Synergistic interactions between edge and area effects in a heavily fragmented landscape

• Published in: Ecology (Durham) 2007, Vol.88 (1), p.96-106
• Main Authors: Ewers, Robert M., Thorpe, Stephen, Didham, Raphael K.
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Animals; area effects; Beetles; Biodiversity; Biological and medical sciences; Coleoptera; Conservation biology; Ecology; Ecosystem; Edge effects; Effects; Entomology; environmental models; Forest cover; Forest ecology; Forest habitats; Fundamental and applied biological sciences. Psychology; General aspects; Habitat fragmentation; Habitats; Insecta; Insects; Invertebrates; landscape ecology; Landscapes; matrix habitat; Metapopulation ecology; New Zealand; Population Dynamics; scale; slope; Species; species diversity; species-area relationship; statistical analysis; statistical models; synergistic interactions; wildlife habitats
• ISSN: 0012-9658; 1939-9170
• DOI: 10.1890/0012-9658(2007)88[96:SIBEAA]2.0.CO;2

Both area and edge effects have a strong influence on ecological processes in fragmented landscapes, but there is little understanding of how these two factors might interact to exacerbate local species declines. To test for synergistic interactions between area and edge effects, we sampled a diverse beetle community in a heavily fragmented landscape in New Zealand. More than 35 000 beetles of ∼900 species were sampled over large gradients in habitat area (10−2—106 ha) and distance from patch edge (20—2ⁱ⁰ m from the forest edge into both the forest and adjacent matrix). Using a new approach to partition variance following an ordination analysis, we found that a synergistic interaction between habitat area and distance to edge was a more important determinant of patterns in beetle community composition than direct edge or area effects alone. The strength of edge effects in beetle-species composition increased nonlinearly with increasing fragment area. One important consequence of the synergy is that the slopes of species—area (SA) curves constructed from habitat islands depend sensitively on the distance from edge at which sampling is conducted. Surprisingly, we found negative SA curves for communities sampled at intermediate distances from habitat edges, caused by differential edge responses of matrix- vs. forest-specialist species in fragments of increasing area. Our data indicate that distance to habitat edge has a consistently greater impact on beetle community composition than habitat area and that variation in the strength of edge effects may underlie many patterns that are superficially related to habitat area.