Introduction to Ecosystems - Online Tutor, Practice Problems & Exam Prep

Ecosystems consist of communities of organisms and their environments, where energy flows and matter cycles. Energy, primarily from the sun, is transferred through trophic levels, with only about 10% efficiency at each level, leading to a pyramid of net production. Matter, however, is recycled, as seen in biogeochemical cycles like the carbon and nitrogen cycles. Limiting factors such as nutrient availability and temperature affect productivity. Decomposers play a crucial role in returning nutrients to the ecosystem, while biomagnification highlights the concentration of toxins at higher trophic levels.

Introduction to Ecosystems

This video, we're going to begin our introduction to ecosystems and review a handful of key terms that you should already be familiar with coming into this video. But these terms are very important to this chapter, so let's go on and get started. So first, let's recall from our previous lesson videos that the term ecosystem refers not only to the living community but it also refers to abiotic components in a given area. And the area or size of an ecosystem can vary drastically from being a tiny puddle underneath a small rock with only a small handful of organisms to being several hundred or even thousands of miles in size with many organisms. Now, ecosystems really have two key properties that we highlight down below.

The first is one-way energy flow. All of the energy that enters ecosystems is going to be flowing in one way through the ecosystem. This is because energy is going to be continuously lost in the form of heat with every single energy transfer within the ecosystem. Now the second key property of ecosystems is chemical cycling, and so unlike energy, which is going to have a one-way flow through the ecosystem, chemicals are actually able to be recycled within ecosystems, and we'll get to talk a lot more about this chemical recycling later in our course when we talk about biogeochemical cycles. But for now, let's take a look at this image down below where we can piece together these ideas and review a handful of important terms. Notice on the far left-hand side over here, we're showing you the sun, which is going to serve as the primary energy source for most ecosystems.

Energy from the sun is able to enter into ecosystems via entry points, which are organisms which we call autotrophs, where the root 'auto' means self, the root 'troph' means nutrients. Autotrophs generate their own nutrients themselves, and we also call them primary producers. The autotroph or primary producer here in this image is this plant, which is able to capture energy from the sun using the process of photosynthesis. Now some of the energy captured by this plant is able to be transferred up the food chain to other organisms, which we call heterotrophs, where the root 'hetero' means different. The root 'troph' once again means nutrients.

So heterotrophs are organisms that obtain their nutrients by consuming different organisms. This is why we also call them consumers. The heterotroph or consumer here in this image is this insect. Now as energy is transferred from the plant to this insect, with every single energy transfer, some of that energy is going to be lost in the form of heat. And really, it's this continuous loss of energy in the form of heat that causes energy to flow through ecosystems in one particular way.

And because energy is constantly being lost as heat, ecosystems are going to require a constant input of energy, whether that constant input of energy comes from the sun or whether it comes from a different source such as, for example, hydrothermal vents from deep underneath the ocean. Now once again, we know that chemicals can be recycled within ecosystems, and these greenish bluish arrows that you can see here in a circular pattern represents that chemical recycling. Chemicals from plants can be passed on to heterotrophs. And when these organisms die, their chemicals can be passed on to decomposers, such as this fungi here, which, recall from previous lesson videos, decomposers are really just a specific type of heterotroph that consume and break down dead organic matter and wastes. And the chemicals can be returned to the soil by these decomposers, and then the soil can serve as a reservoir for the primary producers to obtain their chemicals once again, and so that completes the cycle.

Now it is also worthy of noting that chemicals can be added into an ecosystem, indicated by this arrow down below right here, and chemicals can also exit ecosystems as you can see indicated by this arrow up above. But once again, unlike energy, which has a one-way flow through the ecosystem, chemicals are actually able to be recycled within ecosystems. And so ecosystems do not necessarily require a constant addition of chemicals into the ecosystem because those chemicals can be recycled. So this here concludes our brief introduction to ecosystems. We'll be able to learn a lot more moving forward, so I'll see you all in our next video.

Introduction to Ecosystems Example 1

So here we have an example problem that asks what will eventually happen to all of an ecosystem's incoming energy? And we've got these 6 potential answer options down below. Now, option A says it will be used in photosynthesis. And at first, this might seem like a tempting correct answer option, but it's not actually correct. And that's because much of the incoming energy will actually be reflected and won't actually get captured and absorbed and used in photosynthesis.

Additionally, not all ecosystems on Earth are going to rely on photosynthesis to capture their energy. For example, ecosystems that are deep under the ocean and don't receive any sunlight at all may actually rely on organisms that perform chemosynthesis by obtaining energy from hydrothermal vents. And so that's another reason we could have eliminated answer option A. Now moving on, option B says it will be transferred to decomposers. But we know that with every single energy transfer, there's going to be some energy lost in the form of heat.

And so not all of the energy is going to be capable of being transferred to the decomposers for that reason. And so that's why we can eliminate option B. Now option C says it will be transferred from one trophic level to the next. But once again, we know that with every single transfer of energy, there's going to be some amount of energy lost in the form of heat. So not all of the energy will be able to be transferred from one trophic level to the next, and that's why we can eliminate answer option C.

So now we're between either option D, E, or F. And notice that option E says that all of the ecosystem's incoming energy is going to get continuously cycled, but we know from our previous lesson video that this is not going to be true, that, because energy is going to be continuously lost as heat, this causes energy to flow through the ecosystem in one direction and it's not going to be recycled for any extended period of time. So for that reason, we can eliminate answer option E and notice that answer option D says it will be dissipated as heat and this is going to be the correct answer. All of an ecosystem's incoming energy will eventually be dissipated as heat. So we can indicate that D here is the correct answer and of course this means F is not going to be correct.

None of these options are true because we know option D is true. So that concludes this problem. I'll see you in our next video.

Imagine the ecosystem of your local park has gone through a harsh winter, and the total energy contained within the ecosystem is relatively low. To increase the total amount of energy entering the ecosystem, which of the following types of organism could you introduce into the park?

• A. Primary producers (autotrophs).
• B. Primary consumers.
• C. Consumers (heterotrophs).
• D. Decomposers.

Which of the following terms encompasses all the others? 

• A. Primary consumers.
• B. Herbivores.
• C. Carnivores.
• D. Heterotrophs.
• E. Decomposers.
• F. Secondary consumers.

Grazing & Detritus-Based Food Chains

In this video, we're going to differentiate between grazing food chains and detritus based food chains. First, recall from our previous lesson videos that the term "trophic level" refers to an organism's position in a food chain or a food web. Trophic levels include primary producers, primary consumers, secondary, tertiary up to quaternary consumers, and decomposers as well. A grazing food chain is a food chain where the primary consumers feed on live plants. All of the food chains that we've looked at so far in our course have been grazing food chains.

So, it's nothing new. A detritus based food chain, on the other hand, is a food chain where the primary consumers feed on detritus, which recall is just dead organic matter and waste. It is possible for a single organism to participate in multiple food chains, including a grazing food chain and a detritus based food chain. Just as you can see down below, the screech owl is participating in both food chains. It's also possible for a single organism to feed at different trophic levels in different food chains.

So, it's possible for a single organism to serve as a primary consumer in one food chain but then to serve as a tertiary or quaternary consumer in a different food chain. That being said, let's take a look at this image down below where we can further differentiate between a grazing food chain here on the left and a detritus based food chain here on the right. The main differences are at the primary producer level and the primary consumer level. For a grazing food chain, the primary producer is going to be alive, which is why we're showing you a live plant here. The primary consumer is going to be an herbivore that consumes the living plant or the living primary producer.

For a detritus based food chain, the primary producer is going to be detritus, which again is just going to be dead organic matter and waste. Here we're showing you a dead plant. The primary consumer in a detritus based food chain is going to be a decomposer and or a detritivore, which would consume the detritus. Here we're showing you an oyster mushroom. The black arrows that you can see throughout this image indicate the path that nutrients take through the food chain.

What you'll notice is that when all of these organisms at each of these trophic levels die, the nutrients and chemicals that they contain can end up cycling back to these fungi and bacteria that serve as decomposers. These decomposers are the recyclers that complete the chemical cycling within the ecosystem. Every single ecosystem is going to rely on these decomposers and contain decomposers to complete the chemical cycle. However, the rates of decomposition can be different in different environments. The last note that I'll leave you all off with here is that decomposition rates actually have a tendency to increase with increasing amounts of these three factors, which are temperature, moisture, and oxygen.

This is why decomposition rates tend to be greatest near the equator, which has the highest amount of precipitation and the highest temperatures on average as well. This here concludes our lesson, and moving forward, we'll be able to get some practice. So I'll see you in our next video.

Introduction to Ecosystems Example 2

So here we have an example problem that asks, in which of the following locations would decomposition occur at the fastest rate and why? And we've got these four potential answer options down below. Now of course, we need to recall from our last lesson video that decomposition rates tend to increase with increasing amounts of temperature, moisture, and oxygen availability. Now keeping that in mind, notice option a says a field in a temperate grassland because the high wind speeds speed up decomposition. Now in our previous lesson videos, we never said that wind speeds are a major factor in impacting decomposition rates.

And so for that reason, we can go ahead and eliminate answer option a, it's not correct. Now taking a look at option c, it says a beach on the East Coast of the USA because the salty air speeds up decomposition. But once again, we've never said in our previous lesson videos that the salt in the air is what's going to speed up decomposition rate. So that's also just not going to be true. And then answer option d says that decomposition would occur at the same rate in all three locations, but we know from previous lesson videos that different environments can have different decomposition rates.

So these three different environments would have different decomposition rates and they're not all going to be the same here. So we can eliminate option d. And, of course, this leaves answer option b as the only option, and it is the correct answer, which says a tropical rainforest because decomposers work faster in wet and warm conditions. And we know this is consistent with what we've said in our previous lesson videos, decomposition rates increase with increasing temperature and increasing moisture and precipitation. So wetter and warmer conditions would lead to faster decomposition rates.

So option b is the correct answer to this example. That concludes this problem, and I'll see you in our next video.

According to the following food web:

• A. The bullfrog is a primary consumer.
• B. The largemouth bass is an apex predator.
• C. Nutrients in detritus are not recycled within the ecosystem.
• D. The otter acts as both a secondary consumer & a tertiary consumer.

Decomposers are unique in that they:

• A. Return nutrients from dead organisms back to primary producers in an inorganic form.
• B. Can act as both primary producers & primary consumers.
• C. Can consist of animals, plants, prokaryotes, or fungi.
• D. Detoxify detritus, allowing primary producers to use the nutrients.

According to the following food web diagram:

• A. #2 represents a primary producer.
• B. #3 represents an apex predator.
• C. #7 represents a decomposer.
• D. #6 represents a primary consumer.

Here’s what students ask on this topic:

What is the difference between energy flow and matter cycling in ecosystems?

In ecosystems, energy flow and matter cycling are two fundamental processes. Energy flow refers to the transfer of energy through trophic levels, starting from the sun to primary producers (autotrophs) and then to various consumers. This process is inefficient, with only about 10% of energy being transferred to the next trophic level, and most energy is eventually lost as heat. In contrast, matter cycling involves the recycling of elements like carbon, nitrogen, and phosphorus through biogeochemical cycles. Matter is not lost but continuously reused within the ecosystem. For example, carbon cycles through photosynthesis and respiration, while nitrogen is fixed by bacteria and used by plants. Thus, energy flows through ecosystems and is lost, whereas matter is recycled.

What are trophic levels and how do they function in a food chain?

Trophic levels describe the hierarchical positions organisms occupy in a food chain based on their feeding habits. The primary producers, or autotrophs, form the base of the food chain by converting inorganic matter into biomass through photosynthesis or chemosynthesis. Primary consumers, usually herbivores, feed on these producers. Secondary consumers are carnivores that eat primary consumers, and tertiary consumers are carnivores that feed on other carnivores. Decomposers, or detritivores, play a crucial role by breaking down dead organic matter and returning nutrients to the ecosystem. This linear sequence of energy transfer from one trophic level to the next forms a food chain, which can interlink to form a more complex food web.

What is biomagnification and how does it affect higher trophic levels?

Biomagnification is the process by which certain substances, such as toxins, become more concentrated at higher trophic levels in a food web. These substances are often not easily digested or excreted, leading to their accumulation in organisms' tissues. As organisms at lower trophic levels are consumed by those at higher levels, the concentration of these substances increases. For example, if primary producers contain a small amount of a toxin, primary consumers that eat large quantities of these producers will accumulate more of the toxin. This process continues up the food chain, resulting in the highest concentrations of toxins in top predators, which can have harmful effects on their health and survival.

What are the main limiting factors for primary production in aquatic and terrestrial ecosystems?

In aquatic ecosystems, the main limiting factors for primary production are light penetration and nutrient availability. Light is essential for photosynthesis, and its penetration can be limited by water depth and turbidity. Nutrient availability, particularly nitrogen and phosphorus, is often the bottleneck for primary production in aquatic environments. In terrestrial ecosystems, temperature and water availability are the primary limiting factors. Soils also have limiting nutrients, usually nitrogen and phosphorus, which are crucial for plant growth. These factors influence the rate of photosynthesis and biomass production, thereby affecting the overall productivity of the ecosystem.

How do decomposers contribute to nutrient cycling in ecosystems?

Decomposers, such as bacteria, fungi, and detritivores, play a vital role in nutrient cycling by breaking down dead organic matter and waste products. They decompose complex organic materials into simpler inorganic compounds, which are then released back into the soil and water. This process returns essential nutrients like carbon, nitrogen, and phosphorus to the ecosystem, making them available for uptake by primary producers. Decomposers ensure the continuous recycling of matter, maintaining the balance of nutrients in the ecosystem and supporting the growth and survival of various organisms.