SCI1192 Lecture 10

1. Populations, Communities and
Change
The Blue Planet: Chapter 16

2. Outline
• Populations
• Communities
• Biodiversity

3. Populations
• A population is a group of individuals of
the same species, which interbreed and
share genetic information
• Populations can be affected by
– Intrinsic factors
• Specific to the characteristics of a particular
species or population
– Extrinsic factors
• External to the population that can influence
health and survival

4. Populations
• Intraspecific
– Interaction occur between individuals of the
same species within a population
• Interspecific
– Interactions occur between individuals of
different species
– Because populations live in communities of
many interacting species

5. Populations

6. Populations
• Population dynamics is the growth and
change of a population
– Growth rate is the change in number of
individuals in a population over time
• Given sufficient energy and nutrients,
life forms are capable of incredible rates
of growth
– For short periods, this can be exponential

7. Populations

8. Populations
• Under constant conditions and constant
food supply, a population will grow
smoothly until limited by extrinsic factors
– Logistic growth curve (S-curve)
• As the number of individuals per unit
area (population density) increases
– Environment becomes more crowded
– Food and resources are limited
– Growth and reproductive rate decline

9. Populations

10. Populations

11. Populations
• The biotic potential of the population is
the growth in optimal conditions
• Anything that acts to control population
growth is called a limiting factor
– Limitations to food, water, space, or light
– Barriers to reproductive success
– Competition, predation, disease
– Climate change

12. Populations
• Carrying capacity
– The theoretical maximum number of
individuals in a population that can be
supported by that particular ecosystem
• The ability to support a population at a
particular level of abundance on a long-term
basis without incurring serious damage to the
ecosystem is sustainability
• Population stability
– Is in a steady state, at carrying capacity

13. Populations
• A period of rapid population increase is
called boom
– A booming population can overshoot the
carrying capacity of the ecosystem
• A sudden dieback, or bust, can result
from rapid resource depletion or from
overabundance of predators
• Boom and bust oscillation

14. Populations

15. Populations

16. Outline
• Populations
• Communities
• Biodiversity

17. Communities
• A community is a group of interacting,
interdependent organisms of different
species in the same environment
• There are three basic interactions
– Competitive relationships
– Exploitative relationships
– Mutualistic or symbiotic relationships

18. Communities
• Competitive relationships
– Individuals vie against each other for
scarce resources
– One of the main factors that controls
population in a community
– Related to the principle of natural selection
– Can be intraspecific or interspecific

19. Communities

20. Communities
• Exploitative relationships
– One organism exploits another for its own
gain, a relationship that is decidedly
beneficial to one and harmful to the other
– Parasitism
• One partner benefits (parasite) while the other
is harmed (host)
– Predation
• One organism (predator) eats the other (prey)

21. Communities

22. Communities
• Mutualistic relationships
– Species interacting in ways that are not
harmful to either
– Symbiosis and mutualism
• Relationships that are beneficial to both of the
organisms; different species living in close
physical contact, may involve coevolution
– Commensalism
• One partner benefits without affecting the other

23. Communities

24. Communities
• Ecosystems are open systems in which
species interact in immeasurably
complex ways
• A species that plays a fundamental role
in an ecosystem, or whose influence is
much greater than might be expected
given its abundance, is called a
keystone species

25. Communities

26. Communities
• The physical environment in which a
population or an organism lives or could live
is its habitat (its address)
• An organism’s functional role and use of
resources within a community is its niche (its
profession)
– The conditions in which species A occurs when it
has no competition from species B is called its
fundamental niche
– The conditions under which it persists in the
presence of species B is called its realized niche

27. Communities

28. Communities

29. Communities

30. Communities

31. Communities
• The competitive exclusion principle
– States that two species that have exactly the same
requirements cannot coexist in exactly the same
habitat and niche
• An invasive species
– An introduced or foreign species that outcompetes
and displaces native species
• To avoid direct competition, species specialize to
fill slightly different niches, this is niche
differentiation by resource partitioning

32. Communities

33. Communities

34. Communities

35. Communities
• The more species there are in different
niches, the greater the likelihood that some of
them will survive a catastrophe
• Generalists
– Species that have a wide range of tolerance and
occupy large, broadly defined niches
• Specialists
– Species with a narrower range of tolerance occupy
smaller, more narrowly defined niches
– Have more specific requirements for survival

36. Communities

37. Communities
• Speciation, the process whereby a new
species arises, depends on a sub-
population of an existing species becoming
reproductively isolated from the original
population
– Allopatric speciation
• Arises through complete geographic isolation
– Sympatric speciation
• Arises in the absence of any geographic barrier,
through reproductive isolation

38. Communities

39. Communities
• Species vulnerability
– On the basis of habitat and niche, and the
intrinsic and extrinsic factors that affect
population growth and stability, we can
begin to make predictions about which
species may be at greatest risk as a result
of environmental change

40. Outline
• Populations
• Communities
• Biodiversity

41. Biodiversity
• The richness and variety of species of
life forms is called biodiversity
• High diversity makes communities more
resilient, more able to adapt to change,
and more likely to withstand major
environmental upheavals

42. Biodiversity
• Genetic diversity
– Refers to the variability or heterogeneity
that is available among the DNA of
individuals within a population or species
– When a large population is descended
from just a few individuals, their genetic
diversity is extremely limited, this is called
a genetic bottleneck

43. Biodiversity

44. Biodiversity
• Habitat diversity
– Ecosystem diversity
– Refers to the variety of habitat types
available in an ecosystem, and the
biological richness and complexity of those
habitats
– Experts believe that preserving habitat
diversity is the key to preserving biodiversity

45. Biodiversity

46. Biodiversity

47. Biodiversity

48. Biodiversity

49. Biodiversity

50. Biodiversity
• Species diversity
– The number of species that live in specific
ecosystems
– Species richness
• Refers to the number of species in an
ecosystem or community
– Species evenness
• The relative abundance of individuals within
each species of a community

51. Biodiversity

52. Biodiversity

53. Biodiversity
• Endangered species
– A species in imminent danger of extinction
– Currently about 1500 in North America
– More than 16,000 worldwide
• Threatened species
– A species that has shown a significant
decrease in population or range, or shows
signs of imminent local extinction

54. Biodiversity

55. Biodiversity
• As many as 85% of endangered species
have been affected by the destruction of
their natural habitat
• Habitat fragmentation happens when
large tracts of natural area are broken up
into smaller patches by roads and other
disruptions
• Island biogeography provides insight into
the study of habitat fragmentation

56. Biodiversity

57. Biodiversity

58. Biodiversity
• Natural habitat and wilderness are under
increasing pressure from economic and
political forces that promote industrial
development, urbanization, and the
exploitation of natural lands and resources
• 6.4% of the world’s lands outside of
Antarctica is protected
• Protected areas are not always the same as
the areas that host the greatest
concentrations of biodiversity

59. Biodiversity

60. Biodiversity
• As people clear the land and modify th
environment, the diversity of habitats is
reduced and specialist species are impacted
• When a population drops too low or its
habitat has become too damaged, it may be
impossible for the species to endure on its
own in situ
– In these cases, preservation of the species is
though ex situ conservation like captive breeding

61. Biodiversity

62. Biodiversity
• There are two main arguments
concerning the value of biodiversity
– Utilitarian
• Based on the usefulness of the species and
biodiversity for humans
– The intrinsic value of species and
biodiversity

63. Biodiversity

64. Biodiversity
• Utilitarian (anthropocentric) arguments
– Medical and pharmaceutical
– Direct economic value
• Food, lumber…
– Recreational and tourism value
– Aesthetic value
– Ecological benefits and services

65. Biodiversity
• Intrinsic value arguments
– Deep ecology
– Holistic and integrated vision of the
environment in which the cumulative value
of species and ecosystems together is
worth incalculably more than individual
species considered separately

66. The Resource Cycle
The Blue Planet: Chapter 17

67. Outline
• Resources from the Earth System
• Renewable Resources: Seeking Balance
• Limits to Growth

68. Resources from the Earth System
• Human history and civilization are
inexorably linked to natural resources
– Renewable resources are replenished by
new growth each season
– Nonrenewable resources are renewed
naturally, but over millions of years

69. Resources from the Earth System

70. Resources from the Earth System

71. Resources from the Earth System

72. Resources from the Earth System
• The human economy is an open
system, driven by resources and energy
• However, these raw materials and
outputs of waste and pollution come
from and are disposed of in the closed
Earth system, which has limits
• Each stage in our resource cycle needs
management improvement

73. Resources from the Earth System

74. Resources from the Earth System

75. Resources from the Earth System
• Managing nonrenewable resources
– A resource’s stock is like the content of a
reservoir, the more used, the less remains
– Resources like copper and oil are not
replenished within a human timescale
– Availability can only be extended through
conservation, substitution, reuse or recycling

76. Resources from the Earth System

77. Resources from the Earth System
• Managing renewable resources
– Living resources like fish and trees are
renewable if managed properly
– When resources are used at a rate faster
than they replenish, they are depleted
– When used at exactly their replenishment
rate, the stock is at a steady state
– When renewable resources become
severely depleted, they can reach a point
where they will never regenerate

78. Resources from the Earth System

79. Outline
• Resources from the Earth System
• Renewable Resources: Seeking Balance
• Limits to Growth

80. Renewable Resources:
Seeking Balance
• Forest resources
– 95% are natural, 5% are plantations
– A forest that has endured hundreds or
thousands of years without human
intervention is an old-growth forest
– Timber, fuel, latex, nuts, fruits, oils and bush
meat are all forest products
– Trees also stabilize soil, provide it organic
matter, are important in the hydrologic
cycle, are an enormous carbon reservoir,
and harbor extensive biodiversity

81. Renewable Resources:
Seeking Balance

82. Renewable Resources:
Seeking Balance

83. Renewable Resources:
Seeking Balance
• Clear-cutting is the most economically
efficient way to harvest wood, but is the
most ecologically damaging
• More ecologically sound forest
management include
– Selective cutting
– Reduced-impact logging
– Agroforestry
• These focus on a replenishment and a
sustainable yield

84. Renewable Resources:
Seeking Balance

85. Renewable Resources:
Seeking Balance
• Deforestation: loss of forest cover
– The three remaining large expanses of
tropical rain forest are in South America
(Brazil), Central Africa (Congo), and
Southeast Asia (Indonesia)
– Results in loss of biodiversity and habitat
– Leaves soil susceptible to drying,
compaction, and erosion

86. Renewable Resources:
Seeking Balance

87. Renewable Resources:
Seeking Balance
• Wilderness: natural forests where
people do not live
– Protected areas, wildlife refuges
– Conservation: the conscientious
management of natural heritage and
resources
– Preservation: the maintenance of natural
wilderness areas in near-pristine condition

88. Renewable Resources:
Seeking Balance
• Fisheries resources
– Under increasing pressure from
overharvesting and environmental change
– Assessment of the resources is challenging
because it relies upon individual fishing
vessels to be truthful
– Capture fisheries account for the majority of
world production
– Atlantic cod were fished to commercial
extinction

89. Renewable Resources:
Seeking Balance

90. Renewable Resources:
Seeking Balance

91. Renewable Resources:
Seeking Balance
• Aquaculture
– The raising of fish, shellfish, crustaceans,
and aquatic plants in captivity
– Focuses on products that have high
economic value (salmon, shrimp)
– Can have significant environmental costs if
not properly managed
• Gene pool contamination
• Spread of disease
• Loss of coastal wetlands

92. Renewable Resources:
Seeking Balance

93. Renewable Resources:
Seeking Balance
• Soil resources
– Arable soil: soil that is suited for agriculture
– Crucial for the global food supply
– Soil needs fallow time to replenish nutrients
– Traditional agriculture had crop diversity in a
single field, modern trends to monoculture
– Soil is degraded by erosion, contamination,
compaction and loss of nutrients

94. Renewable Resources:
Seeking Balance

95. Renewable Resources:
Seeking Balance
• The green revolution
– Development of high-yield, disease-resistant
seed types through bioengineering
– Expansion of land use and irrigation, and use
of agrochemicals and fertilizers
– There are limits to these increases
– With global population growth, per capita
yield begins to stagnate and decline

96. Renewable Resources:
Seeking Balance

97. Renewable Resources:
Seeking Balance
• Erosion and loss of soil
– Erosion removes soil from agricultural land,
but moves it generally into a body of water
where it can clog or contaminate
– Tolerable annual rate of loss is a rate of
erosional loss that is balanced by
regeneration
– Management of fertile soil is imperative to
be able to feed a global population of 8-10
billion by the middle of the 21st century

98. Renewable Resources:
Seeking Balance
• Water resources
– Reliable fresh water is crucial for people,
ecosystems, industry, agriculture,
recreation, transportation, and fisheries
– Irrigation accounts for 75% of water demand
– Global water use has tripled since 1950
– Excessive groundwater withdrawal leads to
resource depletion as well as depression of
the water table, drying of springs, streams
and wells, compaction and subsidence

99. Renewable Resources:
Seeking Balance

100. Renewable Resources:
Seeking Balance

101. Renewable Resources:
Seeking Balance
• Irretrievable water consumption results
in lost water, water that is not returned
to the local hydrologic cycle
• A water-stressed region has supplies of
1000-2000 m3
per person
• A water-scarce region has <1000 m3
• 29 countries, 450 million people, suffer
from significant water shortages

102. Renewable Resources:
Seeking Balance

103. Renewable Resources:
Seeking Balance
• A mismatch between local supply and
demand of water leads to diversion and
inter-basin transfer
– Northern to southern California
– Aral Sea
• Issues around allocation and regulation
of water and water rights continue

104. Outline
• Resources from the Earth System
• Renewable Resources: Seeking Balance
• Limits to Growth

105. Limits to Growth
• It is difficult to know Earth’s carrying
capacity, or if we have surpassed it
• The guiding principle in renewable
resource management is sustainable
development
– Cautious, planned use of Earth resources
– Without degradation to ecosystems
– Without jeopardizing the future

106. Extras

107. Extras