Ecology NOTES Part 5: Populations & Human Impact on Ecosystems (Chapter 14.3-14.5, & Chapter

Ecology NOTES Part 5: Populations & Human Impact on Ecosystems (Chapter 14.3-14.5, & Chapter

Ecology NOTES Part 5: Populations & Human Impact on Ecosystems (Chapter 14.3-14.5, & Chapter 16)

Population Density and Distribution (Ch 14.3)

Recall that a population is all of the individuals of a species that live in the same area.

population density – number of individuals that live in a defined area

- important measure of the health of a species in an area

- fluctuations indicate that changes need to be made to keep the population

population dispersion – the way in which individuals of a population

are spread in an area

- clumped – individuals live close together in groups; facilitates

mating, protection, and access to food and other resources

- uniform – individuals live specific distances from each other;

results from territoriality and competition

- random – individuals are spread randomly (no pattern, within the area

Population Growth Patterns (Ch 14.4)

- population size changes, increasing, decreasing, or staying fairly constant

- factors affecting population size include:

  • immigration – individuals coming INTO a population
  • births – individuals being born into a population
  • emigration – individuals going OUT of a population
  • deaths – individuals being removed from the population through death

Typical growth patterns:

exponential growth – J-curve; occurs when a population size increases dramatically over a period of time

- may occur when a species is introduced into an uninhabited area

- typical of bacteria and small animals

logistic growth – S-curve; occurs when a population begins with slow growth, followed by a period of rapid growth, before leveling off at a stable size

- the “leveling off” is called the carrying capacity and is a result of limited resources

carrying capacity – maximum number of individuals of a

particular species that the environment can normally and

consistently support

population crash – dramatic decline in the size of a population over a short
period of time

limiting factor – the characteristic or resource that has the greatest effect in limiting (keeping down) the size of a population

density-dependent limiting factors – those that have more effect with increasing population density


  • competition
  • predation
  • parasitism
  • disease


  • density-independent limiting factors – those that limit a population’s growth regardless of the population density


  • unusual weather
  • natural disasters
  • human activities


Ecological Succession (Ch 14.5)

succession – sequence of biotic changes in a community

primary succession – establishment and development of an ecosystem in an area that was previously uninhabited

  • pioneer species – typically lichens and some mosses; first organisms that live in an uninhabited area on bare rock
  • example - moss growing on a rock, a glacier melts and uninhabited soil is exposed

secondary succession – reestablishment of a damaged ecosystem in an area where the soil was left intact.

  • never-ending process; small disturbances always start the area over on different scales
  • example- a forest fire destroys a heavily forested area and overtime a grassland forms in its place

Human Population Growth and Natural Resources (Ch 16.1)

Earth’s human population continues to grow. The current human population of 7 billion has far exceeded earlier predictions of Earth’s carrying capacity for humans.

The growing human population exerts pressure on Earth’s natural resources

nonrenewable resources – a resource that is used faster than it can be reformed

- ex) fossil fuels – oil, coal, natural gas

renewable resource – a resource that can be replaced at the same rate it is used. ex) wind energy, solar energy, drinking water*** - we are pulling water out of lakes and aquifers (groundwater) faster than it is being replaced

ecological footprint – the amount of land necessary to produce and maintain enough food and water, shelter, energy and waste

- size depends on

- amount and efficiency of resource use

- amount and toxicity of waste produced

- US citizens have one of the largest ecological footprints in the world, larger than 24 football fields per person

Air Quality (Ch 16.2)

Pollutants accumulate in the air

pollution – any undesirable factor, or pollutant, that is added to the air, water, or soil; especially synthetic (man-made) chemicals and materials added to the Earth that cannot be integrated into normal ecosystem functions

Smog and Ozone (O3)- fossil fuels (coal, oil, natural gas) produce the most common pollutants in our air

acid rain – precipitation produced when pollutants in the water cycle cause rain pH to drop below normal levels

- pollutants released from factories, cars, power plants, etc.

- pH of 5.6 or lower affects organisms in lakes and streams by decreasing pH of the water

- causes a decline in growth rates of organisms like trees, and leaves trees vulnerable to disease and harsh weather

- also destroys rock (and buildings) by increasing weathering

Air pollution is changing Earth’s biosphere

- Earth’s atmosphere has naturally occurring cycles of high and low levels of carbon dioxide

- high levels of CO2 correspond to higher atmospheric temperatures; low levels with lower temperature

greenhouse effect – occurs when carbon dioxide, water, and methane molecules absorb energy reradiated by Earth’s surface and slow the release of this energy from Earth’s atmosphere

greenhouse gases – CO2, H2O, and CH4 – gases capable of absorbing heat energy, resulting in an increase in temperature

Water Quality (Ch 16.3)

Water pollution (sediment, toxins, fertilizer, heat, etc.) affects ecosystems

eutrophication – process resulting from pollution of water from runoff, especially from fertilizers, that causes algae blooms, fish kills, and finally the filling of the body of water with debris and sediment

indicator species – also called bioindicators; species that provide a sign or indication of the quality of the ecosystem’s environmental conditions; typically the first organisms in an ecosystem to be affected by pollution

ex) tadpoles, frogs, salamanders, lichens, some birds

Biomagnification causes accumulation of toxins in individuals’ bodies in the food chain

biomagnification – process in which fat-soluble pollutants (toxins) move up the food chain as predators eat prey, accumulating in higher concentrations in the bodies of predators, with the most serious effects in the bodies of the top predators

- this process is why pregnant women should not eat predatory fish like salmon or tuna which accumulate heavy metals like mercury, causes brain damage in baby.

Threats to Biodiversity (Ch 16.4)

Preserving biodiversity is important to the future of the biosphere

- loss of habitat and pollution affect animal and plant populations

- a loss of biodiversity can reduce an ecosystem’s stability and make it more difficult for the ecosystem to handle future change

- biodiversity is highest in the rainforests of the world, which are being lost at the rate of about 1% per year. The diagram below shows the deforestation of the island of Borneo from 1950 – 2010 with a prediction of what the island will look like in 2020 if the process is not stopped.

Habitat destruction - Loss of habitat eliminates species

habitat fragmentation – when a barrier forms that prevents an organism from accessing its entire home range

- often resulting from urban sprawl (many people moving into an area) which creates small areas of native habitat

- to help, people are building overpasses for wildlife! 
and leaving green belts and open spaces in cities

introduced species – any organism that was brought to an ecosystem as the result of human actions

- threaten the stability of ecosystems; better competitors or are predators of native species

- examples include: fire ants, kudzu, zebra mussels, purple loosestrife, Burmese pythons in the Florida Everglades

- can cause tremendous damage, including economic damage in the millions of dollars

Zebra mussels / Purple loosestrife / Burmese python habitat


Sustainable development manages resources for present and future generations

sustainable development – practice in which natural resources are used and managed in a way that meets current needs without hurting future generations

ex) clear-cutting forests destroys the ecosystems; selective cutting allows the ecosystem to persist

ex) global fisheries – overfishing has depleted fish stocks; solutions: rotate species caught or reduce harvests so populations recover, change fishing gear to minimize habitat damage, and ban fishing in some areas

Conservation practices focus on a few species but benefit entire ecosystems

- laws that protect endangered or threatened species also protect their habitat and other organisms around them

- umbrella species – the endangered species that also protects other species, such as the grizzly bear of North America and the Florida panther

A Sustainable Earth

- No part of the Earth is untouched by human influence, even if we haven’t physically been there

- However:

- We have the ability to control how fast our population grows by controlling birth rates

- We can develop technology to produce more food and produce less waste

- We can change our practices and take action to protect and maintain ecosystems. In some cases, we can reduce or even eliminate the pressures we place on the planet’s biogeochemical processes