English

Dynamics of populations. : Proceedings of the Advanced Study Institute on Dynamics of numbers in populations, Oosterbeek, the Netherlands, 7-18 September 1970

The following question is posed and discussed. Under what environmental conditions will the action of natural enemies prevent competitive exclusion between species of their prey? My studies on marine animal populations and rain forest trees both suggest that fluctuations in the physical environment and subsequent effects on the supply of resources reduce the effectiveness of natural enemies and allow the prey to increase to sufficiently high densities that they compete for resources. Fluctuations in weather may (1) reduce the populations of enemies more than their prey, (2) allow the prey to get a head start after an unfavourable season and (3) reduce the degree of specialization of the enemies. With lesser amplitude and/or more regularity of fluctuations, natural enemies are more effective in preventing competition. However, these conditions also lead to stronger defenses by the prey and greater effectiveness of the secondary enemies attacking the ones in question. In regions of very favorable physical conditions, the only defense against natural enemies seems to be rarity and widely scattered distributions, which together preclude competitive exclusion. · 611 pages ; 25 cm · Incl

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