Problem 12 - Campbell Biology

Question

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

Step-by-Step Solution

Answer

Kangaroo rats help maintain wildflower diversity by feeding on the most competitive species. Supporting evidence would include observing feeding habits and verifying competitive resource use.

Step 1: Understand the Experiment

Comprehend the details of the experiment involving two plots with sagebrush plants and wildflowers. One plot is fenced to exclude kangaroo rats, while the control plot remains open.

Step 2: Identify Key Observations

Note the key observations: in the fenced plot, four wildflower species disappeared, one species became abundant, and the control plot's species diversity remained constant.

Step 3: Hypothesize Based on Community Ecology

Based on the principles of community ecology, propose a hypothesis. The likely hypothesis is that kangaroo rats play a crucial role in maintaining the species diversity of wildflowers by feeding on the most competitive species, thereby preventing it from outcompeting the others.

Step 4: Predict Additional Evidence

Determine what additional evidence would support the hypothesis. This could include: finding that the abundant species in the fenced plot is particularly competitive for resources, observing the feeding habits of kangaroo rats to confirm they prefer the competitive species, and replicating the experiment in other areas to see if the same results occur.

Key Concepts

species diversity

Species diversity refers to the variety of different species within a particular area. It encompasses both species richness, which is the number of different species, and species evenness, which accounts for the abundance of each species.
In our ecologist's experiment, the control plot initially had five species of wildflowers, showing a certain level of species diversity.
When the plot was fenced to exclude kangaroo rats, four of these species disappeared, leading to a significant drop in species diversity.
This tells us that species diversity can be highly influenced by the presence or absence of certain animals within an ecosystem.

• Species richness: Initially, there were five different species of wildflowers.
• Species evenness: These species were in roughly equal numbers before the exclusion of kangaroo rats.
• Species loss: Four species disappearing indicates a severe drop in diversity.

Changes in species diversity can offer insights into the underlying ecological processes and the roles different species play within a community.

competitive exclusion

The principle of competitive exclusion states that two species competing for the same limited resources cannot coexist at constant population values. One will always outcompete the other, leading to the local extinction of the lesser competitor.
This principle can help explain why four wildflower species disappeared from the fenced plot in our ecologist’s experiment.

Without kangaroo rats, which probably ate the seeds of the most competitive wildflower species, this dominant species could thrive uncontested.
Consequently, it outcompeted the other four wildflower species for resources like nutrients, water, and sunlight, leading to their disappearance.

• Resource competition: With the removal of a predator, competition for resources increased.
• Dominant species: The highly competitive wildflower species became more abundant without predation pressure.
• Species extinction: The less competitive species could not survive the increased competition.

Competitive exclusion illustrates the importance of natural predators in maintaining balanced and diverse ecosystems.

kangaroo rats interaction

Kangaroo rats play a pivotal role in desert ecosystems, particularly through their interactions with plant species. In our experiment, they influenced the species diversity of wildflowers.
These small, seed-eating mammals likely feed on the seeds of the most competitive wildflower species, preventing it from dominating the ecosystem.

When kangaroo rats were excluded by a fence, this competitive species could grow abundantly and outcompete other species for essential resources.
Hence, the presence of kangaroo rats is crucial for regulating plant competition and maintaining species diversity.

• Seed predation: Kangaroo rats consume seeds, controlling wildflower population dynamics.
• Competitive suppression: By eating the seeds of competitive species, they prevent any one species from becoming too dominant.
• Biodiversity maintenance: Their activities ensure a variety of wildflowers can coexist.

This interaction highlights the intricate relationships in an ecosystem and how the removal of one species, even a small one, can have significant ecological repercussions.