CHAPTER 49 ECOSYSTEMS

Transcription

1 CHAPTER 49 ECOSYSTEMS I. INTRODUCTION A. An ecosystem 1. Whereas a community consists of all the organisms in a certain boundary that are close enough for some sort of interaction, an ecosystem: -is defined as all the biotic and abiotic factors in the community. 2. Boundaries of ecosystems are not well defined and an ecosystem could be your goldfish bowl at home to an aquarium, terrarium, grassland, Arctic tundra, or tropical rainforest B. An ecosystem involves two processes not seen at other levels: 1. Energy flow a) Energy enters in the form of light b) is converted to an organic chemical form by autotrophic organisms c) these chemical forms (food) are passed along to heterotrophs and in the process of digestion some of this energy is lost as heat. d) Energy cannot be recycled. 2. Chemical or Nutrient Cycling a) Carbon cycle b) Nitrogen cycle c) Phosphorus cycle d) Water cycle e) These cycles all involve the original form of various elements and follow them as they change form as they become part of (assimilated by ) various organisms and then returned to the planet II. TROPHIC STRUCTURE DETERMINES AN ECOSYSTEM/S ROUTES OF ENERGY FLOW AND CHEMICAL CYCLING A. Introduction 1. Trophic Structure a. a web of feeding relationships and within this web are the ways in which energy and nutrients are passed between organisms. 2. Trophic Level a) consists of species of organisms based on how they obtain their nutrition; that is do they make it themselves, eat plants, eat animals, etc. b) Primary Producer: autotrophs -most are photosynthetic

2 c) all other organism depend on the autotrophs to some degree d) Primary Consumer e) Secondary Consumers f) Decomposers 3. Food Chains and Food Webs B. Producers 1. Plants are the main producers in terrestrial ecosystems C. Consumers 1. Herbivores-primary consumers a) On land: insects, small vertebrates as well as grazing mammals, like cows, goats, birds. b) A primary consumer simply eats plants, not animals 2. Secondary Consumers

3 D. Decomposers III. AN ECOSYSTEM'S ENERGY BUDGET DEPENDS ON PRIMARY PRODUCTIVITY A. Introduction 1. So the light is used to make organic molecules like sugars through photosynthesis 2. And these organic molecules, like the sugars, can then be metabolized for energy or converted into other needed substances or to make ATP 3. So... the more photosynthesis that occurs the greater potential for a nice large energy budget... kind of like having lots of money to spend on things. In this case, the energy is is used to support other organisms B. The Global Energy Budget

4 C. Primary Productivity 1. Definition: the conversion of light energy to chemical energy over a a small period of time and there are several kinds 2. Gross Primary Productivity a) Some of the energy stored as sugars is used to live, you know, to respire and keep you warm. b) GPP represents all the stored light energy even that portion that eventually gets used to live. 3. Net Primary Productivity a) this is the mathematical difference between GPP and the amount of this energy used to make ATP and to survive 4. NPP tells us how much energy is available to consumers 5. Biomass 6. Different ecosystems differ in their NPP 7. Factors that limit productivity a) In terrestrial ecosystems

5 b) In Seas c) In Freshwater Ecosystems IV. AS ENERGY FLOWS THROUGH AN ECOSYSTEM, MUCH IS LOST AT EACH TROPHIC LEVEL. A. Secondary Productivity 1. Definition: so this relates to how much of the biomass (energy) the primary consumers consumed is really converted into their own biomass. B. Ecological Efficiency and Ecological Pyramids 1. Ecological Efficiency

6 2. Biomass Pyramid a) Each level represents the total dry weight of all organisms at that level. b) Biomass pyramids usually narrow or get smaller as you go to the top. c) So the carnivores are very inefficient at converting energy from the level below it. Lots of energy is lost. V. MATTER CYCLES WITHIN AND BETWEEN ECOSYSTEMS A. We Have Finite Amounts of Chemical Elements 1. Therefore, these elements must be recycled 2. If they are converted into a form that is hard to extract them from, this makes life harder. 3. The movement of these chemicals or nutrients involves both biotic (living) and abiotic (nonliving) components. a) Biogeochemical cycles B. Route of a Particular Chemical 1. Depends on the particular element and the trophic structure 2. Two General Categories of Biogeochemical Cycles a) Global -Gaseous forms of S, O, C, N and thus can move throughout the atmosphere b) Localized or Regional -less mobile elements such as P, K, Ca, and trace elements since these may be tied in soils and rocks as minerals. C. General Model of Nutrient Cycling (cont'd on next page)

7 VI. A COMBINATION OF BIOLOGICAL AND GEOLOGICAL PROCESSES DRIVES CHEMICAL CYCLES A. The Water Cycle 1. Since water makes up so much of each cell's volume and is a medium for transport and serves as an environment for many organisms,... it is essential 2. It helps to move nutrients between ecosystems and within ecosystems 3. It serves to move nutrients within and between biogeochemical cycles 4. The Cycle a) Water evaporates -more evaporates from oceans than precipitates into oceans b) Evaporated water moves over land regions, cools and precipitates -more water precipitates over land than evaporates c) Runoff water and ground water return water back to ocean and lake sinks d) These are all physical processes; no chemical change in the water molecule itself B. The Carbon Cycle

8 C. Nitrogen Cycle 1. Role of Nitrogen : amino acids and proteins 2. Availability of N 3. How does N enter ecosystems? D. Phosphorus Cycle 1. P is needed in ATP, nucleic acids, phospholipids ( these make up your cell membranes), bones. 2. No movement in the atmosphere, only through minerals and plants, animals 3. Main form of concern is phosphate, PO P Cycle a) removed or weathered from rocks and will travel then to nearby soil or a waterway b) Producers will take up this phosphate, and store in nucleic acids, ATP, membranes.

9 c) Producers are eaten by consumers so now the consumers gain the phosphates. d) Phosphates get excreted, decomposers pick them up. e) some phosphate is help in the soil and can then re-enter water ways. 5. P is thought to be Limiting Nutrient a) aquatic habitats and algal growth b) phosphates can also enter waterways through fertilizer runoff and stimulate algal growth. E. Variations In Nutrient Cycling Time 1. Tropical Rain Forests 2. Temperate Forests 3. Aquatic Ecosystems VII. FIELD EXPERIMENTS REVEAL HOW VEGETATION REGULATES CHEMICAL CYCLING A. In A Forest Ecosystem-Natural 1. Determined the mineral requirements for several valleys by measuring mineral input and mineral output. a) this way they could see how much was retained and thus needed by the forest. b) Measured rainfall and dissolved minerals input c) Measured water loss of mineral loss at water outflow areas (creeks) 2. Results: in a mature ecosystem, most minerals are conserved

10 B. Forest Ecosystem-Logged 1. Prepared land by logging it and spraying with pesticides to prevent regrowth 2. Inflow of water and minerals was compared to outflow a) Water runoff increased after deforestation b) Mineral losses were huge C. Conclusions from study VIII. THE HUMAN POPULATION IS DISRUPTING CHEMICAL CYCLES THROUGHOUT THE BIOSPHERE A. Introduction 1. Our actions have disrupted trophic levels, energy flow, and the chemical cycling in most of the world. a) Sometimes these effects are local and other times global -acid rain (precipitation) -CFC's and ozone depletion -SF Bay Pollution 2. We can add or remove nutrients thus disrupting their cycles. a) Whether we remove / deplete a nutrient in one area or dump / add a nutrient in another area we are still disrupting the equilibrium that once allowed us to use the area to our advantage -nutrients from crop lands appear in lakes and streams. So we deplete the soil and add the excess to the water system 3. Humans have affected so many cycles that whenever we study ecosystems we must take into account human influence a) Many of the affects have involved the addition of toxic substances B. Agricultural Effects on Nutrient Cycling (cont'd on next page)

11 C. Accelerated Eutrophication of Lakes 1. Oligotrophic lake: a "young" lake where productivity is low, since there aren't a lot of minerals around to encourage the the growth of algae. 2. Eutrophic Lake: a "well nourished" lake with a lot of primary productivity 3. Cultural Eutrophication: our actions have increased the speed at which lakes age by the addition of sewage, factory discharges, animal wastes, fertilizers. a) This increases the growth of algae or the primary producers to such an extent that algal blooms occur -Clear Lake D. Poisons in Food Chains (cont'd on next page)

12 E. Intrusions In The Atmosphere F. Carbon Dioxide Emissions and the Greenhouse Effect

13 G. Depletion of Atmospheric Ozone 1. Ozone protects us from UV radiation by absorbing the radiation and converting the O3 into O + O2 -this occurs about 30,000 feet up 2. Ozone is being destroyed by its reaction with chlorofluorocarbons, CFCs. The O3 reacts with the Cl in the CFC and breaks it away from the CFC. The Cl that is free floating is now able to react with other O3 and break down other O3 molecules. a) This one Cl atom can react bunches of times. b) CFCs were once thought to be good for refrigeration, propellants and are very unreactive at sea level. But not when they rise into the stratosphere. 3. Results of O3 Depletion -skin cancer -cataracts -possibly destroy primary productivity by the algae -crops may be harmed -some sheep are reported as having increased #s of cataracts IX. HUMAN ACTIVITIES ARE ALTERING SPECIES DISTRIBUTION AND REDUCING BIODIVERSITY A. Introduction Of Exotic Species

14 B. Habitat Destruction and the Biodiversity Crisis 1. Clear-cutting of timber a) US has only 15 % of the original primary forest. -is that a bad thing though?? -maybe we are replanting sufficiently 2. Tropical Rain Forest Destruction a) these are one of the most productive ecosystems and they are seriously in danger. 3. War and Chemical Defoliants a) destroyed vegetation b) Oil spills in marine ecosystems 4. Overall the concern is the loss of organisms or biodiversity a) The preservation of some species is especially difficult if the are migratory. Now we need to be concerned about at least two locations for their survival. Possibly a feeding ground and a breeding ground. b) Monarch Butterfly -migrates from Canada to Mexico -milkweed, which is required by the Monarch is considered a pest in Canada and is eradicated. In the US, herbicides and pesticides are affecting the monarch 5. We should care because: X. THE SUSTAINABLE BIOSPHERE INITIATIVE IS REORIENTING ECOLOGICAL RESEARCH