Chapter 48 Notes: Humans as a Planetary Force

Humans as a Planetary Force

Humans exert a strong influence on the planet's surface due to sheer numbers and diverse technologies.

The Anthropocene

  • Our impact is a result of population size and individual/societal choices.
  • The human population has grown exponentially.

Ecological Footprint

  • Highly developed countries have large ecological footprints.
  • It takes approximately 8 hectares of land to support an average American.

Greenhouse Gases

  • CO2 is one of several important greenhouse gases, including water vapor and methane.
  • These gases trap heat, making life possible.
  • Too much greenhouse gas puts life at risk.

Human Activities and Global Temperatures

  • Measurements show a persistent temperature increase over the past 70 years.
  • Models that include human activities match observed temperature trends well.
  • Models using only solar and volcano data do not accurately reflect observed trends.
  • Evidence strongly suggests human activities are changing the world.

Climate Change Impacts

  • Climate change impacts all levels of the biological hierarchy.
  • Mean annual temperature has generally increased over the last 150 years.

Plants and Responses to Environmental Change

  • The mean date of first flower formation has shifted earlier by about 1 week over 150 years.
  • Many populations may not have time to evolve and adapt through natural selection given the pace of climate change.
  • Populations may migrate, change distribution, or face extinction.

The Deadly Trio: Effects of Increasing CO2 on Oceans

  • Increasing CO2 levels affect the oceans in three ways:
    • Increase in ocean temperature due to greenhouse gases.
    • Decrease in seawater pH (acidification).
    • Decrease in seawater's capacity to store oxygen (deoxygenation).

Rising Atmospheric CO2 Levels

  • Focus should be on reducing CO2 input and enhancing removal.

The Human Impact on the Nitrogen Cycle

  • Fertilizers add nitrogen to the biosphere each year.
  • Much of the nitrate fertilizer runs off into rivers, lakes, or the ocean.

Eutrophication and Dead Zones

  • Agricultural runoff adds nutrients, leading to eutrophication.
  • Algae and cyanobacteria populations increase, then sink and are consumed by bacteria.
  • High rates of aerobic respiration by bacteria deplete oxygen in bottom waters, creating dead zones (hypoxic zones).

Nutrient Influx Concerns

  • Higher productivity can result in increased respiration by bacteria feeding on sinking algal material, depleting oxygen.

Feeding a Growing Population

  • As population growth accelerates, the need to grow more food remains strong.
  • Two options to meet these needs:
    • Devote more land to crops.
    • Increase the yield of fields already in place.

Deforestation and Tropical Habitat Loss

  • Habitat loss in tropical rainforests is a major threat to biological diversity.

Habitat Fragmentation

  • Example of habitat fragmentation.

Overexploitation of Species

  • Graph depicting fish catch in tons from 1860 to 2020.

Invasive Species

  • Harmful nonnative species that become established in new ecosystems are termed invasive species.
  • Invasive species lack natural predators and are strong competitors.
  • Introduced for food or aesthetic purposes, some have dramatically affected natural ecosystems.

Examples of Invasive Species

  • Examples a, b, and c given.

Amphibians as Indicators of Environmental Disruption

  • One-third of amphibian species are threatened with extinction.
  • Amphibians are sensitive to environmental disruption due to narrow environmental tolerances and gas exchange through their skin.
  • Habitat destruction, pesticides, and fungal infections contribute to amphibian declines.

Conservation Biology

  • Percentages of critically endangered, endangered, and vulnerable species are given for various groups (mammals, birds, reptiles, etc.).

Conservation Efforts

  • Reserves protect habitats, restore degraded environments, and manage areas.
  • Animals and people must coexist for corridors to be effective.

Habitat Patches and Corridors

  • Small populations are more likely to go locally extinct.
  • Isolated patches show lower species diversity.
  • Corridors facilitate movement between patches, aiding in population persistence.

Biological Reserve Design Rationale

  • Biological reserves designed for a single species will protect other species in the reserve.

Goal of Modern Conservation Biology

  • Conservation biology concentrates on preserving levels of species diversity in communities to maintain ecosystem services provided by the species in that community.

Impact of Biologists

  • Various impactful roles for biologists: doctor, science teacher, biochemist, government advisor, volunteer.

The Impact of Biological Sciences

  • Knowledge of biology is crucial for sustaining humanity's future.