Final answer:
Variation within an ecosystem is desirable because it enhances biodiversity, which increases ecosystem productivity, stability, and resilience to disturbances. It provides various ecosystem services essential for the environment and human well-being.
Step-by-step explanation:
Variation within an ecosystem is indeed desirable. This is because biodiversity contributes positively to ecosystem productivity and stability by providing a wider range of functions and services, such as nutrient cycling and energy flow. Diverse ecosystems are thought to be more robust in the face of disturbances and less susceptible to fluctuations in conditions. For example, during a drought, ecosystems with a variety of species maintain productivity far better than less diverse systems.
There are key effects of variation on stability and function in ecosystems. First, the presence of a variety of species increases the chances that some will be exceptionally productive (sampling-competition effect). Second, different species often utilize resources in complementary ways, improving conditions for one another (facilitation effect). In the case of guppies, if they possess genetic variation, they can contribute to the ecosystem's resilience by adapting to changing conditions, thereby supporting the stability of the ecosystem they inhabit.
Moreover, local biodiversity is also crucial for delivering ecosystem services such as air and water purification, waste detoxification, soil fertility maintenance, and pollination, all of which are essential for human well-being. Thus, promoting diversity within ecosystems is not only beneficial for the environment but also for the economies and health of human communities dependent on these critical ecosystem services.