Unformatted text preview: The Human Animal
Population Dynamics and
Dept Molecular Biology
UCSD Factors that Limit Population
Growth Density-dependent Factors Predation
Social Mechanisms Density-independent Factors Temperature
Man-created Global Environmental Disasters Exponential Growth
Occurs when organisms are
density-independent. Birth rate exceeds death rate. Both rates are constant.
Both Both rates are proportional to the
numbers of individuals present.
CAN THIS CONTINUE
INDEFINITELY? Only as long
as r is constant!
Mathematical r=0, N does not change
r>0, N increases without limit
r<0, N decreases to 0 Exponential Growth in Nature
Bacteria, yeast, insects, mice, humans, etc.
However… Exponential growth can NEVER be sustained
Populations are eventually limited by densityindependent factors if not by density-dependent
factors. Population Dynamics
Population The life span, number of offspring per adult,
and mortality rate at each stage of life affect
the growth rate of a population.
Mortality Curves: Three Types: Type I: Organisms have few young and usually die
of old age.
Type II: All organisms have an equal chance of
dying throughout their lives.
Type III: High mortality when young; the few
adults that survive have relatively long life spans.
adults Survivorship Curves
r-Strategists Many offspring
Little to no parental
Type III survivorship
K-Strategists Few offspring
Reproduce more than
once in a lifetime
Much energy is
invested in raising
Type I (or II)
survivorship What factors determine the survival
pattern of K-strategists ?
pattern Because of long life span, K-strategists have the
opportunity to overexploit resources if limits are
Population growth is determined by:
Population Reproductive rate,
Density of the previous generation, and
Availability of resources, e.g., the food supply. If resources in the habitat are consumed faster than
the rate of replenishment, the population ALWAYS
experiences an eventual crash.
experiences Reindeer of St. Matthew Island
Reindeer Reindeer were introduced on an island with no predators.
The population grew exponentially.
When the herd outstripped available resources, the population
crashed. Sustainable, K-strategist population oscillations were observed until the
agricultural revolution (about 8000 BC; pop’n < one million).
Then, with agriculture, the first increase of numbers occurred (pop’n at
1 AD ~ 100 million; doubling time > 1000 yrs).
The second increase resulted from the industrial/scientific revolution.
We are still in near exponential growth (pop’n now at 7.0 billion;
doubling time ~ 30 yrs).
doubling Overpopulation, Carrying Capacity, and
Time Humans (K-strategists) are designed to produce few
young on which they must lavish exceptional care for
Now, worldwide, we produce lots of young
(250,000/day - births over deaths).
While we have increased our carrying capacity with
technology, we have also increased our impact on the
All K-strategist populations experience time lags:
exponentially growing populations overshoot their
carrying capacity before experiencing population
losses. Promises of the Green Revolution of
the Eliminate hunger and need.
Increase the Earth’s carrying capacity.
Increase productivity and yields.
Increase technological knowledge.
Distribute food and other necessities throughout the
Indefinite prosperity for all!!!
THESE PROMISES WERE REASONABLE
EXCEPT THAT THEY DIDN’T TAKE INTO
ACCOUNT HUMAN POPULATION GROWTH,
RESOUCE DEPLETION or HUMAN GREED.
RESOUCE The Green Revolution failed to: Curb world hunger
Fairly distribute resources Problems of the Green Revolution: Increased food supplies led to an increase in
More mouths to be fed meant more would go
Increased living standards increased resource use.
Negative impacts on the environment resulted. Impact of a Population on its
Environment Impact = P x A x T
Impact P = population size
A = per capita affluence (resource consumption)
T = environmental disruptiveness of the
Formula published by Ehrlich and Ehrlich, 1990 Differences in Resource
Consumption 1 Child born in the US = 2 in Sweden or Switzerland
3 in Italy
13 in Brazil
35 in India
140 in Bangladesh
280 in Chad Information from Dr. Martha Groom, NCSU Zoology Department, 1998 Corrected Impact of a Population
on its Environment
on Impact = P x A x T x W P = population size
A = per capita affluence
T = environmental disruptiveness of the
W = per capita wastage
Formula by Saier, 2005 (unpublished)
Formula Human ecologists predicted a human
population crash in the late 1900s.
Were they right or wrong?
They were both right and wrong.
They were right to predict a population
crash, but they got the time constant
Skeptics took their error to mean that
the entire concept was wrong! They
concluded we have nothing to worry
about. We can live high on the hog!! BUT:
The Human Animal
is subject to all of the
laws of Nature,
including those of
Population One and only one humane
solution is available to save us
from the pending disaster:
EARTH PRESERVATION 1, On what major issues did
Darwin prove to be correct?
2, Plz describe the causes of an
organismal population crash.
3, Why is it appropriate to refer
to humans collectively as “the
4, Contrast a K-strategist with
QUIZ - QUIZ - QUIZ - QUIZ - QUIZ ...
View Full Document