Movement responses of dabbling ducks to a changing climate and implications for the dispersal of aquatic propagules
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As freshwater wetlands are often rather isolated units surrounded by a vast 'sea of land', dispersal of aquatic propagules between wetlands relies on mediums such as wind and animals. Waterfowl, and dabbling ducks (Anatini) in particular, are among the most important dispersers in wetlands due to their abundance, widesprad distribution, long distance movements and preference for aquatic propagules as resources. Dabbling ducks movements are greatly influenced by resource abundance and local weather conditions, both of which are expected to change in the future as a consequence of large-scale climatic alterations. This could cause major shifts in the movements or even distribution of dabbling ducks. As they are important dispersers this could have serious implications for the distribution of aquatic invertebrates and plants. In this study we started by reviewing all factors that affects the spatial unit and movements of dabbling ducks in the Holarctic range. Subsequently, we examined how current and future climate change is influencing these factors. The last step was to implement these results in order to predict what the impact is on the role of dabbling ducks as dispersers of aquatic propagules. Factors found to affects movements were weather conditions, resource availability, water depth, vegetation cover and amount of seasonal and semi-permanent wetlands. How these factors are affected by climate change depends on location and season. Our results showed that at breeding sites, rising water levels and elevated temperatures could increase per capita food resources through lower duck densities in combination with greater invertebrate abundance due to northward expansion of temperate species. Consequently forage related movements are expected to decrease, and thus dispersal of aquatic propagules likewise. For the winter half-year we argue that movements to escape extreme weather conditions should decrease as a consequence of warming. Furthermore, different movement responses are predicted depending on the location of wintering ground. In relatively cold wintering areas reduced snow and ice cover is going to increase forage related movements, whereas in more temperate wintering areas movements are expected to decrease due to lower energy requirements. Hence, temperate regions are more susceptible to movement decreases, whereas colder regions are more prone to increases in duck movements. Dispersal shall respond accordingly. In addition, we show that droughts have the potential to affect the rol of dabbling ducks as dispersers throughout the year. Droughts could cause a northward shift of southerly populations and has the potential to cause large-scale dabbling duck mortality. Finally, we show migration distances shall decrease as a result of warming and migrations routes could be altered as a consequence of droughts. Overall, movement changes are going to be pronounced, potentially causing serious alterations in the distribution of aquatic propagules.