Transcript Ecology: Ch 42 – 43 - Biology with Radjewski

Ecology: Ch 42 – 43
AP Biology
2013
Basic Terms to Remember
•
•
•
•
•
Abiotic vs. Biotic
Ecology
Who came up with the term ecology?
Haeckel
Hierarchy of Ecological Systems
Biome
• Biome—a distinct physical environment
inhabited by ecologically similar organisms
with similar adaptations.
• Can be terrestrial or aquatic
– Terrestrial biomes are characterized by their
vegetation, and soil characteristics
– Aquatic biomes are determined by physical factors
such as water depth and current, temperature,
pressure, salinity, and substrate characteristics.
Ch 43
POPULATIONS
Population Density vs. Population Size
• Population Density – the number of
individuals per unit of area (for terrestrial
organisms) or volume (for organisms that live
in air, soil or water)
– Is dynamic – changes over time
• Population Size – the total number of
individuals in the population
Births Increase and Deaths Decrease
Population Size
• Change in population size depends on the
number of births and deaths over a given
time.
• “Birth–death” or BD model of population
change:
Nt 1  Nt  B  D
N = population size
B = number of births
in the time interval
from time t to time
t+1
D = number of deaths
in same interval
BD Model
• Equation is used to calculate population size in
the future and most often it changes over
time – it will either grow or shrink
• The rate of change is called the growth rate of
the population
• Growth rate can be calculated:
Nt 1  Nt  N  B  D
N
BD
BD


 BD
T (t  1)  t
1
• Per capita birth rate (b)—number of
offspring an average individual produces
• Per capita death rate (d)—average
individual’s chance of dying
• Per capita growth rate (r) = (b – d) = average
individual’s contribution to total population
growth rate
N
 rN
T
What happens during population
changes?
• If b > d, then r > 0, and the population grows.
• If b < d, then r < 0, and the population shrinks.
• If b = d, then r = 0, and population size does
not change.
Life History
• Life history—time course of growth and
development, reproduction, and death during
an average individual’s life
• Life histories are quantitative descriptions of
life cycles.
• Example: the life cycle of the black-legged tick.
Life Tables
• A life table shows ages at which individuals
make life cycle transitions and how many
individuals do so successfully.
• Life tables have two types of information:
• survivorship—fraction of individuals that
survive from birth to different life stages or
ages
• fecundity—average number of offspring each
individual produces at those life stages or ages
Life Histories Vary
• Life histories vary among species: how many
and what types of developmental stages, age
of first reproduction, frequency of
reproduction, how many offspring they
produce, and how long they live.
• Life histories can vary within a species. For
example, different human populations have
different life expectancies and age of sexual
maturity.
Resources shape life histories
• Individual organisms require resources
(materials and energy) and physical conditions
they can tolerate.
• Rate at which an organism can acquire
resources increases with the availability of the
resources.
•
Examples: photosynthetic rate increases
with sunlight intensity, or an animal’s rate of
food intake increases with the density of food.
Exponential Growth of Populations
• Population growth is multiplicative—an everlarger number of individuals is added in each
successive time period.
• Charles Darwin was aware of the power of
multiplicative growth:
•
“As more individuals are produced than can
possibly survive, there must in every case be a
struggle for existence.”
• This ecological struggle for existence, fueled by
multiplicative growth, drives natural selection
and adaptation.
Limitations
• Populations do not grow multiplicatively for
very long. Growth slows and reaches a more
or less steady size:
Per capita growth rate, r
• r decreases as the population becomes more
crowded; r is density dependent.
• As the population grows and becomes more
crowded, birth rates tend to decrease and
death rates tend to increase.
• When r = 0, the population size stops
changing—it reaches an equilibrium size
called carrying capacity, or K.
Human Populations
• The human population is unique. It has grown
at an ever-faster per capita rate, as indicated
by steadily decreasing doubling times.
• Technological advances have raised carrying
capacity by increasing food production and
improving health.
BIDE Model
• The BIDE model of popultion growth adds the
number of immigrants (I) and emigrants (E) to
the BD growth model.
Nt 1  Nt  B  I  D  E