Patterns in Communities & Succession

Species Richness • Species richness: number of species in a

community

• Species evenness: relative abundance of species

• Biodiversity: the variety of life forms in an area

DiversityDiversity • Genetic

diversity is the variety of genetic information

• ecosystem diversity is the variety of different ecosystems in the world

Insects

BacteriaFungi

Plants

Protists Other Animals

54.4%

4.2%

18%

3.4%0.3%

19.7%

Diversity of different groups of organisms

Latitude and habitat size

• Latitude impacts species richness– The closer to the equator the greater the species richness

• Hypothesis: Ice age, climate stability, year round photosynthesis (see textbook for details)

• The increase in species richness as habitat area increases is known as the species- area effect – Habitat loss = decrease in species richness

Factors that impact species richness

• Species interactions: a predator can prevent competitive exclusion among prey species

• Disturbance: flood, fire, clear cutting, plowing, non-native species all disrupt communities– Some communities are

more stable, resistant to disturbance.

Why biodiversity is importantWhy biodiversity is important

• Food – There are 80,000 edible wild plant species

that could be use by humans

• Medical – Over 50% of all medicines contain natural

products

Ecological servicesEcological services Nature does things that would cost trillions of dollars

for humans to do• Provide clean water• Maintain healthy soils & prevent erosion • Control pests & disease-carrying organisms• Buffer against storms • Pollinate crops

Succession• A series of

predictable changes to an ecosystem, in response to natural or human disturbances

Primary succession

• Begins where no soil exists. Change is slow

• Pioneer species such as lichen and moss create soil

• Later, grasses and other annual plants move in along with insects and the animals that eat them.

Secondary succession • Change after a disturbance like fire or farming• Soil still exists

– Shrubs replace grasslands– Trees replace shrubs

• Climax community is the last stage (forest community)

– Until the habitat is disturbed again

Summary review

1. What is the difference between species richness and species evenness?

2. What factors influence biodiversity?

3. Name the ecological services nature provides.

4. What is the difference between primary and secondary succession? Describe the types of communities at each stage of succession.

5. Reflect on the importance of natural disturbance and why human disturbance is different.