Explore AP Biology 8.6.B questions on how adding or removing species, producers, or keystone components changes food webs, biodiversity, resilience, and ecosystem structure.
Buffelgrass, an invasive grass species in southwestern desert ecosystems, is threatening the
saguaro cactus, a keystone species in these ecosystems. Buffelgrass is drought-tolerant and can
survive wildfires. However, the dry buffelgrass also acts as fuel for wildfires, causing the fires
to be more severe. Older saguaro cacti can survive wildfires; however, many of the young cacti
cannot.
Scientists conducted an experiment to determine whether they could control the abundance
of the buffelgrass population. The scientists identified several native grass species that, when
grown with buffelgrass, might reduce the abundance of buffelgrass. They grew buffelgrass
in the presence of several different native grass species in greenhouses, in 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.
Describe the effect that removing a keystone species will have on an ecosystem.
Describe the effect that removing a keystone species will have on an ecosystem.
Examples of acceptable responses may include the following:
- (Removal of a keystone species) reduces biodiversity/diversity/resilience (of the ecosystem).
1 point