Using a data set from 36 studies, we evaluated variation in ungulate biomass across a rainfall gradient using polynomial models, aiming to: (1) compare neotropical and palaeotropical dry and wet forests as well as African savannas; and (2) evaluate the usefulness of polynomial models to predict ungulate biomass at neotropical sites using data from a dry forest (Chamela-Cuixmala Biosphere Reserve, CCBR) and a wet forest (Montes Azules Biosphere Reserve, MABR) in Mexico. Our results showed that an overestimation of expected ungulate biomass can be obtained for some tropical forests if data from African savannas are included in the model. This overestimation was particularly high for predicted ungulate biomass in neotropical dry forests. These ecosystems sustain different ungulate biomass values even when rainfall is similar. This was particularly true for some tropical dry forests and savannas. Rainfall predicted the expected ungulate biomass in neotropical ecosystems relative to that of palaeotropical ones under similar precipitation regimes, but did not correctly predict the observed ungulate biomass at local level if data outside the Neotropics are included in the model. This was more evident when we compared observed biomass against predicted biomass in the tropical dry forest of CCBR, while some polynomial models successfully predicted the observed biomass for the tropical wet forest of MABR. Factors such as Pleistocene extinctions and the absence of large, native grazers (i.e. Bovidae) that have kept ungulate richness and standing biomass relatively low in neotropical forests should be accounted for when comparing data sets from different regions.
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