Generalist and Specialist Natural Enemies in Insect Predator-Prey Interactions

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Abstract
(1) The dynamics of a predator-prey, or parasitoid-host, interaction are considered where the predator or parasitoid is a generalist whose population is buffered against changes in the particular prey being considered. (2) The interaction is then broadened to include, in addition, a specialist natural enemy, and three questions are examined within the framework. (i) Under what conditions can a specialist ''invade'' and persist in an existing generalist-prey interaction? (ii) How does the addition of the specialist natural enemy alter the prey''s population dynamics? (c) How does the relative timing of specialist and generalist in the prey''s life cycle affect the dynamics of the interaction? (3) The following conclusions emerge. (i) A specialist can invade and co-exist more easily if acting before the generalists in the prey''s life cycle. (ii) A three-species stable system can readily exist where the prey-generalist interaction alone would be unstable or have no equilibrium at all. (iii) In some cases the establishment of a specialist leads to higher prey populations than existed previously with only the generalist acting. (iv) In some cases, a variety of alternative stable states are possible, either alternating between two-species and three-species states, or between three-species states.