3.2A Human impacts on biodiversity Notes

1. Human activities have become the main driver of biodiversity loss, disrupting natural systems both directly (through exploitation and hunting) and indirectly (by altering habitats and global processes).
2. While direct threats involve immediate harm to species, indirect threats alter ecosystems, making survival difficult over time.
3. These factors are causing species extinctions, habitat degradation, and ecosystem imbalances, affecting global biodiversity.
4. Impacts can be divided into:
   1. Direct threats: Activities that directly target organisms or their populations.
   2. Indirect threats: Activities that alter environmental conditions and indirectly affect living organisms.

Direct Threats to Biodiversity

1. Overharvesting and Overexploitation

1. Overharvesting occurs when species are extracted faster than they can reproduce or recover.
2. This includes overfishing, overhunting, and excessive logging.
3. Once overharvesting crosses the maximum sustainable yield, species populations can collapse, disrupting food chains.

2. Poaching

1. Poaching involves illegal hunting or capture of wildlife for trade, food, or cultural uses.
2. It often targets large mammals and endangered species due to high market demand for ivory, skins, horns, or traditional medicine.
3. The bushmeat trade also drives hunting of primates and forest mammals, reducing population sizes and increasing the risk of zoonotic disease transmission.

3. Illegal Pet and Wildlife Trade

1. The illegal wildlife trade is worth approximately US$23 billion annually, ranking fourth after arms, drugs, and human trafficking.
2. Species traded include parrots, turtles, primates, snakes, and big cats.
3. Poaching for the pet trade destabilizes wild populations and increases extinction risk.
4. The Convention on International Trade in Endangered Species (CITES) helps regulate and restrict global wildlife trade.

Indirect Threats to Biodiversity

1. Habitat Loss and Fragmentation

1. Habitat destruction is the greatest cause of biodiversity loss.
2. Activities such as agriculture, urban expansion, logging, and mining destroy or fragment ecosystems.
3. Fragmented habitats reduce gene flow, isolate populations, and increase extinction risk.

2. Climate Change

1. Climate change alters temperature, rainfall, and sea levels, shifting habitats and migration patterns.
2. Polar species like polar bears and penguins are losing habitat due to melting ice.
3. Coral reefs experience bleaching due to temperature stress, leading to mass die-offs.
4. Species with narrow niches or slow reproductive rates cannot adapt quickly enough, leading to population declines.

3. Pollution

1. Pollution affects air, soil, and water ecosystems, disrupting physiological processes in plants and animals.
2. Major forms:
   1. Chemical pollution (pesticides, heavy metals, fertilizers).
   2. Plastic pollution: marine animals ingest or become entangled in waste.
   3. Oil spills: destroy marine habitats and smother wildlife.
   4. Eutrophication from nutrient runoff: causes algal blooms and oxygen depletion.

4. Invasive Alien Species

1. Introduced (non-native) species can outcompete, prey on, or hybridize with native species.
2. They often thrive because they lack natural predators in their new environment.

The Amplifying Effects of Multiple Human Impacts on Ecosystems

1. Most ecosystems are affected by more than one human activity simultaneously.
2. These compounding pressures, such as pollution, invasive species, and climate change, interact and amplify each other’s effects.
3. Reduced biodiversity weakens ecosystem resilience, meaning ecosystems recover more slowly after disturbances.

1. Interaction Between Climate Change and Other Stressors

1. Climate change intensifies the impact of other threats like pollution and invasive species.
2. Warmer temperatures expand the range of invasive pests (e.g., mosquitoes, bark beetles).
3. Coral reefs, already stressed by ocean acidification, are further damaged by pollution and overfishing.
4. Droughts and floods driven by climate change worsen the effects of deforestation and soil degradation.

2. Pollution and Habitat Degradation

1. Pollutants can weaken ecosystems already fragmented by human expansion.
2. Urbanization creates impermeable surfaces that prevent water absorption, intensifying flooding and soil erosion.

3. Invasive Species in Stressed Ecosystems

1. When ecosystems are degraded or climate-stressed, native species lose competitiveness.
2. Invasive species exploit the weakened conditions, spreading faster and reducing native biodiversity.

Investigating Human Impact on Biodiversity (Fieldwork Application)

Objective:

To study how human activity affects biodiversity using field sampling techniques.

Method 1: Transect Sampling

1. Place a transect line perpendicular to a source of disturbance (e.g., road, factory, or urban edge).
2. Use quadrats at intervals along the transect to record:
   1. Species presence and abundance
   2. Percentage vegetation cover
3. Analyze results using Simpson’s Diversity Index to quantify biodiversity change.

Method 2: Random Sampling Comparison

1. Select two contrasting habitats (e.g., polluted vs. unpolluted lake).
2. Randomly place quadrats and record species diversity and abundance.
3. Use statistical tests such as a t-test or Mann–Whitney U test to determine if differences are significant.