7 - Spatial predator–prey systems

Summary

Gause's conclusion that a predator–prey system is inherently self-annihilating without some outside interference such as immigration (Section 6.1.2) was questioned by Huffaker (1958). He claimed that Gause had used too simple a microcosm, and so set out to learn whether an adequately large and complex experiment could be constructed in which the predator–prey relation would not be self-exterminating. We therefore now ask, ‘What will be the effect, if any, of accepting that individuals rarely mix homogeneously over the whole site but that they develop instead within separate sub-regions?’.

This question is an old one, for as early as 1927 A. J. Nicholson asked Bailey (1931) to investigate mathematically the abundance of two species which interact in the following manner. Members of the host species lay eggs and then die. These eggs are then searched for by members of the parasite species who traverse at random a specific area during their lifetime. Host eggs which survive this search develop into adults; those that are found are attacked and a parasite egg is deposited on them. New generations then repeat this process indefinitely.

Huffaker's experiments

Huffaker selected the six-spotted mite, Eotetranychus sexmaculatus, as the prey species and the predatory mite, Typhlodromus occidentalis, as the predator species because earlier observations had revealed this Typhlodromus as being a voracious enemy of the six-spotted mite. It was known to develop in great numbers on oranges infested with the prey species, to destroy essentially the entire infestation, and then to die en masse.