Date of Award:

5-1-1982

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Department name when degree awarded

Life Sciences:Biology

Committee Chair(s)

Ivan G. Palmblad

Committee

Ivan G. Palmblad

Committee

Mary Barkworth

Committee

George Bohart

Committee

Richard J. Shaw

Abstract

The primary nectar robbing of Mertensia oblongifolia (Nutt.) G. Don, a long-tubed bee-pollinated borage was investigated. The primary robbers, short-tongued Bombus occidentalis Cresson queens, removed nectar through a hole made in the corolla. These robber bumble bees were never observed to act as pollinators. The long-tongued solitary bee pollinators of M. oblongifolia concentrated their visits (>80%) during the hours 0900-1400 (MST). Pollinators did not seem to discriminate in visits between robbed and non-robbed flowers. Robber visits were more widely distributed from 0730 to 1500 (MST). During the part of the season when pollinators were most active their level of visitation (visits/flower/day) was estimated to be at least eight times higher than that of robbers. Pollinators also had a faster rate of visitation (14 flowers/minute) than robbers (9 flowers/minute). Because of these differences in timing, frequency, and rate of robber and pollinator flower visitation, nectar robbing may have little effect on pollinator use of M. oblongifolia. During the portion of the season when poor weather conditions curtailed pollinator activity, robbers continued to use M. oblongifolia flowers and may have been finding greater nectar reward than during periods of high pollinator activity. The amount of nectar taken by robbers was probably limited by the small population of these bees, consisting only of queens. The proportion of flowers punctured by robbers was not correlated with density at the 5 m2 block size in two of the three weeks studied. An inverse correlation (p≤.05) was suggested in the third week. The possibility exists that robbers may have different spatial use patterns of flowers than do pollinators. The results of this study suggest a preliminary robber-community picture in which 1) the pollinator:flower resource ratio is high during a significant portion of the blooming season and 2) the robber use of "stolen" nectar is limited by low robber populations, relatively low rates of robber visitation, or by alternative nectar sources for robbers.

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