Pace of life and mobility as key factors to survive in farmland – Relationships between functional traits of diurnal Lepidoptera and landscape structure

Abstract

Agricultural intensification is known to lead to biotic homogenization by selecting against habitat and resource specialist species, but most studies on this phenomenon have been limited to certain parts of the landscape diversity gradient. We aimed to reveal the relationships between functional traits of diurnal Lepidoptera and landscape structure along a wide environmental gradient from nature reserves to intensive farmland in Baden-Württemberg, SW Germany. Butterflies and burnet moths were sampled along 1500 m long transects using ‘Pollard walk’ in 99 sites. Twenty nature reserves, 39 grassland-dominated and 40 arable-dominated agricultural landscapes were selected as study sites. Landscape structure was assessed within a 100 m buffer around each transect. The RLQ method and the ‘fourth-corner’ approach were combined to find statistical relationships between environmental factors and functional traits of Lepidoptera. We found a strong environmental gradient determined by landscape diversity and proportion of arable fields. Mobility, voltinism and overwintering stage were significantly correlated with these environmental variables. Butterflies with high mobility, high voltinism and non-larval overwintering stage were most abundant in landscapes with high proportion of arable fields and low landscape diversity. The second environmental gradient explained much less variance and separated less-intensively managed grasslands in nature reserves from conventionally managed grasslands in agricultural landscapes. Habitat specialization was correlated with this gradient as specialist butterflies were more abundant in grasslands in nature reserves. Larval diet breadth was not correlated with any environmental gradient or variable. We conclude that the mobility trait syndrome – comprising mobility, voltinism and overwintering stage – is independent from habitat and resource specialization and plays a primary role in shaping diurnal Lepidoptera communities in intensive agricultural landscapes with high cover of arable fields. We suggest that insect monitoring schemes should include some simple assessment of environmental variables to gain insight into the functioning of ecological communities beyond abundance trend estimations.