从生态学和地理学上讲，生态区小于生物区，而生物区又小于生物地理分布区。生态区涵盖了大范围的陆地或水域，有着独特的天然群落和物种的组合。植物、动物和生态系统的生物多样性使得某一生态区与其他生态区有显着不同。理论上来说，生物多样性或生态保护区中不同物种和群落之间在任一时间点的交会的概率应保持相对稳定，并在可接受范围（这一点在很大程度上是不确定的）内变化。对于所有的生物地理学区划方法，有三条注意事项。首先，没有任何一个生物地理学的框架适合所有分类群，生态区反映了最好的折衷方案。其次，生态区的边界很少形成生硬的边缘，而是由生态过渡带和动物栖地镶嵌其间。第三，大多数生态区包含着与所属生物群系不同的动物栖地。

An ecoregion (ecological region) is an ecologically and geographically defined area that is smaller than a bioregion, which in turn is smaller than an ecozone. All three of these are either less or greater than an ecosystem. Ecoregions cover relatively large areas of land or water, and contain characteristic, geographically distinct assemblages of natural communities and species. The biodiversity of flora, fauna and ecosystems that characterise an ecoregion tends to be distinct from that of other ecoregions. In theory, biodiversity or conservation ecoregions are relatively large areas of land or water where the probability of encountering different species and communities at any given point remains relatively constant, within an acceptable range of variation (largely undefined at this point).