13.1 Ecologist study relationships

Ecologist study the environment at different levels of organization.

  • Ecology is the study of the interactions among living things, and between living things and their surroundings.
  • An organism is an individual living thing, such as an alligator.
  • A population is a group of the same species that lives in one area.
  • A community is a group of different species that live together in one area.
  • An ecosystem includes all of the organisms as well as the climate, soil, water, rocks and other non-living things in a given area.
  • A biome is a major regional or global community of organisms characterized by the climate conditions and plant communities that thrive there.

Ecological research methods include observation, experimentation, and modeling.

  • Observation is the act of carefully watching something over time.
  • Observations of populations can be done by visual surveys.
  • Direct surveys for easy to spot species employ binoculars or scopes.
  • Indirect surveys are used for species that are difficult ot track and include looking for other signs of their presence.

13.2 Biotic and Abiotic Factors

An ecosystem includes both and abiotic factors.

Biotic factors are living things

  • Plants
  • Animals
  • Fungi
  • Bacteria

Ecosystem includes both biotic and abiotic factors

13.5 Cycling of Matter

Water cycles through the environment

  • The hydrologic, or water, cycle is the circular pathway of water on Earth.
  • Organisms all have bodies made mostly of water.

Elements essential for life also cycle through ecosystems

  • A biogeochemical cycle is the movement of a particular chemical…
  • Oxygen cycles indirectly through an ecosystem by the cycling of other nutrients.

Carbon is the building ­block of life.

  • The carbon cycle moves carbon from the atmosphere, through the food web, and returns to the atmosphere.
  • Carbon is emitted by the burning of fossil fuels.
  • Some carbon is stored for long periods of time in areas called carbon sinks.

The nitrogen cycle mostly takes place underground

  • Some bacteria convert gaseous nitrogen intro ammonia through a process called nitrogen fixation
  • Some nitrogen-fixing bacteria live in nodules on the roots of plants; others live freely in the soil.

The phosphorus cycle takes place at and below ground level.

  • Phosphate is released by the weathering of rocks.
  • Phosphorus moves through the food web and returns to the soil during decomposition
  • Phosphorus leaches intro groundwater from the soil and is locked in sediments.
  • Both mining and agriculture add phosphorus intro the environment.

An energy pyramid shows the distribution of energy among trophic levels

  • Energy pyramids compare energy used by producers and other organisms on trophic levels.
  • Between each tier of an energy pyramid, up to 90 percent of the energy is lost into the atmosphere as heat.

Other pyramid models illustrate an ecosystems biomass and distribution of organisms.

  • Biomass is a measure of the total dry mass of organisms in a given area.

A pyramid of numbers shows the numbers of individual organisms at each trophic level in an ecosystem.

What is a niche?

  • Composed of all of the physical, chemical, and biological factors that species need to survive.
  • Niche includes: type of food a species eats, tolerating certain types of abiotic conditions, and a species behavior

How it lives?

  • Habitat is like an address in an ecosystem and a niche is like the job in an ecosystem.

Resource availability

  • Provides structure to communities.

What is a community?

  • Different groups of species.

Many species share similar habitats and use some of the same resources.

  • Habitats & Resources

Competitive Exclusion

  • Can present a problem if two species use the same resource in the same way.
  • One specie will always be better adapted than others.

Competitive Exclusion

  • States that when two species are competing for the same resources, one species will be better suited to the niche, and the other species will be pushed into another niche or become extinct.


In Great Britain, North American gray squirrel (better suited) introduced and pushed out the native European red squirrel.

Other outcomes from competitive exclusion

Niche partitioning

  • Divide resources based on competitive advantages.

Evolutionary response

  • Different sizes of teeth could affect the way they eat.

Ecological equivalents

  • Are species that occupy similar niches but live in a different geographical region.

Community Interactions

  • Competition and predation are two important ways in which organisms interact.
  • Competition occurs when two organisms fight for the same limited resources

Two types of competition

  • Interspecific competition
  • Intraspecific competition


  • Process by which one organism captures and feeds upon another organism.

More Community interactions


  • Any relationship where two species live closely together and interact

3 types:

  • Mutualism: both species benefit from the relationship.
  • Commensalism: One organism benefits while the other is unaffected.
  • Parasitism: One organism benefits while the other is harmed.

Two types of parasites:

  • Ectoparasite: lives on the outside of an organism, attaching itself to the outside of the host.
  • Endoparasite: found on the inside of living organisms, feed on nutrients ingested by their host.

What is a population?

  • A group of the same species of an organism living in the same area.

How do populations grow?

  • Geographic distribution describes the area inhabited by a population.
  1. Clumped dispersion
  2. Uniform dispersion
  3. Random dispersion
  • Population density number of individuals per unit area
    1. Population Density = # of individuals / area (units2)
  • Growth rate
  • Age structure

Survivorship Curve

  • Type I: low level of infant mortality & a population that generally will survive until old age.
  • Type II: at all times, these species have equal chances of living or dying.
  • Type III:  organisms have a very high birth rate and also a very high infant mortality.

Population growth

  • Number of births
  • Number of deaths
  • Number individuals that enter and leave the population
  • Immigration – movement into an area.
  • Emigration – movement out of an area.

Population growth based on available resources

Growth is a function of the environment.

Exponential growth

  • Population has abundant space and food
  • Occurs when the individuals in a population reproduce at a constant rate
  • Lack of limiting factors (causes population growth to decrease)

More on exponential growth

  • When a population has unlimited resources and continues to grow to its full living potential, it is called its biotic potential
  • A population that has reached biotic potential has reached its maximum reproductive capacity

Limiting Factors

Is a factor that causes population growth to the decrease

  • Density-dependent

Effect of Predation

  • Population size often controlled by predation
  • Takes place in the predator-prey relationship
  • Best mechanism of population control

Parasitism and Disease

  • Limit growth of population
  • Take nourishment at the expense of their hosts often
  • Weakening them and causing disease and death


  • Natural causes, not caused by animals within the population.

Age structure

  • Population growth depends on how many people of different ages make up a given population
  • Populations with large numbers of young offspring have greater potential for rapid growth

Ecological succession

  • Succession means the sequence of biotic changes that regenerate a damaged community in a previously uninhabited area
  • Can result from show changes in the physical environment
  • Sudden natural disasters or human activities also play a role on ecological succession

Primary succession

  • Establishment and development of an ecosystem in an area that was previously uninhabited
  • Occurs on land where no soil exists
  • Occurs on surfaces formed as volcanic eruptions build new islands or cover the land with lava rock or volcanic ash
  • Can also occur on bare rock

Secondary succession

1. Begins in a place that already has soil and was once the home of living organisms
2. Occurs faster and has different pioneer species than primary succession
3. Often see this after a natural disaster such as a forest fire or volcano

Glacier > Soil formation > Mass lichens > Grass annual plants > biannual plants > Pines