Human population disrupts chemical cycles

Nutrient enrichment: when a nutrient cycle is disrupted and nutrients are taken away from one part of the biosphere and added to another where they build up excessively. It is especially dangerous if the material is toxic.

Acid precipitation: rain, snow, or fog with a pH below 5.6. Burning wood and fossil fuels lets sulfur oxides and nitrogen oxides out in into the atmosphere and they react with water to form sulfuric and nitric acid.

Biological magnification: toxins become more concentrated in higher levels of the food web.

Greenhouse effect: Earth absorbs heat due to gases, such as carbon dioxide and water vapor, which absorb infrared radiation and reflect it back to Earth.

Global warming is caused by burning fossil fuels, which increases the amount of carbon dioxide levels in the atmosphere.

The ozone layer protects us from harmful UV rays. It is a very thin layer that is being destroyed due to chlorine compounds such as CFCs. Many of these chemicals are no longer used.

Biological and Geochemical processes

Biogeochemical cycles: nutrient cycles with both biotic and abiotic factors

The Nitrogen Cycle

In nitrogen fixation, microorganisms convert N₂ to ammonium (NH₄⁺) a more usable form of nitrogen because N₂, which is more abundant, is unusable by plants.

Nitrification: ammonium (NH₄⁺) is oxidized to nitrite (NO₂⁻) and then nitrate (NO₃⁻) by bacteria.

Denitrification: undoes nitrification so that bacteria can get the oxygen they need from nitrate rather than O₂

Ammonification: nitrogen is changed back to ammonium

Hydrologic Cycle: Water Cycle

Very little water is chemically hanged by biotic and abiotic factors. This cycle is more physical than chemical.  

Carbon Cycle

Photosynthesis and respiration cause most of the transformations of carbon. The return of CO₂ in the atmosphere by photosynthesis is balanced by its removal through respiration. Unfortunately, the burning of wood and fossil fuels upsets this balance, increasing the amount of atmospheric carbon dioxide.

Phosphorus Cycle

Phosphorus is not significantly present in atmospheric gases, so it tends to cycle over a small area. Weathering of rocks adds phosphate into the atmosphere. Plants use phosphate, an organic form of phosphorus, for organic synthesis. It is then transferesd to consumers and added to the soil by decomposers.

Energy Flow

Primary Producers: autotrophs, organisms that make their e their energy own food and receive their energy from the sun. They support others in the ecosystem.

Heterotrophs: consumers in trophic levels above primery producers.

Primary Consumers: herbivores that eat primary consumers.

Secondary Consumers: carnivores that eat herbivores.

Tertiary Consumers: carnivores that eat other carnivores.

Detrivores, or decomposers, get their energy from dead plant and animal matter, detritus.

ex. fungi and bacteria, earthworms, insects, vultures.

Disturbance influences diversity and composition

Ecological Succession is the change in the composition of species over time, which can be very unpredictable.

Primary Succession: plants and animals invade a region that has never supported living things

Secondary Succession: when an existing community has been destroyed by a damaging event.

California Wildfire in Fall 2007

Biodiversity: the diversity of species in a community, which is also determined by size and geographic location.

Community Structure

Trophic structures are the feeding relationships that include predator-prey, parasite-host and plant-herbivore relationships. Trophic levels are the links in trophic structures that reflect the main energy source of organisms.

A food chain shows a linear flow chart of the transfer of energy between specific organisms. More than one of these makes up a more expanded food web.

Biomass is the total weight of all members in a population. Dominant species, usually producers, have the highest biomass.

Community Interactions

Community: different species living closely and interacting

Interspecific Competitions: competition between different species when resources are in short supply.

competitive exclusion principle: when two species compete for the same resources, one is likely to be more successful and the other will be eliminated.

Ecological niche: the total sum of biotic and abiotic resources in an environment

Predation: an interaction between two species, in which a predator eats the prey

Animal Defense:

• Cryptic coloration – animals are camouflaged by their coloring

• Aposematic coloration – poisonous animals are brightly colored to warn other animals

• Batesian mimicry – a nonpoisonous animal evolves to mimic the coloration of a poisonous animal

hover fly

• Müllerian mimicry – two bad-tasting species resemble each other so that predators learn to avoid them quickly

Monarch (left), Viceroy (right)

• Herbivory: an interaction in which an herbivore eats part of a plant or alga to distinguish toxic from nontoxic plants

Parasitism: the parasite benefits from the living arrangement, while the host is harmed. Parasites change the behavior of their hosts to help themselves. They can affect the survival, reproduction, and density of a population.

tomato hornworm with wasp pupae

Commensalism: one species benefits and the host remains unaffected.

clownfish protected from predators not immune to sting of anemone

Mutualism: both species benefit from the symbiotic relationship and can increase the survival and reproduction of both species.

The flower is pollinated by the insect, while the bee receives food, pollen and nectar.

Exponential population growth in an ideal, unlimited environment

Population: a group of individuals of the same species living in the same area


Exponential population growth: population growth under ideal conditions

Carrying Capacity: the maximum population size that a certain environment can support at a particular time.

Biotic and Abiotic influences on populations

Density Dependent: death rises; population density rises. (i.e. competition resources)

Density Independent: death rate doesn’t change with population density (i.e. natural disasters)

Abiotic Factors:

• temperature
• water - freshwater vs. saltwater
• sunlight
• wind
• soil and rocks - nutrients