Disruption to Ecosystems (College Board AP® Biology): Study Guide

Mutation & adaptation

• An adaptation can be defined as:

a genetic variation that is favored by selection and that is manifested as a trait that provides an advantage to an organism in a particular environment

• Adaptations arise due to mutations

  • Mutations occur randomly during DNA replication and not a result of specific environmental pressures

• Adaptations increase an organism's fitness

• Mutations that result in advantageous traits are favored by selection and so are passed on to the subsequent generations; they can become widespread within a population

  • This is natural selection

Invasive species

• Invasive species are species that move into an ecosystem where they were not previously present

• Invasive species often arrive in ecosystems due to human activity, either intentionally or unintentionally

  • Intentional introductions: species may be traded or transported as biological controls for pests

  • Unintentional introductions: species may be transported unknowingly due to global transport of goods and people, e.g. in seawater present inside ships

Impact on ecosystem dynamics

• Invasive species can often exploit a new niche when they arrive in their new ecosystem; this is because they may lack natural predators or competitors

• This can lead to uncontrolled population growth of the invasive species and significant ecological changes

  • Competition: native species may be displaced or driven to extinction due to competition for resources like prey, soil nutrients, light, or space

  • Predation: invasive species may cause drastic declines in prey populations

  • Disease introduction: native species may lack immunity to diseases brought by invasive species

  • Biodiversity loss: a reduction in biodiversity decreases ecosystem productivity and stability

Example: kudzu

• Kudzu (Pueraria montana) is a plant, native to Japan and southern China, that was was introduced to the US for ornamental purposes and soil erosion control

• The plant grows extremely fast, up to 30 cm (1 foot) per day, spreading aggressively via runners

• Kudzu overwhelms ecosystems, creating "kudzu graveyards" by covering and out-competing native plants

CC BY-SA 4.0, Rhododendrites, via Wikimedia Commons

Example: zebra mussels

• Zebra mussels (Dreissena polymorpha), native to the Black Sea and Caspian Sea, spread to Europe and North America via ships

• They are known for clogging waterways and water treatment systems due to high reproductive success

• Zebra mussels disrupt ecosystems by competing with native species and altering aquatic environments

CC BY-SA 1.0, User Lamiot on fr.Wikipedia, via Wikimedia Commons

Human activities

• Ecosystems naturally change over time due to environmental factors, but human activities significantly accelerate these changes

• Human-driven changes increase as the human population increases and include

  • the introduction of diseases

  • habitat destruction

  • climate change,

• This leads to alterations in ecosystem structure, biodiversity, and species distributions, e.g.:

  • accelerated biodiversity loss

  • reduced ecosystem productivity

  • disrupted species interactions

• These negative effects then contribute to decreased ecosystem resilience, making ecosystems more vulnerable to further environmental changes

Human impact on ecosystems

Introduction of new diseases

• Human actions can introduce diseases to new regions, devastating native species with no natural immunity, e.g.:

  • Dutch elm disease: a fungal infection spread by human activity, decimating elm populations

  • potato blight: a pathogen introduced through trade, causing widespread crop failures and ecosystem disruption

Habitat change

• Human activities such as urbanization, agriculture, and resource extraction destroy or fragment habitats, reducing biodiversity,e.g.:

  • global climate change has seen changes in weather patterns and species distributions, leading to habitat loss and forcing migrations

  • logging and deforestation disrupt ecosystems, resulting in habitat destruction and soil degradation

  • urbanization converts natural landscapes into developed areas, displacing native species

  • mono-cropping causes simplification of ecosystems, reducing plant and insect diversity, which impacts food chains

Geological & meteorological activity

• Geological and meteorological events, such as El Niño, continental drift, and meteor impacts, create significant abiotic and biotic changes in ecosystems

  • In turn these may lead to shifts in habitat, species distribution, and ecosystem dynamics over time

• These events are not necessarily anthropogenic, but human activity may accelerate their occurrence or effects

Example: El Niño

• An El Niño climate event occurs every 2–7 years, characterized by sea temperatures rising 0.5°C or more above average in the eastern Pacific

• Effects:

  • Warmer ocean temperatures off Peru cause thermal expansion and sea level rise

  • Cooler waters near Australia and Indonesia result in reduced precipitation and droughts

  • Changes in water temperature and precipitation affect forest and wetland ecosystems, causing vegetation die-offs, altered drainage, and soil acidification

  • Abiotic and biotic changes disrupt ecosystem balance, affecting species interactions

Example: continental drift

• The movement of tectonic plates reshapes continents and alters ecosystem distribution over geological time

• Effects:

  • Changes in mineral resource distribution, critical for life

  • Seismic events like earthquakes and volcanoes redistribute heat from the Earth’s mantle, creating abiotic changes across ecosystems

  • Plate movements can result in dramatic shifts in species habitats and resource availability

Example: meteor impact

• Meteor impacts can cause sudden, dramatic ecosystem changes, as illustrated by the Chicxulub impact 66 million years ago

• Effects:

  • The asteroid impact likely caused the mass extinction event that ended the age of dinosaurs

  • Clouds of hot dust and vapor made conditions lethal for many species

  • Iridium deposits near the impact site and the fossil record confirm this event

  • New abiotic conditions led to the evolution of new species and ecosystems