Population evolve to maximise their reproductive fitness, also called Darwinian fitness (high r value) in the habitat in which they live . Under a particular set of a selection pressure, organisms evolved towards the most efficient reproductive strategy. Some organisms are breed only one time in their life time some examples are pacific salmon fish, Bamboo etc.while other breed many times during their life time (most birds and mammals) . Some produce a large number of small seized offspring there examples are Oysters, Pelagic fishes etc. While other produce a small number of large seized of offspring there examples are birds, mammals etc. So, which are desirable for maximising fitness? Ecologists suggest that life history traits of organisms have evolved in relation to the constraint imposed by the abiotic and the biotic components of the habitat in which they live. Evaluation of life history traits in different species is currently an important area of research being conducted by ecologists.
On earth the minimal requirement is one more species on which it can feed . Even a plant species, which made its own food, cannot survive alone , it needs soil microbes to break down the organic matter in soil and return the inorganic nutrient for absorption.
