Fiveable
Fiveable

or

Log in

Find what you need to study


Light

Find what you need to study

8.3 Population Ecology

7 min readdecember 18, 2022

Caroline Koffke

Caroline Koffke

Jillian Holbrook

Jillian Holbrook

Caroline Koffke

Caroline Koffke

Jillian Holbrook

Jillian Holbrook

Population

 is defined as a group of the same species living in the same area. Example populations include humans residing in Seattle, a colony of bees living in a hive, or a group of pine trees growing in a forest. 🐝🌲

Populations can vary in size, , and —characteristics subject to change when environmental changes occur, like resource availability and . They also vary in terms of genetic makeup, which can affect the ability of species to adapt to changing conditions.

In , the focus is on understanding the dynamics of the and how a is affected by various factors, such as , , and availability, as these factors impact the health and growth of species.

Understanding populations affects how humans approach and in addition to informing how affect the overall functioning of ecosystems.  

Population Survival

A number of factors are important for a to survive. These factors can be divided into two broad categories: , which are related to the interactions between members of the and other living organisms, and , which are related to the physical and chemical characteristics of the environment. Some key examples that are important for survival include:

  1. : Populations need access to sufficient , such as food, water, oxygen, and shelter, in order to survive and reproduce. The availability of these can influence the size and of a .
  2. : Populations need a suitable in which to live and reproduce. loss and degradation can have significant impacts on survival. 🌱
  3. : Populations within or between species may compete with each other for limited , including food, water, and mating partners. This can influence the survival and reproductive success of individual members of the .
  4. : Populations may be preyed upon by other species, which can have significant impacts on their survival and reproduction.
  5. Disease: Populations can be impacted by the spread of diseases, which can lead to a decrease in size.
  6. Climate: Populations may be influenced by changes in climate, such as changes in temperature, precipitation, and extreme weather events, which can affect the availability of and the suitability of the for species. 🌧️

The relative importance of these factors varies depending on the species and the specific environment in which it lives.

Mathematical Equations

Interactions and events within a can be measured using a number of mathematical equations. Most simply, a can be measured using the following equation for growth:

dN / dt = B - D

where:

dN is the change in

dt is the chage in time

B is the

D is the

This simple equation shows that the overall change in a over time is equal to the number of births in that minus the number of deaths in that .

Ex. In a of iguanas, there are 42 births and 17 deaths over the past year. What is the change in over the course of the year? 🦎

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2FScreen%20Shot%202020-04-05%20at%207.45.04%20PM.png?alt=media&token=30d406e3-ec61-461a-ab4e-62daf4a4563f

The overall change in is +25, meaning that the increased by 25 iguanas over the course of the year.

Exponential Growth

Exponential growth is a type of growth in which the number of individuals in a increases geometrically at a constant rate over time. For exponential growth to occur, some of the following conditions must be met:

  1. There are no : If a has unlimited access to and suitable , it can potentially grow exponentially.
  2. The has a high : Exponential growth is more likely to occur in species that have a high , meaning they can produce a large number of offspring in a short period of time.
  3. The has a low : If a has a low (i.e. a high survival rate), it has the potential to grow exponentially because the of new individuals in the will be greater than the rate that current individuals die off.

Exponential growth is not sustainable in the long term because eventually, the will reach the of its environment, meaning it will no longer be able to continue growing at the same rate due to limited and other factors. However, in the short term, exponential growth can have significant impacts on the environment and the availability of for other species.

There is another formula used to calculate :

dN / dt = (r max) (N)

where: 

dN is the change in size

dt is the change in time

r max is the maximum of the

N is the size 

Ex. A of 862 iguanas has a of 0.05. What is the growth of the after one year? What is the new size? 🦎

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2FScreen%20Shot%202020-04-05%20at%207.46.42%20PM.png?alt=media&token=923bf387-0682-44c6-857f-31638f96f18d

The grew by 43 iguanas in one year. The new is 862 + 43, or 905 iguanas.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-mZBcx1iiBTGn.webp?alt=media&token=b6ca8ea1-8c0a-47fe-a71d-d93985ccb7e1

Image courtesy of Giphy.

Example of Exponential Growth

An example of is the introduction of European rabbits to Australia in the 19th century. 🐇 Rabbits were originally brought to Australia for hunting purposes, but they quickly became an and spread across the continent due to their high . In general, female European rabbits can have up to six litters per year, with an average of four to six offspring per litter.

The of the European rabbits created detrimental impacts on Australian ecosystems, including:

  1. with native species: The rabbits competed with native species for , such as food and , which led to declines in the populations of many native species.
  2. destruction: The rabbits caused significant damage to the landscape by burrowing and feeding on native vegetation, leading to loss and degradation.
  3. Economic impacts: The rabbits damaged crops and pastures, leading to losses for farmers and ranchers.

Despite efforts to limit the rabbit , including fences and chemical control, following the rabbit invasion has allowed the European rabbit to continue damaging Australia today. 

Logistic Growth

However, most growth is logistic, characterized by an S-shaped curve, with a rapid increase in size at first, followed by a slowing of the rate of increase as the approaches its . begins exponentially, but growth is limited by resource availability, , and quality. These can act to decrease the rate of increase as the size increases, eventually leading to a stabilization of the size at or near the of the environment, the number of individuals that an environment can support.

For example, take the reintroduction of wolves to Yellowstone National Park in the mid-1990s. serves as a limiting factor for growth in the relationship between wolves and elk. Because wolves prey on elk for food, the elk decreased after wolves returned to Yellowstone because they experienced to check the size of their . 🐺

Importantly, this relationship works in both directions. If the wolf grows too large, there will not be enough elk to prey on. This means that the elk exerts a bottom-up limiting factor on wolves while wolves provide a top-down limiting factor on elk.

Learning Summary

is a subfield of ecology that focuses on the dynamics of species populations and how they interact with their environment. It involves the study of factors that affect the size and of populations, as well as their survival and reproductive success. Some of the key concepts in include growth and regulation, , , and .

ecologists use a variety of tools and techniques, including , experiments, and , to understand the factors that influence dynamics. Understanding how populations grow and change is valuable because it helps us to understand the factors that influence the abundance and of species, which has important implications for and .

Using mathematical equations, growth and are modelable. In combination with factors necessary for survival, these equations help predict how populations may change over time.

Changes in populations are caused by various biotic and . Some of them include and resource availability, interactions with other organisms in the environment, and the effects of climate and disease. These impacts will be further examined with upcoming topics on and .


-----

Key Terms to Review (29)

Abiotic Factors

: Abiotic factors are non-living parts of an environment that can affect living organisms and functioning ecosystems. They include sunlight, temperature, wind patterns etc.

Biotic Factors

: Biotic factors are all living things or materials from living things affecting an ecosystem. They include plants, animals, bacteria, fungi etc.

Birth Rate

: The birth rate is the number of live births per 1,000 individuals in a population in a year.

Carrying Capacity

: The maximum number of individuals of a particular species that an environment can support indefinitely under stable conditions.

Community Ecology

: Community ecology is the study of how groups of different species interact with each other and their environment within a defined area.

Competition

: Competition refers to the struggle between organisms for limited resources such as food, water, territory or mates.

Conservation

: Conservation refers to the protection, preservation, management, or restoration of natural environments and wildlife.

Death Rate

: The death rate is the number of deaths per 1,000 individuals in a population in a year.

Density

: In ecology, density refers to the number of individuals per unit area or volume.

Distribution

: Distribution refers to how individuals within a population are spaced within their region. This could be random, uniform/regularly spaced, or clumped/aggregated distribution based on resource availability and interactions between organisms.

Exponential Growth

: Exponential growth describes when something increases rapidly due to constant proportionality - meaning it grows more and more quickly as it gets larger.

Field Observations

: Field observations are data and insights collected by scientists in natural environments rather than in a laboratory or controlled conditions.

Habitat

: A habitat is the natural environment where an organism lives. It includes all aspects such as climate, food sources, predators, and other species interactions.

Invasive Species

: An invasive species is a non-native organism that causes harm to the ecosystem into which it has been introduced.

Limiting Factors

: Limiting factors are environmental conditions that limit the growth, abundance, or distribution of an organism or a population of organisms in an ecosystem.

Logistic Growth

: Logistic growth refers to the growth pattern where expansion is rapid initially due to abundant resources, but slows down as resources become limited leading to stabilization around carrying capacity.

Management Efforts

: Management efforts refer to the strategies and actions taken to manage natural resources and ecosystems, often with the goal of sustainability and conservation.

Mathematical Modeling

: Mathematical modeling is the process of using mathematical structures and concepts to represent real-world situations or phenomena.

Mortality Rate

: A measure of the number of deaths in some population, scaled to the size of that population per unit time.

Mutualism

: Mutualism is a type of symbiotic relationship where both organisms involved benefit from each other.

Per Capita Growth Rate

: The per capita growth rate is the rate at which a population of a species increases or decreases for a given set of resources and conditions, such as food availability or predation.

Population

: A population in biology refers to a group of individuals of the same species living in a specific geographical area and capable of interbreeding.

Population Density

: Population density refers to the number of individuals per unit area or volume in an ecological community. It's an important concept in ecology because it influences how organisms interact with each other and their environment.

Population Ecology

: Population ecology is the study of how populations — groups of individuals of the same species living in a specific area — interact with their environment and change over time.

Predation

: Predation is an interaction where one organism (the predator) kills another (the prey) for food.

Predation Pressure

: Predation pressure refers to the impact predators have on their prey's population size and behavior within an ecosystem.

Reproductive Rate

: The average number of offspring produced by an individual organism during its lifetime.

Resources

: In biology terms, resources refer to any substance that is required by a living organism for normal growth, maintenance, and reproduction. These could include food/nutrients, light/sunlight for photosynthesis in plants etc.

Species Interactions

: Species interactions refer to the ways in which species interact with each other within an ecosystem. These can include predation, competition, symbiosis (mutualism, commensalism, parasitism), and more.

8.3 Population Ecology

7 min readdecember 18, 2022

Caroline Koffke

Caroline Koffke

Jillian Holbrook

Jillian Holbrook

Caroline Koffke

Caroline Koffke

Jillian Holbrook

Jillian Holbrook

Population

 is defined as a group of the same species living in the same area. Example populations include humans residing in Seattle, a colony of bees living in a hive, or a group of pine trees growing in a forest. 🐝🌲

Populations can vary in size, , and —characteristics subject to change when environmental changes occur, like resource availability and . They also vary in terms of genetic makeup, which can affect the ability of species to adapt to changing conditions.

In , the focus is on understanding the dynamics of the and how a is affected by various factors, such as , , and availability, as these factors impact the health and growth of species.

Understanding populations affects how humans approach and in addition to informing how affect the overall functioning of ecosystems.  

Population Survival

A number of factors are important for a to survive. These factors can be divided into two broad categories: , which are related to the interactions between members of the and other living organisms, and , which are related to the physical and chemical characteristics of the environment. Some key examples that are important for survival include:

  1. : Populations need access to sufficient , such as food, water, oxygen, and shelter, in order to survive and reproduce. The availability of these can influence the size and of a .
  2. : Populations need a suitable in which to live and reproduce. loss and degradation can have significant impacts on survival. 🌱
  3. : Populations within or between species may compete with each other for limited , including food, water, and mating partners. This can influence the survival and reproductive success of individual members of the .
  4. : Populations may be preyed upon by other species, which can have significant impacts on their survival and reproduction.
  5. Disease: Populations can be impacted by the spread of diseases, which can lead to a decrease in size.
  6. Climate: Populations may be influenced by changes in climate, such as changes in temperature, precipitation, and extreme weather events, which can affect the availability of and the suitability of the for species. 🌧️

The relative importance of these factors varies depending on the species and the specific environment in which it lives.

Mathematical Equations

Interactions and events within a can be measured using a number of mathematical equations. Most simply, a can be measured using the following equation for growth:

dN / dt = B - D

where:

dN is the change in

dt is the chage in time

B is the

D is the

This simple equation shows that the overall change in a over time is equal to the number of births in that minus the number of deaths in that .

Ex. In a of iguanas, there are 42 births and 17 deaths over the past year. What is the change in over the course of the year? 🦎

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2FScreen%20Shot%202020-04-05%20at%207.45.04%20PM.png?alt=media&token=30d406e3-ec61-461a-ab4e-62daf4a4563f

The overall change in is +25, meaning that the increased by 25 iguanas over the course of the year.

Exponential Growth

Exponential growth is a type of growth in which the number of individuals in a increases geometrically at a constant rate over time. For exponential growth to occur, some of the following conditions must be met:

  1. There are no : If a has unlimited access to and suitable , it can potentially grow exponentially.
  2. The has a high : Exponential growth is more likely to occur in species that have a high , meaning they can produce a large number of offspring in a short period of time.
  3. The has a low : If a has a low (i.e. a high survival rate), it has the potential to grow exponentially because the of new individuals in the will be greater than the rate that current individuals die off.

Exponential growth is not sustainable in the long term because eventually, the will reach the of its environment, meaning it will no longer be able to continue growing at the same rate due to limited and other factors. However, in the short term, exponential growth can have significant impacts on the environment and the availability of for other species.

There is another formula used to calculate :

dN / dt = (r max) (N)

where: 

dN is the change in size

dt is the change in time

r max is the maximum of the

N is the size 

Ex. A of 862 iguanas has a of 0.05. What is the growth of the after one year? What is the new size? 🦎

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2FScreen%20Shot%202020-04-05%20at%207.46.42%20PM.png?alt=media&token=923bf387-0682-44c6-857f-31638f96f18d

The grew by 43 iguanas in one year. The new is 862 + 43, or 905 iguanas.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-mZBcx1iiBTGn.webp?alt=media&token=b6ca8ea1-8c0a-47fe-a71d-d93985ccb7e1

Image courtesy of Giphy.

Example of Exponential Growth

An example of is the introduction of European rabbits to Australia in the 19th century. 🐇 Rabbits were originally brought to Australia for hunting purposes, but they quickly became an and spread across the continent due to their high . In general, female European rabbits can have up to six litters per year, with an average of four to six offspring per litter.

The of the European rabbits created detrimental impacts on Australian ecosystems, including:

  1. with native species: The rabbits competed with native species for , such as food and , which led to declines in the populations of many native species.
  2. destruction: The rabbits caused significant damage to the landscape by burrowing and feeding on native vegetation, leading to loss and degradation.
  3. Economic impacts: The rabbits damaged crops and pastures, leading to losses for farmers and ranchers.

Despite efforts to limit the rabbit , including fences and chemical control, following the rabbit invasion has allowed the European rabbit to continue damaging Australia today. 

Logistic Growth

However, most growth is logistic, characterized by an S-shaped curve, with a rapid increase in size at first, followed by a slowing of the rate of increase as the approaches its . begins exponentially, but growth is limited by resource availability, , and quality. These can act to decrease the rate of increase as the size increases, eventually leading to a stabilization of the size at or near the of the environment, the number of individuals that an environment can support.

For example, take the reintroduction of wolves to Yellowstone National Park in the mid-1990s. serves as a limiting factor for growth in the relationship between wolves and elk. Because wolves prey on elk for food, the elk decreased after wolves returned to Yellowstone because they experienced to check the size of their . 🐺

Importantly, this relationship works in both directions. If the wolf grows too large, there will not be enough elk to prey on. This means that the elk exerts a bottom-up limiting factor on wolves while wolves provide a top-down limiting factor on elk.

Learning Summary

is a subfield of ecology that focuses on the dynamics of species populations and how they interact with their environment. It involves the study of factors that affect the size and of populations, as well as their survival and reproductive success. Some of the key concepts in include growth and regulation, , , and .

ecologists use a variety of tools and techniques, including , experiments, and , to understand the factors that influence dynamics. Understanding how populations grow and change is valuable because it helps us to understand the factors that influence the abundance and of species, which has important implications for and .

Using mathematical equations, growth and are modelable. In combination with factors necessary for survival, these equations help predict how populations may change over time.

Changes in populations are caused by various biotic and . Some of them include and resource availability, interactions with other organisms in the environment, and the effects of climate and disease. These impacts will be further examined with upcoming topics on and .


-----

Key Terms to Review (29)

Abiotic Factors

: Abiotic factors are non-living parts of an environment that can affect living organisms and functioning ecosystems. They include sunlight, temperature, wind patterns etc.

Biotic Factors

: Biotic factors are all living things or materials from living things affecting an ecosystem. They include plants, animals, bacteria, fungi etc.

Birth Rate

: The birth rate is the number of live births per 1,000 individuals in a population in a year.

Carrying Capacity

: The maximum number of individuals of a particular species that an environment can support indefinitely under stable conditions.

Community Ecology

: Community ecology is the study of how groups of different species interact with each other and their environment within a defined area.

Competition

: Competition refers to the struggle between organisms for limited resources such as food, water, territory or mates.

Conservation

: Conservation refers to the protection, preservation, management, or restoration of natural environments and wildlife.

Death Rate

: The death rate is the number of deaths per 1,000 individuals in a population in a year.

Density

: In ecology, density refers to the number of individuals per unit area or volume.

Distribution

: Distribution refers to how individuals within a population are spaced within their region. This could be random, uniform/regularly spaced, or clumped/aggregated distribution based on resource availability and interactions between organisms.

Exponential Growth

: Exponential growth describes when something increases rapidly due to constant proportionality - meaning it grows more and more quickly as it gets larger.

Field Observations

: Field observations are data and insights collected by scientists in natural environments rather than in a laboratory or controlled conditions.

Habitat

: A habitat is the natural environment where an organism lives. It includes all aspects such as climate, food sources, predators, and other species interactions.

Invasive Species

: An invasive species is a non-native organism that causes harm to the ecosystem into which it has been introduced.

Limiting Factors

: Limiting factors are environmental conditions that limit the growth, abundance, or distribution of an organism or a population of organisms in an ecosystem.

Logistic Growth

: Logistic growth refers to the growth pattern where expansion is rapid initially due to abundant resources, but slows down as resources become limited leading to stabilization around carrying capacity.

Management Efforts

: Management efforts refer to the strategies and actions taken to manage natural resources and ecosystems, often with the goal of sustainability and conservation.

Mathematical Modeling

: Mathematical modeling is the process of using mathematical structures and concepts to represent real-world situations or phenomena.

Mortality Rate

: A measure of the number of deaths in some population, scaled to the size of that population per unit time.

Mutualism

: Mutualism is a type of symbiotic relationship where both organisms involved benefit from each other.

Per Capita Growth Rate

: The per capita growth rate is the rate at which a population of a species increases or decreases for a given set of resources and conditions, such as food availability or predation.

Population

: A population in biology refers to a group of individuals of the same species living in a specific geographical area and capable of interbreeding.

Population Density

: Population density refers to the number of individuals per unit area or volume in an ecological community. It's an important concept in ecology because it influences how organisms interact with each other and their environment.

Population Ecology

: Population ecology is the study of how populations — groups of individuals of the same species living in a specific area — interact with their environment and change over time.

Predation

: Predation is an interaction where one organism (the predator) kills another (the prey) for food.

Predation Pressure

: Predation pressure refers to the impact predators have on their prey's population size and behavior within an ecosystem.

Reproductive Rate

: The average number of offspring produced by an individual organism during its lifetime.

Resources

: In biology terms, resources refer to any substance that is required by a living organism for normal growth, maintenance, and reproduction. These could include food/nutrients, light/sunlight for photosynthesis in plants etc.

Species Interactions

: Species interactions refer to the ways in which species interact with each other within an ecosystem. These can include predation, competition, symbiosis (mutualism, commensalism, parasitism), and more.


© 2024 Fiveable Inc. All rights reserved.

AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.


© 2024 Fiveable Inc. All rights reserved.

AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.