Biol 208: Lecture 26 - Primary Production (Terrestrial + Aquatic)

Define ecosystem + What ecosystem ecology focuses on + What the Key processes are

Ecosystem = Biological community together with its associated physical and chemical environment

Ecosystem Ecology = Understanding how organisms interact with their environment and how this influences the flow of energy + the cycling of nutrients

Key processes = Primary production, decomposition + Nutrient cycling

What is the unit of measurement for Primary production

kgC/m² or KgC/m³

• weight of carbon per unit area

Define Primary productivity

• Fixation of Energy

• And the unit of measurement

= The amount of Energy fixed by autotrophs over an Interval of time

• Fixation of energy = use solar E to convert CO2 into sugar + other forms of biomass → Photosynthesis

Units = KgC/m³/year

2 Measures of Primary production

• GPP

• NPP

Why do we need to know the difference

GPP = gross primary production

• TOTAL amount of E fixed by ALL autotrophs in the ecosystem

• = Photosynthesis

NPP = Net primary production

• Total amount of E fixed by all autotrophs MINUS the cost associated with its fixation

• = Photosynthesis - Respiration

Why we need to know the difference?

• Because ONLY NPP refers to the amount of energy available to consumers in an ecosystem

What is Remote sensing?

• How does it work?

A method of measuring ecosystem level primary production

Remote sensing = science of acquiring info about the earth’s surface without contact

How it works = Senses + records the amount of Reflected or emitted energy

• uses camera sensors on satellites (Landsat 1 = first)

What is TERRESTRIAL Primary productivity Mainly limited by?

Moisture + Temperature

• NPP = low in the arctic zone (Temp limits)

• NPP = low in southern prairies (Moisture limits)

NPP increases with increasing precipitation (point do not fall perfectly on the line indicating there are other factors that are also important for NPP)

What is AET?

• Units?

• How does it change with precipitation + Temperature

Actual Evapotranspiration = The amount of water that evaporates + transpires off a landscape during a given time

• Units = mm water/time

Measure that accounts for BOTH TEMP + PRECIPITATION

• AET increases with increased precipitation + temp

Soil Fertility

• Liebig’s Law of the Minimum

Soil fertility limits NPP (adding nutrients = increases NPP)

Liebig’s law of the minimum: Plant growth is not limited by the Total amount of all soil nutrients but by the single MOST LIMITED nutrient that is present in the lowest quantity

Do all plants respond the same to nutrient addition?

• Why or Why not?

NO

Some species have high nutrient efficiency = Grow best under low nutrient (competition avoidance). When nutrients are added theses species are outcompeted

How does DIVERSITY affect NPP?

• Which 3 plant functional groups had the highest NPP?

Greater Primary producer diversity = Greater NPP

C4, grasses + legumes had the highest NPP

What is NPP mainly limited by in AQUATIC SYSTEMS?

Nutrient availability

Where is MARINE NPP usually the greatest

• 3 reasons why

Near the shores

why:

1. Nutrients runoff from terrestrial

2. Nutrient UPWELLING (@ equator as well)

3. Nutrient availability from breakdown of organic matter

Info Dump on the Nutrient Enrichment experiment done on samples from the Baltic sea

• Methods

• What is the limiting nutrient in marine ecosystems?

Water samples in flasks with nutrient enrichment treatment: Nitrogen, Phosphorus + Control

• Measured Chlorophyll concentration

NITROGEN = most limiting nutrient

• amount of chlorophyll increased with addition of Nitrogen

What is the limiting nutrient in FRESHWATER ecosystems?

Algal NPP is correlated with PHSOPHORUS

Info Dump on the Whole lake experiments at ELA

• What is ELA

• Manipulation of Lake 266: Methods + Results

ELA = Experimental lake area in Ontario (58 lakes)

• Area for international research for long term fresh-water experiments

• Eutrophication experiments

Lake 266:

• Vinyl curtain to divide the lake

• Fertilize from 1973-1980 with C, N + P

Results: Phytoplankton biomass increased 4-8x’s with the addition of Phosphorus

• Phosphorus was banned in detergents + other cleaning products

Eutrophication Define

• what things can it cause

= Nutrient enrichment of a water body through natural processes or pollution

causes:

• Rapid Algal growth

• Hypoxia

• Dead zones

Define Hypoxia + Dead zones

Hypoxia = Low water O2 levels less than 2mg O2/L

Dead zones = Areas of Hypoxias → DEVOID OF LIFE

• typically the consequence of pollution, eutrophication and high rates of decomposition

Where are Global Hypoxia hotspots located?

Near where there is High HUMAN activity

Primary Production + Consumer Influence

Define:

• Trophic cascade

• Bottom up vs. Top-down control

Trophic cascade = Effects of Predators on prey that alter abundance, biomass or productivity of community

Bottom up = Abiotic factors that limit primary prod (eg. Temp + nutrients) = control primary prod.

Top down = Consumers in an ecosystem = control primary productivity

How does increasing Predators affect Planktivore, Herbivore + Phytoplankton (NPP)

Decrease Planktivore

Increase Herbivore

Decrease phytoplankton = Decrease NPP

How did Grazing by large animals affect primary production?

Intermediate grazing = OVERCOMPENSATION of plants = INCREASE NPP

Secondary production Define

Production of biomass by heterotrophic consumer organisms

• Ecosystem with greater primary prod generally support high levels of secondary prod

Define: Trophic dynamics + Ecological Efficiency

Trophic Dynamics = Transfer of E from one part of the ecosystem to another

Ecological Efficiency = Percent biomass produced at lower trophic levels that is transferred to biomass produced at next higher level

Top-down vs. Bottom up control on SECONDARY PRODUCTION

• Which is more important?

Top down = higher influence on Herbivore population

Why does Top-down control have Less effect on MINER in this graph when top down is the most important control of herbivore populations?

Miner larvae = in the middle of the leaf + protected from predators

What is the WORLD IS GREEN hypothesis?

Dominance of plants on our planet is evidence that herbivore populations are being kept in check by the predators

• Evidence of Top-Down control on herbivores/ secondary producers