Evolution Lab Write-Up

Topics: Carrying capacity, Population ecology, Evolution Pages: 5 (1452 words) Published: March 9, 2014
Evolution Lab

A.
1.
a.The default value of 20 cm of rainfall is relatively low compared the range that the island may receive, which is anywhere between 0 cm to 100 cm. b.From an average of 20 cm of rainfall I would expect more hard seeds to be produced. 2.

a.The beak size of 12 mm is relatively shallow compared to the available range from 10 mm to 30 mm. b.The shallow beak size of 12 mm is not suited for the hard seeds that are available because of the low rainfall of 20 cm. 3.The beak size went up on the islands as time progressed because only hard seeds were available to the finches. Therefore the average beak size increased over time because the trait of larger more deep beaks were more suitable for survival in the given environment. As more finches with larger beaks more easily reproduced under the given conditions, the larger beak trait would be more likely to be passed down to the next generation. 4.The population reaches a maximum value because of the clutch size and island size. The population of finches is limited to the number of eggs that can be produced (clutch size), and the carrying capacity of the island (island size).

B.
1.
a.

b.Beak size increases more rapidly on Wallace compared to Darwin because the precipitation for Wallace is 5 cm compared to 20 cm for Darwin. Therefore the trait for larger beaks in the Wallace community is favored to reproduce over those with shorter beaks, and over time the heritability of this trait is seen in the offspring of the large beaked Wallaces. c.Wallace shows an initial population dip because the shorter beaked Wallaces had traits that were not suitable for the low precipitation and harder seeds. Therefore the population decreased because the short beaked Wallaces were not able to produce as well. Then once the population of shorter beaked Wallaces decreased there were less of the short beaked traits to make with larger beaked Wallaces, therefore the population of larger beaked Wallaces increase sharply. This is because the heritable trait of large beaks was suitable for the conditions and there were less Wallaces unable to reproduce due to small beaks and significantly more large beaked Wallaces mating with one another. 2.

a.

b.The change in beak size is different on Wallace and Darwin because of the amount of precipitation. Due to the fact that on Darwin the rainfall is considered low at 20 cm the larger beak size is more suitable for reproduction. Therefore on Darwin the beak size gradually increases as time goes on because the larger beaked Darwins have more suitable traits to reproduce. Meanwhile on Wallace the average beak size stays relatively constant with the starting beak size of 12 cm, but may have a slight decrease to an average beak size of 10 cm. The very little change in beak size of Wallace is due to the very high precipitation of 95 cm. Since the initial beak size of 12 cm is considered small it is more favored for softer seeds from increased rainfall, because the rainfall is very high the smaller beak size trait is more likely to be inherited to the next generations of Wallaces. c.The pattern for population growth differs between Wallace and Darwin because of the amount of precipitation that determines which traits are more favorable for survival. On Darwin, the larger beaks are more favorable, therefore the population increase is steady as the average beak size of the Darwins increase. The population of Wallace spikes in the beginning then levels out because the initial beak size is suitable for the higher precipitation; therefore the population does not decrease due to the unsuccessful reproduction from poor traits, but instead increases because the trait is suitable for the environment. The population then levels off because at approximately 900 Wallaces the island has reached its carrying capacity. d.By increase the precipitation to 95 cm on Wallace the...
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