8.1 Responses to the Environment

1. AThe length of the light period each day
   A student who thinks plants measure day length picks this. Treatments 3 and 4 have the same 8-hour light period, yet only treatment 3 led to flowering, so the light period does not decide the response.
2. BThe length of the uninterrupted dark period Correct
   Plants flowered only in treatment 3, which had a 16-hour dark period without a break. Treatment 4 had the same 8-hour light period and nearly the same hours of darkness, but a brief flash split the night into two 8-hour periods, and the plants did not flower.
3. CThe total quantity of light received each day
   A student who thinks plants flower when they receive enough light picks this. The flash in treatment 4 adds very little light compared with treatment 3, yet it prevented flowering, and treatment 1, with the most light, did not flower.
4. DThe total number of hours of dark each day
   A student who thinks a brief stimulus is too small to matter picks this. Treatment 4 has almost the same total hours of dark as treatment 3, but the brief flash breaks it into two shorter periods, and the plants did not flower.

CED 8.1.A.1 · Read this in Fix

1. AFish given water with injured-skin extract hid in the shelters in their tanks.
   A student who thinks one treatment's result is enough picks this. Without fish given plain water for comparison, the hiding could be normal behavior unrelated to the chemical.
2. BFish that could see an injured fish hid more often than fish that could not see it.
   A student who thinks any comparison will do picks this. This comparison changes what the fish can see, not whether a chemical is present, so it tests a visual cue rather than the claim.
3. CA group exposed to the extract hid more than a group given plain seawater. Correct
   The two groups differ only in whether the injured-skin extract is present, so more hiding in the exposed group shows that the fish respond to the chemical.
4. DOne fish stayed hidden for more than an hour after extract was added to its tank.
   A student who thinks one striking case is good evidence picks this. A single fish's behavior could be due to chance or other causes; a comparison of groups is needed.

CED 8.1.A.2 · Read this in Fix

1. AMales with higher-pitched songs will attract more mates, on average, than those with low-pitched songs. Correct
   Song is a signal that changes female behavior. Near the highway, low-pitched songs are masked, so females respond more to higher-pitched songs, and males that sing them are expected to have greater reproductive success.
2. BEach male with a low-pitched song will change his genes to make his song heard over the noise.
   A student who thinks individuals change their genes to suit the environment picks this. Individuals cannot change their genes in response to noise; differences in mating success arise among males that already differ.
3. CSong pitch will not affect mating success, because singing is an innate behavior that cannot change.
   A student who thinks innate behaviors cannot be affected by the environment picks this. Whether or not song is innate, noise changes how well females hear it, and so changes which males attract mates.
4. DMales with low-pitched songs will die sooner, because the noise lowers their chance of survival.
   A student who thinks fitness is about survival picks this. The stem describes an effect on how well females hear songs, which affects mating success, not survival.

CED 8.1.B.1.i · Read this in Fix

1. ALearned behaviors are favored because the skills an individual learns are passed on in its genes.
   A student who thinks learned behavior is inherited genetically picks this. Learned skills are not passed on in genes; learned behaviors increase fitness through their effect on the learner's own survival and reproduction.
2. BBoth innate and learned behaviors are favored when they increase survival and reproductive success. Correct
   Behaviors, innate or learned, that increase survival and reproductive success are the ones fitness favors. A learned behavior, such as learning where food is found, can increase the number of offspring an individual leaves.
3. COnly innate behaviors are favored, because learned behaviors are not passed on to offspring in genes.
   A student who thinks selection can act only on genetically inherited behavior picks this. Learned behaviors that increase survival and reproduction also increase fitness.
4. DA behavior is favored when it lengthens an individual's life, whatever its effect on reproduction.
   A student who equates fitness with survival picks this. Fitness is measured by reproduction; a behavior that lengthens life but reduces reproduction lowers fitness.

CED 8.1.B.2.i · Read this in Fix

1. AFail to reject the null hypothesis, because the difference seen is not significant. Correct
   χ² = (30 − 25)²/25 + (20 − 25)²/25 = 2.00. With 1 degree of freedom the critical value at p = 0.05 is 3.84; 2.00 is less than 3.84, so the difference from the expected 25 on each side is not significant: a difference this size could be due to chance.
2. BReject the null hypothesis, because more of the animals were found on the moist side.
   A student who thinks any difference from the expected counts shows a real effect picks this. Counts vary by chance; χ² (2.00) is below the critical value (3.84), so this difference is not significant.
3. CReject the null hypothesis, because χ² is less than the critical value of 3.84.
   A student who thinks a small χ² means a significant result picks this. A χ² smaller than the critical value means the data are close to the expected counts, so the null hypothesis is not rejected.
4. DFail to reject the null hypothesis, which proves that these animals have no preference.
   A student who thinks failing to reject the null hypothesis proves it picks this. The data do not show a significant preference, but a real preference might exist and be too small to detect with 50 animals.

Working Expected counts under the null hypothesis: 50/2 = 25 on each side. χ² = Σ(o − e)²/e = (30 − 25)²/25 + (20 − 25)²/25 = 25/25 + 25/25 = 2.00. Degrees of freedom = 2 categories − 1 = 1; the critical value at p = 0.05 is 3.84. Since 2.00 < 3.84, the null hypothesis is not rejected: the difference between 30 and 20 could be due to chance. This does not prove that the animals have no preference.

CED 8.1.A.1 · Read this in Fix

1. AGroup 3, which gets no light at all, so that light is absent
   A student who thinks a control must lack the factor entirely picks this. Group 3 differs from group 1 in having no light, so it tests the presence of light, not its direction.
2. BGroup 4, which is lit from one side but is a different species
   A student who thinks any other group can serve as a control picks this. Group 4 has the same light direction as group 1 and differs in species, so it cannot show the effect of light direction.
3. CNo other group, as bending in group 1 alone would show the effect
   A student who thinks one result is enough picks this. Without a group lit from a different direction, bending in group 1 could be a response to light itself rather than to its direction.
4. DGroup 2, which gets the same light from a different direction Correct
   Group 2 differs from group 1 only in the direction of the light: same species, same light intensity, light from above instead of one side. A difference in bending can therefore be attributed to the direction of light.

CED 8.1.A.1 · Read this in Fix

1. APlant Q increases its defenses only after caterpillars begin feeding on its own leaves.
   A student who thinks plants cannot detect other plants picks this. The model shows plant Q undamaged when its defensive compounds rise, in response to the chemical from P.
2. BPlant Q increases its defenses in response to a chemical released by damaged plant P. Correct
   The model shows plant P being eaten and releasing an airborne chemical that reaches plant Q, which is not damaged and whose defensive compounds rise. Q changes in response to information carried by the chemical from P.
3. CPlant P releases the chemical because it wants to warn plant Q of the danger it is facing.
   A student who explains signals by intentions picks this. Plants have no intentions; the model shows only that P releases a chemical and Q responds to it.
4. DPlant P releases the chemical so that the species as a whole is protected from attack.
   A student who thinks behaviors exist for the good of the species picks this. The model shows a chemical passing from one plant to another, not a benefit to the species; responses evolve through effects on individuals and their relatives.

CED 8.1.A.2 · Read this in Fix

1. AMales are attracted mainly by seeing the female, since 23 came to the mesh cage.
   A student who draws a conclusion from one treatment picks this. Comparing treatments shows that seeing the female is not needed: 21 males came when she was hidden, and 1 came when she was visible behind glass.
2. BMales are attracted partly by sight, since one male came to the sealed glass cage.
   A student who treats any difference as a real effect picks this. One male among the treatments is a very small count that could arrive by chance, and hiding the female barely reduced the number of males.
3. CMales are attracted mainly by sounds the female makes, which pass through mesh.
   A student who assumes animal signals are usually sounds picks this. The paper rubbed on females makes no sound, yet 19 males came to it.
4. DMales are attracted mainly by an airborne chemical, since they came whenever air could pass. Correct
   Males came in large numbers whenever air could pass from the female or her scent to the outside (23, 21 and 19 males), whether or not she could be seen, and almost none came when air was blocked (1 male). Paper rubbed on females, which cannot be seen or heard, was enough.

CED 8.1.B.1 · Read this in Fix

1. ADisplaying more often caused males to fledge more offspring.
   A student who takes a correlation as proof of cause picks this. The data show that display rate and offspring increase together; another factor, such as the male's condition, could affect both.
2. BEvery male fledged more offspring than all males that displayed less.
   A student who reads a trend as applying to every individual picks this. Some males fledged fewer offspring than males that displayed less often (for example, 4 displays per hour and 1 offspring, compared with 3 and 2).
3. CMales that displayed more often tended to fledge more offspring. Correct
   The points rise from left to right: males displaying 2–4 times per hour fledged 1–2 offspring, while males displaying 11–13 times per hour fledged 5–6. This is a positive relationship, with some variation among individual males.
4. DDoubling a male's display rate doubled the offspring fledged.
   A student who assumes the relationship is proportional picks this. A male with 6 displays per hour fledged 2 offspring, the same number as a male with 3, and a male with 12 fledged 5, not 4.

CED 8.1.B.1.i · Read this in Fix

1. ABoth the song and the tone were shown to delay the settling of new males, compared with silence.
   A student who treats any difference between means as real picks this. The tone's mean (1.6 days) is higher than silence (1.3 days), but their error bars overlap, so a delay from the tone has not been shown.
2. BThe tone and silence led to exactly the same mean time for new males to settle.
   A student who reads overlapping error bars as equal means picks this. The means were 1.6 and 1.3 days; overlap shows only that a difference was not established.
3. CEvery territory with song stayed empty longer than every territory with the tone.
   A student who thinks error bars show the range of individual values picks this. The bars show ±2 SE of the mean; individual territories can lie outside them.
4. DSong delayed settling compared with silence, but a delay from the tone was not shown. Correct
   The ±2 SE bars for song (3.4–5.0) and silence (0.8–1.8) do not overlap, so song likely delayed settlement. The bars for tone (1.0–2.2) and silence overlap, so no effect of the tone was shown. Song, not just any sound, delayed settlement.

Working No test statistic is calculated; the decision rests on the ±2 SE error bars. Song: mean 4.2, bar 3.4–5.0. Tone: 1.6, bar 1.0–2.2. Silence: 1.3, bar 0.8–1.8. Song vs silence: no overlap (3.4 > 1.8), so song likely delayed settlement. Tone vs silence: the bars overlap (1.0–1.8), so no significant difference is shown, although the means differ (1.6 vs 1.3). The SE bars describe the means, not the range of individual territories.

CED 8.1.B.1.ii · Read this in Fix

1. AFish fled faster because they needed to escape, and this need made each generation's response faster.
   A student who thinks traits evolve because organisms need them picks this. Need does not change the alleles passed on; the response changed because fish with faster responses left more offspring.
2. BFish that learned to flee faster during their lives passed their improved speed to their offspring.
   A student who thinks learned behavior is inherited picks this. Learning during a fish's life does not change the alleles it passes on; the change came from selection on heritable differences.
3. CFish that fled quickly survived and reproduced more, passing alleles for fast fleeing to more offspring. Correct
   There was heritable variation in the response, and fish that fled quickly were more likely to escape birds and reproduce. Their offspring inherited alleles for fast fleeing, so the response became more common: natural selection acting on a response to information.
4. DFish fled faster so that enough members of the species would survive to keep the species going.
   A student who thinks behaviors evolve for the good of the species picks this. Selection acts through the survival and reproduction of individuals with different responses, not for the benefit of the species.

CED 8.1.B.2 · Read this in Fix

1. AOpen-field foraging has higher fitness, as it yields more offspring per bird on average. Correct
   Fitness is measured by offspring. Per bird at the start of the season, open-field foragers produced 0.60 × 5 = 3.0 offspring on average, and bush foragers 0.90 × 2 = 1.8, so open-field foraging has the higher fitness despite lower survival.
2. BBush foraging has higher fitness, as a larger proportion of the birds that use it survive.
   A student who equates fitness with survival picks this. Bush foragers survive better (90% vs 60%), but they produce fewer offspring per bird (1.8 vs 3.0), and offspring are what fitness measures.
3. CThe two behaviors have equal fitness, as the costs and benefits of each one balance each other.
   A student who thinks advantages and disadvantages in nature always balance out picks this. Calculating offspring per bird shows unequal fitness: 3.0 for open-field foragers and 1.8 for bush foragers.
4. DNeither behavior decides fitness, which depends on how strong and large each bird is.
   A student who equates fitness with strength picks this. Fitness is measured by reproductive success, and the data show that the two foraging behaviors differ in offspring produced.

Working Mean offspring per bird at the start of the season = proportion surviving × mean offspring per survivor. Open field: 0.60 × 5 = 3.0. Bushes: 0.90 × 2 = 1.8. Open-field foraging gives more offspring per bird on average, so it has the higher fitness, even though fewer of these birds survive.

CED 8.1.B.2.i · Read this in Fix

1. AFood per individual rose with every increase in the number of individuals in a pack.
   A student who thinks larger cooperative groups always benefit each member more picks this. Food per individual fell in packs larger than 4.
2. BFood per individual doubled when pack size doubled from 1 to 2 individuals.
   A student who assumes the relationship is proportional picks this. Food per individual rose from 1.2 to 1.9 kg/day, an increase, but not a doubling.
3. CIndividuals that hunted alone obtained the most food per individual of any pack size.
   A student who thinks cooperation always costs the individual picks this. Lone hunters obtained the least food per individual (1.2 kg/day); every pack size shown gave more.
4. DFood per individual rose as pack size increased to 4, then fell in larger packs. Correct
   Food per individual rose from 1.2 kg/day for a single hunter to a peak of 2.6 kg/day in packs of 4, then fell to 2.2 kg/day in packs of 6 and 1.7 kg/day in packs of 8.

CED 8.1.B.2.ii · Read this in Fix

1. ACallers' relatives, which share many of their alleles, survive better, so alleles for calling are passed on. Correct
   Relatives share many alleles with the caller, including, on average, alleles that contribute to calling. When calls help relatives escape and reproduce, these alleles are passed on through the relatives even though the caller bears a cost (kin selection).
2. BCallers sacrifice themselves for the good of the species, which keeps the species from dying out.
   A student who thinks behaviors evolve for the good of the species picks this. A behavior that lowers the caller's survival persists only if it increases the passing on of the alleles for it, here through relatives.
3. CCallers know that their relatives are in danger and decide to warn them because they care for them.
   A student who explains behavior by intentions and feelings picks this. Evolutionary explanations rest on how the behavior affects the passing on of alleles, not on what the animal knows or wants.
4. DCallers learn to give alarm calls and pass this learned behavior on to their offspring in their genes.
   A student who thinks learned behavior is inherited genetically picks this. Learning is not passed on in genes; calling persists because relatives that share the alleles survive and reproduce.

CED 8.1.B.2.ii · Read this in Fix