For in a sense images do indeed behave like species or life-forms. They come into being, reproduce, thrive, and propogate from region to region and century to century -- or else they fail and become extinct. In order to survive and endure, images require ecological niches or ecosystems that provide hospitable habitats or environments for their future growth: such as workshops, ataliers, and academies, as well as related ecosystems for display -- churches, courts, museums, galleries. In our time they require the massive ecosystem of reproductive media: books, newspapers, magazines, television, Internet.

Though Bryson doesn't mention it by name, the definition provided in the second sentance is similar to Richard Dawkins' notion of the behavior of a 'meme' -- a transmitted idea. The Wikipedia entry is illuminating.