Effects of density and group sizes on (a) mate encounter rate, (b) individual daily mating rate (log-scale), and (c) average egg mass weight. Graphs depict raw data (cf. Table 1), with each data point representing the mean ± SE of 5 replicates. Regression lines illustrate the overall effect of density when group sizes are combined, after correcting for variation between experimental runs. Panels (a) and (b) show fitted linear regression lines and their 95% confidence intervals (grey shades, see Material and Methods for details), panel (c) shows the fitted quadratic regression term.