What is a typical island chain formation?
- Subduction zone results in upwelling of magma, which can create volcanoes and islands overtime.
- 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.
How was the islands of Hawaii formed?
Islands formed by plate moving over a hot spot (magma column).
Explain the atoll formation.
After the loss of volcanic activity, the soil erosion is no longer offset by new land added through volcanic activity - landmass will erode into the surrounding marine environment.
Sediments erode - creates shallow sea shelves for corals to grow.
Coral reefs surrounding the island grows as terrestrial land erodes - all that remains is the coral ring.
When do most of Hawaii’s founder species come from? Why?
Asia.
The jet streams (powerful winds) can transport spores, small seeds, insects and flying animals across the ocean.
What abiotic and biotic factors on Hawaii have contributed to existing species and trait diversity?
- Abiotic factors:
- climatic heterogeneity
- open niches - Biotic factors:
- random genetic drift
- founder effect
- population size
What is random genetic drift and how does it occur?
Populations can change randomly overtime.
If 2 populations of the same species are isolated, genetic drift can eventually result in completely different species.
Sub-populations can also gain new mutations, or lose previous alleles.
What is the founder effect?
New population colonizing an island = a founder population.
- Smaller than source population.
- Contains only a sub-set of the genetics of the original population.
- May also have harmful recessive founder mutations.
What is a founder mutation?
Rare mutation in one of the founding members of a population.
Why does a smaller population lead to faster evolution?
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.
What is environmental heterogeneity? Why is it important?
A diverse range of different climatic conditions.
A greater diversity of different abiotic climatic conditions = greater diversity of niches.
Leads to a greater diversity of species to fill those niches.
What conditions did the founder species experience when they arrived in the Hawaiian Islands? What happened because of this?
- Temperature ranging from 0 to 30C.
- Elevation ranging from 0 to 4000m.
- Rainfall ranging from 200mm to 10m.
4 Large difference between windward and leeward climates (wind).
- Rain shadow effect.
- wet and dry climates.
Diverse climate niches!
What kind of niches are available in island habitat and what are its consequences?
Often fewer species available to fill typical species niches in an environment.
May lead to unique traits in unexpected species.
Hawaii’s habitat resulted in multiple adaptive radiations in founder species
Why are islands vulnerable to invaders/non-native species?
Loss of defenses.
Lack of large predators on islands leads to a loss of defenses compared to mainland counterparts because there is no need to maintain energetically expensive defenses if there are no predators.
How do disturbance cycles contribute to diversity on Hawaii?
Many islands are still volcanically active - cycle of destruction from 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.
- contributes to soil formation —> more plants.
What is the evolution of biomass overtime and why does it occur at those stages?
- After disturbance.
- plants begin to grow, replete with new nutrients.
- lowest biomass. - Intermediate substrate ages.
- plant biomass/growth is greatest. - End of evolutions.
- nutrient supply exhausted, biomass begins to decline.
Explain the disturbance cycle on Hawaii.
- Volcanic activity.
- destructive in the short run, but provides land area and mineral for plant growth in the long run. - Soil eroded to ocean.
- brings minerals to marine environments. - Terrestrial biodiversity decreases, but marine biodiversity increases.
- Circle of life completed.
- growing, eroding, forming an atoll.
