Steppe islands in a sea of fields: Where island biogeography meets the reality of a severely transformed landscape

Abstract

Questions: Steppes are among the most transformed and fragmented biomes in the world, but studies on the impact of habitat loss and fragmentation on these zonal grasslands are scarce. In many regions, steppe has survived only on small habitat islands, particularly on kurgans (ancient burial mounds) surrounded by intensive croplands. We asked how the size of kurgans, their isolation and other landscape and local factors influence their species richness. Location: Southern Ukraine. Methods: We recorded all species of vascular plants and assessed local (area, steepness, disturbance level), landscape (distance to the nearest habitat patch, habitat amount in the surroundings, surrounding type, distance to settlements) and climatic (precipitation) conditions of 112 kurgans. We analysed species-area relationships (SARs) for total richness, habitat specialists and generalists. Then, we assessed importance of environmental factors in explaining the residuals of the SAR models. Results: Patch area explained more than 50% of variance in total and specialist species richness. The slopes of the power function SAR (z-values) were higher for specialists than for generalists. Connectivity measures (the distance to the nearest large habitat enclave and share of habitat in the surroundings) were more important for richness of specialists than for that of generalists, which were more controlled by the kurgan's surroundings. Conclusions: We found that for specialist species the steppe "islands" follow the theory of island biogeography closely, but less so for generalist species. Combined with the revealed importance of connectivity for specialist species richness, we conclude that the conservation value of the kurgans in the long term likely can only be achieved with larger steppe areas in the surroundings.

Species–area relationship and small‐island effect of vascular plant diversity in a young volcanic archipelago

“…Therefore, the case that we observed in the Aeolian Islands is likely dependent on the combination of local factors depending on the specific biogeographical history of the archipelago as well as on the history of human colonisation, closeness to Sicily or Italian mainland and landscape transformation. This is coherent with the conclusions of similar studies carried out in southern oceanic islands (Chown et al, 1998) and even in continental ‘insular’ ecosystems generated by different land use matrices (Dembicz et al, 2020).…”

Ancient Burial Mounds Provide Safe Havens for Grassland Specialist Plants in Transformed Landscapes—A Trait-Based Analysis

“…Nowadays, there are ∼400-600,000 kurgans in Eurasia that were built by steppic cultures predominantly during the Bronze and Iron ages (Deák et al, 2016). Their typical height is 0.5-15 meters and their area is generally smaller than one hectare (Dembicz et al, 2020). Due to their cultural significance and the fact that their steep slopes hinder tilling, kurgans often preserve the last remnants of dry grassland vegetation and maintain a high diversity of grassland specialist species even in intensively used landscapes (Sudnik-Wójcikowska et al, 2011;Deák et al, 2020a,b;Dembicz et al, 2020).…”

“…Due to the marked changes in the landscape composition and configuration of fertile lowland areas, kurgans often function as terrestrial habitat islands (Deák et al, 2016(Deák et al, , 2020aDembicz et al, 2020;Kuli-Révész et al, 2021). The colonization and persistence of grassland specialists in grassland islands are considerably influenced by the special environmental characteristics (such as area, management, microclimate, soil fertility) and the degree of isolation providing several abiotic and biotic filters shaping the local species assemblages (Szabó et al, 2012;Heinken and Weber, 2013;Deák et al, 2018;Dembicz et al, 2020;Ottaviani et al, 2020). For revealing mechanisms affecting species occurrences and driving patterns of local community assembly in insular ecosystems and fragmented landscapes, trait-based approaches may provide a powerful tool (Janečková et al, 2017;Keppel et al, 2018).…”

What defines insularity for plants in edaphic islands?

“…Within such ‘terrestrial archipelagos', we may expect that edaphic islands with the largest size and highest specialist species richness will putatively serve as species sources for the rest of edaphic islands. Although matrix‐derived species also occur on edaphic islands, they are expected to be less sensitive to the differences in edaphic conditions between the island and the landscape matrix, thus experiencing less isolation than specialists (Horsák et al 2018, Horsáková et al 2018, Dembicz et al 2020, Goedecke et al 2020) (Fig. 1).…”