Evolution 1
The of Island Finches
by Natural Selection
By
April D. Wells
Hossam Ashour, Instructor
October 5, 2011
The Evolution of Island Finches by Natural Science
The evolution lab is an experiment conducted to study the effect of precipitation on the
evolution of the beak size of finches on two different islands in the Galapagos. These two islands
are Darwins Island and Wallace Island. In this study, the finches on Darwin and Wallace Islands
feed on seeds produced by plants growing on these islands. The seeds produced can be grouped
into three categories based on a seeds hardness. Soft seeds are produced by plants that are
constantly in wet conditions, while intermediate seeds are produced by plants that do best under
moderate precipitation. And last, hard seeds are produced by plants that grow well in drought
conditions.
The lab also expressed a range of beak sizes that is measured as beak depth from 10mm
to 30mm. In the experiment, the size of the finchs beak affected the type of seed that the birds
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are able to eat. For instance, the larger beaks are able to crack open harder seeds. The proportion
of available seeds is determined by the amount of precipitation on the island. Wetter climates
produce harder seeds, and dry climates produce softer ones. If beak size varies among the
population, and seed availability changes over time due to changes in precipitation, birds with
beaks that are best suited for the available seeds should be favored over birds with beaks not
suited. The object is to find out if change in precipitation affects the proportion of seed types on
the island, which should affect the fitness of finches with different size beaks. Overall, wetter
climates should cause finch beaks to get larger over time, and dryer climates should cause finch
beaks to get smaller over time.
Materials Needed:
The material needed to complete the experiment is a computer and access to the
Evolution Lab available on the student website.
Methods or Procedures:
First, log onto http://www.biologylabsonline.com/axia/EvolutionLab/evlab.php and begin
the lab by clicking on the Start Lab button. The first screen that you will see will present an
initial summary (Input Summary) of the default values for each of the parameters that you can
manipulate. You should notice that the default values on both of the islands are the same. Click
on the Change Inputs button at the left of the screen in order to begin an experiment. A view of
the initial beak sizes will now appear. In the Change Input view you can change the biological
and environmental parameters to design an experiment. Then click on the Precipitation button
to view the distribution of seed types on both islands. Change the precipitation on Darwin Island
to 80.0 cm, and leave the precipitation on Wallace Island at 20.0 cm as shown in figure 1 below.
Next, click the Done button to return to the input summary view. Finally, click Run
Experiment.
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Figure 1. Distribution of seed types on Darwin and Wallace
Island due to differences in precipitation.
Data, Discussion and Results:
Parameter
DARWIN
WALLACE
-----------------------------------------------------Initial Beak Size: 12.0 mm
12.0 mm
Heritability:
0.7
0.7
Variance:
1.0
1.0
Clutch Size:
10.0 eggs
10.0 eggs
Precipitation:
80.0 cm
20.0 cm
Population:
200.0 birds
200.0 birds
Island Size:
0.5 km
0.5 km
====================
Experimental Results
====================
Year Dar Beak Dar Pop |Wal Beak Wal Pop
+
199711
.94200|12.04200
199811
.99440|12.
131
60
199911
.89715|12.
19180
200011
.91754|12.32188
200111
.89780|12.35281
200211
.84769|12.48301
200311
.81769|12.57275
200411
.8719|12.75259
200511
.79716|12.68272
200611
.78729|12.7
4279
200711
.8732|12.71342
4
200811
.72681|12.75329
200911
.66738|12.71344
201011
.65642|12.72416
201111
.677
46|12.8387
201211
.67709|13.03318
201311
.637
44|13.22319
201411
.66788|13.21338
201511
.58724|13.3289
201611
.55664|13.37355
201
711
.53697|13.47358
201811
.54821|13.45297
201911
.61736|13.52285
202011
.58730|13.56337
202111
.51772|13.62382
202211
.49684|13.7
4350
202311
.51738|13.66292
202411
.42714|13.6379
202511
.36757|13.56341
202611
.26725|13.7348
202711
.26681|13.67301
202811
.25724|13.65308
202911 18775|13.7322
.
203011
.09710|13.9353
203111
.07711|14.03363
203211
.0171
7|13.9292
203311
.047
40|14.03330
203411
.04764|14.08398
203511
.05767|14.07383
203611 1652|14.04328
.
203711
.09752|14.
15356
203811 12772|14.34407
.
203911 1670|14.45473
.
204011
.08796|14.47357
204111 13764|14.49349
.
204211 147
.
43|14.6329
204311 18675|14.64363
.
204411 1
. 7734|14.89367
204511 18756|14.77380
.
204611 13691|14.88419
.
204711
.09789|15.0421
204811
.06759|15.
15414
204911
.05688|15.05436
205011
.047
43|15.
14437
205111
.0757|15.06454
205210.93783|15.
14403
205310.91796|15.25389
205410.88769|15.39420
205510.91768|15.59432
205610.87733|15.5461
205710.83805|15.57404
205810.79751|15.61466
205910.77750|15.64358
206010.78759|15.85352
5
206110.75815|15.81440
206210.727
40|1
6.02349
206310.72750|1 15328
6.
206410.73735|1 16433
6.
206510.72818|16.3442
206610.69738|1
6.41492
206710.767
48|1
6.48426
206810.75807|16.51477
206910.78809|1
6.63437
207010.71682|16.67440
207110.72755|1
6.81428
207210.63773|1
6.89494
207310.57708|1
6.99475
207410.57805|1.0531
7
207510.47697|1.01526
7
207610.42766|1.05495
7
207710.43751|1.08548
7
207810.38811|1.
715554
207910.39760|1.35478
7
208010.4795|1.44577
7
208110.42723|1.47542
7
208210.31800|1.5519
7
208310.29798|1.58528
7
208410.3733|1.67488
7
208510.27753|1.83443
7
208610.327
49|1.93468
7
208710.38771|1.97546
7
208810.42701|18.02506
208910.39816|18.01515
209010.42692|18.07551
209110.39713|18.09565
209210.43707|18.0947
4
209310.46795|18.
16489
209410.39730|18. 7477
1
209510.43695|18.27490
209610.49811|18.37542
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The table and graph above represents the change in the average beak size in two
populations of finches on different islands after 100 generations. Initial beak sizes are 12mm for
each population. This can certainly prove that this lab allows simulation of how changes in beak
size and other characteristics of finch populations influence evolution of beak size and
population numbers. Therefore, the hypothesis for this experiment was accepted.
Conclusion:
The average beak size changed in over a 100 year period in response to differences in the
proportion of seed types brought about by differences in precipitation between Darwin Island and
Wallace Island. I noticed in the experiment that the average beak size on Wallace Island got
larger, while average beak size on Darwin Island got smaller. These changes were the result of
difference in fitness for different beak sizes brought about by the difference in the food that was
available. On Wallace Island, decreased precipitation led to a greater proportion of hard seeds.
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Finches with larger beaks were able to feed on the harder seeds and were more likely to survive
to reproduce, which ultimately passed the genes to larger beaks to their offspring.
On Darwin Island, increased precipitation led to a greater proportion of soft seeds.
Finches with smaller beaks were able to feed on the softer seeds and were more likely to survive
and reproduce, passing the genes for smaller beaks to their offspring. The resulting differences in
selective pressure for different beak sizes on different islands led to changes in the average beak
size over time.
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References:
Harvard University (2010, March 1). Simple math explains dramatic beak shape variation in
Darwins finches. ScienceDaily. Retrieved October 2, 2011, from
http://www.sciencedaily.com/releases/2010/02/100222182153.htm.
Weizmann Institute of Science (2010, April 6). Darwins finch and the evolution of smell.
ScienceDaily. Retrieved October 4, 2011, from
http://www.sciencedaily.com/releases/2010/04/100406093516.htm.