Countryside Biogeography of Moths in a Fragmented Landscape: Biodiversity in Native and Agricultural Habitats

Abstract

Studies of fragmented landscapes, especially in the tropics, have traditionally focused on the native fragments themselves, ignoring species distributions in surrounding agricultural or other human-dominated areas. We sampled moth species richness within a 227-ha forest fragment and in four surrounding agricultural habitats (coffee, shade coffee, pasture, and mixed farms) in southern Costa Rica. We found no significant difference in moth species richness or abundance among agricultural habitats, but agricultural sites within 1 km of the forest fragment had significantly higher richness and abundance than sites farther than 3.5 km from the fragment. In addition, species composition differed significantly between distance classes (but not among agricultural habitats), with near sites more similar to forest than far sites. These results suggest that (1) different agricultural production regimes in this region may offer similar habitat elements and thus may not differ substantially in their capacities to support native moth populations and (2) that the majority of moths may utilize both native and agricultural habitats and move frequently between them, forming "halos" of relatively high species richness and abundance around forest fragments. Correlations between species richness and the amount of nearby forest cover, measured over circles of various radii around the sites, suggest that halos extend approximately 1.0-1.4 km from the forest edge. The extent of these halos likely differs among taxa and may influence their ability to survive in fragmented landscapes. Biogeografía Rural de Polillas en un Paisaje Fragmentado: Biodiversidad en Hábitats Nativos y AgrícolasRicketts et al. Countryside Biogeography of Moths 379circundante, medida en círculos de diferente radio alrededor de los sitios de estudio, sugiere que los halos se extienden aproximadamente 1.0-1.4 km del borde del bosque. La extension de estos halos posiblemente difiere entre taxones y puede influenciar sus habilidades para sobrevivir en paisajes fragmentados.

Habitat specialization, body size, and family identity explain lepidopteran density–area relationships in a cross-continental comparison

“…This result is important because it may improve our ability to predict future density changes to fragmentation through inclusion of species characteristics such as wing span. Third, the DAR slope for habitat specialists was largely positive whereas the slope for habitat generalists and matrix specialists was negative, which is consistent with community-level studies suggesting that small patches have a community composition resembling the matrix (8,32). This pattern seemingly occurs for different reasons in moths and butterflies.…”

Biotic interactions, ecological knowledge and agriculture

“…This requires an expansion beyond habitat management at the field level to incorporate larger landscape patterns and processes, a still relatively unexplored area. In addition to the size and distance between habitat patches, we are beginning to realize the importance of the 'matrix' between patches for insect movement (Ricketts et al 2001). Many species that live in habitat patches also utilize resources outside the habitat patch, a desirable attribute for biological control since we want natural enemies to migrate into agricultural fields.…”

Species richness and abundance of native leaf miners are affected by the presence of the invasive horse-chestnut leaf miner

“…Various environmental variables may influence species richness and abundance of insects (Ricketts et al 2001). Confounding factors were minimized in the Swiss and French samples by selecting paired sites with similar characteristics.…”