1. Chapter 51
Ecosystems

2. Ecosystems
Population: all the individuals of a certain species that live in a particular area
Community: all the different species that interact together within a particular area
Ecosystems consist of all the organisms that live in an area along with the nonbiological (abiotic) components.

3. Ecosystems Many global environmental problems have emerged recently.
Ecosystem ecology follows the flow of energy and nutrients through ecosystems
Humans have artificially affected the flow of these components

4. Energy Flow within Ecosystems
Energy enters an ecosystem primarily though sunlight:

5. Energy Flow and Trophic Structure
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)

6. Different Trophic Levels in an Ecosystem4 3 2 1
Feeding strategy
Secondary carnivore
Carnivore
Herbivore
Autotroph
Grazing food chain
Decomposer food chain
Cooper’s
hawk
Owl
Shrew
Earthworm
Dead maple leaves
Robin
Cricket
Maple tree leaves
Figure: 51.6a
Caption:
(a) Each trophic level in an ecosystem is defined by a distinct feeding strategy. The organisms illustrated in this table furnish an example for each trophic level in the grazing and decomposer food chains of a temperate-forest ecosystem. Many other species exist at each trophic level in this ecosystem.

7. Energy Flow in an ecosystem
External energy source
PRIMARY
PRODUCERS
CONSUMERS
DECOMPOSERS
ABIOTIC ENVIRONMENT
Figure: 51.1
Caption:
Primary producers harness an external energy source to manufacture ATP and reduced carbon compounds, which are then available to consumers. When primary producers and consumers die, their remains are digested by decomposers. Primary producers, consumers, and decomposers all exchange energy and matter with the soil, atmosphere, water, and other aspects of the abiotic environment.

8. Decomposers Predators of decomposers: Primary decomposers: Spider
Salamander
Centipede
Puffball
Puffball
Mushroom
Figure: 51.5
Caption:
Dead leaves, sticks, and other types of detritus are fed upon by an enormous variety of organisms. These decomposers, in turn, are fed upon by salamanders, shrews, spiders, centipedes, and other predators.
Earthworm
Millipede
Primary decomposers:
Bacteria and archaea
Nematodes
Pillbugs
305 nm
49.4 µm

9. Energy Flow and Trophic Structure
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.

10. Ecological Efficiency: percent of energy transferred from one trophic level to the next
Energy source:
1,254,000
kcal/m2/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
Figure: 51.2
Caption:
In a temperate forest ecosystem, energy from sunlight is transformed to chemical energy by photosynthesis. The products of photosynthesis go, in part, to fuel new plant growth. Plant tissue is either consumed by herbivores in the grazing food web or falls into the decomposer food web when the plant dies.

11. Ecosystem Processes
Production: rate at which energy/nutrients are converted into growth
Includes Primary Production: growth by autotrophs
Includes Secondary Production - growth by heterotrophs
Consumption - the intake and use of organic material by heterotrophs
Decomposition - the chemical breakdown of organic material

12. Terrestrial productivity
Figure 51.3a
Terrestrial productivity
0–100
100–200
200–400
400–600
600–800
>800
Figure: 51.3a
Caption:
(a) The terrestrial ecosystems with the highest primary productivity are found in the tropics, where warm temperatures and high moisture encourage high photosynthetic rates. Tundras and deserts have the lowest productivity.
Productivity ranges
(g/m2/yr)

13. Figure 51.3b Marine productivity Productivity ranges (g/m2/yr) <35
35–55
55–90
>90
Figure: 51.3
Caption:
(b) The highest productivity in the oceans occurs in nutrient-rich coastal areas.
Productivity ranges
(g/m2/yr)

14. Very little of the energy consumed by primary consumers are used for secondary production
80.7% respiration
17.7% excretion
1.6% growth and reproduction
Energy derived from plants
Figure: 51.4
Caption:
Very little of the energy consumed by chipmunks, a primary consumer (herbivore), is used for secondary production. Most of the energy is used for cellular respiration.

15. Pyramid of productivity4
Secondary carnivore 3
Carnivore 2
Herbivore 1
Autotroph
Productivity
Pyramid of productivity
Example: 100g of plant becomes 5-20g of grasshopper then g of mouse
Figure: 51.6b
Caption:
(b) In all ecosystems, productivity is highest at the first trophic level and declines at higher levels. This pattern is called the pyramid of productivity.

16. The Different Trophic levels in an ecosystem is often pictured as a Food chain
Pisaster
(a sea star)
Thais
(a snail)
Bivalves
(clams, mussels)
Figure: 51.7a
Caption:
(a) An example of a food chain in an intertidal zone.

17. Energy Flow and Trophic Structure
Food chains and food webs
Food chains are typically embedded in more complex food webs.
Many organisms feed at more than one trophic level

18. Food web Pisaster Thais Limpets Acorn barnacles Gooseneck barnacles
Figure: 51.7b
Caption:
(b) Food chains are embedded in food webs that include more species and different feeding relationships.
Limpets
Acorn
barnacles
Gooseneck
barnacles
Chitons
Bivalves

19. Energy Flow and Trophic Structure
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.

20. Food chains tend to have few links.10 8 6 4 2
Average number
of links = 3.5
Streams
Lakes
Terrestrial
Number of observations
Figure: 51.7c
Caption:
(c) The y-axis on this graph plots the number of research studies that described food chains with from 1 to 6 links in stream, lake, and terrestrial habitats. 1 2 3 4 5 6
Number of links in food chain

21. Biogeochemical Cycles
The path an element takes as it moves from abiotic systems through living organisms and back again is referred to as its biogeochemical cycle.
Examples: nitrogen cycle, carbon cycle, phosphorus cycle

22. Figure 51.8 Plants Assimilation Herbivore Feces or urine Death
Consumption
Herbivore
Assimilation
Feces or urine
Death
Figure: 51.8
Caption:
Nutrients cycle from organism to organism in an ecosystem as a result of assimilation by primary producers, consumption, and decomposition. Nutrients are exported from ecosystems through the migration of organisms out of the area or, more commonly, in flowing water or groundwater.
Death
Detritus
Uptake
Soil nutrient pool
Decomposer
food web
Loss to erosion or leaching into groundwater

23. Biogeochemical Cycles
A key feature in all cycles is that nutrients are recycled and reused.
The overall rate of nutrient movement is limited most by decomposition of detritus.

24. Boreal forest: nutrients are put back into the soil slowly, so organic material builds up
Figure: 51.9a upper
Caption:
In boreal forests, decomposition rates are limited by cold soil temperatures. The input of detritus into the soil thus exceeds the decomposition rate, and organic matter builds up.

25. Tropical rain forest: decomposition is rapid so there is very little organic build up
Figure: 51.9 lower
Caption:
In tropical rain forests, warm temperatures allow decomposition to proceed rapidly so that organic matter does not build up.
Result: if living material is removed from tropical rain forests, the soil is nutrient poor to support new growth

26. The rate of nutrient loss is a very important characteristic in any ecosystem.
Devegetation experiment
Choose two similar watersheds.
Document nutrient levels in soil organic matter, plants, and streams.
Figure: 51.10a upper
Caption:
(a) An experiment to test the effects of vegetation removal on nutrient cycling. Question: In effect, this experiment removed one of the arrows in Figure Which one?

27. Devegetate one watershed and leave the other intact.
Clearcut
Control
Figure: 51.10a lower
Caption:
(a) An experiment to test the effects of vegetation removal on nutrient cycling. Question: In effect, this experiment removed one of the arrows in Figure Which one?
Devegetate one watershed and leave the other intact.
Monitor the amount of dissolved substances in streams.

28. Nutrient export increases dramatically in devegetated plot
Net dissolved substance (kg/ha)
1965–66
1966–67
1967–68
1968–69
1969–70
Control
1000
800
600
400
200
Year
Nutrient runoff results
Figure: 51.10b
Caption:
(b) Nutrient export increased dramatically in the devegetated watershed. 

29. Biogeochemical Cycles
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.

30. Humans are adding significant amounts of carbon into the atmosphere
THE GLOBAL CARBON CYCLE
All values in gigatons of carbon per year
Atmosphere: 750 (in 1990)
+3.5 per year
Photosynthesis:
102
Respiration: 50
Fossil fuel use:
6.0
Deforestation:
1.5
Physical
and chemical processes: 92
Decomposition: 50
Physical
and chemical processes: 90
Land, biota, soil, litter, peat: 2000
Figure: 51.11
Caption:
The arrows in this diagram indicate how carbon moves into and out of ecosystems. Note that deforestation and fossil fuel use are adding 7.5 gigatons of carbon to the atmosphere each year. Of this 7.5 gigatons, two are fixed by photosynthesis in terrestrial ecosystems and two are fixed by physical and chemical processes in the oceans. 2
Rivers: 1
Ocean: 40,000
Aquatic ecosystems
Terrestrial ecosystems
Human–induced
changes

31. Human-induced increases in CO2 flux over time6 5 4 3 2 1
Fossil fuel use
Annual flux of carbon (1015g)
Land use
Figure: 51.12a
Caption:
(a) Carbon fluxes from fossil-fuel burning and land-use changes have been increasing since  Question Why are atmospheric CO2 concentrations low in the northern hemisphere during the summer and high in winter? What pattern would you expect in the southern hemisphere?
1860
1880
1900
1920
1940
1960
1980
Year

32. Figure 51.12b Atmospheric CO2 CO2 concentration (ppm) Year 360 350 340
330
320
310
CO2 concentration (ppm)
Figure: 51.12b
Caption:
(b) Scientists have been collecting air samples and measuring CO2 concentrations at the Mauna Loa Observatory in Hawaii since Because the site is far from large-scale human influence, it should accurately represent the average condition of the atmosphere in the northern hemisphere.  Question Why are atmospheric CO2 concentrations low in the northern hemisphere during the summer and high in winter? What pattern would you expect in the southern hemisphere?
1960
1970
1980
1990
Year

33. THE GLOBAL NITROGEN CYCLE
Only nitrogen-fixing bacteria can use N2
make ammonia (NH3) or nitrate (NO3)
limiting nutrient (demand exceeds supply) for plants
All organisms require nitrogen to make protein
Animals get nitrogen from their diets, not the air
Nitrogen
fixing cyanobacteria
Mud
Decomposition of detritus into ammonia
Nitrogen-fixing bacteria in roots and soil
Protein and
nucleic acid synthesis
Atmospheric nitrogen (N2) =78%
Bacteria in mud
use N-containing molecules as energy sources, excrete (N2)
Run–off
Lightning and rain
Figure: 51.13a
Caption:
(a) Nitrogen enters ecosystems as ammonia or nitrate via fixation from atmospheric nitrogen. Within ecosystems, nitrogen cycles through producers and consumers. Eventually it reaches the decomposer food web. Nitrogen is exported from ecosystems in runoff and as nitrogen gas given off by bacteria that use nitrogen-containing compounds as an electron acceptor.
Industrial fixation

34. Human activities now fix almost as much nitrogen each year as natural sources
Human sources
Amount of nitrogen (gigatons/year)
160
140
120
100
80 60 40 20
Sources of nitrogen fixation
Lightning
Biological fixation
Fossil fuels
Nitrogen fertilizer
Nitrogen- fixing crops
Figure: 51.13b
Caption:
(b) Human activities now fix almost as much nitrogen each year as natural sources. Thus, human activities have almost doubled the total amount of nitrogen available to organisms.