Browsing by Subject "bioclimatic modelling"

As a result of climate change, species are forced adapt and/or change their distribution patterns. Freshwater environments are species rich and are particularly threatened because of alterations in thermal and precipitation processes greatly disturb the balance in these ecosystems. In this master’s thesis, species distribution modelling was used to investigate the current distribution of a large sized freshwater fish, wels catfish (silurus glanis) in Europe and predictions were made for its potential distribution in 2061-2080. The study also explored, which climate factors affect the changes in distribution of the species. In this study the Global Biodiversity Information Facility (GBIF) data was used together with climate data sourced from the WorldClim database. The study utilizes climate data with a spatial resolution of 2.5x2.5 arcminutes The current climate is based on historical records from 1970-2000, and the future climate is based on SSP climate scenario predictions. The distribution patterns were compared with three different modelling methods: the generalized linear model (GLM), the maximum entropy method (Maxent) and the generalized linear mixed model (GLMM). The accuracy of the models was evaluated by cross-validation by dividing the data into training data, which covered 80% of the observations, and test data, which covered the remaining 20%. In addition, the reliability of the models was examined by comparing the AUC-values. The results showed that the current distribution of wels catfish covers an area between southern France and Sweden, as well as areas in the United Kingdom, Italy, and the Balkans. The predictions based on climate scenarios revealed that the potential distribution of catfish increases almost everywhere in its current range and is expected to spread north in all longitudes. Certain climate variables, including temperature seasonality, precipitation in the warmest quarter, annual mean temperature, and rainfall seasonality, were identified as having the most significant effects. The presence of a continental climate diminished the likelihood of occupancy, suggesting that the temperature moderating influence of seas benefits the species, but only in circumstances where the rainfall is moderate. In the Mediterranean region, the catfish's favorable habitat is narrowing due to the heat and droughts during summer. The northernmost populations of catfish live at the limits of the species' climatic tolerance, but as a warm favoring fish, it is likely that because of climate change species will spread norther from current range. This is also supported by the region's predicted increase in rainfall during the summer and the leveling off temperature fluctuations between summer and winter. When examining the potential spread, the threshold value was significant factor. When changing the threshold value from the often used 0.5 to, for example, 0.4, the distribution area was significantly larger and more continuous. In summary, the changes in the climate in Europe's thermal and precipitation systems cause significant effects on the distribution of catfish. These variables should also affect the hydrology, which should be investigated because the species prefers river systems that are large and slow flowing. Future research on the species is needed, because as a top predator the catfish has a significant impact on biotic communities. There are still quite a few macro-level studies, and in addition to climate variables, topographical, hydrological, and human-caused factors should also be further addressed in research.