Chapter 9: Population Dynamics, Carrying Capacity, and Conservation Biology

1
Chapter 9 Population Dynamics, Carrying
Capacity, and Conservation Biology

• AP Environmental Science

2
Characteristics of Population

• Size (number of individuals)
• Density (number of individuals in a certain
  space)
• Dispersion (spatial pattern such as clumping,
  uniform, or random)
• Age Distribution (proportion of individuals of
  each age in a population)

3
Population Dynamics Occur in Response To

• Environmental Stress
• Changes in Environmental Conditions

4
Population Change

• Population Change (births immigration) -
  (deaths emigration)
• These variables depend on changes in resource
  availability or other environmental change.

5
What Limits Population Growth?

• Biotic Potential - a populations capacity for
  growth
• Intrinsic Rate of Increase (r) - the rate at
  which a population would grow if it had unlimited
  resources.
• Those that have a high intrinsic rate
• Reproduce early in life
• Have short generation times
• Can reproduce many times
• Have many offspring each time they reproduce
• Environmental Resistance - includes all of the
  factors acting together to limit the growth if it
  had unlimited resources.

6
What is Carrying Capacity?

• The population species in a given place and time
  is determined by its biotic potential and
  enviornmental resistance.
• Carrying Capacity - the number of individuals of
  a given species that can be sustained
  indefinitely in a given space (area or volume)
• Minimum Viable Population (MVP)
• Individuals need to find mates without
  interbreeding
• Provides opportunities for adaptation to new
  environmental conditions

7
Exponential Population Growth

• Occurs when a population has few if any resource
  limitations
• Starts out slowly and then proceeds faster and
  faster as the population increases - double time!
• Yields a J-shaped curve

8
Logisitic Population Growth

• Involves exponential population growth, but when
  exposed to environmental resistance and/or the
  carrying capacity, it levels off
• Yields a S-shaped curve

9
Exceeding the Carrying Capacity

• Overshoots or exceeds the carrying capacity of
  the environment
• Caused by a reproductive time lag - the period
  needed for the birth rate to fall and the death
  rate to rise in response to resource
  overconsumption
• Dieback or crash unless excess individuals move
  or switch to new resources

10
Carrying Capacity Can Be Affected By...

• Competition within and between species
• Immigration and Emigration
• Nature and human-caused events
• Seasonal fluctuations in the supply of food,
  water, hiding places, and nesting sites
• Technology, social and cultural changes

11
Density - Independent Population Controls

• Affect a population size regardless of its
  density
• Floods
• Fires
• Hurricanes
• Unseasonable Weather
• Habitat Destruction
• Pesticide Spraying

12
Density - Dependent Population Controls

• Have a greater effect as the populations density
  increases
• Competition for resources
• Predation
• Parasitism
• Disease

13
Population Curves In Nature

• Stable - a species who population size fluctuates
  slightly above and below its carrying capacity
• Irruptive - species who have normally stable
  populations that may occasionally explode or
  irrupt to a high peak and then crash to a more
  stable lower level
• Explosions caused by favorable weather, more
  food, fewer predators
• Irregular - no recurring pattern
• Cyclic - cycles of population size over a regular
  time period
• Lemmings - populations rise and fall every 3 - 4
  years

14
Top-Down Control Hypothesis

• The top-predator controls the population
• Lynx preying on hares reduce their population
• The shortage of hares reduces the lynx population
• The hare population builds up again
• The lynx population builds up again due to the
  increased hares
• Hares have been shown to have this cycle when
  there arent any lynx around
• Wolves controlling deer and moose populations
• Large predator fish controlling other fish
  populations

15
Bottom-Up Control Hypothesis

• Controlled by the bottom of the food web
• Hares consume too many plants
• Create a decrease in the quality and quantity of
  their food supply
• Once the hare population crashes, the plants
  recover, and then the hare population rises again

16
Reproductive Patterns and Survival

• Asexual Reproduction
• Sexual Reproduction
• Ecological Costs and Risks
• Females need to produce twice as many to maintain
  the same number of young as asexually reproducing
  organisms
• Genetic errors and defects
• Mating entails cost, time, injury, delay
• Why use it?
• More genetic diversity
• Males can help the females

17
R-Selected Species

• Have a capacity for a high intrinsic rate of
  increase (r)
• Reproduce early
• Most energy goes into reproduction
• Have many, small offspring
• Short generation times
• No parental care or protection
• Short lived lives
• Opportunists! --gt the reproduce and disperse
  rapidly when conditions are favorable or when a
  disturbance opens up
• Bacteria, rodents, annual plants, insects

18
K-Selected Species

• Tend to do little when in competitive situations
  when their population size is nearing the
  carrying capacity
• Put little energy into reproduction
• Tend to reproduce late in life mature slowly
• Few offspring with long generation times
• Put most of their energy into nurturing and
  protecting their young
• Develop inside their mothers
• Cared for by one or both parents
• Follow a logistic growth curve
• Large mammals, birds of prey, large and
  long-lived plants
• Prone to extinction
• Thrive best in constant ecosystem

19
Survivorship Curves

• Shows the number of survivors of each age group
  for a particular species
• Late Loss Curves - typical for K-selected
  species few young and care for them until
  reproductive age
• Early Loss Curves - typical for R-selected
  species have many offspring, high rate of
  juvenile mortality, and high survivorship once
  the surviving young reach a certain age and size
• Constant Loss Curves - typical for intermediate
  reproductive patterns constant rate of mortality
  in all age classes
• Life Table - shows the number of individuals at
  each age from a survivor ship curve
• Projected life expectancy and probability of
  death for each age

20
Conservation Biology

• A multi-disciplinary science that uses the best
  available science to take action to preserve
  species and ecosystems
• Species in extinction?
• Status of functioning ecosystems and what
  ecosystem services are we in danger or losing?
• What measures can be taken to sustain ecosystem
  functions and populations of wild species?
• Bioinformatics

21
Modifying Ecosystems

• Fragmented and degraded habitat
• Simplified natural ecosystems
• Using, wasting, destroying NPP
• Strengthing some pest species
• Eliminate some predators
• Deliberately or accidentally introducing new or
  nonnative species
• Overharvesting renewable resources
• Interfering with the normal chemical cycling and
  energy flow

22
Challenges

• Maintain a balance between simplified,
  human-altered ecosystems and more complex natural
  ecosystems
• Slow down the rates at which we are altering
  nature for our purpose

23
How can we learn from nature about living more
sustainably?

• Learn about the process and adaptation by which
  nature sustains itself
• Lives are dependent on the sun and the earth
• Everything is connected to everything else
• We can never do merely one thing
• We should limit the damage we cause
• We should use care, restraint, humility, and
  cooperation with nature