Populations

Populations = groups of individuals of the same species living in the same place•Individuals within a population:

▫occupy the same general area▫rely on the same resources▫influenced by the same environmental

conditions

Population Dynamics

•Three Key Features of Populations▫Size▫Density▫Dispersion

Three Key Features of Populations

1. Size: number of individuals in an areaPopulation Size Depends on 4 Factors:

Natality – number of births (increase population)Mortality – number of deaths (decrease population)Immigration – number of individuals moving into an area

(increase population).Emigration – number of individuals moving out of an area

(decrease population).

Population Change

•Population size increases and decreases over time.

• population changepopulation change = (natality + = (natality + immigration) – (mortality + emigration)immigration) – (mortality + emigration)

Population Limiting Factors•Density-dependent factors

▫Any factor in the environment that depends on the number of members in a population per unit area

▫Usually biotic (living) factors▫These include

Predation Disease Parasites Competition (for mates, resources) Food shortage

Population Limiting Factors•Density-independent factors

▫Factors that limit population size, regardless of population density.

▫These are usually abiotic (non-living) factors Natural weather events: Drought, flooding,

extreme heat or cold, tornadoes, hurricanes, fires

Pesticides Destruction of habitat Pollution

2. Density: measurement of population per unit area or unit volume

Pop. Density = # of individuals ÷ unit of space

Three Key Features of Populations

3. Dispersion: The pattern of spacing a population within an area

▫ 3 main types of dispersion Clumped Uniform Random

▫ The primary cause of dispersion is resource availability

Three Key Features of Populations

Clumped Distribution

•Most common pattern in nature.

•Result of unreliable resources. ▫Individuals of the population will clump

around resources. ▫Also found among many animals to aid

predation or fend off predators.

Uniform Distribution

•Uniform Distribution = The tendency for populations to be found evenly distributed about their habitat.

•Individuals use the resources found immediately around them, and spread out as to use all of the available resources

• Happens because of interactions between individuals in the population.

Random Distribution• Uncommon in nature.• Is the tendency for populations to be found

randomly about their habitat.• This pattern occurs in the absence of strong

attraction or repulsion from another individual.• Animals

▫Able to move about their habitat, so that at any given instance, they can be found anywhere about their environment.

• Plants ▫Spores are randomly distributed by the wind▫Usually have the ability to live anywhere in a

given habitat.

Carrying Capacity

•Carrying Capacity = the size of a population that can live indefinitely using the resources available where that population lives.

Factors that Affect Carrying Capacity

1. Materials and energy – populations are limited by the amount of usable energy from the sun and the supply of water, carbon, etc.

2. Food chains – populations are limited by food supply and their predators.

3. Competition – each species shares the same needs. Competition for food, water, mates, space, etc. can limit population growth.Intraspecific competition – among

members of the same species

Interspecific competition – between different species

4. Density – species have differing needs for space. This determines an organism’s population density. Overcrowding can increase stress, promote disease, increase aggression, neglect of offspring, etc.

Death rates increase and birth rates decrease so that the population goes down.

Alien and Invasive Species

•Alien species – a species that is accidentally or deliberately introduced into a new location

•Invasive species – a species that can take over the habitat of native species

Deer: Predation of Starvation

•Graphing Exercise

Human Population Growth

•http://video.nationalgeographic.com/video/the-magazine/the-magazine-latest/ngm-7billion/

World population density- 7 billionhttp://www.worldometers.info

/world-population/

Graphing Question (submit response)

•Does the Human Population have a carrying capacity?