Fig. 5 Resource availability determines the optimal rate of digestion and relative rate of colonisation. Panels ( a – d ) show the optimal rates of digestion for fungi, motile, autolytic, and immobile cells, and panels ( e – h ) show the corresponding rates of colonisation for each unit volume colonised, for varying total amounts of resource availability set by the radius of digestion κ , on wood ( a , e ), leaf litter ( b , f ), fresh dung ( c , g ), or malt agar ( d , h ). Each type of substrate is modelled by assuming an appropriate C:N:P ratio and recalcitrance value τ . In each case, the total dry mass for each unit volume of the substrate is 0.5 g ml − 1 , and growing the metabolic core of an organism requires a total of 0.33 g ml − 1 , at a C:N:P ratio of 168:14:1. These fi gures account for both the material contained in the organism and the C lost in respiration set by the CUE (see Supplementary Note 6). Note that when the environment contains enough resource for fungi to grow, fungi almost always have the highest rate of digestion ( a – d ). Also note that across the different media, growth rates vary by nearly 2 orders of magnitude according to the y -axis units ( e – h ). C:N:P ratios were taken from the literature 39,41 , and recalcitrance values were set to match growth rates that are typically observed on each type of