Emus as non‐standard seed dispersers and their potential for long‐distance dispersal

Abstract

Long-distance seed dispersal may have important consequences for species range, migration rates, metapopulation dynamics, and gene flow. Plants have evolved various adaptations for seed dispersal by standard agents, with typical dispersal distances associated with them. Seeds may also be dispersed by non-standard agents for which they do not show any apparent adaptation and may reach long distances. By sampling the droppings of emus Dromaius novaehollandiae at three localities in Western Australia, we investigated their potential to act as long-distance dispersers of seeds with adaptations for dispersal modes other than endozoochory, such as unassisted, ant, wind and exozoochory, for which they act as non-standard agents. Seventy-seven plant species with five types of dispersal syndromes were found in the 112 droppings analysed, with at least 68 having viable seeds. Although endozoochory was the most frequent syndrome, the presence of other syndromes was important in terms of number of species (61%) and seeds (50%). Estimates of species richness indicated that an increase in sampling effort would increase the number of species observed, especially among non-endozoochores. As a consequence of their long gut retention times and high mobility, emus can provide long-distance dispersal opportunities that may be especially relevant for species with dispersal modes of typically short distances (unassisted, ant). Our results suggest that the role of emus as non-standard agents for long-distance dispersal should be taken into account for understanding current geographic ranges, gene flow and metapopulation dynamics of some plant species, as well as for predicting their future responses to climate change and fragmentation

Comparative digesta retention patterns in ratites

“…Given that voluminous guts that allow long retention times are usually considered a precondition for the successful exploitation of plant fiber as a nutritional strategy (Stevens and Hume 1998), the known difference between Ostriches and Emus matches the difference in the natural diet reported for these species. Whereas Ostriches are considered strict herbivores (Williams et al 1993, Cooper and Palmer 1994, Milton et al 1994, the natural diet of Emus reportedly also contains fruits, seeds, and insects in proportions that exceed those expected from accidental ingestion (Long 1965, Davies 1978, Calviño-Cancela et al 2006, Mills et al 2008, Dunstan et al 2013. Nevertheless, these reports also indicate that at times, Emus ingest plant material only.…”

“…The results can also be helpful for assessing the impact of ratites as seed dispersers (Miller 1996, Calviño-Cancela et al 2006, Renison et al 2010, Schetini de Azevedo et al 2013). …”

Study of seed dispersal by Emu (Dromaius novaehollandiae) in the Jarrah (Eucalyptus marginata) forests of south-western Australia through satellite telemetry

“…The Emu is already known to be a potentially important dispersal agent for species that have endozoochorous dispersal morphologies, as well as for those that do not have adaptations for dispersal by frugivores (Calviño-Cancela et al 2006). The Emu's generalist diet (Dunstan et al 2013) makes it an ideal general seed disperser, and likely contributes to the demography of many species.…”

“…forests of south-western Australia, where up to 22% of the flora has developed vertebrate dispersal mutualisms (Willson et al 1990). The Emu is also an important non-standard dispersal agent for plants that have not evolved traits for dispersal by frugivores, as it ingests seeds of many species with various dispersal morphologies (Calviño-Cancela et al 2006, 2008. Seed dispersal is fundamentally important for plant demography and some key ecological processes driving the dynamics of communities and ecosystems (Howe and Smallwood 1982).…”

Rook Spring Seed Dispersal in the Agricultural Landscape – Frugivory, Granivory or Accidental Transport?

“…Saltmarsh seeds (mainly Chenopodiaceae) were found in 13−44 % of droppings and pellets of shorebird species wintering in Spain; seeds of 31 species (Poaceae and Chenopodiaceae among them) were present in droppings of plains-waders Pedionomus torquatus and diaspores of 122 genera were found in the stomach of the common snipe Gallinago gallinago (Green et al 2002 and literature cited there). In droppings of the emu Dromaius novaehollandiae, an omnivorous, but mostly herbivorous bird, seeds of 77 plant species were found, 61 % of which were not adapted to endozoochory (Calviño-Cancela et al 2006). Dry fruits of sedges and grasses and seeds without obvious adaptations to endozoochory were also found in droppings of Darwin's finches Geospizinae (Guerrero and Tye 2009), and in pellets and faeces of waders (Sánches et al 2006).…”