Ecosystem Ecology

Define what ecosystem ecology includes that community ecology does not.

Communities plus abiotic environment (nutrients and energy) Ecosystem ecology focuses on the movement of energy, nutrients, and matter among the various community members within the ecosystem and the environment.

Explain why energy transfer is inefficient within communities (trophic efficiency), and identify the consequences for biomass at each trophic level. Know what approximate proportion of the energy at each trophic level is transferred to the next level up. Use these ideas to explain why food chains are generally short (<6 links). Explain how this trophic inefficiency is relevant to human diet choices.

Only a fraction of production (biomass/energy) is transferred from one trophic level to the next. Average: 10%. Trophic efficiencies have important implications for the human population. Our agriculture system could feed many more people if we ate more plants and less meat. In particular, plant-based diets tend to be much more energy efficient than livestock-based diets. This is mainly because livestock animals must be fed lots of plants.

Describe the major processes in the water cycle: what moves water up, what moves it down, and how it moves from ocean to land and back again. (This is partly in the reading.)

Over the oceans: Evaporation > precipitation.Over land: Evaporation < precipitation.Result:Clouds move water from ocean to land.

Define transpiration and explain how plants contribute to rainfall.

Plants draw up water from the soil and release it through their leaves. Transpiration is responsible for a lot of the rain that falls on land.Cutting down trees causes droughts.The Amazon rainforest is close to its tipping point.

Describe the process by which nutrients are made available to primary producers.

autotrophs use light energy to synthesize sugars & other organic compounds, which they then use as fuel for cellular respiration and as building material for growth Primary producers convert minerals/organic mass into a usable form for the primary consumers . Ex. Nitrogen fixation, photosynthesis

List the overall pathways and processes in the cycling of nitrogen. What is the major reservoir of nitrogen? How does it get into primary producers and from there to consumers and decomposers? Don't memorize the details (ammonification, nitrification, etc.) but be able to briefly describe the role that bacteria and legumes play. (This is in the reading.) Describe how human activities have influenced nitrogen cycles, and how this has affected ecosystems (e.g., dead zones).

Major reservoir of nitrogen is atmospheric N2 N enters biological pathways primarily through nitrogen fixation which, in nature, is mostly accomplished by microbes. They convert N2 into organic compounds that can be used by plants and animals. Many human activities have a significant impact on the nitrogen cycle. Burning fossil fuels, application of nitrogen-based fertilizers, and other activities can dramatically increase the amount of biologically available nitrogen in an ecosystem. Excess nitrogen can cause overstimulation of growth of aquatic plants and algae. Excessive growth of these organisms, in turn, can clog water intakes, use up dissolved oxygen as they decompose, and block light to deeper waters. Nitrogenous runoff adds TONS of nitrogen to the Gulf of Mexico and other coastal areas. - Influx of nutrients increases algae populations (algal blooms). - Respiration by bacteria depletes oxygen.Result: Dead zone, particularly on shallow sea floors. - Shrimp die. Fish leave or die.

Define net primary production (NPP) and explain why it is an important measurement.

Net Primary Production (NPP):All the biomass/energy that primary producers make, minus what they use themselves for cellular respiration. Net primary production in terrestrial systems controlled by: (1) rate of photosynthesis increases with light availability (2) temperature also affects rate of photosynthesis (but alsoaffects respiration). (3) water: when soil moisture approaches a plant's wilting point, stomata close to reduce water loss; rate of photosynthesis slows. (4) Nutrient limitation commonly occurs. critical for understanding the energy balance in plants and in whole ecosystems

Given a world map or a description of ecosystems, be able to predict which large areas have higher or lower net primary production and explain why.

Net primary production (NPP) of terrestrial ecosystems:Highest in warm, wet areas because that promotes plant growth.

Describe the experiment at the Hubbard Brook Experimental Forest: what was measured, what experimental treatment was performed, what the consequences were for water and nitrogen runoff, and what was concluded about the role of plants in nutrient and water retention. (This is in the reading.)

Since 1963, ecologist Gene Likens and colleagues have been studying nutrient cycling at the Hubbard Brook Experimental Forest in the White Mountains of New Hampshire. They collected rainfall at several sites to measure the amount of water and dissolved minerals added to the ecosystem. They found that about 60% of the water added to the ecosystem as rainfall and snow exits through the stream, and the remaining 40% is lost by evapotranspiration. Experimental deforestation of a watershed dramatically increased the flow of water and minerals leaving the watershed (Figure 55.15b). Over three years, water runoff from the newly deforested watershed was 30-40% greater than in a control watershed, apparently because there were no plants to absorb and transpire water from the soil. Most remarkable was the loss of nitrate, whose concentration in the creek increased 60-fold, reaching levels considered unsafe for drinking water. The Hubbard Brook deforestation study showed that the amount of nutrients leaving an intact forest ecosystem is controlled mainly by the plants.

Explain where phosphorus comes from naturally. (This is in the reading).

The largest accumulations of phosphorus are in sedimentary rock of marine origin

Explain why nutrients cycle within ecosystems but energy flows through them. Trace the cycling of matter and flow of energy through ecosystems.

The nutrient cycle is a system where energy and matter are transferred between living organisms and non-living parts of the environment. This occurs as animals and plants consume nutrients found in the soil, and these nutrients are then released back into the environment via death and decomposition. At the base of the pyramid are the producers, who use photosynthesis or chemosynthesis to make their own food using energy from the sun. At each step up the food chain, only 10 percent of the energy is passed on to the next level, while approximately 90 percent of the energy is lost as heat.