Population Dynamics

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Population Dynamics

• Chapter 8

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Sea Otter the other, other white meat

• Why are sea otters considered keystone species?
• They control urchin populations which feed on
  kelp, hence they keep the kelp forests healthy
• Why did their populations decline?
• Originally due to hunting, now chemical pollution
  is suspected

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Characteristics of a population

• Size number of organisms
• Density number /space
• Dispersion spatial distribution
• Age distribution pre-breeding, breeding, or
  post breeding age
• Population dynamics how these factors change
  due to environmental stresses

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Population growth

• Population change (growth) (births
  immigration) (deaths emigration)
• ZPG zero population growth is when incoming
  equals outgoing
• Biotic potential max growth for that particular
  population
• Intrinsic rate of increase rate of growth with
  unlimited resources

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High intrinsic growth rates

• Reproduce early in life
• Have short time between generations
• Reproduce many times
• Have many offspring each time
• Roaches, mice, fish, flies

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Environmental Resistance

• These are the vast assortment of environmental
  factors which help keep populations from growing
  out of control
• This is a way a population finds an equilibrium
  point

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Fig. 9.3, p. 200
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Carrying capacity

• Biotic potential and environmental resistance
  will determine the population a given area can
  hold and sustain indefinitely
• A population must not drop below the minimum
  viable population or lowest number needed to keep
  population from disappearing due to environmental
  resistance

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2.0
1.5
Number of sheep (millions)
1.0
.5
1800
1825
1850
1875
1900
1925
Fig. 9.5, p. 201
Year
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Logistic growth

• Exponential growth (J curve) is not possible
  forever because resources and space eventually
  run out. When a population reaches a certain
  point, environmental resistance increases causing
  the population size to stabilize. This is known
  as logistic growth (s curve) and this generally
  happens to all populations

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K
Population size (N)
Population size (N)
Time (t)
Time (t)
Exponential Growth
Logistic Growth
Fig. 9.4, p. 201
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Can you overshoot your carrying capacity?

• Absolutely, it happens all the time
• When you have too many individuals for the area
  to support you will have a population crash
• If the overshoot was not too drastic, and the
  crash was small the population re-stabilizes

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Types of population curves

• Stable nearly flat line
• Irregular widely fluctuating pattern with no
  periodicity
• Cyclic regular growth and crash at set
  intervals, usually seasonal
• Irruptive normally stable, but with a random
  spike or crash

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Irregular
Stable
Number of individuals
Cyclic
Irruptive
Time
Fig. 9.7, p. 202
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Top-down or bottom-up?

• Evidence seem to show both happening
• Top-down predators hunt and kill prey keeping
  their population stable
• Bottom-up prey are the food source that allow
  predators to keep the populations up

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Types of reproduction

• Asexual cloning, single parent donates both
  parts of DNA (bacteria)
• Sexual two parents donate DNA
• Females have to give birth more (males do not as
  in asexual)
• More genetic errors from combining
• Mating is more damaging, and energy intensive
• Does provide more genetic diversity, hence a
  stronger species

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R-selected species

• Also known as r-strategists and fill generalist
  niche
• Have many offspring
• Reach reproductive age early
• Short time between generations
• Little to no parental care and adapted to
  unstable climate (low survivorship)
• Short life span (usually under a year)
• Algae, rodents, bacteria, annual plants and
  insects

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r-Selected Species
cockroach
dandelion
Many small offspring Little or no parental care
and protection of offspring Early reproductive
age Most offspring die before reaching
reproductive age Small adults Adapted to
unstable climate and environmental
conditions High population growth rate
(r) Population size fluctuates wildly above and
below carrying capacity (K) Generalist niche Low
ability to compete Early successional species
Fig. 9.10a, p. 205
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K-selected species

• K-strategists or competitors, specialist niche
• Fewer, larger offspring (usually develop inside)
• Mature slowly (often protected while vulnerable)
• Lower population growth rate
• Long lived with stable population near carrying
  capacity
• Depend heavily upon suitable habitat
• Large mammals, birds of prey, long lived plants
  such as oaks, redwoods, some cacti

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K-Selected Species
elephant
saguaro
Fewer, larger offspring High parental care and
protection of offspring Later reproductive
age Most offspring survive to reproductive
age Larger adults Adapted to stable climate and
environmental conditions Lower population growth
rate (r) Population size fairly stable and
usually close to carrying capacity
(K) Specialist niche High ability to compete Late
successional species
Fig. 9.10b, p. 205
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Survivorship curve

• Late loss - typical for k-strategists
• Early loss typical for r-strategists
• Constant loss for species in the gray area
  in-between k and r strategists with intermediate
  reproductive patterns
• Song birds, lizards, and small mammals

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Fig. 9.11, p. 206
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Conservation biology

• Sensible use of natural resources
• Originated in 1970s uses current science
• Investigate human impact on the biodiversity
• Develop practical approaches to maintain
  biodiversity
• Maintain endangered species, wildlife reserves,
  ecological restoration, ecological economics,
  environmental ethics

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Assumptions of conservation bio

• Biodiversity is necessary
• Humans should not affect extinction or vital
  environmental processes
• Protecting ecosystems is the best way to protect
• Based on Aldo Leopolds ethical principle, that
  if we maintain the earths life-support system it
  is appropriate

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Human impact on ecosystems

• Fragmentation breaking up large tracts with
  roads, fences, towns, etc.
• Habitat loss/degradation pollution, lumber,
  mining, etc.
• Simplifying ecosystems lower biodiversity
  through habitat change (monocultures)
• Strengthening species pesticide use, antibiotics

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Human impact continued

• Predator elimination wolves, coyotes, bear,
  etc.
• Introduce alien species
• Overharvest potentially renewable resources
  trees, soil, other biomass (grasses, nuts, etc)
• Interfere with natural chemical cycling clear
  cutting, monocultures, pesticides (we kill and
  simplify a system)

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Way to go humans!! Youre the best!

• Goals for the future (if we want to be a part of
  it)
• Maintain balance between human impacted simple
  ecosystems and natural rich ecosystems
• Slow down rates at which we alter nature for our
  own purpose
• Realize that we never do merely one thing,
  everything is interdependent and unpredictable

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How can you help

• Use consumer power buy products that are
  friendly to the environment
• Use voting power elect officials that will
  strive to protect the environment
• Educate most people have no idea about the
  consequences of their actions
• Identify mother culture that says spend, buy,
  consume and learn to tune it out
• Exploit nature for its aesthetics and renewable
  resources

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Thats all folks

• Have a nice day