Department of Biology, Temple University, Philadelphia, Pennsylvania 19122, USA.
Ecology. 2013 Jun;94(6):1370-7. doi: 10.1890/12-1382.1.
Latitudinal patterns of nonnative species richness suggest fewer successful invasions in the tropics, relative to temperate regions. One main hypothesis for this pattern is that biotic resistance to invasion is stronger in the tropics than at higher latitudes. Biotic resistance can limit the distribution and abundance of nonnative species and, in extreme cases, can prevent establishment. We provide the first experimental test of this hypothesis, comparing the strength of biotic resistance in a tropical and a temperate marine ecosystem. Predation is one mechanism of biotic resistance, and since predation can be stronger at lower latitudes, we predicted that predation will serve to increase biotic resistance more in the tropics than at higher latitude. We conducted predator-exclusion experiments on marine epifaunal communities, a heavily invaded system, focusing on nonnative tunicates as a model fauna. The effect of predation on species richness of nonnative tunicates was more than three times greater at sites in tropical Panama than in temperate Connecticut, consistent with the prediction of stronger biotic resistance in the tropics. In Connecticut, predation reduced the abundance of one nonnative tunicate but did not affect the abundances of any other nonnative tunicate species, and no species were excluded from communities. In contrast, predation resulted in striking reductions in abundance and often exclusion of nonnative tunicates from experimental communities in Panama. If proved to be general, latitudinal differences in the biotic resistance of communities to nonnative species establishment may help explain emerging patterns of global invasions.
非本地物种丰富度的纬度格局表明，与温带地区相比，热带地区的成功入侵较少。这种模式的一个主要假设是，与高纬度地区相比，热带地区的生物入侵阻力更强。生物入侵阻力可以限制非本地物种的分布和丰度，在极端情况下，还可以阻止其建立。我们首次对这一假设进行了实验检验，比较了热带和温带海洋生态系统中生物入侵阻力的强度。捕食是生物入侵阻力的一种机制，由于在低纬度地区捕食作用可能更强，我们预测在热带地区，捕食作用对生物入侵阻力的增强作用将超过高纬度地区。我们对海洋附生群落（一个受到严重入侵的系统）进行了捕食者排除实验，重点研究了作为模型动物群的外来被囊动物。在巴拿马热带地区，捕食作用对非本地被囊动物物种丰富度的影响比康涅狄格州温带地区大 3 倍以上，这与热带地区生物入侵阻力更强的预测一致。在康涅狄格州，捕食作用减少了一种非本地被囊动物的丰度，但没有影响任何其他非本地被囊动物的丰度，也没有物种从群落中被排除。相比之下，在巴拿马，捕食作用导致非本地被囊动物的数量明显减少，而且经常将其从实验群落中排除。如果这一结果被证明具有普遍性，那么群落对非本地物种建立的生物入侵阻力的纬度差异可能有助于解释全球入侵的新兴模式。
