Introduced galliforms as seed predators and dispersers in Hawaiian forests

Abstract

In altered communities, novel species' interactions may critically impact ecosystem functioning. One key ecosystem process, seed dispersal, often requires mutualistic interactions between frugivores and fruiting plants, and functional traits, such as seed width, may affect interaction outcomes. Forests of the Hawaiian Islands have experienced high species turnover, and introduced galliforms, the largest of the extant avian frugivores, consume fruit from both native and non-native plants. We investigated the impact of two galliform species on seed dispersal processes in Hawaiian forests. Using captive Kalij Pheasants (Lophura leucomelanos) and Erckel's Francolins (Pternistis erckelii), we measured the probability of seed survival during gut passage and seed germination following gut passage. We also examined which seeds are being dispersed in forests on the islands of O'ahu and Hawai'i. We found that galliforms are major seed predators for both native and non-native plants, with less than 5% of seeds surviving gut passage for all plants tested and in both bird species. Gut passage by Kalij Pheasants signi cantly reduced the probability of seeds germinating, especially for the native plants. Further, largerseeded plants were both less likely to survive gut passage and to germinate. In the wild, galliforms dispersed native and non-native seeds at similar rates. Overall, our results suggest the introduced galliforms are a double-edged sword in conservation efforts; they may help reduce the spread of nonnative plants, but they also reduce seed dispersal of native plants. Broadly, we show mutualism breakdown may occur following high species turnover, and that functional traits can be useful for predicting outcomes from novel species' interactions.

Mechanisms underlying interaction frequencies and robustness in a novel seed dispersal network: lessons for restoration

“…We focused on avian dispersers because birds form the overwhelming majority of dispersers on O‘ahu [9,10], while other animals such as rats [36] and even larger birds (e.g. [37]) act mostly as seed predators and no other mammal, ant or lizard is known to disperse seeds on O‘ahu. To obtain evidence of frugivory, passerine birds were caught in mist-nets, on two consecutive days, every seven weeks from November 2014 to December 2017 in each of the seven sites.…”

“…For game birds, which were rarer than most passerine dispersers on O'ahu [35], we collected faecal samples from the ground opportunistically from February 2017 to December 2018 in the three sites where Lophura leucomelanos and Pternistis erckelii are common (' Ekahanui (EKA), Kahanah aiki (KAH), Pahole (PAH)) and which coincide with areas or habitat types where passerine birds were mist-netted [10]). Specifically, we collected 33 samples for L. leucomelanos (EKA = 7, KAH = 18 and PAH = 8) and 93 samples for P. erckelii (EKA = 3, KAH = 48 and PAH = 42) (see [37], for further details). Species identity for game bird samples was determined using DNA barcoding of the cytochrome b region using the cytb-2RC/cytb-wow primers [38], with sequences compared to those in GenBank.…”

Threatened species are disproportionately important interactors in a seed dispersal network in Southeast Asia

“…For most species without at least one confirmed seed dispersal interaction, dispersal was confirmed in co‐generic taxa or at the family level within the Khao Yai data sets. For three families (Phasianidae, Trogonidae, Psittacidae) we used published studies from other regions to confirm the taxa could function as a seed disperser (Blanco et al, 2016; Case et al, 2022; Wenny, 2000). For animals that were also seed predators, we included (i) confirmed seed dispersal interactions, and (ii) frugivory interactions in which the seed was very hard, and where the animal did not consume depulped seeds.…”

Exploitation competition between seed predators and dispersers introduced toHawaiian forests

“…For instance, all frugivores native to O‘ahu have gone extinct, and many non‐native frugivores have been introduced (Case & Tarwater, 2020). These non‐native frugivores include both species thought to be primarily seed dispersers and seed predators (Case et al, 2022; Vizentin‐Bugoni et al, 2021). Specifically, passerines appear to be primarily seed dispersers (Vizentin‐Bugoni et al, 2019).…”

“…Specifically, passerines appear to be primarily seed dispersers (Vizentin‐Bugoni et al, 2019). Rodents (Rodentia) primarily depredate seeds during frugivory or seed caching (Hays et al, 2018) and galliforms (Galliformes, Case et al, 2022) and doves (Columbiformes) have powerful gizzards filled with stones which can crush seeds during gut passage (Lambert, 1989). Further, species thought to be seed dispersers and seed predators are known to consume fruit of the same plant species on O‘ahu (Vizentin‐Bugoni et al, 2021).…”