Ecology: energy and matter

[polaris93]

Each species on the Earth is like a tiny piece in a four-dimensional jigsaw, interlocking with other species, and a tiny conducting part of the energy flowing through the living world. But what if species are also stacked together like a giant house of cards, each supporting other species in some small (or large) way so that if enough species are kicked out of place by their extinction, the entire house falls down? Did that happen at the end of the Paleozoic? Did enough species get killed off to bring down a sudden torrent of extinction, removing 90 percent of the Earth's creatures? And how far from that cliff are we today?

-- Peter D. Ward, Rivers in Time: The Search for Clues to Earth's Mass Extinctions, p. 82