The Living World: Ecosystems unit test
A test on this unit alone, marked as a percentage and a letter grade — for the test your class is actually sitting, rather than for May. Answer everything, then submit once: seeing the answer to question 3 before attempting question 4 makes the final percentage meaningless.
Nitrification and denitrification
Nitrogen fixation
Ammonification
Terrestrial biomes
Biomass pyramid inversions
Detritivores vs decomposers
Food chain vs food web
Predation, competition and resource partitioning
Fast carbon pool vs slow carbon pool
Reading a climatogram
Trophic levels and the 10% rule
Producer and primary productivity
Short answer 1. Define or explain: How humans doubled the nitrogen cycle
3 ptsShort answer 2. Define or explain: Competitive exclusion principle
3 ptsShort answer 3. Define or explain: Sulfur cycle
3 ptsShort answer 4. Define or explain: Where the lost 90% goes
3 ptsFree response
10 ptsDESIGN AN INVESTIGATION. Chickadees are a K-selected species of bird that eat insects and spiders. Spiders consume insects, and many insects consume plants, as in the food chain: Plants → Insects → Spiders. Chickadee habitat includes forests and residential yards; residential yards often contain nonnative plants introduced by humans. Scientists measured the average number of insects and spiders in relation to the percentage of nonnative plants (FIGURE 1), and the chickadees' average population growth rate (FIGURE 2). FIGURE 1 — Average number of individuals per sample against percent nonnative plants (0–100%). Spiders decline steadily from about 2.5 at low percentages to about 1.0 at 100%; at 25% nonnative plants the spider value is 2.0. Insects decline from about 1.2 to nearly 0 across the same range. FIGURE 2 — Chickadee population growth rate (r) against percent nonnative plants. The curve starts near r = +0.15 at 0%, crosses r = 0 (the dashed "replacement level" line) at roughly 25%, and falls to about r = −0.45 at 100%. For parts F and G: a group of students investigated ant biodiversity at two sites near their school — a frequently mowed urban park and an unmowed grassland. They loaded 10 identical baited traps per site, placed them randomly, collected them after 24 hours, and counted the number of different ant species per trap (species richness). Their results: the urban park contained species A, B and C; the grassland contained species A, B, C, D and E (species F was found at neither site).
A. Describe one reproductive strategy used by a K-selected species such as the chickadee.
B. Based on the information provided, explain how a decrease in spider populations could affect a lower trophic level.
C. Based on the data in Figure 1, identify the number of spiders per sample at 25% nonnative plants.
D. Based on the data in Figure 1, describe the trend in the number of insects per sample in relation to the percentage of nonnative plants.
E. Scientists hypothesized that the population of chickadees would be stable or growing with fewer than 25% nonnative plants. Describe one way that the data in Figure 2 support this hypothesis.
F(i). Identify a likely scientific question for the students’ investigation of ant diversity.
F(ii). Identify the dependent variable in the students’ investigation.
G(i). Explain why the ant community of the unmowed grassland would be more likely to recover from a disturbance, such as a flood or fire, than the ant community in the mowed urban park would.
G(ii). Explain how the results of the investigation could have been altered if students had measured ant biodiversity at a paved playground rather than in the grassland.
H. Habitat fragmentation has impacts on a variety of species, and paved roads can lead to it. Describe one effect that a paved road in a forest can have on animal species such as deer or bears.