Chapter 54: Ecosystems and Global Change

Biogeochemical Cycles

All nutrients ever available for biological systems are constantly recycled between abiotic and biotic components

Detritivores and decomposers

Link all of the other trophic levels together

Four compartments where nutrients accumulate

Nutrient molecules & ions are either available or unavailable
Nutrients move rapidly within available compartments
Nutrients are either present in organic or inorganic material
Nutrients are slow moving into and out of unavailable compartments

Gross primary productivity

Rate at which producers convert solar energy into chemical energy for an ecosystem

Net primary productivity

Producers use energy for their own maintenance (cellular respiration)
Whatever remains is the ecosystem’s net primary productivity
Usually 50-90% of gross primary productivity
Producers use between 10-50% of the energy they capture for their own respiration

Net primary productivity is a measure of

the rate at which producers accumulate energy & the rate at which new biomass is added to an ecosystem

Biomass

Dry weight of biological material per unit area/volume of habitat
Dry because water content has no energetic value

Standing crop biomass

Total dry weight of plants present at a given time

Relationship between biomass and standing crop

Net primary productivity is the rate at which the standing crop produces new biomass

Influencing factors on primary productivity on land

Sunlight, temperature, and the availability of nutrients and water

Limiting nutrient

Runs out before supplies of other nutrients exhausted
Its absence limits productivity

Influencing factors on primary productivity in freshwater/marine ecosystems

Depth of water, sunlight and nutrients

Ecosystems covering large areas (primary productivity)

Contribute more to overall net primary productivity even if productivity is low

Ecosystems that are geographically restricted (primary productivity)

make large contributions if productivity is high
Ex. rainforests and the open ocean make contribute about the same amount equally to global productivity because oceans are big but rainforests are really productive

Secondary productivity

Energy is transferred from producers to consumers and some of that energy is stored in new consumer biomass

Two factors that cause energy to be lost from the ecosystem when it moves trophic levels

Maintenance or movement of animals
Some of the chemical energy released by cellular respiration is converted into heat

Ecological efficiency

The ratio of net productivity at one trophic level to net productivity at the trophic level below it

Ecological efficiencies of consumers determined by 3 processes

Harvesting food, assimilating ingested energy, and producing new biomass

Harvesting efficiency

Ratio of energy content of food consumed to energy content of food available

Assimilation efficiency

ratio of energy absorbed from consumed food to the food’s total energy content
Assimilation efficiency is much lower for prey that is bones and stuff as well as plants which is mostly cellulose and not digestible

Production efficiency

Ratio of the energy content of new tissue produced to the energy assimilated from food
Varies with maintenance costs taking into account stuff like growth and reproduction vs. maintaining body conditions

Pyramid of Energy

Represents trophic levels and the decreasing transfer of energy
Pyramid of Biomass - Does the same thing

Inverted Pyramids of Biomass - Where are they found and why? How can the food web still be stable?

In freshwater and marine ecosystems
Because primary consumers eat primary producers almost asap as they appear
The food web is still stable because producers (plankton) reproduce so fast
Cumulative total biomass of primary producers is still much larger than the primary consumers

Biological Magnification

The accumulation of harmful compounds at high concentrations
Materials, including both nutrients and toxic compounds, become concentrated in individuals at higher trophic levels
Bad nutrients build up as energy levels pass bad nutrients up and it reaches the top consumer in a large amount

Trophic cascade

Predator-prey effects that are effective through the population interactions at two or more trophic levels
Kind of like the domino effect if you remove a predator then the ecosystem will crash

Hydrologic cycle

Cycling of water from the ocean into the atmosphere, to land, through freshwater, and back to the ocean.
Solar energy -> water evaporates from oceans, lakes, rivers, soils, and organisms
Water remains in atmosphere & falls as precipitation
Rain percolates into the soil & reenters ocean reservoir through streams and rivers

How does hydrologic cycle maintain balance

The total amount of water that enters the atmosphere is equal to the amount that falls as precipitation

Carbon cycle

Carbon enters food webs when producers convert CO2 into carbohydrates.
Global carbon cycle cause

Nitrogen cycle

Movement between huge atmospheric pools of gaseous molecular nitrogen (N2) and several smaller pools of nitrogen-containing compounds

Three processes for nitrogen cycle

Nitrogen fixation, ammonification, and nitrification convert unusable nitrogen into nutrients for producers

Nitrogen fixation

Molecular nitrogen converted to NH3 and NH4^+

Causes of nitrogen fixation

Nitrogen fixers

Ammonification

Bacteria and fungi convert organic nitrogen to NH3 from detritus, which dissolves to NH4^+

Nitrification

Nitrites (NO2^-) converted to usable nitrates (NO3^-) by bacteria

Denitrification

Conversion of nitrites/nitrates into N2O and N2, completing the cycle.

Denitrification condition

Low oxygen availability

Phosphorus cycle

Weathering and erosion carry phosphate ions from rocks to soil and into rivers, then into the ocean. There, some phosphorus enters marine food webs. But most of it accumulates for millions of years as insoluble deposits which are only released by seafloor being uplifted.

Phosphorus importance

Crucial for energy transfers within cells of all organisms & constructing nucleic acids
All heterotrophs release phosphate in waste, which is absorbed by plants.

Greenhouse effect

Prevents Earth from being cold

Greenhouse gases examples

foster the accumulation of heat in the lower atmosphere
CO2, water, ozone, methane, nitrous oxide, etc.

Cause of increasing greenhouse gases

Burning of fossil fuels and wood, less producers due to climate change

Effect of increasing greenhouse gases

Climate change means ocean temps increasing, and water expands when heated, meaning sea level is rising & increasing forest fires

Disruption of the nitrogen cycle

Use of nitrogenous fertilizers, farming and livestock, combustion of fossil fuels.

Fertilizer runoff

Causes nitrogen to enter aquatic ecosystems & create a lot of plants

Burning fossil fuels

N2 combines with O2 in the atmosphere to create NO and be converted into NO2 (a greenhouse gas) or HNO3 (nitric acid vapors)

Acidification of Aquatic Habitats (What happens and what effects)

CO2 reacts with H2CO3 -> H^+ and HCO3^-
Increased amount of CO2 created more carbonic acid (H2CO3) in ecosystems to decrease oceanic pH
Causes death of corals and algae, disruption of CaCO3 shells on organisms

Declining Primary Productivity

Increased CO2 should increase producer productivity -> not the case because climate change causes droughts
Warming of surface water also prevents it from mixing with nutrient-rich deep water -> phytoplankton productivity declines