Populations and Communities

Populations and Communities

Holt ES Ch. 8.1Holt ES Ch. 8.1

Population: a group of organisms of the same species that live together in one place at one time and interbreed.

Population growth is important because populations of different species (including humans) interact in communities

Population: a group of organisms of the same species that live together in one place at one time and interbreed.

Population growth is important because populations of different species (including humans) interact in communities

Populations can be described 3 ways;Populations can be described 3 ways;

Size Total number of individuals

Density # individuals per unit Area

Dispersion Arrangement in space

Even, clumped, random

Size Total number of individuals

Density # individuals per unit Area

Dispersion Arrangement in space

Even, clumped, random

DispersionDispersion

Population growth depends on 4 factors:

Population growth depends on 4 factors:

1. Births

2. Deaths

3. Immigration (movement of individuals into a population)

4. Emigration (movement of individuals out of a population)

1. Births

2. Deaths

3. Immigration (movement of individuals into a population)

4. Emigration (movement of individuals out of a population)

Biotic PotentialBiotic Potential

Fastest rate at which a population can grow…depends on …

reproductive potential --- The maximum number of offspring that each member can produce

Fastest rate at which a population can grow…depends on …

reproductive potential --- The maximum number of offspring that each member can produce

Reproductive potentialReproductive potential

Varies widely: flies vs. whales

Higher when individuals Produce more offspring at a time Reproduce more often Reproduce earlier in life

Greatest effect because it shortens generation time

Varies widely: flies vs. whales

Higher when individuals Produce more offspring at a time Reproduce more often Reproduce earlier in life

Greatest effect because it shortens generation time

Reproductive strategiesReproductive strategies

R strategy – where biotic and abiotic factors fluctuate

K strategy – where biotic and abiotic factors are more stable

R strategy – where biotic and abiotic factors fluctuate

K strategy – where biotic and abiotic factors are more stable

Characteristics of r- and K-selected

organisms

Characteristics of r- and K-selected

organisms r-organisms K-organisms short-lived long-lived small large weak strong or well-protected waste a lot of energy energy efficient less intelligent more intelligent have large litters have small litters reproduce at an early age reproduce at a late age fast maturation slow maturation little care for offspring much care for offspring strong sex drive weak sex drive small size at birth large size at birth Note: Not all characteristics apply to all organisms. Cybernetica, http://pespmc1.vub.ac.be/DEFAULT.html

r-organisms K-organisms short-lived long-lived small large weak strong or well-protected waste a lot of energy energy efficient less intelligent more intelligent have large litters have small litters reproduce at an early age reproduce at a late age fast maturation slow maturation little care for offspring much care for offspring strong sex drive weak sex drive small size at birth large size at birth Note: Not all characteristics apply to all organisms. Cybernetica, http://pespmc1.vub.ac.be/DEFAULT.html

Two kinds of population growth:

Two kinds of population growth:

Exponential

logistic

Exponential

logistic

Exponential growthExponential growth

Numbers increase by a certain factor in each time period

J-shaped graph Lag time

Numbers increase by a certain factor in each time period

J-shaped graph Lag time

Logistic growthLogistic growth

Begins with a minimum number of individuals and reaches a maximum at the carrying capacity of the habitat

S - shaped graph Lag time

Begins with a minimum number of individuals and reaches a maximum at the carrying capacity of the habitat

S - shaped graph Lag time

Carrying capacityCarrying capacity

The maximum population an environment can support at any given time

The maximum population an environment can support at any given time

Actual logistic growthActual logistic growth

Logistic growth curveLogistic growth curve

Factors affecting population size

Factors affecting population size

Abiotic factors: Weather, climate

Biotic factors:foodpredators diseaseparasiteshumans

Abiotic factors: Weather, climate

Biotic factors:foodpredators diseaseparasiteshumans

Density-dependent factors limiting growth

Density-dependent factors limiting growth

Variables that are affected by the number of individualsnumber of individuals present

Ex: availability of nest sites, food, water,competition, migration

Variables that are affected by the number of individualsnumber of individuals present

Ex: availability of nest sites, food, water,competition, migration

Density-independent factors affecting growthDensity-independent

factors affecting growth

Variables that affect a population regardless of population sizeregardless of population size

Ex: weather, flood, fire

Variables that affect a population regardless of population sizeregardless of population size

Ex: weather, flood, fire