Session

Orthoptera are a group of insects especially reliant on grasslands and the megafauna. The latter are responsible for i. a. maintaining the open or semi-open character of environments, providing a wide range of habitats for other organisms. Large herbivores have been present across Europe for the last 35 Myr, but have been extirpated at the end of Pleistocene by early humans. Since the Neolithic revolution livestock and other human land-use have restored some of the functions lost with the wild large herbivores. However, livestock grazing has been banned or abandoned across much of Europe during the 20th century, with possibly strong effects on biodiversity. In the Tatra Mountains livestock grazing was banned in 1960s, thus, overgrowing and degradation of grassland habitats may have become a serious threat since then. We surveyed Orthoptera communities of the Tatra National Park in 2022 and 2023, visiting 29 localities and collected 912 species records. We extracted data on historical species abundances. We calculated relative species abundances by dividing the value for each species by summed-up abundance of all species, and computed diversity indices. We found that evenness (Shannon diversity index) decreased in the 2010s (1950: 2.7; 2010s: 2.47) but increased again in 2020s (2.68). In the 1950s the communities were dominated by cold-adapted species with a substantial presence of xeric species (e.g., Myrmeleotettix maculatus). The reduction in evenness in the 1990s was driven by the relative increase in 2 species (Euthystira brachyptera – thermophilus and Roeseliana roeselii – eurytopic). While these species remained dominant in 2020s, one thermophilus (Chrysochraon dispar), and three cold-adapted species (Gomphocerippus rufus, Isophya camptoxypha, and Metrioptera brachyptera) increased in relative abundance. We hypothesize that the strong increase in thermophilus species may have been driven by climate change, while the increase in cold-adapted species and the strong decrease in xeric species (Myrmeleotettix maculatus – 5th most abundant species in 1950s – probably extinct now) may be due to grazing abandonment and the associated densification of the herb-layer.