ABSTRACT

DISPERSAL AND PERSISTENCE OF PREDATOR-PREY INTERACTIONS:
AN EXPERIMENTAL LABORATORY TEST OF TWO ALTERNATIVE MECHANISMS

by
Robert Richard Glesener

Chairman:  John H. Vandermeer
     The mechanisms underlying an increased persistence of predator-prey interactions in complex laboratory environments are examined and found to correspond to independently derived theoretical models incorporating dispersal rates and spatial heterogeneity.   A method is outlined whereby these factors can be isolated and independently varied in laboratory experiments with Paramecium (prey) and Didinium (predator).  It was demonstrated that predator and prey populations unable to coexist locally could persist regionally if the degree of interhabitat exchange, particularly that of the predator, was low.  This ability to persist was shown to be further increased, perhaps indefinitely, in so-called heterogeneous environments where some habitats were relatively inaccessible.  The prey population became concentrated in these hard to find habitats and it was suggested that the increased persistence was, in part, associated with Type III predator functional response to prey availability.
     In most experiments that persisted for any length of time, cycles were observed in both population density and the number of habitats occupied.  These oscillations varied in a consistent way over the various treatment levels although sample sizes are small.  Both reduced predator dispersal and increased heterogeneity (variance of habitat accessibilities) reduce their magnitude.  In the more heterogeneous environments, predator and prey cycles became increasingly dissimilar with the role the dispersal events becoming more and more clear.  This was reflected by a greater similarity between the periodic behavior of the population size for a given species with that of habitats occupied rather than population size for the interacting species.  One consequence of this effect was that the reduce oscillations of these latter experiments could be partitioned into a frequency component for prey and an amplitude one for the predator.  The possible implications of these results to the interpretation of field data are discussed.
 
 

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