Ecosystem Dynamics

Characteristics of Ecosystems: 1) abiotic and biotic factors 2) Energy Flow: Sun  Producers (autotrophs)  Consumers (heterotrophs)  Decomposers - eventually all the assimilated energy is dissipated as heat (Second Law of Thermodynamics – proceed toward entropy or disorder) – energy cannot be recycled

3) Chemical Cycling between abiotic and biotic components – recycling of matter on the molecular level - chemical cycling also follows the trophic level path, but instead of ending with the decomposers, the decomposers complete the cycle and return the chemicals back to the producers

Figure 54.2 Tertiary consumers Microorganisms and other detritivores Detritus Primary producers Primary consumers Secondary consumers Tertiary consumers Heat Sun Key Chemical cycling Energy flow

Ecosystems, Energy, and Matter Ecosystems obey physical laws The law of conservation of energy states that energy cannot be created or destroyed but only transformed. Plants and other photosynthetic organisms convert solar energy to chemical energy, but the total amount of energy does not change. The total amount of energy stored in organic molecules plus the amounts reflected and dissipated as heat must equal the total solar energy intercepted by the plant. The second law of thermodynamics states that some energy is lost as heat in any conversion process. -as the energy flows through the ecosystem, more and more of the captured solar energy is lost as heat, therefore the resulting biomass of the upper trophic levels is less and less as well

Primary Production in Ecosystems Primary Production: amount of light energy converted into chemical energy IMPORTANCE: the amount of energy fixed by primary production is the only energy that is available for the upper trophic levels – if primary production declines, all upper trophic levels will suffer and diminish - of the visible light that reaches photosynthetic organisms, less than 1% is converted to chemical energy which results in the production of 170 billion tons of organic material per year.

Examining Primary Production: GROSS PRIMARY PRODUCTION (GPP) Total primary production in an ecosystem is known as gross primary production (GPP). This is the amount of light energy that is converted into chemical energy per unit time. NET PRIMARY PRODUCTION (NPP) However, not all of this energy is of use to the upper trophic levels since plants use some of these molecules as fuel in their own cellular respiration (R) - the remaining energy is known as the Net primary production (NPP) NPP = GPP – R

MEASUREING PRIMARY PRODUCTION: Biomass added per unit of time – how much plant material grows over a certain period – NOT: How much is there, but how it has changed Total Biomass = Standing Crop (amount of producers at any time) Although a forest has a large standing cross biomass, its primary production may actually be less than that of some grasslands, which do not accumulate vegetation because animals consume the plants rapidly.

Different ecosystems differ greatly in their production as well as in their contribution to the total production of the Earth. Tropical rain forests are among the most productive terrestrial ecosystems. Estuaries and coral reefs also are very productive, but they cover only a small area compared to that covered by tropical rain forests. The open ocean has a relatively low production per unit area but contributes more net primary production than any other single ecosystem because of its very large size. Overall, terrestrial ecosystems contribute two-thirds of global net primary production, and marine ecosystems contribute approximately one-third.

Figure 54.4a–c Lake and stream Open ocean Continental shelf Estuary Algal beds and reefs Upwelling zones Extreme desert, rock, sand, ice Desert and semidesert scrub Tropical rain forest Savanna Cultivated land Boreal forest (taiga) Temperate grassland Tundra Tropical seasonal forest Temperate deciduous forest Temperate evergreen forest Swamp and marsh Woodland and shrubland 10 20 30 40 50 60 500 1,000 1,500 2,000 2,500 5 15 25 Percentage of Earth’s net primary production Key Marine Freshwater (on continents) Terrestrial 5.2 0.3 0.1 4.7 3.5 3.3 2.9 2.7 2.4 1.8 1.7 1.6 1.5 1.3 1.0 0.4 125 360 3.0 90 2,200 900 600 800 700 140 1,600 1,200 1,300 250 5.6 1.2 0.9 0.04 22 7.9 9.1 9.6 5.4 0.6 7.1 4.9 3.8 2.3 65.0 24.4 Figure 54.4a–c

Figure 54.5 180 120W 60W 0 60E 120E North Pole 60N 30N Equator 30S 60S South Pole

FACTORS LIMITING PRIMARY PRODUCTION: Aquatic ecosystems: light and nutrients Light is limited to the photic zone More than light, nutrients limit primary production in aquatic ecosystems. A limiting nutrient is an element that must be added for production to increase in a particular area.

Marine Systems: N and P - low in photic zone, high in aphotic zone - upwellings bring nutrients to the surface and support growth of phytoplankton

Figure 54.6 (a) Phytoplankton biomass and phosphorus concentration (b) Phytoplankton response to nutrient enrichment Great South Bay Moriches Bay Shinnecock Starting algal density 2 4 5 11 30 15 19 21 24 18 12 6 Unenriched control Ammonium enriched Phosphate enriched Station number (millions of cells per mL) Phytoplankton 8 7 3 1 Inorganic phosphorus (g atoms/L) (millions of cells/mL) CONCLUSION Since adding phosphorus, which was already in rich supply, had no effect on Nannochloris growth, whereas adding nitrogen increased algal density dramatically, researchers concluded that nitrogen was the nutrient limiting phytoplankton growth in this ecosystem. Inorganic phosphorus RESULTS Phytoplankton abundance parallels the abundance of phosphorus in the water (a). Nitrogen, however, is immediately taken up by algae, and no free nitrogen is measured in the coastal waters. The addition of ammonium (NH4) caused heavy phytoplankton growth in bay water, but the addition of phosphate (PO43) did not induce algal growth (b).

Role of Iron: usually low because not near land The iron factor in marine ecosystems is related to the nitrogen factor. When iron is limiting, adding iron stimulates the growth of cyanobacteria that fix nitrogen which stimulates phytoplankton growth

Fresh Water Lakes: N and P Sewage and fertilizer pollution can add nutrients to lakes. Additional nutrients shifted many lakes from phytoplankton communities dominated by diatoms and green algae to communities dominated by cyanobacteria. – Known as ALGAL BLOOMS This process is called eutrophication: - excess primary production leads to higher day time oxygen production, but also for higher oxygen consumption during the night when the producers and decomposers are respiring – can lead to FISH KILLS

Terrestrial ecosystems: temperature and moisture - MOST PRODUCTIVE: Tropical rain forests - warm, wet and most direct sun - Least Productive: dry (deserts) or dry and cold (arctic tundra). Rate of Productivity is reflected in the actual evapotranspiration, which is the amount of water annually transpired by plants and evaporated from a landscape. Actual evapotranspiration increases with precipitation and with the amount of solar energy available to drive evaporation and transpiration. Other Terrestrial Factors: - Mineral nutrients in soil – most common limiter is N and P

Secondary Production in Ecosystems Secondary Production: the amount of food converted to biomass by a consumer The efficiency of energy transfer between trophic levels is usually less than 20% AVERAGE = 10% production efficiency = net secondary production / assimilation of primary production Net secondary production is the energy stored in biomass represented by growth and reproduction. Assimilation consists of the total energy taken in and used for growth, reproduction, and respiration.

Figure 54.11 Tertiary consumers Secondary Primary producers 1,000,000 J of sunlight 10 J 100 J 1,000 J 10,000 J

Production efficiency is thus the fraction of food energy that is not used for respiration. This differs among organisms. Birds and mammals: 1% and 3% (endotherms) Fishes: 10%. Insects: 40%. Salamanders: up to 80% efficient.

Trophic efficiency is the percentage of production transferred from one trophic level to the next. Trophic efficiencies must always be less than production efficiencies - energy lost to respiration, undigested food - energy used for growth, maintenance and reproduction Trophic efficiencies usually range from 5% to 20%. In other words, 80–95% of the energy available at one trophic level is not transferred to the next.

This loss is multiplied over the length of a food chain and is seen in a PYRAMID OF NET PRODUCTION – Pg 1192 If 10% of energy is transferred from primary producers to primary consumers, and 10% of that energy is transferred to secondary consumers, then only 1% of net primary production is available to secondary consumers. Reflected in the BIOMASS PYRAMID - pg 1193 - Result  Small biomass of top-level carnivores which tend to be larger than the prey they eat

Most biomass pyramids Show a sharp decrease at successively higher trophic levels Figure 54.12a (a) Most biomass pyramids show a sharp decrease in biomass at successively higher trophic levels, as illustrated by data from a bog at Silver Springs, Florida. Trophic level Dry weight (g/m2) Primary producers Tertiary consumers Secondary consumers Primary consumers 1.5 11 37 809

Certain aquatic ecosystems Have inverted biomass pyramids Figire 54.12b Trophic level Primary producers (phytoplankton) Primary consumers (zooplankton) (b) In some aquatic ecosystems, such as the English Channel, a small standing crop of primary producers (phytoplankton) supports a larger standing crop of primary consumers (zooplankton). Dry weight (g/m2) 21 4

In a pyramid of numbers, the size of each block is proportional to the number of individuals present in each trophic level. The dynamics of energy through ecosystems have important implications for the human population. Eating meat is an inefficient way of tapping photosynthetic production. Worldwide agriculture could feed many more people if humans all fed as primary consumers, eating only plant material. Be Green by Eating Greens – let the cows run free

Number of individual organisms Pyramids of Numbers A pyramid of numbers Represents the number of individual organisms in each trophic level Figure 54.13 Trophic level Number of individual organisms Primary producers Tertiary consumers Secondary consumers Primary consumers 3 354,904 708,624 5,842,424

Trophic level Secondary consumers Primary producers

The Cycling of Chemical Elements in Ecosystems  Biogeochemical Cycles KEY PLAYERS  Decomposers – complete cycle Types of Biogeochemical Cycles: Global – atmosphere and ocean Regional – stuff found in the soil NUTRIENT RESEVOIRS: PAGE 1195

Productivity Calculations Biomass Dissolved Oxygen Fixed Carbon Dioxide