Symbiosis

1
Concepts in Ecology

• Symbiosis

2
Symbiosis interactions between organisms.

• ___________________ - one organism lives with or
  on another (oftentimes for the sake of gaining
  shelter) neither harming or benefitting the
  host.
• ___________________ - the relationship in which
  both species benefit.
• ___________________ - a symbiotic relationship
  with one species benefitting greatly and the
  other harmed.

3
Concepts in Ecology

• Population dynamics

4
In 1798, Thomas Malthus, an economist,
wrote Principles of Populations (an essay).
5
Essentially stated The human population has
the potential to increase faster than the food
supply.
6
In the 1840s Charles Darwin expanded this
idea The potential for a population to outgrow
its resources exists in all populations.
7
Categories of Population Growth A. Exponential
Growth if a population is left to its own means
and has unlimited food supply the rate of growth
of ____________________
8
of births exceed of deaths
of indiv.
The J Curve
Time

• Reproduction occurs at maximum rate
• All offspring survive to reproduce
• Death occurs only at old age.

The closer a population gets to these, the higher
the rate of growth.
9
The value r can be positive, meaning the
population is increasing in size or negative,
meaning the population is decreasing in size or
zero, where the populations size is unchanging,
a condition known as zero population growth. A
further refinement of the formula recognizes that
different species have inherent differences in
their intrinsic rate of increase (often thought
of as the potential for reproduction), even under
ideal conditions. Obviously, a bacterium can
reproduce more rapidly and have a higher
intrinsic rate of growth than a human. The
maximal growth rate for a species is its biotic
potential, or rmax, thus changing the equation
to dN dT  r max N  (4) Logistic Growth
Figure 1 When resources are unlimited,
populations exhibit exponential growth, resulting
in a J-shaped curve. When resources are limited,
populations exhibit logistic growth. In logistic
growth, population expansion decreases as
resources become scarce, and it levels off when
the carrying capacity of the environment is
reached, resulting in an S-shaped curve.
10
WHAT KEEPS A POPULATION FROM GROWING
EXPONENTIALLY?
11
                                              
                                 Population
pyramid. The pyramids show the age distribution,
by sex, for typical European and African
nations. The pyramids have the same total area,
so the wide base of the African pyramid reflects
the high birth-rate, and its fast-tapering shape
indicates the low expectation of life.

12

• Bangladesh population to hit 17.240m by 2021 
  

13

• To determine growth rate of a population (or the
  change in pop. size over time)
• MUST CONSIDER
• Birth rate
• Death rate
• Immigration ( of indiv. entering the
  population).
• Emigration ( of indiv. leaving the population).
• Populations __________ in size if the number of
  births ____________ the number of deaths.
• Formula
• Rate of increase birth rate (b) death rate
  (d)
• population
  size (N)

14
Solve a population of Canada geese (Branta
canadensis) has 1000 individuals b30/yr.
d10/year What is the rate of increase?
15
Critical Writing Human Population
According to Hans Rosling from TED TALK, the
world population is expected to reach 9 billion
by 2050. The US population is currently over
320 million. Explain in detail ( not list), 3
ways this global increase in population will
affect your life in the United States? (and
yes, your life will be affected).