Download (20MB) - Repository@Napier

CHAPTER 2
THE SMALL- To MESO-SCALE SPATIAL DISTRIBUTION OF
MARINE BENTHIC INVERTEBRATES ON DRUM SANDS, WITH
PARTICULAR REFERENCE TO PYGOSPIO ELEGANS
INTRODUCTION
Spatial heterogeneity is a fundamental characteristic of animal and plant populations
(Connell, 1963; Taylor, 1984), as well as the physical environment which the
organisms inhabit. The assessment of the spatial variability of some variable, e.g.,
abundance of an organism, is often the starting point from which questions and
hypotheses about important processes on the population or community level are
generated (Andrew and Mapstone, 1987; Myers and Giller, 1988; Levin, 1992).
Furthermore, Hall et al. (1993) recommended that an analysis of spatial pattern in
both field experiments and survey programmes should be a priority for benthic
ecologists.
There are numerous techniques available for the identification of spatial pattern, such
as spectral analysis (Renshaw and Ford, 1984), quadrat-variance (Greig-Smith, 1952),
spatial autocorrelation analysis (Cliff and Ord, 1973; Legendre and Fortin, 1989),
dispersion indices (Morisita, 1962; Elliot, 1977; Krebs, 1989) and nested hierarchical
analysis of variance (Morrisey et al., 1992; Lindegarth et al., 1995). These different
techniques all provide different information on spatial pattern, require different
sampling strategies and are more or less suitable at different spatial scales. For
example, while a hierarchical nested analysis of variance requires a nested sampling
design and is most suitable for determining large-scale (100m-kms) variation
(Lindegarth et al., 1995), spatial autocorrelation analysis, which requires a more
regular sampling design (Thrush et al., 1989) determines the underlying spatial
structure and is more suitable for smaller-scale investigations (Morrisey et al., 1992).
Methods such as Greig-Smith's (1952) quadrat-variance technique, or related
techniques such as the paired-quadrat variance (PQV) and two-term local quadrat
15