CHAPTER 36 Communities and Ecosystems

1. CHAPTER 36Communities and Ecosystems

2. Dining In • Waspsand Pieris caterpillars form an unusual three-step food chain • The 4-mm-long wasp Apanteles glomeratus stabs through the skin of a Pieris rapae caterpillar and lays her eggs • The caterpillar will be destroyed from within as the wasp larvae hatch and nourish themselves on its internal organs

3. A female ichneumon will pierce the caterpillar and deposit her own eggs inside of the Apanteles larvae • Ichneumon wasps can detect when a Pieris caterpillar contains Apanteles larvae

4. Usually, only the chalcids will emerge from the dead husk of the caterpillar • Finally, yet another wasp, a chalcid, may lay its eggs inside the ichneumon larvae

5. A biological community derives its structure from the interactions and interdependence of the organisms living within it • Ecosystem functioning depends on the complex interactions between its community of organisms and the physical environment

6. 36.1 A community is all the organisms inhabiting a particular area • All the organisms in a particular area make up a community • A number of factors characterize every community • Biodiversity • The prevalent form of vegetation • Response to disturbances • Trophic structure (feeding relationships) Figure 36.1

7. Biodiversity has two components • Species richness, or the total number of different species in the community • The relative abundance of different species • Biodiversity is the variety of different kinds of organisms that make up a community

8. STRUCTURAL FEATURES OF COMMUNITIES 36.2 Competition may occur when a shared resource is limited • Interspecific competition occurs between two populations if they both require the same limited resource • A population's niche is its role in the community • The sum total of its use of the biotic and abiotic resources of its habitat

9. Populations of two species cannot coexist in a community if their niches are nearly identical • The competitive exclusion principle Hightide Chthamalus Balanus Ocean Lowtide Figure 36.2

10. One of the populations, using resources more efficiently and having a reproductive advantage, will eventually eliminate the other • Natural selection may lead to resource partitioning • Competition between species with identical niches has two possible outcomes

11. 36.3 Predation leads to diverse adaptations in both predator and prey • Predation is an interaction where one species eats another • The consumer is called the predator and the food species is known as the prey • Parasitism can be considered a form of predation

12. This process of reciprocal adaptation is known as coevolution • Example: Heliconius and the passionflower vine • As predators adapt to prey, sometimes natural selection also shapes the prey's defenses Eggs Sugardeposits Figure 36.3A

13. Mechanical defenses, such as the quills of a porcupine • Prey gain protection against predators through a variety of defense mechanisms

14. Animals with effective chemical defenses are often brightly colored to warn predators • Example: the poison-arrow frog • Chemical defenses are widespread and very effective Figure 36.3B

15. Example: the gray tree frog • Camouflage is a very common defense in the animal kingdom Figure 36.3C

16. Batesian mimicry occurs when a palatable or harmless species mimics an unpalatable or harmful one • The mimicry can even involve behavior • This hawkmoth larva puffs up its head to mimic the head of a snake Figure 36.3D

17. Müllerian mimicry is when two unpalatable species that inhabit the same community mimic each other • Example: the cuckoo bee and the yellow jacket Figure 36.3E

18. 36.4 Predation can maintain diversity in a community • A keystone species exerts strong control on community structure because of its ecological role • A keystone predator may maintain community diversity by reducing the numbers of the strongest competitors in a community • This sea star is a keystone predator Figure 36.4A

19. Predation by killer whales on sea otters, allowing sea urchins to overgraze on kelp • Sea otters represent the keystone species Figure 36.4B

20. 36.5 Symbiotic relationships help structure communities • A symbiotic relationship is an interaction between two or more species that live together in direct contact • There are three main types of symbiotic relationships within communities • Parasitism • Commensalism • Mutualism

21. The parasite benefits and the host is harmed in this symbiotic relationship • A parasite obtains food at the expense of its host • Parasites are typically smaller than their hosts • Parasitism is a kind of predator-prey relationship

22. The rabbits destroyed huge expanses of Australia • They threatened the sheep and cattle industries • In 1950, a parasite that infects rabbits (myxoma virus) was deliberately introduced to control the rabbit population • In the 1940s, Australia was overrun by hundreds of millions of European rabbits Figure 36.5A

23. Commensalism is a symbiotic relationship where one partner benefits and the other is unaffected • Examples of commensalism • Algae that grow on the shells of sea turtles • Barnacles that attach to whales • Birds that feed on insects flushed out of the grass by grazing cattle

24. Mutualism is a symbiotic relationship where both partners benefit • Examples of mutualism • Nitrogen-fixing bacteria and legumes • Acacia trees and the ants of the genus Pseudomyrmex Figure 36.5B

25. 36.6 Disturbance is a prominent feature of most communities • Disturbances include events such as storms, fires, floods, droughts, overgrazing, and human activities • They damage biological communities • They remove organisms from communities • They alter the availability of resources Figure 36.6

26. Ecological succession is a transition in the species composition of a community following a disturbance • Primary succession is the gradual colonization of barren rocks by living organisms • Secondary succession occurs after a disturbance has removed the vegetation but left the soil intact

27. 36.7 Talking About Science: Ecologist Frank Gilliam discusses the role of fire in ecosystems • Ecologist Frank Gilliam is especially interested in the role that fire plays in shaping ecosystems • According to Dr. Gilliam, fire is a key abiotic factor in many ecosystems • Grasslands are so dependent on fire that its absence is considered a disturbance Figure 36.7A

28. Following a fire in southeastern pine forest, the numbers and variety of nonwoody plants usually increase dramatically • Fire makes more nutrients available to these plants Figure 36.7B

29. ECOSYSTEM STRUCTURE AND DYNAMICS 36.8 Energy flow and chemical cycling are the two fundamental processes in ecosystems • A community interacts with abiotic factors, forming an ecosystem • Energy flows from the sun, through plants, animals, and decomposers, and is lost as heat • Chemicals are recycled between air, water, soil, and organisms

30. A terrarium ecosystem Chemical cycling(C, N, etc.) Chemicalenergy Heatenergy Lightenergy Figure 36.8

31. 36.9 Trophic structure is a key factor in ecosystem dynamics • A food chain is the stepwise flow of energy and nutrients • from plants (producers) • to herbivores (primary consumers) • to carnivores (secondary and higher-level consumers)

32. TROPHIC LEVEL Quaternaryconsumers Carnivore Carnivore Tertiaryconsumers Carnivore Carnivore Secondaryconsumers Carnivore Carnivore Primaryconsumers Herbivore Zooplankton Producers Plant Phytoplankton Figure 36.9A A TERRESTRIAL FOOD CHAIN AN AQUATIC FOOD CHAIN

33. Decomposition is essential for the continuation of life on Earth • Detritivores decompose waste matter and recycle nutrients • Examples: animal scavengers, fungi, and prokaryotes • Decomposition is the breakdown of organic compounds into inorganic compounds Figure 36.9B

34. 36.10 Food chains interconnect, forming food webs • A food web is a network of interconnecting food chains • It is a more realistic view of the trophic structure of an ecosystem than a food chain

35. Wastes anddead organisms Tertiaryandsecondaryconsumers Secondaryandprimaryconsumers Primaryconsumers Producers Detritivores (Plants, algae,phytoplankton) (Prokaryotes, fungi,certain animals) Figure 36.10

36. 36.11 Energy supply limits the length of food chains • Biomass is the amount of living organic material in an ecosystem • Primary production is the rate at which producers convert sunlight to chemical energy • The primary production of the entire biosphere is about 170 billion tons of biomass per year

37. A pyramid of production reveals the flow of energy from producers to primary consumers and to higher trophic levels Tertiaryconsumers 10 kcal Secondaryconsumers 100 kcal Primaryconsumers 1,000kcal Producers 10,000 kcal 1,000,000 kcal of sunlight Figure 36.11

38. Only about 10% of the energy in food is stored at each trophic level and available to the next level • This stepwise energy loss limits most food chains to 3 - 5 levels • There is simply not enough energy at the very top of an ecological pyramid to support another trophic level

39. 36.12 Connection: A production pyramid explains why meat is a luxury for humans • The dynamics of energy flow apply to the human population as much as to other organisms • When we eat grain or fruit, we are primary consumers • When we eat beef or other meat from herbivores, we are secondary consumers • When we eat fish like trout or salmon (which eat insects and other small animals), we are tertiary or quaternary consumers

40. Because the production pyramid tapers so sharply, a field of corn or other plant crops can support many more vegetarians than meat-eaters TROPHIC LEVEL Secondaryconsumers Humanmeat-eaters Cattle Primaryconsumers Humanvegetarians Corn Corn Producers Figure 36.12

41. 36.13 Chemicals are recycled between organic matter and abiotic reservoirs • Ecosystems require daily infusions of energy • The sun supplies the Earth with energy • But there are no extraterrestrial sources of water or other chemical nutrients • Nutrients must be recycled between organisms and abiotic reservoirs • Abiotic reservoirs are parts of the ecosystem where a chemical accumulates

42. Water cycle • Carbon cycle • Nitrogen cycle • Phosphorus cycle • There are four main abiotic reservoirs

43. 35.14 Water moves through the biosphere in a global cycle • Heat from the sun drives the global water cycle • Precipitation • Evaporation • Transpiration

44. Solar heat Net movementof water vaporby wind (36) Water vaporover the land Water vaporover the sea Evaporationandtranspiration(59) Precipitationover the land(95) Precipitationover the sea(283) Evaporationfrom the sea(319) Oceans Surface waterand groundwater Flow of waterfrom land to sea(36) Figure 36.14

45. 36.15 The carbon cycle depends on photosynthesis and respiration • Carbon is taken from the atmosphere by photosynthesis • It is used to make organic molecules • It is returned to the atmosphere by cellular respiration

46. CO2 in atmosphere Burning Cellular respiration Plants,algae,cyanobacteria Photosynthesis Higher-levelconsumers Primaryconsumers Wood andfossil fuels Decomposition Detritivores(soil microbesand others) Detritus Figure 36.15

47. 36.16 The nitrogen cycle relies heavily on bacteria • Nitrogen is plentiful in the atmosphere as N2 • But plants cannot use N2 • Various bacteria in soil (and legume root nodules) convert N2 to nitrogen compounds that plants can use • Ammonium (NH4+) and nitrate (NO3–)

48. Some bacteria break down organic matter and recycle nitrogen as ammonium or nitrate to plants • Other bacteria return N2 to the atmosphere

49. Nitrogen (N2) in atmosphere Amino acidsand proteins inplants and animals Assimilationby plants Nitrogenfixation Denitrifyingbacteria Detritus Nitrogen-fixingbacteria in rootnodules of legumes Nitrates(NO3–) Detritivores Nitrogen-fixingbacteria in soil Decomposition Nitrifyingbacteria Nitrogenfixation Ammonium (NH4+) Figure 36.16

50. 36.17 The phosphorus cycle depends on the weathering of rock • Phosphates (compounds containing PO43-) and other minerals are added to the soil by the gradual weathering of rock • Consumers obtain phosphorus in organic form from plants • Phosphates are returned to the soil through excretion by animals and the actions of decomposers