Ecology 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.
Ten percent rule
Logistic growth
Carrying capacity (K)
Symbiosis types
Aposematic coloration
Competitive exclusion principle
Simpson's diversity index
Trophic levels
Nitrogen fixation
Phosphorus cycle
Decomposers and detritivores
Primary vs secondary consumers
Short answer 1. Define or explain: Population growth rate
3 ptsShort answer 2. Define or explain: Biogeochemical cycling
3 ptsShort answer 3. Define or explain: Species richness vs evenness
3 ptsShort answer 4. Define or explain: Resource partitioning
3 ptsFree response
4 ptsBuffelgrass, an invasive grass in southwestern desert ecosystems, is threatening the saguaro cactus, a keystone species in those ecosystems. Buffelgrass is drought-tolerant and survives wildfires; the dry grass also acts as fuel, making fires more severe. Older saguaro cacti can survive wildfires, but many young cacti cannot. Scientists tested whether they could control the abundance of the buffelgrass population. They identified several native grass species that might reduce buffelgrass abundance when grown alongside it. They grew buffelgrass in the presence of several different native grass species in greenhouses, under either nondrought (watered every 3 days) or drought (watered every 9 days) conditions. After twelve weeks they measured the height and dry weight of the buffelgrass in each treatment group.
(a) Describe the effect that removing a keystone species will have on an ecosystem.
(b) Identify a control group the scientists should include in their experiment.
(c) State the null hypothesis of the experiment in which buffelgrass is grown in the presence of native grass species.
(d) Scientists have found that the population growth rates of native grasses are much slower than the population growth rate of buffelgrass following a wildfire. The scientists claim that wildfires will therefore increase the abundance of buffelgrass plants in the ecosystem. Based on the information given, justify the scientists’ claim.