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Lesson 1: Introduction to Ecology






By the end of this lesson, students will be able to:


Click here for the course glossary






What do you see when you look around outside? Flowers blooming? Birds flying? Squirrels jumping from tree to tree? All of the living things that you see live in certain areas for specific reasons. Butterflies that depend on flowers live in areas with many flowers. This ensures that they grow and survive. A plant that needs a lot of sunlight lives in an area where it can get maximum light.


The study of ecology seeks to understand why living things are found in certain areas. This lesson will outline some basic ecological concepts. These concepts help explain why organisms live where they do.






What is Ecology?


Ecology is the study of how organisms interact with their environment. This term comes from the Greek words oikos and logos. Oikos means home, and logos means to study. An organism is any living thing. It may be a plant, an animal, or even a mushroom! An environment is anywhere in which a given organism lives. This could include a desert, an ocean, or a rain forest. 


The environment is made up of abiotic and biotic parts. Abiotic refers to non-living things. The abiotic parts of an environment include water, light, nutrients, and temperature. Biotic refers to living things.



This sea turtle's environment is an ocean.




For example, the picture below shows a White's tree frog resting on a tree branch. The abiotic parts of its environment include sunlight and a warm temperature. The biotic parts include the crickets and beetles that it eats. The tree that the frog commonly rests upon is biotic as well. The snakes that eat the tree frog are also biotic.


White's tree frog



Many interactions take place between an organism and its environment. An interaction can be as simple as a lion pursuing an antelope. Interactions can also be complex. Plants interact with their environment to obtain the nutrients to grow and survive. There are many levels and types of interactions. The next few lessons on ecology will explore these in depth.




Four Levels of Study Within Ecology


Ecologists are scientists that study interactions between organisms and their environments. Ecology can be divided into four levels. Study these levels below. They are listed in order from the smallest level (organism) to the largest level (an ecosystem).  Some ecologists study within a single level. Others study many levels of ecology.


The first level of ecology is organismal ecology. This level is concerned with individual organisms and their environments. Scientists that study at this level may ask why an organism looks the way it does. They may research why an organism behaves a certain way. Such scientists also study the abiotic and biotic forces in an environment. More specifically, they research the effects of these forces on organisms' behavior and make-up. 


An organismal ecologist might ask why

a dolphin feeds in a certain part of the bay.




Many ecologists are interested in the study of populations. A population is a group of organisms of the same species that live in the same area. Population ecologists study the factors that affect the size of a population in a given area. There are many factors that such scientists might consider. How does disease affect the population? How are certain organisms preyed upon by others? What is the environment's temperature?


A population ecologist might ask what

factors limit the number of individuals

of a palm tree species on a hill.




The next level examines the ecology of a community. A community includes many populations of different species living and interacting in the same area. A community ecologist asks questions that relate to various populations. They may research the effects of disease, competition, or predators on community structure.


A community ecologist might ask

how disease and competition for

space affect the diversity of flowers

in the field pictured here.




Finally, some scientists study interactions at the ecosystem level. An ecosystem includes two parts: all of the organisms in an area (a community) and the abiotic factors with which they interact. Ecosystem ecology examines the community and its physical environment.


An ecosystem ecologist might ask what

processes in this lake help recycle its nutrients.




Think About It

What kinds of organisms do you see every day? Describe the environments that they inhabit. What are the abiotic components of these organisms' environments?





What Affects the Distribution of Organisms?


Some organisms are found in certain parts of the world but not in others. Kangaroos are found in Australia but not in the U.S. Researchers of biogeography ask questions about the distribution of organisms all over the world. They look at barriers that may prevent an organism from living in a certain place. They also research why certain organisms are able to live in more parts of the world than others.


Look at the two images of the maps. They depict the population distribution of two different types of owls in the United States. There are many reasons that these owls live in different places with different climates.


This image shows the distribution of the Barred Owlin the U.S. and parts of Canada.  The pink and red shaded areas are where this owl has been found.  The darker the shade of pink, the greater the number of owls found in that area.

This image shows the distribution of the Short-eared Owl in the U.S. and Canada.  The pink and red shaded areas are where this owl has been found.  The darker the shade of pink, the greater the number of owls found in that area.



The next section outlines the four main factors that affect where organisms live. The factors are behavior and habitat selection, biotic factors, abiotic factors, and the presence of introduced species.




Behavior and Habitat Selection


Living things usually have a "range." A range is an area in which they can live. These areas are suitable habitats that contain enough food for them to survive. Some organisms choose to live in a very small part of their range. This is a behavior that scientists do not understand well. The organism, usually an animal, has nothing physically wrong with it. It simply selects a specific habitat in which to live.


The European corn borer, for example, lays

its eggs almost solely on corn plants. This

limits these insects to a small area of their

potential range.




Biotic Factors


An organism's habitat depends in part on other living things around it. The following four biotic factors can limit living things' distribution:



Abiotic Factors


Below are four abiotic factors that can influence where an animal or plant lives:


This is a tortoise basking in the sun to regulate

its body temperature.




seagrass bed underwater




Temperature and water strongly affect where organisms live. The next lesson discusses the climate of various biomes. The lesson also describes the types of plants and animals that live in each. Climate is discussed as a major factor that determines where organisms live.




Introduced Species


Introduced species also affect where organisms live. These are also called exotic species. An organism is exotic if it was first found in an area other than the one it now inhabits. Exotic organisms can be plants, animals, bacteria, or viruses. They often come from a different country. Humans are usually responsible for the introduction of these organisms. The introduction can be intentional or accidental.


Exotic species can have a large impact on native species and their habitat. First, the exotic species often have no natural predators when they invade the new habitat. Therefore, their population can increase quickly. Exotic species may even take over the habitat of the native species. They may also eat the native species' food. Exotic species may also feed on the native species' eggs or offspring. Each of these leads to a decrease in the native species' populations.


The hydrilla plant is an introduced species that has caused many problems for native organisms in the United States. This plant is native to Southeast Asia. It was first brought to central Florida for use in an aquarium. Hydrilla has now overgrown many waterways in Florida. It has had a negative effect on the local plant and animal life by changing nutrient cycling and other aspects of the habitat. The overgrowth of this plant has also made it difficult for boaters to pass through some waterways.


Fishermen collect hydrilla in Lake Seminole

in Northern Florida.



Another introduced species is the Northern Snakehead fish, which originated in China. In 1992, a fisherman found a single snakehead fish in a pond in Maryland. Later, people realized that many of these fish inhabited Maryland's waters. The snakehead eats many native fish. It can live for days out of the water. It also has the ability to move across land. Their population is difficult to control because these fish can move from one water source to another. They kill off native fish species in most ponds they inhabit.


Northern Snakehead fish




Think About It


Imagine that someone from Australia brought a young crocodile to the U.S. to be placed in an aquarium. The aquarium owners decide that they do not want the crocodile. They place it in a lake. What effect would this introduction have on the local ecosystem? Think about the potential effects on humans, animals, and plants. What solution would you propose?





How Evolution and Ecology Relate


Evolution refers to changes that have occurred in organisms over time. Organisms have been changing from Earth's earliest days to the present. Charles Darwin, a famous naturalist, studied these changes. He believed that they are caused by interactions between organisms and their environment.


The effects of interactions are evident over both a short period of time (ecological time) and a longer time period (evolutionary time). Say a snake eats mice in a particular field. There will be an immediate impact on the number of mice in that population. This change occurs over ecological time. This can be seen within a person's lifetime.


In this same scenario, the mice that are not eaten will reproduce and pass on to their offspring the traits that enabled them to survive the snake. One of these traits may be a fur color that blends in with the environment, making it harder for the snake to see them. The camouflaged color is a change that takes place over evolutionary time. It can take place over centuries or millennia.


A flounder (fish) camouflaged with

the gravel on the bottom of a lake





Making Connections


Living things are all around us. We constantly see interactions between organisms. This could be two birds competing for a nesting site in a tree. A bee flying from flower to flower is also an interaction. Humans can affect these interactions in many ways. Cutting down trees to build a house takes away potential animal habitats. Planting a tree adds to the plant diversity in an area and creates a potential animal habitat.


This lesson covered the basics of ecology. The lessons that follow explore these basics in more detail. You will learn more about the biomes in which organisms live. You will also discover the complex interactions between non-living and living parts of an ecosystem. At the end of the ecology lessons, you will know how different ecosystems function. You will also understand the importance of conserving both the organisms and the environments in which they live.