Offensive-Defensive Interactions between Herbivores and Plants: Their Relevance in Herbivore Population Dynamics and Ecological Theory

Abstract

A consideration of known defensive attributes of plants, and others that can be reasonably postulated, leads to the description of 2 alternative offensive strategies of herbivores, termed stealth and opportunism, to counter plant defenses. Stealthy herbivores display adaptations to minimize damage and defensive responses of their food plants. Opportunists take advantage of circumstance, such as physical stress and loss of acquired resistance of food plants, that impair plant defensive capability. Opportunists themselves display adaptations, such as mass-attack behavior, that stress food plants. Herbivore species with low, relatively invariant population levels may be stealthy; those with variable population levels may be opportunistic. Phase changes in herbivores may be the result of transition between the 2 strategies. Interactions within and among species of herbivores are better understood in terms of interference and facilitation than in terms of competition.