Chapter 4. Species Interactions and Community Ecology. Lecture Presentations prepared by Reggie Cobb Nash Community College

Transcription

1 Chapter 4 Species Interactions and Community Ecology Lecture Presentations prepared by Reggie Cobb Nash Community College

2 This lecture will help you understand: Species interactions Feeding relationships, energy flow, trophic levels, and food webs Keystone species The process of succession Potential impacts of invasive species Restoration ecology Terrestrial biomes

3 Central Case Study: Black and White and Spread All Over In 1988, ballast water discharged from a ship accidentally released zebra mussels into Lake St. Clair By 2010, they had spread to 30 states No natural predators, competitors, or parasites They cause millions of dollars of property damage each year

4 Species interactions Species interactions are the backbone of communities Effects of species interactions on the participants:

5 Competition occurs with limited resources Competition Multiple organisms seek the same limited resource Food, water, space, shelter, mates, sunlight, etc. Intraspecific competition Competition between members of the same species High population density: increased competition Interspecific competition Competition between members of different species Strongly affects community composition Leads to competitive exclusion or species coexistence

6 Results of interspecific competition Competition is usually subtle and indirect One species may exclude another from using the resource Zebra mussels displaced native mussels in the Great Lakes Quagga mussels are now displacing zebra mussels Or, competing species may be able to coexist Natural selection favors individuals that use different resources or shared resources in different ways

7 Resource partitioning Resource partitioning Competing species coexist by specializing They use different resources (small vs. large seeds) Or share resources (one species may be active during the day and the other at night)

8 An exploitative interaction: predation Exploitation One member benefits while the other is harmed (+/ interactions) Examples: predation, parasitism, herbivory Predation Process by which individuals of one species (predators) capture, kill, and consume individuals of another species (prey)

9 Predation affects the community Interactions between predators and prey structure food webs The number of predators and prey influences community composition Predators can, themselves, become prey Zebra mussels eat smaller types of zooplankton Zebra mussels are prey for North American predators (fish, ducks, muskrats, crayfish)

10 Predation can drive population dynamics Increased prey populations increase food for predators Predators survive and reproduce Increased predator populations decrease prey Predators starve and their populations decrease Decreased predator populations increase prey populations

11 Predation has evolutionary ramifications Natural selection leads to evolution of adaptations that make predators better hunters Individuals who are better at catching prey Live longer, healthier lives Take better care of offspring Prey face strong selection pressures They are at risk of immediate death They develop elaborate defenses against being eaten

12 Prey develop defenses against being eaten

13 Parasites exploit living hosts Parasitism A relationship in which one organism (parasite) depends on another (host) for nourishment or some other benefit The parasite harms, but doesn t kill, the host Some live within the host Tapeworms Some contact hosts infrequently Cuckoos and cowbirds Some live on exterior of host Fleas, ticks, and sea lampreys

14 Parasites exploit living hosts (cont d) Parasitoids Insects that parasitize other insects and kill the host Example: parasitic wasp Wasp larvae burrow into, and kill, caterpillars Pathogens Parasites that cause disease in hosts Protists, bacteria, and viruses Coevolution Hosts and parasites become locked in a duel of escalating adaptations (evolutionary arms race) Each evolves new responses to the other

15 Herbivores exploit plants Herbivory Animals feed on tissues of plants Widely seen in insects It may not kill the plant but affects its growth and reproduction Defenses against herbivory include Chemicals: toxic or distasteful Thorns, spines, or irritating hairs Herbivores may overcome these defenses

16 Mutualists help one another Two or more species benefit from their interactions Each partner provides a service the other needs (food, protection, housing, etc.) Symbiosis A relationship in which the organisms live in close physical contact (mutualism and parasitism) Microbes within digestive tracts Mycorrhizae: plant roots and fungi Coral and algae (zooxanthellae) Pollination Bees, bats, birds, and others transfer pollen from one flower to another, fertilizing its eggs

17 Ecological communities Community An assemblage of populations of organisms living in the same area at the same time interacting with each other Interactions determine the structure, function, and species composition of the community Community ecologists are interested in how: Species coexist and interact with one another Communities change, and why these patterns exist

18 Energy passes among trophic levels Some of the most important community interactions involves who eats whom Matter and energy move through the community Trophic levels Producers (autotrophs) Consumers Detritivores and decomposers

19 Producers: the first trophic level Producers, or autotrophs ( self-feeders ) Organisms that capture solar energy for photosynthesis to produce sugars Green plants Cyanobacteria Algae

20 Consumers: consume producers Primary consumers (second trophic level) Organisms that consume producers Herbivores: deer, grasshoppers Secondary consumers (third trophic level) Organisms that prey on primary consumers wolves, rodents, birds Tertiary consumers (fourth trophic level) Predators: hawks, owls

21 Detritivores and decomposers Organisms that consume nonliving organic matter Detritivores Scavenge waste products or dead bodies Millipedes, soil insects Decomposers Break down leaf litter and other nonliving material Fungi, bacteria Enhance topsoil and recycle nutrients

22 Energy, numbers, and biomass decrease at higher trophic levels Most energy that organisms use in cellular respiration is lost as waste heat Less and less energy is available in each successive trophic level Each trophic level contains only 10% of the energy of the trophic level below it There are also far fewer organisms and less biomass (mass of living matter) at the higher trophic levels

23 Data Question: Trophic Level Pyramid Using the ratios shown in this example, let s suppose that a system has 3000 grasshoppers. How many rodents would you expect?

24 Weighing the Issues The Footprints of Our Diets What proportion of your diet would you estimate consists of meat, milk, eggs, or other animal products? Would you choose to decrease this proportion in order to reduce your ecological footprint? Describe other ways in which you could reduce your footprint through your food choices.

25 Food webs show feeding relationships and energy flow Food chain A series of feeding relationships Food web A visual map of feeding relationships and energy flow among organisms They are greatly simplified and leave out most species

26 Some organisms play outsized roles in communities Keystone species Has a strong or wide-reaching impact far out of proportion to its abundance Removing a keystone species has substantial ripple effects Alters the food web

27 Species can change communities Trophic cascade Predators at high trophic levels indirectly promote populations at low trophic levels by keeping species at intermediate trophic levels in check Extermination of wolves led to increased deer populations Which overgrazed vegetation Which changed forest structure Ecosystem engineers Physically modify the environment Beaver dams, prairie dogs, ants

28 The Science Behind the Story Determining Zebra Mussels Impacts on Fish Communities Strayer, Hattala, and Kahnle Reviewed data sets on fish populations in Hudson River before and after the 1991 invasion of zebra mussels Hypothesized that zebra mussels would harm open-water fish that ate phytoplankton but would help littoral-feeding fish Data supported their findings

29 The Science Behind the Story (cont d) Determining Zebra Mussels Impacts on Fish Communities (cont d) The fish responded in different ways to zebra mussels Open-water fish populations shifted downstream Away from zebra mussels Littoral-feeding fish populations shifted upstream Toward zebra mussels

30 The Science Behind the Story (cont d) Determining Zebra Mussels Impacts on Fish Communities (cont d) Several populations are beginning to rebound after drastic decreases following the arrival of zebra mussels Native mussels Clams Crustaceans Flatworms Zooplankton

31 Communities respond to disturbance in various ways Disturbance An event that has rapid/dramatic impacts on environmental conditions Removal of keystone species, natural disturbances (fires, floods, etc.) Human impacts cause major community changes Resistance A community resists change and remains stable despite the disturbance Resilience A community changes in response to a disturbance, but later returns to its original state

32 Succession follows severe disturbance Succession The predictable series of changes in a community after a severe disturbance Primary succession Disturbance removes all vegetation and/or soil life Glaciers, drying lakes, volcanic lava covering the land Pioneer species The first species to arrive in a primary succession area Lichens: fungi + algae

33 Succession follows severe disturbance (cont d) Secondary succession A disturbance has removed much, but not all, of the biotic community Fires, hurricanes, logging, farming Aquatic systems can also undergo succession Ponds eventually fill in to become terrestrial systems Climax community Remains in place with few changes until another disturbance restarts succession

34 Communities may undergo shifts Community changes are more variable and less predictable than early models of succession suggested Conditions at one stage may promote another stage Competition may inhibit progression to another stage Chance factors also affect changes Phase (regime) shift: the overall character of the community fundamentally changes Some crucial threshold is passed, a keystone species is lost, or an exotic species invades Example: overfishing and depletion of fish and turtles has allowed algae to dominate coral reef communities

35 Frequently Asked Question Once we disturb a community, won t it return to its original state if we just leave the area alone?

36 Invasive species pose threats to community stability Introduced species A species introduced by to community by people Invasive species Non-native species that spreads widely and becomes dominant in a community Introduced deliberately or accidentally Growth-limiting factors (predators, disease, competitors, etc.) are absent Major ecological effects Pigs, goats, and rats have destroyed island species Some invasive species (e.g., honeybees) help people

37 Data Question: Invasive Mussels Modify Communities What differences do you see between the distribution of quagga mussels and the distribution of zebra mussels? Suggest two hypotheses for one of these differences

38 We can respond to invasive species with control, eradication, or prevention Eradication Total elimination of a population Often difficult to accomplish Control Limit growth, spread, and impact of a population Examples of zebra mussel management Removing them manually Applying toxic chemicals Drying them out, depriving them of oxygen Introducing predators or diseases Stressing them with heat, sound, electricity, carbon dioxide, or ultraviolet light

39 We can respond to invasive species with control, eradication, or prevention (cont d) Control and eradication are difficult and expensive Prevention, rather than control, is the best policy Predicting where a species might spread is important Analyzing the biology of the organism allows scientists to model the environmental conditions they might thrive in. Example: In 2007, researchers applied knowledge of how zebra and quagga mussels use calcium from water to create their shells They mapped high and low-risk and high-risk regions across North America.

40 Altered communities can be restored Humans have dramatically changed ecological systems Severely degraded systems cease to function Restoration ecology The science of restoring an area to an earlier (pre-settlement) condition Tries to restore the system s functionality (Example: filtering of water by a wetland) Ecological restoration The on-the-ground efforts to restore an area Difficult, time-consuming, and expensive It is best to protect natural systems from degradation in the first place

41 Examples of restoration efforts Prairie restoration Replanting native species, controlling invasive species, using controlled fire to mimic natural fires The world s largest project: Florida Everglades Flood control and irrigation removed its water Populations of wading birds dropped 90 95% It will take 30 years and billions of dollars to restore natural water flow

42 Earth s biomes Biome Major regional complex of similar communities recognized by plant type and vegetation structure

43 Climate helps determine biomes The type of biome depends on: Temperature, precipitation, soil conditions, air and ocean circulation Climate diagrams (climatographs) Depict information on temperature and precipitation

44 Aquatic and coastal systems resemble biomes Various aquatic systems comprise distinct communities Coastlines, continental shelves, open ocean, deep sea, coral reefs, kelp forests Some coastal systems (estuaries, marshes, etc.) have both aquatic and terrestrial components Aquatic systems are shaped by: Water temperature, salinity, dissolved nutrients, wave action, currents, depth, light levels, substrate type Animals, not plants, delineate marine communities

45 Temperate deciduous forest Deciduous trees lose their broad leaves each fall They remain dormant during winter Midlatitude forests in Europe, east China, eastern North America Even, year-round precipitation Fertile soils Forests: oak, beech, maple

46 Temperate grasslands More temperature difference between winter and summer Less precipitation supports grasses, not trees Also called steppe or prairie Once widespread, but has been converted to agriculture Animals Bison, prairie dogs, ground- nesting birds, pronghorn

47 Data Question: Temperate Grasslands How would you explain the dry conditions July to September? Given the temperature and precipitation patterns shown, what role do you think evaporation might play, and why?

48 Temperate rainforest U.S. coastal Pacific Northwest Heavy rainfall Coniferous trees Cedar, spruce, hemlock, fir Moisture-loving animals Banana slug Erosion and landslides affect the fertile soil Most old-growth is gone as a result of logging

49 Tropical rainforest Southeast Asia, west Africa, Central and South America Year-round rain and warm temperatures Dark and damp Lush vegetation Diverse species But in low densities Very poor, acidic soils Nutrients are in the plants

50 Tropical dry forest Also called tropical deciduous forest Plants drop leaves during the dry season India, Africa, South America, north Australia Wet and dry seasons Warm, but less rainfall Converted to agriculture Severe soil erosion

51 Savanna Tropical grassland interspersed with trees Africa, South America, Australia, India Precipitation occurs only during the rainy season Animals gather near water holes Zebras, gazelles, giraffes, lions, hyenas

52 Desert Minimal precipitation Sahara: bare, sand dunes Sonoran: heavily vegetated Temperatures vary widely Day vs. night, seasonally Soils (lithosols) High mineral content, low organic matter Animals Nocturnal, nomadic Plants Thick skins, spines

53 Tundra Russia, Canada, Scandinavia Minimal rain, very cold winters Permafrost Permanently frozen soil Residents Polar bears, musk oxen, migratory birds, caribou Lichens, low vegetation, no trees Alpine tundra On mountaintops

54 Boreal forest (taiga) Canada, Alaska, Russia, Scandinavia A few evergreen tree species Cool and dry climate Long, cold winters Short, cool summers Nutrient-poor, acidic soil Animals Moose, wolves, bears, lynx, migratory birds

55 Chaparral Occurs in small patches around the globe Mediterranean Sea, Chile, California, south Australia Densely thicketed, evergreen shrubs Highly seasonal biome Mild, wet winters Warm, dry summers Fire-resistant plants

56 Conclusion Biome classification is informative at the broadest geographic scale Species interactions affect communities Competition, predation, parasitism, herbivory, mutualism Cause weak and strong, direct and indirect effects Feeding relationships are represented by trophic levels and food webs Humans have altered many communities Partly by introducing non-native species Ecological restoration attempts to undo the changes we have caused