Much of our understanding of natural invasions is retrospective, based on data acquired after invaders become established. As a consequence, we know little about the characteristics of the early population growth and habitat use of the invaders during establishment. Here we report on experimental introductions of guppies into natural streams in which we conducted monthly censuses of each population. Two of the four introductions were in streams with thinned canopies, which mimic a common form of habitat disturbance. We conducted similar censuses of natural populations to characterize natural population densities and generate a null distribution against which we could test a priori hypotheses about the establishment of the experimental invaders. We constructed a pedigree for one population, which enabled us to quantify lifetime reproductive success. Population simulations predict that the nature of the introduced population’s life history, in combination with reduced risk of predation in the introduction sites, will result in explosive population growth; however, populations of introduced invaders instead grew to match densities observed in natural streams with intact canopies. Experimental populations in streams with thinned canopies grew to densities that often exceeded those of natural streams with intact canopies. High population densities were associated with the increased use of marginal habitat. Adult females and males that moved into marginal habitat suffered no apparent fitness loss, suggesting lower population densities found there compensated for lower habitat quality. Our results suggest that the ecological setting in which invasions occur plays a role at least comparable in importance to that of the invader’s inherent characteristics in shaping early population growth and habitat use.

中文翻译：

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物种入侵的实验研究：早期种群动态和干扰在入侵成功中的作用

我们对自然入侵的大部分​​理解是回顾性的，基于入侵者成立后获得的数据。结果，我们对侵略者在建立期间的早期种群增长和栖息地利用的特征知之甚少。在这里，我们报告了孔雀鱼在自然流中的实验性引进，在这些实验中我们每月对每个人口进行普查。四个引种中的两个在冠层变薄的溪流中，模仿了常见的栖息地干扰形式。我们进行了类似的自然人口普查，以表征自然人口密度并生成零分布，以此可以检验关于实验入侵者建立的先验假设。我们为一个人口建立了血统书，从而使我们能够量化一生的生殖成功。人口模拟预测，引入人口的生活史的性质，加上引入地点捕食风险的降低，将导致人口爆炸性增长；然而，入侵者的数量却增长了，以与天然河水中完整冠层的密度相匹配。在冠层变薄的溪流中，实验种群的密度往往超过了冠层完整的天然溪流的密度。人口密度高与边缘生境的利用增加有关。移居到边缘栖息地的成年雌性和雄性没有明显的适应性丧失，表明那里发现的较低的人口密度弥补了较低的栖息地质量。