Populations
A population is a group of individuals of a single species that live in the same general area. Members of a population rely on the same resources, are influenced by similar environmental factors, and have a high likelihood of interacting with and breeding with one another. Populations can evolve through natural selection acting on heritable variations among individuals and changing the frequencies of various traits over time.
Characteristics of a Population:
1. Geographic distribution Where are they located? What is their habitat range? Where are the geographic boundaries?
2. Population Density Can be calculated as the number of individuals per unit area or volume.
3. Spacing of Individuals Individuals within a population disperse in a number of ways: clumped, random, and uniform.
Characteristics of a Population:
1. Geographic distribution Where are they located? What is their habitat range? Where are the geographic boundaries?
2. Population Density Can be calculated as the number of individuals per unit area or volume.
3. Spacing of Individuals Individuals within a population disperse in a number of ways: clumped, random, and uniform.
How Can Populations Change?
Natality (birth rates)
Mortality (death rates)
Immigration (individuals coming in)
Emigration (individuals leaving or exiting)
Population growth =
(Natality + Immigration) - (Mortality + Emigration)
Natality (birth rates)
Mortality (death rates)
Immigration (individuals coming in)
Emigration (individuals leaving or exiting)
Population growth =
(Natality + Immigration) - (Mortality + Emigration)
Phases of Population Growth
Phase 1: Exponential growth phase (J curve)
Unlimited population growth
The intrinsic rate of increase (r)
Abundant food, no disease, no predators etc
Phase 2: Decline or transitional phase
Limiting factors (like limited resources or predation) slowing population growth
Phase 3: Plateau phase
The limiting factors balance the population's capacity to increase
The population reaches the Carrying Capacity (K) of the environment
Phase 1: Exponential growth phase (J curve)
Unlimited population growth
The intrinsic rate of increase (r)
Abundant food, no disease, no predators etc
Phase 2: Decline or transitional phase
Limiting factors (like limited resources or predation) slowing population growth
Phase 3: Plateau phase
The limiting factors balance the population's capacity to increase
The population reaches the Carrying Capacity (K) of the environment
Human Population Growth
Want to know the current US and world populations? Click this.
According to the US Census Bureau, our current world human population is about 7.4 billion.
Previous Milestones
Previous Milestones
- 7 billion: 2011
- 5 Billion: 1987
- 4 Billion: 1974
- 3 Billion: 1960
- 2 Billion: 1927
- 1 Billion: 1804
Helpful Videos and websites
Crash Course on Human Population Growth
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Easy to understand video about carrying capacity.
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If you need a quick review, watch this one:
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World Populations websites to explore:
http://www.census.gov/popclock/
http://www.worldometers.info/world-population/
PBR(Population Reference Bureau) World population data 2015
http://www.census.gov/popclock/
http://www.worldometers.info/world-population/
PBR(Population Reference Bureau) World population data 2015
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