Topic 4 Conservation and Biodiversity

4.1 Biodiversity in Ecosystems

Biodiversity

• Coined by Edward Wilson in the 1980s• It is the number and relative abundance of

species in a defined area• It can be measured in terms of:– 1. Species diversity– 2. Habitat diversity– 3. Genetic diversity

1. Species Diversity

• The variety of species per unit area

• This is the number of species present and their relative abundance

• Areas of high species diversity are usually those undisturbed by humans

2. Habitat Diversity

• The range of different habitats in an ecosystem– Rainforest has a high habitat diversity– Desert has a low habitat diversity

3. Genetic Diversity

• The range of genetic material present in a gene pool or population of a species

Plate Tectonics

• First suggested by geologist Alfred Wegener in 1912 • It refers to the movement of parts of the Earth’s

crust• This led to populations of the same species

becoming isolated (over millions of years)• Reproductive isolation under different conditions

provided a mechanism for speciation (in this case allopatric)

• It explains why there are related species in different parts of the world

300 – 200 million years ago

Pangea

200 – 180 million years ago

Lauraisia

Gondwanaland

How does plate movement influence speciation?

• May produce barriers – Mountain ranges– Rift valleys– Oceans

• Movement of land masses apart can isolate species

• Land bridges may form and allow new waves of colonisation

• Movement of plates through new climatic zones creates new habitats

• Subduction of plates sometimes destroys existing habitats

Evolution

Charles Darwin (1809-1882)

EvolutionEvolution is the slow, continual change of organisms over a very long time. All living things on the Earth have developed from the first simple life forms that arrived 3,000,000,000 years ago.

One of the effects of evolution is that species will become better adapted to their environment. If these species don’t adapt they may become extinct due to being unable to deal with any of these factors…

1) Increased competition

2) Changes in the environment

3) New diseases

4) New predators

EvolutionMy key observations:1) All living things produce more offspring

than survive to adulthood2) In spite of this, population sizes remain

roughly constant3) Variation exists among species4) Characteristics can be passed on from

one generation to the next.

These observations led me to the conclusion that species evolve over a along period of time by a mechanism called “Natural Selection”. The main evidence for this is from fossil records.

EvolutionMutations are changes in the structure of the DNA molecule. They can be passed on to daughter cells through cell division. They will result in the wrong proteins being produced.

Mutations can be caused by:

- Ionising radiation (UV, X-rays etc.)

- Radioactive substances

- Certain chemicals

Effects:

- Mostly harmful

- Causes death or abnormality in reproductive cells

- Causes cancer in body cells

- Some CAN be neutral or even beneficial (e.g. the peppered moth)

Natural Selection1) Each species shows variation:

2) There is competition within each species for food, living space, water, mates etc.

4) These survivors will pass on their better genes to their offspring who will also show this beneficial variation.

Yum

3) The “better adapted” members of these species are more likely to survive – “Survival of the Fittest”

Get off my land

Gutted!

A smaller example…Consider the four steps of natural selection in the example of some bacteria that have become resistant to penicillin (an antibiotic):

1) Variation – some strains of bacteria are resistant and some aren’t.

2) Competition – The non-resistant bacteria are killed by the penicillin.

3) Survival of the fittest – the resistant bacteria survive.

4) Passing on of genes – the resistant bacteria reproduce and pass on their adaptations to their offspring.

Bacteria

Penicillin

Evolution is usually divergent (sometimes refered to as adaptive radiation). However, occasionally unrelated species develop similar characteristics due to similar selection pressures. We call this convergent evolution.

Examples of Convergent Evolution

Divergent Evolution• Also called “adaptive radiation”

Ecosystem Stability and Disturbance

• After a disturbance, new habitat is recolonised:– By swimming or floating– By flying (birds, insects, seeds)– By walking or ‘hitch-hiking’ on other animals

Ecosystem Stability and Disturbance

• Jump Dispersal– Long distances travelled by one or few individuals over a very

short timescale

• Diffusion– Slow spread of a population from the edge of a disturbance

into new habitat

• Secular migration– Very slow spread (over thousands or millions of years) that

may involve species undergoing speciation as they move

Disturbance

• 3 factors determine how quickly an ecosystem can recover from a disturbance:– Inertia – resistance to alteration– Resiliance – ability to recover– Diversity – number and proportions of species

Disturbance

• Tropical rainforest– High diversity– High inertia– Low resiliance (takes a long time to recover)

• Grassland– Low diversity– Low inertia– High resiliance

Complex ecosystem therefore has many ways to respond to disturbances. However, soils thin and low in nutrients, and eaily washed away after disturbance

Fairly simple ecosystem. Thick soils with lots of nutrients stored in them. Recover fairly quickly after disturbance

Succession1. Pioneer Species colonise bare rock

2. Growth of these species cause changes in the environment, soil is created

3. New species colonise soil and replace pioneers

4. Growth of root systems stabalise soil

5. Animals begin to colonise

6. A climax community is created

7. New disturbances result in new waves of succession

Primary Succession

Secondary Succession

Note that it is communities that succeed each other, not simply individual speciesEach new community is called a sere. The final stable sere is called the climax community

Questions1. Define species diversity, genetic diversity and habitat

diversity

2. Describe natural selection and artificial selection

3. List 3 different causes of reproductive isolation

4. Describe allopatric speciation and sympatric speciation?

5. Outline the movement of tectonic plates and how it has contributed to species distribution

Questions

1. Give one example of how an ecosystem’s ability to recover from a disturbance depends on resiliance, diversity and inertia

2. In what ways does the complexity of an ecosystem provide stability?

3. Outline the difference between primary and secondary succession