Day 2 Due 1/8 (A) 1/9(B): Food Chains and Energy Flow
Producers and Consumers
The organisms that produce food are extremely important in every ecosystem. Organisms that produce their own food are called producers. There are two ways of producing food energy:
Organisms that use the food energy that was created by producers are named consumers. There are many types of consumers.
The organisms that produce food are extremely important in every ecosystem. Organisms that produce their own food are called producers. There are two ways of producing food energy:
- Photosynthesis: plants on land, phytoplankton in the surface ocean, and some other organisms, described in the Earth's Atmosphere chapter and elsewhere.
- Chemosynthesis: bacteria at hydrothermal vents that produce their own energy.
Organisms that use the food energy that was created by producers are named consumers. There are many types of consumers.
- Herbivores eat producers directly (Figure below). These animals break down the plant structures to get the materials and energy they need.
- Carnivores eat animals; they can eat herbivores or other carnivores.
- Omnivores eat plants and animals as well as fungi, bacteria, and organisms from the other kingdoms.
Feeding Relationships
There are many types of feeding relationships (Figure below) between organisms:predators that feed on prey, scavengers, and decomposers.
There are many types of feeding relationships (Figure below) between organisms:predators that feed on prey, scavengers, and decomposers.
Flow of Energy in Ecosystems
Remember from the Earth's Atmosphere chapter that plants create chemical energy from abiotic factors that include solar energy. Chemosynthesizing bacteria create usable chemical energy from unusable chemical energy. The food energy created by producers is passed to consumers, scavengers, and decomposers.
Trophic Levels
Energy flows through an ecosystem in only one direction. Energy is passed from organisms at one trophic level or energy level, to organisms in the next trophic level. Which organisms do you think are at the first trophic level (Figurebelow)?
Remember from the Earth's Atmosphere chapter that plants create chemical energy from abiotic factors that include solar energy. Chemosynthesizing bacteria create usable chemical energy from unusable chemical energy. The food energy created by producers is passed to consumers, scavengers, and decomposers.
Trophic Levels
Energy flows through an ecosystem in only one direction. Energy is passed from organisms at one trophic level or energy level, to organisms in the next trophic level. Which organisms do you think are at the first trophic level (Figurebelow)?
Most of the energy – about 90% – at a trophic level is used at that trophic level. Organisms need it for locomotion, heating themselves, and reproduction. So animals at the second trophic level have only about 10% as much energy available to them as do organisms at the first trophic level. Animals at the third level have only 10% as much available to them as those at the second level.
Food Chains
The set of organisms that pass energy from one trophic level to the next is described as the food chain (Figure below). In this simple depiction, all organisms eat at only one trophic level (Figure below).
Food Chains
The set of organisms that pass energy from one trophic level to the next is described as the food chain (Figure below). In this simple depiction, all organisms eat at only one trophic level (Figure below).
What does this mean for the range of the osprey (or lion, or other top predator)? A top predator must have a very large range in which to hunt so that it can get enough energy to live.
Why do most food chains have only four or five trophic levels? There is not enough energy to support organisms in a sixth trophic level. Food chains of ocean animals are longer than those of land-based animals because ocean conditions are more stable.
Why do organisms at higher trophic levels tend to be larger than those at lower levels? The reason for this is simple: a large fish must be able to eat a small fish, but the small fish does not have to be able to eat the large fish (Figure below).
Why do most food chains have only four or five trophic levels? There is not enough energy to support organisms in a sixth trophic level. Food chains of ocean animals are longer than those of land-based animals because ocean conditions are more stable.
Why do organisms at higher trophic levels tend to be larger than those at lower levels? The reason for this is simple: a large fish must be able to eat a small fish, but the small fish does not have to be able to eat the large fish (Figure below).
Food Webs
What is a more accurate way to depict the passage of energy in an ecosystem? A food web (Figure below) recognizes that many organisms eat at multiple trophic levels.
What is a more accurate way to depict the passage of energy in an ecosystem? A food web (Figure below) recognizes that many organisms eat at multiple trophic levels.
Even food webs are interconnected. All organisms depend on two global food webs. The base of one is phytoplankton and the other is land plants. How are these two webs interconnected? Birds or bears that live on land may eat fish, which connects the two food webs.
Where do humans fit into these food webs? Humans are an important part of both of these food webs; we are at the top of a food web since nothing eats us. That means that we are top predators.
Questions
1. Why are you so much more likely to see a rabbit than a lion when you’re out on a hike?
2. How much energy is available to organisms on the 5th trophic level compared with those on the 1st? How does this determine how long a food chain can be?
Where do humans fit into these food webs? Humans are an important part of both of these food webs; we are at the top of a food web since nothing eats us. That means that we are top predators.
Questions
1. Why are you so much more likely to see a rabbit than a lion when you’re out on a hike?
2. How much energy is available to organisms on the 5th trophic level compared with those on the 1st? How does this determine how long a food chain can be?