Seed dispersal by neotropical waterfowl depends on bird species and seasonality

Abstract

1. Waterbird-mediated endozoochory is an essential mechanism for the dispersal of sessile organisms in freshwater ecosystems. However, in the neotropics there are no previous studies of how different waterbird species vary in the dispersal functions they perform, and how seasonality influences endozoochory. In this study, we identified plant diaspores dispersed in faeces of five South American waterfowl (Brazilian teal Amazonetta brasiliensis, yellow-billed teal Anas flavirostris, ringed teal Callonetta leucophrys, coscoroba swan Coscoroba coscoroba, and whitefaced whistling-duck Dendrocygna viduata). 2. We collected 165 faecal samples from five wetlands in southern Brazil surrounded by pasture and rice fields, then separated and measured intact seeds and other diaspores. Using generalised linear models, we tested how diaspore abundance and taxonomic richness differed among bird species and between cold (April-September) and warm (October-March) periods. We also analysed bird-specific and seasonal variations in diaspore composition through principal coordinates analysis and permutational multivariate analysis of variance. We used indicator species analysis to determine which diaspore species discriminated between bird species and seasons. Finally, we measured diaspore length in order to analyse differences among waterfowl species in the size of diaspores dispersed. 3. We found 2,066 intact diaspores from 40 different plant taxa, including seeds of 37 angiosperms and diaspores of Lycophyta (Isoetes cf. maxima), Pteridophyta (Azolla filiculoides), and Charophyceae. There was at least one diaspore in 65% of all faecal samples. Diaspores of native amphibious and emergent plants were dominant. We found 1,835 diaspores (from 33 taxa) in the cold period but only 231 (23 taxa) in the warm period. Seeds of the grass Zizaniopsis bonariensis and of the sedge Rynchospora sp. were the most abundant taxa. A strong interaction between bird species and season was the most important predictor of variation in both taxonomic richness and abundance of diaspores. The taxonomic composition of diaspores differed among waterfowl species and season. Indicator species analysis identified 12 plant taxa associated with particular bird species and seasons. Coscoroba swan, the largest bodied species in our study dispersed a higher proportion (8.2%) of large (length >2 mm) seeds. | 79 SILVA et AL.

Revealing the evolutionary history of a reticulate polyploid complex in the genusIsoëtes

“…Unlike most homosporous ferns, which disperse their spores via air currents (Barrington, 1993), spore dispersal in Isoëtes is poorly understood because they are aquatic and produce large megaspores (200-1000μm), unable to be dispersed by wind. Anecdotal evidence suggests they can be dispersed by waterways, waterfowl, or even snails and earthworms (Duthie, 1929; Jermy, 1990; Taylor & Hickey, 1992; Larsén & Rydin, 2016), and recent work has documented spores in waterfowl fecal matter (Silva et al , 2020), confirming previous observations. It is not inconceivable that sporangia, spores, or even whole plants are dispersed in the crops of these migratory animals (Les et al , 2003).…”

Functional Traits Drive Dispersal Interactions Between European Waterfowl and Seeds

“…See Table 1 for full names of bird species. Silva G. G. et al, 2021) showing that differences in the species composition of seeds dispersed by waterfowl species are related to their foraging behavior (note, these studies did not consider plant traits). In contrast, a study of other waterbirds in rice fields found no difference between a gull and stork species in the plants they dispersed (Martín-Vélez et al, 2021).…”

“…Interactions between plants and frugivorous birds (i.e., those feeding on fleshy-fruits) in terrestrial ecosystems are known to depend on many traits of both groups of organisms, such as fruit size and palatability and bill morphology (Wenny et al, 2016;Donoso et al, 2017). On the other hand, despite recent advances in identifying the interactions between different waterfowl and plant species in a particular community (Reynolds and Cumming, 2016;Sebastián-González et al, 2020;Silva G. G. et al, 2021), the trait associations underlying the uptake of seeds by different waterfowl species remain unknown. In general, seed ingestion by non-frugivorous vertebrates is not size limited in a manner comparable to frugivores (Chen and Moles, 2015; but see Gurd, 2008).…”

Do birds disperse mosses? Evidence of endozoochory in upland geese Chloephaga picta and white-bellied seedsnipes Attagis malouinus in sub-Antarctic Chile

“…The behavior of birds can aid in directed and long-distance movement of bryophytes as they may act as dispersers in local sites through foraging and nesting (Calvelo et al, 2006;Parnikoza et al, 2012;Amélio et al, 2017;Parnikoza et al, 2018), and transcontinentally through migratory movements (Chmielewski & Eppley, 2019). Birds can disperse bryophytes long distances via ectozoochory, by external transportation (Lewis et al, 2014), and may be able to do this via endozoochory, through internal ingestion, as has also been shown with ferns and other herbs (Lovas-Kiss et al, 2018;Blanco et al, 2019;Hervías-Parejo et al, 2019;Silva et al, 2020).…”