The adverse effects of invasive species are expected to be proportional to their relative densities. However, interference competition among conspecifics when invasive species are at high densities could limit such effects. These alternative hypotheses inspired us to test the density‐specific effects of red swamp crayfish Procambarus clarkii on experimental populations of the Amargosa Pupfish Cyprinodon nevadensis amargosae. The presence of crayfish had a significant influence on the survival of adult pupfish. In allopatry, adult pupfish survival was nearly 100%. However, the presence of crayfish resulted in significantly lower survival rates for adult pupfish, 84% and 69% survival for the low‐ and high‐density crayfish treatments, respectively. Crayfish also significantly affected the production of juvenile pupfish, with high juvenile production in the allopatric (705 juveniles/mesocosm) and low‐density crayfish treatments (705 juveniles/mesocosm). Juvenile production in both of these groups was significantly higher than that in the groups sympatric with high‐density crayfish (271 juveniles/mesocosm). The same pattern was observed when we evaluated the number of juvenile pupfish that were produced per adult female. We tested the hypothesis that interference competition among the crayfish would decrease predator efficacy by comparing the high‐density crayfish treatment with a fourth high‐density crayfish treatment wherein the crayfish were tethered. There was no significant difference in the rate of adult survivorship of the Amargosa Pupfish in the tethered and untethered high‐density treatment groups (70% and 69%, respectively). However, tethering resulted in a significant increase in juvenile production in the high‐density crayfish treatments (493 and 271 juveniles per mesocosm were produced in the tethered and untethered groups, respectively). The same patterns were observed when we examined the number of juvenile pupfish that was produced per adult female. These findings are inconsistent with the interference competition hypothesis, while supporting the hypothesis of density‐dependent effects of crayfish on Amargosa Pupfish populations. These findings suggest that reducing crayfish density will be a beneficial management tool for reducing the effects of crayfish on benthic fish populations.

中文翻译：

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入侵红色沼泽小龙虾克氏原螯虾对Amargosa up鱼实验种群的密度依赖性影响

预计入侵物种的不利影响与其相对密度成正比。但是，当入侵物种处于高密度时，种间干扰竞争可能会限制这种影响。这些替代假设启发我们测试红色沼泽小龙虾克氏原螯虾对Amargosa up鱼Cyprinodon nevadensis amargosae的实验种群的密度特异性作用。小龙虾的存在对成年p的存活有重要影响。在异养中，成年p的存活率接近100％。然而，小龙虾的存在导致成年p的存活率明显降低，低密度和高密度小龙虾的存活率分别为84％和69％。小龙虾还显着影响了幼小p鱼的生产，同种异体幼鱼的产量高（705个少年/中观），低密度小龙虾处理（705个少年/中观）。这两个组的少年产量均显着高于高密度小龙虾同养组（271个少年/中生代）。当我们评估每位成年雌性产生的幼稚p的数量时，观察到了相同的模式。我们通过比较高密度小龙虾处理方法与第四种高密度小龙虾处理方法（其中将小龙虾拴在一起）来检验小龙虾之间的竞争竞争会降低捕食者功效的假设。栓系和非栓系高密度治疗组的成年Am虫成活率没有显着差异（分别为70％和69％）。但是，拴系导致高密度小龙虾处理中的幼鱼产量显着增加（栓系和非栓系组分别产生493和271只幼鱼/中观）。当我们检查每位成年雌性产生的幼年p鱼的数量时，观察到相同的模式。这些发现与干扰竞争假设不一致，同时支持小龙虾对Amargosa up鱼种群的密度依赖性效应的假设。这些发现表明，降低小龙虾密度将是减少小龙虾对底栖鱼类种群影响的有益管理工具。