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Title: Galapagos Finch Report - Spring 2009

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Assignment Goals
Source Material
Student Instructions
Guiding Questions
Writing Prompt
Calibrations, Average Word Count, and Answer Keys

Assignment Goals

Your goal is to explain what caused the sudden drop in the finch population in 1977

Your goal is to explain what caused the sudden drop in the finch population in 1977. Why did so many finches die? And why did some finches survive? Was it random chance or were there other factors involved? Was there a change in any average characteristics of the population, that is, did evolution occur in this population between 1973 and 1978?

You will explain this in a scientific report that will be reviewed by your peers, giving you useful feedback. You will also gain experience in evaluating scientific work by reviewing three calibration papers and then reviewing three papers submitted by your peers and finally by re-assessing your own paper.

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Source Material

The main source material is the Galapagos Finches software (by bGuile software, http://www

The main source material is the Galapagos Finches software (by bGuile software, http://www.iqwst.northwestern.edu/finchesdownload.html).

You are required to use AT LEAST ONE OUTSIDE SOURCE, secondary literature is especially recommended for relevant background information. You could also use primary literature as support in the discussion, but remember that the emphasis in this paper should be on your judgments based on the data available to you at this point, not what someone else concluded based on 20 or 30 years of data.

Remember with any and all outside sources, be sure to cite them properly and completely both within your text and in a "References Cited" section at the end of your paper. Consult your TA or our Webpage (www.biol.sc.edu/~biol102) for help with proper citation formats.

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Source Material Resources: none

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Student Instructions

Explain the changes in the finch population in a scientific report with Introduction (including background and explicit hypothe

Explain the changes in the finch population in a scientific report with Introduction (including background and explicit hypotheses), Methods, Results (including at least 2 graphs), and Discussion. Include in-text citations and a bibliography for your outside sources and include acknowledgments if you received significant help from someone (TA, lab partner, roommate, professor, etc.)

Guidelines for writing this type of paper are available from your TA, your lab book, and the writing guide by Pechenik.

Upload your text and graphs following instructions from your TA and the lab book. Be sure you PREVIEW your CPR paper before the text entry deadline to make sure your text, formatting, and graphs all show.

When the text entry time ends, review three calibration papers; written comments will not be needed on these. Remember, one calibration will match what we did in lab - just give the same answers and ratings that we did in lab when you see that paper.

Then review three papers by peers. Your reviews here will require written feedback (comments or questions)..

Your TA will judge the quality of your reviews based on your written feedback.

Then review your own paper.

What makes a good review?

Your job as a reviewer will be to provide useful feedback to the writer using the criteria given below for useful reviews. Remember, when in doubt, put yourself in the writer's position - how helpful would you find this feedback?

Useful feedback is:

specific and concrete;

focuses on the quality of the author's argument (are conclusions logical and well supported by the evidence/data?) as well as on the mechanics of the writing, e.g. organization, spelling, and grammar;

identifies assumptions or consequences of author's ideas which the author has not explicitly discussed;

and could reasonably result in meaningful revisions or new content being added to the paper.

Please try to phrase as many of your comments as questions as possible - this often helps you be more specific in your reviews and therefore give better feedback.

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Guiding Questions

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Writing Prompt

Write the paper in the format of a typical scientific paper: Introduction, Methods (very brief with mention of data in the Gala

Write the paper in the format of a typical scientific paper: Introduction, Methods (very brief with mention of data in the Galapagos Finch program), Results referring to at least two graphs, and Discussion. ***

Remember to use in-text citations and references for any ideas or information from outside sources. Acknowledge anyone who gives you significant help, including on your graphs.

*** Papers must be a minimum of 500 words to be uploaded. Papers which meet the criteria for this assignment will easily be longer than that, typically 1000-2000 words.

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Calibrations and Answer Keys

Average Calibration Word Count = 1,534

High Quality Calibration
Introduction

Introduction

Between 1973 and 1978, a team of researchers under Peter and Rosemary Grant studied the evolution of Galapagos finches on the island of Daphne Major. The Geospiza fortis are birds that mate in the wet seasons and feed on seeds, small insects and spiders. Specifically, they feed on Portulaca, Chamae, Cactus, and Tribulus seeds, all which vary in size and rigidity. The finches are relatively small birds weighing an average of 6.2 to 19.1 grams and are brown in color. The main predators of the finch include the Galapagos owls and hawks.

The climate on the Galapagos Island of Daphne Major has dry and wet seasons. In the dry seasons of 1976 and 1977, there was a severe drought with rainfall totaling zero centimeters. While rainfall during wet seasons usually averages in the hundreds of centimeters, the wet season of 1977 experienced only 25 centimeters of rainfall. This shortage of rainfall severely affected the vegetation, thus altering the feeding for many animals on the island.

The drought had an even larger effect on the population of finches as a whole, with numbers dropping by over 80% by the end of 1977. There is much controversy as to cause of this severe drop in population. Over the years, researchers have questioned why so many finches died and whether evolution played a part in their survival.

Did Evolution Occur?

In considering whether evolution occurred, one must look at what traits in the population changed. Although leg length and wing length remained consistent, weight and beak length varied significantly. To deviate from the normal range of variation, a statistically significant variation must exist. During the drought the weight of adult males and females dropped significantly, but this only relates to the depletion of food source and is not an example of evolution. However, an examination of the data shows a significant and continuous increase in average beak size after the period of the drought. This indicates this beak length was a necessity for survival and evidence for evolution.

Possible Causes of Mortality

The following table indicates the hypotheses eliminated from consideration and why.

Hypothesis

Evidence to Reject

Birds died of dehydration

There is no mention of a link between mortality and dehydration in the field notes. Birds died mostly at night, not during the heat of the day.

Human presence altered bird behavior/reproduction

The birds continued to eat, reproduce and carry out normal life functions while cohabitating with the human observers.

Volcanic explosion killed birds

In 1973, the volcano erupts with no significant drop in population. In 1978, a major volcanic eruption occurred as well as a 4.5 earthquake. This data supports that the volcanic eruptions on the island in 1977 did not definitively correlate with a drop in finch population.

http://users.bendnet.com/bjensen/volcano/eastpacific/galapagos-fernandina.html

Birds migrated to another island.

All birds were accounted for in the study by recorded death or survival. The flight capabilities would also limit the ability to migrate to another island.

There was not an increase in mortality, just a reduction in birth rate.

Two adult male finches and one adult female finch died in 1973. Fifteen adults died in 1976. This supports that there was a significant increase in mortality.

The Galapagos Owl ate the finches because of the reduction in plant life resulting in limited foliage cover.

There is no evidence to support that the owl's food source decreased. Owls also have the capability to fly to other islands for food source.

Aside from those eliminated, several plausible hypotheses still exist. One possible explanation for the population drop refers to the drought, but specifically indicates that rain is a necessary factor to induce mating. Michaela Hau of Princeton University has proposed that rain affects how small birds grow gonads. Furthermore, the software data set support an absence of fledglings during the period of the drought. Although this evidence supports the hypothesis that rain is a necessary factor to induce mating, it is imperative to note the field observations during the wet season of 1978. The observer states, "I am surprised that it is this late in the season, yet I do not see any of the males building display nests. I suspect that there just won't be any mating this season." Furthermore, for those finches that did mate, the process occurred later in the season. Although there was no rainfall during the dry season of 1977, the wet season of 1978 received 175 centimeters. This rainfall should have been a sufficient mating cue based on the above hypothesis. If rain as a mating cue is to serve as a significant hypothesis, mating should have resumed immediately following the drought.

A second hypothesis also serves as a plausible explanation. Females could be under greater stress than males due to their investment in reproduction. This indicates that a shortage in food would impact their survival. The software data supports this hypothesis, since more adult males survived than adult females. However, additional evidence shows that males have significantly larger beaks than females. This factor is significant when considering the correlation between beak size and available seed size discussed earlier. Adult males with larger beaks would have easier access to the scarce supply of food. This would put females at a disadvantage, and explain their higher mortality. After addressing these two hypotheses, the third and most plausible hypothesis that explains the finches' mortality is that the drought depleted food sources, causing beak size to become a significant factor to survival.

Examination of Theoretical Processes

According to this hypothesis, natural selection occurred in the finch population. There are several requirements for natural selection. First, there must be a trait that varies in a population. The data supports several instances of directional selection. Although leg size and wing length did vary over time but not significantly, there was a significant increase in beak length. The average beak length for adult surviving males increased from 10.81 mm in the wet season of 1973 to 12.59 mm in the dry season of 1978. Female adult beak length also increased over this period of time from an average of 10 mm to 11.11 mm. Although only a gradual change, the evidence of a 1 mm increase supports that a significant shift occurred.

The second requirement for natural selection requires that these varied traits must be heritable. The data collected between 1973 and 1978 do not test heritability, but it is reasonable to assume that a trait like beak length could be heritable and test that in future research. Evidence collected by Peter and Rosemary Grant during their 30 year study of the Galapagos finches supports this condition. A participant in this study, Peter Boag, observed that the variation in beak size was heritable by measuring the beaks of parents and offspring.

Struggle for existence is the third requirement for natural selection. During the drought, the environment of Daphne Major could only support a limited number of finches due to the depletion of food sources. Therefore, there must have been a variable trait that allowed some finches to survive over others. The competition between finches would have resulted in some winning out over others and therefore providing an advantage for those birds that survived.

Finally, for natural selection to occur, a version of the trait has to provide benefit for survival and reproduction. Peter and Rosemary Grant's study also supports this principle. They observed that the size of the ground finches' beak was correlated with the size and rigidity of seeds it ate. During the drought there were far fewer seeds for the finches to eat. After the already scarce supply of smaller softer seeds were consumed; the finches had to eat the larger harder seeds that were left. Those finches with larger beaks had an advantage over those with smaller beaks since they could better open the tougher seeds. Thus, the variable and heritable trait of a larger beak aided in their survival.

Other theoretical processes such as mutation, genetic drift, and gene flow should be considered, but are not as plausible as natural selection. For mutation to occur, an error in DNA replication would result in a new sequence and a change in the hereditary material of the finches. In this case, the population was too small and the period of time was too short to determine whether the change was due to mutation. For genetic drift to occur, the change in beak size would have been the result of random chance. However, there was a consistent increase in beak length for all finches over the observed period of time. The significance of this evidence supports that genetic drift is an insufficient explanation. If gene flow had occurred, the individuals from one population would have had to breed with a new population. In this case, there was only one population of finches on the island. No observational evidence exists to support that the birds mated with any different population.

Methods and Materials

The majority of the evidence comes from the software dataset on the Galapagos Finches from the wet season of 1973 to the wet season of 1978. Detailed properties and distribution are also given for each type of seed the finches eat. The data set provides field notes for each of the 90 tagged and numbered finches. The data set also allows comparisons to be made between populations and physical traits.

While this is a comprehensive look at the finches between 1973 and 1978, there are many limitations. First, there is a lack of evidence for the years 1974 and 1975. The limited scope of field notes also hinders in reaching a full picture. Birth rates are not included, which could be valuable information in reaching a hypothesis. These and other details are not explained or left out completely, leaving many holes in the data. These discrepancies are typical in any research.

Other evidence used includes primary and secondary literature as well as websites. Primary literature sometimes neglects to consider all alternatives, while secondary literature can sometimes be biased.

Results and Discussion

From the previous discussion, the most plausible explanation for the increase in mortality during and after the drought can be directly attributed to beak length and a dependence on seed availability and size. The drought significantly reduced seed production. The remaining seeds were hard, thorny, and more difficult to open. Since larger beaks are more effective than small beaks for consuming these tougher seeds, these birds enjoyed an evolutionary advantage over smaller beaked birds. Therefore, smaller beaked birds had a lower rate of survival.

a

As the graph above indicates, there were no Chamae seeds after the drought in the wet season of 1977. The Chamae seeds are soft, covered in a molasses like coating, and are the smallest in abundance. In addition, the graph shows no soft Portulaca seeds after the drought. By the dry season of 1977, the only seeds left were cactus and Tribulus seeds, both of which are tougher and larger. Thus, all finches, even birds that had originally preferred the softer seeds like Chamae and Portulaca had no choice but to consume the tougher Tribulus and cactus seeds. This observation is supported by the field notes, which show that many birds with smaller beaks had difficulty opening the larger, tougher seeds.

b

The graph above illustrates the average beak length over time for surviving adult birds. This data supports a directional selection favoring large beak size. As shown, by 1978, the average beak length of adult birds had increased by over one millimeter for both males and females.

c

This last graph looks at beak length for the birds that did not survive. It is important to look at both the surviving and dead birds to see how beak length increased over time. For beak length to be an evolutionary trait, it must be evident in the entire population as a whole. The fact that both of the graphs indicate a significant increase in beak length supports that this was a variable trait that evolved.

Conclusion

Looking at the data set from 1973 to 1978, it is clear that beak length evolved in adult female and male finches as a result of the drought. Since larger beaks served as an advantage in consuming the tougher larger seeds that were available, a directional selection occurred favoring this trait.

The absence of gene flow in regard to the ground finch on the island of Daphne Major directly contributes to the capability of natural selection. For instance, if an island around Daphne Major had a population of finches and did not suffer a drought, their evolution could be quite different. Since allele frequencies change over time, these two separate populations have the potential to become two distinct species. Finches on the island affected by the drought would evolve differently than those on an island not affected. The beak length for finches on the latter island, for example, would probably not have increased. This separation would serve as a significant step in the evolutionary process.

Since evolution is directly linked to environmental changes, there are many possibilities for future development of the Galapagos finches. If another drought were to occur, beak length might continue to increase. In the future, the beak length will remain at its current longer length unless a new mutation, genetic drift, or different reason for natural selection affects the course of evolution for the Geospiza fortis.

Resources

Galapagos Finch Data Set

http://www.eeb.princeton.edu/FACULTY/Hau/Hau-Abstracts.pdf

http://users.bendnet.com/bjensen/volcano/eastpacific/galapagos-fernandina.html




1. Criteria 1: Writer presents relevant and testable hypotheses with a clear rationale. Please write at least one comment/question in the "explanation" box addressing this issue.

Yes
No

Answer: Yes
Feedback : The rationale is very explicit and sophisticated. The author not only makes the link between beak size and the lack of small or soft seeds, but also considers a confounding factor of bird gender. The writer considers a wide variety of hypotheses and eliminates all but one (beak size) using data and evidence. The use of the table was an especially effective and concise presentation. The issue of a possible correlation between beak size and gender should be more thoroughly addressed or experiments to distinguish between these hypotheses shoud be proposed.
2. Criteria 2: Writer provides sufficient background to understand the investigation and put it in context. Please write at least one comment/question in the "explanation" box addressing this issue.

Yes
No

Answer: Yes
Feedback : The background is sufficient, but the information about volcanoes is vague. Outside sources are used in an effective way, but in-text citations and the reference page are not correct.
3. Criteria 3: Relevant data for every hypothesis are presented in a logical format and clearly tied back to hypotheses being tested. Please write at least one comment/question in the "explanation" box addressing this issue.

Yes
No

Answer: Yes
Feedback : The data are mostly relevant, though the discussion of weight as a possible factor seems unfinished. Weight is trait that is influenced more by the environment than by genetics (whether or not offspring are skinny is more determined by the current food supply than by whether or not the parents were skinny). But what were the changes in wieght? You need to discuss more data or observations about what size seeds birds with different beaks can actually eat and whether different size birds use different size seeds.
4. Criteria 4: The writer emphasizes logic and evidence in making their conclusion. Writer makes clear how the data support or refute alternate hypotheses. Please write at least one comment/question in the "explanation" box addressing this issue.

Yes
No

Answer: Yes
Feedback : The conclusion is logical, though it could be more developed. Graph 2 shows a slight increase in beak size before the drought but that is never discussed or explained. Also, assuming lack of food causes the shift in average beak size in the population, the author should discuss what average beak size would be expected once the drought ends and the seed production returns to normal if their hypothesis is right vs. if it's wrong.
5. Criteria 5: The writer presents a persuasive discussion of why the data support one hypothesis over the alternatives for each question. If more than one hypothesis is supported by the current data, the writer describes data or experiments needed to test the hypotheses. Please write at least one comment/question in the "explanation" box addressing this issue.

Yes
No

Answer: Yes
Feedback : The use of the field notes to determine that the timing of the rain in 1978 eliminates the "small gonad" hypothesis is an excellent example of determining what data are needed to distinguish between hypotheses. The author does not actually elminate the hypothesis that females died out in greater numbers because they experience greater physiological stress during reproduction however. You need to show data that would distinguish between hypotheses that gender or beak size are favored. If no such data are available you need to describe what data need to be collected to distinguish between those hypotheses.
6. Criteria 6: The writer explicitly states whether or not he/she thinks evolution occurred. If evolution is concluded to have occurred, the writer explains which evolutionary mechanism (gene flow, genetic drift, mutation, natural selection) was the most likely cause and why. Please write at least one comment/question in the "explanation" box addressing this issue.

Yes
No

Answer: Yes
Feedback : The author clearly states that the trait of beak size evolved in the population over time. The author clearly outlines how the change in beak length over time meets all of the requirements for natural selection to occur. The author provides evidence that the change in beak lenght was not due to gene flow. There is evidence that it was not due to a mutation, though the author does not discuss that well at all. Genetic drift could have produced this change coincidentally with the drought, though the complete absence of small seeds for small beaked birds makes this an unlikely and unpersuasive explanation. The author needs to discuss what data there are (or what data should be collected) to rule out genetic drift and mutation.
7. Criteria 7: A minimum of two graphs are presented (and visible!) which provide relevant data that is connected to hypotheses and conclusions. Please write at least one comment/question in the "explanation" box addressing the quality of the graphs.

Yes
No

Answer: Yes
Feedback : There are graphs which connect and clarify all the main hypotheses with data.
8. Criteria 8: The graphs are clear, easy to understand, and properly labeled. The type of graph and presentation facilitates the readers' understanding.

Yes
No

Answer: Yes
Feedback : The graphs are clear and do help the reader understand. The types of graphs are appropriate though there could be some more effective ways to present some of the data. Graph 1 of Seed Distribution especially might be more effective with a different presentation or even an additional graph to present the nuances of the change in distribution. Graph 3 should not start and end with beak lengths of 0mm.
9. Criteria 9: A clear train of thought is presented and developed throughout the paper (the paper is logical and well organized).

Yes
No

Answer: Yes
Feedback : The paper is logical, though the discussion of natural selection and evolution might be better discussed or at least returned to after the data are presented. It is more traditional to have results separate from, and preceding, the discussion. Having some of the discussion with the background, and before the reader sees the data, is confusing. One or two sentences of overview about the final conclusions would be okay though.
10. Criteria 10: Sentence structure and word usage are correct and facilitate the reader's understanding. The pasages flow nicely. (There are three or fewer errors of structure or word usage.)

Yes
No

Answer: Yes
Feedback : The writer has a nice command of the language, but should not use the word "significant" when describing changes in the data, especially after pointing out that that word implies that statistical tests have been performed. There are a few odd word choices.
11. Criteria 11: Grammar and spelling are correct. (There are three or fewer errors or typos)

Yes
No

Answer: Yes
Feedback : none
12. Criteria 12: Outside source is correctly cited and referenced. At least one outside source is used, preferably for background information.

Yes
No

Answer: No
Feedback : In-text citations should name an author and year, not a URL. The reference list is not complete or in proper bibliographic format! Both the Hau paper and the volcano information should include the full citation (journal, year, pages, title, etc - not just the link to the online version of the paper) and the "30 year study by the Grants" is referred to and the author named, but the reference is not provided at the end. These problems would cause a significant penalty in the final paper. (If the authors weren't named or there were no other in-text citations, these errors would cause the final paper TO FAIL for plagiarism problems.) Reviewers should not exact a penalty for these problems but should identify the problems and give MAJOR warnings!
13. Add at least one additional comments/questions that you think will help the writer. (also - Check YES in the box to match the calibration or other reviewers.)

Yes
No

Answer: Yes
Feedback : These can be on any topic or issue you feel has not been addressed above.
14. How would you rate this text?
10 Highest
9
8
7
6
5
4
3
2
1 Lowest
Rating: 9
Feedback : A very strong paper. Outstanding in some aspects (especially the listing and use of reasoning to reject a variety of alternate hypotheses), but the paper needs more careful discussion of some topics that are raised and better organization. Also some word choices and data presentation could be improved.

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Mid Quality Calibration
Introduction

Introduction

The island of Daphne Major is home to many species including the small brown Galapagos Finch. These finches have been a dominant characteristic of Daphne Major for many years. During the dry season of 1977 there was a crisis within the finch population where more than three-fourths of the finches died. To better understand this crisis we must understand the ecosystem in which the inhabitants of Daphne Major lived. It is also necessary to understand why some finches were able to survive while others were not.

Daphne Major has a diverse ecosystem, an environment that includes not only the finch, but several types of organisms. Daphne Major is home to other animals such as rats, lizards, spiders, other insects and owls as well as various plants. These plants include cactus, chamae, portulaca and tribulus. All of these organisms are in some way interconnected through the food chain. The food chain expresses how the organisms interact with one another and are able to survive. The plants begin the food chain by producing seeds by water and sunlight. The seeds produced serve as food for the finches that also eat insects and spiders. The plant in general serves as food for the various insects which serve as food for the rats, lizards, and spiders. Ending the food chain are the owls, which have the most diverse menu consisting of rats, lizards and finches. The owls also have the ability to fly between the nearby islands in search of more food.

There are many predator-prey relationships on the island of Daphne Major; the most significant is between the owls and the finches. The owl has been spotted preying on and eating the finches, and suffered a population decrease in 1977 as well as the finches. All of the organisms on this island depend on one another for survival. If one were to dissipate then the others may as well; the other organisms would be forced to become accustomed to what was left of their environment. The owl is the only organism that would have the chance to survive if other organisms disappeared, it can fly between islands in search of more food.

The survival of the finches depends on adequate amounts of rainfall; without rainfall the plants will be unable to prosper and produce seeds leaving the finches with little to no food. Throughout the years 1976 to 1978 the amount of rainfall was recorded for each wet and dry season. In 1976 the average amount of rainfall for the wet season was 162cm; for the dry season there was 0cm of rainfall, which seemed very odd. In 1977 the weather experienced a dramatic change as well as the finch population. Daphne Major only received 25cm of rainfall during the wet season and 0cm again during the dry season. This drastic decrease in rainfall caused three-fourths of the finch population to die. Because there was little to no rainfall the plants could not produce seeds for the finches to eat, therefore resulting in the deaths of many finches.

Methods and Materials

Below Graph 1 illustrates the dramatic decrease in rainfall from the dry season of 1976 to the dry season of 1977. Also illustrated is 1978, when the weather returned to normal with 175cm during the wet season and 12cm during the dry season. The finch population also seemed to be experiencing some growth. Because we can see that the finch population decreased at the same time as the rainfall, this proves that the weather, or lack there of, played an important role in the deaths of many plants causing the deaths of three-fourths of the finch population.

Based on the above information, I concluded the hypothesis that many finches died from the limited resources due to lack of rainfall. During 1977 the finch population suffered a drastic decrease due to the lack of food. Because of this lack of food, it is known that the plants were not growing or producing seeds, all because of the change in weather. The finch population began experiencing a decline in the dry season of 1976; there were only 38 finches reported on the island. In 1977 this number decreased even more with 23 in the wet season and 10 in the dry season. The usual finch population consists of about 45 finches on average. The chart below shows the difference in the finch population from 1976 to 1978.

Along with the finch population, the plant population suffered during 1977. The four types of plants, cactus, chamae, portulaca and tribulus, produced a significantly less amount of seeds in 1977 than any other year. This decrease in production was caused by lack of rainfall; plants need adequate amounts of water and sunlight to survive. These four plants produce seeds, which are the main food source of the finches. Therefore, Table 1 describing the number of finches from 1976 to 1978 correlates to Graph 2 describing and comparing the production of seeds from 1976 to 1978. As shown below in Graph 2 the seed production for both seasons of 1977 was significantly less than any other year producing only 120 cactus seeds, 5 chamae seeds, 20 portualca seeds and 320 tribulus seeds the whole year. These are all substantially small amounts of seeds produced compared to previous years recorded, and limited amounts of food for the large finch population. The finches were forced to gather as much food as they could to last them both seasons. The high demand for food caused many finches to starve which lead to many deaths within the finch population. In 1978 the amount of rainfall seemed to be returning to normal which resulted in an increase in the finch population. Because there was adequate water, the plants were able to produce the much-needed seeds for the finches to eat. The above information is also supported in Graph 1.

The above information most accurately explains the decrease in the finch population, but alternative hypotheses have surfaced that better explain how some of the finches survived. There are many physical differences within the finch population that express how natural selection could have been involved in the drastic decrease of the finch population. Some weigh more than others, some have longer legs, some have larger and stronger beaks, and some have a wide wingspan. All of these characteristics could have had a large effect on the survival of the finch population. For example, the longer the legs of the finch the faster he or she could have searched for food. The finches that survived with these characteristics most likely passed them along to the next generation showing how natural selection plays an important role in the success or failure of a population.

Another way the seeds played an important role in the decrease of the finch population was by their variety in size and rigidity. The differences between the seeds are illustrated below in Table 2. The larger and stronger beaks could have helped those finches that were having trouble opening the hard shells of the cactus and mainly the tribulus seeds to survive the change in weather. The cactus seeds were mildly hard to open and eat and were average in size, but the tribulus seeds were extremely hard to open and the largest of all seeds. The portulaca and chamae seeds were soft and rather small, easiest for the finches to eat. Therefore the finches that were smaller or did not have large beaks were at a disadvantage if they only searched for the larger seeds. One of the reasons many of these finches were left with small amounts of food is because they had not yet figured out how to properly and quickly open the shell surrounding the seed. Trying to figure out the best way to open the shell could take days, and the finches would waste valuable time if their attempts to open the seeds were constantly unsuccessful. Another reason many finches died is because they would give up on the hard seeds and would only search for soft seeds, which were not abundant in 1977. Together the portulaca and chamae produced very little in 1977, which is illustrated in Graph 2. The portulaca produced 20 seeds in the wet season and 0 in the dry season while the chamae produced 5 seeds during the wet season and 0 in the dry season as well. Therefore the food supply was extremely limited and the finches that only searched for the scarce soft seeds would most likely starve and possibly die.

Results and Discussion

The finches that were at a disadvantage but survived may have changed their food preferences. Instead of wasting precious time with the harder seeds they could have searched for the softer portulaca and chamae seeds, even though they were both very limited. The finches who had the larger beaks and longer legs may decide to search for the harder shelled seeds, given that there are more and they know how to unshell them quickly. If the finches determine which seeds best fit their abilities then they have a better chance of survival.

The niches of the finches require plenty of moisture from an abundance of rainfall and seeds from the plants found on Daphne Major. If the niches are too dry or do not have enough stored food the finches could become dehydrated or starved which may lead to death. The limited resources in this case are what is actually available to the finches in 1977, a fundamental niche; the amount of nutrients actually consumed by the finches is the realized niche. The realized niche is formed because there are so many finches searching for food at the same time. The plants also need an abundance of water in their niche. The more rainfall the more prosperous the plants become which will lead to the production of an abundance of seeds for the finches to eat and a higher survival rate for the finches.

The conflicting data that does not support my hypothesis is that owls are known predators of the finches and were seen eating the finches. The owls could have preyed on the finches and killed them when there was no other food for the owls to eat causing the decrease in the finch population. The reason that this data conflicts with my hypothesis is that owls have always been predators of finches, why would so many be attacked at one particular point in time. Also, there is no evidence to support that the owls were the cause of the decrease in the finch population. No other drastic decrease in the finch population due to the owls has been reported before. Also, the owl population on Daphne Major decreased at the same time the finch population decreased. It is likely that the owls migrated to another island to search for live prey given that they are able and have migrated previously; therefore this data is irrelevant and insignificant to my hypothesis.

Though many factors can be associated with the deaths of the Galapagos Finches in 1977, the most supported and evident factor was the weather.



1. Criteria 1: Writer presents relevant and testable hypotheses with a clear rationale. Please write at least one comment/question in the "explanation" box addressing this issue.

Yes
No

Answer: Yes
Feedback : The same hypotheses are presented as in the High Quality Calibration paper, but the correlation between the change in beak size and the reduction in seeds is not "proof" of cause, but just support of that hypothesis. It would be useful to know what else finches eat besides seeds and whether or not all of the different seeds were available in 1977. BUT Only the owl hypotheses is considered - no other explanations are examined, even after the author raises the issue that other traits might have mattered. The author needs to actually provide data for or against the other hypotheses that are introduced. If it's possible that leg length could have been the trait that helped finches survive or that owls migrated on and off the island, then the author needs to present data or evidence that show whether those things are actually true. If there isn't any data to evaluate them, then the author needs to describe what data need to be gathered in the next phase of the experiment.
2. Criteria 2: Writer provides sufficient background to understand the investigation and put it in context. Please write at least one comment/question in the "explanation" box addressing this issue.

Yes
No

Answer: Yes
Feedback : The discussion of niches is confusing.
3. Criteria 3: Relevant data for every hypothesis are presented in a logical format and clearly tied back to hypotheses being tested. Please write at least one comment/question in the "explanation" box addressing this issue.

Yes
No

Answer: No
Feedback : The author presents NO data on beak size! (or leg length or other traits discussed!) This author desperately needs to address which trait(s) evolved over time, and whether there is evidence that any trait in the finch population changed over time. Without that evidence, it could be true that mortality and survivorship are completely random.
4. Criteria 4: The writer emphasizes logic and evidence in making their conclusion. Writer makes clear how the data support or refute alternate hypotheses. Please write at least one comment/question in the "explanation" box addressing this issue.

Yes
No

Answer: No
Feedback : The author does a decent job demonstrating the drought caused a decline in the resources used by the finches, but does not address the issue of evolution at all. The issue of whether one trait is favored is raised but not thoroughly examined with evidence. The author needs to show whether the reduction in seeds and plants affected all finches the same (mortality was random) or whether there is evidence that beak size mattered for survival as concluded.
5. Criteria 5: The writer presents a persuasive discussion of why the data support one hypothesis over the alternatives for each question. If more than one hypothesis is supported by the current data, the writer describes data or experiments needed to test the hypotheses. Please write at least one comment/question in the "explanation" box addressing this issue.

Yes
No

Answer: No
Feedback : The author does an adequate job on the first question (why did the finches die?), but is very weak on the second question (Why did some finches survive?) The author does a good job eliminating the owl hypothesis, but does not consider other explanations or eliminate them. Even the hypothesis that the finches died of dehydration is not evaluated.
6. Criteria 6: The writer explicitly states whether or not he/she thinks evolution occurred. If evolution is concluded to have occurred, the writer explains which evolutionary mechanism (gene flow, genetic drift, mutation, natural selection) was the most likely cause and why. Please write at least one comment/question in the "explanation" box addressing this issue.

Yes
No

Answer: No
Feedback : The author does not address this issue sufficiently. No data are presented on this question. It is not clear what the author's conclusion is about evolution or which mechanism might have been involved. If either the beak size or the leg length was important in survival, as the author suggests, but doesn't support with evidence, then natural selection is the likely mechanism but there is no discussion of this. Author suggests that finches could learn to handle seeds differently, which would weaken the importance of inherited beak size, but doesn't provide any evidence for or against this from the field notes.
7. Criteria 7: A minimum of two graphs are presented (and visible!) which provide relevant data that is connected to hypotheses and conclusions. Please write at least one comment/question in the "explanation" box addressing the quality of the graphs.

Yes
No

Answer: Yes
Feedback : Four graphs are presented and are relevant to the data discussed. Sometimes the reader has to combine information from more than one table and graph to understand a point, and that is not as effective as it could be.
8. Criteria 8: The graphs are clear, easy to understand, and properly labeled. The type of graph and presentation facilitates the readers' understanding.

Yes
No

Answer: No
Feedback : The graphs are appropriate but difficult to read in this context. The graph numbers in the text do not correspond to the graphs themselves. Combining graphs 1 and 2 would be a more effective presentation. Additional graphs (owls vs finches, beak or leg length changes) are needed. For graph 4, units for seed length and volume are lacking.
9. Criteria 9: A clear train of thought is presented and developed throughout the paper (the paper is logical and well organized).

Yes
No

Answer: No
Feedback : The paper is logical for the information it does present, it just lacks critical pieces of evidence. BUT, the section headings are not helpful; Methods actually contains results and discussion. And results and discussion should be separated, especially since the paper deals mostly with just one hypothesis.
10. Criteria 10: Sentence structure and word usage are correct and facilitate the reader's understanding. The pasages flow nicely. (There are three or fewer errors of structure or word usage.)

Yes
No

Answer: Yes
Feedback : The writing is clear for the most part. There are a few odd word choice, but the reader can decipher them; "a significantly less amount", "prosperous" plants.
11. Criteria 11: Grammar and spelling are correct. (There are three or fewer errors or typos)

Yes
No

Answer: Yes
Feedback : none
12. Criteria 12: Outside source is correctly cited and referenced. At least one outside source is used, preferably for background information.

Yes
No

Answer: No
Feedback : none
13. Add at least one additional comments/questions that you think will help the writer. (also - Check YES in the box to match the calibration or other reviewers.)

Yes
No

Answer: Yes
Feedback : Do NOT try to write feedback here or for any of the calibration prompts. You will write feedback for student papers (the second set of three papers you read and review.)
14. How would you rate this text?
10 Highest
9
8
7
6
5
4
3
2
1 Lowest
Rating: 6
Feedback : The author only addressed the first question of the assignment: "What caused the finches to die?" but fails to address the second question of the assignment: "Which finches survived and why?" Why aren't the data from 1973 included? If you are only comparing 1976 and 1977, how do you know which year is "normal"?

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Low Quality Calibration
The Galapagos Island ecosystem is one that consists of both dry (desert

The Galapagos Island ecosystem is one that consists of both dry (desert.like) and wet seasons. It is located 500 miles South of the Equador. There are many smaller islands located on the Galapagos Island, one in particular that I will be discussing would be Daphene Major, where many animals, both land and marine live. There are owls that feed mostly on birds, rats, and lizards. The owls live mostly on one island, but tend to fly between islands in search of food. Also, the ground finch, which is one of the many preys of the owl. It is a small brown bird that usually eats on seeds, small insects, and spiders. They usually mate in the wet seasons. The plant life on the island includes Cactus, which produce edible seeds and nectar. Chamae, a shrub.like plant with coarse, spiny purple leaves. Flowers grow in bunches and seeds are covered with a molasses coating, which makes it hard for animals to get into. Portulaca, which grows on small rocky islets, has stems that are thick and contains fleshy leaves. The Tribulus is another plant that is an annual herb, is rarely shrubby and has diffusely branches and its seeds are enclosed in a spiny shell. Some finches have a problem with certain seeds (plants) because of the rigidity of them. This made the finches compete for food. Certain birds (owls/finches) with certain characteristics were able to better adapt to the environment for specific food sources. Example, the owls were bigger so they could over power the finches. And eat them. Also the finches that had certain characteristics such as bigger and stronger beaks, which had the advantage over those with smaller and less strong beaks, therefore only certain seeds, could be eaten.

In 1977, Daphene Major experience a major crisis, which 3/4 of the finch population died. There were many hypotheses to why the finches disappeared from the Galapagos Island, but in the following, I will attempt to explain one specific reason (hypothesis) of why the finches disappeared.1 believe the finch population slowly decreased, because of a decrease in the food supply (seeds) Figure 1 shows a total amount for each individual seed groups produce in both the wet and dry seasons. An example of this is there was a total of 18 finches alive in 1977 from 71 finches alive in 1976 during both wet and dry seasons.

A cause of the decrease in finches was that there was only a total of 100 seed produce in 1977 and 365 total seeds produced in 1976. A decrease in seeds causes a decrease in finches' death. As shown in graph 1, the total amount of seeds being produced each year caused a decrease among the finch population. Example, as the rainfall decreased from year to year especially between 1976 wet season to 1977 dry season, so did the finch population. As shown in graph 2, as the weather changed (such as in the amount of rainfall), so did the amount of finches. Graph 2 shows that where the rainfall decreased so did the finches and also.. as the rainfall increased so did the finches. As the rainfall continued to fall, more seeds were produced which caused the population of the finches to rapidly increase. There were some remaining finches that survived this crisis, these finches probably survived because as the seed population increased (as shown in graph 1), the finch population increased, further data would likely prove this. More of the seed population such as Chamae, which went from 0 in dry 77 to 48 wet 78 and Tribulus, which went from 0 dry 77 to 700 wet 78. Chamae and Tribulus were two of the finches favorite seeds rapidly increase therefore the finch population had a better chance of survival. Graph 3, also shows that as the rainfall increase so did the finches and seed population (it is very noticeable in wet season of 1977 to the wet season of 1978). Without having enough data, but assuming with data I collected from the graphs, one could easily assume that the finch population did increase. In the dry season fewer seeds were being produced, therefore the finches had less food, and during the wet season there were smaller seeds produced than larger ones.

Beaks may have then played a major role because finches ate mostly smaller seeds, they were easier to crush, so they live during the wet seasons, but without rainfall and the right beak sizes the finches have a less chance of survival. So, going back to the rainfall and total amount of seeds both decreasing could cause a decrease in finches. If there were an abundance of seeds and rainfall, the chances of survival of finches would increase. Also, the remaining finches that survived learned how to adapt to the specific niches (competing for resources, etc). For the future generations of finches to survive both wet and dry seasons, they would have to learn how to better adapt to their environment. They could mate to keep finches with stronger beaks, so one could crush smaller, harder seeds. If the birds learned how to eat and do things differently, then those would be the ones to better survive the decrease of seeds and any other triumph that might come their way.

The following conflicted with my data, it was stated that owls of the Daphene Major killed off the finches. As shown in graph 4, there was also a decrease in owls as well as finches. Therefore, whatever killed the finches obviously killed the owls. This data was unable to be proven because there was always a less population of owls than finches, so I thought that this data could have been overlook.



1. Criteria 1: Writer presents relevant and testable hypotheses with a clear rationale. Please write at least one comment/question in the "explanation" box addressing this issue.

Yes
No

Answer: Yes
Feedback : none
2. Criteria 2: Writer provides sufficient background to understand the investigation and put it in context. Please write at least one comment/question in the "explanation" box addressing this issue.

Yes
No

Answer: Yes
Feedback : There is background, but it is confusing and could be greatly improved. Use outside sources and improve the organization to help put this investigation in context.
3. Criteria 3: Relevant data for every hypothesis are presented in a logical format and clearly tied back to hypotheses being tested. Please write at least one comment/question in the "explanation" box addressing this issue.

Yes
No

Answer: No
Feedback : none
4. Criteria 4: The writer emphasizes logic and evidence in making their conclusion. Writer makes clear how the data support or refute alternate hypotheses. Please write at least one comment/question in the "explanation" box addressing this issue.

Yes
No

Answer: No
Feedback : none
5. Criteria 5: The writer presents a persuasive discussion of why the data support one hypothesis over the alternatives for each question. If more than one hypothesis is supported by the current data, the writer describes data or experiments needed to test the hypotheses. Please write at least one comment/question in the "explanation" box addressing this issue.

Yes
No

Answer: No
Feedback : none
6. Criteria 6: The writer explicitly states whether or not he/she thinks evolution occurred. If evolution is concluded to have occurred, the writer explains which evolutionary mechanism (gene flow, genetic drift, mutation, natural selection) was the most likely cause and why. Please write at least one comment/question in the "explanation" box addressing this issue.

Yes
No

Answer: No
Feedback : The data that support this discussion are confused and weak. The author suggests the birds are "learning to adapt", which is using adapt in the common sense, not the biological definition.
7. Criteria 7: A minimum of two graphs are presented (and visible!) which provide relevant data that is connected to hypotheses and conclusions. Please write at least one comment/question in the "explanation" box addressing the quality of the graphs.

Yes
No

Answer: No
Feedback : There were graphs with the paper in class BUT NOT on the CPR screen, so reviewers can't see them.
8. Criteria 8: The graphs are clear, easy to understand, and properly labeled. The type of graph and presentation facilitates the readers' understanding.

Yes
No

Answer: No
Feedback : none
9. Criteria 9: A clear train of thought is presented and developed throughout the paper (the paper is logical and well organized).

Yes
No

Answer: No
Feedback : none
10. Criteria 10: Sentence structure and word usage are correct and facilitate the reader's understanding. The pasages flow nicely. (There are three or fewer errors of structure or word usage.)

Yes
No

Answer: No
Feedback : There are several "sentences" that are not real sentences. Word usage is often imprecise or confusing. "Rainfall continues to fall..." Does this mean precipitation increases or decreases?
11. Criteria 11: Grammar and spelling are correct. (There are three or fewer errors or typos)

Yes
No

Answer: No
Feedback : examples: Daphene, Equador for Equator, increase for increased
12. Criteria 12: Outside source is correctly cited and referenced. At least one outside source is used, preferably for background information.

Yes
No

Answer: No
Feedback : none
13. Add at least one additional comments/questions that you think will help the writer. (also - Check YES in the box to match the calibration or other reviewers.)

Yes
No

Answer: Yes
Feedback : Do NOT try to write feedback here or for any of the calibration prompts. You will write feedback for student papers (the second set of three papers you read and review.)
14. How would you rate this text?
10 Highest
9
8
7
6
5
4
3
2
1 Lowest
Rating: 3
Feedback : This paper contains some interesting ideas, but they are not fully developed with evidence and reasoning. Some passages are very confusing. The mechanics of the paper interfere with the reader's understanding of the paper.

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