Population Regulation of Eschscholzia Californica by Competition and Edaphic Conditions

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Abstract
The species occurs in western North America on well-drained soils of dunes, alluvial fans, river terraces, steep banks and rocky places, frequently associated with grasses. It also occurs on serpentine soils and after fires. To explain these facts populations were grown on soils on which they do and do not occur naturally. The results suggest that the species is insensitive to soil type but that a certain degree of genetic specialization exists. An artificial slope was constructed with constant water table. Eschscholzia and Avena fatua were grown singly and together on it in different proportions. When grown alone, E. californica survives in greater numbers and flowers closer to the bottom of the slope (nearer water table), than when in competition. It responds more plasticly to intra- than to interspecific competition, in which mortality is higher. The results indicate that there is a certain minimum density of Avena above which Eschscholzia is suppressed and cannot reproduce. Eschscholzia grows where grasses cannot exist in densities above this minimum: cocky or steep places, in porous, sterile or toxic soils. It is adapted to these conditions through its deep taproot and inherent tolerance to soil type.

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