An experimental assessment of landscape connectivity

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We experimentally assess the relative movement abilities of two sympatric, ecologically similar species of damselfly, Calopteryx maculata and Calopteryx aequabilis (Odonata: Calopterygidae), within two structurally dissimilar habitat types, forest and pasture. For both species, streams are required resources, forest is a potential resource, and pasture is neutral habitat. Experimental manipulations were conducted at a spatial scale approaching typical inter-stream distances within our study region. A portion of the individuals was displaced away from its required stream habitat within its native landscape, and the remaining individuals were transferred to another landscape of alternate habitat structure (either forest or pasture). Within each habitat type we equate relative movement ability, an essential component of landscape connectivity, with the proportion of displaced individuals observed to have reached the stream, as measured against reobservation rates of control individuals released at the stream. We found that C. maculata, the species more consistent in its use of forest as a resource, moved significantly more readily through 700 m of pasture habitat than through the same distance of forest, while C. aequabilis moved with equal abilities through both habitat types. Historical behavior - whether or not the individuals typically used forest as a resource before the manipulations - did not have a statistically significant effect on the movement abilities of individuals of either species in either habitat type. There was, however, some evidence that C. maculata individuals native to non-forested landscapes moved more readily through forest than their forest-inhabiting counterparts. Both sexes moved with equal abilities irrespective of habitat type, but male C. aequabilis moved with greater ability through forest than females, while the reverse was true within pasture landscapes.

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