EXPERIMENTS

WHY DO SMALL POPULATIONS OF LUPINUS PERENNIS SUFFER REPRODUCTIVE LOSSES?

OPTION 1 LOW POLLINATOR VISITATION

Possible experiment:

  • Compare pollinator visitation in different population sizes


    A specified area in both large and small populations could be marked. For example, 2X2 meter plots may be used. This area would be observed for fifteen minute time intervals. Information to record includes the following: the number and types of pollinators seen, the number of flowers visited on each inflorescence by a pollinator, and the distance the pollinators traveled between visits. General information about weather conditions and habitat quality should also be noted. The observations of both large and small population sizes should be conducted simultaneously or close to the same time to eliminate differences due to factors such as weather conditions.

    DATA

    Visitation rate to flowers did not vary with population density. Population density is measured by the average distance to the nearest neighboring plant ("Mean NND"). Visitation rate is measured by the bee visitation rate per flower in a 15 minute observation period. The letters indicate different sites which were observed.



    OPTION 2 INCREASED SELFING COMBINED WITH INBREEDING DEPRESSION

    Possible experiment
    1. Determine if selfing is occurring

    To determine if selfing is occurring within a population, the genetic variation within that population must be investigated. Genetic methods must be used to assess this information. Techniques in the laboratory such as protein electrophoresis or DNA-based methods may be used.

    2. If selfing is occurring, is it disadvantageous to the population?

    If a population is experiencing selfing, an experiment may be performed to determine what effects it may have on the population. Hand-pollinations can be performed on plants within the population experiencing selfing. First, self-pollen, or pollen from the same plant, can be applied to flowers on an inflorescence. Next, outcross pollen, or pollen from another plant, can be applied to flowers on another inflorescence. The inflorescences chosen to be hand-pollinated should be similar in size and viability. By choosing similar plants, any major differences in offspring quality should reflect a difference due to the type of pollen used- either self or outcross. Inbreeding depression is a decrease in the quality of offspring caused by inbreeding (the mating between related individuals). Therefore, if inbreeding occurs, selfing is disadvantageous and may hurt reproduction.

    DATA

    The graph indicates that small populations have a lower proportion of their seeds germinate than larger populations. It is believed that these results are a result of inbreeding depression.

    OPTION 3 POOR HABITAT QUALITY

    Possible experiment:

  • To test habitat quality, seeds from the same pod should be obtained. Some seeds would be planted in a large population while the others would be planted in a small population. It is important for this experiment to be replicated with many seeds. Accurate results will not be obtained if only a few seeds are used.
  • Another method of assessing habitat quality is to compare the size of the plants if different populations. If a difference in plant size exists in different populations, the quality of the environment may be a contributing factor to the size of the plant. If the plants are the same size in different populations, the quality of the habitat may therefore be similar in both populations.

    DATA
    For this project, there does not appear to be any difference in habitat quality in the various populations being studied. Measurements show that plant size is the same in both large and small populations. Further evidence for similar habitat quality in both population sizes was obtained when soil texture, pH, and nutrient levels were assessed.

  • Note: Data was kindly provided by Dr. Randall Mitchell, Associate Professor of Biology at The University of Akron.