Ecosystem Test - 73

Plagiosere is a series of plant communities that are interrupted or disturbed by an outside agent. A plagioclimax community is an area or habitat in which the influences of the humans have prevented the ecosystem from developing further. The ecosystem may have been stopped from reaching its full climatic climax or deflected towards a different climax by activities such as, cutting down the existing vegetation, burning as a means of forest clearance, planting trees or crops, grazing and trampling by domesticated animals, harvesting of planted crops. These are known as arresting factors. In each case, human activity has led to a community which is not the climax community expected in such an area.

Continental shelf is the seabed from the shore to the edge of the continental slope, covered by relatively shallow seas (known as shelf seas) and gulfs. Generally, it is one of the most productive parts of the ocean. Many benthic, coastal animals have evolved larval stages which swim for a time in the water. Although, the continental shelf zones comprise only 7.6% of the surface area of the world oceans, they provide 15-30% of the oceanic primary production. A special type of ecosystem that can be found on the continental shelves is the kelp forest. This is one of the more productive ecosystems on the continental shelf. Photosynthesis can only occur when enough light penetrates down the water column. This area is called the photic zone and varies from a few metres to as deep as 150 metres in some places. All primary productivity occurs in the photic zone, and as a result, about 90% of all marine life lives in this upper zone mainly.

Primary succession is a process of gradual changes in the ecosystem, that starts where no living organisms are there e.g., bare rock, newly created pond or reservoir. In this period weathering of rocks and formation of soil takes place which is time-consuming process. Whereas secondary succession occurs in areas that somehow, lost all the living organisms, that existed there. Secondary succession begins in areas where natural biotic communities have been destroyed, such as in abandoned farmlands, burned or cut forests, lands that have been flooded. Since some soil or sediment is present, secondary succession is faster than primary succession. 

• The entire sequence of communities, that successively change in a given area is called sere. 
• The individual transitional communities are termed seral stages or seral communities. 
• In the successive seral stages, there is a change in the diversity of species of organisms, an increase in the number of species and organisms as well as an increase in the total biomass. 
• Thus, the correct answer is option C.

The energy flow in ecosystems is unidirectional and there is a progressive decrease of energy along the food chain. The energy is lost as heat in metabolic activities such as respiration, hunting, etc. The primary producers like the autotrophs there is more amount of energy available. The least energy is available in the tertiary consumers. Thus, the shorter food chain has more amount of energy available even at the highest trophic level. The energy pyramid is always upright and vertical. 

Ecological succession is the process of gradual change in an ecological community over time. These changes are fairly predictable and orderly within an ecological community. The species composition will change over time as some species become more prominent while others may fade out of existence. As the community develops over time, vegetation grows taller and the community becomes more established.

Ecological succession is the gradual process by which ecosystems change and develop over time. These are differentiated into primary and secondary. primary succession is one which begins in new habitats and is not influenced  by pre-existing communities. Secondary successions refer to one that is caused due to disruption of a pre-existing community. Cultivated plants in agriculture belong to the late second-degree succession. Thus, the correct answer is option D.

Ecological succession is the change in the flora and fauna of a particular species over a period of time in response to the frequent changing of climatic and edaphic conditions. Pioneer species are the first to colonise previously disrupted or damaged ecosystem. Therefore, the correct answer is option C.