Dear Naya,
Relicts
During the last Ice Age, the region to the west of Graz experienced severe glaciation – large parts of the Alps were covered in a thick sheet of ice. Many animals and plants were driven out of their original areas by the growing ice shields. Wherever they could, they retreated into warmer habitats, known as refuge areas.
Species that were not adaptable or prolific enough became extinct. But on the edges of the Eastern Alps there were also higher peaks that remained free of ice, known as nunataks.
Some of the less prolific species were able to escape to these ice-free areas and survive the Ice Age there.
Several organisms survived the Ice Age on the periphery of the ice sheet. Today’s Koralm, Stubalm and Gleinalm are examples of such peripheral areas where many animal and plant species survived. Once the Ice Age was over, many of the less competitive animals and plants were no longer able to spread. Today they are still isolated ‘relict’ species with a very limited dispersal. The Koralm is home to 5 endemic beetle species. In part, they are to be found in an area measuring just 3 km2. One of these is the Carabid beetle Pterostichus justusi.
Reunification
During the Ice Age, many animals and plants capable of migration or flight escaped into warmer areas. Populations of animal and plant species survived the Ice Age in various refuge areas. Within these refuge areas the remaining populations evolved independent of populations in other refuge areas. Over the course of time, this resulted in the evolution of different species. After the Ice Age ended, the areas that had been glaciated were recolonised. The species that had been split by the Ice Age into southwest and southeast species partly came back into contact with one another and today meet in Central Europe. Individuals from southwest and southeast species sometimes produce offspring together, which are referred to as hybrids. Where the southeast and southwest species encounter each other in Central Europe, zones of hybridisation form.
In Austria there are, for example, areas in which only the yellow-bellied toad or the fire-bellied toad are found. There are however also areas between the distribution areas where crossbreeding occurs between the two species.
Source: Naturkundemuseum Graz