L21 - Hawaii Case Study

Question 1

What is a typical island chain formation?

Answer 1

1. Subduction zone results in upwelling of magma, resulting in volcano formation
   - Where subduction zones exist in the ocean = island formation over time
2. Island formation at diverging regions of tectonic plate formation.
   - The weakness in the crust allows for magma penetration to the surface = volcanic activity and land formation (Galapagos = due to tectonic divergence)

Question 2

How were the Hawaiian islands formed?

Answer 2

• Plate moving over a “hot spot” (magma column)

Question 3

What is atoll formation?

Answer 3

• After the loss of volcanic activity: soil erosion is no longer offset by new land added through volcanic activity
  
  • Landmass will erode into the surrounding marine environment.
• As Sediments erode, shallow sea shelves are created for corals to grow.
• Coral reefs surrounding the island grows as terrestrial land erodes - all that remains is the coral ring.

Question 4

What is Hawaii’s native species composition?

Answer 4

• Lots of flowering plants and insects
• No amphibians or reptiles
• 2 species of mammals
• 5 species of fish

Question 5

What are three different types of dispersal?

Answer 5

• Ocean dispersal
• Avian dispersal (transported by a flying organism)
• Aerial dispersal (transported in air)

Question 6

Define the founder effect and founder species.

Answer 6

• Founder effect: a small group of individuals separated from the population population will have less genetic diversity.
• The resulting new subpopulation may have very different traits from the initial population
• The founder effect contributes to the emergence of new species
• May also have harmful recessive founder mutations due to the lack of genetic diversity
• Founder species: species that emerged from founding populations

Question 7

What is a founder mutation?

Answer 7

Rare mutation in one of the founding members of a population

Question 8

Where do most of Hawaii’s founder species come from? Why?

Answer 8

• 73% are from Asia
• The jet streams (powerful winds) can transport spores, small seeds, insects and flying animals across the ocean.

Question 9

What abiotic and biotic factors on Hawaii have contributed to existing species and trait diversity?

Answer 9

1. Abiotic factors:
   - climatic heterogeneity
   - open niches
2. Biotic factors:
   - random genetic drift
   - founder effect
   - population size

Question 10

What is random genetic drift?

Answer 10

• Small populations can change gradually over time, even when not under selection pressure
• Since nothing in the environment is selecting one allele over another, genetic inheritance is completely random

Question 11

Why does a smaller population lead to faster evolution?

Answer 11

• A small population has few individuals and fewer genes overall in the gene pool.
  
  • Each individual gene counts for more of the overall gene frequency.
• A new mutation in a small gene pool makes a larger contribution to genetic diversity compared to a large population.
• The greater the frequency of a gene in the gene pool, the greater chance it will be passed on in the population.

Question 11

Why does a smaller population lead to faster evolution?

Answer 11

• A small population has few individuals and fewer genes overall in the gene pool.
  
  • Each individual gene counts for more of the overall gene frequency.
• A new mutation in a small gene pool makes a larger contribution to genetic diversity compared to a large population.
• The greater the frequency of a gene in the gene pool, the greater chance it will be passed on in the population.

Question 12

How does environmental heterogeneity lead to greater species diversity?

Answer 12

• Greater diversity of different abiotic climatic conditions = greater diversity of niches
• Often leads to a greater diversity of species suitable to fit those niches
• In island habitats:
  
  • Often fewer species available to fill typical species niches in an environment
  • May lead to unique traits in unexpected species

Question 13

What conditions did the founder species experience when they arrived in the Hawaiian Islands?

Answer 13

• Temperature: 0 - 30 °C
• Elevation: 0 - 4000m
• Rainfall: 200mm -10m
• Rain-shadow effects: wet and dry climates

Question 14

What are typical niches common in many environments?

Answer 14

• Apex predator: often mammals on continents
• Large grazing herbivore: also often mammals on continents
  
  • In Hawaii: ducks = main grazer

Question 15

Why are islands vulnerable to invaders/non-native species?

Answer 15

• Loss of defences: Lack of large predators on islands leads to a loss of defences compared to mainland counterparts
  
  • No need to maintain energetically expensive defences if there are no predators.

Question 16

How do disturbance cycles contribute to diversity on Hawaii?

Answer 16

• Many islands are still volcanically active
• Cycle of destruction: lava flows and regrowth
• After lava flow:
  
  • Complete destruction of existing flora and fauna that can’t move out of the way.
  • Remains of lava flows are mineral rich.
• First colonizers:
  
  • Lichens, ferns, and mosses.
  • Seed plants in cracks of hardened magma.
  • Contributes to soil formation —> more plants.

Question 17

What is the evolution of biomass overtime and why does it occur at those stages?

Answer 17

• After disturbance: lowest biomass
  
  • Plants begin to grow, replete with new nutrients.
• Intermediate substrate ages:
  
  • Plant biomass/growth is greatest.
• End of evolutions:
  
  • Nutrient supply exhausted, biomass begins to decline.