Values of Chesson's α for the dominant diatom species. In the gut contents of the two mayflies (Baetis and Rhithrogena) collected in the dry (a) and wet seasons (b) in the Chichiawan Stream. Asterisks indicate α > 0.05, preference for each algal taxa. Diatom species in the x-axis were ranked in order of descending contributions (%) to the difference between the dry and wet seasons on the insect-excluded bricks. COCPL, Cocconeis placentula var. euglypta; ACHPY, Achnanthidium pyrenaicum; GOMSP, Gomphonema spp.; ACHSP, Achnanthes spp.; ACHMI, Achnanthidium minutissimum; PLALA, Planothidium lanceolatum.