1. Ecosystems
Populations

2. Population – all the individuals of a particular species that occupy a certain geographical area (e.g. 780, 000 human pop of Winnipeg)

3. Stable and Sustainable Population – a population of a species that meets the needs of present and future generations. Over time the population survives and functions, despite constant changes.
Example#1 -trees in a forest (continuous cycling: thrive/burn/regrow)
Example#2 – Rabbit and fox populations

4. Factors that increase a population
Natality - births
Immigration – movement into the area

5. Factors that decrease a population
Mortality- deaths
Emigration – movement out of the area

6. population growth = (births + immigration) – (mortality + emigration)

7. Can a population keep growing forever?
What limits the continuous growth of a population?

8. Limits on Population
A. Biotic Potential (...limits population growth) – the maximum number of offspring that a species could produce if resources were unlimited.
But resources are limited, so biotic potential is limited by 4 factors
Birth potential – number of offspring per year
Ex. Whooping cranes lay 2 eggs per year...only one may survive
2. capacity for survival – the number of offspring that reach reproductive age
ex. female sea turtles lay many eggs…only a few reach the sea…fewer still reach maturity (so many chances to be something else’s prey)

9. procreation – the number of times that a species reproduces each year
ex. elk mate only once per year, during the fall
length of reproductive cycle – the age of sexual maturity and the # of years the individual can reproduce
ex. African elephants reach sexual maturity at about 15 years, but may reproduce until they are 90. (the young can’t make babies, but once mature, they can reproduce for many years to ensure their genes are passed on)

10. So why do you think humans are good at reproducing?

11. B. Biotic and Abiotic Resources
...also limits population growth
Factors that increase populations:
Factors that decrease populations:
Abiotic
favourable light
favourable temp.
favourable chem. environment
too much or too little light
too cold or too warm
unfavourable chem. environment
Biotic
sufficient food
low number or ineffective predators
few or weak parasites or diseases
ability to compete for resources
insufficient food
high number of highly effective predators
many or strong parasites or diseases
inability to successfully compete for resources

12. -produce greater than 50,000 spores in a year
Examples
Ferns
-produce greater than 50,000 spores in a year
-fern population is limited by moisture (abiotic) and grazing animals (biotic)
-without limiting factors: in two generations would cover N.America!!
People
-produce only 1 offspring per year (but all or most survive)
-population is limited by food resources and disease (biotic) and available water, etc (abiotic) (but technology has greatly removed these limits)
-no natural predators (biotic)!

13. What are the abiotic and biotic limiting factors for these species?
Pet cat, dandelion, rabbit, mosquito, spruce trees...

14. C. Density – the number of a given species in a given area (a population is considered ‘dense’ if it is crowded)
Density-Dependent Factors
(factors affecting populations that depend on the density of the pop.)
Density-Independent Factors (factors affecting populations that occur regardless of the size of the population)
food shortage
competition for mates, breeding areas (habitat)
disease caused by micro-organisms or parasites
introduction of an exotic species
increased predation
competition for water and other resources
flood
fire
spraying with pesticides
change in climate or temperature
destruction of habitat
drought
ex. dwarf-mistletoe (in pines) spreads more quickly in Belair Forest than in the city
ex. illness spread more easily in highly populated areas than in the country
ex. colds spread more easily in school than during summer holidays
ex. A disease that damages the bark of willow trees would affect an already crowded population of deer in the bioreserve
ex. waste water dumped into a lake by industry changes the temp. and chem. composition of the lake and kills the fish (no matter how dense the fish pop. was to begin with)
ex. floods will wipe out a farmer’s crops (whether the crop was a good one to begin with or not)
ex. insecticide will kill all the insects present…whether there were few or many to begin with
ex. A very cold winter in the bioreserve will affect the whole deer population, no matter how many there are that year

15. Stress
Limiting factors do not function independently of each other!! For example, if a bird population is already stressed because of human pollution and habitat removal, insecticide spraying (for their food source) could cause further stress on the population, and possibly wipe it out completely. (domino effect)

16. Carrying Capacity – the largest population that an environment can support
Determined by:
1. resources and energy (sun, water, and other essential materials)
2. food chains (populations are limited by their food supply and predators)
3. competition – the demand for resources (food, water, mates and space) results in competition among individuals (same and different species)
ex. field mouse
low # of predators…# of mice grows
as available food drops, mice become diseased and easy prey
mouse pop. declines to re-establish equilibrium