Biodiversity and ecosystem function

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"No man is an island.” This saying is also true for organisms in an ecosystem. **No organism exists in isolation**.  Individual organisms live together in an ecosystem and depend on one another.  In fact, they have many different types of interactions with each other, and many of these interactions are critical for their survival.

So what do these interactions look like in an ecosystem? One category of interactions describes the different ways organisms obtain their food and energy. Some organisms can make their own food, and other organisms have to get their food by eating other organisms. An organism that must obtain their nutrients by eating (consuming) other organisms is called a **consumer**, or a **heterotroph**. While there are a lot of fancy words related to the sciences, one of the great things is that many of them are based on Latin or Greek roots. For example, heterotroph becomes easier to remember when you realize that in Greek, “hetero” means “other” and “troph” means food; in other words, heterotrophs eat other organisms to get their food. They then use the energy and materials in that food to grow, reproduce and carry out all of their life activities. All animals, all fungi, and some kinds of bacteria are heterotrophs and consumers.

Some consumers are **predators**; they hunt, catch, kill, and eat other animals, the prey. The **prey** animal tries to avoid being eaten by hiding, fleeing, or defending itself using various adaptations and strategies. These could be the camouflage of an octopus or a fawn, the fast speed of a jackrabbit or impala, or the sting of a bee or spines of a sea urchin. If the prey is not successful, it becomes a meal and energy source for the predator. If the prey is successful and eludes its predator, the predator must expend precious energy to continue the hunt elsewhere. Predators can also be prey, depending on what part of the food chain you are looking at. For example, a trout acts as a predator when it eats insects, but it is prey when it is eaten by a bear. It all depends on the specific details of the interaction. Ecologists use other specific names that describe what type of food a consumer eats: **carnivores** and **herbivores** are meat eaters and plant eaters, respectively. **Omnivores** eat both animals and plants. Once again, knowing the Latin root helps a lot:  "vor" means "to eat or devour," as in "voracious.” Put "-vore" at the end of a scientific term for a kind of food, and you have described what an organism eats. For example, an **insectivore** is a carnivore that eats insects, and a **frugivore** is an herbivore that eats fruit. This may seem like a lot of terminology, but it helps scientists communicate and immediately understand a lot about a particular type of organism by using the precise terms.

Not all organisms need to eat others for food and energy. Some organisms have the amazing ability to make (produce) their own energy-rich food molecules from sunlight and simple chemicals.  Organisms that make their own food by using sunlight or chemical energy to convert simple inorganic molecules into complex, energy-rich organic molecules like glucose are called **producers** or **autotrophs**. And here’s another quick Greek lesson: “auto” means “self” and “troph” still means “food.” So autotrophs are self-feeding; they make their own food. Plants, algae, and microscopic organisms such as phytoplankton and some bacteria, make energy-rich molecules (in other words, their food) from sunlight, water, and carbon dioxide during the process called **photosynthesis** (“photo” means “light, and “synthesis” means “to make” – photosynthesizers are using sunlight to make food). Some producers are **chemosynthesizers** (using chemicals to make food) rather than photosynthesizers; instead of using sunlight as the source of energy to make energy-rich molecules, these bacteria and their relatives use simple chemicals as their source of energy. Chemosynthesizers live in places with no sunlight, such as along oceanic vents at great depths on the ocean floor.

No matter how long you or a giraffe stands out in the sun, you will never be able to make food by just soaking up the sunshine; you will never be able to photosynthesize. You’ll just get sunburned and thirsty and will still need to go eat another organism if you are hungry. Producers use the food that they make and the chemical energy it contains to meet their own needs for building-block molecules and energy so that they can do things such as grow, move, and reproduce. When a consumer comes along and eats a producer, the consumer gets the building-block molecules and the chemical energy that is in the producer’s body. All other life depends on the energy-rich food molecules made by producers – either directly by eating producers, or indirectly by eating organisms that have eaten producers. Not surprisingly, ecologists also have terms that describe where in the food chain a particular consumer operates. A **primary** **consumer** eats producers (e.g., a caterpillar eating a leaf); a **secondary** **consumer** eats primary consumers (e.g., a robin eating the caterpillar). And it can go even further: a **tertiary** **consumer** eats secondary consumers (e.g., a hawk eating the robin). A single individual animal can act as a different type of consumer depending on what it is eating. When a bear eats berries, for example, it is being a primary consumer, but when it eats a fish, it might be a secondary or a tertiary consumer, depending on what the fish ate!

[[☃ image 1]]All organisms play a part in the web of life and every living thing will die at some point.  This is where **scavengers**, **detritivores** (which eat detritus or parts of dead things), and **decomposers** come in.  They all play a critical role that often goes unnoticed when observing the workings of an ecosystem.  They break down carcasses, body parts and waste products, returning to the ecosystem the nutrients and minerals stored in them.  This interaction is critical for our health and health of the entire planet; without them we would be literally buried in dead stuff. Crabs, insects, fungi and bacteria are examples of these important clean-up specialists.

[[☃ image 1]]Another category of interactions between organisms has to do with close, usually long-term interaction between different types of organisms. These interactions are called symbiosis. The impacts of **symbiosis** can be positive, negative, or neutral for the individuals involved. Organisms often provide resources or services to each other; the interaction is mutually beneficial.  These “win-win” symbiotic interactions are known as **mutualism** **(+ +)**. For example, ants living in a tree may protect the tree from an organism that would like to make the tree its next meal, and at the same time the tree provides a safe home for the ants. Symbiotic relationships are not always positive for both participants. Sometimes there are definite losers. In **parasitism (+ -)**, for example, the parasite benefits and the host is harmed, such as when a tick sucks blood out of a dog. **Predation (+ -)** is another winner-loser relationship but it is not symbiosis. The predator benefits and the prey is harmed lethally, but it is a short-term interaction. In parasitism, the parasite does not usually kill its host, but just feeds on it for a long time while it is living.

Other symbiotic interactions, called **commensalism (+ 0)**, are beneficial for one organism, but do not affect the other in a positive or a negative way. The interaction is seemingly neutral for one of the organisms. For example, a barnacle attached to a whale is able to travel thousands of miles collecting and filtering food from the moving water.  The whale doesn’t seem to be affected by the little hitchhikers. But then again, maybe those little hitchhikers are actually creating a tiny amount of additional drag as the whale moves through the water and therefore the whale has to expend just a little bit of additional energy. If so, that would be a negative impact for the whale. Often, further research reveals that what was originally thought to be neutral for one participant and therefore an example of commensalism, actually has a very subtle positive or negative impact, so the classification is no longer commensalism, but rather mutualism or parasitism. Is a bird nest on a tree limb commensalism, or is there some slight advantage or disadvantage for the tree in having the nest there? It is possible to come up with plausible explanations either way; only detailed research could provide the necessary information to answer the question.

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**Competition** is an interesting example of interactions. When two organisms compete or fight for the same limited resource such as food, shelter, a mate, or sunlight, there is usually a winner and a loser **(+ -)**, but if the competitors fight literally to the death and kill each other, the interaction has become negative for both **(- -)**. Competition is also an interesting example because it is just as likely to be **intraspecific** as **interspecific** (language alert: the prefix “intra” means “within” and the prefix “inter” means "between"). An intraspecific interaction occurs within a species (e.g., two bull elephant seals competing for a harem of females or two English ivy plants competing for space and sunlight), and an interspecific interaction occurs between members of different species (e.g., when two different species of corals compete for space and sunlight on a coral reef by trying to outgrow each other). If the competition is long-term and occurs between two different species, it would be another example of symbiosis.

In summary, there are many different kinds of interactions between organisms in an ecosystem and it is not unusual for any particular organism to wear many hats and play multiple roles at different times. For example, we humans are consumers and predators when we hunt, kill, and eat other animals such as a fish or a deer, or when we eat chicken we have purchased at the grocery store or a restaurant. We also have many mutualistic relationships with other organisms, such as our pets. Competition also occurs between humans for resources, even mates! Interactions between organisms, including humans, are the nature of life and have tremendous impact on the functioning and health of ecosystems.

Have you ever heard the expression “you can’t tell the players without a program” and found it to be true? Sometimes you need background information, a list of the players, their titles or functions, definitions, explanations of interactions and rules to be able to understand a sporting event, a theatrical play or a game. The same is true for understanding the subtle but important differences among the various components that make up an ecosystem. Terms such as **individual**, **population**, **species**, **community** and **ecosystem** all represent distinct ecological levels and are not synonymous, interchangeable terms. Here is your brief guide or program to understanding these ecological players.

You are an individual, your pet cat is an individual, a moose in Canada is an individual, a coconut palm tree on an island in the Indian Ocean is an individual, a gray whale cruising in the Pacific Ocean is an individual, and a tapeworm living in the gut of a cow is an individual, as is the cow itself. An **individual** is one organism and is also one type of organism (e.g., human, cat, moose, palm tree, gray whale, tapeworm, or cow in our example). The type of organism is referred to as the **species**. There are many different definitions of the word species, but for now we’ll leave it simply that it is a unique type of organism. As a grammatical aside, note that the word “species” always ends in an “s”. Even if you are referring to just one type of organism, one species, it is a species; there is no such thing as a specie. That’s just one of those grammatical facts of life.

Each species that has been studied and described by scientists has been given a two-part name, their **binomial** or scientific name, that uniquely identifies it (e.g., humans = _Homo sapiens_; domestic cats = _Felis catus_; moose = _Alces alces_; coconut palms = _Cocos nucifera_; gray whales = _Eschrichtius robustus_; cow tapeworms = _Taenia saginata_; and domestic cows = _Bos taurus_). The power or value of the scientific name is that it makes clear what type of organism you are talking about. Since only one type of organism in the entire world has that unique name, it makes for much clearer communication and understanding than using common names. If you are talking about a gopher, for example, just using its common name like this, you might be referring to a type of mammal that lives underground, a type of snake, or even a type of tortoise, depending on what part of the country you are in.

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If you refer to the gopher _Gopherus polyphemus_, you are talking only about the gopher tortoise.

So what’s a **population**? It’s a group of individuals that all belong to the same species. Populations are geographically based; they live in a particular area. But the size or scale of that area can be variable – we can talk about the human population in a city, a state, a country or a hemisphere. Or we can talk about the population of palm trees on just one island in the Indian Ocean, or on all of the islands that make up the Republic of Seychelles, or all of the islands in the Indian Ocean. The person studying or writing about the population gets to decide what scale to use, what is most appropriate for what they want to study or explain. That’s one of the exciting things about science – there’s a lot of freedom in defining the scope and scale of your project, but that means it is also important to explain clearly what scale you are using.

Species are made up of populations. How many populations? It all depends. It depends on how widespread the species is and how small or large the geographic area is. Some species have very limited ranges or distributions, being restricted, for example, to a single island or the top of a single mountain in the whole world. The single population on the island or mountaintop makes up the entire species. From a conservation perspective, such populations are extremely vulnerable – if anything happens to that one population, the entire species will be lost; the species will go extinct. But many species are more widespread. There are populations of moose, for example, in Yellowstone National Park, Maine, Minnesota, Alberta, Manitoba and other U.S. states and Canadian provinces. If you want to know how many moose there are on Earth, you have to know the sizes of all the different populations in all the different locations.

**Communities** are made up of all the populations of different species in a given area. Why the vague term “in a given area?” Because once again the scale is flexible, determined by the person studying or writing about the community. We might be talking about the community of all the organisms living in the very top or canopy of a single rainforest tree or of all the trees in the forest. What’s most important about the community concept is that it involves multiple populations of all the different species in the given area and how these species interact with each other. Each of the populations is made up of individuals of a particular species, and the individuals interact with each other – with members of their own species (e.g., fighting, grooming, mating, pollinating each other) and with individuals of other species (e.g., hunting them for food, using them as a place to build a nest, growing on them). Community ecologists study the populations in a given area and their interactions. There’s another article in this tutorial about different types of ecological interactions.

That leaves us with the **ecosystem** level. What’s the difference between communities and ecosystems? When you’re talking about ecosystems, you’re not only looking at all the different populations and species in the given area, but you’re also looking at the physical environment, the non-living or **abiotic** conditions (language alert: the prefix “a” means “without” and the root word “bio” means life, so abiotic is literally “without life” or in other words, non-living), and not just what they are, but how they impact the organisms, and in some cases how the organisms impact the physical environment. For example, temperature and rainfall patterns influence where different terrestrial species of plants and animals live; some can survive dry desert conditions, others need the high rainfall found in rainforests. But the forests themselves also influence temperature and rainfall patterns. Have you ever noticed on a hot summer day how much cooler and moist it is in the shade of a forest than out in the open?  And worms change the structure and composition of soil as they churn through it.

What size is an ecosystem? Guess what – it depends on how big or small the scientist or author wants to define it to be. It could be as small as your backyard, or Walden Pond, or the entire Australian outback.  Different sizes or scales will be appropriate for different types of studies, reports and policies. The scientist or author just needs to explain what the size is and why it is appropriate.

[[☃ image 1]]The diagram above will hopefully help you visualize how the different ecological levels are related to each other. Individuals make up a population; populations make up a species; multiple species and their interactions make up a community; and multiple species and their interactions make up ecosystems when you include the abiotic factors. This is the hierarchy of ecology.

Grab your notebook or computer and write out your answer to each of the following questions. Then compare your answer to the suggested answer found in the “Answers to exploration questions” article. Have fun! Hint: the information needed to answer these questions can be found in the video and the articles.

1. After watching the first tutorial, your friend turns to you and says, “Oh, I see! All interactions within an ecosystem network are the same importance, because all species have the same interactions with other species.” Do you agree or disagree with your friend’s statement? Explain why in a few sentences.

2.     Which of the following network diagrams illustrates the most stable ecosystem? Explain your answer in a few sentences.

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3.     The table below shows the data your team collected while documenting the biodiversity on three islands. Based on these results, which of the islands should be categorized as having the greatest biodiversity, using the criterion of species richness? Explain your answer in 2-3 sentences.

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4.     Based on what you saw in the video, explain in 2-3 sentences why the whale in the whale fall scenario is similar to the Google server, in terms of their importance to their networks.

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Hint: the background information that will help you complete these activities is found in the video and the articles.

**1.     Calculating species richness.**

Go outdoors, choose a particular area, such as your backyard or a nearby park, and document the number of different species you find in that area. Don’t worry about the microbes, the things too small too see; just focus on the plants, animals, and fungi that you can see. Use these data to calculate species richness of that outdoor space. Here’s a hint: add up the number of different types of species you find.  You don’t have to know the name of each species, you can just say tree species 1 and tree species 2, for example. If you have a camera, iPad or smart phone, you can take a picture of each different species to help you identify them later. You should also keep track of how many individuals you find for each type of species, which will give you the population size for that species.  But it is the number of species that determines species richness, not the number of individual organisms.

**2.   Documenting ecological interactions.**

Go outside in your backyard, the school grounds, to a park, zoo or aquarium – some place where you will see a variety of living organisms. Observe two organisms that are interacting in some way, and draw or photograph the interaction and describe what you see.  Explain what type of interaction you think is occurring and why.  If you can identify the types of organisms you have observed, you can do some research online or in books to see if your explanation is likely correct.

All of the following terms appear in the video or articles for this tutorial section on biodiversity and ecosystem function. The terms are arranged here in alphabetical order, and nouns are given in just their singular form unless the plural of the term is unusual.

**abiotic**: non-living

**autotroph**: an organism, such as a plant, that can make its own energy-rich food molecules from inorganic materials and an energy source such as sunlight; autotrophs are also called producers

**binomial**: when referring to species, the two-part scientific name that is unique for each type of organism; sometimes also called the Latin name

**biodiversity**: the variety of life on Earth or some other specified geographic region of the planet; the diversity of life occurs at the genetic level, at the species level, at the ecosystem level, and in evolutionary lineages

**Biodiversity Ecosystem Function (BEF)**: an emerging field that studies how the biodiversity within an ecosystem is related to the ecosystem’s function

**carnivore**: an animal that eats meat (i.e., other animals)

**chemosynthesizer**: an organism that makes its own energy-rich food molecules from just simple inorganic chemicals without the use of sunlight; some bacteria are chemosynthesizers

**commensalism**: a type of symbiosis where one organism benefits and the other is not affected in a positive or a negative way

**community**: two or more different species occupying the same geographical area and interacting in some way

**competition**: a type of interaction where two organisms fight for the same limited resource such as food, sunlight or a mate; can occur between individuals of the same or different species

**consumer**: an organism, such as a cow or a shark, that must eat other organisms to obtain energy-rich food molecules because they cannot make the molecules themselves; consumers are also called heterotrophs

**decomposer**: an organism that breaks down organic material over time

**detritivore**: an organism that eats detritus or parts of dead things

**ecosystem**: the community of different species in a particular geographic area and all of their interactions with each other and the physical environment; ecosystems are also called ecological networks

**ecosystem function**: the processes that occur within an ecosystem that are related to species interactions, energy flow and the cycling of materials

**ecosystem network**: the interactions among organisms in an ecosystem and the diagram that illustrates these relationships and how matter and energy move from one species to another; also called an ecological network

**frugivore**: an herbivore that eats fruit

**herbivore**: an animal that eats plants; also called a primary consumer

**heterotroph**: an organism, such as a sea turtle or a hawk, that must eat other organisms to obtain energy-rich food molecules because they cannot make the molecules themselves; heterotrophs are also called consumers

**individual**: one organism

**insectivore**: a carnivore that eats insects

**interspecific**: occurring between members of two or more different species

**intraspecific**: occurring within a single species

**mutualism**: a type of symbiosis where both organisms benefit

**omnivore**: an animal that eats both plants and animals

**organism**: a living or formerly living thing

**parasitism**: a type of symbiosis where one organism (the parasite) benefits and the other (the host) is harmed

**photosynthesis**: the process of capturing the energy in sunlight to create energy-rich organic molecules from inorganic molecules; organisms that photosynthesize are called photosynthesizers

**plankton**: microscopic organisms that live in the ocean and other bodies of water; phytoplankton are plant-like and can photosynthesize; zooplankton are animal-like and cannot photosynthesize

**population**: all the individuals of a particular species that live in a specific geographic area; a species may be made up of one or more populations

**predation**: the act of one animal killing and eating another animal

**predator**: an organism that hunts, catches, kills, and eats other animals

**prey**: an organism that is caught, killed and eaten by a predator

**primary consumer**: an animal or other heterotroph that eats producers or herbivores

**producer**: an organism, such as a plant, that can make its own energy-rich food molecules from inorganic materials and an energy source such as sunlight; producers are also called autotrophs

**scavenger**: an animal that eats dead organisms or parts of dead organisms

**secondary consumer**: an animal that eats primary consumers

**species**: a distinct type of organism

**species richness**: the number of different species in a given geographic area

**succession**: in ecology, the change in the communities of organisms in a geographic area over time

**symbiosis**: a long-term relationship or interaction between individuals from two different types of species; the symbiotic relationship has a positive, negative or neutral impact on the participants

**tertiary consumer**: an animal that eats secondary consumers

If you are wondering where the suggested answers came from, you can review the video and the articles in the ecosystem function section.

1. After watching the first tutorial, your friend turns to you and says, “Oh, I see! All interactions within an ecosystem network are the same importance, because all species have the same interactions with other species.” Do you agree or disagree with your friend’s statement? Explain why in 2 or 3 sentences.

Answer: The statement is incorrect. A complete explanation would mention that interactions between organisms in an ecosystem do not all have the same importance. Some species have a greater influence on the whole network than others, such as the whale fall example in the video.

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2.     Which of the following network diagrams illustrates the most stable ecosystem? Explain your answer in two to three sentences.

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Answer: b. A complete explanation would mention that b has the most connections and interactions among species, and ecosystems with more species and connections are more resistant to disturbances.

3.     The table below shows the data your team collected while documenting the biodiversity on three islands. Based on these results, which of the islands should be categorized as having the greatest biodiversity, using the criterion of species richness? Explain your answer in 2-3 sentences.

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Answer: Using the criterion of species richness, Island A has the greatest biodiversity, because it has the greatest number of species. A complete explanation would mention that the number of species in an ecosystem determines the species richness, and species richness is a key measure of biodiversity. Species richness is not dependent on the number of individuals within each species. So even though Island C has by far the greatest total number of individuals, it has the lowest number of species and therefore does not have the greatest species richness.

4.     Based on what you saw in the video, explain in 2-3 sentences why the whale in the whale fall scenario is similar to the Google server, in terms of their importance to their networks.

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Answer: A complete explanation would mention that the whale is critically important to its ecosystem network because so much of the ecosystem’s energy flows through the whale. Similarly, if the Google server was removed, a large portion of the internet would not function because such a huge amount of information flows through the Google server. The whale and the Google server are both critically important to their networks, much more so than say a crab or one desktop computer, respectively.