Question

What will be the P/R ratio of a climax community and a pioneer community. What explanation could you offer for the changes seen in

P/R ratio of a pioneer community and the climax community.

Answer 1

P/R ratio:

P/R ratio or production/respiration ratio refers to the gross productivity to respiration ratio of the total community of species.

P/R = 1 when there is a steady community

P/R > 1 when there is an accumulation of organic matter.

P/R ratio for a pioneer:

● The Pioneer community, the first stage in ecological succession, consists of species that are the first colonisers of the habitat.

● On bare rock, the pioneer species are usually lichens. They produce more organic matter as compared to the assimilation of this organic matter through respiration.

● Hence the P/R value is more than 1.

P/ R ratio for climax community:

● A climax community is the last stage in ecological succession where the community is well established.

● The species diversity is more.

● As a result, the respiration rate of the community and the production of organic matter are in balance.

● Hence, the P/R value is 1.

Reason for the difference in the P/R ratio:

● When a colony needs to be established more organic matter has to be accumulated. During this stage, the number of species is less. Therefore, the respiratory losses are less and the gross productivity is more.

● In the climax community, the amount of organic matter present in the species balances out the respiratory losses resulting in a steady-state.

● The difference in the P/R ratio is due to the increase in the species composition from the pioneer stage to the climax stage.