Nearest-neighbour graphical analysis of spatial pattern and a test for competition in populations of singing crickets...

The most crowded individuals in a population often compete for space and develop a regular pattern of spacing. Such regularity is not normally recognized because it occurs within high-density regions of a populated area showing overall aggregation. Thus competition for space, as reflected by spatial pattern, often goes undetected when standard tests for spatial randomness are used. The test described in this paper makes use of truncated samples of nearest-neighbour distances arranged in ascending order, so that only the pattern of spacing of the most crowded individuals is analysed. This is the basis of Pielou's test (1962, 1977) for spatial competition. An advantage of the approach described is that the density of the most crowded individuals is determined graphically. The graphical method also provides a means for choosing an appropriate, non-arbitrary, truncation point for the test. The test was applied to two samples of singing crickets to demonstrate the procedure. The biological significance of the spacing patterns identified is discussed.