1. How Ecosystems Work
Chapter 5

2. Lake Victoria’s Ecological Imbalance
World’s second largest freshwater lake
400 species of cichlids, important food source
Nile Perch introduced in 1960s
1985, most catch was perch, ate cichlids
Today, more than 50% of cichlids and other native fish are extinct
Algae eating cichlids disappeared, algal explosion, no Oxygen in bottom of lake dead zone
If the rest of cichlids disappear, perch won’t have anything to eat, and fisher will collapse

3. Lake Victoria’s Ecological Imbalance

4. What is Ecology? Learning Objectives: Define ecology
Distinguish among the following ecological levels: population, community, ecosystem, landscape, and biosphere

5. What is Ecology?
The study of the interactions among organisms and between organisms and their abiotic environment
Environment:
Biotic (living) - all organisms
Abiotic (non-living) - physical factors: space, temperature, sunlight, soil, precipitation, etc.
Focus can be local or global
Broadest field of Biology
Linked to all parts of biology, and to geology, chemistry, physics

6. What is Ecology? Levels of Interest:
Population: a group of organisms of the same species that live in the same place at the same time, e.g., population of marsh grass, walruses
Communities: a natural association that consists of all the populations of different species that live and interact together within an area at the same time, e.g., Alpine meadow, tidal pool
Ecologists would study how species interact with each other, including feeding relationships 6

7. What is Ecology?

8. What is Ecology?
Ecosystem: includes all the biological interactions of a community AND the interactions of organisms with their abiotic environment
Very complex interactions between energy flow and nutrient cycling
Ecologists would study how energy, nutrients, or water level affects the organisms living in a desert
Landscape: studies ecological processes over large areas and several interacting ecosystems

9. What is Ecology?

10. What is Ecology?
Biosphere: the layer of Earth that contains all living organisms
Ecologists study the global interrelationships among water, land, atmosphere, and organisms
Includes organisms, communities, ecosystems, landscapes, etc. depend on the Earth’s other layers:
Atmosphere: layer of air
Hydrosphere: supply of water
Lithosphere: soil and rock of Earth’s crust

11. Global Climate Change What is the definition of ecology?
What is the difference between an ecosystem and a landscape? Between a community and an ecosystem?

12. The Flow of Energy Through Ecosystems
Learning Objectives
Define energy and state the first and second laws of thermodynamics
Distinguish among producers, consumers, and decomposers
Summarize how energy flows through an ecosystem

13. The Flow of Energy Through Ecosystems
Energy: the ability to do work
Potential energy: stored
Kinetic Energy: energy of motion

14. The Flow of Energy Through Ecosystems

15. The Flow of Energy Through Ecosystems
Thermodynamics: study of energy and its transformations
First Law of Thermodynamics
Energy cannot be created not destroyed
Can change from one form to another
Photosynthesis/cellular respiration
Heat - not usable for biological work
Total energy of organisms and surroundings is constant

16. The Flow of Energy Through Ecosystems

17. The Flow of Energy Through Ecosystems
The Second Law of Thermodynamics
The amount of usable energy in the universe decreases over time
As energy is converted form one form to another, some of it is degraded into ‘heat’
Heat: less usable form of energy, disperses into environment, less organized than usable energy
Entropy: a measure of disorder or randomness
Energy conversions are is not 100% efficient

18. The Flow of Energy Through Ecosystems
Producers, Consumers and Decomposers
Producers: manufacture large organic molecules from simple inorganic molecules
Consumers: consume other organisms as a source of energy and bodybuilding materials
Primary Consumers/Herbivores: eat producers
Secondary Consumers/Carnivores: eat primary consumers
Tertiary Consumers/Carnivores: eat secondary consumers
Omnivores: eat everything
Detritivores/Detritus feeders: eat detritus (animal carcasses, leaf litter, feces)
Decomposers: break down dead organisms and waste products
Release simple inorganic molecules that can be re-used by producers

19. The Flow of Energy Through Ecosystems

20. The Flow of Energy Through Ecosystems
The Path of Energy Flow in Ecosystems
Energy Flow
The passage of energy in a one-way direction through an ecosystem, as part of a food chain
Food Chain
A diagram showing linear feeding relationships
grassrabbitsnakeeagle
Trophic level: each link in a food chain
First trophic level: producers
Second: primary consumers
Third: secondary consumers, etc.
Decomposers are at every step
Food Web
A complex of interconnected food webs in an ecosystem

21. The Flow of Energy Through Ecosystems

22. The Flow of Energy Through Ecosystems

23. The Flow of Energy Through Ecosystems
Energy Flow
Linear movement of energy along food chain or food web
From one organism to the next
When ‘food’ energy is converted into ‘work’ energy, some is degraded into heat
Second Law of thermodynamics
The longer the food chain, the less energy is available for higher trophic levels
Limited numbers of trophic levels

24. Global Climate Change
What is the first law of thermodynamics? What is the second?
Why is a balanced ecosystem unlikely to contain only producers and consumers? Only consumers and decomposers? Explain your answer.
How does energy mover through a food web?

25. The Cycling of Matter in Ecosystems
Learning Objectives:
Diagram and explain the carbon, hydrologic, nitrogen, sulfur, and phosphorous cycles

26. The Cycling of Matter in Ecosystems
Biogeochemical Cycles
Matter: the material of which organisms are composed
Biogeochemical: involves biological, geological, and chemical processes
Humans have GREAT influence
Cycling vs. Flow:
Matter cycles through ecosystem
From abiotic environment to organisms to environment
Energy flows through the ecosystem
From producers to consumers to decomposers, to heat

27. The Cycling of Matter in Ecosystems
The Carbon Cycle
The global movement of carbon between the abiotic environment (atmosphere, ocean) and organisms
Atmosphere/oceanphotosynthesiscellular respiration/combustion/decompositionatmosphere/ocean
Carbon is an essential component of organisms’ molecules
Also essential component of abiotic environment

28. The Cycling of Matter in Ecosystems

29. The Cycling of Matter in Ecosystems
The Hydrologic Cycle
Water circulates from the ocean to the atmosphere to the land, and back to the ocean
Provides renewable supply of purified water
Balance of water on land, oceans, and atmosphere
Evaporation
Transpiration
Precipitation
Runoff from watersheds
Percolation

30. The Cycling of Matter in Ecosystems

31. The Cycling of Matter in Ecosystems
The Nitrogen Cycle
Nitrogen is an essential component of proteins and nucleic acids
Atmosphere is 78% Nitrogen gas
Steps:
Nitrogen fixation: N gas into ammonia, by bacteria physical, and human activities
Nitrification: ammonia to nitrate, bacteria
Assimilation: plants absorb nitrate/ammonia
Ammonification: organisms produce N-containing waste
Denitrification: nitrate is converted back into N gas

32. The Cycling of Matter in Ecosystems

33. The Cycling of Matter in Ecosystems

34. The Cycling of Matter in Ecosystems
The Sulfur Cycle
Poorly understood
Most Sulfur is underground
Erosion releases Sulfur to ocean
S gases enter atmosphere from natural sources
Sea delivers sulfates to land
Volcanoes release Hydrogen sulfides and Sulfur oxides
Hydrogen sulfides react with water to form sulfuric acid
Some sulfur compounds in living organisms
Bacteria drive the Sulfur cycle (like the Nitrogen cycle)

35. The Cycling of Matter in Ecosystems

36. The Cycling of Matter in Ecosystems
The Phosphorous Cycle
Cycles from land into living organisms and back
No atmospheric component
Erosion of rocks releases phosphorous into soil
Plants absorb it and use it for nucleic acids and ATP, pass it on to consumers
Decomposers release phosphorous into water
Can be lost at bottom of ocean fro millions of years
Aquatic cycle is also interesting

37. The Cycling of Matter in Ecosystems

38. Global Climate Change
What are the differences and similarities between the five biogeochemical cycles, particularly in the roles organisms play in them?

39. Ecological Niches Learning Objectives:
Describe the factors that contribute to an organism’s ecological niche
Explain the concept of resource partitioning

40. Ecological Niches Niche: Habitat:
The totality of an organism’s adaptations, its use of resources, and the lifestyle to which it is fitted
Describes the place and function of an organism within the ecosystem
Takes into account all aspects of an organism’s existence
The “way of life of an organism”
Habitat:
Part of an organism’s niche, the place where the organism lives

41. Ecological Niches Fundamental Niche: Realized Niche:
The potential, idealized niche of an organism
It’s probably broader than it is in nature
Realized Niche:
The niche an organism actually has and the resources it actually uses
Competition and other factors usually make the realized niche narrower than the fundamental niche

42. Ecological Niches

43. Ecological Niches Resource Partitioning
The reduction in competition for environmental resources among coexisting species, by reducing similarities in their niches
When two species are very similar, their niches may overlap
Ecologists think that species cannot occupy the same niche in a community
Species with similar niches divide up resources in such a way that they reduce competition among themselves

44. What a Scientist Sees

45. Global Climate Change
What are three aspects of an organism’s ecological niche?
What is resource partitioning?

46. Interactions Among Organisms
Learning Objectives:
Distinguish among mutualism, commensalism, and parasitism
Define predation and describe predator-prey relationships
Define competition and distinguish between intraspecific and interspecific competition
Discuss an example of keystone species

47. Interactions Among Organisms
Organisms are not independent from others
Symbiosis
Predation
Competiton
Keystone Species - a special case

48. Interactions Among Organisms
Symbiosis
An intimate relationship or association between members of two or more species
One species lives in or on another species
Relationship may be beneficial, neutral or harmful
Result of coevolution
Interdependent evolution of two interacting species
E.g., plants and pollinators

49. Interactions Among Organisms

50. EnviroDiscovery Bee Colonies Under Threat
Coevolutionary relationships are very specific
If one species is affected suffers, so is the other
Colony Collapse Disorder (CCD)
Since 2006, 30–90% of bees in colonies in US have died
Pesticides, pathogens, parasites, viruses
Bees are necessary for pollination of many important crops and wild species

51. EnviroDiscovery

52. Interactions Among Organisms
Symbiosis
Three types:
Mutualism
An association where both organisms benefit
Bull Horn Acacia and acacia ants
Commensalism
One species benefits, the other doesn’t benefit or is harmed
Tropical trees and epiphytes
Parasitism
One species benefits, the other is harmed
Parasite-Host relationship
Internal and external types of parasites

53. Environmental InSight

54. Interactions Among Organisms
Predation
The consumption of one species (prey) by another species (predator)
Coevolutionary “arms race”
Predator strategies - more efficient ways to catch prey
Prey strategies - more efficient ways to escape/avoid predator

55. Interactions Among Organisms

56. Interactions Among Organisms

57. Interactions Among Organisms
Competition
The interaction among organisms that vie for the same resources in the same environment
Resources are limited
Food, shelter, living space, sunlight, etc.
Intraspecific Competition
Among individuals of the same population (same species)
Interspecific Competition
Among individuals of different species

58. Interactions Among Organisms
Keystone Species
Vital in determining an ecosystem’s species composition
Crucial to the maintenance of an ecosystem
When keystone species is removed other organisms may become more common, more rare, or extinct
Usually not numerous, but very influential
Affect availability of food, water, or other resources
E.g.,
Gray Wolf

59. Global Climate Change What is one example if mutualism? Of parasitism?
What is one example of a predator-prey interaction? Or competition?
What is the difference between interspecific and intraspecific competition?
How does a keystone species affect its ecosystem?

60. Case Study Global Climate Change: How does it affect the Carbon cycle?
Biggest culprit: levels of CO2 in atmosphere
Levels of CO2 have increased 20% in last 50yrs
Generated by burning of fossil fuels, clearing and burning land and forests
Need to stabilize and reduce emissions with ‘stabilization wedges”, each reduces 1 billion tons/yr

61. Case Study