Species’ responses to an ever-changing world

One of nature’s most astonishing features is the diversity of life, as more than a million species has been identified and classified. This diversity not only have a intrinsic value, but sustains us humans through a multitude of ecosystem services. Many of these services are critical for our sustenance. In our current age this diversity is threatened however, in what sometimes is referred to the Earth’s 6th mass extinction as the current frequency of species-extinction is estimated to be over a hundred times over the background rate. The largest threat to biodiversity is human land use and overexploitation. However, in the past decades we have seen the addition of another large threat that can also compound to the extinction rates - climate change. In the first two studies (Paper I and Paper II), I show how species’ dispersal ability might affect their response to climate change. In paper I, I found that when the potential new habitat of a species is homogeneously distributed in the landscape most species in the study were able to emigrate to new habitats. There was a larger variation in heterogenic landscapes where the outcome depended on both the dispersal ability of the species combined with how the habitat were specifically arranged in relation to the climatic optimum of the species. From this also follows that it is not only the amount of habitat that is important but also where the habitat is located in relation to other habitat. I also show that both dispersal ability and habitat might be more important predictors of a successful climatic shift of a species than the speed of climate change. In paper II, I use previously collected data of population abundances and dispersal of a butterfly (Pyrgus armoricanus) in Sweden to model its future distribution. Similar to Paper I we see that low habitat availability, as well as heterogeneous configuration together with low dispersal ability negatively impacts its range expansion. In the third study (Paper III) I examine how the stability of species in small food webs is influenced by the autocorrelation of environmental noise and dispersal rates. I also let modeled basal species independently to see if stability differed when modeling species in isolation. I found that not only does the stability of species abundance depend on the environmental noise and dispersal rates, but the stability also changes non-linearly with changes in autocorrelation and dispersal rate. The lowest stability for a species were not necessarily at the lowest dispersal rate but at a low to medium rate. An analysis of the results shows that at least some species seem to have an equilibrium that is not determined by the autocorrelation of environmental noise. The results thus underline complex mechanisms that might influence the abundance and stability of populations. In the fourth study (Paper IV) we generated ecological networks and compared how simulated networks differed, depending on if selection was included or not. Here we used an allometric model were growth rate, mortality and interactions between phenotypes depend on the body size of the phenotypes. We found that while removing implicit traits such as the intraspecific competition between individuals of the same species made the webs unstable and prone to lose many species during the simulation, networks became much more unstable when introducing selection on the body mass trait. The restructuring of networks due to evolution either led to competitive exclusion of species or a race between plants, with an evolutionary pressure to escape predators, and animals to become larger and larger. Overall the research presented here give new insights into how species’ dispersal ability together with landscape configuration and climatic shift might determine the future distributions of species. Not only is the future climate range of a a species important, but also the mechanisms that would affect a successful range shift. Of these mechanisms the dispersal ability and the distribution and availability of habitat in the landscape are the most important. It is also shown that dispersal ability is important to take into account when planning for conservation actions as to identify which potential habitat will better facilitate range expansion