Ecosystems, Productivity, and Human Impact

Communities vs. Ecosystems

  • Communities involve only biological organisms interacting.
  • Ecosystems include the interaction of organisms and the physical environment.
    • Example: The Great Oxygen Catastrophe, where biological organisms interacted with the atmosphere.

Hydrological Cycle

  • Involves transpiration (water coming out of plants) and evaporation (water evaporating off the ground).
  • Water cycles through the air, plants' roots, and back into the ocean.

Freshwater Availability

  • There is remarkably little fresh water available.
  • Most of the world's water is not fresh.
  • Of the fresh water, a large portion is ice.
  • Only a small fraction of fresh water is accessible for use, including groundwater that requires pumping.

Resource Overuse

  • Limited resources like fresh water are prone to overuse.
  • The atmosphere, though seemingly vast, has a thin layer of usable atmosphere.
  • This thin layer is crucial for reflecting UV rays and radiation.

Heating and Radiation

  • The Earth is experiencing heating due to incoming radiation.
  • Photosynthetic active radiation (PAR) is a part of this.
  • Clouds play a role in reflecting radiation.
  • Pollution is creating a layer of clouds that retains heat, preventing it from bouncing back into space.

Energy Harnessing by Autotrophs

  • Only a small fraction (2%) of the light that hits the Earth is harnessed by autotrophs.
  • Autotrophs feed the entire planet, as heterotrophs depend on them.
  • Net primary productivity is the amount of energy captured by plants after their own growth and reproduction, available to heterotrophs.

Global Patterns of Net Primary Productivity

  • High productivity in the tropics, the Amazon, and the southeastern states of North America.
  • Boreal forests also contribute significantly.
  • In terrestrial environments, flowering plants are the main organisms harnessing photosynthetic active radiation.

Ocean Primary Productivity

  • Oceans exhibit a different pattern compared to land.
  • Areas with high chlorophyll (indicative of primary activity) are productive.
  • Upwelling zones, where nutrient-rich deep ocean water rises, are particularly productive due to phenomena, like thermal healing current.
  • Oceans can be deserts with low average net primary productivity.

Ocean Environment

  • Organisms must be in the upper layer to capture energy from sunlight.
  • Lack of large plants due to water movement.
  • Phytoplankton, small floating organisms, are the primary producers.
  • Light attenuates quickly with depth, limiting primary productivity to the upper meters.

Thermal Healing Current

  • In the northern summer, primary productivity is high where the thermal healing current comes up, near Europe.
  • In the northern winter, primary productivity is high in cold waters.

Nutrient Limitation in Oceans

  • Oceans are nutrient-limited environments.
  • Land contributes about 55% to global net primary productivity, while oceans contribute about 45%.

Ecosystem Contributions

  • Open oceans have low net primary productivity.
  • Tropical rainforests have high primary net primary productivity.
  • Algal beds and coral reefs are very productive.
  • Tundras have low productivity.

Earth Coverage and Productivity

  • Oceans cover 65% of the Earth's surface.
  • Tropical rainforests cover a small percentage of the globe.
  • Different ecosystems contribute varying amounts to global net primary productivity based on their size and productivity per area.
  • Marshes can be more productive than tropical rainforests.
  • Cultivating land leads to a loss of 75% of its net productivity.

Human Use of Net Primary Productivity

  • Humans use about 20% of the total net primary productivity, but this may be a low estimate.
  • Including other factors like agriculture and deforestation, the estimate is closer to 40% (25% aquatic).
  • The remainder is left for all other animals, plants, and fungi.

Human Appropriation of Net Primary Productivity

  • Areas with high population sizes have high use of net primary productivity.
  • Urban centers rely on energy to transport primary productivity from other regions.
  • Due to resource use, the abundance of organisms decreases across ecosystems, with human populations growing and using more energy.

Carbon Mobilization

  • Humans are mobilizing petroleum from deep in the Earth, reintroducing carbon into the atmosphere.
  • This is changing the carbon cycle.
  • Increase in the amount of carbon dioxide is happening.

Carbon Dioxide Levels

  • CO2 levels vary, but there's a clear upward trend.
  • David Keeling's long-term measurements in Hawaii show the increase in CO2 levels over time.

Temperature Rise

  • Temperatures are rising, with a temperature anomaly since 1961-1990 above zero.
  • Data from glaciers and other sources confirm this upward trend.

Effects on Biological Systems

  • Range shifts are occurring, with species moving up mountains or to the north.
  • Warm water species are increasing, and butterfly and bird species are shifting northward.
  • The timing of events (phenology) is changing, with plants flowering and animals breeding earlier.
  • Example: Lilacs in Rochester blooming earlier due to rising temperatures.

Ocean Acidification

  • Increased CO2 in the atmosphere leads to higher CO2 concentrations in the oceans.
  • This decreases the pH, making the oceans more acidic.
  • Increased acidity affects carbonate concentrations, impacting organisms like clams and corals that use carbonates to build their shells.

Coral Reefs

  • Coral shells start to dissolve as oceans become more acidic.
  • Coral reefs are declining due to temperature changes and acidification.
  • Eventually, coral reefs may shift to non-carbonate communities or disappear completely.

Biodiversity and Ecosystem Function

  • Does biodiversity matter for humans?
  • Are more diverse ecosystems more productive, resistant to disturbance, and sustainable?
  • Ecosystem functions include biomass production, decomposition, and seed dispersal.
  • Ecosystem services refer to what ecosystems do for people, such as providing protein, clean water, and erosion control.

Ecosystem Services

  • Ecosystem services are a human-centered way of valuing ecosystems.
  • They include provisioning (food, water), regulating (pollination, erosion control), and cultural (recreation) services.

Relationship between Biodiversity and Function

  • Different species provide different functions in a community.
  • Type 1: Every species contributes equally to function.
  • Type 3: A few species do all the function.
  • Type 2: Most communities follow this, where additional species add to function, but the effect asymptotes.

Cedar Creek Experiment

  • Plots with different numbers of species were studied.
  • Productivity (biomass accrued) increased with the number of species, following a type 2 response.
  • Additional species add to function.

Nitrogen and Plant Cover

  • Too much nitrogen is harmful, leading to algal blooms in streams (eutrophication).
  • Nitrogen is also important for plant growth.
  • More plant cover leads to less nitrate flushing into streams, as plants use the nitrogen.
  • This is an example of an ecosystem function.

Biodiversity Loss and Ecosystem Function

  • Biodiversity loss reduces ecosystem function.
  • This is important for maintaining human society and has economic value.

Valuation of Ecosystem Services

  • Ecosystem services can be assigned a dollar value.
  • Economists are working to value ecosystem services.

Millennium Ecosystem Assessment

  • A group of 1200 people assessed changes in ecosystems over the past 50 years, consequences for humans, future changes, and potential solutions.

Habitat Loss

  • Habitat loss from 1950 to 1990 was significant.
  • Rivers are becoming polluted with nitrates due to agriculture.
  • Example: The Mississippi River has a dead zone in the Gulf of Mexico due to nitrate runoff.

Changes in Ecosystem Services

  • Capture fisheries have declined, and fresh water is being overused.
  • The frequency and magnitude of flood events are increasing.
  • Coral reefs and mangroves are degraded, and the amount of water behind dams has quadrupled.
  • Most ecosystem services are vastly degraded.
  • Technology is accelerating these changes.
  • The decline disproportionately affects poor people.

Abrupt Changes

  • Increased likelihood of abrupt changes (e.g., cod fishery collapse).

Economic Value of Ecosystems I

  • If a value can be shown, people care.
  • Example: The cod fishery collapse cost the Canadian government $2 billion.

Example: Mangrove Ecosystems

  • Mangroves provide services like fish habitat, sediment trapping, pollutant detoxification, and erosion control.

Mangrove Conversion

  • Possible options: cut down mangroves for crops (e.g., shrimp farms) or housing.
  • Comparison of intact mangroves to a manipulated ecosystem.
  • Case study: Honduras converted mangroves to shrimp farms.

Value of Mangrove Forests I

  • Value of wood for construction: $90 per hectare.
  • Value of shrimp farm: $2,000 per hectare.

Considerations for mangroves and farms

  • Fisheries are disrupted by shrimp farms.
  • Mangroves provide coastal protection during hurricanes/storms.
  • Governments may subsidize shrimp farms.
  • Shrimp farm pollution has costs.
  • Restoration costs if the farm pulls out.
  • Ecosystem services are valuable.

New York City Water Supply

  • NYC gets clean water from the Catskill Mountains.
  • In 1990, the water started to degrade, with E. coli contamination.
  • The EPA required a water treatment plant (costing $6-8 billion plus $500 million/year to maintain).

Catskill Restoration Project

  • NYC chose to restore the Catskills instead, which cost $1.4 billion.
  • Investment in buying green space, terracing properties, and rebuilding sewage treatment plants.
  • NYC still does not have a water treatment plant.
  • Forests clean water naturally.
  • This is one of the greatest ecosystem service stories.

Global Ecosystem Services Value

  • Total estimated ecosystem services value of the world is 33 trillion33 \text{ trillion}, which is 1.8 times the global GDP.

Biosphere 2

  • Attempt to build an enclosed, self-sustaining ecosystem (3 acres) in Arizona for potential colonization of other planets.
  • Cost: $200 million construction, a lot to upkeep.

Biosphere 2 Results

  • Contained desert, coral reef, and tropical rainforest ecosystems.
  • Experienced problems with pressure changes, waste management, and human relations.
  • Had a 58% species extirpation rate.
  • The Earth is still a better deal on a per hectare basis.

Public Goods

  • Water, air, and other resources are used by everyone.
  • These are called public goods and tend to get overused.
  • Freshwater and genetic resources are easier to value than cultural services.

Tragedy of the Commons

  • When resources are shared, there tends to be overuse (Hardin, 1964).
  • Example: Four people sharing a pasture.
  • Adding one cow benefits the individual but the cost is shared across all four.
  • The rational response is for everyone to add cows, leading to overgrazing and collapse.

Tragedy of the Commons: Asymmetry

  • There's an asymmetry between the benefit (immediate personal gain) and the cost (shared across everyone).
  • Overuse of hot water in dorms, pollution from cars are examples.

Tragedy Solution

  • Requires education and communication about the costs of overuse.
  • Establishing groups or coalitions to discuss the costs and prevent overuse.
  • The Tragedy of the common happens because of a communication issue, education and having groups talking about the costs can help.