Question

An ecologist studying plants in the desert performed the following experiment. She staked out two identical plots, which included a few sagebrush plants and numerous small, annual wildflowers. She found the same five wildflower species in roughly equal numbers on both plots. She then enclosed one of the plots with a fence to keep out kangaroo rats, the most common grain-eaters of the area. After two years, to her surprise, four of the wildflower species were no longer present in the fenced plot, but one species had increased dramatically. The control plot had not changed. Using the principles of ecology, propose a hypothesis to explain her results. What additional evidence would support your hypothesis?

Answer 1

An ecologist studying plants in the desert performed the following experiment. She staked out two identical plots, which included a few sagebrush plants and numerous small, annual wildflowers. She found the same five wildflower species in roughly equal numbers on both plots. She then enclosed one of the plots with a fence to keep out kangaroo rats, the most common grain-eaters of the area. After two years, to her surprise, four of the wildflower species were no longer present in the fenced plot, but one species had increased dramatically. The control plot had not changed. Using the principles of ecology, propose a hypothesis to explain her results.

Explanation:

• This example highlights the impact of plant predation on species selection. In the fenced off plot animal predation is not a factor on plant selection.
• In this case plants will compete for resources only with each other and in this case one plant had a selective advantage over the other 3 species of plants. In the plot exposed to animal predation the ratio of the four species is equal.
• This is likely do to an increased preference of animals for the plant species that dominates in the fenced off plot and/or anti-animal predation tactics by the other three species.

a.Hypothesis: kangaroo rats are keystone species

-Reintroduce kangaroo rats (and the other locally extinct species)

-Should observe equilibrium re-established

b.Hypothesis: kangaroo rats exert top-down control on community

-Reintroduce kangaroo rats (and other locally extinct species)

-Increase kangaroo rat population in other plot

-Decrease (but don't eliminate) kangaroo rat population in other plot

c.Hypothesis: Locally extinct species inferiorly competed with the extant species of plant

-Remove surviving species from other plot (and remove kangaroo rat population)