Exam 4 Part 4/5

Energy Sources

Energy outputs radiate from the Earth as energy inputs come from the sun

• Energy flows to AND from the Earth (“open”)

• Nutrient cycle WITHIN the Earth (“closed”)

The nutrient cycle is a closed cycle because nutrients are cycled through the earth they dont leave.

Open vs. Closed Systems

Flow of energy considered “open system”

• Nutrient cycles are a “closed system” (E.g nitrogen cycle)

• Water cycle is also a closed system, no water will leave the Earth

Primary energy source: sunlight

• Most energy for life on Earth comes from the Sun.

• First Law of Thermodynamics: “energy cannot be created or destroyed; it can only change form.”

Energy Sources

• Heat and light energy is converted to chemical energy, in the form of glucose, by photosynthesis.

• Where does the most photosynthesis occur?

  • Marine ecosystems (i.e., phytoplankton)( NOT LAND PLANTS)

Energy Process: Photosynthesis

• Photosynthesis transforms solar energy into chemical energy, stored as chemical bonds in sugars and carbohydrates.

* Only ~1% of the sunlight absorbed by plants

Approximately what percentage of light energy is absorbed by primary producers? ~1 %

Diagram of a Simple Ecosystem

Energy flows and nutrient cycling are both closed systems?

1. True

2. False

Trophic Structure

Review: -troph

• Organism that capture sunlight energy are called “autotrophs” = self nourishing or “producers” 

• Troph = Greek word for food

• Organized into “trophic levels” (e.g., level in a food chain)

• Producers are almost always at the “bottom” of any food chain/trophic level

Autotrophs (Producers) vs. Heterotrophs (consumers)

• All non-producers/other organisms are heterotrophs and get energy by consuming other organisms

• Includes herbivores, carnivores, omnivores, detritivores (feed on dead organic material), and decomposers (decompose dead organic material)

Decomposers and Detritovers - essential to our cycle

• Break down or feed on detritus (Dead organic material)

• Decomposers (e.g., bacteria fungi, and worms):

  • Break down large organic molecules into smaller organic molecules that can be reabsorbed

  • Decompose nutrients on a molecular level

• Detritivores (e.g., fungi, worms, insects, sea stars):

  • Eat large amounts of detritus and excrete nutrients

  • Consume material to break it down

Types of Consumers

• Tertiary consumers: usually carnivores apex predators but can also be omnivores

• Secondary consumers: could be carnivores at the third trophic level

• Primary consumers: always the second trophic level as they plants

  • Herbivores tend to be primary consumers

  • Eagle represent a tertiary consumer

• Producers: photosynthetic organisms

Trophic Levels: Energy Pyramids

• You start with a lot of energy at the base of the pyramid but as you climb higher into the ‘food chain’ the less energy there is at the top of the pyramid

1.  trophic level get energy from sun (autotrophs) and sequester C

2. Trophic level: eat plants (primary consumers)

3. Trophic level: omnivores or carnivores that eat herbivores (secondary consumers)

4. Trophic Level: tertiary (apex) consumer that usually eats other carnivores (but can be omnivore)

In a food web, an herbivore can best be described as a: 

1. Primary producer

2. Primary consumers

3. Secondary consumer

4. Tertiary consumer

Food Chain → Link Trophic Levels

1. Shows who consumer who

And

2. Describers the species occupying each trophic level in ecosystem

Direction of chain: Imagine each arrow tip as the mouth of the next trophic level eating the one below it

Food Web: More accurate than “chain”

Keystone species: Regulate other species

A real food web looks like this!

Example of a herring's diet changing over its lifespan, this makes plotting a food web hard because you have to account for the different stages of life and what food they may be consuming.

Food Webs

• Mathematical methods have been developed for describing and quantifying the links between species.

  • When one goes down they have to predict what will happen to species that relied on the species as a food source, and the prey of the species that went down will also be affected.

• VERY Complicated.

Ecosystem Productivity 

• Light energy comes from the sun → absorbed by photosynthetic, primary producers

• Is ALL of the Light energy from the sun used? Nope

• Productivity: rate at which energy is added to the bodies of a group of organisms as biomass → NOT very efficient (e.g., at every trophic level, energy used or escapes? Converted to heat)

•  Barley and light energy (only ~1%) makes it into the plant

• Other ~99% of light energy is absorbed by other materials, reflected or passes through

Ecosystem Productivity

• The ~1% that is absorbed by the producer is called GPP (Gross Primary Productivity)

• GPP is the overall rate of energy captured by the producer (i.e., the amount of energy th a plant actually absorbs from the sun)

• Plant has to survive!

• Cellular respiration requires energy (e.g., how the plant uses light energy from the sun and converts it into ATP).

• Of the 1% of the light energy the plant gets, most is used in respiration.

• Remainder (NPP = Net Primary Productivity) is gross primary productivity

• Accounts for energy used for metabolism and maintenance.

• NPP (“net”) is always lower than GPP (“gross”) because the amount of energy used by the organism to survive must be subtracted.

• NPP(Net should always be lower the GPP (Growth productivity)

Net primary productivity is always lower than gross primary productivity

1. True 

2. False

All organism are either consumed or enter the detritus pool (the ultimate fate of all)

In most ecosystems, most NPP becomes detritus without passing through a heterotroph

Energetics: How energy is transferred

1% of sun energy absorbed by plants (producers)

• Energy is used up (or escapes as heat) moving from level to level

~10% percent goes to the next trophic level!

• Fewer organisms, less biomass at higher trophic levels (inefficient transfer of energy)

Energy; disturbances; ecosystem size; etc. Consequently, food chains tend to have < 5 trophic levels.

Where do people fit into trophic levels?

• People can occupy multiple consumer trophic levels

• To raise ~1 lb of cow meat, need ~10 lbs of plant biomass

• If people ate 1 lb of plants instead, 10 times less plant biomass needed.

• It takes less plants to produce and feed people then it does to make land with plants for cattle to graze and be raised. That's why people are vegans for climate change.

Ecological efficiency

• Describe the efficiency with which energy is transferred from one trophic level to the next.

• Energy transfer among trophic levels is very inefficient!

Ecological Efficiency Case study

• Real world case study: Silver Spring, Florida

  • Very productive wetland riverine environment

Biomass pyramid 

• Another way to measure productivity

• Not measured over time

• Current biomass (“standing crop”)

• Standing biomass

  • Consumers life the fish live for years and they accumulate the biomass = standing biomass

The Energy Pyramid cannot be inverted! Because there won't be enough energy to give to the primary consumers and so forth as energy is lost between trophic levels.

Why do aquatic ecosystems have an inverted biomass pyramid when compared to terrestrial ecosystems? 

•  Primary producers have little biomass in aquatic systems.

• Despite having a low biomass their efficiency and productivity rate help make up for it, being able to support biomasses of consumers higher up the food chain.

Trophic cascades

• Changes in abundance of organism at one trophic level can influence energy flow at the multiple trophic levels

• Example of Deer and Wolves:

  • Deers in the US have started to become over populated as they reproduce quickly and humans are capable of killing them

  • These deer eat the understory of the forest, making the ecosystem less efficient and healthy as when the understory is present.