Waterstriders data. Three independent replications of a point pattern formed by insects.
The territorial behaviour of an insect group called waterstriders was studied in a series of laboratory experiments by Dr Matti Nummelin (University of Helskini). The data were analysed in the pioneering PhD thesis of Antti Penttinen (1984).
a list of three point patterns. Each point pattern gives
the locations of larvae of the waterstrider
Limnoporus (Gerris) rufoscutellatus (larval stage V)
in a homogeneous area about 48 cm square. The point
patterns can be assumed to be independent.
It is known that this species of waterstriders exhibits territorialism at older larvae stages and at the adult stage. Therefore, if any deviation from Complete Spatial Randomness exists in these three point patterns, it is expected to be towards inhibition.
The data were obtained from photographs which were scanned manually. The waterstriders are in a pool which is larger than the picture. A guard area (width about 2.5 cm) has been deleted because it is a source of inhomogeneity to interactions.
Penttinen (1984, chapter 5) fitted a pairwise interaction model with
a Strauss/hardcore interaction (see
with hard core radius 1.5 cm and interaction radius 4.5 cm.
waterstriders is a list of three point patterns
(objects of class
"ppp"). It also has class
so that it can be plotted and printed directly. The point pattern
coordinates are in centimetres.
Penttinen, A. (1984) Modelling interaction in spatial point patterns: parameter estimation by the maximum likelihood method. Jyv\"askyl\"a Studies in Computer Science, Economics and Statistics 7, University of Jyv\"askyl\"a, Finland.