Population Ecology

Populations

A population is a group of individuals of the same species that live in the same area

Population Ecology: Vocabulary

Density: The number of individuals per unit

area/volume Example: 47 elephants/km2

Dispersion: The pattern of spacing among

individuals in a population Clumped Uniform Random

Uniform

Environmental conditions are uniform

Causes COMPETITION or antagonism between organisms

Clumping

Most common Reproductive

patterns favor clumping

Social behaviors lead to clumping

Optimal density is usually intermediate (medium)

Random

No competition No tendency to

group/clump Conditions are

uniform Rarely happens!

Factors That Influence Population Size There are 3 major factors that influence

population size:1. the number of births

2. the number of deaths3. the number of individuals that enter or leave a population- immigration: individuals entering an existing population- emigration: individuals leaving an existing population

Reproductive Episodes

Clutch size: Number of offspring produced at each

reproductive episode Semelparity

A life history in which an organism spends most of its energy in growth and development, expend their energy in one large reproductive effort, and then die

Many insects, annual plants, salmon, etc.

Reproductive Episodes

Iteroparity A life history pattern in which

organisms produce fewer offspring at a time over a span of many seasons

Example: humans, panda bears, etc.

Estimating Population Size

The mark-recapture method can be used to estimate the size of a population

Capture, mark, release Recapture and count Equation: N = Number marked x Total catch 2nd time

Number of marked recaptures

Patterns of Population Growth Exponential Growth:

Occurs in ideal conditions with unlimited resources

J shaped curve Book example:

1 bacterium (reproducing every 20 minutes) could produce enough bacteria to form a 1-foot layer over the entire surface of the Earth in a day

Patterns of Population Growth

Exponential growth cannot continue indefinitely

It is characteristic of populations who are entering a new environment OR those whose numbers are rebounding from a catastrophic events

r- strategists

Grow exponentially when environmental conditions allow; when conditions worsen, population size plummets.

Short life span Reproduce early in life Many offspring/large clutch size Usually small in size Little or no parental care Bacteria, some plants, insects

Patterns of Population Growth

Logistic Growth: Pattern of population

growth which takes into account the effect of population density on population growth

Occurs when resources become more scarce

Characterized by an S-shaped curve

Patterns of Population Growth Carrying capacity (K):

The maximum number of individuals that a particular environment can support over a long period of time

Determined by such limiting factors as crowding and food resources

Graph levels off at carrying capacityK-selected populations (equilibrial

populations) live near or at the carrying capacity

K-strategists

Density stays near carrying capacity.

Large, slow growing organisms Small population sizes Long life span; slow maturation Few young/small clutch size Reproduce late in life Parental care Most large mammals; endangered

species

Carrying Capacity

Boom-and-Bust Cycles

Limiting Factors

There are a number of factors that limit the size of populations:Density-dependent limiting

factorsDensity-independent limiting

factors

Density-Dependent Limiting Factors

The effect of density-dependent limiting factors intensifies as the population increasesIntraspecific competition

Food, space, etc.PredationDisease (if caused by

pathogen/contagious)

Density-Independent Limiting Factors

The occurrence and severity of density-independent limiting factors are unrelated to population size Climate Disease (if not caused by pathogen/not

contagious) Pollution

The Interaction of Limiting Factors

Density-dependent and density-independent limiting factors often work together to regulate the size of a populationDeer in snowy winter

Starve from lack of food (DDLF)Severity of winter/depth of snow

determines access to food (DILF)

Survivorship Curves

Type I- live to old age & die (most large mammals)

Type II- constant mortality rate (rodents, lizards, hydra)

Type III- high mortality at young age, but if they survive they live a long life.

Age-Structure Diagrams

Human Population Growth

Human Population Growth

The human population has been increasing exponentially since approximately 1650

http://www.pbs.org/wgbh/nova/worldbalance/numbers.html

Human Population Growth

Implications of exponential human population growth: Lack of food supplies Lack of space Lack of natural resources (metals, fossil fuels, etc) Lack of sites for waste disposal

Ecologists cannot agree on a carrying capacity for Earth Are we going to reach carrying capacity

through individual choices and/or government programs?

OR Is Earth’s population going to “level off” as a

result of mass deaths?