The matrix enhances the effectiveness of corridors and stepping stones

Conservation strategies often call for the utilization of corridors and/or stepping stones to promote dispersal among fragmented populations. However, the extent to which these strategies increase connectivity for an organism may depend not only on the corridors and stepping stones themselves, but also on the composition of the surrounding matrix. Using an herbivore-host-plant system consisting of the planthopper Prokelisia crocea and its sole host plant, prairie cordgrass (Spartina pectinata), we show that the effectiveness of corridors and stepping stones for promoting planthopper dispersal among patches depended strongly on the intervening matrix habitat. In a low-resistance matrix (one that facilitates high rates of interpatch dispersal), both stepping stones and corridors promoted high connectivity, increasing the number of colonists by threefold relative to patches separated by matrix habitat only. The effectiveness of stepping stones and corridors was significantly lower in a high-resistance matrix (one that promotes low rates of interpatch dispersal), with stepping stones failing to improve connectivity for the planthoppers relative to controls. Thus, we conclude that the matrix is an integral component of landscapes and should be considered together with corridors and stepping stones in strategies designed to increase dispersal among fragmented populations.