intwo phases: geographic isolation and reproductive isolation.

Geographic isolation occurs when groups of the same population of a species become

physically separated for long periods. For example, part of a population may migrate insearch of food and then begin living in another area with different environmental

conditions. Populations also may become separated (1) by a physical barrier (such as amountain range, stream, lake, or road), (2) by a change such as a volcanic eruption or

earthquake, or (3) when a few individuals are carried to a new area by wind or water.

The second phase of speciation is reproductive isolation. It occurs when mutation and

natural selection operate independently in two geographically isolated populations and

change the allele frequencies in different ways. If this process, called divergence, contin-

ues long enough, members of the geographically and reproductively isolated populationsmay become so different in genetic makeup that (1) they cannot interbreed, or (2) if they

do, they cannot produce live, fertile offspring. Then one species has become two, andspeciationhas occurred through divergent evolution.

How Do Species Become Extinct?

After speciation, the second process affecting the number and types of species on theearth is extinction. Extinction is the ultimate fate of all species, just as death is for allindividual organisms. It occurs when the last individual member of a species dies. Local

extinction occurs when a species disappears from a part of its range but persists elsewhere.

Global extinction means that a species becomes extinct everywhere.

Extinction is an irreversible loss: once a species is extinct it can never reappear. Although

extinction is the role of nature, the rate of extinctions has varied greatly over geologic time and

has increased rapidly since the industrial revolution. When environmental conditions change,

a species must (1) evolve (become better adapted), (2) move to a more favorable area (ifpossible), or (3) cease to exist (become extinct).

The earth's long-term patterns of speciation and extinction have been affected by several

major factors: (1) large-scale movements of the continents (continental drift) over

millions of years, (2) gradual climate changes caused by continental drift and slight shiftsin the earth's orbit around the sun, and (3) rapid climate change caused by catastrophic

events (such as large volcanic eruptions, huge meteorites and asteroids crashing into the

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earth, and release of large amounts of methane trapped beneath the ocean floor). Some of

these events create dust clouds that shut down or sharply reduce photosynthesis long

enough to eliminate huge numbers of producers and, soon thereafter, the consumers thatfed on them.

Extinction is the ultimate fate of all species, just as death is for all individual organisms.

Biologists estimate that 99.9% of all the species that have ever existed are now extinct.

As local environmental conditions change, a certain number of species disappear at a

low rate, called background extinction. In contrast, mass extinction is a significant risein extinction rates above the background level.

Causes of ExtinctionCauses of extinction are usually grouped into five categories: population risk, environmental

risk, natural catastrophe, genetic risk, and human actions.

Population Risk

Random variations in population rates can cause a species in low abundance to become extinct.

This is termed population risk. For example, blue whales swim over vast areas of ocean. Becausewhaling once reduced the total population to only several hundred individuals, there were

probably year-to-year variations in the success of individual blue whales in finding mates. If in

one year most whales were unsuccessful in finding a mate, then births could be dangerously low.

Such random variation in populations, typical among many species, can occur without any

change in the environment. It is a risk especially to species that consist of only a single

population in one habitat.

Environmental Risk

Population size can be affected by changes in the environment that occur from day to day, month

to month, year to year, even though the changes are not severe enough to be considered

environmental catastrophes. Environmental risks involve variation in the physical or biological

environment, including variations in predator, prey, symbiotic, or competitor species.In some cases, species are sufficiently rare and isolated that such normal variations (e.g. late

snow & freeze) can lead to their extinction. In other cases, species succumb to catastrophic

variation in the environment.

Natural Catastrophe

A sudden change in the environment not the result of human action is a natural catastrophe. Fires,

major storms, earthquakes, and floods are natural catastrophes on land; changes in currents and

upwellings are ocean catastrophes. The explosion of a volcano on the island of Krakatoa in

Indonesia in 1883 caused the island blown to bits bringing about local extinction of most life

forms there.

Genetic RiskDetrimental change in genetic characteristics not caused by external environmental changes is

called genetic risk. Genetic changes can occur in small populations from reduced genetic

variation, genetic drift, and mutation. In a small population, only some of the possible inherited

characteristics will be found. The species is vulnerable to extinction because it lacks variety or

because a mutation can become fixed in the population.

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Human Actions

Human actions cause extinction of species through (1) intentional hunting or harvesting (for

commercial purposes, for sport, etc); (2) disruption or elimination of habitats; (3) introduction of

new parasites (transported by introduced species), predators (e.g. introduction of exotic species

such as dogs on islands caused extinction of dodo birds, whose eggs, laid on ground, were easyprey for dogs), or competitors of a species; and (4) pollution of the environment.

How Do Speciation and Extinction Affect Biodiversity?

Speciation minus extinction equals biodiversity, the planet's genetic raw material for

future evolution in response to changing environmental conditions. In this long-term

give-and-take between extinction and speciation, mass extinctions and mass depletionstemporarily reduce biodiversity.

Although extinction is a natural process, much evidence indicates that humans have

become a major force in the premature extinction of species. Biologist Stuart Primmestimates that during the 20th century, extinction rates increased by 100-1,000 times the

natural background rate. As human population and resource consumption increase overthe next 50-100 years, we are expected to take over more of the earth's surface. During

this century, this may cause the premature extinction of up to a quarter of the earth'scurrent species. This could constitute a new mass depletion and possibly a new mass

extinction.

On our short time scale, such major losses cannot be recouped by formation of newspecies; it took millions of years after each of the earth's past mass extinctions and

depletions for life to recover to the previous level of biodiversity. Genetic engineering

cannot stop this loss of biodiversity because genetic engineers do not create new genes.Rather, they transfer existing genes or gene fragments from one organism to another and

thus rely on natural biodiversity for their raw material.

Importance of the niches of species

Understanding a species' niche is important because it can help us (1) prevent it from

becoming prematurely extinct and (2) assess the environmental changes we make in

terrestrial and aquatic systems. For example, how will the niches of various species bechanged by clearing a forest, plowing up a grassland, filling in a wetland, or dumping

pollutants into a lake or stream?

Native Species: Species that normally live and thrive in a particular ecosystem areknown as native species.

Ubiquitous species : Species that are found almost everywhere are ubiquitous species.

Humans are ubiquitous, some bacteria (E. coli) as well.

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Endemic Species: A species that is native to a particular area and not native elsewhere is

called an endemic species.Monterey pine is endemic to a portion of California coast and

exotic in New Zealand.

Cosmopolitan species: A species with a broad distribution, occurring all over the world

wherever the environment is appropriate, is called cosmopolitan species. The moose isfound both in North America and Europe and is therefore a cosmopolitan species of

northern boreal forests.

Nonnative species, Exotic, or alien species: Species that migrate into an ecosystem or

are deliberately r accidentally introduced into an ecosystem by humans are called

nonnative species, exotic species, or alien species.

Indicator Species: Species that serve as early warnings that a community or an

ecosystem is being damaged are called indicator species.

Birds are excellent biological indicators because they are found almost everywhere andrespond quickly to environmental change.

Keystone Species: The roles of some species in an ecosystem are much more important

than their abundance. They are known as keystone species.In tropical forests, various

species of bees, bats, ants, and hummingbirds play keystone roles by pollinatingflowering plants, dispersing seed or both.

Interaction between speciesThere are three basic categories of interaction among species: competition, symbiosis,

and predationCompetition: in which outcome is negative for both groups.

Symbiosis: which benefits for both species.

Predation-parasitism: in which the outcome benefits one, and is detrimental to the

other.

The competitive exclusion principle

Competition is related to the principle of natural selection, which says that the organismbest adapted to a particular environment will survive and prevail. This can be restated as

the principle of competitive exclusion, which says that species in direct competition

cannot coexist-one of them will inevitably win out over the other

When competition occurs between two species, then the species that fit more will win out

and persist and the other one that fit less will lose or become extinct.

Example: Gray and Red Squirrels in Great Britain.

Coexistence of species : Species that require the same resources can coexist by utilizing

those resources under different environmental conditions. These species are said to havedifferent ecological niches.Example: Flour beetles that live on white flour.

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Symbiosis:Species interact in ways that are beneficial to one or both; this is called

symbiosis (from the Greek words sum and biosis, meaning "life together"). Symbiosis is

very common; most organisms, even humans, participate in some form of symbiotic

relationship. Humans, for example, host a wide range of microorganisms (about ahundred common ones). Some of them are of benefit to us, such as the organisms that

reside in our intestines and help us digest our food. Some of them are just along for the

ride, such as the mites that inhabit our eyelashes. And some of them can be annoying orharmful if they grow out of control, such as the fungus that causes athlete's foot.

Symbiosis affects biological diversity

Symbiotic microorganisms and the intestine of human body~ 10% of a persons body weight is actually the weight of symbiotic microorganisms in

the intestines. The resident bacteria help us in our digestion. We provide habitats that

supply the needs of those microorganisms.

Rein deer and symbiotic bacteria

A reindeer on the northern tundra may appear to be alone but carries with it manycompanions. The reindeer is a ruminant with a four chambered stomach teeming with

microbes.

In order to save species from extinction, we must save its symbionts along with its niche.

Predation: Predation can increase diversity of prey species by reducing the abundance of

the dominant prey. They can contribute to species evenness by keeping the dominant

species from overwhelming others via competitive exclusion.

The principle of competitive exclusion tells us that species compete against one another

for scarce resources, and no two species can occupy exactly the same niche within anecosystem. This might lead to the conclusion that a single species would eventually and

inevitably come to dominate a given ecosystem, to the exclusion of others. Instead,

competition, symbiosis, and predation, along with constant adaptations to changingenvironmental conditions, have led to increasing richness and variety of species. This

variety of life-forms is called biodiversity.

Biological diversity involves the following concepts:

Genetic diversity: the total number of genetic characteristics, sometimes of a

specific species, subspecies, or group of species Genetic diversity refers to the

amount of variability or heterogeneity that is available among the DNA ofindividuals within a population or species.

Habitat diversity: Habitat diversity (or ecosystem diversity) refers to the variety

of habitat types in an ecosystem and the biologic richness of those habitats.

Species diversity: which, in turn has three qualities:

a. Species richness: the total number of species.

b. Species evenness: the relative abundance of species.c. Species dominance: the most abundance species.

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Environmental factors influencing biodiversity

Factors that tend to increase diversity

1. A physically diverse habitat.

2. Moderate amounts of disturbance.

3. A small variation in environmental conditions.4. High diversity at one trophic level, increasing the diversity at another trophic

level.

5. An environment highly modified by life.6. Middle stages of succession.

7. Evolution.

Factors that tend to decrease diversity

1. Environmental stress.

2. Extreme environments.

3. A severe limitation in the supply of exotic species.

4. Extreme amounts of disturbance.5. Recent introduction of exotic species.

6. Geographic isolation.

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L 8 Biodiversity