Connectivity or area: what drives plant species richness in habitat corridors?
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The relative importance of habitat area and connectivity for species richness is often unknown. Connectivity effects may be confounded with area effects or they may be of minor importance as posited by the habitat-amount hypothesis.
We studied effects of habitat area and connectivity of linear landscape elements for plant species richness at plot level. We hypothesized that connectivity of linear landscape elements, assessed by resistance distance, has a positive effect on species richness beyond the effect of area and, further, that the relative importance of connectivity varies among groups of species with different habitat preferences and dispersal syndromes.
We surveyed plant species richness in 50 plots (25 m2) located on open linear landscape elements (field margins, ditches) in eight study areas of 1 km2 in agricultural landscapes of Northwest Germany. We calculated the area of linear landscape elements and assessed their connectivity using resistance distance within circular buffers (500 m) around the plots. Effects of area and connectivity on species richness were modelled with generalised linear mixed models.
Species richness did not increase with area. Resistance distance had significant negative effects on total richness and on the richness of typical species of grasslands and wetlands. Regarding dispersal syndromes, resistance distance had negative effects on the richness of species with short-distance, long-distance and aquatic dispersal. The significant effects of resistance distance indicated that species richness increased with connectivity of the network of linear landscape elements.
Connectivity is more important for plant species richness in linear landscape elements than area. In particular, the richness of plant species that are dispersal limited and confined to semi-natural habitats benefits from connective networks of linear landscape elements in agricultural landscapes.
KeywordsConnectivity Corridor Dispersal Diversity Resistance distance Species richness
We cordially thank Henrike Ruhmann and Alexander Terstegge for help with the fieldwork and two anonymous referees for their helpful comments on the draft manuscript.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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