31 Years NEET Previous Year Questions: Organisms & Populations - 1 - NEET MCQ

 

The Verhulst-Pearl logistic growth equation you've presented is a fundamental model used to describe how populations grow under limited resource conditions. This model is sensitive to both the variables and coefficients it incorporates:

Here:
N represents the population size at time t.
r  is the intrinsic rate of natural increase, indicating the rate at which the population grows per individual when resources are not limiting.
K represents the carrying capacity of the environment.
In the context of this equation:
The term  is a fraction that reduces the effective growth rate as the population size N approaches the carrying capacity K. This term essentially represents the remaining proportion of resources available as the population grows larger.
Based on this understanding:
Option A: "Intrinsic rate of natural increase" – Incorrect, this is represented by r in the equation.
Option B: "Biotic potential" – Incorrect, biotic potential generally refers to the maximum reproductive capacity of an organism under optimal conditions, often considered similar to r but not specifically the same as K.
Option C: "Carrying capacity" – Correct, as K in the equation is specifically describing the carrying capacity, which is the maximum population size that the environment can sustain indefinitely given the food, habitat, water, and other necessities available in the environment. Option D: "Population density" – Incorrect, while N relates directly to population density at any time, K is about the upper limit of that density sustainable by the environment. Therefore, Option C is the correct answer. The variable K in the Verhulst-Pearl logistic growth equation indeed stands for the carrying capacity.

Gause's 'Competitive Exclusion Principle' states that two closely related species competing for the same resources cannot co-exist indefinitely and the competitively inferior one will be eliminated eventaully. Thus, statement I is correct.
Statement II is incorrect as in general, herbivores and plants appear to be more adversely affected by competition than carnivores. 

• A leopard and a lion in a forest/grassland (A) : These two species are predators that hunt in the same environment and likely compete for the same prey. This is an example of competition (I).
• A cuckoo laying an egg in a crow's nest (B) : The cuckoo is known for laying its eggs in the nests of other birds, such as crows. The crow then raises the cuckoo's young, often at the expense of its own offspring. This is a form of brood parasitism (II).
• Fungi and the root of a higher plant in mycorrhizae (C) : Mycorrhizae are symbiotic relationships between fungi and plant roots, in which the fungi help the plant absorb water and nutrients from the soil, while the plant provides the fungi with carbohydrates. This is an example of mutualism (III).
• A cattle egret and a cattle in a field (D) : Cattle egrets are often seen near cattle, feeding on the insects that the cattle stir up as they move and graze. The egret benefits from this interaction (by getting easy access to food), while the cattle are unaffected. This is an example of commensalism (IV).

Given this information, the correct match is :
Option D : A-I, B-II, C-III, D-IV

• Logistic growth (A) is a type of population growth that occurs under conditions of limited resources (II).
• Exponential growth (B) is a type of population growth that occurs under conditions of unlimited resources (I).
• An expanding age pyramid (C) represents a population where the percentage of individuals in the pre-reproductive age group is the largest, followed by the reproductive and post-reproductive age groups (III).
• A stable age pyramid (D) represents a population where the percentage of individuals in the pre-reproductive and reproductive age groups are approximately equal (IV).

So, the correct match is : A-II, B-I, C-III, D-IV.

If 8 Drosophila in a laboratory population of 80 died during a week, the death rate in the population is  8/80 = 0.1  individuals per Drosophila per week.

In predation, one species is benefited where as the other is harmed. It is (+ −) type of population interaction.

One of the species in predation gains benefit on the expense of the other. Predators help in maintaining species diversity in a community, by reducing the intensity of competition among competing prey species. If a predator is too efficient and overexploits its prey, then the prey might become extinct.

While they do not rule out the occurrence of interspecific competition in nature, they point out that species facing competition might evolve mechanisms that promote co-existence rather than exclusion. One such mechanism is ‘resource partitioning'.

Species interaction refers to direct and indirect interrelationship between different organisms, while on the other hand population attributes include population size, population density, population spacing, and age structure. Mortality is the ratio of deaths in an area to the population of that area; expressed per 1000 per year. Sex ratio is  the ratio of males to females in a population.

Explanation:
The mechanism of competition described in the question is referred to as resource partitioning. Here's a detailed explanation:
1. Definition of resource partitioning:
- Resource partitioning is a mechanism that allows similar species to coexist in the same habitat by dividing and utilizing resources differently.
- It reduces competition between species by allowing them to occupy different ecological niches.
2. Competition between lions and leopards:
- Lions and leopards are both carnivorous animals and have overlapping habitats.
- However, they have different prey preferences.
- Lions primarily prey on larger animals like zebras and wildebeests, while leopards focus on smaller prey like impalas and gazelles.
3. How resource partitioning occurs in this scenario:
- Lions and leopards have divided the available resources (prey) based on their size and hunting abilities.
- By preying on different-sized animals, they reduce direct competition for food.
- This allows both species to coexist in the same habitat without completely excluding one another.
4. Benefits of resource partitioning:
- Resource partitioning allows species to specialize in different ecological niches, leading to more efficient resource utilization.
- It promotes species diversity and prevents competitive exclusion, where one species outcompetes and eliminates another species.
5. Other examples of resource partitioning:
- Darwin's finches in the Galapagos Islands have evolved different beak sizes to utilize different food sources.
- Different species of warblers in North America occupy different parts of trees to feed on insects.
In conclusion, the mechanism of competition described in the question, where lions and leopards occupy the same niche but prey on different-sized animals, is an example of resource partitioning. This strategy allows both species to coexist by reducing direct competition for food resources.

Natality refers to the number of births during a given period in the population that are added to the initial density. Death rate or mortality is the number of deaths in the population during a given time period. Immigration is the number of individuals entering a habitat. Emigration is the number of individuals of the population that left the habitat and had gone elsewhere during a time period.

Asymptote in a logistic growth curve is obtained when population density (N) reaches the carrying capacity (K), i.e., N = K.

Logistic growth of a population size occurs when resources are limited. The formula we use to calculate logistic growth adds the carrying capacity as a moderating force in the growth rate. 

► The logistic model is given as dN/dt = rN(1-N/K) 

When the value of N/K is one, then,

► dN/dt = rN(1-N/K) 
► dN/dt = rN(1-1)
► dN/dt = rN(0)
► dN/dt = 0 (zero)

So, the growth rate of the population will be equal to zero.

Gause's principle of competitive exclusion can be restated to say that no two species can occupy the same niche indefinitely when resources are limiting.

Gause's theory predicts that when two species coexist on a long-term basis, either resources must not be limited or their niches will always differ in one or more features; otherwise, one species will outcompete the other and the extinction of the second species will inevitably result, a process referred to as competitive exclusion.

Competition occurs for light, food and space among organisms in which all partners are adversely affected in an ecosystom.