Process of Science and hypothesis tes2ng in Behavioral Ecology

Transcription

1 Process of Science and hypothesis tes2ng in Behavioral Ecology

2 Goal: understand the way that scien2fic hypotheses and methodologies are used to gain knowledge. What separates science from non- science?

3 Goal of any science: to gain knowledge. Goal of biology: understand how nature works How? Making inferences about natural phenomenon based on observa2ons

4 Induc&ve reasoning: making generaliza2ons based on specific observa2ons. E.g., All swans I have seen are white therefore all the swans in the world are white. Unless we can falsify the possibility of alterna2ve outcomes, the generaliza2on reached via induc2ve reasoning could be false. Deduc&ve reasoning: a conclusion is drawn from deduc&ons that move from given statements, which are assumed to be true, to conclusions, which must be true if the given statements are true. Ex.: All men are mortal, Socrates is a man, therefore, Socrates is mortal A conclusion reached by deduc2ve reasoning is true only if all of the assump2ons leading to the conclusion are correct.

5 INDUCTIVE REASONING DEDUCTIVE REASONING Observa2on Observed morphological varia2on in finches across islands GENERALIZATION PREDICTION Used induc2ve reasoning to generate hypothesis of natural selec2on Hypothesis Evolu2onary biologists use deduc2ve reasoning to test the predic2ons of this hypothesis (do observed results support or reject the hypothesis?)

6 Hypothe&co- Deduc&ve method and Falsifiability Observa2ons generate ques2ons. Hypothesis developed that suggests an answer. Hypothesis generates predic2ons that can then be tested. What makes a good hypothesis and test of the hypothesis? Falsifiability: a hypothesis is scien2fic only if it is refutable that is, the hypothesis specifies the types of observa2ons that would not support the hypothesis.

7 Disconfima&onal vs. Confirma&onal Observe: group of house finches foraging on the ground. Ques2on: why are these birds foraging in a group? Hypothesis: individual birds join other birds and forage in the group because the group dilutes that individual s risk of being eaten by a predator.

8 Confirma2onal predic2on if hypothesis is correct: more predators = more birds Why is this a problem? Because it is not based on deduc2ve reasoning we have not falsified other possible outcomes Confirma2onal predic2on if hypothesis is not correct: no rela2onship btw # predators and # birds Why is this a problem? Because we may have made errors in data collec2on

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10 More hypotheses are bemer than one. REVISION of Scien2fic method: Devise alterna2ve hypotheses (note mul$ple hypotheses). Devise a crucial experiment, with alterna2ve possible outcomes, each of which will exclude one or more of the hypotheses (note falsifiability). Carry out the experiment to get "clean" results. Recycle the procedure, making sub- hypotheses or sequen2al hypotheses to refine the remaining hypotheses.

11 Example: Meerkats forage in groups. Some2mes an individual will stop foraging and act as a sen2nel, watching for predators and giving an alarm. alarm call Hypothesis 1: Kin Selec2on. Meerkat sen2nels help others at a personal cost because they receive indirect gene2c benefits from saving kin. Hypothesis 2: Reciprocity. Meerkat sen2nels help others at a personal cost now because they expect to be repaid in the the future Hypothesis 3: Personal Safety. Meerkat sen2nels are the animals that are sated, so they obtain no costs to engaging in the behavior but benefit from detec2ng predator first

12 Fed Unfed

13 Behavioral Research Methods 1. Observa2on method 2. Experimental method 3. Correla2onal method 4. Compara2ve method 5. Cost- benefit analysis

14 Behavioral Research Methods 1. Observa2onal Methods Systema2c recording of behavior Mul2ple individuals Marking vs. naming Mul2ple 2mes (e.g., varying seasons; day vs. night) Mul2ple observers Construc2on of Ethograms

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16 Bigger boxes show more popular tac2cs. Smaller boxes show less common maneuvers. Thicker arrows show the most likely next move dis2nct figh2ng loop that dominates the aggressive behavior: slow approach to a wing threat to a fast approach

17 Behavioral Research Methods 1. Observa2onal Methods Goals: Generate ques2ons and hypotheses *inability to yield causal conclusions; lack of experimental control*

18 Behavioral Research Methods 2. Experimental Methods Manipula2ng something (independent variable) and measuring its effect on something else (dependent variable) while holding other factors constant

19 Behavioral Research Methods 2. Experimental Methods Example: Method of isola2on Bird song in white- crowned sparrows

20 Behavioral Research Methods 2. Experimental Methods Problems with laboratory studies Difficult to generalize Ar2ficial situa2on affects behavior Live tutors Acquired songs beyond 50 days of age Learned heterospecific song

21 Behavioral Research Methods 2. Experimental Methods Problems with field studies Lack of control; inability to hold certain variables constant But does not preclude their usefulness if planned out well.

22 Behavioral Research Methods 3. Correla2onal Methods Measurable changes in animals behavior that are predictable from some other variable that we can measure E.g., temperature and ac2vity (Higher T = more ac2vity) Does T cause ac2vity to increase?

23 Behavioral Research Methods 3. Correla2onal Methods Problem: cannot infer causa2on Ac2vity could be affected by many other uncontrolled factors that also vary with temperature - - greater food availability, greater sunlight, higher humidty, biological clock, etc. Get data on all the fires in Blacksburg for the last ten years. Correlate the number of fire engines at each fire and the damages in dollars at each fire. Note the significant rela2onship between number of fire engines and the amount of damage. Conclude that fire engines cause the damage.

24 Behavioral Research Methods 3. Correla2onal Methods Problem: cannot infer causa2on Solu2on? Manipulate poten2al causal factor (experimental)

25 Behavioral Research Methods 4. The Compara2ve Method Comparisons of behavior within species or between species Idea that animals are op2mally adapted to their environment

26 The Compara2ve Method Test predic2ons about evolu2on of a behavior in one species by examining the behavior in other species. How do we know which species to compare? Need to know something about the evolu2onary history!

27 Phylogene2c Tree Branching diagram extant species all on same level closely related species are together 2me

28 Compara2ve method If a behavior is an adapta2on to X, then closely related species without X should lack the behavior. Mobbing behavior in black- headed gulls an adapta2on to deterring preda2on for a ground- nes2ng species?

29 Predic2on: gulls that don t nest on the ground and don t face nest preda2on should NOT mob (behavior lost)

30 Another way to use the compara2ve method is to look for analogous traits cases of convergent evolu2on.

31 If a behavior is an adapta2on to X, then species in other lineages with X should show the behavior Swallows have colonial- nes2ng species that mob predators, but one species that does not mob, and also lacks nest predators.

32 Behavioral Research Methods 5. Cost- Benefit Analysis Behavior is examined in terms of cost to animal vs. gain to animal Assump2on that animals behave to maximize gains and minimize costs

33 Behavioral Research Methods 5. Cost- Benefit Analysis Example: Tinbergen and black- headed gulls Observa2ons: Gulls remove eggshells from nest 1 hour amer hatching Cost? Energy/2me spent moving shells; leaving the nest (preda2on risk) Benefit?

34 Behavioral Research Methods 5. Cost- Benefit Analysis More informa2on: Nest in open Numerous nest predators Nests are unguarded while parents forage Cryp2c nest, offspring, and eggs Inside of egg is white

35 Behavioral Research Methods 5. Cost- Benefit Analysis Hypothesis? (ul2mate cause) Removal of egg shells decreases likelihood of preda2on Test? Establish ar2ficial nests Place eggshells at 15 cm, 100cm and 200cm

36 Behavioral Research Methods 5. Cost- Benefit Analysis Ques2on: Why had black- headed gulls evolved a special response to eggshells in their nest Hypothesis: Eggshell removal had become common because it helped gulls conceal their offspring Predic2on: Predators would use eggshell as a cue for finding eggs Experiment: Find out what predators did Conclusion: Match data to hypothesis

37 Results: Percent depredated Distance from nest (cm) Do these data support the idea that eggshell removal is reproduc2vely advantageous?

38 Black- headed Gulls Experimental method Nests with eggshells near them more likely to predated Compara2ve method The Kiowake ignores shells; has no nest predators

39 Rules of Scien2fic certainty 1. Hypotheses cannot be 100% proven they can only gain support 2. Hypotheses become beqer supported as a. Plausible alterna2ves are eliminated b. Numerous predic2ons of the same hypothesis are supported

40 Types of Research Ques2ons Species- Oriented: Why do Amazon mollies and sailfin mollies coexist? Concept- Oriented: What condi2ons lead to the maintenance of asexual species? Problem- Oriented: Can we get rid of the pest Poecilia species in introduced popula2ons?

41 Levels of behavior

42 Variables Dependent variables the behaviors you are studying Independent variables subject animal characteris2cs and the environmental parameters. systema2cally varied (measure effects) controlled