Interactions among Individuals within Population of Timothy

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  • WAKIMOTO Takashi
    Hokkaido Prefectural Central Agricultural Experiment Station
  • KIRA Kenji
    Hokkaido Prefectural Konsen Agricultural Experiment Station

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Other Title
  • チモシーの同一集団内における個体間の相互作用
  • チモシー ノ ドウイツ シュウダンナイ ニ オケル コタイカン ノ ソウゴ サ

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Description

This experiment was carried out not only to understand the relationships between population densities and individual variations but to estimate the nature of the interractions among individuals in a population indirectly from the type and the time trend of the frequency distribution of the agronomic characters of timothy. Two kinds of population namely, a variety, which is genetically heterogeneous, and a clone, which is genetically homogeneous but more or less variable among plantlets, of timothy were grown at three densities, 5, 10 and 15cm square respectively, under high and low fertilizations and were cut two times in one year over four year experiment. The plant height, the tiller number and the dried plant weight were recorded for individual plants. 1. The frequency distributions of the plant height changed with cutting times. The appearance of the negatively or positively skewed distributions together with the normal ones led to a supposition that the equalization and the competitive interaction of the plant height may be at work in opposing directions. 2. The frequency distributions of the tiller number were positively skewed under all treatments. The developments of the skewness for the variety population were greater than that for the clonal population. In many cases, the positive skewness of the frequency distribution was promoted by increasing plant density under the high fertilization. 3. The frequency distributions of the plant weight were more skewed than those of the tiller number. The responses in the development of the skewness for the plant weight by the treatments were identical with the pattern for the tiller number. 4. The relationship of the plant height and the tiller number to the plant weight was investigated. The tiller number showed a higher association with the plant weight than the plant height. 5. The marked variations of the size of plants at dense populations planted at 10cm or 15cm square could be of value to selection by a clearer distinction between low and high-yielding plants.

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