Keeler-Wolf Todd
Department of Biology, University of California, Santa Cruz, CA, USA.
Oecologia. 1986 Sep;70(2):309-317. doi: 10.1007/BF00379257.
The Barred Antshrike (Thamnophilus doliatus) is the most abundant insectivorous foliage-gleaning vertebrate in both closed rain forest and second growth on the island of Tobago. However, it occurs only in second growth on the larger neighbor island of Trinidad and on the neotropical mainland.Habitat niche expansion into Tobago forest has been facilitated by several behavioral traits which set the antshrike apart from other foliage-gleaners of forest and second growth on Tobago. The antshrike captures a higher diversity of foliage, branch & trunk, and terrestrial arthropods. It forages over a wider range of heights and under a wider variety of crown cover situations than any of its closest ecological counterparts on Tobago. The antshrike also takes a wider range of prey sizes and regularly uses additional food sources, including fruit and ants, not taken by other guild members. The broad foraging niche of the antshrike enables it to breed during many times of the year when other narrower-niched foliage-gleaners do not.On Trinidad, although the most common foliagegleaner in second growth, the antshrike was not observed in adjacent closed rain forest. Several facts suggest that diffuse competition may be excluding antshrikes from Trinidad forest: 1) a general pattern of rarity or absence in other parts of its range where there are more guild members; 2) more species and individuals of foliagegleaners with an overall higher biomass in Trinidad forest than in Tobago forest; 3) foliage arthropod resources are significantly (1.7x) lower in Trinidad forest than Tobago forest, suggesting that Trinidad forest guild members may be depressing the quantity of important resources for antshrikes; and 4) Trinidad forest species with the highest foraging similarity to antshrikes have a greater precentage of prey captures comprised of relatively specialized attack behaviors than do Tobago forest antshrikes.Foraging generalists like the Barred Antshrike appear to expand or contract their habitat niches depending upon the number of ecologically similar species in a given habitat. They may occur in high densities in habitats typically foreign to them provided competitors are few and there is sufficient food to supply their catholic requirements.
横斑蚁鵙（Thamnophilus doliatus）是多巴哥岛封闭雨林和次生林中数量最多的食虫性叶层觅食脊椎动物。然而，在较大的邻国岛屿特立尼达岛以及新热带大陆上，它仅出现在次生林中。几种行为特征促进了其栖息地生态位向多巴哥岛森林的扩展，这些特征使横斑蚁鵙有别于多巴哥岛森林和次生林中的其他叶层觅食者。横斑蚁鵙捕食的叶层、树枝与树干以及陆生节肢动物的种类更为多样。与多巴哥岛任何与其生态关系最密切的同类物种相比，它在更广泛的高度范围内觅食，且在更多样化的树冠覆盖情况下觅食。横斑蚁鵙捕食的猎物大小范围也更广，并且经常利用包括果实和蚂蚁在内的其他食物来源，而其他同资源种团成员并不食用这些食物。横斑蚁鵙广泛的觅食生态位使其能够在一年中的许多时候繁殖，而其他生态位较窄的叶层觅食者则不能。
在特立尼达岛，横斑蚁鵙虽是次生林中最常见的叶层觅食者，但在相邻的封闭雨林中未被观察到。有几个事实表明，扩散竞争可能正在将横斑蚁鵙排除在特立尼达岛森林之外：1）在其分布范围的其他地区，若有更多同资源种团成员，它通常较为稀少或不存在；2）特立尼达岛森林中叶层觅食者的物种和个体数量更多，总体生物量也高于多巴哥岛森林；3）特立尼达岛森林中叶层节肢动物资源比多巴哥岛森林显著减少（减少了1.7倍），这表明特立尼达岛森林的同资源种团成员可能压低了横斑蚁鵙重要资源的数量；4）在特立尼达岛森林中，与横斑蚁鵙觅食相似度最高的物种，其捕食猎物中由相对特殊攻击行为构成的比例高于多巴哥岛森林中的横斑蚁鵙。
像横斑蚁鵙这样的广食性动物似乎会根据特定栖息地中生态相似物种的数量来扩展或收缩其栖息地生态位。如果竞争者较少且有足够的食物满足其广泛的需求，它们可能会在通常不属于它们的栖息地中高密度出现。
