Provide your best answer for the following question. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The question is: What is an example that ecosystems are an interconnected world?
animals' numbers decreasing when food decreases
A butterfly pollinating a flower, which in turn provides food for a bee, which then collects nectar to make honey for bears