Corridor Length and Patch Colonization by a Butterfly, Junonia coenia

Corridors have been proposed to reduce isolation and increase population persistence in frag mented landscapes, yet little research has evaluated the types of landscapes in which corridors will be most effective. I tested the hypothesis that corridors increase patch colonization by a butterfly, Junonia coenia, regardless of the butterfly’s initial distance from a patch. I chose J. coenia because it has been shown to move betweenpatchespreferentially through corridors. Individuals were released 16-192 m awayfrom open experimentalpatches into adjacent open corridors or forest. Neither corridors nor distance bad a significant effect on patch colonization, but there was a significant interaction between the presence or absence of corridors and distance. At small distances (16-64 m), J. coenia was more likely to colonize open patches when released within forest than within open corridors, most likely because J. coenia used corridors as habitat. Nevertheless, patch colonization by butterflies released within forest decreased rapidly as distance from patches increased, as predicted by a null model of random movement. Colonization did not change with distance in the corridor, and at long distances (128-192 m), butterflies released in corridors were twice as likely to colonize open patches as those released in forest. These results suggest that one criticalfactor, interpatch distance, may determine the relative effectiveness of corridors and other landscape configurations, such as stepping stones, in reducing isolation in fragmented landscapes. When distances between patches are short compared to an animal’s movement ability, a stepping stone approach may most effectively promote dispersal. Alternatively, the conservation value of corridors is highest relative to other habitat configurations when longer distances separate patches in fragmented landscapes. Extensibn de Corredores y Colonizacibn de Parches por una Mariposa,JunonQ coenia Resumen: Se ban propuesto corredores coma una medida para reducir el aislamiento y aumentar la persistencia de poblaciones en paisajes fragmentados. Sin embargo, pocos estudios ban evaluado 10s tipos de paisajes en 10s que 10s corredores serian mds efectivos. Realice’ pruebas para evaluar la hiphesis de que 10s corredores aumentan la colonizacihz de parches por la mariposa Junonia coenia independientemente de la distancia initial entre la mariposa y elparche. Escogi Junonia coeniaporque ya se ha demostrado que esta especie se mueve entre parches usando corredores preferentemente. Se liberaron individuos entre 16 a 192 m de distancia de corredores adyacentes abiertos o deparches experimentales de bosque abiertos. Ni 10s corredores ni la distancia tuvieron efectos significativos sobre la colonizacidn de 10s parches. Sin embargo, hubo una interaccih entre la presencia o ausencia de 10s corredores y la distancia. A distancias pequetias (16-64 mj, Junonia coenia colonizc5 con mds frecuencia parches abiertos cuando fue liberada dentro de1 bosque, que cuando fue liberada dentro de corredores abiertos, probablemente debido a que utilizb 10s corredores corn0 hdbitat. Sin embargo, la conlonizacibn deparchespor las mariposas liberadas en el bosque disminuyd r&idamente en correlacih con el aumento en la distancia hacia 10s parches, tal coma es establecido enpredicciones de un modelo de movimiento al azar. La colonizacidn de parches por mariposas liberadas en corredores no cambib con la distancia, y a distancias largas (128-192 m), la probabilidad de que las mariposas liberadas en corredores colonizaran parches abiertos fue doble de la de las mariposas liberadas en el bosque. Estos resultados sugieren que un factor critico, la distancia entre parches, puede determinar la efectividad relativa de corredores y otras configuraciones de1 paisaje, coma lo son 10s escalones, en la reduccidn de1 ais*Current address: Department of Zoology, Box 76I 7, North Carolina State University, Raleigh, NC 27695, USA., email [email protected] Paper submitted January 22, 1999; revised manuscript accepted September 29, 1999.