Ecology through time

Question 1

The creation of the Atlantic

Answer 1

• Isolation: the biota of the Americas and Africa become isolated, creation of new mountain ranges split continents
• New shallow seas - hotspot for diversification (centres of biodiversity)
• New ocean seaways and terrestrial land bridges: Biotic exchange
• Subduction creates oceanic islands; dispersal and isolated evolution

Question 2

Tectonic and mass extinctions

Answer 2

• Mass extinction events linked to multiple drivers - bolide impacts
• But all 5 mass extinctions linked to marine regression/transgression events

Question 3

Biotic interchange

Answer 3

Biotic interchange: large-scale exchange of species from two distinct and isolated biota
- Barriers to species dispersal are reduced :
- Usually bc two continents come together
- Or a seaway opens to connect previously separated oceans

Question 4

Great American Biotic Interchange (GABI)

Answer 4

• GABI triggered by the formation of a land bridge between N and S America
  -The combination or dispersal, species interactions, extinction and revelation had dramatic effects on biodiversity of two continents
• Focus on mammals - the best fossil record
• Mammals evolved 220 million year ago
• Pangaea - S America becomes isolated 140-75 million years ago and mammal families evolved in isolation

Question 5

GABI

Answer 5

• Isolation not continuous, later land bridges and long distance dispersal events added primates
• Added diversity upon arrival and all the groups diversified
• By 3.5 million years ago S America had developed unique mammal biota - a small pool of species but diversification and adaptive radiation

Question 6

Adaptive Radiation

Answer 6

• It is a rapid increase in the number of species with a common ancestor, characterised by great ecological and morphological diversity

Question 7

Why is there such an unbalanced interchange?

Answer 7

1. Nothern species have a high greater dispersal ability - NA contained more savanna specialists so greater migration over the land bridge (filter effects)
2. Nothern species had higher survival and speciation rates - a higher proportion of SA species that arrived in NA subsequently went extinct

Question 8

Biodiversity on islands

Answer 8

• Tectonics create new landmass + control isolation of existing landmasses
• Dispersal, speciation and extinction
• Species richness tends to increase with increasing area
• Increase in species slows with increasing island size

Question 9

Species-isolation relationship

Answer 9

• Islands far away from continents have fewer species
• Species richness declines with isolation
• Most islands have 0 species and they are added by dispersal and colonisation
• Once arrived species can only be lost by local extinction

Question 10

Equilibrium Theory of Island Biogeography

Answer 10

• McArthur and Wilson 1967
• Species richness on the island will result from immigration on the island and extinction of species on the island
  Extinction rate = Extinction risk * number of species
• Extinction rate increases as SR increase in the island bc number of species at risk increases
• Also increasing extinction risk bc fewer resources per species

Question 11

Equilibrium Theory of Island Biogeography

Answer 11

• Number of new species arriving on the island is
  matched by the number of species going extinct
• Equilibrium species richness is lower
• Dispersal is more unlike to more isolated areas
• Immigration rate is lower of new species

Question 12

Endemism: Global scale patterns

Answer 12

• Endemic species: a species restricted to a particular area like an area
• Islands have fewer species than the continents but have far more endemic species
• Remote oceanic islands are hotspots of endemism

Question 13

Why do islands have more endemics?

Answer 13

• Few founding events
• Low gene flow from the continents
• New unexploited niches
• Larger islands = lower extinction
• Greater resources
• Larger population sizes
• Greater range of niches
• Larger islands = higher probability of vicariance

Question 14

How and why are islands dynamic?

Answer 14

1. Uplift and weathering e.g atoll life cycle
2. Successional processes e.g. the development of soil + change in topography
3. Long-term climate changes (and sea level)

Question 15

How isolated are oceanic islands?

Answer 15

• Modern Hawaiian islands contain many species that initially colonised on now submerged islands
• Exposed seamounts exposed during low sea levels act as stepping stones for dispersal

Question 16

Volcanic archipelagos - island hopping?

Answer 16

• Species can disperse in both directions
• Each island provides opportunity for divergence
• Colonisatiion along the chain
• Islands in a chan influence each other