Population Growth

Biology Index

Where are we going with this? The information on this page should increase understanding related to this standard:  Understand the environment and how each organism fits in and analyze the biogeochemical cycles.

Article includes ideas, images, and content from Troy Smigielski (2022-04)

Population Growth

(So, the population gets bigger?)

When people think about the word "population" it is frequently in the context of how many people live in an area. When applied to ecology, the concept is very similar. 

Recall that in ecology, population is "a group of organisms of one species that interbreed and live in the same place at the same time" (Souce, 2022-04)

So, in that context, population growth is… when the number of organisms increases (duh).

The number of individuals in a certain area is known as its population density.

So, the total population is a number. Population density is how closely they live to one another.

The more things in an area, the greater the density. Or, if the same number of things have to live in a smaller area (such as what occurs with habitat destruction), the density will go up, also.

Think of it like this… six people on a bus is not very dense. Six people in a compact car IS dense. Six people on a moped… Well, too dense!

Population size is affected by:

• Number of births
• Number of deaths
• Number of individuals that enter the population.
• Number of individuals that leave the population.

If more individuals are born than die in a period of time, the population will increase. If more individuals die than are born in a period of time, population will decrease.

When someone enters or leaves a population by a means other than birth or death, it is called migration.

Immigration is the movement of individuals into an area. This causes population to increase.

Emigration is the movement of individuals out of an area. This causes population to decrease.

Migration causes people to either bring in new genes to a population or carry their genes out of a population. This causes something called gene flow. Gene flow is the transfer of genetic variation.

Models of Population Growth

(Why do I feel like we are about to get mathed!)

The two models of population growth are exponential and logistic.

Exponential growth occurs when individuals in a population reproduce at a constant rate. This occurs when resources are unlimited.

This makes the population grow faster as it gets larger.

Cases will increase as long as there are resources (hosts)
that can sustain the organism.

Under the logistic growth model, the population levels off at the maximum population point called the carrying capacity.

Populations move into logistic growth when resources become limited. This is pretty logical. If the environment has the capacity to feed 1000 organisms, once the population reaches that level, it will stop growing.

Side note… A lot of video games like Forge of Empires provides boxes into which you can build things. Once the boxes are all filled, the population of buildings can grow no more… not until you get more resources (land). The number of boxes are analogous to carrying capacity.

Limiting Factors

Within an ecosystem, populations stop growing when the resources are fully utilized. The size to which a population can grow is controlled by limiting factors. A limiting factor is any factor that prevents a population from growing too large. In other words, limiting factors determine the carrying capacity of an environment for a species.

Examples:

•  Competition (for resources)
•  Disease
•  Weather/natural disasters
•  Available space
•  Predators 

There are 2 types of limiting factors. They both deal with population density.

Population density is the number of individuals in a given area.

Recall that… 

Biotic factors are factors that are living (competition, predation, etc.)

Abiotic factors are factors that are non-living (weather, natural disasters, etc.)

A density-dependent limiting factor is one that regulates a population depending on its size. As a general rule, these will typically be biotic factors such as competition, predation, parasitism, or disease.

They have a greater effect with greater population. Disease will have a greater effect on population growth in a large population over a small one.

A common example of a density-dependent limiting factor is competition and/or predation.

Neither animal can get too large in population size, so they are limiting each other.

A density-independent limiting factor is one that affects all populations in similar ways regardless of population size. As a general rule, these will typically be abiotic factors such as weather or natural disasters.

They have the same effect with greater population. A tornado will kill any animal unlucky enough to be within its path. It does not matter how dense the population is.

___________

Death rates are now lower than birth rates which would lead to population growth. However, they used to be equal.

What is one reason why death rates are now lower than birth rates?

Less people are dying due to new medical technologies.

More people are being born due to larger populations and different cultures.

Population growth can be measured using an age-structure diagram. This can then be used to predict future growth or decline.

The predictions from these diagrams are greatly influenced by how many people in different age groups are present in a population.

You can also compare birth rates for certain age groups. In these diagrams, Country 1 has a higher birth rate for young children than the others.

Biomagnification is the process by which a pollutant’s concentration is increased through the trophic levels. 

The animals that eat the pollutant do not digest it, so it keeps piling up in that organism’s tissue. So, over time, the concentration greatly increases.

A classic example of biomagnification is DDT (dichloro-diphenyl-trichloroethane) which was used as an insecticide in the 1940s.

As humans sprayed this liberally, it moved up into the environment and was ingested by birds.

Once in a bird's system, it will alter the bird's calcium metabolism in a way that results in thinner eggs. When the birds try to warm their eggs, they crush them.

As this happened, we learned that it is a probable carcinogen and is toxic to wildlife and the environment.

Ecological Succession

Biology Index

Where are we going with this? The information on this page should increase understanding related to this standard:  Understand the environment and how each organism fits in and analyze the biogeochemical cycles.

Article includes ideas, images, and content from Troy Smigielski (2022-04)

Ecological Succession

(Hmm… Not exactly the same word as success is it?)

Ecological succession is a series of predictable events that occur in a community over time.

Primary succession is succession that begins in an area that has no remnants of an older community. In the first image to the right, there was no plant life or soil to begin with.

In primary succession, the first species to colonize the area is called a pioneer species. The pioneer species in primary succession is often a lichen.

Let's say a new island is formed from a volcano… That could (does) happen!

• Once the lava stops, it will become a mass of solid rock.
• Lichens become the pioneer species and begin to form soil. This allows small plants to grow.
• As the smaller plants die and decompose, more nutrients are available for larger plants.
• Over time, there is enough soil for bigger plants

Primary Succession in Maui, HI

Kauai, HI - Waimea Canyon

Secondary succession is succession that occurs when a disturbance affects an existing community but doesn’t completely destroy it. There was plant life and soil to begin with.

Secondary succession is often caused by a natural disaster.

• Fire can help return nutrients to the soil killing larger trees.
• This allows grasses and smaller plants to grow.
• These attract herbivores and their predators to return.
• This can lead to ecological restoration.

Examples…

Number 1: A volcano erupts covering a small pond in lava rock. Eventually, lichens break down the rock into soil.

This is primary succession.

Number 2: Humans clear land for farming, which allows new plants to grow.

This is secondary succession.

Number 3: Humans clear land for farming, which allows new plants to grow.

This is primary succession.

Number 4: A wildfire in northern California burned down several acres of forest, which left fresh, nutrient-rich soil for a new ecosystem to form.

This is secondary succession.

Succession will eventually reach a stable point where the community is at its peak. This is called a climax community.

In most ecological climax communities, there are a lot of different organisms.

Biodiversity is the variety of life in a particular place. It allows organisms and ecosystems to adapt to environmental change. It also contributes to medicine and agriculture.

It also aids ecological communities in recovery from sudden disruptions. Resilience is the ability of an organism or ecosystem to recover after a disturbance. The more biodiversity an ecosystem has, the more resilient it is likely to be.

Communities and Ecosystems Dynamics

Biology Index

Where are we going with this? The information on this page should increase understanding related to this standard:  Understand the environment and how each organism fits in and analyze the biogeochemical cycles.

Article includes ideas, images, and content from Troy Smigielski (2022-04)

Communities and Ecosystems Dynamics

(So, how things interact and change?)

Each ecosystem has its own set of conditions, which include climate and weather.

Wait! How is climate different than weather?

Weather is the day-to-day conditions. Climate is the average, year-to-year conditions.

A serious issue relating to global climate in the 21st Century is the Greenhouse Effect. What is that?

So, the sun radiates energy to the earth. Passing through the atmosphere, it warms the air and when it strikes the surface of the earth, it warms that, too. Some of the energy will bounce off the atmosphere back into space. The warmed parts of the earth also, after being heated up by the sun, radiate some of the heat back into space.

Enter the greenhouse gases (such as carbon dioxide).

Some of the heat that would radiate back into space is absorbed by greenhouse gases and reflected back to the planet's surface. 

A greenhouse works this way. The radiated light from the sun passes into the greenhouse and warms up everything. The warmed up everything then gives off heat that is trapped by the glass of the greenhouse. Partly, this has to do with the frequencies and wavelengths of the radiation coming in and the heat going out. To keep is simple, just know that the sun's energy goes in and the heat gets "trapped."

The greenhouse effect in global climate works the same way. Some of the energy that would have radiated back into space is trapped and the result is an overall increase in temperatures.

Moving on…

Each ecosystem also has a group of biotic and abiotic factors.

The biotic factors all have their own place in the ecosystem. What is the term that describes where an animal lives?

A habitat is an area with a particular combination of physical and biological environmental factors that influence which organisms can live within it.

There are smaller habitats within each habitat. These are called microhabitats.

Each microhabitat can have its own set of environmental conditions called its microclimate.

Climate plays a big role in determining what can live where. To a certain degree, climate establishes if a habitat is suitable for a particular organism.

Can humans live in 140° heat for a long time period?

However, most organisms can live within a range of conditions.

Tolerance is the range of external conditions within which a species can survive and reproduce.

Within a given habitat, not all organisms live in all of the places. Within a habitat, each species occupies a niche. This includes the range of conditions it can live in as well as the resources it needs and the way it obtains these resources.

For instance, within a single type of tree, different species of warblers occupy different parts.

A niche basically refers to how an organism fits into an ecosystem.

Each organism must fill a particular role within an ecosystem. Perhaps it is more clear to say that within an ecosystem are a variety of resources. Different organisms make use of those different resources in their own ways. In doing so, they fill a particular role.

Why do organisms have to fill a specific role?

In order to reduce competition!

Competition is when organisms attempt to use the same resource in the same place at the same time. There are two types of competition in an ecosystem.

Intraspecific competition is between members of the same species. That is members within the same species.

Interspecific competition is between members of different species.

Oh! Yeah! Intra means between and Inter means within!

The competitive exclusion principle states that no two species can occupy the same niche in the same place at the same time.

This is why the birds must stay at different parts of the tree.

Let's take a look at an example… with a graph!

Can both species successfully live in this area if left alone? Yes, they can (dotted lines).

Based on the graph, can these species live in the same place at the same time?

Hmm… looks like when they try to occupy the same space, they are forced to compete for resources. This means one species will end up beating out the other.

However, not all relationships between organisms is competitive. 

Some relationships between organisms is beneficial.

Symbiosis refers to how two organisms interact with each other, usually favorably. It is the "interaction between two different organisms living in close physical association, typically to the advantage of both;

a mutually beneficial relationship between different people or groups" (Source 2022-04).

Mutualism is when both organisms in a relationship benefit from each other, and it can be written as +/+.

The fish is protected.The anemones are cleaned.

Commensalism is when one organism benefits while the other is unaffected, and it can be written as +/0.

The tree frog uses plants for protection, but the plant is unaffected.

Some relationships between organisms is harmful.

Parasitism is when one organism lives inside or on another organism and benefits itself while harming the host, and it can be written as +/-.

The tick gains nutrients while the human can get sick.

Some crustaceans attach to reef fish and take their sustenance.

There are also ways that more than two organisms interact with each other. Simply put, this is a normal functioning ecosystem.

A keystone species is a species that plays a vital and unique role in maintaining structure, stability, and diversity in an ecosystem.

The keystone species is a species that other species largely depend on, such that if it were removed, the ecosystem would change dramatically.

Further thoughts…

1. What happened to the ecosystem at Yellowstone National Park when the wolves were removed?
   
   
2. Based on this, is it fair to say that wolves are a keystone species?
   
   
3. What happened to the ecosystem at Yellowstone National Park when the wolves were reintroduced in 1995?

Cycles of Matter in Ecology

Biology Index

Where are we going with this? The information on this page should increase understanding related to this standard:  Understand the environment and how each organism fits in and analyze the biogeochemical cycles.

Article includes ideas, images, and content from Troy Smigielski (2022-03)

Cycles of Matter in Ecology

(Life is a merry-go-round?)

The Law of Conservation insist that matter can neither be created nor destroyed; rather, it only changes forms. So, where does the rain come from? If plants, in a remote jungle without human interaction, use up the nitrogen in the soil, how does more get there?

Nature handles this! There are several cycles of matter within nature!

The Water Cycle

"The water cycle shows the continuous movement of water within the Earth and atmosphere. It is a complex system that includes many different processes. Liquid water evaporates into water vapor, condenses to form clouds, and precipitates back to earth in the form of rain and snow" (Source, 2022-03).

Source, 2022-03

1. Water leaves the tree through transpiration.
   
   
2. Water leaves bodies of water or the ground through evaporation.
   
   
3. Water condenses within the cloud through condensation.
   
   
4. Water comes down to earth through precipitation.
   
   
5. Water moves down by force of gravity; this movement is called runoff.
   
   
6. Water leaks into the ground through seepage.
   
   
7. Water is taken back up by plants through root uptake. 

Runoff into the ocean produces nutrient-rich coastal waters.

This causes coastal waters to be more productive in terms of energy.

The Carbon Cycle

"The carbon cycle is nature's way of reusing carbon atoms, which travel from the atmosphere into organisms in the Earth and then back into the atmosphere over and over again. Most carbon is stored in rocks and sediments, while the rest is stored in the ocean, atmosphere, and living organisms.

On Earth, most carbon is stored in rocks and sediments, while the rest is located in the ocean, atmosphere, and in living organisms. These are the reservoirs, or sinks, through which carbon cycles.

Carbon is released back into the atmosphere when organisms die, volcanoes erupt, fires blaze, fossil fuels are burned, and through a variety of other mechanisms" (Source, 2022-03).

Source 2022-03

CO2 is found as gas in the atmosphere. How does it get there?

CO2 is also found dissolved in the ocean. This is because water dissolves CO2.

Last, carbon is found as coal, petroleum, and calcium carbonate rock in the ground.

Look at the image above and answer these questions:

What contributes to CO2 in the ocean?

What are three activities that put CO2 into the atmosphere?

What are the two activities that take CO2 out of the atmosphere?

The Nitrogen Cycle

The nitrogen cycle is a repeating cycle of processes during which nitrogen moves through both living and nonliving things: the atmosphere, soil, water, plants, animals and bacteria. Microscopic living organisms that usually contain only one cell and are found everywhere. Bacteria can cause decomposition or breaking down, of organic material in soils.. In order to move through the different parts of the cycle, nitrogen must change forms. In the atmosphere, nitrogen exists as a gas (N2), but in the soils it exists as nitrogen oxide, NO, and nitrogen dioxide, NO2, and when used as a fertilizer, can be found in other forms, such as ammonia, NH3, which can be processed even further into a different fertilizer, ammonium nitrate, or NH4NO3.

(Source, 2022-03)

The nitrogen cycle describes how nitrogen moves between plants, animals, bacteria, the atmosphere, and soil in the ground.

For nitrogen to be used by different life forms, it must be changed into different states.

The nitrogen found in the atmosphere is N2.

Other forms of nitrogen used are:

• Nitrates (NO3)
• Nitrites  (NO2)
• Ammonium  (NH4)

There are 4 important processes that occur during the nitrogen cycle:

1. Nitrogen fixation is when bacteria change nitrogen into ammonium.

2. Ammonification is when decomposers turn the nitrogen from a dead plant or animal back into ammonium so it can re-enter the nitrogen cycle.

3. Nitrification is when ammonium in the soil is converted to a state that plants can use. This is done by nitrifying bacteria.

4. Denitrification is when extra nitrogen in the soil gets put back into the air. This is done by denitrifying bacteria.

One way nitrogen can be aided in entering a plant is through lightning storms.

Source, 2022-03

The Phosphorus Cycle

"The Phosphorus Cycle is the biogeochemical cycle that describes the transformation and translocation of phosphorus in soil, water, and living and dead organic material" (Source, 2022-03).

Phosphorus is mostly contained in rocks and minerals. Phosphorus is an essential nutrient for life as it makes up parts of DNA.

In the phosphorus cycle, phosphorus moves between the soil and plants. The animals use phosphorus, and then their waste products help return it to the soil.

Some of the phosphorus in soil can be washed away into water basins. Another source of phosphorus in water comes from man-made pollution.

Too much phosphorus in water can lead to plant overgrowth which essentially strangles all other life forms in the water.

Bottom Line:

Phosphorus is trapped in rocks and released when rain (which can be acidic) erodes the rocks.