Writing Assignment 1

Transcription

1 Writing Assignment 1 Writing Assignment #1 Due Wednesday October 15th at the beginning of lecture To read: A Tephritid Fly Mimics the Territorial Displays of its Jumping Spider Predators Erick Greene; Larry J. Orsak; Douglas W. Whitman Alternative Male Strategies: Genetic Differences in Crickets Author(s): William H. Cade Assignment can be found on the class website. Please note the clarifications about the graphs for the second paper. Course Website:

2 Writing Assignment 1 Writing Assignment #1 Due Wednesday, October 15th at beginning of lecture To write: Discuss how behaviors can evolve via natural selection. Use the two papers as a focus for your discussion, but you can also draw upon examples from class. Be sure to answer all of the following questions in your paper. What three things are needed for a behavior to evolve via natural selection? How can researchers test for each of these three requirements? What were the predictions/hypotheses about the expected outcome of natural selection that were made in each of the two papers? What were the selective forces in nature or the lab? What kinds of controls did the researchers use in their experiments to determine if a behavior has evolved according to a particular hypothesis? Please write an essay about the topic. Do not simply answer the questions above, because the questions are meant to give you ideas about how to phrase your answer. Instead, imagine that you are a reporter, and you have to write a story about how natural selection can affect behavior. As part of your report, you have read the two assigned papers and are using them to describe the latest evidence.

3 Niko Tinbergen s Four Questions (Mnemonic for Tinbergen s Questions) A Animal B Behavior C Causation (Proximate) D Development (Proximate) E Evolution (Ultimate) F Function (Ultimate) Proximate Factors: What are the mechanisms involved? Genetics, Developmental biology, Neuroscience, Endocrinology, etc. Ultimate Questions: Why did the behavior evolve? Evolution and ecology

4 How to test hypotheses in behavioral ecology 1. Scientific method 2. Examples of how the founders of behavioral ecology tested hypotheses. 3. Other examples of tests in behavioral ecology

5 The Nature of Science 1. The purpose of science is to learn about our universe. 2. Science relies on evidence from the natural world and the evidence is interpreted through logic. 3. Scientific claims are based on testing explanations against observations of the natural world and rejecting the ones that fail the test. 4. Scientific claims are subject to peer review and replication. (Want theories that are useful and predictive.) 5. Theories are not absolutely proven. However, science corrects itself and theories become more reliable.

6 The real scientific method

7 How science works The real scientific method

8 Carl Sagan s tools for skeptical thinking 1. Independent confirmation (replication) of the facts. 2. Test more than one hypothesis. 3. Try not to get attached to a hypothesis because it is yours. 4. Quantify: Makes it is easier to discriminate among hypothesis. 5. In a chain of argument, all links (including the premise) must work. 6. Occam s Razor: When two hypotheses fit the data equally well, choose the simpler. 7. Always ask if the hypothesis can be falsified. 8. Arguments from authority carry little weight.

9 The Nobel Prize in Physiology or Medicine 1973 Nikolaas Tinbergen ( ) Formally developed Ethology Studied the survival value of behavior in black-headed gulls. Konrad Lorenz ( ) Studied imprinting (Geese) Studied social behaviors Wrote King Solomon s Ring Karl Von Frisch ( ) Decoded bee language

10 Tinbergen and the Beewolf

11 Tinbergen and the Beewolf How do beewolves find their homes among so many nest in the dunes? Proximate question Hypothesis 1: The wasps actually took in the features of the burrow s surroundings while circling above. Test 1: Swept areas around the burrows clean of landmarks. Result 1: Wasps stopped 4 feet in air from nests as if confused. Repeated the approach again and again. Dropped prey and searched randomly on the ground.

12 Tinbergen and the Beewolf Hypothesis 2: If a wasp used landmarks it should be possible to do more than merely disturb her by throwing her beacons all over the place; I ought to be able to mislead her, to make her go to the wrong place, by moving the whole constellation of her landmarks over a certain distance. Test 2a: Moved all landmarks one foot to the southeast. Result 2a: The wasp female landed 1 ft to the southeast of her nest. Test 2b: Moved landmarks back. Result 2b: Wasp came directly back to her nest.

13 Tinbergen and the Beewolf Hypothesis 3: Wasps could be trained to new landmarks. Test 3: Put rings of pinecones around nests. Two days later, moved the circle of pinecones. Result 3. Wasps landed within the circle of pinecones, rather than at their nests.

14 Tinbergen and the Black-Headed Gulls

15 Tinbergen and the Black-Headed Gulls Why do black-headed gulls remove broken eggshells from the nest after the chick hatch? Ultimate question Hypothesis: It evolved because gulls with the behavior gained reproductive success. Removing eggshells eliminates visual cues that could give the nest away to predators. Prediction: The presence of broken eggshells should help predators locate food. Test: Took intact gull eggs and placed them around the sand dunes. Placed broken egg shells at different distances away from the eggs.

16 Tinbergen and the Black-Headed Gulls Distance from eggshell to egg (cm) Eggs taken by crows Eggs not taken by crows Percentage Eaten Result: Eggs closest to white eggshell bits were more likely to be eaten by crows.

17 Karl Von Frisch and the Bees Hypothesis: Bees can communicate information about distance. Bee video

18 Karl Von Frisch and the Bees Distance to feeding place (m) Result: Longer distances correspond to longer waggle dances.

19 Karl Von Frisch and the Bees Hypothesis: Bees can take in information about the direction of a food source.

20 Karl Von Frisch and the Bees

21 Konrad Lorenz and Social Bonds in Birds Konrad Lorenz Hypothesis 1: Imprinting is the result of an instinct. That is, a genetically predetermined response that is "released" by a limited set of stimuli from the environment. Hypothesis 2: Imprinting occurs during a "critical period" = a limited time in an animal s early life.

22 Overview on how to test hypotheses 1. Observations: observe behavioral interactions, observe genetic relatedness, observe the context of the behavior, etc. 2. Experiments: allow controlled manipulation of the factors involved in a behavior. 3. Comparative Method: Observe the results of natural experiments conducted over evolutionary time 4. Modeling: Clarify thought about how the world works, can allow testable predictions.

23 Overview on how to test hypotheses 3. Comparative Method: Observe the results of natural experiments conducted over evolutionary time a. Example: Differences in social organization of weaver birds.

24

25

26

27 Comparisons among species of weaver birds 3. Comparative Method: Observe the results of natural experiments conducted over evolutionary time a. Example: Differences in social organization of weaver birds. Habitat Food Monogamous Polygynous Solitary Grouped Colonial Forest Insects Forest Insects and seeds Savannah Seeds Grassland Seeds From Krebs, Davies and West, 2012

28 Comparisons among species of weaver birds John Crook s Hypotheses 1. Insect food in the forest is dispersed so birds feed solitarily and defend territories to monopolize scattered resources. Both parents need to provide parental care. 2. Seeds in the savannah are patchily distributed but locally very abundant. Groups can cover a wider area to search for food and food many not be limiting when a supply is found. Nests cannot be hidden in open areas so are put in protected areas like acacia trees, which may be limited in number. Large nests may also provide thermal insulation. Food is abundant so females can raise offspring alone. Males may therefore be able to spend time attracting other mates. 3. Seeds in grasslands are patchy, so groups are favored. Nests are vulnerable in open areas, which favors spacing them out.

29 Overview on how to test hypotheses 1. Observations: observe behavioral interactions, observe genetic relatedness, observe the context of the behavior, etc. 2. Experiments: allow controlled manipulation of the factors involved in a behavior. 3. Comparative Method: Observe the results of natural experiments conducted over evolutionary time 4. Modeling: Clarify thought about how the world works, can allow testable predictions.

30 Goals for the class 1. Gain an understanding of the theories that have been used to understand behavior. 2. Learn examples of how those theories have been tested. It is important to know the evidence that shows that the theories are useful and predictive. 3. Understand ways in which hypotheses about behavior can be rigorously tested. 4. Learn that many alternative hypotheses may need to be tested because different mechanisms can lead to similar outcomes.