Primary Productivity/Trophic Levels/10% Rule/Food Webs

Primary Productivity

Rate at which solar energy is converted into organic compounds via photosynthesis over a unit of time

- rate of photosynthesis of all producers in an area over a given period of time

**ALSO -> the amount of plant growth in an area over a given period of time.

kcal/m2/yr (energy/area/time)

units if primary productivity in energy, area, and time

high plant growth = lots of food/shelter for animals. Also more biodiverse

Higher primary productivity =

NPP = GPP - RL

equation for calculating primary productivity

Net Primary productivity (NPP)

The amount of energy (biomass) leftover for consumers after plants have already used some for respiration

Respiration loss (RL)

Plants use up some of the energy they generate via photosynthesis by doing cell. respiration

- movement, internal transportation, etc.

Gross Primary Productivity (GPP)

The total amount of sun energy (light) that plants capture and convert to energy (glucose) through photosynthesis

ecological efficiency

The portion of consumed or captured energy that can be passed from one trophic level to the next

1) Generally, only 1% of all incoming sunlight is captured and converted into GPP via photosynthesis

2) The other 99% is in a wavelength unusable by plants

3) Of that 1%, an average of 40% (or 0.4% of total

incoming solar energy) is converted into biomass/plant

growth (NPP)

4) After this, energy transfer is roughly ~10% efficient from

trophic level to trophic level (10% rule)

**Note: Some ecosystems are more efficient (higher NPP) than others

Trends in productivity (terrestrial)

1) The more productive a biome is, the wider the diversity of animal life it can support (high biodiversity)

2) Water availability, higher temperature, and nutrient availability are all factors that lead to high NPP

- Shortage of any of these three factors will lead to

decreased NPP

- ex. Desert (low water and nutrients), tundra (low temp and liquid water), open ocean (low nutrients, photosynthesis restricted to photic zone)

Photic zone and light

In aquatic systems, productivity is restricted to the photic zone, where sunlight can reach.

Wavelengths of Light:

- Red light is the first to go, absorbed in the upper 1 meter of water.

- Blue light can penetrate the deepest, reaching over 100 meters in very clear water.

- Aquatic photosynthesizers have developed specialized mechanisms and pigments to capture the specific wavelengths of light available at their depth.

1st law of thermodynamics

Matter and energy are neither created or destroyed; they only change forms

- ex. Tree dies & the C/N/H2O/P are returned to the soil & atmosphere

- ex. Sun rays (light energy) hit leaves & are converted into

glucose (chemical energy)

**Note: Biogeochemical cycles demonstrate conservation of matter

(C/N/H2O/P)

Example of food webs demonstrating conservation of energy

When a rabbit eats a leaf, the energy from the leaf (glucose) is transferred to the rabbit & stored as body tissue like

fat/muscle

2nd law of thermodynamics

Each time energy is transferred, some is lost as heat

- Applied to food webs: the amount of usable energy decreases as you move up the food chain (organisms use up most of it for movement, development, etc.)

Trophic pyramid

Because *available* energy decreases with each step up

the food chain, a _______ is used to model how energy moves through an ecosystem

10% rule

in trophic pyramids, only about 10% of the energy from one level makes it to the next level; the other 90% is used by the organism & lost as heat

Tertiary consumers

animals that eat secondary consumers and omnivores

Secondary consumers

animals that eat primary consumers or herbivores

Primary consumers

animals that eat plants (herbivores)

Producers

plants, convert sunlight into glucose for energy

10% rule's application to biomass (mass of all living things at each trophic level)

Since energy is needed for growth & only 10% of energy transfers from one level to the next, only 10% of the biomass of the previous trophic level can be grown/supported by the available energy

move the decimal place one spot to the left, OR divide by 10

- ex: Tertiary = 95 J, Secondary = 950 J

Calculating biomass energy or each troph level energy

Food web basics

Shows how matter and energy flow through an ecosystem,

from organism to organism

- When one organism preys on (eats) another, the matter (C/N/H2O/P) and energy (glucose, muscle tissue, etc.) are passed on to the predator

- Arrows in food webs indicate direction of energy flow (point

to the org. taking in the energy)

Food chains

only show one linear path of energy and matter

Food webs

- They have at least 2 different, interconnected food chains

- Webs show that organisms can exist at different trophic levels

Food web - Interactions

Food webs show how increases or decreases in population size of a given species impact the rest of the food web

- ex: Increase in python population:

= Decrease in frog & rat populations

=Increase in grasshopper population

=Decrease in corn

Trophic cascade

Removal or addition of a top predator has a ripple effect down through lower trophic levels

- ex. Decline in wolf pop. = increase in deer population which

leads to overgrazing & decline in trees