Populations & Ecosystems Test - 5

The natural reservoir of phosphorous  is rock , which contains phosphorus in the form of phosphates . Sea water, animal bones and fossils are reservoirs of carbon.

Xerarch refers to series of developmental stages in an arid area like bare rock. Lichen stage is the first stage in Lithosere (or succession on bare rock).

The  community  begins with relatively few pioneering plants and animals and develops through increasing complexity until it becomes  stable  or self-perpetuating as a climax community . The "engine "of  succession, the cause of  ecosystem  change, is the impact of established species upon their own environments.

• Option A: It begins on a bare rock. This is incorrect as it describes primary succession, not secondary.

  Option B: It occurs on a deforested site. This is correct. Secondary succession occurs in areas where a community has been removed; it is the series of community changes which take place on a previously colonized, but disturbed or damaged habitat.

  Option C: It follows primary succession. While secondary succession does come after primary succession, this statement on its own is not fully descriptive of secondary succession.

  Option D: It is similar to primary succession except that it has a relatively fast pace. This is also correct; however, it is less specific than Option B. Secondary succession is typically faster than primary succession because the soil already exists, and often some remnants of the previous community remain.

  The most accurate and specific statement for secondary succession is:

  Option B: It occurs on a deforested site.

Phosphorus is a chemical element found on Earth in numerous compound forms, such as the phosphate ion (PO₄^3- ), located in water, soil, and sediments.

The quantities of phosphorus in soil are generally small, and this often limits plant growth. That is why people often apply phosphate fertilizers on farmland. Animals absorb phosphates by eating plants or plant-eating animals.

Azospirillum is a nitrogen-fixing bacterium in paddy fields . It is a very useful soil and root bacterium. It is an associative symbiotic  N₂  -fixing bacteria. When it is added to the soil, it multiplies in millions and can supply 20-40 Kg of nitrogen per hectare, per season.

Nutrients ultimately are chemical compounds. So, there is this natural pathway where the living matter is constantly circulated.

Nutrients are never lost from an ecosystem. Recycling of these nutrients happens at every stage, known as  the  nutrient cycle or biogeochemical cycle.

• Denitrifying bacteria, microorganisms whose action results in the conversion of nitrates in soil to free atmospheric nitrogen, thus depleting soil fertility and reducing agricultural productivity.
• Pseudomonas aeruginosa can, under anaerobic conditions (as in swampy or water-logged soils), reduce the amount of fixed nitrogen (as fertilizer) by up to 50 percent.

Ecological pyramids are the graphical representation of the trophic structure and function at successive trophic levels.
Ecological pyramids are of three general types :
(i) Pyramid of numbers , showing the number of organisms at each level.
(ii) Pyramid of biomass , showing the total dry weight of living matter.
(iii) Pyramid of energy , showing the rate of energy flow/productivity at successive trophic levels.

Hence, option C is correct.

Compensatory adjustment of organism to change in the environment, in nature or natural condition is known as acclimatization . Adjustment to seasonal changes in temperature come under acclimatization.