Environmental variability and population dynamics: do European and North American ducks play by the same rules?

Spatial and Temporal Variations in Waterfowl Assemblage Structures in Mongolian Lakes and the Changes Linked to the Gradient of Lake Surface Areas

Lakes and wetlands provide top-priority hotspots that play a key role in maintaining and protecting threatened and migratory waterfowl. Identifying seasonal and spatial variations in aquatic bird communities and their responses to environmental factors is vital conservation efforts. However, there is a lack of information on waterfowl in Mongolian lakes and their associated wetlands. The purpose of this study was to investigate the spatial–seasonal changes in waterfowl assemblage structures in Mongolian lakes, as well as to determine how they respond to various environmental factors (lake surface area, elevation, and geographical distribution). Statistical analyses were performed using seasonal data (May, July, and September) for 28 waterfowl collected from 54 lakes across the country between 2016 and 2018. Seasonal heterogeneity in species richness and abundance was observed in lakes in each geographical region (Eastern, Central, and Western Mongolia). The composition of waterfowl in the lake was also relatively similar between May and September compared to July. This was due to the overlapping migration seasons in spring and autumn. Regionally, the number of waterfowl was much higher in the Eastern Mongolian lakes, followed by Central Mongolian lakes and then Western Mongolian lakes. This is likely due to differences in habitat availability and water levels between the regions. Eastern Mongolian lakes tend to have more wetlands and shallow water habitats, while Central and Western Mongolian lakes tend to have deeper open-water habitats. These differences in habitat types could contribute to the observed differences in waterfowl abundance among the regions. Additionally, some small lakes and the group of small lakes supported a greater abundance and diversity of waterfowl compared to some medium-sized and large lakes, suggesting that they are important for conservation. Indices of diversity (H’) and species dominance (D’) showed positive and negative correlations with lake surface area, respectively. Perhaps the increased surface area of the lake decreases the habitat overlap for designated waterfowl due to habitat heterogeneity. Accordingly, the indices (H’ and EH) increased as the waterfowl species composition became relatively equivalent in large lakes. Overall, spatial variations among the lakes were primarily attributable to the individual features of the lakes (shallowness, small lake groupings, and surface area), and seasonal variation in the lakes depended majorly on the compositional changes of the waterfowl due to migration.

Large-scale changes in marine and terrestrial environments drive the population dynamics of long-tailed ducks breeding in Siberia

Migratory animals experience very different environmental conditions at different times of the year, i.e., at the breeding grounds, during migration, and in winter. The long-tailed duck Clangula hyemalis breeds in the Arctic regions of the northern hemisphere and migrates to temperate climate zones, where it winters in marine environments. The breeding success of the long-tailed duck is affected by the abundances of predators and their main prey species, lemmings Lemmus sibiricus and Dicrostonyx torquatus, whose population fluctuation is subject to climate change. In the winter quarters, long-tailed ducks mainly eat the blue mussel Mytilus edulis. We examined how North-west Siberian lemming dynamics, assumed as a proxy for predation pressure, affect long-tailed duck breeding success and how nutrient availability in the Baltic Sea influences long-tailed duck population size via mussel biomass and quality. Evidence suggests that the long-tailed duck population dynamics was predator-driven on the breeding grounds and resource-driven on the wintering grounds. Nutrients from fertilizer runoff from farmland stimulate mussel stocks and quality, supporting high long-tailed duck population sizes. The applied hierarchical analysis combining several trophic levels can be used for evaluating large-scale environmental factors that affect the population dynamics and abundance of migrants from one environment to another.

Structure formation in a conserved mass model of a set of individuals interacting with attractive and repulsive forces

We study a set of interacting individuals that conserve their total mass. In order to describe its dynamics we resort to mesoscopic equations of reaction diffusion including currents driven by attractive and repulsive forces. For the mass conservation we consider a linear response parameter that maintains the mass in the vicinity of a optimal value which is determined by the set. We use the reach and intensity of repulsive forces as control parameters. When sweeping a wide range of parameter space we find a great diversity of localized structures, stationary as well as other ones with cyclical and chaotic dynamics. We compare our results with real situations.

Northern range shift may be due to increased competition induced by protection of species rather than to climate change alone

Few long-term, large-scale studies have been conducted about the factors likely to explain changes in species abundance and distribution in winter. Range shifts are generally attributed to the climate change or land use. This study shows that other factors such as species protection and the ensuing increasing numbers of individuals and competition could be involved. It details the progressive conquest of France, the most important European wintering area for great cormorant, in three decades as its legal protection by the EU Birds Directive. It is based on 13 exhaustive national counts. Cormorants first occupied the farthest areas (Atlantic and Mediterranean lagoons, then larger rivers) from the main-core European breeding area, with only progressive occupancy of the northeastern part later. This strategy mainly resulted from competition for optimal available feeding areas. Suboptimal areas (smaller wetlands harboring smaller night roosts, colder northeastern French areas) and progressive fragmentation of large night roosts into smaller, better located ones minimized flight costs. The coldest areas were occupied last, once other areas were saturated. Their occupancy was favored locally by the global climate change, but it played a minor role in these strategies. Both factors induced only a small NNE shift of the weighted centroid range of the wintering population (2.6 km/year) which mainly resulted from competition (buffer effect). Only the 2009 cold wave decreased the total number of wintering cormorants at the national scale, once the population had probably reached the carrying capacity of the country, while the previous cold waves had a minor effect. Comparatively, there was a greater SSE range shift of the weighted centroid of the breeding population (4.66 km/year). Range shifts of other recently protected species have been attributed to the sole climate change in the literature, but competition due to the saturation of usual wintering or breeding areas should be considered too.