Additionally, categorizing species into qualitative classes based on diet – especially using a coarse classification system of herbivore, carnivore, and omnivore – leads to a loss of information. Species with highly varied diets are clustered into potentially uninformative groupings. An additional problem with using a categorical variable is the need to choose diet categories and set boundaries between them, resulting in a lack of standardization of diet categorization in the literature. A quantitative, continuous classification of diet based on food consumption percentages may be preferred, as downstream results are less impacted by arbitrary cutoffs decided upon earlier in the study.

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OUR STUDY

In our study, we had three main objectives. First, we traced the evolutionary history of diet in Mammalia by identifying shifts in degrees of carnivory and dietary specialization. Second, we assessed the relative importance of carnivory and dietary specialization on speciation rates in different mammalian clades. Third, we identify significant relationships between diet and speciation rates across various taxonomic levels.

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Our observations reveal that degree of carnivory significantly impacts speciation rates in Mammalia, while dietary specialization does not. At lower phylogenetic levels, degree of carnivory significantly affected speciation in ungulates, carnivorans, bats, eulipotyphlans, and marsupials, while dietary specialization only had a significant impact in carnivorans. Across Mammalia, we found that omnivores exhibit the lowest speciation rates.

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We argue that treating variables such as diet as continuous instead of categorical reduces information loss and avoids the problem of contrasting macroevolutionary signals caused by differential discretization of biologically continuous traits.