Functional traits of avian frugivores have shifted following species extinction and introduction in the Hawaiian Islands

Abstract

1. The extinction and introduction of species can alter ecological processes owing to the loss or gain of species roles. In vertebrate-dependent seed dispersal, mutualisms between frugivores and fruiting plants depend, in part, on matching of functional traits. High species turnover of frugivores has occurred on the Hawaiian

Ecological correlates of species’ roles in highly invaded seed dispersal networks

“…While lack of historical data prevents direct comparisons of the species' roles between the original (precolonization) and current (novel) networks in Hawaii, evidence shows that gape width and body mass have significantly shifted downward following frugivore extinctions and introductions (46). These shifts have likely caused broad patterns of dispersal limitation in largeseeded plants (46), ultimately resulting in the secondary roles of large-seeded plants that we found here. Extinct large-bodied and large-gaped frugivores, such as corvids and terrestrial anatids, likely had core roles in the past SDNs consuming a large range in seed sizes and a large quantity of seeds (46).…”

“…These shifts have likely caused broad patterns of dispersal limitation in largeseeded plants (46), ultimately resulting in the secondary roles of large-seeded plants that we found here. Extinct large-bodied and large-gaped frugivores, such as corvids and terrestrial anatids, likely had core roles in the past SDNs consuming a large range in seed sizes and a large quantity of seeds (46). Similarly, we found here that introduced frugivores with larger gape widths consumed a greater number of plant species.…”

No Effect of Selective Maturation on Fruit Traits for a Bird-Dispersed Species, Sambucus racemosa

“…Individual seeds produced from selective maturation were often, but not always, larger or heavier than seeds produced after random removal ( Table 2 ). However, we did not investigate individual seed size, which also affects dispersal efficiency, although a larger seed may not necessary be of higher fitness because of complex plant-animal interaction including seed dispersal [ 49 ] and post-dispersal predation [ 50 ]. Therefore, the effects of selective abortion should be investigated for a diversity of species with different plant-animal interactions.…”

“…The differences in fruit volume between the treatment and control trees were tested using the GLMM (family = Gamma (link = “log”) with basically the same random effects as described above, with the modification that because the fruit volumes were measured only for the individuals from the forest site, site random effects were not incorporated for the analysis. We used a Gamma error distribution because it is used to describe continuous and positive variables [ 49 , 90 ].…”

Ecomorphological relationships and invasion history of non‐native terrestrial bird species on O‘ahu, Hawai‘i, suggest ecological fitting during novel community assembly

“…For instance, all of the native frugivores (i.e., animals that eat fruit and disperse seeds) have gone extinct or have been extirpated from O‘ahu (Heinen et al, 2018) and were predominantly replaced by four non‐native passerine species (Japanese white‐eye— Zosterops japonicus , red‐billed leiothrix— Leiothrix lutea , red‐vented bulbul— Pycnonotus cafer , and red‐whiskered bulbul— Pycnonotus jocosus ; Vizentin‐Bugoni et al., 2019). However, the non‐native species in Hawai'i are only partially fulfilling the functional roles of the now extinct native frugivores (Aslan et al., 2014; Chimera & Drake, 2010; Vizentin‐Bugoni et al., 2019), in large part due to morphological mismatch between seed size and gape width (Pejchar, 2015 and see Case & Tarwater, 2020 for a detailed comparison of native and non‐native morphologies). Understanding the ecomorphological relationships of these non‐native species is critical for understanding and predicting plant–animal interactions and ecosystem functioning in this novel system.…”