Stepping stones and corridors are not equivalent in ecological networks

What is it about?

We compared the habitat association and trait composition of invertebrate (carabid and spider) assemblages between core patches (valuable patches of remaining semi-natural grass-heath habitat on which many scarce specialist species depend); 'movement corridors' (linear network elements within a forest mosaic landscape) and transient 'stepping-stones' (short lived patches of suitable sandy habitat created by forestry operations). Each network element supported distinct arthropod assemblages with differing functional trait composition. Core patches were dominated by specialist dry-open habitat species while generalist and woodland species contributed to assemblages in connectivity elements. Nevertheless, transient patches (and to a lesser degree, corridors) supported species associated with dry-open (heathland) habitats that are generally thought to be characteristic of the focal grass-heath sites. Trait associations differed markedly among these three landscape elements. Dispersal mechanisms and their correlates differed between taxa, but dry-open species in transient patches were characterised by traits favouring dispersal (large running hunter spiders and large, winged, herbivorous carabids), in contrast to wingless carabids in corridors. This means that core patches, dispersal corridors and transient stepping-stones were not functionally interchangeable within this system.

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Why is it important?

Corridors and Stepping Stones are both advocated in attempts to restore the ecological connectivity of landscapes. However, they can support different sets of species. Semi-natural core patches supported a filtered subset of the regional fauna, rather than unique biota. Landscape strategies should not be based on evidence from single taxa, as eidence for enhanced connectivity through percolation (corridors) or meta-population dynamics (stepping stones) differed between spiders and carabids.

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