1. 2.6 Ecosystem Changes

2. Population Growth
Population: a group the same species that live in the same place at the same time
Resources: food, water, shelter, space and mates
In theory populations can grow to an infinite size, but they are limited by resources
This causes individuals to compete for resources (remember intraspecific and interspecific competition!).

3. Factors that Control Populations
There are 4 main factors controlling population sizes:
Natality - births increase the population
Mortality - deaths decrease the population
Immigration - movement of individuals into an area increases the population
Emigration - movement of individuals out of an area decreases the population

4. Carrying Capacity
Carrying capacity: maximum number of individuals of a species that can be sustained indefinitely in a given space
No population can grow indefinitely! Resources = Limited!!

5. Limiting Factors of Populations
Factors (biotic or abiotic) which prevent population numbers from growing too large and overrunning an ecosystem.
Example:
Disease/ parasites
disasters
hunting & predation
competition for resources
(food, oxygen, nutrients)

6. Patterns of Population Growth
“J” population growth curve
Exponential growth = starts out slow and then proceeds faster and faster
Occurs when a population has few resource limitations
Sudden collapse
('diebacks')

7. Patterns of Population Growth
“S” growth curve
(S for sigmoid)
Initially shows exponential growth then levels off at the carrying capacity.
Occurs when a population has limited resources.
Results in stable population

8. J Curve vs. S Curve

9. Population Dynamics
A look at the factors that tend to increase or decrease the size of a population
The population size is determined by the interplay of biotic potential and environmental resistance.
Biotic potential- growth rate with unlimited resources
Environmental resistance - all the factors acting jointly to limit population growth

10. Biotic Potential vs. Environmental Resistance
(Growth Factors)
Environmental resistance
(Decrease Factors)
Favorable light, temperature
High reproductive rate
Adequate food supply
Ability to migrate habitats
Ability to adapt to environmental change
Too much or too little light and temperature
Low reproductive rate
Inadequate food supply
Inability to migrate habitats
Inability to adapt to environmental change

11. Biotic Potential vs. Environmental Resistance

12. Reproductive StrategiesK
Stable environment, density r
Unstable environment,
Small size
Many offspring are produced
Early maturity
Short life span
Each individual reproduces once
Type III survivorship curve
Large size
Few offspring produced
Late maturity (long parental care)
Long life span
Individuals reproduce more than once
Type I or II survivorship curve

13. Survivorship Curves
Type I - high survival rate of the young, live most of their expected life span and die in old age. (ex. Humans)
Type II - relatively constant death rate, could be due to hunting or diseases. (ex. coral, squirrels, honey bees and many reptiles)
Type III - have many young, most of which die very early in their life. (ex. plants, oysters and sea urchins).

14. Survivorship Curves

15. Pop Quiz Which type of survivorship curve does the cheetah have?
What does parental care have to do with the shape of these curves?
If you drew separate survivorship curves for female and male cheetahs, what would they look like?
What do you think the survivorship curve would be for a white-tailed deer population?

16. Density Dependent Factors
Depend on the size of the population
Effects of the factors increase as the population grows
Act as negative feedback
Tend to be biotic
Two categories:
Internal factors = Within a single species
limited resources
reduced fertility rates
External factors = between species
populations of predators or prey
diseases spread more easily in densely-populated areas

17. Snowshoe Hare and Canada Lynx
Figure 5.18: This graph represents the population cycles for the snowshoe hare and the Canadian lynx. At one time, scientists believed these curves provided evidence that these predator and prey populations regulated one another. More recent research suggests that the periodic swings in the hare population are caused by a combination of top-down population control—through predation by lynx and other predators—and bottom-up population control, in which changes in the availability of the food supply for hares help to determine their population size, which in turn helps to determine the lynx population size. (Data from D. A. MacLulich)

18. Density Independent Factors
Do NOT depend on the size of the population
Tend to be abiotic
Effect the population regardless of its size
Examples:
1. Weather
2. Earthquakes
3. Floods
4. Fires
R-strategists are most
affected by these factors

19. Ecological Succession: Change over Time
Two Types of Succession
Primary succession - An ecosystem starts from bare rock
Secondary succession – Ecosystem is built from a previous ecosystem
Starts with soil

20. Important Terms Sere: A set of stages of changes in an ecosystem.
A snapshot of ecosystem
Pioneer organisms: First species that begin to populate a sere, typically r-strategists.
Ex. Weeds, lichens
Climax community: Populations of organisms living together in a sere where all species are in balance.
Ex. A mature forest, many K-strategists

21. Pioneer Species

22. Primary Succession No soil in a terrestrial system
No bottom sediment in an aquatic system
Takes hundreds to thousands of years
Need to build up soils/sediments to provide necessary nutrients

23. Primary succession will occur after a volcanic eruption

24. Primary succession occurs after a glacier retreats
Image source:

25. Primary succession occurs after a glacier retreats

26. Primary succession occurs after a glacier retreats

27. Glacier Bay, Alaska

28. Primary Ecological Succession
Balsam fir,
paper birch, and white spruce forest community
Jack pine,
black spruce,
and aspen
Heath mat
Small herbs
and shrubs
Lichens and
mosses
Exposed
rocks
Time

29. Secondary Succession Begins with soil from previous ecosystem
Ecosystem has been
Disturbed, Removed, or Destroyed
Abandoned farms
Burned forests
Deforestation
A huge storm

30. Mature oak and hickory forest
Secondary Succession
Mature oak and hickory forest
Young pine forest
with developing
understory of oak
and hickory trees
Shrubs and
small pine
seedlings
Perennial
weeds and
grasses
Annual
weeds
Time

32. Secondary Ecological Succession in Yellowstone Following the 1998 Fire
Figure 5.21: These young lodgepole pines growing around standing dead trees after a 1998 forest fire in Yellowstone National Park are an example of secondary ecological succession.

33. Conditions during succession
Early Stages Gross Productivity is Low
Not many producers
Later Stages Gross Productivity is High
Climax Community