Ecology Reading 1: What Affects How Many Organisms and How Many Kinds of Organisms Live in an Ecosystem? (HS-LS2.1, 2.2)

Reading: What Affects How Many Organisms an Ecosystem Can Hold?

Every ecosystem can only hold a certain number of organisms. This is called the carrying capacity. If too many organisms live in one place, they might not have enough food, water, or space, and some will die or leave.

Ecosystems also have biodiversity. This means having many different kinds of living things.

Species diversity means there are many different types of animals and plants. An ecosystem with a higher species diversity is more able to recover after a disruption.
Genetic diversity means there are variations within the genes of a single species. Populations with a high genetic diversity are more likely to be able to survive an environmental change.

Two types of things affect carrying capacity and biodiversity:

Biotic factors – These are living things that affect other living things.
- Feeding relationships, like when a lion eats a zebra. If a predator increases, its prey will decrease. If prey increases, the number of predators increase.
- Another is symbiosis, when two organisms live closely together in a relationship where at least one benefits. Examples of symbiosis include mutualism, commensalism, and parasitism.
  - Mutualism: A relationship between two species where both benefit from the interaction, such as bees pollinating flowers while obtaining nectar.
  - Commensalism: A relationship where one species benefits while the other is neither helped nor harmed, such as barnacles attaching to a whale.
  - Parasitism: A relationship between two species where one benefits at the expense of the other, such as a tick feeding on a mammal's blood.
- Competition is when animals or plants fight for food, water, or space. When two organisms compete, an increase in one population will lead to a decrease in the other.
- Disease can also hurt populations when many organisms get sick. Disease is more common when populations are high and individuals are crowded.
Abiotic factors – These are non-living things that affect living things.
- Climate and weather conditions are things like temperature and rainfall.
- Natural disasters like floods, fires, and hurricanes can destroy habitats.
- Availability of resources means how much food, water, and shelter are around.

We use data sets (groups of facts or numbers) to study how these factors change ecosystems. For example:

A simulation (computer model) might show how a flood changes the number of fish.
Historical data (information from the past) can show how weather has changed animal populations.

We also use mathematical representations to explain what happens. These are ways of using math to study ecosystems:

We can find the average (the typical number of something).
We can look at trends (patterns over time, like whether a population is growing or shrinking).
We can make graphs to compare different groups of data.

By looking at the math, we can see how biotic and abiotic factors change biodiversity and carrying capacity. For example:

If a disease spreads, a graph might show the number of animals dropping.
If there is more rain, a trend might show more plants growing, which helps more animals survive.

We can also refer to this data to help us understand why some populations increase or decrease.

Populations increase when there are more than enough resources for all the individuals in the population. Births and immigration both cause populations to increase.

Populations decrease when there are not enough resources. Predation, competition, and disease can also contribute. Deaths and emigration cause populations to decrease.

Understanding these changes helps scientists protect ecosystems.

Vocabulary List (with explanations)

Ecosystem – A place where living and non-living things live and work together.
If the ecosystem is healthy, animals and plants can survive well.
Carrying capacity – The largest number of organisms an ecosystem can support.
If too many animals live in one place, some may die because there are not enough resources.
Biodiversity – Many different kinds of living things in one place.
High biodiversity helps ecosystems stay healthy.
Species diversity – Many different types of animals and plants.
More species diversity means the ecosystem has many kinds of organisms.
Genetic diversity – Differences in the genes of the same species.
High genetic diversity helps a species survive changes and disease.
Biotic factors – Living things that affect other living things.
More predators (like wolves) can lower the number of prey (like rabbits).
Abiotic factors – Non-living things that affect living things.
A drought (no rain) can kill many plants and animals.
Feeding relationships – How animals get their food, like predators and prey.
If predators eat too many prey, prey numbers go down.
Symbiosis – When two different organisms live closely and at least one benefits.
Bees help flowers by moving pollen; flowers give bees food.
A. Mutualism: A relationship between two species where both benefit from the interaction, such as bees pollinating flowers while obtaining nectar.
B. Commensalism: A relationship where one species benefits while the other is neither helped nor harmed, such as barnacles attaching to a whale.
C. Parasitism: A relationship between two species where one benefits at the expense of the other, such as a tick feeding on a mammal's blood.
Competition – When organisms fight for food, water, or space.
If many animals compete, weaker ones may die.
Disease – When many organisms get sick.
Disease can lower the population of animals or plants.
Climate and weather conditions – Temperature, rainfall, storms, and other weather.
If it is too dry or too cold, some plants and animals cannot live there.
Natural disasters – Big bad events like floods, fires, or hurricanes.
These can destroy habitats and kill living things.
Availability of resources – How much food, water, and shelter are available.
If resources are low, fewer animals can live there.
Data sets – Groups of numbers or facts collected from studies.
We use data sets to understand changes in ecosystems.
Simulation – A model or computer program that shows what might happen.
Simulations help predict how ecosystems change.
Historical data – Information from the past.
We look at historical data to see how ecosystems have changed over time.
Mathematical representations – Ways to use math to explain things, like averages, trends, and graphs.
Math helps scientists understand changes in ecosystems.
Average – The typical number when you add numbers and divide.
We can find the average number of animals in an area.
Trends – Patterns over time, like going up or down.
A trend might show more plants growing each year.
Graphs – Pictures that show data, like bar graphs or line graphs.
Graphs help us compare information easily.