Corridor length and patch colonization by a butterfly, Junonia coenia

Corridors have been proposed to reduce isolation and increase population pe rsistence in fragmented landscapes, yet little research has evaluated the t ypes of landscapes in which corridors will be most effective. I tested the hypothesis that corridors increase patch colonization by a butterfly, Junon ia coenia, regardless of the butterfly's initial distance from a patch. I c hose J. coenia because it has been shown to move between patches preferenti ally through corridors. Individuals were released 16-192 m away from open e xperimental patches into adjacent open corridors or forest. Neither corrido rs nor distance had a significant effect on patch colonization, but there w as a significant interaction between the presence or absence of corridors a nd distance. At small distances (16-64 m), J. coenia was more likely to col onize open patches when released within forest than within open corridors, most likely because J. coenia used corridors as habitat. Nevertheless, patc h colonization by butterflies released within forest decreased rapidly as d istance from patches increased, as predicted by a null model of random move ment. Colonization did not change with distance in the corridor, and at lon g distances (128-192 m), butterflies released in corridors were twice as li kely to colonize open patches as those released in forest. These results su ggest that one critical factor, interpatch distance, may determine the rela tive effectiveness of corridors and other landscape configurations, such as stepping stones, in reducing isolation in fragmented landscapes. When dist ances between patches are short compared to an animal's movement ability, a stepping stone approach may most effectively promote dispersal. Alternativ ely, the conservation value of corridors is highest relative to other habit at configurations when longer distances separate patches in fragmented land scapes.