Population Ecology

1
Population Ecology

• Asim Zia
• Introduction to Environmental Issues
• EnvS 001, Spring 2007
• Department of Environmental Studies
• San Jose State University

2
Chapter 8 Overview Questions

• What are the major characteristics of
  populations?
• How do populations respond to changes in
  environmental conditions?
• How do species differ in their reproductive
  patterns?

3
Core Case Study Southern Sea Otters Are They
Back from the Brink of Extinction?

• They were over-hunted to the brink of extinction
  by the early 1900s and are now making a
  comeback.

Figure 8-1
4
Core Case Study Southern Sea Otters Are They
Back from the Brink of Extinction?

• Sea otters are an important keystone species for
  sea urchins and other kelp-eating organisms.

Figure 8-1
5
POPULATION DYNAMICS AND CARRYING CAPACITY

• Most populations live in clumps although other
  patterns occur based on resource distribution.

Figure 8-2
6
Changes in Population Size Entrances and Exits

• Populations increase through births and
  immigration
• Populations decrease through deaths and
  emigration

7
Age Structure Young Populations Can Grow Fast

• How fast a population grows or declines depends
  on its age structure.
• Prereproductive age not mature enough to
  reproduce.
• Reproductive age those capable of reproduction.
• Postreproductive age those too old to reproduce.

8
Limits on Population Growth Biotic Potential
vs. Environmental Resistance

• No population can increase its size indefinitely.
• The intrinsic rate of increase (r) is the rate at
  which a population would grow if it had unlimited
  resources.
• Carrying capacity (K) the maximum population of
  a given species that a particular habitat can
  sustain indefinitely without degrading the
  habitat.

9
Exponential and Logistic Population Growth
J-Curves and S-Curves

• Populations grow rapidly with ample resources,
  but as resources become limited, its growth rate
  slows and levels off.

Figure 8-4
10
Exponential and Logistic Population Growth
J-Curves and S-Curves

• As a population levels off, it often fluctuates
  slightly above and below the carrying capacity.

Figure 8-4
11
Exceeding Carrying Capacity Move, Switch Habits,
or Decline in Size

• Members of populations which exceed their
  resources will die unless they adapt or move to
  an area with more resources.

Figure 8-6
12
How Would You Vote?

• To conduct an instant in-class survey using a
  classroom response system, access JoinIn Clicker
  Content from the PowerLecture main menu for
  Living in the Environment.
• Can we continue to expand the earth's carrying
  capacity for humans?
• a. No. Unless humans voluntarily control their
  population and conserve resources, nature will do
  it for us.
• b. Yes. New technologies and strategies will
  allow us to further delay exceeding the earth's
  carrying capacity.

13
Population Density and Population Change Effects
of Crowding

• Population density the number of individuals in
  a population found in a particular area or
  volume.
• A populations density can affect how rapidly it
  can grow or decline.
• e.g. biotic factors like disease
• Some population control factors are not affected
  by population density.
• e.g. abiotic factors like weather

14
Types of Population Change Curves in Nature

• Population sizes may stay the same, increase,
  decrease, vary in regular cycles, or change
  erratically.
• Stable fluctuates slightly above and below
  carrying capacity.
• Irruptive populations explode and then crash to
  a more stable level.
• Cyclic populations fluctuate and regular cyclic
  or boom-and-bust cycles.
• Irregular erratic changes possibly due to chaos
  or drastic change.

15
Types of Population Change Curves in Nature

• Population sizes often vary in regular cycles
  when the predator and prey populations are
  controlled by the scarcity of resources.

Figure 8-7
16
Case Study Exploding White-Tailed Deer
Populations in the United States

• Since the 1930s the white-tailed deer population
  has exploded in the United States.
• Nearly extinct prior to their protection in
  1920s.
• Today 25-30 million white-tailed deer in U.S.
  pose human interaction problems.
• Deer-vehicle collisions (1.5 million per year).
• Transmit disease (Lyme disease in deer ticks).

17
REPRODUCTIVE PATTERNS

• Some species reproduce without having sex
  (asexual).
• Offspring are exact genetic copies (clones).
• Others reproduce by having sex (sexual).
• Genetic material is mixture of two individuals.
• Disadvantages males do not give birth, increase
  chance of genetic errors and defects, courtship
  and mating rituals can be costly.
• Major advantages genetic diversity, offspring
  protection.

18
Sexual Reproduction Courtship

• Courtship rituals consume time and energy, can
  transmit disease, and can inflict injury on males
  of some species as they compete for sexual
  partners.

Figure 8-8
19
Reproductive PatternsOpportunists and
Competitors

• Large number of smaller offspring with little
  parental care (r-selected species).
• Fewer, larger offspring with higher invested
  parental care (K-selected species).

Figure 8-9
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Reproductive Patterns

• r-selected species tend to be opportunists while
  K-selected species tend to be competitors.

Figure 8-10
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Survivorship Curves Short to Long Lives

• The way to represent the age structure of a
  population is with a survivorship curve.
• Late loss population live to an old age.
• Constant loss population die at all ages.
• Most members of early loss population, die at
  young ages.

22
Survivorship Curves Short to Long Lives

• The populations of different species vary in how
  long individual members typically live.

Figure 8-11