Eating down the food chain: generalism is not an evolutionary dead end for herbivores

The role of trophic specialisation in taxonomic diversification remains unclear. Plant specialists diversify faster than omnivores and animalivores, but at shorter macroevolutionary scales this pattern sometimes reverses. Here, we estimate the effect of diet diversification on speciation rates in noctilionoid bats, controlling for tree shape, rate heterogeneity and macroevolutionary regimes. We hypothesise that niche subdivision among herbivores positively relates to speciation rates, differing between macroevolutionary regimes. We found the rate at which new herbivorous lineages originate decreases as rates of diet evolution increase. Herbivores experience higher speciation rates, but generalist herbivores and predominantly herbivorous omnivores speciate faster than specialised herbivores, omnivores and animalivores. Generalised herbivory is not a dead end. We show that analysing ecological traits and diversification requires accounting for macroevolutionary regimes and within- and between-clade variation in evolutionary rates. Our approach overcomes the high false-positive rates of other methods and illuminates the roles of herbivory and specialisation in speciation.