Population Ecology

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Population Ecology
G. Tyler Millers Living in the Environment 14th
Edition Chapter 9 Pages 163-174
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Key Concepts

• Factors affecting population size

• Species reproductive patterns

• Species survivorship patterns

• Conservation biology and human impacts on
  ecosystems

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CASE STUDY Sea Otters

• live in kelp forests
• eat sea urchins
• hunted in 1900s
• 1977 declared endangered
• Increased from 300 to 2800
• keystone species
• ? protect kelp forest

OMG
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9-1 Population Dynamics and Carrying Capacity
OBJ 9.1

• Population dynamics
• study of how populations change in size, density,
  and age distribution
• populations respond to their environment
• change according to distribution

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Factors Governing Changes in Population Size
OBJ 9.2

• Four variable
• births, deaths, immigration and emigration
• Population Change (births immigration)
  (deaths emigration)

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Age Structure Stages

• PREREPRODUCTIVE AGE
• - Not mature enough to reproduce
• REPRODUCTIVE AGE
• - Capable of reproducing
• POSTREPRODUCTIVE AGE
• - too old to reproduce

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LIMITING FACTOR
OBJ 9.3
DEFINITION anything that tends to make it more
difficult for a species to live and grow, or
reproduce in its environment
ABIOTIC - temperature - water -
climate/weather - soils (mineral component)
BIOTIC - competition  interspecific and
intraspecific - predation/parasitism -
amensalism - mutualism
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LIMITS TO POPULATION GROWTH Resources
Competition
Biotic potential capacity for growth Intrinsic
rate of increase (r) rate at which a population
would grow if it had unlimited resources Environme
ntal resistance all factors that act to limit
the growth of a population Carrying Capacity (K)
maximum of individuals of a given species that
can be sustained indefinitely in a given space
(area or volume)
Fig. 9-3 p. 166
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Exponential and Logistic Growth
OBJ 9.4
LOGISTIC GROWTH - Rapid exp. growth followed by
steady dec. in pop. Growth w/time until pop. Size
levels off

• EXPONENTIAL GROWTH
• Population w/few resource limitations grows at a
  fixed rate

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OBJ 9.5
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Population Density Effects
OBJ 9.6

• Density-independent controls
• - floods, hurricanes, unseasonable weather,
  fire, habitat destruction, pesticide spraying,
  pollution
• - EX Severe freeze in spring can kill plant
  pop. regardless of density

• Density-dependent controls
• - competition for resources, predation,
  parasitism, infectious diseases
• - EX Bubonic plague swept through European
  cities in 14th century

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Natural Population Curves
OBJ 9.7
Fig. 9-7 p. 168
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• STABLE
• pop. Size fluctuates above or below its carrying
  capacity
• Stable population size
• EX undisturbed tropical rain forests
• IRRUPTIVE
• pop. Growth occasionally explodes to a high peak
  then crashes to stable low level
• EX Algae, insects
• CYCLIC
• Fluctuations occur in cycles over a regular time
  period
• EX Lynx snowshoe hare
• IRREGULAR
• No recurring pattern in changes of population
  size

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The Role of Predation in Controlling Population
Size
OBJ 9.8

• Bottom-up control
• - the hare pop. may cause changes in lynx pop.

• Top-down control
• - lynx preying on hares periodically reduce the
  hare pop.

Fig. 9-8 p. 168
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How do Species Reproduce

• ASEXUAL REPRODUCTION
• all offspring are exact genetic copies of a
  single parent
• Common in single celled species (bacteria)
• Each cell divides to produce 2 identical cells
• SEXUAL REPRODUCTION
• Organisms produce offspring by combining sex
  cells or gametes from both parents
• Produces offspring with combination of genetic
  traits from each parent
• Provides greater genetic diversity in offspring
• DISADVANTAGES
• Males do not give birth
• Increased chance of genetic errors and defects
• Courtship mating rituals consume time energy
  and transmit diseases

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Reproductive Patterns and Survival
OBJ 9.10

• r-selected species vs. K-selected species

Fig. 9-10 p. 170
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Survivorship Curves
OBJ 9.11

• Shows the of members in a pop. Surviving at
  different ages

• LATE LOSS
• High survivorship to certain age then high
  mortality
• EX elephants, rhinos, humans
• CONSTANT LOSS
• Fairly constant death rate at all ages
• EX songbirds
• EARLY LOSS
• Survivorship is low early in life
• EX annual plants, bony fish sp.

Fig. 9-11 p. 171
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Human Impacts on Ecosystems

• Habitat degradation and fragmentation

• Ecosystem simplification

• Genetic resistance

• Predator elimination

• Introduction of non-native species

• Overharvesting renewable resources

• Interference with ecological systems

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