This chapter will help you understand: Species interactions Competition Results of interspecific competition Niche: an individual s ecological role

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1 This chapter 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 Species interactions Species interactions are the backbone of communities Natural species interactions: = both species are harmed = one species benefits and the other is harmed Predation, parasitism, and herbivory = both species benefit Competition = multiple organisms seek the same limited resources Food, space, water, shelter, mates, sunlight = between members of the same species High population density = increased = between members of 2 or more species Strongly affects community composition Leads to competitive exclusion or species coexistence Results of interspecific competition = one species completely excludes another species from using the resource Zebra mussels displaced native mussels in the Great Lakes = neither species fully excludes the other from resources, so both live side by side This produces a stable point of, with stable population sizes Species minimize competition by using only a part of the available resource (niche) Niche: an individual s ecological role = the full niche of a species = the portion of the fundamental niche that is actually filled Due to competition or other species interactions Resource partitioning = species use different resources, or they use shared resources in different ways Ex: one species is active at night, another in the day Ex: one species eats small seeds, another eats large seeds Character displacement 1

2 = competing species diverge in their physical characteristics Due to the evolution of traits best suited to the resources they use Results from Birds that eat larger seeds evolve larger bills Birds that eat smaller seeds evolve smaller bills Competition is reduced when two species become more different Exploitation: predation = one member exploits another for its own gain (+/- interactions) Predation, parasitism, herbivory = process by which individuals of one species (predators) capture, kill, and consume individuals of another species (prey) Structures food webs The number of predators and prey influences community composition Zebra mussel predation on phytoplankton Zebra mussels eat phytoplankton and zooplankton Both populations decrease in lakes with zebra mussels Zebra mussels don t eat cyanobacteria Population increases in lakes with zebra mussels Zebra mussels are becoming prey for some North American predators Diving ducks, muskrats, crayfish, flounder, sturgeon, eels, carp, and freshwater drum Effects of predation on populations Increased prey populations increase predators Predators survive and reproduce Increased predator populations decrease prey Predators starve Decreased predator populations increase prey populations 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 Prey develop elaborate defenses against being eaten Exploitation: 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 are free-living Infrequent contact with their hosts Ticks, sea lampreys Some live within the host Disease, tapeworms Parasites evolve in response to each other = insects that parasitize other insects, killing the host 2

3 = hosts and parasites become locked in a duel of escalating adaptations Has been called an evolutionary arms race Each evolves new responses to the other It may not be beneficial for the parasite to kill its host Exploitation: herbivory = animals feed on the tissues of plants Widely seen in insects May not kill the plant But affects its growth and survival Defenses against herbivory include: Chemicals: toxic or distasteful Thorns, spines, or irritating hairs Other animals: protect the plant Mutualism Two or more species benefit from their interactions = mutualism in which the organisms live in close physical contact Each partner provides a service the other needs (food, protection, housing, etc.) Microbes within digestive tracts Mycorrhizae: plant roots and fungi Coral and algae (zooxanthellae) = bees, bats, birds and others transfer pollen from one flower to another, fertilizing its eggs Pollination In exchange for the plant nectar, the animals pollinate plants, which allows them to reproduce Relationships with no effect on one member = a relationship in which one organism is harmed while the other is unaffected Difficult to confirm, because usually one organism benefits from harming another = certain plants release harmful chemicals Or, is this a way to outcompete another for space? = a relationship in which one organism benefits, while the other remains unaffected Ecological communities = an assemblage of populations of organisms living in the same place at the same time Members interact with each other Interactions determine the structure, function, and species composition of the community Community ecologists are people interested in how: Species coexist and relate to one another Communities change, and why patterns exist Energy passes through trophic levels One of the most important species interactions Who eats whom? Matter and energy move through the community = rank in the feeding hierarchy 3

4 Producers (autotrophs) Consumers Detritivores and decomposers Producers: the first trophic level = ( self- feeders ) organisms capture solar energy for photosynthesis to produce sugars Green plants Cyanobacteria Algae bacteria use the geothermal energy in hot springs or deep-sea vents to produce their food Consumers: consume producers consumers = second trophic level Organisms that consume producers consume plants Deer, grasshoppers consumers = third trophic level Organisms that prey on primary consumers consume meat Wolves, rodents Consumers occur at higher trophic levels Consumers = fourth trophic level Predators at the highest trophic level Consume secondary consumers, also carnivores Hawks, owls = consumers that eat both plants and animals Detritivores and decomposers Organisms that consume nonliving organic matter Enrich soils and/or recycle nutrients found in dead organisms = scavenge waste products or dead bodies Millipedes, soil insects = break down leaf litter and other non-living material Fungi, bacteria Enhance topsoil and recycle nutrients Energy, biomass, and numbers decrease Most energy organisms use is lost as waste heat through Less and less energy is available in each successive trophic level Each level contains only % 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 A human vegetarian s ecological footprint is than a meat-eater s footprint Food webs show relationships and energy flow = a series of feeding relationships = a visual map of feeding relationships and energy flow Includes many different organisms at all various levels Greatly simplified; leaves out most species 4

5 Some organisms play big roles Community dynamics are complex Species interactions differ in strength and over time = has a strong or wide-reaching impact Far out of proportion to its abundance Removal of a keystone species has substantial ripple effects Alters the food chain Species can change communities = predators at high trophic levels indirectly affect 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 and changed forest structure Ecosystem = physically modify the environment Beaver dams, prairie dogs, ants, zebra mussels Communities respond to disturbances Communities experience many types of disturbance Removal of keystone species, spread of invasive species, natural disturbances Human impacts cause major community changes = community of organisms resists change and remains stable despite the disturbance = a community changes in response to a disturbance, but later returns to its original state A disturbed community may never return to its original state Primary succession = the predictable series of changes in a community following a disturbance = disturbance removes all vegetation and/or soil life Glaciers, drying lakes, volcanic lava = the first species to arrive in a primary succession area (i.e. lichens Secondary succession = a disturbance dramatically alters, but does not destroy, all local organisms The remaining organisms form building blocks which help shape the process of succession Fires, hurricanes, farming, logging = remains in place with few changes Until another disturbance restarts succession Communities may undergo shifts The dynamics of community change are more variable and less predictable than thought Conditions at one stage may promote another stage Competition may inhibit progression to another stage Chance factors also affect changes = the overall character of the community fundamentally changes Some crucial threshold is passed, a keystone species is lost, or an exotic species invades 5

6 i.e. overfishing and depletion of fish and turtles has allowed algae to dominate corals Community cohesion = viewed communities as cohesive entities, with integrated parts Its members remain associated over space and time The community shared similar limiting factors and evolutionary histories = maintained that each species responds independently to its own limiting factors Species join or leave communities without greatly altering the community s composition The most widely accepted view of ecologists today Invasive species threaten stability = non-native (exotic) organisms that spread widely and become dominant in a community Introduced deliberately or accidentally from elsewhere Growth-limiting factors (predators, disease, competitors, etc.) are removed or absent They have major ecological effects Chestnut blight from Asia wiped out American chestnut trees Some species help people (i.e., European honeybees) Controlling invasive species Techniques to control invasive species Removing them manually Applying toxic chemicals Drying them out Depriving them of oxygen Stressing them with heat, sound, electricity, carbon dioxide, or ultraviolet light Control and eradication are hard and expensive Prevention, rather than control, is the best policy Altered communities can be restored Humans have dramatically changed ecological systems Severely degraded systems cease to function = efforts to restore communities Restoration is informed by restoration ecology = the science of restoring an area to an earlier condition To restore the system s functionality (i.e. filtering of water by a wetland) It is difficult, time-consuming, and expensive It is best to protect natural systems from degradation in the first place Restoration efforts Prairie restoration = replanting native species, controlling invasive species The world s largest project = Flood control and irrigation removed water Populations of wading birds dropped 90-95% It will take 30 years and billions of dollars to restore natural water flow Widely separated regions share similarities = major regional complex of similar communities recognized by Plant type Vegetation structure Multiple factors determine a biome The type of biome depends on abiotic factors Temperature, precipitation, soil type, atmospheric circulation 6

7 = a climate diagram showing An area s mean monthly temperature and precipitation Similar biomes occupy similar latitudes Aquatic systems have biome-like patterns 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, and dissolved nutrients Wave action, currents, depth, light levels Substrate type, and animal and plant life Temperate deciduous forest trees lose their leaves each fall They remain dormant during winter Mid-latitude forests in Europe, East China, Eastern North America Even, year-round precipitation Fertile soils Forests = oak, beech, maple Temperate grasslands More extreme temperature difference between winter and summer Less precipitation Also called steppe or prairie Once widespread, but has been converted to agriculture Bison, prairie dogs, ground-nesting birds, pronghorn Temperate rainforest Coastal Pacific Northwest Great deal of precipitation Coniferous trees: cedar, spruce, hemlock, fir Moisture-loving animals Banana slug Erosion and landslides affect the fertile soil Lumber and paper Most old-growth is gone Tropical rainforest Southeast Asia, west Africa Central and South America Year-round rain and warm temperatures Dark and damp with lush vegetation Diverse species But in low densities Very poor, acidic soils Tropical dry forest Also called tropical 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 7

8 Savanna Grassland interspersed with trees Africa, South America, Australia, India Precipitation is only during the Animals gather near water holes Zebras, gazelles, giraffes, lions, hyenas Desert Minimal precipitation Some are bare, with sand dunes (Sahara) Some are heavily vegetated (Sonoran) They are not always hot Temperatures vary widely Saline soils Animals = nocturnal, nomadic Plants = thick skins, spines Tundra Russia, Canada, Scandinavia Minimal precipitation Extremely cold winters = permanently frozen soil Melting due to climate change Few animals: polar bears, musk oxen, caribou, migratory birds Lichens, low vegetation, few trees 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 Moose, wolves, bears, lynx, migratory birds Chaparral Occurs in small patches around the globe Mediterranean Sea, Chile, California, south Australia High seasonal biome Mild, wet winters Warm, dry summers Frequent Densely thicketed, evergreen shrubs Altitudes create latitudinal patterns Vegetative communities rapidly change along mountain slopes The climate varies with altitude A mountain climber in the Andes begins in the tropics and ends on a glacier = air going over a mountain releases moisture, creating an arid region on the other side Hiking up a mountain in the southwest U.S. is like walking from Mexico to Canada Conclusions Biomes and communities help us understand how the world functions Species interactions affect communities Predation, parasitism, competition, mutualism 8

9 Causing weak and strong, direct and indirect effects Feeding relationships are represented by trophic levels and food webs Humans have altered many communities Ecological restoration attempts to undo the negative changes that we have caused 9