Ecosystem Sciences Division, Department of Environmental Science, Policy, and Management, University of California, 37 Mulford Hall, Berkeley, CA 94720-3114, USA.
Oecologia. 2010 Jun;163(2):385-93. doi: 10.1007/s00442-010-1566-8. Epub 2010 Feb 5.
The ideal free distribution (IFD) predicts that organisms will disperse to sites that maximize their fitness based on availability of resources. Habitat heterogeneity underlies resource variation and influences spatial variation in demography and the distribution of populations. We relate nest site productivity at multiple scales measured over a decade to habitat quality in a box-nesting population of Forpus passerinus (green-rumped parrotlets) in Venezuela to examine critical IFD assumptions. Variation in reproductive success at the local population and neighborhood scales had a much larger influence on productivity (fledglings per nest box per year) than nest site or female identity. Habitat features were reliable cues of nest site quality. Nest sites with less vegetative cover produced greater numbers of fledglings than sites with more cover. However, there was also a competitive cost to nesting in high-quality, low-vegetative cover nest boxes, as these sites experienced the most infanticide events. In the lowland local population, water depth and cover surrounding nest sites were related with F. passerinus productivity. Low vegetative cover and deeper water were associated with lower predation rates, suggesting that predation could be a primary factor driving habitat selection patterns. Parrotlets also demonstrated directional dispersal. Pairs that changed nest sites were more likely to disperse from poor-quality nest sites to high-quality nest sites rather than vice versa, and juveniles were more likely to disperse to, or remain in, the more productive of the two local populations. Parrotlets exhibited three characteristics fundamental to the IFD: habitat heterogeneity within and between local populations, reliable habitat cues to productivity, and active dispersal to sites of higher fitness.
理想自由分布（IFD）预测，生物将根据资源的可利用性分散到最大程度提高其适应性的地点。栖息地异质性是资源变化的基础，影响着种群的空间动态和分布。我们将在委内瑞拉的一个箱巢繁殖的 Forpus passerinus（绿颊鹦鹉）种群中，在十年来多次测量的多个尺度上的巢位生产力与栖息地质量联系起来，以检验 IFD 的关键假设。在当地种群和邻里尺度上的繁殖成功率的变化对生产力（每年每巢箱育雏数）的影响比巢位或雌鸟身份的影响大得多。栖息地特征是巢位质量的可靠线索。植被覆盖较少的巢位比植被覆盖较多的巢位产生的育雏数更多。然而，在高质量、低植被覆盖的巢箱中筑巢也存在竞争成本，因为这些巢位经历了最多的杀婴事件。在低地当地种群中，巢位周围的水深和覆盖与 F. passerinus 的生产力有关。低植被覆盖和更深的水与更低的捕食率有关，这表明捕食可能是驱动栖息地选择模式的主要因素。鹦鹉也表现出定向扩散。更换巢位的成对更有可能从低质量的巢位扩散到高质量的巢位，而不是相反，并且幼鸟更有可能扩散到或留在两个当地种群中生产力更高的种群中。鹦鹉表现出 IFD 的三个基本特征：当地种群内和种群间的栖息地异质性、生产力的可靠栖息地线索以及向更高适应性地点的积极扩散。
