Pests co-operate across species so barriers that stop one admit another

Evidence

Just as there is honor among thieves, so there is solidarity and co-operation among plant and animal pests. Where one pest is stopped by natural barriers, another arrives to breach the same wall by a new approach. In the end every region and every resource get their quota of uninvited ecological guests. — Aldo Leopold, A Sand County Almanac, 545

Categorization

• DEFINE: Articulates the pattern by which invasions succeed each other, relevant to land-use reading.