1. POPULATIONS AND HOW THEY GROW

2. Biosphere Ecosystems Community Population Figure 1.1
ECOSYSTEM LEVEL Eucalyptus forest
COMMUNITY LEVEL All organisms in eucalyptus forest
POPULATION LEVEL Group of flying foxes
ORGANISM LEVEL Flying fox
Brain
Spinal cord
ORGAN SYSTEM LEVEL Nervous system
ORGAN LEVEL Brain
Nerve
TISSUE LEVEL Nervous tissue
CELLULAR LEVEL Nerve cell
MOLECULAR LEVEL Molecule of DNA
Figure 1.1

3. POPULATIONS
Population-all of the individuals of a species that live together in one place at one time.
Demography-the statistical study of populations. It is used to predict how the size of a population will change.

4. Counting Populations direct observation-count
indirect observation-estimate
sampling-count small number in a small area
and multiply to get the number in the large
area
mark and recapture studies-capture, mark,
release

5. mark-recapture method depends on likelihood of recapturing the same individual
Figure 35.2A

6. KEY FEATURES OF POPULATIONS
1. Population size
is the number of individuals in a population.
had an important effect on the ability of the population to survive.
A small population is more likely to become extinct:
in the case of random events or natural disaster
due to inbreeding where the population is more genetically alike.
with reduced variability it is harder to adapt to changes.

7. KEY FEATURES OF POPULATIONS, con’t
2. Population density
– the number of individuals in a given area.
– if they are too far apart they may only rarely encounter one another resulting in little reproduction.

8. KEY FEATURES OF POPULATIONS, con’t Population size is limited by:
density-dependent factors
Disease
Competition
Predators
Parasites
Food
Crowding
The greater the population, the greater effect these factors have.
Ex. Black plague in the Middle Ages – more deaths in cities
density-independent factors
Volcanic eruptions
Temperature
Storms
Floods
Drought
Chemical pesticides
Major habitat disruption (as in the New Orleans flooding)
Most are abiotic factors

9. KEY FEATURES OF POPULATIONS, con’t
3. Dispersion
– the way in which the individuals are arranged.
Most common

10. Population Growth Population Growth
Three factors can affect population size:
number of births (natality)
the number of deaths (mortality)
the number of individuals that enter or leave the population (immigration and emigration).
* Simply put, a population will increase or decrease in size depending on how many individuals are added to it or removed from it

11. Immigration & Emmigration
the movement of individuals into an area, is another factor that can cause a population to grow.
Emigration
the movement of individuals out of an area, can cause a population to decrease in size.

12. PREDICTING POPULATION GROWTH, con’t
Nearly all populations will tend to grow exponentially as long as there are resources available.
Two of the most basic factors that affect the rate of population growth are the birth rate, and the death rate.
r(rate of growth)=birth rate – death rate

13. PREDICTING POPULATION GROWTH, con’t
Exponential growth curve: population growth plotted against time.
As a population gets larger, it also grows at a faster rate.
Maximum population growth under ideal circumstances.
Includes plenty of room, unlimited resources (food, water) and no predators.
FACT: No population exhibits this type of growth for long.

14. PREDICTING POPULATION GROWTH, con’t
Logistic model: This model accounts for the declining resources available to populations as they grow.
It assumes the birth and death rates are not constant.
As the population grows, births decline and death rises.
Eventually birth=death so the population stops growing.
Carrying capacity (K): The number of organisms of one species that an environment can support indefinitely.

15. PREDICTING POPULATION GROWTH, con’t Two modes of population growth.
The Exponential curve (also known as a J-curve) occurs when there is no limit to population size.
The Logistic curve (also known as an S-curve) shows the effect of a limiting factor (in this case the carrying capacity of the environment).

16. POPULATION GROWTH STRATEGIES
There are 2 ways a population can prosper:
Depends on the rate of growth (r)
Influenced by the carrying capacity (K)

17. POPULATION GROWTH STRATEGIES, con’t
r-strategists: “boom and crash” characterized by exponential growth, which results in temporarily large populations, followed by sudden crashes in population size. Ex. Insects, bacteria, some plants
live in unpredictable and rapidly changing environments
Reproduce quickly when
conditions are favorable
Many offspring: small,
mature rapidly, no
parental care
r = rate of growth

18. POPULATION GROWTH STRATEGIES, con’t
K-strategists: characterized by a high degree of specialization. Ex. Trees, whales, tigers, etc.
Live in stable and predictable environments
Can compete effectively
Reproduce late in life
Few offspring: large,
mature slowly, often
much parental care
K = carrying capacity

19. POPULATION GROWTH STRATEGIES, con’t
Human Populations:
K- strategist characteristics
But, recently, humans learned to expand carrying capacity of environment by increasing food supply, combating pests and curing diseases.
Can Earth support this increase?

20. doubled three times in the last three centuries
THE HUMAN POPULATION
doubled three times in the last three centuries
about 7 billion and may reach 9.3 billion by the year 2050
improved health and technology have lowered death rates
Rapid growth after 10k years of slow growth. Estimates vary on current pop size as well as growth rate. Estimates of doubling time of 51 yrs.
Birth rate is not increasing, but death rate is decreasing. Antibiotics made a big difference. Exception: in European countries, demographic transition began around Triggered by ?

21. The history of human population growth
Resembles which model? Exponential
Agriculture provided stable food supply, about 10K years ago.
Expansion into different environments, allowed by uses of concentrated energy sources.
Note: depending on graph, can give different impression of these data. Change of scale on both axes can flatten this curve.
Figure 35.8A

22. Will Earth Sustain All Life?
Figure 2.10x