Ecosystems: Feeding Relationships

1. Ecosystems: Feeding Relationships Unit 8, Part 1

2. Interactions Among Organisms • Picture a lake and all the organisms that make up that community: different species of fish, plants in and around the water, birds, algae and fungi in the water, snakes, frogs, and turtles. • Understanding the relationships between these organisms can help you to make informed decisions about the environment.

3. Questions to Consider • In what ways do these many organisms interact with one another? • How does each organism obtain the materials and energy it needs to remain alive? • Do the organisms depend upon one another in ways other than as food resources? • Could the community continue to exist if the diversity of life forms were altered in some way?

4. Communities and Relationships • Just as homes, schools, and businesses make up a community, populations of organisms living together in the same area make up an ecological community. • Within any community, the organisms interact with members of their own species and with those of other species. These relationships are called biotic factors. • These organisms interact with their environment as well. This organism-environment interaction is called an ecosystem.

5. Interactions and Trophic Levels • How do organisms interact with each other? • The most obvious way in which organisms interact is by feeding on one another. Because food is a source of energy, availability is a limiting factor in some ecosystems. • In most ecosystems, the primary source of energy is sunlight. The light can be used directly only by autotrophs (organisms that make their own food) such as grass, trees, and algae.

6. Because only autotrophic organisms can process sunlight, all other organisms rely on them for energy. • Energy stored in energy-rich organic molecules is transferred from one organism to another as they feed upon each other. • Each organism represents a feeding step, or trophic level in the passage of energy and materials.

7. Niches • All organisms within an ecosystem have functions in that ecosystem. • An organism’s niche describes how an organism fits into an ecosystem. • Where an organism lives, what it eats and what eats it, and how it interacts with all the biotic and abiotic parts of the ecosystem describe its niche. • Since each type of organism plays a unique role, no two different organisms can occupy the same niche.

8. Consumers • In order for a community to function, people depend on other people. The same is true for organisms within an ecosystem. • In order for an ecosystem to be successful, energy must first pass from producers to consumers. • A consumer that feeds directly on a producer is called a first-order consumer. They are also called herbivores, like cows and deer.

9. Consumers that feed on other consumers are called second-order consumers or third-order consumers. We also call them carnivores. • For example, a mouse(1st order) is eaten by a snake (2nd order), which is then eaten by an owl (3rd order).

10. Omnivores • Omnivores are organisms that eat both producers and consumers. Humans are examples. • Can you think of any other examples?

11. Decomposers • Decomposers are another type of consumer. Decomposers include protists and fungi, as well as vultures. • Decomposers break down and consume dead organisms and wastes, recycling a large part of the broken-down substances back to the producers.

12. Food Chains • The transfer of materials and potential energy from organism to organism (trophic level to trophic level) forms a series called a food chain. • A food chain is represented using arrows that indicate the direction in which materials and energy are transferred from one organism to another.

14. Food Webs • A food web shows all the possible feeding relationships that exist in an ecosystem. • For example, grass can be eaten by mice and rabbits. Snakes may eat mice and rabbits, but the mice may also be eaten by mountain lions. Birds and mice may eat shrubs, and the birds can be eaten by hawks, which also eat mice and rabbits. • These show the many directions that energy circulates within an ecosystem.

16. Ecosystems: Cycling of Energy and Nutrients Unit 8, Part 2

17. Pyramid of Energy • Food chains enable all organisms to obtain a part of the energy entering the ecosystem. However, some energy is lost between each link in the chain. • The amount of energy actually transferred at each level depends on the ecosystem. • The transfer is referred to as the pyramid of energy because the amount decreases as you go up each trophic level. It is estimated that only about 10% of the available energy makes it to the next level.

19. Conservation of Energy? • So, what happens to the energy that is lost from one step to the next? • According to the law of conservation of energy, it is not lost, but it is in an unusable form. • Remember, some of the energy must be stored by producers to carry out life processes. Some energy is bound up in molecules the consumer cannot digest. Much of the energy is converted to heat energy during cellular respiration.

20. Reasons for Energy Loss • There are many explanations as to why 100% of the energy from the producers is not found in third order consumers. • One is that some organisms die and are acted on by decomposers. • Also, not every part of an organism is eaten or broken down (digested) by consumers, so some energy remains with the left-overs.

21. Pyramid of Numbers • So much energy is lost at each trophic level that enough energy seldom remains to support 4th and 5th order consumers, which is why a food chain rarely has more than 4 links. • The loss of energy also explains why there are fewer organisms in each higher trophic level than in the previous level. • This is called a pyramid of numbers.

22. Pyramid of Biomass • Biomass refers to the total amount of dried weight of organic matter. • If data such as biomass is graphed, the familiar pyramid shape is seen. This is called a pyramid of biomass. • This is true for most ecosystems on land, but the reverse is usually seen for aquatic ecosystems, because the producers are mostly microscopic algae, which have very low biomass.

23. Cycling of Materials • Although energy is lost in an ecosystem, it is constantly replaced by sunlight energy. • As a result, an ecosystem always has a new supply of energy. • However, if loss of materials occurred, an ecosystem could not survive because the amount of matter is limited. No new matter is being made. • Thus, matter must be recycled if an ecosystem is to continue.

24. The Carbon Cycle • The next slide shows the carbon cycle. Almost every member of an ecosystem contributes to the cycling of carbon. • Producers do so as they carry out both photosynthesis and aerobic respiration. • Consumers do so as they undergo aerobic respiration. • The products of aerobic respiration, carbon dioxide and water, are cycled to producers, which use those to make sugars and other organic compounds in photosynthesis.

26. The Nitrogen Cycle • Many decomposers recycle materials other than carbon. Some break down organic nitrogen-containing molecules, such as nucleic acids, proteins, and urea, and convert them to inorganic ions. • These ions can be converted to nitrates, which are absorbed by producers. • Producers use nitrates to make those molecules mentioned above, which can then be passed along food chains.

28. The Water Cycle • The water cycle is carried out by the environment itself and is made up of several steps. • Evaporation - liquid water from rivers, oceans, lakes, etc. is converted to gas and enters the atmosphere • Condensation - gaseous water condenses into liquid and forms clouds • Precipitation - liquid water falls to the earth • Transpiration - moisture from plants is taken up into the atmosphere

30. Other Important Cycles • In addition to carbon and nitrogen, organisms can cycle phosphorus and sulfur in similar methods. • Availability of these inorganic materials is crucial, and the supply of them may act to limit distribution of organisms and the size of their populations.

31. Ecosystems: Abiotic Relationships Unit 8, Part 3

32. Abiotic Factors of the Environment • Organisms are not only affected by other organisms, but also by physical factors of the environment. These are called abiotic (non-living) factors. • Think back to the lake in the beginning of the chapter. • Why are grasses only outside the lake? Why are algae only near the surface? Does the temperature of the water affect the kinds of animals that live there? Do different animals live at different depths?

33. Water • Water is crucial for organisms in many ways. Some organisms must live in it, it is a major component of cytoplasm, and it is a substance in which numerous metabolic functions take place. • Because water is so important to so many organisms, availability of water can affect the distribution of organisms.

34. Soil • Most land plants are anchored in soil, which is a source of water and minerals. Soil is the surface upon which many animals move and it’s home for many decomposers and microorganisms. • These organisms enrich and aerate the soil, cycling the materials to other organisms in the ecosystem.

35. Soil Formation • Soil formation begins with a mechanical process in which weathering breaks rock into small mineral particles. • After the breakdown of rock into soil begins, organic material is added as organisms die (this layer is called humus). More plants take root in the soil, and then the diversity of animal and plant life increases. • Humus contains organic material that enriches the soil. It also increases the soil’s capacity for holding the water and air necessary for plant growth.

36. Types of Soil • The amounts of minerals present in soil determines what plants and animals will live in an area. • While there is no ‘best’ type of soil, some soils support more plant life than others, which in turn supports more animal life. • The pH of soil also determines its fertility.

37. Light • By photosynthesis, light energy is changed to the chemical energy needed by every living system. • Because light cannot penetrate deep into water, most algae live near the surface. • In a forest, trees are exposed to the greatest amount of light through their leaves. Other plants are adapted to grow in dim light on the forest floor. • Light is also important to animals for visual purposes. It is a factor in the migration of birds and the flowering of certain plants.

38. Temperature • Temperature, along with wind and rainfall, play an important role in the distribution of organisms. • In general, temperature changes with latitude and altitude. Thus, the types of organisms found in Alaska or on a mountain are different from those living in Florida or a valley. • Organisms are adapted to survive within particular temperature ranges. • Temperature and day length also affect the movement of organisms from place to place.

39. Disruption of the Balance • An ecosystem’s balance can be altered temporarily by natural biotic and abiotic factors. • Natural occurrences such as flood, earthquake, and volcano can upset the balance of an ecosystem. These events cannot be prevented. • Other events, like deforestation by humans, can also greatly affect an ecosystem, and can be prevented. • These types of events can affect the homes of organisms, the soil pH, the water purity, even the temperature and amount of light.