Lesson 7 of 13 · 9 min
Population interactions
NCERT §11.1.4
Out at the lake, Rohan watches cattle egrets walking beside grazing buffaloes and asks, 'Are they friends?' Ma'am hands him a table instead of an answer.
The lesson in notes
In short
No natural habitat holds just one species. Every species needs at least one other species to feed on.
Even a plant that makes its own food needs soil microbes to break down organic matter and return inorganic nutrients, and often an animal to pollinate it.
Plants, animals and microbes therefore interact and together form a biological community.
Interspecific interactions are those between populations of two different species. For each species the effect can be beneficial (+), detrimental (−) or neutral (0).
Mutualism (+, +): both species gain. Competition (−, −): both lose.
Predation and parasitism (+, −): one gains (predator, parasite) and the other is harmed (prey, host).
Commensalism (+, 0): one gains and the other is neither helped nor harmed. Amensalism (−, 0): one is harmed and the other is unaffected.
Predation, parasitism and commensalism have one feature in common: the two species live closely together.