Human Impact and Biodiversity
Evaluate how habitat loss, invasive species, pollution, climate change, and resource use affect ecosystems. Compare conservation strategies using evidence.
A lesson of Biology, in Homeostasis, Body Systems, and Ecology, about 10 minutes.
By the end of this lesson, you will be able to describe the major ways humans affect ecosystems, explain the value of biodiversity, describe the causes and consequences of species extinction, and understand conservation biology approaches.
The Big Idea
Humans have become the dominant force shaping Earth's ecosystems. The scale of human impact — habitat destruction, climate change, pollution, invasive species, overexploitation — is causing the sixth mass extinction in Earth's history. Understanding the science behind these impacts is essential for making informed decisions about conservation and sustainability.
Major Threats to Biodiversity
Habitat destruction/fragmentation (greatest threat):
- Deforestation (tropical rainforests harbor ~50% of all species)
- Wetland draining, coral reef bleaching, grassland conversion
- Habitat fragmentation: large habitats broken into isolated patches → edge effects; reduced gene flow; extinction risk
Climate change:
- Rising temperatures → range shifts (many species moving poleward or to higher elevations)
- Phenological mismatches (e.g., flowers bloom before pollinators arrive)
- Ocean acidification → coral bleaching, shell dissolution
- Melting ice → polar species loss
Invasive species:
- Non-native species introduced to new areas → outcompete native species, predation, disease
- Examples: cane toads in Australia, pythons in Florida Everglades, purple loosestrife in US wetlands
Overexploitation:
- Overfishing → fish population collapse (Atlantic cod, many shark species)
- Bushmeat hunting, poaching (elephants, rhinos)
- The passenger pigeon (once the most numerous bird in North America) was hunted to extinction by 1914
Pollution:
- Eutrophication: excess nutrients → algal blooms → dead zones (hypoxia)
- Pesticide bioaccumulation (DDT → thinning raptor eggshells → population collapse)
- Microplastics accumulating in marine food webs
Why Biodiversity Matters
Ecosystem services: benefits biodiversity provides:
- Provisioning: food, medicine, timber, fresh water
- Regulating: climate regulation, flood control, pollination, water purification
- Supporting: nutrient cycling, soil formation, primary production