Every year the Eurasian crane travel from northern Africa to northern Europe and Asia. On their migration route they need to rest and often choose places around shallow lakes in agriculture landscapes. During their time in these resting sites the cranes forage in agriculture fields surrounding the lakes, which often cause crop-damage and thereof also financial loses. The last 30 years the population has increased radically, resulting in more extensive crop-damage. This study was set out to gain a better understanding how these migrating cranes choose sites to forage, based on four environment factors: roads, water, buildings, trees and shrub. A study-area in north of Lake Tåkern was selected and during six days in the spring all the cranes in the area were counted and marked on a map. The results showed that the factors affected the occurrence of cranes in the fields. They wanted to be close to shallow water and keep a distance to buildings, roads, trees and shrub. The cranes often spend the night in shallow water and search for food in the area close by to not lose too much energy, which probably was the main reason for the birds to stay close to the water. The distance to buildings and roads suggests that the cranes want to avoid interference from humans and the distance to trees and shrub that they want to have a good awareness of their surroundings. Through this understanding, areas with higher risk to attract groups of cranes can more easily be identified.

Knowledge about dispersion is of utmost importance for understanding populations’ reaction to changes in the environment. Expansion of a population range brings with it both spatial sorting and over time, spatial selection. This means that dispersion rates increases over time at the expanding edge. Most studies have so far been performed on continuously expanding populations. This study aims to bring more knowledge about dispersal biology in dynamic systems. I studied dispersal traits in two permanent and two seasonal vegetation habitats of an isopod (Asellus aquaticus), for which differentiation between habitat types has previously been shown. I quantified differences in displacement (dispersal rate) and three morphological traits, head angle (body streamline) and leg of the third and seventh pair of legs. Isopods from the seasonal vegetation had higher displacement rates than animals from permanent vegetation. This inclines that mechanisms driving spatial selection in expanding population ranges also exist in dynamic systems. The more streamlined isopods found in seasonal sites further points towards spatial sorting by dispersion capability. Because no effect of permanence was found on leg length and there was no correlation between streamlining and displacement, the higher dispersion among animals from seasonal habitats most likely derives from behavioral differences.

Benthic invertebrates play important roles as feeding resources for many organisms in different food webs. Shifts in predation of these organisms can generate cascading effects and potentially lead to the disappearance of one or more species from a site. Cascading effects can bring impacts to organisms who aren’t even directly involved, why studies in this field are important for understanding sudden changes in ecosystems. I examined the predation from fish and waterfowl on benthic invertebrates in the shallow and eutrophic Lake Tåkern in the plains of Östergötland County, southern Sweden. The study was experimental and used exclosures (three types, eight replicates) in the shape of 130-liter cages to examine the composition of invertebrates. It was conducted during early spring, a relatively unexamined period for this kind of study. I found no significant differences in the control treatment compared to any of the other treatments regarding biodiversity. The invertebrate fauna was dominated by a small number of species, with a relatively patchy spread throughout the sediment area. Furthermore, the results indicate that the fish hadn’t had the time to properly activate their predatory habits due to prolonged winter temperatures. The waterfowl were considered too absent during the test period to affect the invertebrate community. Future studies in this area are recommended to work with a greater sampling area, to reduce the influence of extreme values.

There are a number of species of geese in Sweden that can be found in large flocks during spring migration, but are also relatively numerous during breeding. The accumulation of geese can cause damage to growing crops, something that costs farmers and the state a large amount annually. In this study, nesting geese were counted in fields in the vicinity of Lake Tåkern, Southern Sweden, during six days in the spring in the year 2015. Their location on the fields was noted to investigate any preferences regarding distances to the lake, buildings, trees and roads. The conclusion is that proximity to water was the factor that had the greatest importance in field selection, but it also showed that they avoid trees but not settlements and roads.