1. CHANGES to ECOSYSTEMS and POPULATIONS

2. Population Fluctuations
Natality (birth) rates
Mortality (death) rates
Emigration
Immigration
(Natality + Immigration) –
(Mortality + Emigration)

3. Calculations Birth rate = number of births in a given time
Initial population
= births per 100 (or as a %)
Death rate = number of deaths in given time
= deaths per 100 (or as a %)

4. POPULATION GROWTH CURVES
Basic Features
J-Curve
Overshoot
Stable phase
maximum number of individuals of a species that can be supported by a particular ecosystem on a long-term basis
Exponential growth
Lag phase
S-Curve
Environmental resistance

5. Population Growth Result of positive feedback mechanisms  change
S-curves
start with exponential growth (no limiting factors affect growth at this stage)
above a certain population size, the growth rate slows down gradually
finally result in a constant population size
growth is slowed down more in larger populations (pattern is consistent with density dependent limiting factors)
Result of negative feedback mechanisms  stability
J-curves
show ‘boom and bust’ pattern
population grows exponentially at first, followed by sudden collapse
collapses are called diebacks (population exceeds carrying capacity before collapse occurs i.e. overshoot)
does not show the gradual slow down of population growth with increasing population size (therefore likely that density independent limiting factor is causing population decrease)
growth curve typical of microbes, invertebrates, fish and small mammals

6. Typical S and J curves
dieback

7. Carrying Capacity Carrying capacity can be determined by:
Examining the requirements of the species
Examining the available resources

8. Limiting Factors Factors that act as limits on population growth:
Density-independent: effect does not vary with population density
- lack of suitable habitat
- adverse weather
(b) Density-dependent: effect varies with population density
- regulate or keep populations within a narrow range of change (in equilibrium)
- operate as negative feedback mechanisms  stability
- Eg: Food
Water
Shelter
Disease

9. Population Equilibrium
Mechanisms that tend to keep population change within a narrow range are:
Predator-prey dynamics
Parasites
Plant-herbivore interaction
Keystone species
Competition
Biotic potential - factors which tend to promote population growth
Environmental resistance - factors which tend to inhibit or discourage population growth and keep populations within their carrying capacity

11. Environmental Resistance
Forces or factors which tend to inhibit or discourage population growth and keep populations within their carrying capacity or in equilibrium (population forms an S-curve)