1. Chapter 8: Population Dynamics, Carrying Capacity, and Conservation Biology
8-1 POPULATION DYNAMICS & CARRYING CAPACITY Population – all members of the same species living in a particular area
POPULATION
POPULATION
NOT A POPULATION

2. Major Characteristics of Populations = POPULATION DYNAMICS
Size – number of individuals
Density – number of individuals in a certain space
Dispersion - how they are spaced out across the range
Age Distribution – the proportion of individuals at each age
RANDOM
UNIFORM
CLUMPED

3. Factors Affecting Population Growth
Birth and death rates
Birth Rate > Death Rate  Growth
Immigration and emigration
Immigration > Emigration  Growth
Population Change =
(Births + Immigration) – (Deaths + Emigration)

4. Biotic Potential
Biotic Potential = growth factors, capacity of a population for growth
Intrinsic rate of increase (r) - rate at which a population would grow if it had unlimited resources
Characteristics of populations with high biotic potential
Reproduce early in life
Have short generation times
Can reproduce many times
Produce many offspring each time they reproduce
Limits to populations include shortage of…
Light
Water
Space
Nutrients

5. Environmental Resistance
Environmental Resistance = decrease factors, all the factors acting jointly to limit the growth of a population
Determine carrying capacity (K) – the number of individuals of a given species that can be sustained indefinitely in a given area
Carrying capacity determined by interplay of biotic potential and environmental resistance

7. Biotic Potential vs. Environmental Resistance
Growth Factors
(Biotic Potential)
Decrease Factors
(Environmental Resistance)
Abiotic
Favorable light
Favorable temperature
Favorable chemical environment)
Too much light or too little light
Temperature too high or too low
Unfavorable chemical environment
Biotic
High Reproductive rate
Generalized niche
Adequate food supply
Suitable habitat
Ability to compete for resources
Ability to hide from or defend against predators
Ability to resist diseases and parasites
Ability to migrate and live in other habitats
Ability to adapt to environmental change
Low reproductive rate
Specialized niche
Inadequate food supply
Unsuitable or destroyed habitat
Too many competitors
Insufficient ability to hide from or defend against predators
Inability to resist diseases and parasites
Inability to migrate and live in other habitats
Inability to adapts to environmental change

8. Types of Population Growth
Exponential Growth – unlimited growth of a population
Occurs when population has food, space, protection from predation/disease, removal of waste products
Each future generation will grow faster than the last
Ex: bacteria

9. Types of Population Growth
Logistical Growth – population grows, slows, and eventually reaches carrying capacity
Phase 1 – exponential growth
Phase 2 – slows down
Due to: BR decreases, DR increases, immigration decrease, emigration increases
Phase 3 – population stabilizes, reaches carrying capacity
Carrying Capacity – maximum number of individuals than a particular environment can support

10. Factors Affecting Carrying Capacity
Limiting Factors – factors that control the growth of a population
Density Dependent Factors – factors that depend on the density of the population; control the populations and keep numbers in check
Non-native species have a tendency to elude this and grow uncontrollably due to lack of natural predators, etc.
Density Independent Factors – factors that do NOT depend on the density of the population; will affect all populations equally, regardless of their size

11. Density Dependent Factors
Competition
Fighting for space, food, water, sunlight, mates, etc.
Can be within the same or different species
Some will survive and reproduce, some will survive but NOT reproduce, some will die :0(
Herbivory
Predators to plant species
Large loss of plant species may affect other primary consumers

12. Density Dependent Factors
Predation
Cyclic relationship (rise of one may induce the fall of the other; trend of rises and falls continues)

13. Density Dependent Factors
Parasitism – feed at the expense of their hosts
Ticks feeding on blood of dogs
Disease – can cause a dramatic drop in a population due to infestation of a disease; decrease in one population may trigger a rise in another!

14. Density Dependent Factors
Stress from Overcrowding – species fighting amongst themselves may lead to high levels of stress which may affect an organism’s ability to fight disease!
Hmmmm….might explain why students get sick right before tests….maybe????

15. Density Independent Factors
Weather
Hurricanes, droughts, floods
Natural Disasters
wildfires
2004 Sri Lanka Tsunami

16. Density Independent Factors
Sometimes “density-independent” factors
do still depend slightly on population size
Example:
Increase in moose population after a drastic decrease in wolf population
Cold winter with huge snowfall covered plants that moose feed on
Island population  no chance for emigration
Large population  more competition
This density-independent factor may have affected a smaller population less

17. Population Change Curves in Nature
4 general types of population fluctuations:
Stable – population size fluctuates slightly above and below carrying capacity
Usually found in undisturbed areas or where there is little change in climate
Irruptive – fairly stable populations that have a population explosion but then return to a lower size rather quickly
Impacted by favorable weather, increase in food supply, decrease in predator

18. Population Change Curves in Nature
4 general types of population fluctuations:
Chaotic Behavior – irregular changes in size with no real pattern seen
Cyclic – changes occur in a pattern over a regular period of time
Lynx and hare (10-year cycle)