co-evolution
When taxa have an ecological relationship so that they affect each other’s evolution. If the relationship is mutually beneficial they may become reliant on each other, or in a host-parasite relationship the evolution of a slight competitive advantage to one leads to natural selection in the other so that virulence and resistance broadly keep pace with each other. When these gradual step-wise processes continue in regions isolated from each other a native host may be wiped out by an alien parasite, or it may spread uncontrollably..
This definition is abridged from A – Z of tree terms: A companion to British arboriculture.
Read the preface. Order the book.