Kirkendall Lawrence R, Stenseth Nils Chr
Division of Zoology, Department of Biology, University of Oslo, P.O. Box 1050, Blindern, N-0316, Oslo 3, NORWAY.
Evolution. 1990 May;44(3):698-714. doi: 10.1111/j.1558-5646.1990.tb05949.x.
Pseudogamous females reproduce parthenogenetically but require sperm. We analyze a density- and frequency-dependent model for the ecological and evolutionary stability of bisexual populations exposed to invasion by pseudogamous clones. In particular, we examine the effects of partial niche overlap and asymmetric competition between sexual and asexual forms. The model predicts that for a variety of relative fitness values for asexual females, pseudogamous forms can successfully invade bisexual populations. The probability of successful invasion increases as niche overlap decreases. Furthermore, invaded populations are often likely to be stable; for the parameter values analyzed, only combinations of nearly complete niche overlap and high asexual fitness will lead to extinction. Even such combinations will be stable under pronounced asymmetric competition. Asymmetric competition does not, however, affect the invadability of bisexual populations. The model predicts that stable populations cannot have more than three or four females per male; populations with more biased sex ratios are expected to be unstable. We analyze available sex ratio data for pseudogamous insects, fish, and salamanders, and find significant changes in roughly one-half of the asexual-dominated populations, but in only one sexual-dominated population. This analysis includes previously unpublished data on population sex ratios in a pseudogamous bark beetle, Ips acuminatus. Some asexual-dominated populations have far more than four females per male, contrary to predictions of the model.
伪配雌体通过孤雌生殖进行繁殖，但需要精子。我们分析了一个密度和频率依赖模型，用于研究暴露于伪配克隆入侵的两性种群的生态和进化稳定性。特别地，我们研究了两性和无性形式之间部分生态位重叠和不对称竞争的影响。该模型预测，对于无性雌体的各种相对适合度值，伪配形式可以成功入侵两性种群。成功入侵的概率随着生态位重叠的减少而增加。此外，被入侵的种群通常可能是稳定的；对于所分析的参数值，只有几乎完全的生态位重叠和高无性适合度的组合才会导致灭绝。即使是这样的组合在明显的不对称竞争下也会是稳定的。然而，不对称竞争并不影响两性种群的可入侵性。该模型预测，稳定种群中每只雄性的雌性数量不能超过三到四只；性别比更偏向的种群预计是不稳定的。我们分析了伪配昆虫、鱼类和蝾螈的现有性别比数据，发现在大约一半以无性为主的种群中有显著变化，但在只有一个以有性为主的种群中有变化。该分析包括之前未发表的关于伪配树皮甲虫尖尾扁小蠹种群性别比的数据。一些以无性为主的种群每只雄性的雌性数量远远超过四只，这与模型的预测相反。
