Organisms And Populations

(A) Step 1: Co-evolution is a process where two or more species reciprocally affect each other’s evolution.
Step 2: In the case of Ophrys, the orchid flower mimics the female bee in appearance and scent.
Step 3: This mimicry attracts the male bee for mating, during which pollination occurs.
Step 4: The specific bee species and Ophrys have co-evolved to maintain this highly specialized pollination strategy.
Conclusion: This precise and exclusive interaction is one of the best examples of co-evolution.
OR
(B) Step 1: Correct order of decomposition steps:

1. Fragmentation
2. Leaching
3. Catabolism
4. Humification
5. Mineralisation

Step 2: Explanation of the fourth step — Humification:

• Humification leads to the formation of a dark-colored, amorphous substance called humus.
• Humus is highly resistant to microbial action and hence persists in the soil for a long time.
• It plays a key role in soil fertility by improving its texture and water-holding capacity.

(A) Step 1: Mutualism is an interaction where both species benefit from each other.
Step 2: In the case of fig tree and wasp:

• The fig tree is pollinated only by its specific species of wasp.
• The wasp lays eggs inside the fig fruits.
• The fig provides shelter and nourishment for the larvae.
• Both species are dependent on each other for survival and reproduction.

Step 3: This is a classic example of co-evolved mutualism.

OR

(B) Step 1: The ecological pyramid of number represents the number of organisms at each trophic level. In this case, the pyramid is upright.
Step 2: Representation of the pyramid:

Step 3:

• The number of organisms decreases from producers to top consumers.
• A single banyan tree supports many insects, which in turn are preyed upon by more birds.

Thus, this pyramid shows how energy flow supports different populations.

1. • [(i)] When unlimited resources are available, populations exhibit exponential growth. The population size increases rapidly without any environmental resistance.
   • [(ii)] The equation for exponential growth is: where:
     • = population size
     • = intrinsic rate of natural increase
     • = change in population size per unit time
   • [(iii)] The growth curve is called the J-shaped curve. It shows rapid increase initially and continues rising steeply without a plateau.
2. • [(i)] Alexander von Humboldt observed that within a region, species richness increases with increasing area but only up to a certain limit.
   • [(ii)] The Species-Area relationship equation is: where:
     • = species richness
     • = area
     • and = constants
   • [(iii)] Graphical Representation:
   • 

(a) (i) Description of the Population Growth Curve:

In nature, when resources such as food, water, and space are unlimited, the population of a species shows an exponential growth pattern. This means that the population increases rapidly over time, as every individual reproduces at its maximum potential. There are no environmental resistance factors like competition, disease, or predation to limit growth.

(ii) Equation of the Growth Curve:

The exponential population growth is mathematically described by the following equation:

Where:

• N = Population size
• r = Intrinsic rate of natural increase
• = Rate of change of population size over time

(iii) Name and Graphical Representation:

The curve is called a J-shaped growth curve.

OR

(b) Species-Area Relationship

(i) Conclusion by Alexander von Humboldt:

During his explorations in the South American jungles, Alexander von Humboldt observed that within a given region, the species richness (i.e., number of species) increased with increasing explored area. However, the increase was not linear — it increased rapidly at first and then slowly. This gave rise to the concept of the Species-Area Relationship.

(ii) Equation of the Species-Area Relationship:

The relationship is described mathematically by the equation:

Where:

• S = Number of species (species richness)
• A = Area
• C = Constant (y-intercept)
• Z = Slope of the line (varies for different taxa and areas)

(iii) Graphical Representation:

The graphical representation of species richness against area is shown below. It is a curve that flattens out with increasing area.

Depiction and Description:

The ecological pyramid of number represents the number of individuals at each trophic level in an ecosystem. In this case, we have:

• Primary Producers (Banyan Tree): The base of the pyramid consists of one banyan tree, which is a producer (autotroph). It forms the first trophic level.
• Primary Consumers (Insects): At the second level, 20 insects feed on the banyan tree, making them the primary consumers. They depend directly on the producer for energy.
• Secondary Consumers (Birds): The third level consists of 32 birds that feed on the insects, making them secondary consumers. These birds depend on the primary consumers (insects) for food.

Trophic Levels:

• Trophic Level 1: Banyan tree (Producer)
• Trophic Level 2: Insects (Primary Consumers)
• Trophic Level 3: Birds (Secondary Consumers)

Graphical Representation:

(a) (A) When a population of any species grows in a habitat with limited resources, it follows a logistic growth curve. Initially, the population grows exponentially due to abundant resources, but as resources become limited, the growth rate slows and finally stabilizes at the carrying capacity ( ) of the environment. (B) The equation for logistic growth is: where,
= Population density at time ,
= Intrinsic rate of natural increase,
= Carrying capacity. (C) The name of this curve is the Logistic Growth Curve (S-shaped curve). Graphical representation of Logistic Growth Curve

OR
(b) (A) The Species-Area Relationship states that the number of species (species richness) increases with increasing area, but at a decreasing rate. In a natural forest, as we explore larger and larger areas, we find more species. When plotted, this forms a rectangular hyperbola. However, for a wide variety of taxa, the graph becomes a straight line on a logarithmic scale. (B) The graph between species richness and area is: (C) The equation for the Species-Area Relationship on a logarithmic scale is: where,
= Species richness,
= Area,
= Y-intercept constant,
= Slope of the line (regression coefficient).

Step 1: Commensalism is an interaction where one species benefits while the other is neither harmed nor benefited.
Step 2: In the case of sea anemone and clownfish:

• The clownfish lives among the tentacles of sea anemones.
• The tentacles protect the clownfish from predators, as they are stinging in nature.
• The clownfish is immune to these stings due to a protective mucus layer on its body.
• The sea anemone does not receive any benefit or harm from this association.

Step 3: This interaction is a classic example of commensalism — clownfish benefits from protection while sea anemone remains unaffected.