GRE Subject Test: Biology : Understanding Environmental Impacts
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Example Questions
Example Question #2 : Ecological Succession
Which of the following provides the most accurate example of primary succession?
Lichen and grass communities establishing themselves on a recently-formed island, resulting from an uplift in the ocean bedrock
Coral reef and aquatic wildlife communities that have re-established themselves in regions of the South Pacific that were evacuated following the nuclear tests conducted by the U.S. military
Seedlings establishing themselves in a heavily logged area where the seed-tree cutting method was employed
Lichens re-establish themselves on rocks and shallow soil beds following a tundra fire
Native grass communities forming after a wildfire burned through a meadow/woodland ecosystem
Lichen and grass communities establishing themselves on a recently-formed island, resulting from an uplift in the ocean bedrock
Primary succession is characterized by plants establishing themselves in areas that were initially devoid of soil (usually bedrock). Grasses establishing themselves on a newly-formed island that is mostly bedrock is the best fit for this definition.
Example Question #4 : Ecological Succession
Which of the following would NOT contribute significantly to primary succession?
Wind-carried soil particles and nutrients
Feces from wildlife populations that occupy the region
Soil nutrients deposited by a nearby river
Pre-existing nitrogen-fixing plant communities
The time-consuming process of weathering the bedrock into smaller particles
Pre-existing nitrogen-fixing plant communities
Primary succession is characterized by pioneer species establishing themselves in areas that are predominantly bedrock and devoid of organic material. The formation of organic material in these areas typically occurs with the accumulation of wind-carried soil erosion, nutrients deposited by flowing bodies of water, and erosion of bedrock. Wildlife populations are also a significant contributor of soil nutrients, with feces being rich in both nitrogen and phosphorus. In contrast, pre-existing nitrogen-fixing plants (or any pre-existing plant communities) are uncommon to nonexistent in an area with no established soil system.
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