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

Population Change Curves in Nature

4 general types of population fluctuations:

Chaotic Behavior – irregular changes in size with no real pattern seen

4. Cyclic – changes occur in a pattern over a regular period of time

Lynx and hare (10-year cycle)