Biodiversity and Genetics
A forest contains several different species of trees, birds, and insects. However, all the trees belong to the same species and the tree species typically do not crossbreed with other trees or species. Which level of biodiversity is especially low among the trees?
genetic diversity
A community harvests timber, collects wild berries, and uses plants to produce medicine from a nearby forest. What category of ecosystem services do these resources represent?
provisioning services
Two islands are the same distance from the mainland, but Island A is much larger than Island B. Based on island biogeography theory, which island would generally support more species, and why?
Island A, because larger islands generally provide more habitat types and resources and support larger populations, reducing extinction rates.
A glacier retreats, exposing bare rock with almost no developed soil. Lichens begin growing on the rock. Which type of succession is occurring, and what makes this process different from succession after a typical forest fire?
Primary succession; it begins where developed soil is absent, whereas a typical forest fire leaves soil behind and is followed by secondary succession.
A student observes that plants capture sunlight and use it to produce glucose. What process converts light energy into chemical energy stored in organic molecules?
What is photosynthesis?
Forest A contains 15 species of trees, while Forest B contains 8 species of trees. Assuming all other information is unavailable, which forest has greater species richness, and what does this measurement tell us?
Forest A; species richness measures the number of different species present, not their relative abundance.
Farmers notice that crop yields decline after the local bee population decreases. Explain how the loss of this ecosystem service can affect both agricultural production and food availability.
Reduced pollination can lower the reproductive success and yields of crops that depend on animal pollinators, decreasing food production and potentially increasing prices.
An island bird species feeds almost exclusively on one type of native insect. An invasive insect arrives and competes with the native insect for resources. Why might the bird be more vulnerable to this change than a bird with a varied diet?
The specialist bird has a narrow niche and fewer alternative food sources, so the loss of its preferred prey could cause its population to decline.
Lichens colonize bare rock and gradually contribute to soil formation. Explain why these organisms are important for the establishment of later plant communities.
Lichens weather rock and contribute organic matter as they grow and decompose, helping form soil and making it possible for other plants to establish.
Producers in a grassland store 10,000 kcal of energy. Assuming the 10% rule, approximately how much energy would be available to secondary consumers?
100 kcal (10,000 → 1,000 → 100).
A wildfire kills 90% of a rabbit population. The surviving rabbits happen to carry only a small portion of the original population's genetic variation. Which evolutionary mechanism has occurred, and what long-term risk might the population face?
The bottleneck effect; reduced genetic diversity may limit the population's ability to adapt to environmental changes or disease.
A town restores a wetland instead of building a concrete flood-control channel. During heavy rainfall, the wetland absorbs and stores water, reducing downstream flooding. Identify the ecosystem service and explain how it benefits the town.
A regulating service; the wetland stores and slows the movement of water, reducing flood damage and potentially lowering infrastructure costs.
A fish species survives between 10°C and 30°C, but its growth and reproduction decline sharply below 15°C and above 25°C. If the water temperature rises to 28°C, how would you describe the fish's condition, and why could its population decline even though it has not exceeded its survival limit?
The fish is experiencing physiological stress within its tolerance range; reduced growth and reproduction can decrease population size even before conditions become lethal.
A farmer abandons a field that has been cultivated for decades. Grasses appear first, followed by shrubs and eventually young trees. Identify the type of succession and explain why it can proceed faster than succession on bare rock.
Secondary succession; existing soil, nutrients, microorganisms, seeds, and roots can help plants reestablish more quickly.
A lake receives excess nitrogen and phosphorus from agricultural runoff. Explain how these nutrients can cause fish populations to decline, even though they initially increase algae growth.
Nutrient enrichment causes algal blooms. When algae die, decomposers consume oxygen as they break down the organic matter, potentially causing hypoxia and fish kills.
A small, isolated population of wolves begins mating with close relatives. After several generations, more offspring have genetic disorders and lower reproductive success. Identify the process responsible and explain why it reduces population fitness.
Inbreeding depression; mating between relatives increases the likelihood that harmful recessive alleles will be expressed, reducing survival or reproduction.
A national park attracts visitors who hike, photograph wildlife, and participate in nature-based educational programs. If the park's wildlife populations decline, which category of ecosystem services may be reduced, and why?
Cultural services; wildlife viewing, recreation, education, and aesthetic experiences may become less valuable or accessible.
A population of insects contains a mutation that allows some individuals to tolerate a new pesticide. After repeated pesticide applications, the resistant insects make up a larger proportion of the population. Explain how mutation and natural selection contributed to this change.
Mutation introduced genetic variation. Pesticide exposure favored resistant individuals, which survived and reproduced more successfully, increasing the frequency of resistance alleles over generations.
After a disturbance, grasses establish first, followed by shrubs and trees. Explain how changes in shade and competition for resources can cause the dominant plant species to change over time.
Early colonizers often grow quickly in open conditions. As vegetation develops, shade and competition for light, water, and nutrients increase, favoring species better adapted to the new conditions.
Two ecosystems have the same gross primary productivity (GPP), but Ecosystem A has a much higher rate of producer respiration than Ecosystem B. Which ecosystem has the higher net primary productivity (NPP), and why?
Ecosystem B, because NPP = GPP − respiration. Less energy used in producer respiration means more energy remains for growth and reproduction.
Two wetlands contain the same number of species, but Wetland B is almost completely dominated by a single species. Describe the Species Richness and Evenness of the two and explain Which wetland would likely be more resilient if one species disappeared?
Wetland A and Wetland B have the same species richness, but Wetland A has more evenness than B. Wetland A will be more resilient because it have more species diversity.
A developer proposes draining a wetland to build a shopping center. The project would generate tax revenue and jobs, but the wetland currently filters water and reduces flooding. Explain why a decision based only on the land's market price could lead to an environmentally harmful outcome.
The market price may exclude the economic value of water filtration and flood regulation. If these external benefits are ignored, the development may appear more beneficial than it truly is to society.
A new highway divides a large forest into several smaller patches. Over time, scientists observe declining populations of interior-forest birds and increasing numbers of disturbance-tolerant species near the road. Explain how natural selection could lead to this creating a new species
Allopatric Speciation occurs, and populations are isolated, this can lead to genetic drift and new species forming.
A recovering forest gains biomass and develops more complex vegetation over several decades. However, scientists find that its net primary productivity eventually levels off. Explain why biomass can continue to accumulate during succession even if net primary productivity does not continually increase.
Biomass is the amount of living material accumulated, while net primary productivity (NPP) is the rate at which producers store energy as new biomass after respiration. A forest can retain accumulated biomass even when annual NPP levels off or declines as respiration and maintenance costs increase.
A region experiences widespread deforestation. Predict how this could affect both the carbon cycle and the water cycle in the region.
Carbon storage and carbon uptake by photosynthesis decrease, while carbon released through burning or decomposition may increase atmospheric CO₂. Transpiration and interception of rainfall also decrease, potentially increasing surface runoff, erosion, and flood risk while reducing local atmospheric moisture.