Evolution Lab

10 October 2016

The finches on Darwin and Wallace Islands feed on seeds produced by plants growing on these islands. There are three categories of seeds: soft seeds, produced by plants that do well under wet conditions; seeds that are intermediate in hardness, produced by plants that do best under moderate precipitation; and hard seeds, produced by plants that dominate in drought conditions.

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The lab is based on a model for the evolution of quantitative traits-characteristics of an individual that are controlled by large numbers of genes. These traits are studied by looking at the statistical distribution of the trait in populations and investigating how the distribution changes from one generation to the next. For the finches in Evolution Lab, the depth of the beak is the quantitative trait. I investigated how this trait changes under different biological and environmental conditions.

I manipulated various biological parameters (initial mean beak size, heritability of beak size, variation in beak size, fitness, and clutch size) and one environmental parameter (precipitation) of the system, and observed changes in the distributions of beak size and population numbers over time. Assignment 2: The Influence of Precipitation on Beak Size and Population Number The first experiment is designed to study the influence of beak size on finch population numbers. For finches, deep beaks are strong beaks, ideally suited for cracking hard seeds, and shallow beaks are better suited for cracking soft seeds.

I experimented first with the finches’ adaptation and evolution of their population over 300 years, and changed the Wallace birds beak size to 28mm, and Darwin’s birds stayed at the default of 12mm. I hypothesize a since there are more hard seeds (64%) on the islands than soft seeds (4%). The birds with the smaller beak (Darwin) will not be able to get enough food which may cause some of the birds to die, resulting in a decrease in the smaller beak bird’s population and an increase in the larger beak (Wallace) birds population because of the larger beak size better able to eat hard seeds.

Darwin: Red Wallace: Blue I observed that the Darwin birds (smaller beak) actually grew up to about 25mm, as well as the Darwin bird’s population grew over time. The Wallace bird’s beak stayed the same as well as the population stayed steady but grew. The data actually refutes my hypothesis because I didn’t expect the smaller beak sized birds to grow to adapt to the seeds, I expected them to die off. This next experiment is designed to explore the effect of precipitation on finch beak size and population numbers.

The experiment was to see how a decrease in precipitation on Darwin Island might affect beak size and how a decrease in precipitation might influence population numbers for these finches over time. I hypothesize a decrease in rain will produce more hard seeds because the hard seeds favor drought conditions, while the other seeds will not increase. And the decrease in rain may only slightly cause the finch population to decrease at first, but then will increase and stay steady as the birds have time to adapt to the drought conditions and their beaks will evolve.

I observed that the beak sized for Darwin’s birds supported my hypothesis in that the birds beak sized increased with time. And the population did what I thought too, in that it decreased at first and then increased steadily. I then ran another experiment for 200 and 300 years separately. I observed that the 200 years population and beaks did about the same as the 100 year experiment. Which still confirm my hypothesis. But the 300 years, the bird’s populations and beaks sizes on both islands increased, but that the Darwin birds eventually passed Wallace’s birds in population and beak sized.

I then performed the same experiment for both Wallace Island and Darwin Island simultaneously. I noticed that the 100 and 200 years beak size and population both increased and, but Darwin’s birds were still behind Wallace island birds. But then at the 300 year both beaks and populations were almost the same increase. My hypothesis on how an increase in precipitation on Darwin will influence beak size is that the beak sizes should become smaller and more shallow because the increase in rain will make softer seeds and smaller, shallow beaks are better for soft seeds. And the bird’s population will increase..

I observed just what I hypothesized – the beaks grew smaller and their populations grew huge. When I reran the experiment I observed that Wallace island birds also followed the similar growth for beaks and population as the Darwin birds. When I ran the experiment by increasing precipitation on Wallace Island to 50 cm/year and increasing beak size to 28 mm, for 300 years, I observed the beak sized actually decreased slightly and the population stayed steady and in line with the Darwin birds. Next experiment I decreased beak size on both of the islands to an intermediate value. I decreased rainfall on one island to a value close to zero.

On the other island, I increase rainfall close to the maximum value and ran the experiment for 300 years. I observed different effects on each island. On the Darwin island with a medium beak size and almost no rain had increase in beak size and population. The Wallace birds with a medium beak size and lots of rain had a decrease in beak size and a steady increase in population. Assignment 4: Effect of Island Size My hypothesis for what effect an increase in island size will have on beak size and finch populations is that the beak size will have an increase and population will increase.

I began my experiment by leaving all other parameters at their default values. Then changed the island size of Darwin to the highest it could go to 1km. The beak sized increased as predicted and so did the population increased. When I decreased island size, the beak size grew and the population dropped off first in the beginning but then increased with time. Based on previous experiments if I decrease the clutch size the birds populations will decrease a great deal. Also if I decrease the heritability parameter, and decrease clutch size the populations decrease – which looked like to the point of extinction.

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