Population Ecology Ch. 9

1
Population Ecology Ch. 9
2
Population Ecology Outline

• 9-1 Population Dynamics and Carrying Capacity
• 9-2 Reproductive Patterns and Survival
• 9-3 Effects of Genetic Variations n Pop. Size
• 9-4 Human Impacts and Working with Nature

3
9-1 Population Dynamics and Carrying Capacity

• Population - individuals of the same species,
  inhabiting the same area at the same time.
• Population Dynamics Population change due to
• Population Size - number of individuals
• Population Density - population size in a certain
  space at a given time
• Population Dispersion - spatial pattern in
  habitat
• Age Structure - proportion of individuals in each
  age group in population

4
Population Density

• Population Density (or ecological population
  density) is the amount of individuals in a
  population per unit habitat area
• Some species exist in high densities - Mice
• Some species exist in low densities - Mountain
  lions
• Density depends upon
• social/population structure
• mating relationships
• time of year

5
Population Dispersion

• Population dispersion is the spatial pattern of
  distribution. There are 3 main patterns of
  dispersion
• Clumped individuals are
• lumped into groups
• ex. Flocking birds or
• herbivore herds due to
• resources that are clumped
• or social interactions
• most common

http//www.johndarm.clara.net/galleryphots/
6
Population Dispersion
http//www.calflora.net/bloomingplants/creosotebus
h2.html
2) Uniform Individuals are regularly spaced in
the environment - ex. Creosote bush due to
antagonism between individuals. 3) Random
Individuals are randomly dispersed in the
environment ex. Dandelions due to random
distribution of resources in the environment, and
neither positive nor negative interaction between
individuals rare because these conditions are
rarely met
www.agry.purdue.edu/turf/ tips/2002/clover611.htm

7
Age Structure

• The age structure of a population is usually
  shown graphically.
• The population is usually divided up into
  
• Prereproductives (not mature enough to reproduce)
• reproductives (capable of reproduction)
• Postreproductives (too old to reproduce)
• The age structure of a population dictates
  whether is will grow, shrink, or stay the same
  size.

8
Age Structure Diagrams
Positive Growth Zero Growth
Negative Growth (ZPG) Pyramid
Shape Vertical Edges Inverted
Pyramid
9
Limits to Pop. Growth

• Biotic Potential- Ability of populations of a
  given species to increase in size
• Abiotic Growth Factors (biotic potential)
• Favorable Light conditions
• Favorable Temperatures
• Favorable Chemical environment optimal levels
  of nutrients
• Biotic Growth Factors
• High reproductive rate
• Generalized niche
• Ability to migrate or disperse
• Adequate defense mechanisms against predators
• Ability to cope with adverse conditions
  migration, resistance to diseases, adapt to evtl.
  changes, etc.

10
Biotic Potential continued

• Intrinsic rate of increase (r) rate at which a
  pop. could grow if it had UNLIMITED resources.
• Not realistic!
• No pop. can grow indefinitely due to factors that
  will slow growth eventually.

11
Limits to Pop. Growth continued

• Environmental Resistance- all the factors that
  can limit the growth and size of pops.
• Abiotic Decreasing Factors
• Unfavorable light conditions too little or too
  much
• Unfavorable Temperatures
• Unfavorable chemical environment - nutrients
• Biotic Decreasing Factors
• Low reproductive rate
• Specialized niche
• Inability to migrate or disperse
• Too many competitiors
• Inadequate defense mechanisms
• Inability to cope with adverse conditions- not
  resistance to disease or unable to adapt to
  envtl. changes

12
Environmental Resistance continued

• There is a dynamic balance between biotic
  potential and environmental resistance.
• Carrying capacity (K) - maximum number of
  individuals a habitat can support over a given
  period of time due to environmental resistance
  (sustainability)

13
(No Transcript)
14
(No Transcript)
15
Population Change and Carrying Capacity

• Basic Concept
• Over a long period of time, populations of
  species in an ecosystem are usually in a state of
  equilibrium (balance between births and deaths)

16
Measuring Pop. Growth

• Population growth depends upon
• birth rates
• death rates
• immigration rates (into area)
• emigration rates (exit area)
• Pop. change (b i) - (d e)

17
Population Growth Diagrams

• Populations show two types of growth
• Exponential
• J-shaped curve
• Growth is independent of population density
• Logistic
• S-shaped curve
• Growth is not independent of population density

18
Exponential growth (J curve)

• Fixed rate of increase, starting slowly and
  growing rapidly
• Exponential curve is not realistic for long
  periods of time, due to carrying capacity of area.

19
Logistic Growth (S curve)

• Because of environmental resistance, population
  growth decreases as density reaches carrying
  capacity
• Graph of individuals vs. time yields a sigmoid or
  S-curved growth curve
• Reproductive time lag causes population overshoot
• Population will not be steady curve due to
  resources (prey) and predators

20
(No Transcript)
21
(No Transcript)
22
Density-Dependent Controls

• Competition for resources
• Predation
• Parasitism
• Disease

23
Density-Independent Controls

• Natural disasters
• Severe weather
• Pollution
• Pesticide spraying

24
9-2 Reproductive Patterns and Survival

• Goal of every species is to produce as many
  offspring as possible!
• Each individual has a limited amount of energy to
  put towards life and reproduction
• This leads to a trade-off of long life or high
  reproductive rate
• Natural Selection has lead to two strategies for
  species r - strategists and K - strategists

25
r - Strategists

• Spend most of their time in exponential growth
• Maximize reproductive life
• Minimum life

K
26
r - Strategists

• 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

27
K - Strategists

• Maintain population at carrying capacity (K)
• Maximize lifespan

K
28
K- Strategist

• 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

r and K strategists summary animation
29
Survivorship Curves

• Late Loss (Type I) K-strategists that produce
  few young and care for them until they reach
  reproductive age thus reducing juvenile mortality
• Constant Loss (Type II) typically intermediate
  reproductive strategies with fairly constant
  mortality throughout all age classes
• Early Loss (Type III) r-strategists with many
  offspring, high infant mortality and high
  survivorship once a certain size and age

30
Population Growth Self Quiz!
Late Loss
Constant Loss
Early Loss
31
9-3 Effects of Genetic Variations in Pop. Size

• Variations in genetic diversity can affect
  small, isolated populations. Most large pops.
  genetic diversity remains fairly constant.
• Genetic variations that can affect small
  populations could include
• Founder effect few individ. colonize a new area
  thats geographically isolated from others in the
  population
• Demographic Bottleneck effect When a pop. is
  destroyed by natural disaster, and only a few
  individs. Survive May lack genetic diversity to
  carry on and rebuild population.
• Genetic drift random changes in genes
  frequencies that could lead to unequal
  reproductive success founder effect could cause
  genetic drift
• Inbreeding when individuals of small pops. mate
  and could increase likelihood of passing on
  defective genes to offspring and affect long term
  survival.

32
Genetic changes in a pop. due to the Bottleneck
effect
Genetic Drift
33
9-4 Human Impacts and Working with Nature

• Nine major ways humans impact the environment to
  meet OUR needs and wants
• Fragmentation, degrading and destroying habitats
• Simplifying/ homogenizing natural ecosystems (1
  crop)
• Using, wasting and destroying NPP that support
  all consumers.
• Strengthening some populations of pest species
  and disease-causing bacteria by overuse of
  pesticides
• Elimination of some predators (sharks)
• Deliberately or accidentally introducing new
  species (exotic)
• Overharvesting potentially renewable resources
  (farmland, fish)
• Interfering with the normal chemical cycling and
  energy flows in ecosystem (excessive CO2
  emissions)
• Increasingly more dependent on nonrenewable
  energy (fossil fuels)

34
Working with NaturePrinciples of Sustainability

• To maintain a balance between our altered
  environments and natural environments, we need to
  learn the important features of nature.
• Nature sustains itself through
• (diagram on back cover of book!)
• Uses of unlimited solar energy
• Biodiversity
• Nutrient recycling
• Population Control

35
Ecological Principles for Sustainability(Message
of the book and this class! )

1. We are part of, not apart from, the earths
   dynamic web of life.
2. Our lives, lifestyles, and economies are totally
   dependent on the sun and the earth.
3. We can never do merely one thing (first law of
   human ecology Garret Hardin).
4. Everything is connected to everything else we
   are all in it together.