Graduate Thesis Or Dissertation

 

Foraging ecology of pollinators in the early stages of secondary succession in the western hemlock (Tsuga heteropohylla (Raf.) Sarg.) zone of the Oregon Coast Range Public Deposited

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  • The early stages of secondary succession of the McDonald and Paul Dunn State Forests, Corvallis, Oregon, were grouped into three stages; herb, herb-shrub, and shrub, based on vegetation types. Flowers of herbaceous species and residual shrubs dominated in the early years after clear-cutting. Woody plants became increasing abundant in the shrub-dominated period. Flowers of native plant species were common in the spring, while the introduced species were abundant in the summer. The important floral resources for pollinators in the spring were Rubus ursinus, and Rubus leucodermis. Rubus discolor and Cirsium spp. dominated and contributed to early summer and late summer flowering peaks, respectively. Insect pollinators partitioned floral resources by foraging at different times of the season or at different times of the day, or utilizing different sizes of flower patches, or by concentrating on different flower species. Differences in seasonal activity of the bees were due to innate features of the life-histories. Daily activities were strongly influenced by the ambient temperature in early spring, and by resource availability in the summer. Eighty of the ninety-six species of pollinators were bees. Common native bee genera were Andrena, Bombus, Halictus, Lasioglossum, and Osmia. The most dominant flower-visitor was the introduced honey bee (Apis mellifera). The foraging levels of the honey bees depressed flower visitation of certain wild bee taxa, especially Bombus. The supplementation and removal of the cordovan honey bees during late summer indicated a competitive release on flower visitation by Bombus. Competition from Apis was probably crucial in the spring, as demonstrated by the increase in visitation rates of Bombus when Apis were excluded from the flower patches of Rubus leucodermis.
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