Cactus height increases the modularity of a plant–frugivore network in the Caatinga dry forest

Abstract

Cacti fruits are key resources to many frugivorous animals in Neotropical arid and semiarid regions. However, most studies have focused on a particular animal group or cacti species, but few have explored the overall interactions of such species at the community level. Here we monitored frugivory on five cacti species using camera traps that sampled diurnal and nocturnal interactions. We investigated the structure of interactions with bird, mammal, and reptile frugivores in the Brazilian Caatinga dry forest. We hypothesized that the height of cacti limit interactions with different types of frugivores, which would result in highly structured and modular interaction networks. In 2929 camera‐days, we recorded 23 vertebrate species feeding on cacti fruits, including seven new records, all determined to be primary seed dispersers. As predicted, the cacti‐frugivore network was modular and non‐nested, with the two shortest cacti species grouped in a module dominated by interactions with reptiles and non‐flying mammals. The tallest cacti species were dominated by frugivory interactions with birds and had comparatively less interaction diversity than shorter cacti species. Our results support the contention that cacti are keystone species in semiarid ecosystems where they produce small‐seeded fleshy fruits year‐round.

Mast seeding is stronger in taller plants

“…As EOS is the main selective force for masting ( Kelly and Sork, 2002 ), the close correlation between adult plant height and mast seeding intensity implies that increased plant height may also provide EOS through either enhancing pollination efficiency and/or increasing satiation of seed predators. Strong correlations between plant height and flower number ( Gomez, 2003 ; Trunschke et al., 2017 ), as well as increased attraction of pollinators, pollination success, and modularity of frugivorous network with plant height have been well observed ( Klinkhamer et al., 1989 ; Weber and Kolb, 2013 ; Dupont et al., 2014 ; Paixão et al., 2023 ), which are important for enhancing pollination efficiency. Evidence has shown that increased plant height significantly promotes pollen dispersal and then strongly increases pollination success ( Friedman and Barrett, 2009 , 2011 ; Harder and Johnson, 2009 ; Sletvold et al., 2010 ; Aljiboury and Friedman, 2022 ), which also provides EOS.…”