Ecosystems, Productivity, and Global Change

Lab Report Comments

• When writing lab reports:
  • Use italics for scientific names (e.g., Brassica rapa).
  • Write concisely and formally.
    • Avoid vague statements like "The result of this experiment are shown in the graphs" (no information) or personal opinions like "I was surprised, we wondered, etc.".
  • Refer to generations instead of figures (e.g., "In the first generation…" instead of "Figure 1 shows…").
  • Use in-text citations in the Works Cited section (e.g., "…showed that trichomes are adaptive (Smith, 2020).").
  • In the Discussion section:
    • Relate findings to a larger topic.
    • Avoid making up errors.
    • Ensure proper paragraph structure.

Ecosystems and Restoration Ecology

Ecosystem

• An ecosystem includes:
  • All the living organisms in an area.
  • The abiotic factors with which they interact.

Productivity

• Productivity: The rate at which organisms in a trophic level collectively synthesize new organic matter.
  • Primary Productivity: The productivity of the primary producers.
    • Measured in grams of Carbon bound into organic material per square meter per year (gC/m^2/y).
  • NPP (Net Primary Productivity): Gross Primary Productivity (GPP) minus Respiration.
    • $NPP = GPP - Respiration$
    • NPP is, on average, about half of GPP.

Ecosystem Productivity

• Tropical rain forests, estuaries, and coral reefs are among the most productive ecosystems per unit area.
• Marine ecosystems are relatively unproductive per unit area but contribute significantly to global net primary production due to their size.

Factors Limiting Primary Productivity

• Aquatic Systems:
  • Light.
  • Nutrients.
• Terrestrial Systems:
  • Temperature.
  • Moisture (precipitation).
  • Nutrients can be important.

Eutrophication

• Eutrophication: The process where primary production increases as an ecosystem changes from nutrient-poor to nutrient-rich.
• Excess nitrogen runoff fertilizes phytoplankton, causing algal blooms and fatally low oxygen concentrations in marine "dead zones."

Processing Energy

• Only a small fraction (around 1%) of incoming solar radiant energy is captured by primary producers per year.
  • Primary producers capture this energy in chemical bonds.
    • They use some of this energy for their own respiration, with losses to heat.
  • Heterotrophs obtain chemical-bond energy from the biomass of primary producers.

Limits on Food Chain Length

• Energetic Hypothesis: Food chain length is limited by inefficient energy transfer.

  • Only about 10% of the energy stored in organic matter at each trophic level is converted to organic matter at the next trophic level.
    • For example, 100 kg of plant material can support about 10 kg of herbivore biomass and 1 kg of carnivore biomass.

• Energy Partitioning: Within a food chain link, energy is partitioned into:

  • Feces.
  • Growth.
  • Respiration.

• Number of trophic levels and individuals at the top level is limited by energy availability.

• Pyramid of Biomass:

  • About 10% of "food" energy gets transferred to the next trophic level.

• Is it better energetically for humans to eat smelt or trout?

Energy Flows, Chemicals Cycle

• Focus on the carbon cycle.

Human Influence on the Carbon Cycle

• Human activities significantly impact the carbon cycle.

Changes in the Carbon Cycle

• The carbon cycle may proceed faster in one direction over time.
  • Earth’s present reserves of coal and other fossil fuels were built up over geological time.
  • Human burning of fossil fuels is creating large imbalances in the carbon cycle.
  • Deforestation also contributes.
• The concentration of $CO_2$ in the atmosphere is increasing year by year, leading to rising temperatures.

The Greenhouse Effect

• The atmosphere allows shortwave radiant energy from the Sun to enter but traps longwave radiant energy from the Earth, preventing its escape.
• 2024 was the warmest year on record.

Global Warming

• The top 10 hottest years on record have all occurred in the last 10 years.
• NASA analysis shows that 2024 was $2.65°F$ ($1.47°C$) warmer than the 1850-1900 baseline.
  • Dangerously close to the Paris Agreement goal of limiting global warming to $2.7°F$ ($1.5°C$) above pre-industrial levels.

Biological Effects of Climate Change

• Climate change has reduced geographic ranges and caused population declines in hundreds of species.
  • For example, geographic distributions of 67 bumblebee species have decreased in size.
• Organisms that cannot disperse rapidly or find suitable habitat are less likely to survive rapid climate change.
• Rapid change lessens the time for natural selection to lead to adaptation to new conditions.
• Northern ecosystems and tundra show the strongest effects of global warming.
  • Melting snow and ice uncover darker, absorptive surfaces that reflect less radiation into the atmosphere.
  • Tree death in the coniferous forests of western North America has increased due to higher temperatures, decreased snowfall, and longer dry periods.
  • In recent decades, fires have burned twice the usual area of the boreal forest.
• Some Arctic regions have switched from being $CO<em>2$ sinks to $CO</em>2$ sources.

Ecosystem Effects of Global Warming

• Global temperature change has affected ecosystems in the past and is doing so now.
  • Shifts or reductions in species’ geographic ranges.
  • Shifts in timing of life history events:
    • Migratory birds arrive earlier at their summer breeding grounds.
    • Insects and amphibians breed earlier.
    • Not all species shift the same, so end up with mismatched timing.

Effects on Populations

• Earlier spring plant growth has resulted in food shortages and a fourfold drop in caribou offspring production.
  • Start of caribou calving compared to start of spring plant growth.

Thinking Like a Scientist: What’s Next?

• Solutions to greenhouse gas emissions may come from:
  • Individual choices.
  • Local action.
• Personal choices impact carbon footprint.
• Impacts of today will continue long into the future.