Spatial interaction models: from human geography to plant-herhivore interactions

Authors

  • S. P. Oom,

  • A. J. Hester,

  • D. A. Elston,

  • C. J. Legg


S. P. Oom and A. J. Hester, Macaulay Inst., Craigiebuckler, Aberdeen, UK AB15 8QH (s.oom@macaulay.ac.uk). –D. A. Elston, Biomathematics and Statistics Scotland, Environmental Modelling Unit, Macaulay Inst., Craigiebuckler, Aberdeen, UK AB15 8QH. –C. J. Legg, Inst. of Ecology and Resource Management, The Univ. of Edinburgh, Darwin Building, The King's Buildings, Mayfield Road, Edinburgh, UK EH9 3JU.

Abstract

The spatial pattern of defoliation by mammalian herbivores across vegetation mosaics bas been frequently discussed, but rarely spatially quantified. Here we considered the role of plant-herbivore interactions in determining the spatial distribution of shrub defoliation by a large mammalian herbivore across a grass-shrub mosaic.
We investigated the spatial pattern of heather defoliation by sheep in heather-grass mosaics. Heather-grass mosaics are two-phased vegetation mosaics, in which a spatially localized plant community (grass) fulfils nutritional needs, whilst a spatially extensive plant community (heather) meets energy requirements but is nutritionally marginal.
We used a spatial analysis method, originating from human geography, to show that heather defoliation was not spread across the mosaic homogeneously, but that the spatial pattern was determined by geometric characteristics of the mosaic, grazing intensity, and the contrast between preferred and less preferred communities.
The spatial analysis method proved to be a powerful tool to describe the spatial pattern of shrub defoliation. Applications of the method are explored and the implications of the spatial distribution of shrub defoliation are discussed.

Ancillary