Roadmap for remaining lectures:

1. Combine the abiotic (Earth + Climate) with the biotic world (life).

A. Discuss “Ecosystems”, and generally about how life, elements, and energy move and interact on Earth (this lecture, microbes on Monday).

B. Talk specifically about how “energy” moves and cycles on Earth, and how that relates to food supplies and human impacts (lecture on productivity and trophic levels); includes a Case study of an important ecosystem (tropical rainforest lecture)

2. Learn about climate change specifically – past, present, and future. Need to discuss global cycles of important elements like Carbon and Nitrogen (lectures on ice ages, climate control by oceans, modeling future climate; then two lectures on carbon and nitrogen cycles)

3. Give examples of applying scientific principles to real-life environmental problems – (climate change in the Great Lakes lecture; exploding lakes lecture)

“Life is like a blind watchmaker”

1. FACTS

Physical constants of CO2:

Mol. Weight Density mag. sus. ref. index

Cp delta H 44.01 1.799 -21.0 1.663 29.14

-110.5

2. CONCEPTS

O-C-O

Lake Nyos, CameroonExploded in 1986, killed ~2000 people

The CO2 gas cloud killed people up to 26 km away from the lake.

Lake Nyos

1. Fact/Concept ratio Low = ?

2. Fact/Concept ratio High = ?

Philosophy

Engineering, Medicine

Scientific Concepts:

1. Standing Stock

2. Mass Balance

3. Material Flux Rate

4. Residence Time

5. Negative/Positive Feedback

= Stock/Flux Rate

The Concept of the “Ecosystem”

What we wish to learn:

• What is an ecosystem, and how can we study one?

• Is the earth an open or closed system with respect to energy and elements?

• What is a biogeochemical cycle?

• What controls the function of ecosystems?

• What factors determine the distribution of ecosystems and biomes?

Levels of Ecological StudyLevels of Ecological Study

• The ecology of ecosystems examines the dynamics of the entire system, with a particular emphasis on energy pathways and limiting nutrients.

• The ecology of communities examines how species affect one another in two-way and multi-way interactions.

• The ecology of populations includes individual ecology, but also examines population growth, limiting factors, and interactions with other species.

• The ecology of individual organisms includes their physiological adaptations, their niche use, and their behavior.

What is an ecosystem?What is an ecosystem?

• The main processes governing ecosystem function: Energy Transformations and

Biogeochemical Cycling.

• The study of ecosystems emphasizes certain processes that link the living, or biotic, components to the non-living, or abiotic components and that determine how they all function together.

• An ecosystem consists of the biological community that occurs in some place, and the physical and chemical factors that make up its non-living or abiotic environment.

Components of an Components of an EcosystemEcosystem

ABIOTIC COMPONENTS

sunlighttemperatureprecipitation

water or moisturesoil chemistry

etc.

BIOTIC COMPONENTS

primary producersherbivorescarnivoresomnivoresdetritivores

etc.

All of these vary over Space and Time

Energy Transformations

• Ultimately, all energy or carbon “fixed” by primary producers is “respired” by the entire community.

CO2 Organic matter CO2

• Primary producers capture energy from the sun through photosynthesis (and they are a “functional group”).

• Carbohydrates (CHO) are formed, with C derived from CO2 fixation (photosynthesis).

• Organisms that obtain their energy in the same way occupy the same trophic (feeding) level: primary producers, herbivores, carnivores, decomposers.

Energy and Element Flow

• The earth is an “open” system with respect to energy.• The earth is a “ ??? ” system with respect to elements.

A Simple Food Chain

These food chains are really “conceptual”, because they only illustrate the ideas of energy and element flow in ecosystems, but don’t capture any of the real complexity in nature.

Decomposers feed on dead organic matter, also called “detritus”

A Real Food “Web”, found in nature

A Web of Interactions

Webs of interactions are found everywhere, and it is always a challenge to understand them

Take Home Message

““Everything is connected to Everything is connected to everything else”everything else”

- the trick is determining the strength of the interactions -

But HOW?But HOW?

Biogeochemical CyclesBiogeochemical Cycles• Chemical elements such as P and N

“cycle” between the abiotic (geological and chemical) and biotic components of ecosystems.

• Elements cycle because their supply is fixed. The earth is a closed system with respect to elements essential to life.

• All major environmental problems today can be understood through “biogeochemistry”

• Element cycles interact !!Element cycles interact !!

Biogeochemical Principles and Biogeochemical Principles and ToolsTools

1. ELEMENT RATIOS* Important elements are “conservative” and found in relatively constant proportions in organisms

Element

# of Atoms

C 106

N 16

P 1

Fe 0.01

Algal Composition:

Called the “REDFIELD RATIO”

In Normal Algae, N:P = 16:1 = 16

If N:P = 32 ??

2. MASS BALANCE

* Describes whether a system is changing and how fast

NET CHANGE = INPUT + OUTPUT + INTERNAL CHANGE

OutputInternal Change

InputInput

(a) INPUTS:

RAIN to the Catchment = 100 moles H+/yr

STREAM into the Lake = 50 moles H+/yr(b) OUTPUT IN STREAM = - 20 moles H+/yr

(c) INTERNAL CHANGE = - 10 moles H+/yr

NET CHANGE = INPUT+OUTPUT+INTERNAL CHANGE

= 50 – 20 – 10

= 20 moles H+/yr

Lake is acidifying!

3. NUTRIENT OR ELEMENT CYCLING

A. CLOSED SYSTEM1. Rate = # of cycles / time

• As rate increases, productivity increases

2. Pathways are important

B. OPEN SYSTEM 1. Rate 2. Pathways 3. Residence time = RT = time spent

cycling before being lost from the system

• RT = [total amount of NH4 in box

(system) / Input or output rate of NH4]• Units = kg / (kg/yr) = year

Algae

NH4Fish

Algae

NH4Fish

NH4 NH4

Residence Time ExampleResidence Time Example

RT = Stock / Input Rate = 100 kg / 100 (kg/yr) = 1 yr

* System must be at “STEADY STATE” or “EQUILIBRIUM”

- Homework -

OutputStock = 100 kg

Input Rate = 100 kg / year

Controls on Ecosystems

1. Nutrient supply drives 1o Prod, and 1o production drives 2o production …

= “Bottom-Up” Control

2. Predation and grazing control all trophic levels …

= “Top-Down” Control

2 Theories:

Which theory is correct?

Nutrients 1o Producers 2o Prods 3o Prods Top Predators

“Bottom-Up” Effect Strong (Bottom-Up Weak) (Top-Down Weak) “Top-Down” Effect Strong* Evidence to date shows that both theories

operate and exert control, but not complete control, on ecosystems.

• Bottom-up applies “direct” control upward on trophic levels

• Top-down applies “alternating” control downward on trophic levels

The Geography of Ecosystems

• Many different ecosystems are found on earth, from tundra to rain forest.

• When an ecosystem type extends over a large area, we often refer to this as a “biome”

• Climate is the primary determinant of the distribution of biomes

The Distribution of Biomes

Climate Patterns Affect Biome Distributions

There is a clear relationship between the biome and the combination of temperature and precipitation (i.e., climate) on Earth.

But, there is still tremendous variety in Ecosystems…

• An ecosystem combines the biological community and the physical and chemical parts of the abiotic environment.

• Energy enters an ecosystem in light energy, and fixed into organic energy by photosynthesis. All energy fixed in photosynthesis is lost in respiration (sooner or later).

• Organic energy is transferred by consumers in both grazing and detritus-based food chains.

• Biogeochemistry is the study of how elements cycle and interact in the environment.

• Ecosystems are controlled by both top-down and bottom-up processes.

• The global distribution of ecosystem types and biomes is determined by climate.

Summary