Organisms and Populations

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Learning Objectives

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Learning Objectives

Understand the concept of populations in ecology.
Identify attributes that populations possess that individuals do not.
Explain the significance of birth rates and death rates in population dynamics.
Describe the logistic growth model and its implications for population ecology.
Analyze the interactions between different species within a community.
Define and provide examples of various types of interspecific interactions (e.g., mutualism, parasitism, competition).
Discuss the importance of age distribution and sex ratio in understanding population structure.
Evaluate the impact of environmental factors on population size and growth.

Revision Notes & Summary

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Chapter 11: Organisms and Populations

11.1 Populations

Understanding Populations

Populations are groups of individuals of a species living in a defined geographical area.
They share or compete for similar resources and can interbreed.
Examples of populations include:
- All cormorants in a wetland
- Rats in an abandoned dwelling
- Teakwood trees in a forest tract
- Bacteria in a culture plate
- Lotus plants in a pond

Attributes of Populations

Birth Rates and Death Rates:
- Populations have birth rates and death rates, expressed as per capita rates.
- Example: If a pond has 20 lotus plants and 8 new plants are added, the birth rate is 8/20 = 0.4 offspring per lotus per year.
Sex Ratio:
- A population has a sex ratio (e.g., 60% females, 40% males).
Age Distribution:
- Age distribution can be represented as an age pyramid, indicating growth status:
  - Growing
  - Stable
  - Declining

Population Growth Patterns

Exponential Growth:
- Occurs when resources are unlimited.
Logistic Growth:
- Occurs when resources become limited, leading to competition.
- Growth is limited by the carrying capacity (K) of the environment.
- Described by the Verhulst-Pearl Logistic Growth equation.

Ecological Interactions

Populations interact in various ways:
- Competition: Both species suffer.
- Predation and Parasitism: One benefits, the other suffers.
- Commensalism: One benefits, the other is unaffected.
- Mutualism: Both species benefit.

Important Concepts

Intrinsic Rate of Natural Increase (r):
- A measure of a population's potential to grow.
Age Pyramid:
- Graphical representation of age distribution in a population, indicating growth trends.

Example of Exponential Growth

The anecdote of the chess game illustrates exponential growth:
- A single grain of wheat doubles on each square of the chessboard, leading to an astronomical number of grains by the end.

Diagram Descriptions

Population Structures: Illustrates Expanding, Stable, and Declining populations with labeled sections for age groups.
Factors Affecting Population Density: Includes natality, immigration, mortality, and emigration, showing their impacts on population density.

Exam Tips & Common Mistakes

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Common Mistakes and Exam Tips

Common Pitfalls

Misunderstanding Population vs. Individual: Students often confuse the attributes of populations with those of individuals. Remember, populations have birth rates, death rates, sex ratios, and age distributions, while individuals do not.
Ignoring Interactions: Failing to recognize the different types of species interactions can lead to incorrect answers. Be clear on definitions and examples of mutualism, commensalism, parasitism, etc.
Confusing Growth Patterns: Students may mix up exponential and logistic growth patterns. Understand that exponential growth occurs with unlimited resources, while logistic growth considers carrying capacity.

Exam Tips

Clarify Definitions: Make sure you can define key terms such as population, community, and the various types of species interactions clearly.
Use Diagrams: When asked to describe growth patterns or interactions, use diagrams where possible to illustrate your points.
Practice Calculations: Be comfortable with calculating birth rates and death rates using provided data, as these are common exam questions.
Review Age Pyramids: Understand how to interpret age pyramids and what their shapes indicate about population growth status.
Study Interaction Outcomes: Familiarize yourself with the outcomes of interspecific interactions and be able to categorize them correctly.

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Practice Test – MCQs, True/False

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Multiple Choice Questions

The population will increase due to reduced competition.

The population will remain stable due to compensatory reproduction.

The population will decrease due to increased mortality.

The population will evolve new defensive traits immediately.

Correct Answer: C

Solution:

The immediate effect of increased predation is an increase in mortality, leading to a decrease in population size.

Exponential growth model

Logistic growth model

Linear growth model

Geometric growth model

Correct Answer: B

Solution:

The logistic growth model describes a population that grows rapidly at first and then stabilizes as resources become limited, forming an S-shaped curve.

Broad at the base, narrow at the top

Narrow at the base, broad at the top

Uniform width throughout

Irregularly shaped

Correct Answer: C

Solution:

A stable population is characterized by an age pyramid that has a uniform width throughout, indicating balanced proportions of pre-reproductive, reproductive, and post-reproductive individuals.

The population is declining.

The population is stable.

The population is growing.

The population is extinct.

Correct Answer: C

Solution:

The population is growing because the birth rate (0.3) is higher than the death rate (0.2), leading to a net increase in population size.

The population is declining.

The population is stable.

The population is expanding.

The population is decreasing.

Correct Answer: C

Solution:

An age pyramid with a broad base indicates a large number of young individuals, suggesting an expanding population.

It shows the population density

It indicates the growth status of the population

It measures the birth rate

It reflects the sex ratio

Correct Answer: B

Solution:

The age pyramid reflects the age distribution of a population and indicates whether it is growing, stable, or declining.

K-strategy

r-strategy

Iteroparity

Semelparity

Correct Answer: D

Solution:

Semelparity is an evolutionary strategy where an organism breeds once in its lifetime, producing many offspring, as opposed to iteroparity, where organisms breed multiple times.

Approximately 300 rabbits

Approximately 450 rabbits

Approximately 500 rabbits

Approximately 550 rabbits

Correct Answer: B

Solution:

Using the logistic growth equation, dN/dt = rN(1 - N/K), we calculate the population size over time. The population approaches the carrying capacity asymptotically, and after 10 months, it is expected to be approximately 450 rabbits.

Exponential Growth

Carrying Capacity

Competitive Exclusion

Mutualism

Correct Answer: B

Solution:

The scenario describes a population reaching its carrying capacity, where the environment can no longer support additional individuals despite available resources.

Birth rates

Metabolism

Growth

Respiration

Correct Answer: A

Solution:

A population has attributes like birth rates and death rates, which are not applicable to individual organisms.

Carrying capacity of the environment

Intrinsic rate of natural increase

Total population size

Rate of immigration

Correct Answer: B

Solution:

The term 'r' represents the intrinsic rate of natural increase, which is a measure of the inherent potential of a population to grow.

Exponential growth model

Logistic growth model

Linear growth model

Geometric growth model

Correct Answer: B

Solution:

The logistic growth model describes a population that grows rapidly when resources are abundant but slows and stabilizes as resources become limited, reaching the carrying capacity of the environment.

Natality

Immigration

Predation

Emigration

Correct Answer: C

Solution:

Population density changes are directly influenced by natality, immigration, mortality, and emigration. Predation affects population indirectly.

To establish territory

To attract mates

To scare away predators

To signal food availability

Correct Answer: B

Solution:

The primary evolutionary advantage of singing during the breeding season is to attract mates by demonstrating fitness and readiness to reproduce.

Exponential growth without limits

Growth limited by carrying capacity

Growth with unlimited resources

Decline due to lack of resources

Correct Answer: B

Solution:

The logistic growth model describes population growth that is limited by the carrying capacity of the environment, resulting in a sigmoid curve.

Birth rate

Immigration

Mortality

Carrying capacity

Correct Answer: D

Solution:

Carrying capacity is a limit to population growth, not a direct factor in calculating population density.

The population continues to grow exponentially.

The population size stabilizes and fluctuates around the carrying capacity.

The population immediately declines to zero.

The population splits into two separate populations.

Correct Answer: B

Solution:

When a population reaches its carrying capacity, it stabilizes and fluctuates around this limit due to limited resources.

The population is growing rapidly.

The population is stable.

The population is declining.

The population is experiencing exponential growth.

Correct Answer: B

Solution:

A stable age distribution indicates that the population size remains constant over time, suggesting a balance between birth and death rates.

4000 bacteria

8000 bacteria

16000 bacteria

32000 bacteria

Correct Answer: D

Solution:

The population doubles every 30 minutes, so in 3 hours (which is 6 half-hour periods), the population will double 6 times. Therefore, the population size will be 500 * 2^6 = 32000 bacteria.

Organisms

Cells

Communities

Biomes

Correct Answer: B

Solution:

Ecology is concerned with organisms, populations, communities, and biomes, not cells.

200

3200

1600

6400

Correct Answer: C

Solution:

The population doubles every hour, so after 5 hours, the population size will be 100 * 2^5 = 3200 bacteria.

Total number of trees

Biomass

Percentage cover

Average tree height

Correct Answer: B

Solution:

In cases where a species has a low population density but a large biomass, biomass is a more meaningful measure of population size as it accounts for the significant ecological role of the species.

The study of macromolecules and cells.

The study of interactions among organisms and their environment.

The study of individual organisms only.

The study of chemical reactions in organisms.

Correct Answer: B

Solution:

Ecology is concerned with the interactions among organisms and between organisms and their physical environment.

It assumes unlimited resources for population growth.

It describes population growth with limited resources leading to a carrying capacity.

It only applies to human populations.

It predicts a constant population size over time.

Correct Answer: B

Solution:

The logistic growth model describes population growth in environments with limited resources, leading to a carrying capacity.

500

800

1000

1200

Correct Answer: C

Solution:

Under logistic growth, the population will stabilize around the carrying capacity, which is 1000 rabbits in this case.

Commensalism

Mutualism

Predation

Amensalism

Correct Answer: C

Solution:

This is an example of predation, where one species (the predator) benefits by feeding on another species (the prey), leading to a decline in the prey population.

0.1

0.2

0.3

0.4

Correct Answer: A

Solution:

The birth rate is calculated as the number of births divided by the initial population size: 10/100 = 0.1.

The population is stable.

The population is declining.

The population is expanding.

The population is fluctuating.

Correct Answer: D

Solution:

High birth and death rates suggest that the population size is fluctuating, as these rates can lead to rapid changes in population size depending on which rate is higher at any given time.

The maximum population size a habitat can support

The inherent potential of a population to grow

The average lifespan of individuals in a population

The ratio of males to females in a population

Correct Answer: B

Solution:

The intrinsic rate of natural increase (r) is a measure of the inherent potential of a population to grow.

Exponential growth

Logistic growth

Linear growth

Cyclic growth

Correct Answer: B

Solution:

The growth pattern observed is logistic growth. Initially, the bacteria grow rapidly due to abundant resources, but as the nutrients become limited, the growth rate decreases and stabilizes, forming a sigmoid curve typical of logistic growth.

Competition

Parasitism

Mutualism

Amensalism

Correct Answer: C

Solution:

Mutualism is an interaction where both species benefit from the relationship.

Mutualism

Competitive Exclusion Principle

Commensalism

Parasitism

Correct Answer: B

Solution:

This scenario illustrates the Competitive Exclusion Principle, which states that two species competing for the same limited resources cannot coexist indefinitely. Eventually, one species will outcompete the other, leading to the decline of the less competitive species.

A lion hunting a zebra

A bee pollinating a flower

A fungus decomposing dead organic matter

A parasite feeding on a host

Correct Answer: B

Solution:

Mutualism is a type of interaction where both species benefit. In the case of a bee pollinating a flower, the bee gets nectar while the flower gets pollinated.

The plant population will increase exponentially.

The plant population will stabilize at a new carrying capacity.

The plant population will decline due to lack of pollination.

The plant population will evolve to become self-pollinating.

Correct Answer: C

Solution:

The plant population will decline due to lack of pollination because the specific pollinator required for reproduction is declining, reducing the plant's ability to reproduce successfully.

150

200

250

300

Correct Answer: C

Solution:

The net growth rate is 0.5 - 0.2 = 0.3 per hour. After 3 hours, the population size is 100 * (1 + 0.3)^3 = 100 * 1.3^3 = 219.7, approximately 220.

Exponential growth

Logistic growth

Linear growth

Oscillating growth

Correct Answer: B

Solution:

The yeast population is exhibiting logistic growth, characterized by an initial exponential growth phase followed by a slowdown as the population approaches the carrying capacity of the environment.

All the cormorants in a wetland

A single oak tree in a forest

A lone wolf in a forest

A single fish in an aquarium

Correct Answer: A

Solution:

A population consists of a group of individuals of the same species living in a defined area, such as all the cormorants in a wetland.

Natality

Immigration

Color of the species

Mortality

Correct Answer: C

Solution:

Population density is affected by natality, immigration, mortality, and emigration, not by the color of the species.

Linear growth

Exponential growth

Logistic growth

Declining growth

Correct Answer: C

Solution:

The population will eventually exhibit logistic growth as it approaches the carrying capacity of the lake. This pattern is characterized by an initial exponential growth phase, followed by a slowdown as resources become limited, and finally stabilizing at the carrying capacity.

They determine the color of organisms

They affect the survival and reproduction of species

They have no impact on the ecosystem

They only occur in aquatic environments

Correct Answer: B

Solution:

Interspecific interactions affect the survival and reproduction of species, contributing to the dynamics of ecosystems.

Lag phase

Exponential phase

Deceleration phase

Asymptotic phase

Correct Answer: C

Solution:

In logistic growth, the population initially experiences a lag phase, followed by an exponential phase where resources are abundant. As the population approaches the carrying capacity, resource limitations cause the growth rate to slow down, entering the deceleration phase. Eventually, the population stabilizes at the carrying capacity, reaching the asymptotic phase.

The population will increase.

The population will decrease.

The population will remain stable.

The population will experience random fluctuations.

Correct Answer: B

Solution:

A sudden reduction in food availability will likely lead to a decrease in the population size as the carrying capacity of the environment is reduced.

K-strategy

r-strategy

Logistic growth

Exponential growth

Correct Answer: B

Solution:

An r-strategy involves producing a large number of offspring with low survival rates, maximizing reproductive success in unpredictable environments.

A group of individuals of the same species living in a defined area.

A collection of different species living in a habitat.

An individual organism interacting with its environment.

A group of ecosystems interacting with each other.

Correct Answer: A

Solution:

A population is defined as a group of individuals of the same species living in a defined geographical area, sharing or competing for similar resources.

The maximum growth rate of a population

The maximum number of individuals a habitat can support

The initial population size

The number of offspring produced per individual

Correct Answer: B

Solution:

Carrying capacity (K) is the maximum number of individuals a habitat can support.

450

550

500

600

Correct Answer: B

Solution:

The net growth rate is 0.2 - 0.1 = 0.1 per year. Therefore, the population size after one year will be 500 + (0.1 * 500) = 550.

Exponential growth

Logistic growth

Geometric growth

Linear growth

Correct Answer: B

Solution:

With unlimited food but limited space, the population will initially grow rapidly but will eventually stabilize as it reaches the carrying capacity of the space, following a logistic growth model.

1100 birds

1200 birds

1300 birds

1400 birds

Correct Answer: A

Solution:

The net growth rate of the population is the birth rate minus the death rate, which is 0.3 - 0.2 = 0.1. Therefore, the population will increase by 0.1 * 1000 = 100 birds in one year, resulting in a total population of 1100 birds.

Mortality

Emigration

Natality

Predation

Correct Answer: C

Solution:

Natality, or birth rate, is a positive influence on population density as it increases the number of individuals.

The insect population will increase.

The insect population will decrease.

The insect population will remain stable.

The insect population will fluctuate randomly.

Correct Answer: B

Solution:

The introduction of a new predator will likely lead to an immediate decrease in the population of the prey species, in this case, the herbivorous insects.

The total number of births in a year.

The number of offspring per individual per unit time.

The number of births minus the number of deaths.

The ratio of males to females.

Correct Answer: B

Solution:

Birth rate in a population refers to the number of offspring produced per individual per unit time.

Mutualism

Competition

Commensalism

Parasitism

Correct Answer: B

Solution:

The introduction of a new flower species that relies on a specific non-native bee for pollination may lead to competition with native pollinators for resources, as they may be attracted to the new flower, thereby reducing the resources available for native plants.

Exponential growth followed by a plateau

Linear growth followed by a decline

Exponential growth followed by logistic growth

Logistic growth followed by exponential growth

Correct Answer: C

Solution:

The logistic growth model describes a population that initially grows exponentially but slows down as it approaches the carrying capacity, resulting in a sigmoid curve.

The maximum number of individuals an environment can support

The speed at which a population grows

The average lifespan of individuals in a population

The total biomass of a population

Correct Answer: A

Solution:

Carrying capacity is the maximum number of individuals that an environment can support sustainably.

A linear curve

An exponential curve

A sigmoid curve

A parabolic curve

Correct Answer: C

Solution:

The logistic growth model results in a sigmoid curve as the population reaches its carrying capacity.

Mutualism

Parasitism

Competition

Commensalism

Correct Answer: A

Solution:

Mutualism is affected because both the plant and insect benefit from the interaction; the plant gets pollinated, and the insect gets food.

2000

4000

8000

16000

Correct Answer: C

Solution:

The population doubles every 20 minutes. After 1 hour (which is 3 doubling periods), the population will be 1000 * 2^3 = 8000.

True or False

Correct Answer: False

Solution:

A population is a group of individuals of a given species sharing or competing for similar resources in a defined geographical area.

Correct Answer: False

Solution:

Even groups of individuals resulting from asexual reproduction are considered populations for ecological studies.

Correct Answer: True

Solution:

The anecdote demonstrates how rapidly a population can grow when it doubles each time, similar to exponential growth.

Correct Answer: False

Solution:

In a population, birth rates and death rates are expressed as per capita rates, indicating the change in numbers with respect to members of the population.

Correct Answer: True

Solution:

The birth rate is calculated by dividing the number of new individuals by the total number of individuals in the population.

Correct Answer: True

Solution:

A population has attributes like birth rates and death rates, while an individual organism does not.

Correct Answer: False

Solution:

The logistic growth model is based on the concept of carrying capacity, which limits population growth when resources become limited.

Correct Answer: False

Solution:

Population density can be measured in different ways such as numbers, biomass, or per cent cover.

Correct Answer: False

Solution:

Ecology studies the interactions among organisms and between organisms and their physical environment.

Correct Answer: True

Solution:

Ecology is concerned with four levels of biological organization: organisms, populations, communities, and biomes. This is consistent with the excerpt which states that ecology studies interactions at these levels.

Correct Answer: True

Solution:

A population growing in a habitat with limited resources shows a sigmoid curve when plotted over time.

Correct Answer: False

Solution:

In nature, populations of different species interact in many ways and do not live in isolation.

Correct Answer: False

Solution:

Interspecific interactions can be beneficial, detrimental, or neutral (neither harm nor benefit) to the species involved.

Correct Answer: False

Solution:

A group of individuals from asexual reproduction is considered a population for ecological studies, as noted in the excerpts.

Correct Answer: False

Solution:

Ecology studies interactions at multiple levels of biological organization, including organisms, populations, communities, and biomes.

Correct Answer: True

Solution:

The intrinsic rate of natural increase (r) reflects a population's potential to grow, as mentioned in the excerpts.

Correct Answer: True

Solution:

The logistic growth model accounts for the finite nature of resources, which become limiting, leading to a sigmoid growth curve as populations reach carrying capacity.

Correct Answer: False

Solution:

Logistic growth occurs when resources are limited, leading to competition and a population reaching its carrying capacity.

Correct Answer: True

Solution:

The intrinsic rate of natural increase (r) measures the inherent potential of a population to grow.

Correct Answer: False

Solution:

A population is composed of individuals of the same species that live in groups in a well-defined geographical area.

Correct Answer: False

Solution:

A population can also consist of individuals resulting from asexual reproduction, as long as they share or compete for similar resources in a defined area.

Correct Answer: True

Solution:

Ecology studies the interactions among organisms and between the organism and its physical (abiotic) environment.

Correct Answer: True

Solution:

Ecology studies the interactions among organisms and between organisms and their abiotic environment.

Correct Answer: True

Solution:

Ecology examines interactions among organisms and between organisms and their environment at these four levels, as stated in the excerpts.

Correct Answer: True

Solution:

Age pyramids show age distribution and their shape reflects the growth status of the population.

Correct Answer: True

Solution:

Growth is ultimately limited by the carrying capacity of the environment.

Organisms and Populations

Learning Objectives

Learning Objectives

Revision Notes & Summary

Chapter 11: Organisms and Populations

11.1 Populations

Understanding Populations

Attributes of Populations

Population Growth Patterns

Ecological Interactions

Important Concepts

Example of Exponential Growth

Diagram Descriptions

Exam Tips & Common Mistakes

Common Mistakes and Exam Tips

Common Pitfalls

Exam Tips

AI Learning Assistant

Practice Test – MCQs, True/False

Multiple Choice Questions

Q1.A certain wetland ecosystem contains a population of fish that exhibits a stable age distribution. If a sudden increase in predation occurs, which of the following is the most likely immediate effect on the fish population?

Correct Answer: C

Q2.In a laboratory experiment, a population of bacteria is grown in a petri dish with limited nutrients. Initially, the population grows rapidly but then stabilizes. Which growth model best describes this scenario?

Correct Answer: B

Q3.In a study of a forest ecosystem, it is found that the population of a certain tree species is stable. The age pyramid for this population is most likely to be:

Correct Answer: C

Q4.A population of rabbits in a meadow is observed to have a birth rate of 0.3 per rabbit per year and a death rate of 0.2 per rabbit per year. What can be inferred about the population's growth status?

Correct Answer: C

Q5.What does an age pyramid with a broad base indicate about a population?

Correct Answer: C

Q6.What is the significance of the age pyramid in population studies?

Correct Answer: B

Q7.In a certain ecosystem, a species of bird is observed to breed only once in its lifetime, producing a large number of offspring. What evolutionary strategy is this an example of?

Correct Answer: D

Correct Answer: B

Q9.In a hypothetical ecosystem, a plant species is observed to have a high birth rate and low death rate. Over time, the population of this plant reaches a point where it no longer grows despite the availability of resources. Which concept best explains this phenomenon?

Correct Answer: B

Q10.Which of the following is a characteristic of a population but not of an individual organism?

Correct Answer: A

Q11.In the context of population ecology, what does the term 'r' represent?

Correct Answer: B

Q12.In a hypothetical scenario, a population of frogs in a pond initially experiences rapid growth due to abundant resources. However, over time, the growth rate slows and eventually stabilizes. Which growth model best describes this scenario?

Correct Answer: B

Q13.Which factor is NOT a direct component of population density changes?

Correct Answer: C

Q14.In a certain bird species, the males sing during the breeding season. What is the primary evolutionary advantage of this behavior?

Correct Answer: B

Q15.What does the logistic growth model describe in population ecology?

Correct Answer: B

Q16.Which factor is NOT directly considered in calculating population density?

Correct Answer: D

Q17.What happens to a population when it reaches its carrying capacity?

Correct Answer: B

Q18.A population of deer in a forest is observed to have a stable age distribution. What does this imply about the population's growth status?

Correct Answer: B

Q19.Consider a population of bacteria that doubles every 30 minutes. If the initial population is 500 bacteria, what will be the population size after 3 hours, assuming unlimited resources?

Correct Answer: D

Q20.Which of the following is NOT a level of biological organization studied in ecology?

Correct Answer: B

Q21.In an experimental setup, a culture of bacteria is observed to double in number every hour. If the initial population is 100 bacteria, what will be the population size after 5 hours, assuming no limitations on resources?

Correct Answer: C

Q22.In a forest ecosystem, a particular tree species is observed to have a low population density but a large biomass. Which measure would best represent the population size of this tree species?

Correct Answer: B

Q23.Which of the following best describes the study of Ecology?

Correct Answer: B

Q24.What is the significance of the logistic growth model in population ecology?

Correct Answer: B

Q25.Consider a population of rabbits in a forest where the carrying capacity is 1000 rabbits. If the intrinsic rate of natural increase (r) is 0.1 per month, what is the expected population size after 6 months, assuming logistic growth?

Correct Answer: C

Q26.In a forest ecosystem, the introduction of a new predator species results in a significant decline in the population of a native herbivore species. This is an example of which type of interspecific interaction?

Correct Answer: C

Q27.In a population of 100 rabbits, if 10 new rabbits are born, what is the birth rate?

Correct Answer: A

Q28.A population of fish in a lake is observed to have a high birth rate and a high death rate. What can be inferred about the population's growth status?

Correct Answer: D

Q29.What does the intrinsic rate of natural increase (r) measure in a population?

Correct Answer: B

Q30.In a controlled experiment, a population of bacteria is grown in a petri dish with limited nutrients. Initially, the population grows rapidly, but over time, the growth rate decreases and stabilizes. Which of the following best describes the growth pattern observed?

Correct Answer: B

Q31.Which of the following interactions is beneficial to both species involved?