Ecosystem MCQs

Ecological pyramids are highly simplified models of ecosystems. What are the recognized limitations of ecological pyramids?

I. They do not take into account the same species belonging to two or more trophic levels.
II. They assume a simple food chain, which almost never exists in nature.
III. They do not accommodate a food web.
IV. Saprophytes are completely excluded from these pyramids.

Spatiotemporal dietary habits of animals complicate trophic classifications. Consider the dietary habits of a sparrow:

I. A sparrow is a primary consumer when it eats seeds, fruits, and peas.
II. A sparrow is a secondary consumer when it eats insects and worms.
III. A sparrow occupies the first trophic level when it functions as a primary consumer.
IV. The sparrow's feeding habits demonstrate that a trophic level represents a functional level rather than a static species.

Tree ecosystems present fascinating structural shapes when plotted. Analyze the statements regarding a tree-dominated ecosystem:

I. If we count the number of insects feeding on a single big tree, we obtain an inverted pyramid at that step.
II. If small birds feed on those insects, and larger birds feed on smaller birds, the pyramid of numbers remains perfectly upright.
III. In an ecosystem dominated by a single big tree, the pyramid of numbers is spindle-shaped or inverted.
IV. The pyramid of biomass for a tree ecosystem is generally inverted.

Terrestrial ecosystems generally show stable thermodynamic pyramids. Read the following generalizations:

I. In most terrestrial ecosystems, all standard pyramids (number, biomass, energy) are upright.
II. Primary producers are generally more in number and biomass than herbivores.
III. Herbivores are always fewer in number and biomass than carnivores.
IV. Energy at a lower trophic level is always more than at a higher level.

Climatic variables impose strong biological controls over soil microflora. Consider these statements regarding decomposition rates:

I. Temperature and soil moisture are the most important climatic factors regulating decomposition.
II. Soil microbes are highly active in cold and dry environments, which accelerates decomposition.
III. Low temperature and anaerobiosis inhibit decomposition, resulting in a build-up of organic materials.
IV. Humus undergoes decomposition at an extremely slow rate because it is highly resistant to microbial action.

Ecological succession represents a predictable and orderly change in species composition. Study the following statements regarding the general concepts of ecological succession:

I. The gradual and fairly predictable change in the species composition of a given area is called ecological succession.
II. During succession, some species colonize an area and their populations become more numerous, whereas populations of other species decline and even disappear.
III. The entire sequence of communities that successively change in a given area are called seral stages or seral communities.
IV. Succession and evolution would have been parallel processes at the time of the origin of life on Earth.

The starting point of ecological succession differs greatly depending on the initial state of the habitat. Read the statements below regarding primary and secondary succession:

I. Primary succession begins in areas where no living organisms ever existed, such as bare rock or newly cooled lava.
II. Secondary succession begins in areas that lost all the living organisms that existed there, such as abandoned farm lands or burned forests.
III. Primary succession is incredibly rapid compared to secondary succession because the bare substrate is completely sterile.
IV. In secondary succession, since some soil or sediment is already present, the rate of succession is much faster.

Succession is classified based on the nature of the moisture conditions of the habitat. Analyze the following statements:

I. Hydrarch succession takes place in wet areas and the successional series progress from hydric to mesic conditions.
II. Xerarch succession takes place in dry areas and the series progress from xeric to mesic conditions.
III. Both hydrarch and xerarch successions lead to a medium water condition called mesic condition.
IV. Climax community in xerarch succession is dominated by highly xerophytic lichens and mosses.

Seral stages of hydrarch succession show distinct vegetational shifts. Arrange and analyze these statements regarding the sequence of hydrarch succession:

I. The pioneer species in a water body are small phytoplanktons.
II. Over time, the phytoplanktons are replaced by rooted-submerged plants, then rooted-floating angiosperms, and then free-floating plants.
III. The next stages are reed-swamp, marsh-meadow, and scrub stages.
IV. The ultimate stable climax community is a forest.

Xerarch succession on bare rock involves specific pioneers and chemical weathering. Read the statements below:

I. Lichens are the pioneer species on a bare rock.
II. Lichens secrete organic acids to dissolve rock minerals, helping in weathering and soil formation.
III. Mosses succeed lichens and can hold a tiny amount of soil, paving the way for bigger plants.
IV. Herbaceous plants are directly followed by climax forest trees without any intermediate shrub stage.