Abiotic, Biotic, and Populations Study Guide

Chapter 1: Ecosystems

 

Strand 1: Interactions with Organisms and Their Environment

Chapter Outline

1.1 Abiotic Factors, Biotic Factors and Populations (Bio.1.1)

1.2 Energy and Matter Cycles (Bio.1.2)

1.3 Carbon Cycle (Bio.1.3)

1.4 Stability and Change Ecosystems (Bio.1.4)

1.5 Human Impact(Bio.1.5)

 

The cycling of matter and flow of energy are part of a complex system of interactions within an ecosystem. Through these interactions, an ecosystem can sustain relatively stable numbers and types of organisms. A stable ecosystem is capable of recovering from moderate biological and physical changes. Extreme changes may have a significant impact on an ecosystem’s carrying capacity and biodiversity, altering the ecosystem. Human activities can lead to significant impacts on an ecosystem.

 

 1.1 Abiotic Factors, Biotic Factors and Populations (Bio.1.1)

Explore this Phenomenon

Organisms that live in tide pools have to be able to live in changing conditions. Sometimes they are submerged in ocean water, but other times their environment is dry.

1. Besides changes to the amount of water, what environmental changes would these organisms experience?
2. How might the changing conditions in the tidepool affect the individuals and populations that live there?
3. How could you investigate and collect data that you could use to better understand how the changing conditions in a tide pool affect the populations of organisms living there.

 

 Bio.1.1 Abiotic Factors, Biotic Factors and Populations

Plan and carry out an investigation to analyze and interpret data to determine how biotic and abiotic factors can affect the stability and change of a population. Emphasize stability and change in populations’ carrying capacities and an ecosystem’s biodiversity. (LS2.A, LS2.C)

It is important to understand how different factors affect the stability or change of populations. As you read this chapter, look for different factors that cause populations to remain stable, and for factors that cause populations to change.

 

Ecosystem Structure

 

Where can you find an ecosystem?

Just about everywhere you could go in nature, you would be taking a field trip to an ecosystem. There are underwater ecosystems and terrestrial ecosystems. There are small scale ecosystems and large ones. There are even ecosystems inside your body!

 

What is an ecosystem?

An ecosystem is a group of living things and their environment. The word ecosystem is short for “ecological system.” Like any system, an ecosystem is a group of parts that work together. Ecosystems exist on different scales. The forest pictured below is a big ecosystem. Besides trees, what living things do you think are part of the forest ecosystem? Smaller scale ecosystems exist within the larger forest ecosystem. The dead tree stump in the same forest is a small ecosystem. It includes plants, mosses, and fungi. It also includes insects and worms.

This forest is a big ecosystem.  Besides trees, what living things so you think are part of the forest ecosystem? A dead stump is in the same forest is a small ecosystem.  It includes, plants, mosses, and fungi.  It also includes insects and worms.  An ecosystem can be big or small. A small ecosystem can be part of a larger ecosystem.

 

Abiotic Factors

Abiotic factors are the nonliving parts of ecosystems. They include air, sunlight, soil, water, and minerals. These are all things that are needed for life. They determine which living things—and how many of them—an ecosystem can support. Pictured below is an ecosystem and its abiotic factors.

 

Which abiotic factors do you see here?

 

Biotic Factors

Biotic factors are the living parts of ecosystems. They are the species of living things that reside together.

A species is a unique type of organism. Members of a species can interbreed and produce offspring that can breed (they are fertile). Organisms that are not in the same species cannot do this. Examples of species include humans, lions, and redwood trees. Can you name other examples?

All the members of a species that live in the same area form a population. Many different species live together in an ecosystem. All their populations make up a community. What populations live together in the grassland pictured below?

 

Biodiversity

Some ecosystems can support a greater variety of species than other ecosystems. Biodiversity is a measurement of the amount of variation of life that exists in a given area. More specifically, biodiversity can be defined as the variety of life and its processes, including the variety of living organisms, the genetic differences among them, and the communities and ecosystems in which they occur. How might the abiotic factors in an ecosystem affect the amount of biodiversity in the system?

The rainforest shown below is an ecosystem with a high level of biodiversity. If abiotic factors in the rainforest changed, how would its biodiversity be affected? For example, if the temperature, amount of sunlight or water, or minerals in the system changed, how would the variation of life change?

 

Learn more about biodiversity and the role of keystone species in ecosystems in this Bozeman Science video from Paul Anderson:

https://www.youtube.com/watch?time_continue=370&v=0-PE3ve3w2w

 

Population Growth Limits

How many geese are the right number for this area?

As many as can survive and have healthy offspring! The figure above shows a flock of snow geese at the Kenai National Wildlife Refuge. Their population will tend to grow as big as it can for the resources it needs. Once it is too large, some of its members will die off. This keeps the population size at the right number.

 

 

Carrying Capacity

A population usually grows when it has what it needs. If there’s plenty of food and other resources, the population will get bigger. For example, a single bacteria cell in a container of nutrients will be able to get all of the nutrients it needs. If the bacteria divides every 30 minutes, there were more than a million bacterial cells after just ten hours! If the bacterial population keeps growing at this rate, will there be enough nutrients for all of the bacteria?

A population can’t keep growing bigger and bigger forever. Sooner or later, it will run out of  things it needs. For a given species, there is a maximum population that can be supported by the environment. This maximum is called the carrying capacity. When a population gets close to the carrying capacity, it usually grows more slowly. When the population reaches the carrying capacity, it stops growing.

A population can’t get much larger than the carrying capacity. What might happen if it did?

 

Limiting Factors to Population Growth

For a population to be healthy, factors such as food, nutrients, water, and space must be available. What happens when there are not enough resources to support the population?

Limiting factors are resources or other factors in the environment that can lower the population growth rate. Limiting factors include a low food supply and lack of space. Limiting factors can lower birth rates, increase death rates, or lead to emigration.  If there were no limiting factors, a population would grow exponentially.

Curve A on the graph below represents the exponential growth of a population. As a population grows, it approaches the carrying capacity of the ecosystem. The carrying capacity is the maximum population size that a particular area can support without destroying the habitat. As a population approaches the carrying capacity, individuals must compete for food, water, space, and other resources. This competition causes a decline in the population growth.

Curve B on the graph below shows how the growth rate changes as the population size approaches the carrying capacity. How would the carrying capacity change if the amount of resources increased or decreased?

Curve A shows the growth of the population with no limiting factors. Curve B shows how population growth changes as the population approaches the carrying capacity.

 

 

Examples of Limiting Factors

If there are 12 hamburgers at a lunch table and 24 people sit down at a lunch table, will everyone be able to eat? At first, maybe you will split hamburgers in half, but if more and more people keep coming to sit at the lunch table, you will not be able to feed everyone. This is what happens in nature. But in nature, organisms that cannot get food will die or find a new place to live. It is possible for any resource to be a limiting factor; however, a resource such as food can have dramatic consequences on a population.

Other limiting factors include light, water, nutrients or minerals, oxygen, the ability of an ecosystem to recycle nutrients and/or waste, disease and/or parasites, temperature, space, and predation.

Weather can also be a limiting factor. Whereas most plants like rain, an individual cactus-like Agave americana plant actually likes to grow when it is dry. Rainfall limits reproduction of this plant which, in turn, limits growth rate. Can you think of some other factors like this?

Human activities can also limit the growth of populations. Such activities include the use of pesticides, such as DDT, use of herbicides, and habitat destruction. These activities can result in the death of individuals or affect the resources available to other species.

 

What other factors could limit population growth?

In nature, when the population size is small, there is usually plenty of food and other resources for each individual. When there is plenty of food and other resources, organisms can easily reproduce, so the birth rate is high. As the population increases, the food supply, or the supply of another necessary resource, may decrease. When necessary resources decrease, some individuals will die. Overall, the population cannot reproduce at the same rate, so the birth rates drop. This will cause the population growth rate to decrease.

When the population decreases to a certain level that allows every individual to get enough food and other resources, and the birth and death rates become stable, the population has leveled off at its carrying capacity.

 

Putting It Together

 

Organisms that live in tide pools have to be able to live in changing conditions. Sometimes they are submerged in ocean water, but other times their environment is dry.

1. After learning about how abiotic factors and biotic factors affect populations, how have your ideas about the effects of changing conditions in the tidepool on the populations living there changed?
2. Review your investigation design. How could you revise your investigation to collect data on factors that affect the population growth or carrying capacity in this ecosystem?