III. Changes in abundance and diversity due to spatial and temporal dynamics of dominant species.

We have quantified the temporal and spatial abundance of two exotic predator species in the KBS-LTER agricultural landscape: Coccinella septempunctata and Harmonis axyridis. When the LTER was initiated in 1989, C. septempuntata was concluding an outbreak phase and thus was the dominant coccinellid. We have observed that this species exhibits a 5-year population cycle which influences the temporal diversity and abundance of the ladybird beetle complex. In 1994, we detected the exotic species, H axyridis in the LTER landscape. This species reached outbreak proportions and thus became a dominant ladybird species in all habitats. Before the arrival of H. axiridis the dominant coccinellids in the agricultural landscape were Coccinella septempunctata, and Coleomegilla maculata lengi. Both species primarily inhabit field crops, forage, and herbaceous plants in old-field habitats. Neither species forages in arboreal habitats during the summer. Coccinellid species that foraged in deciduous trees in the Michigan landscape before the arrival of H. axyridis included B. ursina, C. stigma, and C. munda. This situation indicates that most resident species of coccinellids occupy only part of the habitats that H. axyridis can potentially use. We believe that H. axyridis’ broad habitat utilization has allowed it to maintain high populations in a mixed agricultural-forest landscape, thereby enabling it to become a dominant coccinellid in this southern Michigan landscape. The decline in the numbers of some ladybird beetle species in deciduous habitats indicates that competitive displacement by H. axyridis is already occurring. Populations of H. axyridis in Michigan peak early and late in the season, depending on the habitat, whereas populations of C. septempunctata peak during mid-season. Both differences in habitat preference and time of occurrence may help both exotic species avoid competition between themselves in the mixed agricultural-forest landscapes of southwest Michigan.

Publications Colunga-G, M. and S.H. Gage. 1998. Arrival, Establishment, and Habitat Use of the Multicolored Asian Lady Beetle Harmonia axyridis (Pallas)(Coleoptera) in a Michigan landscape. Environ. Entomol. 27: 1574-1580

Posters Colunga-G M. and S.H. Gage. 2000. Patterns of Abundance of Insect Predators in a Diversified Agricultural Landscape: a 12-year synthesis in the KBS-LTER. Long Term Ecological Research all Scientist Meeting. Snowbird, Utah.