1. Based on the data, which of the following is the most likely effect of a period of increased volcanic activity that significantly decreases the amount of sunlight reaching a particular ecosystem for several years?

1. A) There will be a decrease in the population sizes of most species and a decrease in the number of trophic levels.
2. B) The population sizes of plant species will stay the same, but the average biomass of individual plants will increase.
3. C) There will be an increase in the population sizes of omnivores because they can eat other animals instead of the plants.
4. D) The biodiversity of the ecosystem will increase as new niches arise and become occupied by new species.

1. A) There will be a decrease in the population sizes of most species and a decrease in the number of trophic levels.

1. Which of the following is an appropriate null hypothesis for the student's experiment?

1. A) The absence of light negatively affects the mass of the grass.
2. B) An increase in light promotes grass growth.
3. C) A change in light intensity changes the rate of grass growth.
4. D) The presence of light has no effect on the mass of the grass.

1. D) The presence of light has no effect on the mass of the grass.

1. Based on the data, which of the following is the best approximation of the rate of growth per week in section IIII from day 14 to day 21 ?

1. A) 3.2g/week
2. B) 4.5g/week
3. C) 5.1g/week
4. D) 9.6g/week

1. B) 4.5g/week

1. Which of the following best explains the observed difference in mass between the grass in section I after 14 days and the grass in section III after 21 days?

1. A) The grass in section III required more energy for metabolic processes than the grass in section I.
2. B) The grass in section III performed more photosynthesis than the grass in section I.
3. C) Only the grass in section III used energy from the seed for growth and development.
4. D) Mass lost by cell respiration in section III was not replaced by photosynthesis.

1. D) Mass lost by cell respiration in section III was not replaced by photosynthesis.

1. Climate change could affect the ecosystem of the Elkhorn Slough in many ways. From the information provided, which of the following predictions about the direct, local effects of climate change is most likely?

1. A) Ocean warming will favor population growth of nonnative species as their habitats shift northward.
2. B) Ocean warming will decrease eelgrass habitat area as a result of increased herbivory by nonnative species.
3. C) Harmful algal blooms will decrease otter populations as a result of increased mortality of otter prey species.

1. A) Ocean warming will favor population growth of nonnative species as their habitats shift northward.

1. As otters were removed during the hunting years, there was a large decrease in the catches of fish species from the eelgrass habitats. Which of the following best explains why this decrease happened?

1. A) Otters are a keystone species, so their disappearance from the area affected the population size of one other species.
2. B) Otters are a keystone species, so their disappearance from the area resulted in the collapse of an entire community.
3. C) Otters have mutualistic relationships with many other species, so their disappearance from the area affected the population size of another species.
4. D) Otters have mutualistic relationships with many other species, so their disappearance from the area resulted in the collapse of an entire ecosystem.

1. B) Otters are a keystone species, so their disappearance from the area resulted in the collapse of an entire community.

1. Based on the information provided in the passage, which of the following best describes the effect of harmful algal blooms on otter populations?

1. A) They are a density-dependent factor that increases otter mortality in larger populations.
2. B) They are a density-dependent factor that reduces otter numbers at lower population sizes.
3. C) They are a density-independent factor that negatively affects the otter population regardless of its size.
4. D) They are a density-independent factor that increases otter mortality in only larger populations.

1. C) They are a density-independent factor that negatively affects the otter population regardless of its size.

1. Based on the information, an increase in the sea slug population would most likely be directly related to which of the following?

1. A) An increase in the eelgrass population
2. B) The introduction of nonnative invertebrates
3. C) A decrease in algae availability
4. D) A decrease in the crab population

1. D) A decrease in the crab population

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

A)The population decreased in size as a result of a loss of genetic diversity.

B)The population decreased in size as a result of habitat loss.

C)The population lost genetic diversity as a result of a bottleneck effect.

D)The population lost genetic diversity as a result of the founder effect.

C)The population lost genetic diversity as a result of a bottleneck effect.

1. Scientists studying a wild population of mantled howler monkeys found the average birth rate to be 0.22 and the average death rate to be 0.12. At the start of the study, the population consisted of 13

monkeys.

Assuming no immigration or emigration, which of the following best describes the change in population size that will occur over the next year

• The population will increase because more monkeys are being born each year than are dying.

• The population will increase because more monkeys are being born each year than are dying.

1. In the early 1970s, researchers hypothesized that carbon was the limiting nutrient in many aquatic ecosystems. To test this hypothesis, the researchers divided a small lake in two roughly equal halves with an impermeable curtain that was fastened and sealed to the bedrock of the lake. Beginning in 1971 the researchers treated one side of the lake with sucrose and the other side with both sucrose and phosphate. From 1971 to 1983 the researchers monitored the phytoplankton biomass in both parts of the lake. The results are shown in Figure 1.

Which of the following claims is best supported by the data?

• Phosphate was a limiting factor for phytoplankton in the lake.

• Phosphate was a limiting factor for phytoplankton in the lake.

1. Wolves, once native to Yellowstone National Park, were hunted to the point of complete extinction in the park. As a result, the elk population in the park flourished, putting extra demands on the carrying capacity of the park. Many other species, such as certain trees and beavers, were negatively affected by the increase in elk.

Years later, wolves were reintroduced into the park. While the elk population decreased after the wolves returned, the beaver and songbird populations began to increase as did the populations of various plant species.

Which of the following best explains how wolves are a keystone species in this ecosystem?

• Wolves help balance the population sizes of other species, allowing more species to thrive in the wolves' presence than in their absence.

• Wolves help balance the population sizes of other species, allowing more species to thrive in the wolves' presence than in their absence.

1. Which of the following treatments would have been the best control treatment for the experiment?

1. A small pool of the lake water maintained in a controlled laboratory environment
2. A different lake that was treated with sucrose and phosphate
3. An untreated section of the lake
4. A section of the lake that was treated with phosphate but not sucrose

1. An untreated section of the lake

1. The average growth rate of the phytoplankton population from 1971 to 1975 in the side of the lake treated with sucrose and phosphate is closest to which of the following?

1. 6,000 (mg/m3)/year
2. 1,000 (mg/m3)/year
3. 125 (mg/m3)/year
4. 1,500 (mg/m3)/year

1. 1,500 (mg/m3)/year

1. Which of the following was most likely a direct consequence of the addition of phosphate to the lake?

1. The amount of energy available to consumers in the lake increased
2. The amount of biomass in the first trophic level decreased.
3. The amount of energy available to producers in the lake increased.
4. The amount of biomass in the second trophic level decreased.

1. The amount of energy available to consumers in the lake increased