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Macromoths of Northwest Forests and Woodlands

Biodiversity Studies

Information on biodiversity of macromoths is useful for understanding many ecological concerns, in particular, (1) determining food web relationships and the degree of dependency between plants, moths, and predators of moths; (2) recognizing special, rare, or endangered species and habitats; and (3) assessing the impact of land management practices. Two important measures of biodiversity are species richness and abundance of individuals. However, values for these measures require an ecosystem context for insightful interpretation of ecological function. Lepidoptera function in the dynamics of forested ecosystems by serving as defoliators, decomposers, prey or hosts to carnivores, and pollinators (Miller 1993). Therefore it is straight forward that measures such as species richness and abundance can be linked into assessing an ecosystem by documenting how many individuals and how many species are present or absent in a given habitat.

The abundance and species richness of macromoths is readily measured by various sampling techniques including light traps to capture night flying moths, aerial net collecting to capture day flying moths, and clipping or beating foliage to capture caterpillars. We have found that an average of 350 species of macromoths occur in a typical forested site dominated by Douglas-fir. Our record high collection of species from a single trap night was 104, but a count of 20-50 species per trap night is more typical.

A list of the species, plant and animal, present at a given location is an important part of conducting ecological studies; however, a list of species is most meaningful when it is interpreted into components relating each species to various ecological functions. Thus, a species list may be translated into an ecological database by relating life history attributes of the species to each name and then creating functional groups according to the life history attributes and the number of species exhibiting those attributes. For instance, in a comparison of two habitats in the Pacific Northwest, one in western Oregon and the other in eastern Oregon, we found that when the species list was translated into categories of macromoth species according to the host plant of the caterpillar that we could determine the importance of the plant communities on the biodiversity of the macromoths (Hammond and Miller 1998). The macromoth species were classified into three major vegetation groups: (1) conifers, (2) hardwood trees and shrubs, and (3) herbs and grasses.

The results showed that conifers supported only 10-12 percent of the species, whereas flowering trees and shrubs supported 52-66 percent of the species, and herbs-grasses supported 20-33 percent of the species. The most apparent difference between the two sites was in the proportion of individuals associated with an herb-grass feeding habit. The number of individual moths at the drier eastern site was dominated, 55 percent, by individuals that feed on herbs and grasses, whereas only 11 percent of moth abundance in the wetter western site was associated with herbs-grasses. By contrast, abundance of macromoths in the western site was dominated, 69 percent, by hardwood feeders compared with the eastern site where only 39 percent of the macromoths were associated with hardwood plant species.

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