Organisms are the fundamental units of life, and populations are groups of organisms of the same species living in a particular area. The study of organisms and populations helps us understand the interactions between living beings and their environment.
Population Attributes
- Population Density: The number of individuals of a species per unit area.
- Birth Rate: The number of births per individual per unit time.
- Sex Ratio: The ratio of males to females in a population.
- Age Distribution: The proportion of individuals in different age groups.
Population Growth
- Exponential Growth: A population grows at an increasing rate, without any limiting factors.
- Logistic Growth: A population grows initially at an exponential rate but eventually levels off due to limiting factors.
Limiting Factors
- Biotic Factors: Living organisms that can affect population growth, such as predators, prey, and competitors.
- Abiotic Factors: Non-living factors that can affect population growth, such as temperature, humidity, and availability of resources.
Ecological Interactions
- Predation: One organism (predator) feeds on another (prey).
- Commensalism: One organism benefits, while the other is neither harmed nor benefited.
- Mutualism: Both organisms benefit from the interaction.
Population Ecology
- Ecological Succession: The gradual change in a community over time.
Exercise
1. List the attributes that populations possess but not individuals.
Ans :
Density
Distribution: The spatial arrangement of individuals within a population (e.g., clumped, uniform, random).
Age structure: The distribution of individuals in different age groups.
Sex ratio
Growth rate: The rate at which a population increases or decreases in size.
Carrying capacity: The maximum number of individuals that an environment can support.
Genetic diversity: The variation in genetic makeup among individuals in a population.
2. If a population growing exponentially double in size in 3 years, what is the intrinsic rate of increase (r) of the population?
Ans :
The population growth rate can be calculated using the following formula:
N(t) = N(0) * e^(rt)
Where:
- N(t)
- N(0) is the initial population size
- e is the mathematical constant (approximately 2.71828)
- r is the intrinsic rate of increase
- t is time
In this case, we know that the population doubles in 3 years. So, N(t) = 2*N(0) and
t = 3.
2N(0) = N(0) * e^(r3)
Simplifying, we get:
2 = e^(3r)
Taking the natural logarithm of both sides:
ln(2) = 3r
Therefore, the intrinsic rate of increase (r) is:
r = ln(2) / 3 ≈ 0.231
So, the population is growing at a rate of approximately 23.1% per year.
3. Name important defence mechanisms in plants against herbivory.
Ans :
Plants have evolved various defense mechanisms to protect themselves from herbivory, which is the consumption of plant material by animals. Here are some important defense mechanisms:
Physical Defenses
- Spines and Thorns: Spines and thorns are sharp structures that deter herbivores from eating the plant.
- Tough Leaves: Thick, leathery leaves can be difficult for herbivores to chew and digest.
- Trichomes: Hair-like structures on the plant’s surface that can irritate herbivores or trap insects.
- Waxy Cuticle: A waxy coating on the leaves that can make them less palatable or difficult to digest.
Chemical Defenses
- Secondary Metabolites: Plants produce a variety of secondary metabolites, including alkaloids, terpenoids, and phenols, that are toxic or distasteful to herbivores.
- Toxins: Some plants produce toxins that can poison or kill herbivores.
- Repellents: Plants can release volatile compounds that repel herbivores.
Behavioral Defenses
- Mimicry: Some plants mimic the appearance or behavior of toxic or distasteful plants to deter herbivores.
- Compensation: Plants can compensate for herbivory by growing faster or producing more seeds.
4. An orchid plant is growing on the branch of mango tree. How do you describe this interaction between the orchid and the mango tree?
Ans :
The relationship between the orchid and the mango tree is an example of commensalism.
- Commensalism: In this type of ecological interaction, one organism benefits (the commensal), while the other is neither harmed nor benefited.
- Orchid and Mango Tree: The orchid benefits from the relationship by obtaining a stable platform to grow on the mango tree’s branch. It also receives sunlight and nutrients from its surroundings. The mango tree, however, is neither significantly helped nor harmed by the presence of the orchid.
5. What is the ecological principle behind the biological control method of managing with pest insects?
Ans :
The ecological principle behind the biological control method of managing pest insects is predation.
In biological control, natural enemies of the pest insect, such as predators, parasites, or pathogens, are introduced into the environment to reduce the pest population. This is based on the principle of predation, where one organism (the predator) feeds on another organism (the prey).
6. Define population and community
Ans :
Population: A population refers to a group of organisms of the same species living in a particular area at a given time. They share a common gene pool and interact with each other.
Community: A community is a group of populations of different species living together in a particular habitat and interacting with each other. It involves the interactions between various species and their physical environment.
7. Define the following terms and give one example for each:
(a) Commensalism (b) Parasitism (c) Camouflage
(d) Mutualism (e) Interspecific competition
Ans :
(a) Commensalism
- Definition: A type of ecological interaction where one species benefits, while the other is neither harmed nor benefited.
- Example: Barnacles living on a whale’s skin. The barnacles benefit by having a stable attachment surface and access to food, while the whale is neither harmed nor helped.
(b) Parasitism
- Definition: A type of ecological interaction where one organism (the parasite) benefits at the expense of another organism (the host).
- Example: Tapeworms living in the intestines of a human. The tapeworm obtains nutrients from the host’s food, while the host may experience discomfort or health problems.
(c) Camouflage
- Definition: The ability of an organism to blend in with its surroundings, making it difficult for predators to detect.
- Example: A chameleon changing its color to match its environment.
(d) Mutualism
- Definition: A type of ecological interaction where both species benefit from the relationship.
- Example: Bees pollinating flowers. The bees obtain nectar and pollen as food, while the flowers are pollinated and can reproduce.
(e) Interspecific Competition
- Definition: Competition between individuals of different species for the same resources, such as food, water, or space.
- Example: Lions and hyenas competing for prey in the African savanna.
8. With the help of suitable diagram describe the logistic population growth curve.
Ans :
A logistic population growth curve is an S-shaped curve that describes the growth of a population over time. It reflects the impact of limiting factors, such as resource availability, on population growth.
9. Select the statement which explains best parasitism.
(a) One organism is benefited. (b) Both the organisms are benefited. (c) One organism is benefited, other is not affected. (d) One organism is benefited, other is affected.
Ans :
The correct answer is (d) One organism is benefited, other is affected.
The parasite obtains nutrients and shelter from the host, while the host may experience harm, discomfort, or even death.
10. List any three important characteristics of a population and explain.
Ans :
1. Population Density: This refers to the number of individuals of a species per unit area or volume. It is a key factor in determining the availability of resources and the intensity of competition within a population.
2. Age Structure: The age structure of a population is the distribution of individuals in different age groups. It can have significant implications for the population’s growth rate, reproductive potential, and vulnerability to diseases. For example, a population with a large proportion of young individuals is likely to experience rapid growth, while a population with a large proportion of elderly individuals may face challenges related to healthcare and social services.
3. Population Distribution: This refers to the spatial arrangement of individuals within a population. It can be clumped, uniform, or random. Clumped distribution is common in species that rely on resources that are clustered in patches (e.g., trees in a forest). Uniform distribution is often found in species that compete for resources or territory.
