The four fitted contact–density functions were: c=1.14(N/A)0 (constant), c = 0.0092(N/A) (linear), c=0.124(N/A)0.5 (power), c=2.13/(1+e−0.05 ((N/A)−101.2)) (sigmoid). As shown in figure 1, a sigmoid contact–density function resulted in the best fit to contact–density data measured for M. natalensis in a previous field experiment , while the constant function clearly did not fit the data well. AIC values for the functions were 59.7 (constant), 39.7 (linear), 42.6 (power), 34.3 (sigmoid). Akaike weights were 0.00 (constant), 0.06 (linear), 0.01 (power), 0.92 (sigmoid), providing additional support for the much better fit of the sigmoid function.