SSHS Biology Ecology Unit Topic 4

ECOLOGY

Populations

and Disturbance

Topical Understanding

Populations, collections of individuals of the same species that regularly interbreed, are the functional unit of both ecology and evolution. Most populations, under ideal conditions, tend to grow exponentially until one or more environmental variables limits grow. Population size is regulated by both biotic and abiotic factors. These factors can be categorized as density-dependent or density-independent. Carrying capacity describes the maximum number of organisms the ecosystem can support over time.

Because humans interact with local and global food webs and biogeochemical cycles, human activity has changed the flow of energy and the cycling of nutrients in the biosphere. These changes have occurred at both local and global levels. While the Earth’s resources can be classified as renewable or nonrenewable, abiotic (land, mineral, air, water) or biotic (forest, ocean, biodiversity). The rate at which these resources are use and/or consumed determines if their use can be sustained over time. Human use of resources and the effects of this use over time have resulted in complicated ethical and political dilemmas.

Essential/Probing Questions

  • What would happen if a population grew exponentially forever?
  • How do the ecological pyramids and feeding relationships serve as factors in regulating population size?
  • Are humans beginning to experience density-dependent population regulating factors?
  • Can humans continue to change the carrying capacity of the planet through improved technology? In other words, is there an ultimate carrying capacity?
  • While all living organisms impact and change the environment, how have humans impacted/changed the environment to a greater extent than any other species? Is the extent of our impact justifiable?
  • Are we currently experiencing a “tragedy of the commons”? Is sustainable use possible?
  • Do humans have a moral obligation to future generations for the condition of the Earth and its resources?

Areas of Focus

= Population Growth

= Limits to Growth

= Human Activities and their Impact on the Biosphere

= Biodiversity and Conservation Biology

Knowledge and Skills

= Population Growth

Characteristics of populations

  • Geographic distribution and density
  • Growth and Age Structure

Population growth

  • Births/Deaths
  • Immigration/Emigration

Exponential

Logistic growth

  • Carrying capacity

= Limits to Growth

Limiting factors

Density-dependent factors

  • Competition
  • Predation (predator –prey relationships)
  • Parasitism and disease

Density-Independent factors

= Human Activities and their Impact on the Biosphere

The Earth as an island

Human activities

  • Subsistence hunting and gathering
  • Agriculture and the Green Revolution
  • Industrial growth and urbanization

= Renewable and Nonrenewable Resources

The Tragedy of the Commons

Classifying resources

Sustainable development

Land resources

  • Soil erosion and Desertification

Forest Resources

  • Deforestation and forest management

Fishery Resources

  • Overfishing, sustainable use and aquaculture

Air Resources

  • Smog and acid rain

Freshwater resources

= Biodiversity and Conservation Biology

The Value of Biodiversity

  • Ecosystem diversity, species diversity and genetic diversity

Threats to Biodiversity

  • Endangered species and extinction

Habitat alteration

Demand for wildlife products

Pollution

  • Biological magnification

Introduced species

  • Invasive species

Conserving Biodiversity

  • Strategies and challenges

= Global Changes

Ozone depletion

Global climate change

The value of a healthy biosphere

Revised 8/11