BiodiversitySections 18.4. 16.4, and 30.1

• The word “diversity” is used in many contexts.

• What is “genetic diversity” within a species?

• What is meant by “species diversity” within an ecosystem?

• Can there be genetic diversity within an ecosystem?

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Biodiversity is:

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25% 25%25%25%1. The number of species in a region.

2. The types of alleles found in the gene pool.

3. The number of individuals found in an ecosystem.

4. The number of individuals in a population.

Biodiversity

• The total number of species in a region is known as biodiversity.

• Besides the number of species, the numbers within each species is important. If one population grows in size and dominates an ecosystem, that ecosystem can lose biodiversity.

Different areas of the world differ in their relative amounts of biodiversity. Why?

Studying Biodiversity

• The number of named species falls far behind the estimated number of actual species.

• Some groups, such as insects are studied far more than others. Why? Notice this is just

Eukaryotes!

Estimates vary about the number of species yet to be discovered and named, but it’s clear that

we have a long way to go!

How do scientists estimate how many species have not been discovered

yet?

1 2 3

33% 33%33%1. They count known species, then multiply by 10 as a guess.

2. They base the number on sampling methods that determine species richness.

3. They don’t. It’s just too hard.

• Species richness: the number of species in a given area.

• A species area curve plots the number of species encountered as a function of sampling area size.

• Species richness: Often used to describe species within the same trophic level.

• In many ecosystems, most species are present in small numbers of individuals. Only a few species are present in high numbers of individuals.

Species equitability: another measure of evenness of distribution of individuals among the species in

a community.

Both of these “ecosystems” are equally diverse. Which is more equitable?

High species diversity is found in tropical rainforests and coral reefs. Why?

Extinction Risks

• Specialization and resource partitioning increase diversity.

• However, the tradeoff is that organisms become more vulnerable to extinction if the environment drastically changes.

Localized Distribution

• By living in a limited area, a population avoids competition with other populations.

• The risk is that a natural disaster will destroy the limited habitat.

The Devil’s Hole Pupfish lives in a single waterhole

in Nevada.

Overspecialization• Organisms that

have specialized feeding habits reduce competition with other species.

• If the limited food source goes extinct, so does the species feeding on it. Fender’s Blue Butterfly

feeds only on Kinkaid’s Lupine.

Interactions• Isolation reduces

competition and predation.

• If a new predator or competitor is introduced, a formerly isolated species may be hunted or out-competed to extinction.

Many Hawai’ian birds were driven to extinction by introduced predators.

Habitat Loss

• The greatest cause of extinction is habitat loss.

• Organisms with highly specialized habitat needs may avoid competition, but risk extinction if their habitat is threatened. Tropical rain forests are being

logged at an alarming rate, mostly for grazing cattle.

Species are at LEAST risk for extinction if they:

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25% 25%25%25%1. Are highly

specialized for their niche.

2. Have a widespread distribution.

3. Are losing their habitat.

4. Must compete with invasive species.

Humans and Biodiversity• Humans change ecosystems:

deforestation, use of land for farming, pollution, altering rivers, and more. Habitat destruction reduces biodiversity.

• Ecosystems also impact humans: Loss of forests, farmland, clean water, flood protection, and more can directly impact human life.

• Habitat destruction worldwide threatens – or may have destroyed – many species that have not even been named.

• Recent discoveries of new mammal species have found the animals already on the brink of extinction.

Ecosystem services

Indirect, beneficial services• maintaining soil fertility• pollination• seed dispersal• waste decomposition• regulation of local climate• flood control• erosion control• pollution control• pest control• wildlife habitat• repository of genes

Directly used substances• food plants and animals• building materials• fiber and fabric materials• fuel• medicinal plants• oxygen replenishment

“Ecosystem services” are direct and indirect benefits humans receive from the

environment.

Humans have directly benefitted from biodiversity.

Drugs derived from plants and animals.

Andean Potatoes

Forest mushrooms

Tropical fruits

A diverse ecosystem yields a diversity of foods.

Modern agriculture relies on vast monocultures of crop plants; the exact

opposite of diversity. Monocultures are easier to harvest, but more vulnerable to diseases

and pests than mixed crops.

Permaculture and mixed-crop

agriculture supports a diverse soil food web,

which supports the crops. These methods

tend to be more labor-intensive.

• It is estimated that the Native Americans on the east coast used over 200 different plants and several dozen different animals for food. By comparison, how diverse is our food supply?

• What grains do you eat regularly? List as many as you can think of.

• What other plants have you eaten in the past week? List as many as you can think of.

• What animals and animal products (milk, eggs) have you eaten in the pats week ,if any? List as many as you can think of.

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Natural rivers meander, creating a richly diverse wetland ecosystem.

Humans also benefit indirectly from intact, diverse ecosystems.

Channelizing rivers, reducing wetlands, and

cutting down trees along rivers changes the

ecosystem.

Loss of wetland diversity means loss of species. Sediments that would be deposited along the

river system and in islands around the

mouth of the river flows straight out to sea.

New Orleans was once protected by

the many islands in the Mississippi

Delta.

Much of the sediment that built those islands now

runs out to the sea. The islands have

eroded, leaving less protection against

hurricanes.

The term “ecosystem services” refers to:

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33% 33%33%1. Direct and indirect benefits humans receive from the ecosystem.

2. How the ecosystem supplies our needs even when we extract resources at a high rate.

3. When humans do service projects to help restore ecosystems.

E.O. Wilson on Biodiversity

TED Presentation

• According to E.O. Wilson, what is the importance of discovering and naming all the species on Earth?

• Have we named all or nearly all of the species on our planet?

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Recap• Biodiversity refers to the number of

different species in an ecosystem.

• Measures of biodiversity also take into account the relative population sizes of different species.

• Humans have a powerful effect on the biodiversity of many ecosystems. Loss of biodiversity can affect humans in turn.