Do we live in a largely top-down regulated world?

Based on a review of mostly recent literature for a public lecture, the question is discussed whether we live in a largely "top-down" regulated world rather than one formed "bottom-up" by the resources for plant and animal growth. Of course, the top-down mechanism is predicated by bottom-up production, especially by the plants. Examples for the effects of grazing and predation for the land and the open sea, but including coral reefs, are discussed. The answer to the question posed by the title is affirmative. Ecosystems altered by man and urgent needs for marine conservation are briefly treated.