Landscape-scale connectivity and fragment size determine species composition of grassland fragments

Gallé, Róbert and Korányi, Dávid and Tölgyesi, Csaba and Lakatos, Tamás and Marcolin, Fabio and Török, Edina and Révész, Kitti and Szabó, Ágota Réka and Torma, Attila and Marja, Riho and Szitár, Katalin and Deák, Balázs and Batáry, Péter (2022) Landscape-scale connectivity and fragment size determine species composition of grassland fragments. BASIC AND APPLIED ECOLOGY, 65. pp. 39-49. ISSN 1439-1791

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Abstract

As a consequence of agricultural intensification and habitat fragmentation since the mid-20th century, biological diver- sity has declined considerably throughout the world, particularly in Europe. We assessed how habitat and landscape-scale heterogeneity, such as variation in fragment size (small vs. large) and landscape configuration (measured as connectivity index), affect plant and arthropod diversity. We focused on arthropods with different feeding behaviour and mobility, spiders (predators, moderate dispersal), true bugs (mainly herbivores and omnivores with moderate dispersal), wild bees (pollinators with good dispersal abilities), and wasps (pollinators, omnivores with good dispersal abilities). We studied 60 dry grassland fragments in the same region (Hungarian Great Plain); 30 fragments were represented by the grassland component of forest-steppe stands, and 30 were situated on burial mounds (kurgans). Forest-steppes are mosaics of dry grasslands with small forests in a matrix of plantation forests. Kurgans are ancient burial mounds with moderately disturbed grasslands surrounded by agricultural fields. The size of fragments ranged between 0.16�6.88 ha (small: 0.16�0.48 ha, large: 0.93�6.88 ha) for forest-steppes and 0.01�0.44 ha (small: 0.01�0.10 ha and large: 0.20�0.44 ha) for kurgans. Fragments also represented an isolation gradient from almost cleared and homogenous landscapes, to landscapes with rel- atively high compositional heterogeneity. Fragment size, connectivity, and their interaction affected specialist and generalist species abundances of forest-steppes and kurgans. Large fragments had higher species richness of ground-dwelling spiders, and the effect of connectivity was more strongly positive for specialist arthropods and more strongly negative for generalists in large than in small fragments. However, we also found a strong positive impact of connectivity for generalist plants in small kurgans in contrast to larger ones. We conclude that besides the well-known effect of enhancing habitat quality, increasing connectivity between fragments by restoring natural and semi-natural habitat patches would help to maintain grassland biodiversity.

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