Interactions between habitat quality and connectivity affect immigration but not abundance or population growth of the butterfly, Parnassius smintheus

• Published in: Oikos 2009-10, Vol.118 (10), p.1461-1470
• Main Authors: Matter, Stephen F., Ezzeddine, Maya, Duermit, Elizabeth, Mashburn, Jeffery, Hamilton, Rebecca, Lucas, Tiffany, Roland, Jens
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal populations; Animal, plant and microbial ecology; Biogeography; Biological and medical sciences; Butterflies; Butterflies & moths; Connectivity; Emigration; Female animals; Flowers & plants; Forest habitats; Fundamental and applied biological sciences. Psychology; General aspects; Habitats; Insecta; Invertebrates; Meadows; Metapopulation ecology; Nectar; Parnassius smintheus; Population growth
• ISSN: 0030-1299; 1600-0706
• DOI: 10.1111/j.1600-0706.2009.17438.x

Habitat geometry has been a primary focus in studies of spatially structured systems. Recent studies have indicated that a more comprehensive approach including habitat quality may be needed, however most previous studies have neglected potential interactions between quality and geometry. We investigated the effects of habitat quality for the butterfly Parnassius smintheus among a series of 17 sub-populations. Specifically, we examined how habitat connectivity and local nectar flower density affect dispersal, and local population abundance and growth. We first determined which flower species were potentially important by examining nectar flower electivity and then quantified nectar flower density in meadows over a five year period (2003-2007). These data along with meadow connectivity were compared to local population statistics derived from mark-recapture over the same time period. The number of immigrants to a meadow increased as meadow connectivity increased, but showed no direct relationship with nectar flower density; however, there was a significant interaction between meadow connectivity and nectar flower density such that meadows with high connectivity and a high density of nectar flowers received the greatest number of immigrants. The number of emigrants from a meadow increased with increasing habitat quality and connectivity, but showed no interactive effect. The abundance of butterflies increased with meadow connectivity, but showed no relationship with habitat quality or any interactive effect. Separate experiments showed that access to nectar flowers significantly increased female reproductive output, but not lifespan. Despite the effects on immigration and reproductive output, local population growth rates also showed no relationship to nectar flower density. Our results indicate that habitat quality can be important for immigration in spatially structured populations; however, effects of habitat quality may not necessarily translate into higher abundance or population growth. Additionally, habitat quality should not be considered independently from habitat isolation, particularly if it directly affects dispersal. Preserving or augmenting habitat quality will do little to bolster immigration or colonization without adequate connectivity.