This lesson covers:
- The difference between food chains and food webs
- Key terminology related to feeding interactions
- How organisms are interdependent in food webs
Food chains versus food webs
Food chains show feeding relationships between different organisms whereas food webs show how food chains interconnect in an ecosystem.
Feeding interactions – Producers and consumers
These terms are used to describe organism roles within food webs:
- Producer – Plants that generate food and energy for the ecosystem (shown in green above, e.g. carrots, grasses and wheat).
- Consumer – Heterotrophs that rely on other organisms for food (shown in red above).
Feeding interactions – Types of consumer
Consumers can be divided into:
- Primary consumers – Animals that eat producers (shown in red above, e.g. rabbits).
- Secondary consumers – Animals that eat primary consumers (shown in purple above, e.g. owls).
- Tertiary consumers – Animals that eat secondary consumers (shown in orange above, e.g. foxes when they eat birds).
Some animals can occupy more than one role. For example birds are primary consumers when the eat wheat but secondary consumers when they eat grasshoppers.
Feeding interactions – Carnivores, herbivores and omnivores
These terms are used to describe what consumers eat:
- Herbivore – Animals that only consume producers/plants (shown in teal, e.g. grasshoppers).
- Carnivore – Animals that only eat other consumers (shown in red, e.g. owls).
- Top carnivore – Carnivores not predated within that food web (shown in orange, e.g. foxes).
- Omnivore – Animals that eat both plant and animal matter (shown in blue, e.g. birds).
Interdependency in food webs
The arrows in food web diagrams demonstrate the flow of energy between organisms.
This interdependency means a change in one organism’s population can affect other organisms that depend on it for food.
For example:
- If a disease kills all the wheat plants, mice will not longer have a food source and will die.
- This means they foxes also have less food to eat so their population would also decline.
Practice Quiz
1. What is a food web?
Answer: A food web is a complex network of interconnected food chains within an ecosystem, illustrating how different organisms are related through feeding relationships.
2. What is the difference between a food chain and a food web?
Answer: A food chain is a linear sequence showing the feeding relationships between organisms, while a food web is a more complex network showing multiple interconnected food chains.
3. What is a producer in a food web?
Answer: A producer is an organism, typically a plant, that can produce its own food through photosynthesis and serves as a primary source of energy for other organisms in the ecosystem.
4. What is a consumer in a food web?
Answer: A consumer is an organism that relies on other organisms for food. Consumers can be herbivores, carnivores, or omnivores.
5. What is a primary consumer?
Answer: A primary consumer is an herbivore that eats producers, such as plants. Examples include rabbits, deer, and grasshoppers.
6. What is a secondary consumer?
Answer: A secondary consumer is a carnivore that eats primary consumers. Examples include frogs, snakes, and owls.
7. What is a tertiary consumer?
Answer: A tertiary consumer is a carnivore that eats secondary consumers. Examples include lions, hawks, and sharks.
8. What is a top carnivore?
Answer: A top carnivore, or apex predator, is a carnivore at the top of the food chain that is not preyed upon by other organisms within that ecosystem. Examples include wolves, eagles, and great white sharks.
9. What is an omnivore?
Answer: An omnivore is an organism that eats both plants (producers) and animals (consumers). Examples include bears, humans, and pigs.
10. What is an herbivore?
Answer: An herbivore is an organism that exclusively eats plants. Examples include cows, elephants, and caterpillars.
11. What is a carnivore?
Answer: A carnivore is an organism that primarily eats other animals. Examples include tigers, crocodiles, and hawks.
12. How do food webs show energy flow?
Answer: Food webs show energy flow through arrows pointing from one organism to another, indicating who eats whom and how energy is transferred within the ecosystem.
13. What is interdependency in a food web?
Answer: Interdependency in a food web refers to the reliance of organisms on one another for food. Changes in the population of one organism can impact the populations of others.
14. How does the removal of a species affect a food web?
Answer: The removal of a species can disrupt the balance of a food web, leading to population declines or increases in other species that are directly or indirectly connected to the removed species.
15. What is the role of decomposers in a food web?
Answer: Decomposers, such as fungi and bacteria, break down dead organic matter, returning nutrients to the soil and supporting the growth of producers.
16. How are food webs and ecosystems related?
Answer: Food webs represent the feeding relationships within an ecosystem, showing how energy and nutrients flow between organisms in that ecosystem.
17. What is the significance of a keystone species in a food web?
Answer: A keystone species has a disproportionately large impact on its ecosystem relative to its abundance. Its presence or absence significantly affects the structure and stability of the food web.
18. What is the difference between a detritivore and a decomposer?
Answer: Detritivores, such as earthworms and vultures, consume dead organic matter directly, while decomposers, like fungi and bacteria, chemically break down dead organic matter into simpler substances.
19. What is the role of photosynthesis in a food web?
Answer: Photosynthesis, performed by producers, converts solar energy into chemical energy in the form of glucose, which serves as the primary energy source for other organisms in the food web.
20. How do environmental changes impact food webs?
Answer: Environmental changes, such as climate change, habitat destruction, or pollution, can alter the availability of resources, disrupt species populations, and ultimately affect the balance of food webs.
21. What is a trophic level?
Answer: A trophic level refers to the position an organism occupies in a food chain or web, based on its source of energy. Primary producers are at the first trophic level, primary consumers at the second, and so on.
22. What is the role of apex predators in food webs?
Answer: Apex predators help regulate the populations of other species, maintaining the balance and health of the ecosystem by controlling the numbers of herbivores and other consumers.
23. How can human activities disrupt food webs?
Answer: Human activities, such as overfishing, deforestation, and pollution, can lead to the decline or extinction of species, disrupt feeding relationships, and destabilize food webs.
24. What is biomagnification in a food web?
Answer: Biomagnification refers to the increasing concentration of toxins, such as pesticides or heavy metals, in organisms at higher trophic levels of a food web.
25. How do invasive species affect food webs?
Answer: Invasive species can outcompete native species for resources, alter habitat structures, and disrupt existing food webs by preying on or displacing native species.
26. What is a food pyramid and how does it relate to food webs?
Answer: A food pyramid visually represents the distribution of energy and biomass across different trophic levels, with producers at the base and apex predators at the top, reflecting the structure of food webs.
27. How does energy efficiency vary between trophic levels?
Answer: Energy efficiency decreases at higher trophic levels due to energy losses from metabolic processes, with only about 10% of energy transferred from one level to the next.
28. What is a detrital food web?
Answer: A detrital food web focuses on the decomposition and recycling of organic matter, involving detritivores and decomposers that break down dead organisms and waste products.
29. How do seasons affect food webs?
Answer: Seasonal changes can affect the availability of food resources, migration patterns, and reproductive cycles, influencing the dynamics and interactions within food webs.
30. What are the main components of a terrestrial food web?
Answer: Main components include producers (plants), primary consumers (herbivores), secondary and tertiary consumers (carnivores and omnivores), and decomposers (fungi and bacteria).
31. What are the main components of an aquatic food web?
Answer: Main components include producers (phytoplankton), primary consumers (zooplankton and small fish), secondary and tertiary consumers (larger fish and marine mammals), and decomposers (bacteria and fungi).
32. How do parasites fit into food webs?
Answer: Parasites feed on hosts and can affect their health and behavior, influencing population dynamics and interactions within food webs.
33. What is the role of mutualistic relationships in food webs?
Answer: Mutualistic relationships, such as pollination or symbiosis, provide benefits to both organisms involved and can enhance the stability and productivity of food webs.
34. How do food webs illustrate biodiversity?
Answer: Food webs illustrate biodiversity by showing the variety of species and their interactions within an ecosystem, highlighting the complexity and interdependence of life.
35. What is the impact of climate change on food webs?
Answer: Climate change can alter species distributions, affect food availability, and disrupt timing of life cycles, leading to changes in feeding relationships and food web dynamics.
36. How do top-down and bottom-up controls affect food webs?
Answer: Top-down controls involve the influence of predators on lower trophic levels, while bottom-up controls involve the availability of resources like nutrients and primary production affecting higher trophic levels.
37. What are keystone species and their importance in food webs?
Answer: Keystone species have a critical role in maintaining the structure and function of an ecosystem. Their presence or absence significantly affects other species and the overall health of the food web.
38. How do decomposers contribute to nutrient cycling in food webs?
Answer: Decomposers break down dead organic matter, releasing nutrients back into the soil or water, making them available for producers and supporting the entire food web.
39. What is an example of a simple food chain?
Answer: A simple food chain example: Grass (producer) → Rabbit (primary consumer) → Fox (secondary consumer).
40. What is an example of a complex food web?
Answer: A complex food web includes multiple interconnected food chains, such as a forest ecosystem with plants, herbivores (deer, rabbits), primary carnivores (wolves, hawks), and decomposers (fungi, bacteria).
41. How do detritivores differ from scavengers in a food web?
Answer: Detritivores consume dead organic matter and contribute to decomposition, while scavengers feed on the remains of dead animals, often breaking them down into smaller pieces for detritivores and decomposers.
42. What are some adaptations of producers in food webs?
Answer: Producers have adaptations like chlorophyll for photosynthesis, extensive root systems for nutrient uptake, and structures like leaves to maximize light capture.
43. How do predators affect prey populations in food webs?
Answer: Predators regulate prey populations by controlling their numbers, preventing overgrazing, and maintaining balance within the ecosystem.
44. What is the role of energy transfer in food webs?
Answer: Energy transfer in food webs involves the movement of energy from producers to various levels of consumers, highlighting the flow of energy through the ecosystem.
45. How do food webs differ between biomes?
Answer: Food webs differ between biomes based on the unique environmental conditions and species present, resulting in distinct feeding relationships and energy flow patterns.
46. What are some human impacts on food webs?
Answer: Human impacts include habitat destruction, pollution, introduction of invasive species, overfishing, and climate change, all of which can disrupt food webs and reduce biodiversity.
47. How can food web studies inform conservation efforts?
Answer: Food web studies can identify key species and interactions essential for ecosystem stability, helping to prioritize conservation efforts and restore damaged ecosystems.
48. What is a trophic cascade?
Answer: A trophic cascade is a series of changes in population sizes and interactions across multiple trophic levels, often initiated by the addition or removal of a top predator.
49. How do energy pyramids relate to food webs?
Answer: Energy pyramids represent the amount of energy available at each trophic level, illustrating the efficiency of energy transfer and the structure of food webs.
50. What is the significance of biodiversity in maintaining stable food webs?
Answer: Biodiversity ensures a variety of species and interactions, making food webs more resilient to disturbances and changes, and supporting ecosystem health and productivity.