Ecosystems. 1. Population Interactions 2. Energy Flow 3. Material Cycle

Transcription

1 Ecosystems 1. Population Interactions 2. Energy Flow 3. Material Cycle

2 The deep sea was once thought to have few forms of life because of the darkness (no photosynthesis) and tremendous pressures. But in 1977, a whole new kind of community was discovered in the deep sea.

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4 The invertebrates supply the bacteria with CO 2, O 2, and sulfides at higher rates than they could get if they were free-living. The symbiosis is therefore a mutualism and results in higher productivity than if the organisms lived separately.

5 Chemoautotrophic bacteria arrive first, sometimes in very high densities. Tube worms are often the first invertebrates to arrive. Clams and other mollusks are better competitors and over time they increase in abundance at the expense of the tube worms.

6 Succession in Hydrothermal Vent Communities

7 Ecosystem Energetics Sunlight is the most significant source of energy Solar energy (photons) Used by photoautotrophs Drives weather, water cycle, and causes the currents of air and water

8 Ecosystem Energetics Energy flows through the ecosystem The flow of energy is subjected to physical laws

9 The Laws of Thermodynamics Energy exists in two forms Potential energy - stored energy Kinetic energy - energy in motion Work is the storage of energy and the arranging or ordering of matter

10 The Laws of Thermodynamics Govern Energy Flow Two laws of thermodynamics govern the expenditure and storage of energy The first law of thermodynamics The second law of thermodynamics

11 The Laws of Thermodynamics Govern Energy Flow The first law of thermodynamics: energy is neither created nor destroyed Exothermic - energy released Endothermic- energy absorbed

12 One-way flow of energy Heat + 1 C 6 H 12 O 6 6 CO H 2 O energy rich energy poor

13 The Laws of Thermodynamics The second law of thermodynamics: energy is is always lost during transfer Entropy a measure of disorder in a system disorder spontaneously increases over time Matter has a tendency to reach a higher state of entropy and lower state of potential energy

14 The Rule of Ten or 10% Law

15 Ecological Pyramids Primary producers are bases for successive tiers of consumers Biomass pyramid Dry weight of all organisms Energy pyramid Usable energy decreases as it is transferred through ecosystem

16 Pyramids of biomass What causes there to be less biomass at higher levels? Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig a

17 Pyramids of energy Fig What causes there to be a loss of energy at each tropic level? Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

18 Energy Flow Primary Productivity Gross primary productivity Net primary productivity

19 Concept 20.1 Primary Production Primary production is the chemical energy generated by autotrophs during photosynthesis and chemosynthesis. It is the source of energy for all organisms, from bacteria to humans.

20 Concept 20.1 Primary Production Autotrophs store energy as carbon compounds Carbon is the currency used to measure primary production. Primary productivity is the rate of primary production.

21 Concept 20.1 Primary Production Gross primary production (GPP) total amount of carbon fixed by autotrophs. GPP depends on photosynthetic rate. Photosynthetic rate is influenced by climate and leaf area index (LAI) leaf area per unit of ground area.

22 Concept 20.1 Primary Production LAI varies among biomes: Less than 0.1 in Arctic tundra (less than 10% of the ground surface has leaf cover). 12 in boreal and tropical forests (12 layers of leaves between the canopy and the ground, on average).

23 Concept 20.1 Primary Production Because of shading, the incremental gain in photosynthesis for each added leaf layer decreases.

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25 Concept 20.1 Primary Production Plants use about half of the carbon fixed in photosynthesis for cellular respiration. Plants with a lot of nonphotosynthetic tissue (e.g., trees) have higher respiratory carbon losses. Respiration rate increases with temperature, so tropical forests have higher respiratory losses.

26 Concept 20.1 Primary Production Net primary production (NPP) = GPP Respiration NPP results in an increase in biomass (living plant matter). NPP is the energy left over for plant growth and for consumption by detritivores and herbivores.

27 Concept 20.1 Primary Production Plants can respond to environmental conditions by allocating carbon to the growth of different tissues. Example: Grassland and desert plants allocate more NPP to roots because soil nutrients and water are scarce.

28 Allocation of NPP to Roots

29 Concept 20.1 Primary Production Allocation of NPP to storage products (e.g., starch) provides insurance against loss of tissue to herbivores, disturbances such as fire, and climatic events such as frost. Substantial amounts of NPP (up to 20%) may be allocated to defensive secondary compounds.

30 Concept 20.1 Primary Production NPP varies during succession, as LAI (ratio of photosynthetic to nonphotosynthetic tissue) and species composition all change. Highest NPP is usually during intermediate stages when plant diversity and nutrient supply tend to be highest.

31 The Trajectory of Succession Highest diversity and NPP

32 Concept 20.1 Primary Production In old-growth forests, NPP may decline as LAI and photosynthetic rates decrease. Old-growth ecosystems have large pools of stored carbon and nutrients and provide habitat for many animal species. The decrease in NPP over time is far less pronounced in grasslands than in forests.

33 Temperature, Water, and Nutrients Control Primary Production in Terrestrial Ecosystems Temperature and precipitation influence one another and thus have interacting effects on primary productivity Warm air temperatures increase the potential for evaporation and increase transpiration rates and water demand If temperatures are low, rates of photosynthesis and productivity will be low regardless of water availability

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35 Temperature, Water, and Nutrients Control Primary Production in Terrestrial Ecosystems Warm temperatures and an adequate water supply for transpiration give the highest primary productivity Actual evapotranspiration (AET) is the combined value of surface evaporation and transpiration

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37 Temperature, Water, and Nutrients Control Primary Production in Terrestrial Ecosystems NPP increases with increasing nutrient availability Nitrogen availability drives patterns of forest primary productivity Increasing primary productivity with available nitrogen

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39 Temperature, Water, and Nutrients Control Primary Production in Terrestrial Ecosystems NPP increases with increasing nutrient availability

40 Temperature, Water, and Nutrients Control Primary Production in Terrestrial Ecosystems Global productivity patterns reflect the influence of climate in terrestrial ecosystems and the global patterns of temperature and precipitation

41 Temperature, Water, and Nutrients Control Primary Production in Terrestrial Ecosystems The regions of highest NPP are located in the equatorial zone Year-round warm temperatures and ample precipitation

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43 Concept 20.1 Primary Production It is important to be able to measure NPP: NPP is the ultimate source of energy for all organisms in an ecosystem. Variation in NPP is an indication of ecosystem health. NPP is associated with the global carbon cycle.

44 Concept 20.1 Primary Production Terrestrial ecosystems: NPP is estimated by measuring increase in plant biomass in experimental plots and scaling up to the whole ecosystem.

45 Concept 20.1 Primary Production Harvest techniques: Measure biomass before and after growing season. This is a reasonable estimate of aboveground NPP if corrections are made for herbivory and mortality.

46 Concept 20.1 Primary Production Harvest techniques are impractical for large or biologically diverse ecosystems. Chlorophyll concentrations can be a proxy for GPP and NPP: Estimate using remote sensing methods that rely on reflection of solar radiation.

47 Spectral Signatures of Vegetation Clear Water, and Bare Soil

48 Primary Production NDVI (normalized difference vegetation index): NDVI ( NIR ( NIR red ) red ) NIR = Near-infrared wavelengths ( nm) red = red wavelengths ( nm)

49 Concept 20.1 Primary Production Vegetation has a high NDVI value; water and soil have low NDVI values. NDVI over large spatial scales is measured using satellite sensors.

50 Concept 20.1 Primary Production NDVI and remote sensing can be used to estimate CO 2 uptake and NPP, deforestation, desertification, atmospheric pollution, and other phenomena.

51 Remote Sensing of Terrestrial NPP

52 Concept 20.1 Primary Production Phytoplankton do most of the photosynthesis in aquatic habitats. Phytoplankton have short life spans, so biomass at any given time is low compared with NPP; harvest techniques are not used.

53 Concept 20.1 Primary Production Remote sensing of chlorophyll concentrations in the ocean using satellites provides good estimates of marine NPP. Indices are developed to indicate how much light is being absorbed by chlorophyll, which is then related to NPP.

54 Remote Sensing of Marine NPP