AP Biology Unit 7: Natural Selection and Evolution

Many species of corals are threatened by the increasing temperatures and decreasing pH of ocean waters. One species, Stylophora pistillata, has been found to thrive in water that is warmer and has a lower pH than the water that corals typically thrive in. Additionally, researchers have found that the tolerance for the new water conditions is heritable.

In 1981 a single immature male Geospiza conirostris finch flew more than 100 kilometers from the Galápagos island of Española to the Galápagos island of Daphne Major, where no G. conirostris finches were living. The immigrant finch bred with a female G. fortis, a species of finch common on Daphne Major. The $\mathrm{F}_{1}$ finches and later generations interbred only within their lineage. By 2012 scientists counted 23 individuals, including eight breeding pairs, within this hybrid lineage on Daphne Major. The hybrid lineage became known as Big Bird.

Birds with different beak shapes and sizes eat different types of food. The dimensions of the Big Bird beaks relative to the beaks of the major competitor finch species on Daphne Major are shown in Figure 1.

A sample of a culture of E. coli is plated onto two LB agar plates: plate

1 containing LB agar and no antibiotic (LB) and plate 2 containing LB

agar with 50 micrograms/mL of the antibiotic ampicillin (LB + amp).

Both plates are incubated at 37°C for 24 hours. Bacteria from plate 1

are plated onto two more plates: one with LB agar (plate 3) and the

other containing LB agar with 50 micrograms/mL of the antibiotic

ampicillin (plate 4). Bacteria from plate 2 are plated onto plate 5

(containing LB agar) and plate 6 (containing LB agar with 250

micrograms/mL of the antibiotic ampicillin). This second round of

plates are all incubated at 37°C for 24 hours. A diagram of the

experiment is shown below.

Questions 40-44 Sea otters are native to the western coast of North America. Between 1750 and 1850, hunting had reduced the population from hundreds of thousands to only one thousand individuals. In the early 1900s, a small population of sea otters was discovered in Elkhorn Slough, an estuary in central California near a large human population center. The otters were then protected by the international fur seal treaty, which banned sea otter hunting. The sea otter population has rebounded to nearly three thousand individuals today. Otters live in kelp forests and eelgrass beds and feed on crabs and shellfish (Figure 1). Most herbivores in the habitat eat algae that grows on the eelgrass and not the eelgrass itself. If there is too much algae, the eelgrass does not receive enough light for photosynthesis. As the otter population has increased, the eelgrass habitat has increased.

Recently, however, scientists have noticed the presence of two nonnative, predatory invertebrate species that may be colonizing the Elkhorn Slough, which would have been too cold for them three decades ago. Scientists have also observed that otters in the area are experiencing increased mortality because of an increase in harmful algal blooms, which occur as a result of nutrient pollution. The harmful algae are ingested by shellfish, which the otters eat.

Which of the following best describes what happened to the otter population between 1750 and 1850 ?