ABSTRACT: Biotic interactions can determine species distributions and range limits, but little theoretical background exists regarding variation in commensalistic associations across latitudes. We estimated the geographic variation of the epibiont limpet Scurria parasitica’s association with its obligate host chiton species Enoplochiton niger across their distribution from Peru to northern Chile (12-30°S), to test the influence of host size variation on epibiont occurrence, individual spatial distribution, and body size. We analyzed the contribution of chiton body size to the pattern of abundance and distribution of occupancy of the epibiont limpet. We also examined the relationship between limpet shell size, coverage, and incidence probability function and chiton body size across latitudes. For some localities across the range edge of the host grazer’s distribution (i.e. 28-30°S), incidence and densities of the epibiont limpet were higher on larger chitons. Unoccupied host chiton proportions decreased at the poleward edge of the host-epibiont species range compared with sites located to the north. Increased variation in the epibiont limpet distribution on the host chiton plates suggests that limpets’ spatial segregation may have a role in lessening intraspecific interference competition with the host species at southern latitudes. Therefore, local and large-scale processes seem to contribute to modify the host-epibiont association pattern. Further studies are necessary to determine if this association shifts from commensalistic to antagonistic across the distributional range of both species.

中文翻译：

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Grazer 共生现象在物种范围边缘各不相同：寄主石鳖大小影响表皮生物帽贝发生率和空间隔离

摘要：生物相互作用可以确定物种分布和范围限制，但几乎没有关于跨纬度共生关联变化的理论背景。我们估计了表生帽贝Scurria parasitica与其专性寄主石鳖种Enoplochiton niger关联的地理变异。跨越它们从秘鲁到智利北部（12-30°S）的分布，以测试宿主大小变化对表皮生物发生、个体空间分布和体型的影响。我们分析了chiton体型对epibion​​t limpet的丰度和占用分布模式的贡献。我们还研究了跨纬度的帽贝壳大小、覆盖率和发生概率函数与石螟体大小之间的关系。对于跨越寄主食草动物分布范围边缘的一些地方（即 28-30°S），在较大的石鳖上，表生体帽贝的发生率和密度更高。与位于北部的地点相比，寄主 - 表皮生物物种范围的极地边缘的未占用寄主石壳虫比例减少。寄主石蚴板上表生物帽贝分布的变化增加表明，帽贝的空间隔离可能在减少与南纬寄主物种的种内干扰竞争方面发挥作用。因此，局部和大规模过程似乎有助于修改宿主-表皮生物关联模式。需要进一步研究以确定这种关联是否在两个物种的分布范围内从共生转变为对抗。