Migratory strategies of waterbirds shape the continental‐scale dispersal of aquatic organisms

Abstract

Long distance dispersal (LDD) of propagules is an important determinant of population dynamics, community structuring and biodiversity distribution at landscape, and sometimes continental, scale. Although migratory animals are potential LDD vectors, migratory movement data have never been integrated in estimates of propagule dispersal distances and LDD probability. Here we integrated migratory movement data of two waterbird species (mallard and teal) over two continents (Europe and North America) and gut retention time of different propagules to build a simple mechanistic model of passive dispersal of aquatic plants and zooplankton. Distance and frequency of migratory movements differed both between waterbird species and continents, which in turn resulted in changes in the shapes of propagule dispersal curves. Dispersal distances and the frequency of LDD events (generated by migratory movements) were mainly determined by the disperser species and, to a lesser extent, by the continent. The gut retention time of propagules also exerted a significant effect, which was mediated by the propagule characteristics (e.g. seeds were dispersed farther than Artemia cysts). All estimated dispersal curves were skewed towards local‐scale dispersal and, although dispersal distances were lower than previous estimates based only on the vector flight speed, had fat tails produced by LDD events that ranged from 230 to 1209 km. Our results suggest that propagule dispersal curves are determined by the migratory strategy of the disperser species, the region (or flyway) through which the disperser population moves, and the propagule characteristics. Waterbirds in particular may frequently link wetlands separated by hundreds of kilometres, contributing to the maintenance of biodiversity and, given the large geographic scale of the dispersal events, to the readjustment of species distributions in the face of climate change.

Seascape-scale trophic links for fish on inshore coral reefs

“…predation (Fortin et al 2005;Andrews and Harvey 2013), and propagule dispersal (Hougner et al 2006;Viana et al 2012).…”

Herbivory on freshwater and marine macrophytes: A review and perspective

“…Dispersal by most inland-water herbivores contributes to the redistribution of individuals within single wetlands and among nearby ones; while waterbirds (most notably, migratory species) are the main vector of long-distance dispersal among wetlands situated at separated watersheds, from regional to continental scales (Viana et al, 2013b;Viana et al, in press). …”

“…Among waterbirds, the frequency and scale of long-distance dispersal events is known to vary with the vector's morphology, to depend on the migratory strategy and to scale negative with body mass (Green and Figuerola, 2005;Viana et al, 2013b;Viana et al, 2013a). In the marine environment, biotic dispersal by herbivores (sea turtles, ducks and fish) has been reported for seagrasses (Sumoski and Orth, 2012) and passive transport of other organisms is also known to occur (e.g.…”

“…Travelling distance Larger travelling distances results in further potential dispersal, particularly for migratory species that cover long distances in single leaps Viana et al (2013b) Habitat use Animals with specialized use of aquatic habitats are more likely to deposit the propagules in suitable habitat. In particular, targeted arrival to aquatic habitats at stopovers may increased the deposition of propagules ingested at departure sites, especially after the first drinking and feeding bout.…”

Ecosystem services provided by waterbirds

“…For example, Levey, Tewksbury & Bolker (2008) consider 'long-distance dispersal' by terrestrial birds to be that over 150 m. By contrast, distances that seeds and eggs are moved by aquatic birds remain unclear and poorly studied, but generally much greater distances can be expected, with maxima of hundreds of kilometers likely for many migratory species (Green et al, 2002b;Figuerola et al, 2010;Sánchez et al, 2012;Viana et al, 2013). However, there is an urgent need to integrate new studies of bird movements using the latest global positioning system (GPS) technologies with studies of seed dispersal, to produce accurate seed shadows.…”