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Transcript
CHAPTER 3 Communities and Ecosystems Dining In • 1) Wasps and Pieris caterpillars form an unusual three-step food chain – a) The 4-mm-long wasp Apanteles glomeratus stabs through the skin of a Pieris rapae caterpillar and lays her eggs Dining In • 1. The caterpillar will be destroyed from within as the wasp larvae hatch and nourish themselves on its internal organs – b) Ichneumon wasps can detect when a Pieris caterpillar contains Apanteles larvae • 1. A female ichneumon will pierce the caterpillar and deposit her own eggs inside of the Apanteles larvae Dining In Dining In – c) Finally, yet another wasp, a chalcid, may lay its eggs inside the ichneumon larvae • 1. Usually, only the chalcids will emerge from the dead husk of the caterpillar Dining In • 2) A biological community derives its structure from the interactions and interdependence of the organisms living within it – a) Ecosystem functioning depends on the complex interactions between its community of organisms and the physical environment The Community • 1) All the organisms in a particular area make up a community – a) A number of factors characterize every community • 1. Biodiversity • 2. The prevalent form of vegetation • 3. Response to disturbances • 4. Trophic structure (feeding relationships) The Community • 2) Biodiversity is the variety of different kinds of organisms that make up a community – a) Biodiversity has two components • 1. Species richness, or the total number of different species in the community • 2. The relative abundance of different species Competition Within Communities • 1) Interspecific competition occurs between two populations if they both require the same limited resource – a) A population's niche is its role in the community • 1. The sum total of its use of the biotic and abiotic resources of its habitat • 2) The competitive exclusion principle – a) Populations of two species cannot coexist in a community if their niches are nearly identical High tide Chthamalus Balanus Ocean Low tide Competition Within Communities • 3) Competition between species with identical niches has two possible outcomes – a) One of the populations, using resources more efficiently and having a reproductive advantage, will eventually eliminate the other – b) Natural selection may lead to resource partitioning Predation • 1) Predation is an interaction where one species eats another – a) The consumer is called the predator and the food species is known as the prey – b) Parasitism can be considered a form of predation • 2) As predators adapt to prey, sometimes natural selection also shapes the prey's defenses – a) This process of reciprocal adaptation is known as coevolution Eggs Sugar deposits Predation • 1. Example: Heliconius and the passionflower vine – b) Prey gain protection against predators through a variety of defense mechanisms • 1. Mechanical defenses, such as the quills of a porcupine Predation • 3) Chemical defenses are widespread and very effective – a) Animals with effective chemical defenses are often brightly colored to warn predators • 1. Example: the poison-arrow frog • 4) Camouflage is a very common defense in the animal kingdom – a) Example: the gray tree frog • 5) Batesian mimicry occurs when a palatable or harmless species mimics an unpalatable or harmful one – a) The mimicry can even involve behavior • 1. This hawkmoth larva puffs up its head to mimic the head of a snake • 6) Müllerian mimicry is when two unpalatable species that inhabit the same community mimic each other – a) Example: the cuckoo bee and the yellow jacket Diversity in a Community • 1) A keystone species exerts strong control on community structure because of its ecological role • 2) A keystone predator may maintain community diversity by reducing the numbers of the strongest competitors in a community – a) This sea star is a keystone predator – b) Predation by killer whales on sea otters, allowing sea urchins to overgraze on kelp • 1. Sea otters represent the keystone species Symbiotic Relationships • 1) A symbiotic relationship is an interaction between two or more species that live together in direct contact – a) There are three main types of symbiotic relationships within communities • 1. Parasitism • 2. Commensalism • 3. Mutualism Symbiotic Relationships – b) Parasitism is a kind of predator-prey relationship • 1. The parasite benefits and the host is harmed in this symbiotic relationship • 2. A parasite obtains food at the expense of its host • 3. Parasites are typically smaller than their hosts 2) In the 1940s, Australia was overrun by hundreds of millions of European rabbits – a) The rabbits destroyed huge expanses of Australia – b) They threatened the sheep and cattle industries • a) In 1950, a parasite that infects rabbits (myxoma virus) was deliberately introduced to control the rabbit population Symbiotic Relationships • 3) Commensalism is a symbiotic relationship where one partner benefits and the other is unaffected – a) Examples of commensalism • 1. Algae that grow on the shells of sea turtles • 2. Barnacles that attach to whales • 3. Birds that feed on insects flushed out of the grass by grazing cattle – b) Mutualism is a symbiotic relationship where both partners benefit • 1. Examples of mutualism –a. Nitrogen-fixing bacteria and legumes –b. Acacia trees and the ants of the genus Disturbance • 1) Disturbances include events such as storms, fires, floods, droughts, overgrazing, and human activities – a) They damage biological communities – b) They remove organisms from communities – c) They alter the availability of resources Disturbance • 2) Ecological succession is a transition in the species composition of a community following a disturbance – a) Primary succession is the gradual colonization of barren rocks by living organisms – b) Secondary succession occurs after a disturbance has removed the vegetation but left the soil intact Talking About Science • 1) Ecologist Frank Gilliam is especially interested in the role that fire plays in shaping ecosystems – a) According to Dr. Gilliam, fire is a key abiotic factor in many ecosystems – b) Grasslands are so dependent on fire that its absence is considered a disturbance • 2) Following a fire in southeastern pine forest, the numbers and variety of nonwoody plants usually increase dramatically – a) Fire makes more nutrients available to these plants Energy Flow and Chemical Cycling • 1) A community interacts with abiotic factors, forming an ecosystem – a) Energy flows from the sun, through plants, animals, and decomposers, and is lost as heat – b) Chemicals are recycled between air, water, soil, and organisms A terrarium ecosystem Chemical cycling (C, N, etc.) Light energy Chemical energy Heat energy Trophic Structure • 1) A food chain is the stepwise flow of energy and nutrients – a) from plants (producers) – b) to herbivores (primary consumers) – c) to carnivores (secondary and higherlevel consumers) TROPHIC LEVEL Quaternary consumers Carnivore Carnivore Tertiary consumers Carnivore Carnivore Secondary consumers Carnivore Carnivore Primary consumers Herbivore Zooplankton Producers Plant Phytoplankton A TERRESTRIAL FOOD CHAIN AN AQUATIC FOOD CHAIN 2) Decomposition is the breakdown of organic compounds into inorganic compounds – a) Decomposition is essential for the continuation of life on Earth – b) Detritivores decompose waste matter and recycle nutrients • 1. Examples: animal scavengers, fungi, and prokaryotes Food Chains • 1) A food web is a network of interconnecting food chains – a) It is a more realistic view of the trophic structure of an ecosystem than a food chain Wastes and dead organisms Tertiary and secondary consumers Secondary and primary consumers Primary consumers Producers (Plants, algae, phytoplankton) Detritivores Energy Supply • 1) Biomass is the amount of living organic material in an ecosystem – a) Primary production is the rate at which producers convert sunlight to chemical energy • 1. The primary production of the entire biosphere is about 170 billion tons of biomass per year 2) A pyramid of production reveals the flow of energy from producers to primary consumers and to higher trophic levels Tertiary consumers 10 kcal Secondary consumers 100 kcal Primary consumers 1,000 kcal Producers 10,000 kcal 1,000,000 kcal of sunlight Energy Supply • 3) Only about 10% of the energy in food is stored at each trophic level and available to the next level – a) This stepwise energy loss limits most food chains to 3 - 5 levels • 1. There is simply not enough energy at the very top of an ecological pyramid to support another trophic level Production Pyramid • 1) The dynamics of energy flow apply to the human population as much as to other organisms – a) When we eat grain or fruit, we are primary consumers – b) When we eat beef or other meat from herbivores, we are secondary consumers – c) When we eat fish like trout or salmon (which eat insects and other small animals), we are tertiary or quaternary consumers • 2) 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 Secondary consumers Primary consumers Human meat-eaters Human vegetarians Cattle Corn Corn Producers Figure 36.12 Chemicals are Recycled • 1) Ecosystems require daily infusions of energy – a) The sun supplies the Earth with energy • 1. But there are no extraterrestrial sources of water or other chemical nutrients – b) Nutrients must be recycled between organisms and abiotic reservoirs • 1. Abiotic reservoirs are parts of the ecosystem where a chemical accumulates Chemicals are Recycled • 2) There are four main abiotic reservoirs – a) Water cycle – b) Carbon cycle – c) Nitrogen cycle – d) Phosphorus cycle Water • 1) Heat from the sun drives the global water cycle – a) Precipitation – b) Evaporation – c) Transpiration Solar heat Water vapor over the sea Precipitation over the sea (283) Net movement of water vapor by wind (36) Evaporation from the sea (319) Water vapor over the land Evaporation and transpiration (59) Precipitation over the land (95) Oceans Flow of water from land to sea (36) Surface water and groundwater The Carbon Cycle • 1) Carbon is taken from the atmosphere by photosynthesis – a) It is used to make organic molecules – b) It is returned to the atmosphere by cellular respiration CO2 in atmosphere Burning Cellular respiration Plants, algae, cyanobacteria Photosynthesis Higher-level consumers Primary consumers Wood and fossil fuels Decomposition Detritivores (soil microbes and others) Detritus The Nitrogen Cycle • 1) Nitrogen is plentiful in the atmosphere as N2 – a) But plants cannot use N2 • 1. Various bacteria in soil (and legume root nodules) convert N2 to nitrogen compounds that plants can use –a. Ammonium (NH4+) and nitrate (NO3–) The Nitrogen Cycle – b) Some bacteria break down organic matter and recycle nitrogen as ammonium or nitrate to plants • 1. Other bacteria return N2 to the atmosphere Nitrogen (N2) in atmosphere Assimilation by plants Denitrifying bacteria Amino acids and proteins in plants and animals Nitrogen fixation Detritus Nitrogen-fixing bacteria in root nodules of legumes Nitrates (NO3–) Detritivores Nitrifying bacteria Decomposition Nitrogen fixation Ammonium (NH4+) Nitrogen-fixing bacteria in soil The Phosphorus Cycle • 1) Phosphates (compounds containing PO43-) and other minerals are added to the soil by the gradual weathering of rock – a) Consumers obtain phosphorus in organic form from plants • 1. Phosphates are returned to the soil through excretion by animals and the actions of decomposers Uplifting of rock Phosphates in organic compounds Weathering of rock Phosphates in rock Animals Plants Runoff Detritus Phosphates in solution Phosphates in soil (inorganic) Decomposition Rock Precipitated (solid) phosphates Detritivores in soil Ecosystem Alteration • 1) Experimental studies have been performed to determine chemical cycling in ecosystems – a) A study to monitor nutrient dynamics has been ongoing in the Hubbard Brook Experimental Forest since 1963 – b) Dams were built across streams at the bottom of each watershed to monitor water and nutrient losses 2) In 1966, one of the valleys was completely logged – a) It was then sprayed with herbicides for 3 years to prevent plant regrowth – b) All the original plant material was left in place to decompose • 3) Researchers found that the total removal of vegetation can increase the runoff of water and loss of soil nutrients Ecosystem Alteration • 4) Environmental changes caused by humans can unbalance nutrient cycling over the long term – a) Example: acid rain David Schindler • 1) Eutrophication is a process in which nutrient runoff from agricultural lands or livestock operations causes photosynthetic organisms in ponds and lakes to multiply rapidly – a) The result is algal bloom • 2) Algal bloom can cause a pond or lake to lose much of its species diversity – a) Human-caused eutrophication wiped out fisheries in Lake Erie in the 1950s and 1960s • 3) Dr. David Schindler is an ecologist who worked at the Experimental Lakes Project in northern Ontario – a) He performed several classic experiments on eutrophication that led to the ban on phosphates in detergents David Schindler • 4) According to Dr. Schindler, there are three serious threats to freshwater ecosystems – a) Acid precipitation – b) Climate warming – c) Changes in land use Zoned Reserves • 1) The human alteration of ecosystems threatens the existence of thousands of species – a) To slow the disruption of ecosystems, some nations are establishing zoned reserves • 1. These are undisturbed wildlands surrounded by buffer zones of compatible economic development Zoned Reserves – b) Costa Rica has established eight zone reserves • 1. Costa Rica looks to its zoned reserve system to maintain at least 80% of its native species 2) On this map, the reserves are shown in green and the buffer zones in yellow NICARAGUA COSTA RICA Guanacaste Caribbean Sea Llanuras de Tortuguero La Amistad Arenal Bajo Tempisque Cordillera Volcanica Central Pacifico Central Peninsula de Osa Pacific Ocean