In this model, the term \(\theta\) parameterises the strength and the direction of the interaction between koalas. A value of \(\theta\ <1\)means repulsion, \(\theta=1\) means no interaction and \(\theta>1\)means aggregation. The term \(\varphi\) provides a measure of the spatial scale of interaction. If \(\theta>1\) and \(\varphi\) is large then koalas aggregate in large areas. When \(\theta>1\) and\(\varphi\) is small koalas aggregate in smaller areas.

The likelihood function given by the above equation was maximized using a numerical optimization procedure implemented in the ”nlimnb” function in the R (version 3.5.1) software environment. Since the model specified was not available in any of the existing R packages, the algorithm used in this analysis was developed in R.