1. Chapter 5: Ecosystems: Concepts and Fundamentals

2. Overview The Ecosystem: Sustaining Life on Earth
Ecosystem Communities and Food Chains
Ecosystems as Systems
Biological Production and Ecosystem Energy Flow
Biological Production and Biomass
Energy Efficiency and Transfer Efficiency
Ecological Stability and Succession
Chemical Cycling and Succession
How Species Change Succession

3. The Ecosystem: Sustaining Life on Earth
Sustaining life on Earth requires more than individuals
Ecosystem
Interactions of many organisms functioning together in ecosystems
Physical and chemical environments

4. Basic Characteristics of Ecosystems
Ecosystems have several fundamental characteristics
Grouped into
Structure
Processes

5. Basic Characteristics of Ecosystems
Structure
Made up of two major parts
Living (ecological community)
Non living (physical & chemical environment)
Processes
Cycling of chemical elements
Flow of energy

6. Basic Characteristics of Ecosystems
At its simplest a community will have:
At least one species that is a producer
Another species that is a decomposer
Plus a fluid medium
Never this simple

7. Basic Characteristics of Ecosystems
Ecosystem chemical cycling
For complete recycling of chemical elements, several species must interact
Photosynthetic organisms produce sugar from carbon dioxide and water
From sugar and inorganic compound they make other organic compounds (protein, woody tissue)
Need decomposers to get back to inorganic compounds

8. Ecological Communities and Food Chains
Ecological community definitions
A set of interacting species found in the same place and functioning together to maintain life
In practice it is difficult to identify the interacting species
All the species found in an area, whether or not they interact
Operational definition

9. Food Chains Food chain Grouped by trophic level
Linkage of who feeds on whom
Energy, chemicals and some compounds are transferred from creature to creature along food chains or food webs (more complex)
Grouped by trophic level
Number of feeding levels away from original source of energy

10. Trophic Levels First trophic level Second trophic level
Use energy from the sun and carbon dioxide from the air to photosynthesizes
Green plants, algae and certain bacteria
Called autotrophs
Second trophic level
Organisms that feed on autotrophs
Called herbivores

11. Trophic Levels Third trophic level Forth trophic level
Feed directly on herbivores
Called carnivores (meat eaters)
Forth trophic level
Carnivores that feed on third-level carnivores
Decomposers- feed on waste and dead organisms of all trophic levels

12. A Food Chain Example Example: Yellowstone Hot Springs
1st level - photosynthetic algae and bacteria
2nd level - Ephydrid flies (larvae feed on the bacteria and algae)
3rd level - dolichopodid fly (larvae feed on herbivorous flies)
4th level - parasites and predators to the flies

14. An Oceanic Food Chain Tend to have more trophic levels
1st level - planktonic algae and planktonic bacteria
2nd level - zooplankton and some fish
3rd level - fish and invertebrates feed on herbivores, baleen whales
4th+ levels - killer whales, predatory fish

16. Complex Food Web - Harp Seal
Most species feed on several trophic levels
Harp seal (shown at 5th level)
Feeds on flatfish (4th level)
But also feed on foods from 2nd – 4th
A species that feeds on several levels placed in a category one above the highest level it feeds on

18. Ecosystem as Systems
An ecosystem is the minimal entity that has the properties required to sustain life
Vary greatly in:
Structural complexity and clarity of their boundaries
Size
Composition
Proportion of non-biological constituents
Degree of variation in time and space

19. Sharp and Distinct Transition - lake to forest

20. Watershed
Watershed
Commonly used practical delineation of the boundary of an ecosystem
Determined by topography
United in terms of chemical cycling

21. Ecosystem Energy flow All life requires energy Ecosystem energy flow
Ability to do work
Ecosystem energy flow
Movement of energy through an ecosystem from the external environment through a series of organisms and back to the external environment

22. Energy Flow Energy enters an ecosystem by two pathways:
Energy fixed by organisms
Transfer of heat energy by air, water, soil and warm living things

23. Ecosystem Energy Flow Energy is difficult and abstract concept
Most of the time energy is invisible to us
With infrared film we can see difference between warm and cold object

24. Birch forest in New Hampshire
Regular film
Infrared film

25. A nearby rocky outcrop
Regular film
Infrared film

26. Laws of Thermodynamics
First Law of Thermodynamics
Law of conservation of energy
In any physical or chemical change, energy is neither created nor destroyed
Energy merely changed from one form to another
If this is true, why can’t we continually recycle energy within our bodies?

27. Impossible ecosystem because of 2nd law of thermodynamics

28. Laws of Thermodynamics
Energy must continually be added to an ecological system in a usable form
Because inevitably degraded into heat
Net flow of energy is a one way flow
Second Law of Thermodynamics
No use of energy is ever 100% efficient
Energy is lost to heat

30. Energy Efficiency
As energy flows through a food web, it is degraded, and less and less is useable
Entropy
Energy must be continually added to an ecosystem, in usable form

31. Biological Production
Biomass
Total amount of organic matter on Earth or in any ecosystem or area
Measured as the amount per unit surface area
Biological production
Capture of usable energy from the environment to produce organic compounds

32. Biological Production
Gross Production
Increase in stored energy before any is used
Net Production
Change in biomass over a given time
Three measures used for biological production
Biomass
Energy stored
Carbon stored

33. Two Kinds of Biological Production
Primary Production
Autotrophs (& chemoautotrophs)
Photosynthesize or chemosynthesize
Make their own organic matter from energy source and inorganic compounds
Secondary production
Heterotrophs
Cannot make their own organic compounds and must feed on other living things

34. Biological Production
Respiration
Use of energy from organic matter by most heterotrophic and autotrophic organisms
Organic matter combines with oxygen
Releases energy, carbon dioxide and water
Use of biomass to release energy that can be used to do work

35. Energy Efficiency and Transfer Efficiency
Trophic-level efficiency
Ratio of production of one trophic level to the production of the next trophic level
Never very high
1–3% in natural ecosystems
10% may be maximum
90% of all energy lost as heat

36. Ecological Stability and Succession
Ecosystems are dynamic- always changing
Primary succession
Establishment and development of an ecosystem where one did not exist previously (lava flow - left; edge of retreating glacier - right)

37. Ecological Stability and Succession
Secondary succession
Reestablishment of an ecosystem following disturbance
Remnants of previous biological community (soil, seeds, organic material, etc.)
Examples
Forests that develop on abandoned pastures
Development after hurricanes, floods, fires

38. Dune Succession Sand dunes continually formed along sandy shores
Breached and destroyed by storms
After dune forms
Grasses establish
Grass runners stabilize dunes
Other species seeds may germinate and become established

39. Bog Succession
Bog - Open body of water with surface inlets but no surface outlets
Succession:
Sedge puts out floating runners
Wind blows particles into the mat of runners
Seeds land on runners and germinate
Mat becomes thicker and shrubs and trees develop

40. Bog Succession Bog also fills in from the bottom
At the shore, floating mat and sediment meet forming a solid surface
Farther from shore all the vegetation is still floating

42. General Patterns of Succession
Successional stages
Early (1 and 2), middle, and late
Similar patterns seen with animals and other life-forms at each stage
Pioneers - species characteristic of early stage
Late-successional species tend to be slower- growing and longer-lived

43. General Patterns of Succession
In early stages of succession
Biomass and biological diversity increase
In middle stages
Gross production increase and net production decrease
Organic material in soil increases, as does chemical element storage

45. How Species Change Succession
Earlier succession species affect what happens later in succession through:
Facilitation
Interference
Life history differences

46. Facilitation
Facilitators in dune and bog succession are dune grass and floating sedge, respectively
They prepare the way for other species

47. Interference
Certain early species interfere with the entrance of other species
Grasses may form dense mats blocking other seeds from germinating

48. Chronic Patchiness Common in deserts Life tends to build up
Major shrub species grow in patches
Patch persist for long period of time until next disturbance
Life tends to build up
Non-biological processes tend to erode or degrade
In harsh environments degrading dominates and succession does not occur