Presentation on theme: "Chapter 51 Ecosystems. n Population: all the individuals of a certain species that live in a particular area n Community: all the different species that."— Presentation transcript:
Chapter 51 Ecosystems
n Population: all the individuals of a certain species that live in a particular area n Community: all the different species that interact together within a particular area n Ecosystems consist of all the organisms that live in an area along with the nonbiological (abiotic) components.
Ecosystems n Many global environmental problems have emerged recently. n Ecosystem ecology follows the flow of energy and nutrients through ecosystems n Humans have artificially affected the flow of these components
Energy Flow within Ecosystems n Energy enters an ecosystem primarily though sunlight:
Energy Flow and Trophic Structure n Species within an ecosystems are classified into different trophic levels: Primary producers: autotrophs, photosynthetic- plants, algae, some bacteria Consumers Primary consumers: herbivores that eat producers (plants)- deer, rabbits, etc. Secondary consumers: carnivores that eat herbivores: wolf eating a deer Tertiary consumers: carnivores that eat carnivores: a hawk eating a snake that ate a mouse Decomposers: fungi, bacteria that break down organic material (dead plants and animals)
Trophic level Feeding strategy Secondary carnivore Carnivore Herbivore Autotroph Grazing food chain Decomposer food chain Cricket Maple tree leaves Owl Shrew Earthworm Dead maple leaves Coopers hawk Robin Different Trophic Levels in an Ecosystem
External energy source PRIMARY PRODUCERS CONSUMERSDECOMPOSERS ABIOTIC ENVIRONMENT Energy Flow in an ecosystem
Energy Flow and Trophic Structure n Key points about energy flow through ecosystems. Plants use only a tiny fraction of the total radiation that is available to them. Most energy fixed during photosynthesis is used for respiration, not synthesis of new tissues. Only a tiny fraction of fixed energy actually becomes available to consumers. Most net primary production that is consumed enters the decomposer food web.
Energy source: 1,254,000 kcal/m 2 /year 0.8% energy captured by photosynthesis. Of this... …45% supports growth (Net primary production) …11% enters grazing food web …34% enters decomposer food web as dead material …55% lost to respiration Ecological Efficiency: percent of energy transferred from one trophic level to the next
Ecosystem Processes n Production: rate at which energy/nutrients are converted into growth Includes Primary Production: growth by autotrophs Includes Secondary Production - growth by heterotrophs n Consumption - the intake and use of organic material by heterotrophs n Decomposition - the chemical breakdown of organic material
Energy Flow and Trophic Structure n Food chains and food webs The maximum number of links in any food chain or web ranges from 1 to 6. Hypotheses offered to explain this: Energy transfer may limit food-chain length. Long food chains may be more fragile. Food-chain length may depend on environmental complexity.
Number of observations Number of links in food chain Streams Lakes Terrestrial Food chains tend to have few links. Average number of links = 3.5
Biogeochemical Cycles n The path an element takes as it moves from abiotic systems through living organisms and back again is referred to as its biogeochemical cycle. n Examples: nitrogen cycle, carbon cycle, phosphorus cycle
Assimilation Loss to erosion or leaching into groundwater Soil nutrient pool Decomposer food web Detritus Death Herbivore Uptake Plants Feces or urine Figure 51.8
Biogeochemical Cycles n A key feature in all cycles is that nutrients are recycled and reused. n The overall rate of nutrient movement is limited most by decomposition of detritus.
Boreal forest: nutrients are put back into the soil slowly, so organic material builds up
Tropical rain forest: decomposition is rapid so there is very little organic build up Result: if living material is removed from tropical rain forests, the soil is nutrient poor to support new growth
Devegetation experiment Choose two similar watersheds. Document nutrient levels in soil organic matter, plants, and streams. The rate of nutrient loss is a very important characteristic in any ecosystem.
Clearcut Control Devegetate one watershed and leave the other intact. Monitor the amount of dissolved substances in streams.
Devegetated Net dissolved substance (kg/ha) 1965–661966–671967–681968–691969–70 Control Year Nutrient runoff results Nutrient export increases dramatically in devegetated plot
Biogeochemical Cycles n Nutrient flow among ecosystems links local cycles into one massive global biogeochemical cycle. The carbon cycle and the nitrogen cycle are examples of major, global biogeochemical cycles. Humans are now disrupting almost all biogeochemical cycles. This can have very harmful effects.
THE GLOBAL CARBON CYCLE All values in gigatons of carbon per year Physical and chemical processes: 92 2 Ocean: 40,000 Rivers: 1 Land, biota, soil, litter, peat: 2000 Decomposition: 50 Respiration: 50 Photosynthesis: 102 Physical and chemical processes: 90 Deforestation: 1.5 Fossil fuel use: 6.0 Atmosphere: 750 (in 1990) +3.5 per year Aquatic ecosystemsTerrestrial ecosystems Human–induced changes Humans are adding significant amounts of carbon into the atmosphere
Land use Fossil fuel use Year Annual flux of carbon (10 15 g) Human-induced increases in CO 2 flux over time
Year CO 2 concentration (ppm) Figure 51.12b Atmospheric CO 2
Industrial fixation Nitrogen fixing cyanobacteria Mud Decomposition of detritus into ammonia Nitrogen-fixing bacteria in roots and soil Protein and nucleic acid synthesis Atmospheric nitrogen (N 2 ) =78% Bacteria in mud use N-containing molecules as energy sources, excrete (N 2 ) Run–off Lightning and rain Only nitrogen-fixing bacteria can use N 2 make ammonia (NH 3 ) or nitrate (NO 3 ) limiting nutrient (demand exceeds supply) for plants All organisms require nitrogen to make protein Animals get nitrogen from their diets, not the air THE GLOBAL NITROGEN CYCLE
Natural sourcesHuman sources Amount of nitrogen (gigatons/year) Sources of nitrogen fixation Lightning Biological fixation Fossil fuels Nitrogen fertilizer Nitrogen- fixing crops Human activities now fix almost as much nitrogen each year as natural sources