Chapter 5

Population Biology

Describing Populations

• Geographic range – where they are located• Density – how many organisms in a certain

area• Distribution – how they are spread out in

the area-3 patterns

*randomly *uniform*clumped

Population Growth1. General

A. Populations are groups of organisms of the same speciesB. Population growth is the change in the size of a population with timeC. Scientists have found clear patterns of how and why populations grow

-4 things change the populations size*births*deaths*immigration*emigration

2. How fast do populations growA. Populations do not grow in a linear fashionB. Populations grow in an exponential fashion i. The initial increase in # is slow due to the

small # of organisms able to reproduce, then the rate increases rapidly as the total # of organisms potentially reproductive organisms increasesii. Exponential growth occurs when the # of organisms increases by an ever increasing rate, this results in a population explosioniii. This results in a J shaped curve, see fig. 5.3 on page 115

3. Limits of the environmentA. Populations cannot grow indefinitely B. Population size does have a limitC. Populations do have limiting factors in their

environment. These limiting factors slow the growth of a population.

i. Ex. Food availability and space C. This leveling off of population growth results in an s-shaped curve (this is called logistic growth)

i. See fig. 5.4 page 118ii. There is a plateau when the # of organisms

the environment can support is reached

D. The # of organisms of a population that a particular environment can support over a period of time is known as its carrying capacity

i. Often represented by the letter KE. When populations are under the carrying capacity, births will exceed deathsF. If the population overshoots the carrying capacity, deaths will exceed births until populations are once again at carrying capacity

*Life History Patterns1. In nature, some populations remain in equilibrium (a state of rest or balance), some do not

A. This occurs because there are 2 basic growth patterns, called life history patterns, that populations can follow

i. Some populations reproduce very rapidly and produce many offspring (r-selected)

1. Ex. mosquitoesii. Some populations have a slow rate of reproduction with few young (k-selected)

1. Ex. elephantsiii. Which type a specie uses depends mainly on environmental factors

B. Species in an unpredictable and rapidly changing environment survive better with a rapid life history pattern (r-selected species)

i. These organisms usually have similar adaptations1. Ex. Small body size, mature rapidly,

reproduce early, & have short life span, many youngii. Ex. Mosquitoesiii. Populations of these organisms increase and decrease rapidly as their environment changes

1. The small surviving population will begin reproducing exponentially when conditions are favorable again

C. Species that live in a more stable environment usually have a slow rate life history pattern

(k-selected)i. Ex. Elephantsii. Are usually large in size, long lived,

produce few young and mature slowlyiii. These organisms usually maintain

populations near the carrying capacity

Environmental limits to population growth a. Limiting factors regulate the size of a populationb. Ecologists have recognized 2 types of limiting factors

i. Density-dependent factors have an increasing effect on a population as the population increases in size

1. Ex. Disease, parasites, competitionii. Density-independent factors affect all populations regardless of their density

1. Usually abiotic factors2. Ex. Temperature, storms, drought etc.

• Interactions among organisms that limit population size

Populations are also controlled by various interactions among organisms within the community

-Predation/Herbivory-Competition

*interspecific *intraspecific

-Symbiosis-Disease-Overcrowding/Stress

Predation (animals killing and eating other animals) and Herbivory (animals feeding on plants) affects on population size

A. necessary in a community, it ensures the continuation of the flow of energy throughout

the ecosystem (animals have to eat)B. It also may be a limiting factor on a prey population sizeC. Most prey populations are controlled in some way by predators

D. Populations of predators and prey change over years, many in a cyclical fashion

-Usually with the populations increasing and decreasing at the same times E. Predators help to weed out the sick, old, young and week

i. This leaves the strong and well adapted left to reproduce

3. The effects of competitionA. Organisms within a population compete for

resources (food, water, shelter, etc)B. When population is low, resources are abundantC. As population increases the competition for

resource increases and there may not be enough for everyone

D. Density-dependent factorE. When the population becomes to big and the

demand for the resources is greater than the supply of resources, the population size decreases

F. Interspecific – between different speciesG. Intraspecific – within a species

4. The effects of overcrowding and stressA. When populations become crowded, individuals may exhibit stressB. Symptoms of stress from overcrowding include aggression, decrease in parental care, decreased

fertility, and decreased resistance to diseaseC. All of these symptoms can lead to a decrease in population size (which relieves the overcrowding)

Section 2: Human Population*World Population

1. GeneralA. Demography is the study of human population size, density and distribution, movement and birth/death rates

2. Human Population GrowthA. humans consciously change their environment, so human population is different than other populationsB. humans have reduced or eliminated many of their limiting factors which have allowed the human population to grow

i. medical advancesii. agriculture advancesiii. eliminate competition

3. Calculating growth rateA. 4 factors affect human population growth

i. birth rateii. death rateiii. immigration - movement into a populationiv. emigration - movement out of a population

B. to calculate population growth rate we must take all of these factors into account

i. (birth rate + immigration) - (death rate + emigration ) = population growth ii. this just tells how many new individual are in a populationiii. if the PGR is positive it means more individuals are entering the population than leaving it, if the PGR is zero it means that individuals are entering and leaving the population at the same rat, and if the PGR is negative it means that more individuals are leaving the population than entering it

4. Demographic Transition – page 144A. Tracks birth rates and death rates as a country developsB. There is a general trend as the country develops

*stage 1 = high birth and death rates*stage 2 = death rate begins to fall, birth rate remains high for a while*stage 3 = birth rate declines until it meets the death rate

5. Doubling timeA. the time needed for a population to double in sizeB. a country with a slow doubling time is considered a developed country, while a country with a rapid

doubling time is considered a developing country

6. Age StructureA. refers to the proportions of the population that are in different age levelsB. shows the proportions of males and females in each age group and those within child bearing age and elderly (can help us predict trends in population

growth)C. if the percentage of people in each age category is fairly equal the population is considered stable,

rapidly growing populations have higher numbers in lower age groups (more people in child bearing age)

Chapter 6

Biodiversity

The number of different types of organisms in an area

-ecosystem diversity – different types of ecosystems-species diversity – different types of organisms -genetic diversity – different genetics within a population

Biodiversity is important because…-the ecosystem has value to humans

*ex. materials that we use, medicines, food, etc.

-it helps keep the ecosystem stable*if everything in the ecosystem is the same, then everything is susceptible to the same forces

-aesthetic value (beauty)

HIPPO – five ways humans are decreasing biodiversity in nature

H- habitat destructionI – invasive speciesP – population expansionP – pollutionO – over-exploitation