Here's why:

* Ecosystems encompass interactions: An ecosystem is a self-sustaining community of living organisms (biotic) and their non-living environment (abiotic) interacting together. This interaction is crucial for life to exist.

* Biodiversity at the core: Ecosystems are characterized by their unique biodiversity – the variety of life forms within them. This diversity contributes to the overall health and resilience of the biosphere.

* Interconnectedness: Ecosystems are not isolated. They are interconnected, forming a complex network of relationships across the biosphere.

While individual organisms are the building blocks of life, ecosystems are the fundamental units where life thrives and interacts with its environment.