Understanding Food Chains in Ecology

1. Ecology Part 3

2. Food chain is the sequence of organisms including producers (autotrophs), primary consumers (herbivores), secondary consumer, (carnivores eating herbivores), tertiary consumers (carnivore eating carnivores), and decomposers, through which energy and materials may move in a community. In most communities the food chain are called trophic levels.

3. These are 2 food chains for two different environments, terrestrial and marine.

4. The mouse in the food chain to the left is operating as a: A) primary consumer B) secondary consumer C) tertiary consumer D) quaternary consumer E) producer

5. ANS: B The mouse is consuming a grasshopper, which is primary consumer. Secondary consumers “eat” primary consumers.

6. The primary consumer in this food chain is A) the hawk B) the daisy C) the grasshopper D) the mouse E) Snake

7. ANS: C The grasshopper is eating plants, which makes the grasshopper a primary consumer.

8. The phytoplankton in this food chain is operating as a A) primary consumer B) secondary consumer C) tertiary consumer. D) quarternary consumer E) producer

9. ANS: E Phytoplankton (such as algae) are producers that can make their own “food” through photosynthesis

10. In most communities the food chains are completely intertwined to form a food web. The direction of the arrow indicates the movement of energy and material.

11. The successive levels of food and energy in the food chains are called trophic levels. The producers constitute the first trophic level, and the primary consumers, the second and so on. Since many species eat a varied diet, trophic levels are not hard-and-fast categories. At each trophic level there is a loss of energy from the system. Only a small percentage of the energy at one trophic level is available for the next.

12. This pyramid reflects a(n) _____________ in moving from the bottom to the top. • A) a gain in biomass • B) increase in numbers of individuals • C) loss of energy • D) decrease in the size of the organism • in light energy

13. ANS: C There is a loss energy from one trophic level to the next due to % of energy converted to unusable energy, when consumed, not all the energy (matter) is used, and if it is a stable ecosystem some of the food will not be eaten.

14. Less than 10 % of the energy can make it from level to the next. There are reasons why only 10% of the energy can move from one level to the next. 1. Lack of complete consumer harvest of available biomass. 2. The inability to assimilate all that is consumed. 3. Loss of energy due to dissipation of heat energy. 4. Energy used for growth and reproduction.

15. Which of the following is NOT a reason why some of the usable energy is not transferred from one trophic level to another? A) There is a loss in usable energy due to conversion to heat energy. B) There is less food eaten at each successive level C) The supporting trophic level is not completely consumed by the successive trophic level. D) Food consumed is not completely digested. E) A great amount of energy is used for growth and reproduction

16. ANS: B There is a loss energy from one trophic level to the next due to % of energy converted to unusable energy, when consumed, not all the energy (matter) is used, and if it is a stable ecosystem some of the food will not be eaten.

17. This is represented by the pyramid of productivity with the producers at the base and the last consumer at the top. Usually producers are engaged in photosynthesis but the term also includes chemosynthesis. In general only 10% of the energy from one level can move to a successive level. The right is showing the flow of energy.

18. The pyramid of productivity is the basis that a pyramid of biomass exists. In general the decrease of energy at each successive trophic level means that less biomass can be supported at each level. Hence the total mass of carnivores in a given community is almost always less than the total mass of herbivores. However the size, growth rate, and longevity of the species at various trophic levels are important determining factors.

19. Which of the following is not supported by the pyramid of productivity? A) Pyramid of numbers B) Pyramid of net productivity C) Pyramid of energy D) Pyramid of biomass

20. ANS: B Net productivity is the excess amount of carbon that is fixed into organic compounds after the consumers have utilized the organic compounds in the ecosystem. Net productivity can either positive meaning that more carbon is being fixed than consumed or it can be negative meaning that more carbon compounds are being consumed than fixed.

21. Because of energy loss, in general moving from the producers to the tertiary consumers, there is a decrease in biomass. However in certain aquatic ecosystems this is not the case because the reproduction of the algae occurs at a fast rate, and they are consumed at a fast rate. At any one moment, there may be a greater mass of primary consumers than producers (this is an exception!)

22. The pyramid of productivity and the pyramid of biomass support the pyramid of numbers. This is because in general, carnivores are larger than the herbivorous prey . Since total biomass tends to decline at successive trophic levels, it follows the number of individuals must decline at each level (except decomposer which outnumber all other groups combined).

23. Gross primary productivity is the rate at which producers to “fix” or convert carbon dioxide into organic material. Consumers reduce gross primary productivity by consuming the producers. Producers also reduce gross primary productivity because they also engage in cellular respiration. Net primary productivity is the rate at which organic material is produced beyond what is needed by the producers in an ecosystem. A dominant species in an ecosystem is a species present in the greatest numbers or greatest biomass. A keystone species is an important species that can exert an effect on regulating others in a community.

24. Sea otters are considered to be a keystone predator species. Sea otters prey on sea urchins. Sea urchins eat kelp. Where sea otters are plentiful, sea urchins are rare and kelp beds are plentiful. Where sea otters are population is low, sea urchins are plentiful and kelp beds are almost absent. Whales in the last 20 years have been preying on sea otters, this has increased the sea urchin population and decreased the kelp beds off the coast of western Alaska.

25. Which of the following is considered to the keystone species in this drawing? A) whales D) kelp B) otters E) cannot be determined C) sea urchins

26. ANS: B A keystone species is one that would have devasting effects if is were removed from the ecosystem. Otters are the keystone species. For example, otters feed on sea urchins and sea urchins feed on kelp. Where otters are present, sea urchins are rate and kelp beds are abundant. When otters are absent, urchins a plentiful and the kelp beds are reduced. Recently the orca whales have been preying on sea otters. This increases the sea urchins and decreases the kelp beds.

27. Foundation species are species that exert their effect by changing their environment profoundly. Ex. Beavers can profoundly change the environment by damming a creek or river. Species diversity refers to the different number of species in a given area. One should also looks at relative numbers of each species as well. This factor is called species richness. In general, the greater the species diversity of an ecosystem, the more stable the ecosystem. An ecosystem with fewer species may be more susceptible to damage from some sort of disturbance, however it may recover quickly. An ecosystem with more species may be more stable and less resistant to change from a disturbance, however it may be more difficult for the ecosystem to recover when a serious disturbance does occur.

28. While both of these ecosystems have the same number of species of trees, the first community is more stable because of the relative number of individual trees is almost equal unlike the second community where one species dominates. This first community is described as having species richness.

29. Which of the following is more susceptible to damage from some sort of ecological disturbance? A) a desert B) a temperate deciduous forest C) a coniferous forest D) a corn field E) a savannah

30. ANS: D A cornfield typically has only one species of plant. This makes the biome very vulnerable to disease compared to the other biomes

31. Which of the following is true concerning the drawing? A) Community 2 has more species diversity than community 2. B) Community 2 has more species diversity than community 1. C) Community 2 has more species richness than community 1. D) Community 1 has more species richness than community 2.

32. ANS: D Both forest have four different species of trees present but the first forest has almost equal numbers of the four different trees whereas the second drawing has mostly species A. The first drawing is considered to have more species richness than the second drawing.

33. Succession: is the process of change in which one community of organisms replaces another. This happens after some sort of change- volcano, fire, tornado, etc has disturbed the environment. As each community is established, the environment is modified and change making it possible for another community to become establish.

34. Primary succession: begins with bare rock or sand and involves the first building of soil. Once organisms colonize an area, they change it so that other organisms may follow. Examples include what happens after a volcano erupts or glacier retreats.

35. Primary succession: often the first organisms to colonize a “new” area will be lichens followed by mosses. These plants may produce acids as a waste produce that breaks down rocks leading to the formation of soil. Once soil formation is begun, ferns may come in and colonized the area. Its rhizoids helping to form more soil, and as they die and decompose, the soil may become more rich suitable for different types of organisms. It is easy to see that organisms can change the environment they interact with.

37. Another example of succession is that found in a pond. First the pond is barren but then the aquatic plants die and sediments begin to fill in and begins to be ringed by vegetation.

38. The beginnings of pond succession. It is barren with little vegetation. 2 yrs. the pond is ringed by vegetation including cotton wood saplings. 50 yrs. the pond is bordered by mature cottonwood trees. 150-200 yrs. the pond has become a meadow, the pond is ringed by vegetation.

39. Secondary succession- Soil is present and occurs at a much more rapid rate. The disturbance can be the result of fire, tornados, floods and other like events, with secondary succession being the recovery of the community after that disturbance. Examples: abandoned crop lands, unused rail roads etc.

40. Which of the following is an example of an event that would require primary succession to reestablish the biome? A) a retreating glacier D) a flood B) a forest fire E) a hurricane C) a field being plowed

41. ANS: A Primary succession involves the building of soil. Of the conditions listed above, a retreating glacier, would leave an area behind that would require the building of soil.

42. Ecological succession may lead to a stable community of plants and animals called the climax community. Catastrophic events (hurricanes, volcanoes, fires, etc.) may disturb a climax community, causing the process of succession to occur again. A biome is an environment that has a characteristic climax community. The earth has two main types of biomes, land biomes and aquatic biomes.

43. Most land (terrestrial) biomes are named for their climax community or dominant type of plant life. The major types of biomes are the tundra, taiga, temperate deciduous forest, grassland, tropical rain forest, and desert.

44. TUNDRA Where Found: northern North America, Europe, Asia Plants: mosses, lichens, grasses, a few stunted trees Animals: caribou, reindeer, wolves Other Characteristics: permafrost – creates freezing and thawing cycle

45. TAIGA (sometimes called “coniferous forest”) Where Found: most of Canada and Asia Plants: pine trees Animals: bears, wolves, moose, elk, voles, wolverines, Characteristics: long and cold winter, summers completely thaws the soil. Play coniferous forest movie

46. TEMPERATE DECIDUOUS FOREST Where Found: southern Canada, eastern U.S., Europe, and Japan Plants: trees that lose their leaves (oak, maple, birch) Animals: huge variety, including fox, deer, moose, etc. Characteristics: lands cleared by hunting and farming

47. GRASSLANDS Where Found: interior of many continents Plants: grasses and small leafy plants Animals: grazers and browsers Characteristics: Large variation in temperature and seasonal changes. Grazing and prairie fires halts succession.

48. TROPICAL RAIN FORESTS Where Found: South America, S.E. Asia, Central Africa, Central America Plants: rich vegetation in canopy and undergrowth Animals: colorful insects, lizards, amphibians, reptiles, small mammals Characteristics: 200 – 400 cm rain, constant (25o C)

49. DESERTS Where Found: northern Africa, southern Asia, central Australia Plants: cactus and other non-leafy plants Animals: lizards, small rodents Other Characteristics: very little rainfall, although some deserts have seasonal rain

50. Nutrients are recycled into the ecosystem unlike energy which passes through. The major nutrient cycles are water, carbon, nitrogen and phosphorus.