Population Ecology

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Population Ecology
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Definition of Population

• Group of individuals of a single species living
  in a specific geographic region at the same time

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Study of populations in relation to environment

• Environmental influences on
• population density
• age structure
• population distribution (dispersion)

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• Density is the result of a dynamic interaction of
  
• processes that add individuals to a population
  and those that remove individuals from it

• How do these factors
• Contribute to Population Size??
• Births
• Deaths
• Immigration
• Emigration

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Clumped Dispersion

• Individuals aggregate in patches
• May be influenced by resource availability and
  behavior

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Uniform Dispersion

• Individuals are evenly distributed
• May be influenced by social interactions such as
  territoriality

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Random Dispersion

• Position of each individual is independent of
  other individuals

(c) Random. Dandelions grow from windblown seeds
that land at random and later germinate.
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How do wildlife biologists quantify populations?
Defined Populations -complete counts -incomplete
counts -indirect counts
Undefined Populations
Mark and Recapture
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Life history traits are products of natural
selection

• Life history traits are evolutionary outcomes
• Reflected in the development, physiology, and
  behavior of an organism
• Three things needed quantify life history
• When reproduction begins
• How often organism reproduces
• How many offspring produced

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Semelparity Big Bang

• Reproduce a single time and die
• putting all available resources into maximizing
  reproduction at the expense of future life 

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Iteroparity Repeated Reproduction

• produce offspring repeatedly over time
• increased parental care along with enhanced
  energetic investment per offspring

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Trade-offs and Life Histories

• Organisms have finite resources

• Which may lead to trade-offs between survival and
  reproduction

RESULTS

• Kestrels
• Produce a few eggs?
• Can invest more into each, ensuring greater
  survival
• Produce many eggs?
• Costly but if all survive, fitness is better

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More is Better?

• Some plants produce a large number of small seeds
• Ensuring that at least some of them will grow and
  eventually reproduce

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Fewer is Better?

• Other types of plants produce a moderate number
  of large seeds
• That provide a large store of energy that will
  help seedlings become established

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Demography

• Study of the vital statistics of a population
• And how they change over time
• Death rates and birth rates
• Zero population growth
• Occurs when the birth rate equals the death rate

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Exponential Population Growth

• Population increase under idealized conditions
• No limits on growth
• Under these conditions
• The rate of reproduction is at its maximum,
  called the intrinsic rate of increase

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Example-understanding growth
Question I offer you a job for 1 cent/day and
your pay will double every day. You will be
hired for 30 days. Will you take my job offer?
Answer If you said YES, you will have made 21
million dollars for 30 days of work. How is
this possible?????
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1ST DAY OF WORK 1 cent pay/day
30TH DAY OF WORK 10.2 million/day
How is this possible?????
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Exponential Growth Model
Idealized population in an unlimited environment
Very rapid doubling time steep J curve
r?N(b-d)N ?t rinstrinsic rate of growth
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Exponential Growth in the Real World

• Characteristic of some populations that are
  rebounding

• Cannot be sustained for long in any population

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Logistic Population Growth

• More realistic model of population growth
• Carrying capacity (K)
• Is the maximum population size the environment
  can support

• In the logistic population growth model
• The per capita rate of increase declines as
  carrying capacity is reached

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Logistic Population Growth

• Produces a sigmoid (S-shaped) curve

Figure 52.12
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The Logistic Model and Real Populations

• The growth of laboratory populations of
  Paramecium
• Fits an S-shaped curve

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Logistic Growth and The Real World

• Some populations overshoot K
• Before settling down to a relatively stable
  density

What type of feedback loop is this?
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Logistic Growth and the Real World

• Some populations
• Fluctuate greatly around K

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Natural selection (diverse reproductive
strategies) a) Relatively few, large offspring (K
selected species) b) Many, small offspring (r
selected species)
(K selected species)
(r selected species)
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Populations Regulated Biotic and Abiotic Factors

• Two general questions we can ask about regulation
  of population growth

• What environmental factors stop a population from
  growing?
• 2. Why do some populations show radical
  fluctuations in size over time, while others
  remain stable?

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Competition for Resources

• In crowded populations, increasing population
  density
• Intensifies intraspecific competition for
  resources

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• Many vertebrates and some invertebrates are
  territorial
• Territoriality may limit density

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Territoriality Ocean birds

• Exhibit territoriality in nesting behavior

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Health
Population density- Can influence the health and
survival of organisms In dense populations,
pathogens can spread more rapidly
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Fluctuations in Population Size

• Extreme fluctuations in population size
• Are typically more common in invertebrates than
  in large mammals

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Population Cycles

• Many populations undergo regular boom-and-bust
  cycles

• Influenced by complex interactions between biotic
  and abiotic factors

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Human Populations

• No population can grow indefinitely and humans
  are no exception

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Global Carrying Capacity

• Just how many humans can the biosphere support?
• Carrying capacity of earth is unknown.

http//www.youtube.com/watch?v9_9SutNmfFk
http//www.youtube.com/watch?vUUOEcNomakwfeature
rec-LGOUT-exp_freshdiv-1r-8-HM
http//www.youtube.com/watch?v4B2xOvKFFz4feature
related
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• Age structure is commonly represented in pyramids

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Infant Mortality and Life Expectancy

• Infant mortality and life expectancy at birth
• Vary widely among developed and developing
  countries but do not capture the wide range of
  the human condition

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Search for the Missing Sea Otters

• Case Study in Population Community Ecology

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Sea OttersEnhydra lutris
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Otter Behavior
http//www.youtube.com/watch?vdQ2Lrnr0gLc
http//www.youtube.com/watch?vYQXKyTWMvpM
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Population Distribution
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(No Transcript)
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GROUP QUESTION 1) What is happening to sea otter
populations at several locations in the Aleutian
Islands, Alaska? 2) What factors could be
contributing to such a rapid change in the size
of sea otter populations? Create a list of
possible factors.
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Could the otters simply have migrated from one
part of the region to another? To find out, the
researchers analyzed populations over a
500-mile-long stretch of the Aleutians from Kiska
to Seguam . By 1993 otter numbers in that whole
stretch had been cut by half. Here the
geographical scope of the research effort became
critical a smaller region would not have been
large enough to reveal the decline. In 1997, they
found that the population decline had worsened,
to about 90 percent . That told us for sure it
was a very large-scale decline, but we were still
trying to understand the cause, Dr. Estes said
. The researchers ruled out reproductive
failure. Their studies enabled them to keep track
of how often otters gave birth and how many young
survived, and this revealed that reproduction was
continuing to re-supply the population. With
other possible causes eliminated, mortality had
to be the explanation. In the past, they had seen
temporary declines in otter populations because
of starvation, pollution or infectious disease.
In all those cases, Dr. Estes said, we find
lots of bodies. They get weak and tired and come
ashore to die. This time not a single dead otter
was founda clue, he said, that something really
weird was going on. (Excerpted from Stevens,
William K. Search for missing sea otters turns
up a few surprises. New York Times, January 5,
1999.)
Group Question Read above and eliminate some of
the reasons for changes in the relative abundance
of sea otters at several locations in the
Aleutian Islands, Alaska? What does it have to
be?
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Orca or Killer WhaleOrcinus orca
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Male vs. Female
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Orca prey
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Orca predation behavior
https//www.youtube.com/watch?vypNg19etJg0
http//www.youtube.com/watch?vKs40worW_gQ
(hunting sea lions)
Orcas learned hunting behavior? (great white
sharks??) http//www.youtube.com/watch?vSS6NjdG
LVZsfeaturerelated
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Group Questions

1. Make a list of the types of information about
   killer whales you believe the scientists might
   need to test their hypothesis that increased
   predation by the whales was the cause of the sea
   otter decline.
2. Describe two experiments that would allow you to
   test the hypothesis that increased predation by
   killer whales was the cause of the sea otter
   decline. Keep in mind the following key
   components of any good experiment a control
   (something to which to compare the treatment),
   replication (do it more than once), and
   consideration of confounding factors (what might
   cause differences other than what you manipulate
   in your experiment?).

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Group question Interpret the two figures. What
do they show? How does this provide evidence
that orcas were responsible for the decline in
sea otters in Kuluk Bay?
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Group question Why do you think Orcas started
eating Sea Otters? Generate a list of possible
ideas.
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Why did Orcas start eating Sea Otters?

• Fish community of the Bering Sea
• Past
• Ocean perch herring
• High abundance
• Very high oil content

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Why did Orcas start eating Sea Otters?

• Fish community of the Bering Sea
• Present
• Pollock
• High abundance
• Low oil content

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Why this change in species composition?

• Where did the herring perch go???

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What were Orcas eating before?
Harbor Seals
Stellar Sea Lions on Amak Island
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Population decline
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Why care about Sea Otters??

• Habitat

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Giant Kelp Forest
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Biodiversity
Sea urchins (Echinoderms)