Persistence in a Saltmarsh Insect Community: Experiments with Local Extinctions, Dispersal, and Colonization

正如我们对这种新苍蝇所做的工作所表明的那样，当地的胆蚊Asphondylia borrichiae Rossi和Strong种群显然已经灭绝，并经常被移民重新建立起来。唯一的寄主植物--海牛眼雏菊(Borricia Rutescens)的斑块都很小，而且是离散的。这里没有大片的“大陆”地带，为当地灭绝的种群贡献殖民者的蚊子种群的大小与那些已经灭绝的种群差不多。调查者假设这是一个真正的“集合种群”系统(Sensu Levins 1970)，在这个系统中，持久性是由于在大约均匀大小的斑块中局部灭绝后的重新殖民。寄生蜂是一个主要威胁，但它们的影响参差不齐。95%以上的寄生率出现在一些海牛眼斑块中，而其他斑块的寄生率要低得多。寄生率暂时较低的斑块可能会为已经灭绝的当地蚊子种群提供移民。三组实验将评估集合种群的动态。(1)天然海洋牛眼斑块中的蚊虫被迫灭绝，(2)盐沼中新斑块的形成将表明自然迁徙在持久性中的作用。(3)在远离自然蚊虫种群的内陆河口地区创造的新的海牛眼雏菊斑块，将允许比较在有和没有寄生蜂的情况下，在蚊虫迁徙的情况下的持久性。这项调查将产生关于对许多生物系统很重要的相互作用规模的关键信息//

Local populations of the gall midge Asphondylia borrichiae Rossi and Strong apparently become extinct and are re-established by immigrants frequently, as indicated by our work with this new species of fly. Patches of the sole host plant, sea oxeye daisy (Borrichia frutescens) are all small and discrete. There are no vast "mainland" patches, and gall-midge populations contributing colonists to locally extinct populations are about the size of those that have become extinct. The investigator posit that this is a true "metapopulation" system (sensu Levins 1970), in which persistence is due to recolonization after local extintion among roughly even-sized patches. Parasitoids are a major threat but are spotty in their effects. In excess of 95% parasitism occurs in some sea oxeye patches, while other patches have much lower rates. Patches with temporarily low parasitism rates are likely to provide immigrant to extinct local midge populations. Three sets of experiments will assess metapopulation dynamics. (1) Forced extinction of midges in natural sea Oxeye patches and (2) creation of new patches in salt marsh will indicate the role of natural immigration in persistence. (3) New patches of sea oxeye daisy, created in bayou areas far inland from natural midge population, will permit comparisons of persistence, with and without parasitoids, in the absemce of midge immigration. This investigation will yield critical information regarding scales of interactions important to many biological system //