Byers, J.A. 1992. Grid cell contour mapping of point
densities: bark beetle attacks, fallen pine shoots,
and infested trees. Oikos 63:233-243.
A method for calculating and displaying patterns of local density of plants
and animals is presented for use with personal computers. The algorithm, coded
in the BASIC programming language, uses x,y spatial point coordinates of
organisms to calculate and display a coloured or shaded map of local densities
within grid cells. The radius of the local areas about the grid points within
which densities are calculated, the density-class interval boundaries when
colouring the cells, and the grid resolution can all be varied to facilitate
exploratory investigations. Contour density maps resulting from the method are
shown for an attack distribution of the bark beetle Pityogenes chalcographus
on Norway spruce bark, Picea abies, and for a random distribution. Minimum
allowed distance analysis of the attack distribution indicated a distance
of behavioural avoidance of attack sites of about 1.6 cm for the bark beetle.
Density maps of different local radii are also shown for Norway spruce trees
killed by the bark beetle Ips typographus near Trebon, Czechoslovakia.
Density maps using different local radii and density increments are presented
for aggregated patterns of fallen Scots pine shoots, Pinus sylvestris, infested
by Tomicus minor bark beetles in southern Sweden. A method is presented for
statistical comparison of randomly-generated spatial point data with natural
data by using Chi-square analysis of the histograms of differently coloured
Download software: CONT-DEN.ZIPChemical Ecology