Gianino, Jacques Stanley; (1990) The effects of spatial heterogeneity on experimental populations. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The effect of spatial heterogeneity on a number of population interactions was investigated. Populations consisting of 2 artificial prey species differing in colour were presented to wild birds in two spatial arrangements (random or aggregated). Although the overall prey frequencies and densities were the same in both arrangements, rare prey suffered significantly less predation when randomly mixed among a more common prey species than when aggregated with conspecifics. Spatial patterning as well as frequency may be an important component of apostatic selection. This may have an important effect on competition between prey species at the local (ie, within-patch) spatial scale. Spatial heterogeneity in light conditions had a significant effect on interspecific and intraspecific interactions in Drosophila. The more photopositive D. simulans dispersed to brighter areas than D. melanogaster both in the field and in the laboratory, where in heterogeneously lit "RW" population cages, species overlap was less than in the homogeneously lit cages. This reduced interspecific competition but did not lead to long-term coexistence. Light preferences of samples from the RW cages changed during the experiment and were more divergent than samples from the homogeneously lit cages. Light intensity is not an arbitary factor because in homogeneously lit bright white light ("WW") cages there was coexistence between D. simulans and white-eye D. melanogaster (which is effectively blinded in bright light). Light preferences in Drosophila are modifiable by experience. Flies had a significantly greater preference for the light conditions to which they had already been exposed. This learned component increases the flexibility of D. melanogaster to exploit its cosmopolitan (ie, unpredictable) niche. D. simulans, although it has a more restricted and photopositive niche, also has this flexibility. The adaptiveness of this is discussed.

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