Distribution and functional roles of rare and uncommon moths (Lepidoptera: Noetuidae: Plusiinae) across a coniferous forest landscape

The temporal and spatial distribution and abundance of 15 rare to uncommon species of plusiine moths were compared across a watershed landscape dominated by a coniferous forest located on the western slope of the Cascade Mountains in Oregon. The 5-yr study assessed the species in the context of functional roles related to caterpillar host plants categorized into three guilds: conifer, hardwood tree and shrub, and herbaceous-feeding species. Also, the landscape was considered in the context of five geographic zones based on elevation and habitat type. Species richness and abundance were highest within the herb-feeding guild, seven (47%) species and 74 (47%) individuals. The conifer-feeding guild consisted of four species (27%) and 64 (40%) individuals, whereas the hardwood tree and shrub guild consisted of four species (27%) and 21 (13%) individuals. In combination, zones II, III, and IV, high elevation sites with extensive subalpine meadow habitat, exhibited a species richness of 14 (93%) and 119 (75%) individuals. Six species occurred in only one of the five zones, and three of these species occurred in zone II, a mid to high elevation zone with a total of nine plusiine species. Only 3 of the 15 species occurred in all five zones; each of these species represented one of the three feeding guilds and exhibited their highest abundance in zone III, a high elevation site with extensive subalpine meadow habitat. The presence of subalpine meadows contributed to increasing landscape heterogeneity across the watershed and was the primary factor contributing to the overall species richness among the Plusiinae within the H.J. Andrews Experimental Forest by providing a suitable environment for species in the herb-feeding guild. We suggest that, in a context that may be generalized to other environments and other taxa, the additive effects of rare and uncommon species with special or restricted habitat requirements provide an important contribution to the biodiversity within a local landscape. Furthermore, environments with a relatively high degree of temporal variability, such as meadows and other early successional plant communities, can be a major factor in contributing to the biodiversity within a local landscape.