Chapter 41 Community Ecology (Sections 41.6 - 41.9)

1. Chapter 41Community Ecology(Sections 41.6 - 41.9)

2. 41.6 Parasites, Brood Parasites, and Parasitoids • Some plants and animals benefit by withdrawing nutrients from other species • Some species trick others into providing parental care

3. Parasitism • With parasitism, one species (the parasite) feeds on another (the host), without immediately killing it • Endoparasites live and feed inside their host • Ectoparasites feed while attached to a host’s external surface • parasitism • Relationship in which one species withdraws nutrients from another species, without immediately killing it

4. Endoparasites: Intestinal Roundworms

5. Ectoparasites: Ticks

6. Parasites (cont.) • Parasites include a diverse variety of groups: • Bacterial, fungal, protistan, and invertebrate parasites feed on vertebrates • Lampreys attach to and feed on other fish • Some plants parasitize other plants • Many parasites are pathogens that cause disease in hosts

7. Dodder (Devils Hair): A Parasitic Plant

8. Coevolution in Parasites and Hosts • Parasites are adapted with traits that allow the parasite to locate hosts and to feed undetected • Ticks move toward heat and carbon dioxide • Hosts adapt with traits that minimize the negative effects of parasites • Sickle-cell allele protects against malaria

9. Strangers in the Nest • Presence of brood parasites,such as North American cowbirds, decreases the reproductive rate of the host species and favors host individuals that detect and eject foreign young • Brood parasitism also evolved in some bee species • brood parasitism • One egg-laying species benefits by having another raise its offspring

10. Cowbird and Foster Parent

11. Parasitoids • Parasitoids reduce a host population in two ways: • Parasitoid larvae withdraw nutrients and prevent the host from reproducing • Presence of larvae leads to death of the host • As many as 15% of all insects may be parasitoids • parasitoid • An insect that lays eggs in another insect, and whose young devour their host from the inside

12. Biological Controls • Parasites and parasitoids are commercially raised and released in target areas as biological control agents – an environmentally friendly alternative to pesticides • A biological control agent must be adapted to a specific host species, and survive in that species’ habitat • Introducing a biological control species into a community is risky – they sometimes go after nontargeted species

13. Parasitoid Wasp Deposits an Egg in an Aphid

14. Key Concepts • Forms of Species Interactions • Commensalism, mutualism, competition, predation, and parasitism are interspecific interactions • They influence the population size of participating species, which in turn influences the community’s structure

15. ANIMATION: Succession To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

16. 41.7 Ecological Succession • Species often alter the habitat in ways that allow other species to replace them (ecological succession) • The first, opportunistic colonizers of new or newly vacated habitats are pioneer species, which have high dispersal rates, grow and mature fast, and produce many offspring • pioneer species • Species that can colonize a new habitat • Mosses, lichens, some flowering annuals

17. Primary Succession • Primary succession begins when pioneer species colonize a barren habitat with no soil, such as a new volcanic island or land exposed by the retreat of a glacier • Pioneers help build and improve the soil • primary succession • A new community becomes established in an area where there was previously no soil

18. Primary Succession

19. Ecological Succession • Seeds of later species grow in mats of pioneers • Organic wastes and remains accumulate and help other species take hold • Later successional species often shade and eventually displace earlier ones

20. Ecological Succession

21. Secondary Succession • In secondary succession, a disturbed area within a community recovers. • Occurs in abandoned agricultural fields and burned forests • secondary succession • A new community develops in a site where the soil that supported an old community remains

22. Factors That Influence Succession • Species composition of a community changes frequently, and unpredictably – random events can determine the order in which species arrive , and affect the course of succession • Example: 1980 eruption of Mount Saint Helens • Presence of some pioneers helped later-arriving plants become established • Other pioneers kept the same late arrivals out

23. Mount St. Helens: 1980

24. Mount St. Helens: 1990

25. Mount St. Helens: 2002

26. Intermediate Disturbance Hypothesis • intermediate disturbance hypothesis • Species richness is greatest in communities where disturbances are moderate in intensity or frequency

27. Factors in Community Composition • Three factors affect species composition of communities: • Physical factors such as soil and climate • Chance events such as the order in which species arrive • The extent of disturbances in the habitat

28. Key Concepts • Long-Term Change in Communities • The array of species in a community changes over time, although the exact outcome of these changes is difficult to predict • When a new community forms, the early-arriving species often alter the habitat in a way that facilitates their own replacement

29. 41.8 Species Interactions and Community Instability • Loss or addition of even one species (keystone species) may destabilize the number and abundances of species in a community • keystone species • A species that has a disproportionately large effect on community structure

30. A Keystone Species: Sea Stars • Experiment: Sea stars in a rocky intertidal zone in California • Sea stars prey mainly on mussels • Sea stars were removed from experimental plots • With sea stars gone, mussels took over, crowding out seven other species of invertebrates • Conclusion: Sea stars a re a keystone species • They normally keep number of prey species high by preventing competitive exclusion by mussels

31. A Keystone Species: Periwinkles • The impact of a keystone species can vary between habitats that differ in their species arrays • Example: Periwinkle snails • In tidepools, periwinkles eat the most competitive algal species, allowing less competitive species to survive • In the lower intertidal zone, periwinkles eat the less competitive algae, giving dominant algae an advantage

32. Effects of Algal Predation by Periwinkle Snails • Algal diversity in tidepools • Algal diversity in intertidal zone

33. Adapting to Disturbance • Some species adapted to being disturbed are at a competitive disadvantage if the disturbance does not occur • Example: Areas subject to periodic fires • Some plants produce seeds that germinate only after a fire, or resprout quickly after a fire • Because different species respond differently to fire, the frequency of fire affects competitive interactions

34. Adapting to Fire • Toyon resprouts from roots after a fire • In the absence of occasional fire, toyons are outcompeted by other species

35. Indicator Species • Indicator species are the first to do poorly when conditions change, so they can provide an early warning of environmental degradation • Example: Trout are highly sensitive to pollutants and cannot tolerate low oxygen levels • indicator species • Species that is especially sensitive to disturbance and can be monitored to assess the health of a habitat

36. Species Introductions • Exotic species can dramatically alter a natural community • More than 4,500 exotic species have become established in the United States • Visit the National Invasive Species Information Center at www.invasivespeciesinfo.gov • exotic species • A species that evolved in one community and later became established in a different one

37. Exotic Species • Kudzu native to Asia is overgrowing trees across the southeastern United States

38. Exotic Species • Gypsy moths native to Europe and Asia feed on oaks through much of the United States

39. Exotic Species • Nutrias native to South America are abundant in freshwater marshes of the Gulf States

40. Key Concepts • Species Effects on Community Stability • Removing a species from a community or adding one to it can have a dramatic effect on other species • Some species are adapted to disturbances and a change in the frequency of disturbances can affect their number

41. BBC Video: The Devastation of Exotic Species in Hawaii

42. ABC Video: Circle of Life (Ecotourism)

43. 41.9 Biogeographic Patterns in Community Structure • Biogeography is the study of how species are distributed in the natural world • Species richness correlates with differences in sunlight, temperature, rainfall, and other factors that vary with latitude, elevation, or water depth • species richness • Of an area, the number of species

44. Latitudinal Patterns • Species richness is usually greatest in the tropics and declines from the equator to the poles • Tropical latitudes intercept more sunlight, receive more rainfall, and their growing season is longer • Tropical communities have been evolving for a long time • Species richness may be self-reinforcing; more plant species leads to more herbivores, which leads to more predators, and parasites

45. Species Richness by Latitude (Ants)

46. Island Patterns • According to the equilibrium model of island biogeography, the number of species living on any island reflects a balance between immigration rates for new species and extinction rates for established ones • Colonization rates depend on the distance between an island and a mainland source of colonists (distance effect) • An island’s size affects it species richness (area effect)

47. Key Terms • equilibrium model of island biogeography • Predicts the number of species on an island based on the island’s area and distance from the mainland • area effect • Affects immigration and extinction rates; larger islands have more species than small ones • distance effect • Affects immigration rates; islands close to a mainland have more species than those farther away

48. Island Colonization: Surtsey • 1960s: Island formation • 1983

49. Island Colonization: Surtsey • Number of vascular plant species found in yearly surveys

50. Island Biodiversity Patterns