“…The term 'Gibbsian interaction', is derived from statistical mechanics, where these models have been used for nearly a century to describe the behavior of gases (Ripley, 1990;Cressie, 1991). Examples of spatial stochastic models that take into consideration the interaction among events include sequential packing models of non-overlapping discs by Matern (1980), Bartlett (1974), and Diggle et al (1976); Poisson cluster models by Matern (1980) and Diggle (1979); and Strausstype and hard-core models by Strauss (1975), Kelly and Ripley (1976), Gates and Westcott (1980) and Westcott (1982). While most of this work has been theoretical, the increase in computing power makes it possible to estimate the parameters of these models using theoretical approximations to the likelihood function or by using computer simulations (Fiksel, 1988;Ogata and Tanemura, 1981;1984;1985;Ord, 1990;Ripley, 1990).…”