Here's why:

* Ecology is the branch of biology that focuses on the interactions between organisms and their environment. This includes:

* How organisms interact with each other (competition, predation, etc.)

* How organisms interact with the physical environment (temperature, water availability, etc.)

* The flow of energy and nutrients through ecosystems.

While other levels of biology are involved (like genetics, physiology, and behavior), the core focus here is on the interactions within an ecosystem, which falls under the domain of ecology.