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Chapter 8: Population Dynamics, Carrying
Capacity, and Conservation Biology
POPULATION POPULATION NOT A POPULATION
8-1 POPULATION DYNAMICS & CARRYING CAPACITY
Population – all members of the same species living in a particular area
Major Characteristics of Populations = POPULATION DYNAMICS
A) Size – number of individualsB) Density – number of individuals in
a certain spaceC) Dispersion - how they are spaced
out across the rangeD) Age Distribution – the proportion
of individuals at each age
RANDOM UNIFORM CLUMPED
Factors Affecting Population Growth
A) Birth and death rates Birth Rate > Death Rate Growth
B) Immigration and emigration Immigration > Emigration Growth
C) Population Change = (Births + Immigration) – (Deaths +
Emigration)
Biotic PotentialBiotic 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
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
Biotic Potential vs. Environmental Resistance
Growth Factors(Biotic Potential)
Decrease Factors (Environmental Resistance)
Abiotic Abiotic
Favorable lightFavorable temperatureFavorable chemical environment)
Too much light or too little lightTemperature too high or too lowUnfavorable chemical environment
Biotic Biotic
High Reproductive rateGeneralized nicheAdequate food supplySuitable habitatAbility to compete for resourcesAbility to hide from or defend against predatorsAbility to resist diseases and parasitesAbility to migrate and live in other habitatsAbility to adapt to environmental change
Low reproductive rateSpecialized nicheInadequate food supplyUnsuitable or destroyed habitatToo many competitorsInsufficient ability to hide from or defend against predatorsInability to resist diseases and parasitesInability to migrate and live in other habitatsInability to adapts to environmental change
Types of Population Growth
A) 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
Types of Population GrowthB) 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
Factors Affecting Carrying Capacity
A) 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
Density Dependent FactorsA) 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(
B) Herbivory Predators to plant species Large loss of plant species may
affect other primary consumers
Density Dependent Factors
C) Predation Cyclic relationship (rise of one may induce
the fall of the other; trend of rises and falls continues)
Density Dependent FactorsD) Parasitism – feed at the expense
of their hosts Ticks feeding on blood of dogs
E) 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!
Density Dependent Factors
F) 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????
Density Independent Factors
A) Weather Hurricanes,
droughts, floods
B) Natural Disasters wildfires
2004 Sri Lanka Tsunami
Density Independent FactorsSometimes “density-independent” factorsdo still depend slightly on population size
Example: 1. Increase in moose population after a drastic
decrease in wolf population2. Cold winter with huge snowfall covered
plants that moose feed onA) Island population no chance for emigrationB) Large population more competitionC) This density-independent factor may have
affected a smaller population less
Population Change Curves in Nature
4 general types of population fluctuations:
1. Stable – population size fluctuates slightly above and below carrying capacity
Usually found in undisturbed areas or where there is little change in climate
2. 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