HL 2 Biology

D.2d: Macroevolution

<<Divergent Evolution and Adaptive Radiation>>

Adaptive radiation: when population invades a new territory, members spread out and (as its exposed to different selection pressures) diversify into several species occupying different ecological niches

e.g. Beetles

  • most diverse
  • ancestral beetles fed on non-angiosperm plants
  • each switch to feeding on angiosperms = rapid speciation and diversification

<<Punctuated Equilibrium and Gradualism and Convergent Evolution>>

Two theories about pace of evolutionary change: 

  • Gradualism: the idea that species slowly change through a series of intermediate forms

    • predicted that for origin of a new species to occur; long sequence of continuous intermediate forms needed
  • Punctuated  equilibrium:  long periods of relative stability in a species are punctuated by periods of rapid evolution
    • events such as geographic isolation/allopatric speciation & opening of new niches within a shared geographic range => rapid speciation


Adaptive Radiation of Beetles (p.314)

1) 22 (beetles) +9 (flies)+ 8 (wasps)+ 7 (butterflies/moths)+ 13 (other insects)= 59% 

2) Looking at the pie chart, it is evident that the beetles take 22% of the described species. When Haldane mentions how God had “an inordinate fondness for beetles” he may have been referring to how the dominating number of beetles out of the other species shows how God may have liked producing the beetles the most.

3) A switch to feeding on angiosperms could lead to such rapid speciation and diversification because mostly all of the plants are angiosperms. As insects use angiosperms as a source of food, the insects may show adaptive radiation resulting to rapid speciation and diversification.

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