Ecological Equivalents

Ecological equivalents are species that are taxonomically unrelated — sometimes from entirely different families, genera, or even continents — but that occupy very similar niches in similar habitats found in different geographical regions. Because natural selection tends to favour similar body plans and life-histories for similar jobs, two ecologically equivalent species can end up looking and behaving remarkably alike even though their nearest relatives are quite different. The textbook illustrates this with plant examples: certain epiphytic orchids growing on trees in the Western Ghats of India differ taxonomically from the epiphytic orchids of South America, yet both groups are epiphytes filling the same 'grow-on-another-plant-for-support' niche. Likewise, the grass species of the Western Ghats grasslands are taxonomically distinct from the grass species of the temperate Steppe grasslands of North America, but ecologically both sets of grasses are primary producers filling essentially the same role — converting sunlight into biomas …