Which of the following biological controls is characterized by competition among organisms?

The correct answer identifies competition among organisms as a form of biological control, specifically through desirable vegetation. In this context, competition occurs when different plant species vie for the same resources, such as nutrients, water, and light. When desirable vegetation is strategically planted in an ecosystem, it can outcompete unwanted or invasive species, thereby helping to maintain the health of that ecosystem.

This biological control method relies on the natural competitive dynamics of plant communities. By enhancing the population of certain desirable plants, it's possible to suppress the growth of less desirable species, promoting biodiversity and ecological balance. This approach is often more environmentally friendly than chemical control methods and can lead to long-term management of undesired species in a sustainable manner.

In contrast, predators, parasites, and pathogens involve direct interactions where one organism feeds on or harms another, rather than competing for resources. While these forms also play critical roles in ecological balance, they do not illustrate competition in the same way that desirable vegetation does.