The columnar cacti Stenocereus griseus and Subpilocereus repandus in the semi-arid enclave of Lagunillas produce a large biomass of fleshy fruits consumed by both birds and bats. In this paper we quantify the consumption of fruits of both cacti by birds and bats. For two weeks during the fructification periods of S. griseus and C. repandus ripe fruits were offered to birds during the day and to bats at night. Bats consumed larger amount of C. repandus pulp than birds, while the consumption of S. griseus was the same for both groups. Birds consumed more S. griseus than C. repandus fruits, whereas bats consumed the fruits of both cacti species in equal amounts. We believe that the different results are due to the morphological characteristics of these fruits; C. repandus has fruits with cryptic coloring that makes their detection difficult for flying frugivores with color vision, while S. griseus has red fruits, which makes them conspicuous to avian frugivores. An ancillary preference study supports this notion, as birds were more likely to consume red-colored morphs of S. griseus compared to white-colored morphs. On the other hand, bats do not distinguish colors and consume both cacti species in equal amounts. This suggests that S. griseus, at least, presents an intermediate bird-bat dispersion syndrome, which, in principle, would guarantee greater fitness in comparison to C. repandus.
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Vol. 43 • No. 2