Cronin James T
Department of Biological Sciences, Louisiana State University, 206 Life Sciences Building, Baton Rouge, LA 70803, USA.
Oecologia. 2004 May;139(4):503-14. doi: 10.1007/s00442-004-1549-8. Epub 2004 Apr 17.
Few field studies of natural populations have examined the factors influencing local extinctions and colonization of empty habitat patches for a prey species and its predator. In this study, I carried out a census of planthopper (Prokelisia crocea; Hemiptera: Delphacidae) and egg parasitoid (Anagrus columbi; Hymenoptera: Mymaridae) incidence and densities in 147 host-plant patches (Spartina pectinata; Poaceae) over seven planthopper generations in a tall-grass prairie landscape. For both species, the likelihood of going extinct in a patch was related to a number of patch-specific variables: density, temporal variability in density, proportion of hosts parasitized (planthopper only), host-plant density, patch size, patch isolation, and composition of the surrounding matrix. Colonization likelihood was related only to the physical attributes of the patch. There was high patch turnover in this prairie landscape. On average, planthoppers went extinct in 23% of the patches and A. columbi went extinct in 51% of the patches in each generation. For the planthopper, extinction likelihood increased with a decrease in patch size and the proportion of the matrix composed of mudflat. Parasitism of eggs had no effect on the extinction likelihood of local P. crocea populations, suggesting that A. columbi may not play a major role in the patch dynamics of its host. The likelihood of extinction for A. columbi was dependent on factors that spanned three trophic levels. An increase in plant density, decrease in host density and decrease in parasitoid density all increased the likelihood of A. columbi extinction within a patch. The dependency on multiple trophic levels may explain the higher extinction risk for the parasitoid than its host. A. columbi extinction was also affected by the matrix habitat surrounding the patch--the effect was the opposite of that for P. crocea. Finally, vacant patches were colonized at rates of 53% and 34% per generation for the planthopper and parasitoid, respectively. For both species, colonization probabilities decreased with an increase in patch isolation. High host densities in a patch also favored high rates of colonization by A. columbi. I discuss how anthropogenic changes to the prairie landscape can affect the metapopulation dynamics and persistence time of this host-parasitoid interaction.
很少有针对自然种群的实地研究考察过影响猎物及其捕食者在空栖息地斑块中局部灭绝和定殖的因素。在本研究中，我对高草草原景观中147个寄主植物斑块（互生花米草；禾本科）内稻飞虱（克罗氏褐飞虱；半翅目：飞虱科）和卵寄生蜂（哥伦比亚纹翅小蜂；膜翅目：缨小蜂科）的发生情况及密度进行了七代稻飞虱数量普查。对于这两个物种而言，在一个斑块中灭绝的可能性与许多斑块特定变量有关：密度、密度的时间变异性、被寄生的寄主比例（仅针对稻飞虱）、寄主植物密度、斑块大小、斑块隔离度以及周围基质的组成。定殖可能性仅与斑块的物理属性有关。在这片草原景观中斑块更替率很高。平均而言，每一代中23%的斑块内稻飞虱灭绝，51%的斑块内哥伦比亚纹翅小蜂灭绝。对于稻飞虱来说，灭绝可能性随着斑块大小以及由泥滩构成的基质比例的减小而增加。卵的寄生对当地克罗氏褐飞虱种群的灭绝可能性没有影响，这表明哥伦比亚纹翅小蜂在其寄主的斑块动态中可能不发挥主要作用。哥伦比亚纹翅小蜂的灭绝可能性取决于跨越三个营养级的因素。植物密度增加、寄主密度降低以及寄生蜂密度降低均会增加哥伦比亚纹翅小蜂在一个斑块内灭绝的可能性。对多个营养级的依赖可能解释了寄生蜂比其寄主具有更高的灭绝风险。哥伦比亚纹翅小蜂的灭绝还受到斑块周围基质栖息地的影响——其影响与克罗氏褐飞虱相反。最后，空斑块被定殖的速率分别为每代稻飞虱53%和寄生蜂34%。对于这两个物种，定殖概率均随着斑块隔离度的增加而降低。斑块内高寄主密度也有利于哥伦比亚纹翅小蜂的高定殖率。我讨论了草原景观的人为变化如何影响这种寄主 - 寄生蜂相互作用的集合种群动态和持续时间。
