Biodiversity 6 - Extinction

Question 1

What is extinction

Answer 1

• Process through which a species (orother taxonomic category) ceases to exist
• Disappearance of an evolutionary lineage (population, species or higher taxonomic category) because of the death or genetic modification of every single individual

Question 2

Explain holocene mass extinction

Answer 2

• Spans the last 10,000 years
• Difficult to know the total number of species lost
• Estimated that during the last century 20,000 – 2 million species have gone extinct
• The matter of ongoing species loss is made more complex by the fact that most of the Earth’s species have not been described or evaluated for endangerment
• It is predicted that by 2050, 15 - 37% of all species will be extinct.

Question 3

What causes extinction

Answer 3

1. Habitat loss and fragmentation
2. Exotic/Alien invasive species
3. Pollution
4. Overexploitation
5. Disease

Question 4

Explain Habitat loss causing extinction

Answer 4

• Habitat loss is the single biggest cause of species extinctions
• Occurs when the natural habitat of an area is destroyed by humans

Reasons for habitat loss/destruction include:

1. Agriculture
2. Mining
3. Urbansprawl
4. Logging
5. Trawling

Question 5

Explain fragmentation causing extinction

Answer 5

• Habitat fragmentation occurs when a habitat is divided up into smaller parts
• The fragments become isolated from each other and can support fewer species
• As the habitat becomes fragmented, the edge of the habitat increases – this is known as the edge effect

Question 6

Explain edges fully

Answer 6

• Edges are different to the interior of the fragment in climate, soil, environment and species composition
• The edge does not count as effective habitat for species requiring the conditions of the interior

Question 7

Explain polution causing extinction

Answer 7

• Any environmental change that adversely affects living things

Types of pollution that threaten biodiversity:

1. Acid deposition (acid rain)
2. Eutrophication (over-enrichment) of water bodies
3. Ozone depletion
4. Chemicals
5. Global warming

Question 8

Explain green crab

Answer 8

• Native to coastal Europe and North Africa
• Found in South Africa in 1983 (Table Bay)
• One of the most successful marine invasive species
• Highly adaptable, reproduces quickly
• Predator

Question 9

Explain island biogeography

Answer 9

• Islands closer to the mainland have a higher diversity of species than islands further away
• It is easier for individuals to colonize an island close to the mainland (it is easier to get to)
• Larger islands have a higher diversity of species than smaller islands
• A larger island has more resources and can therefore support more populations than a smaller island
• Balance between immigration and extinction will determine species richness

Question 10

Explain island biogeography and conservation

Answer 10

• An area of conserved land can be thought of as an “island” surrounded by a “sea” of uninhabitable land (farms, cities)
• The larger an area of conserved land, and the closer it is to another large area of conserved land, the more species can be preserved

Question 11

Explain exotic species

Answer 11

• Exotic (alien/invasive) species are non-native species that move, or are moved, into an ecosystem
• Second major cause of extinction
• Sometimes have a competitive edge over native species and may become invasive

Question 12

What are the avenues of human introduction

Answer 12

• Colonization
• Horticulture and
  agriculture
• Accidental transport

Question 13

Explain over exploitation

Answer 13

• The use of a natural resource to the extent that it is not sustainable
• The more rare a species, the more it is sought after and the more valuable it becomes
• The market for exotic pets, decorative plants and animal products makes commercial hunting a lucrative business