Topic 9.10 Notes – Human Impacts on Biodiversity

What Human Impacts on Biodiversity Are

Biodiversity can decline in three connected ways:

• Genetic diversity means variation within a species or population. Fewer alleles means less ability to adapt.
• Species diversity means both the number of species and how evenly they are represented.
• Ecosystem diversity means the variety of habitats, communities, and ecological processes.

Biodiversity loss is broader than extinction. It also includes:

• Local extirpation when a species disappears from one area but still exists elsewhere
• Population decline even if the species is still present
• Lower species richness or evenness
• Loss of genetic variation
• Replacement of diverse systems with simplified ones like monocultures

Why this matters:

• Lower stability and resilience when conditions change
• Reduced productivity
• Weaker ecosystem services such as pollination, water purification, and nutrient cycling

The big idea tying the topic together is that human pressures often hit biodiversity at the same time, not one by one.

The HIPPCO Causes of Biodiversity Loss

HIPPCO stands for the six main human pressures.

Habitat destruction

This is when habitat is removed, converted, or degraded so native species cannot use it well.

Common causes include:

• agriculture
• urban development
• roads and pipelines
• logging
• mining
• reservoirs and other infrastructure

Degradation means the habitat still exists physically but is lower quality. A forest with noise, light, contamination, or selective logging may still be there, but many species can no longer thrive. Specialists usually suffer more than generalists because specialists need narrower conditions.

Roads, trails, and utility corridors can also split habitat and create edge effects, where conditions near the opening differ from the forest interior.

Edge effects along a habitat corridor

Invasive species

These are nonnative species that establish and cause ecological harm. They reduce biodiversity through:

• competition
• predation
• disease spread
• habitat alteration
• food-web disruption

Example:

• Burmese python in the Florida Everglades. This invasive predator reduces native mammal and bird populations.

Population growth

As human population grows, demand rises for land, food, water, energy, transportation, and materials. That increases habitat conversion, pollution, emissions, and extraction. Impact depends on per-capita consumption and technology too, not just number of people.

Pollution

Pollution can kill organisms, disrupt reproduction and development, and degrade habitat quality.

Examples you should know:

• pesticides kill nontarget species
• excess nitrogen and phosphorus cause eutrophication and low oxygen
• plastics cause ingestion and entanglement
• sediment buries habitat and blocks light
• acid deposition changes soil and water chemistry
• noise disrupts communication and migration
• artificial light disorients nocturnal and migratory species

Persistent pollutants can bioaccumulate in one organism and biomagnify up the food chain.

Climate change

Climate change alters habitat through:

• temperature change
• precipitation change
• sea level rise
• shifting seasonal timing

This can force range shifts and create phenology mismatches, where linked species no longer line up in timing.

Examples:

• loss of Arctic sea ice
• coastal squeeze, when rising seas push habitat inland but development blocks that movement

Overexploitation

This means harvesting organisms faster than they can recover.

Examples include:

• overfishing
• hunting and poaching
• logging beyond regrowth rates
• wildlife trade

Example:

• North Atlantic cod fisheries collapse

Habitat Fragmentation and Why Scale Matters

Habitat fragmentation happens when a large continuous habitat is broken into smaller isolated patches.

Main causes:

• roads
• pipelines
• agriculture
• urban development
• logging

Main effects:

• smaller patch size
• greater isolation
• less movement and gene flow
• more inbreeding risk
• more edge habitat and stronger edge effects
• more human access, hunting, invasives, and disturbance

Edge effects mean edge areas get more sunlight, wind, temperature swings, noise, pollutants, light, predators, invasive species, and roadkill, with lower humidity than interior habitat.

Species respond differently. What matters includes home-range size, dispersal ability, specialization, need for interior habitat, migratory behavior, reproductive rate, and tolerance of roads or people. There is no single fragmentation threshold that harms every species.

Domestication and Reduced Genetic Diversity

Domestication means humans manage and selectively breed organisms for desired traits. That can shrink genetic diversity if reproduction comes from a small number of commercial lines.

Risks of low genetic diversity:

• fewer alleles
• less adaptability
• greater disease vulnerability

Examples:

• honeybee colonies
• domestic livestock

A species can stay abundant and still lose genetic diversity. That distinction gets tested.

How Biodiversity Loss Can Be Reduced

Protected areas

These include parks, reserves, refuges, and marine protected areas.

• Benefit: limit habitat conversion and extraction, protect breeding and feeding areas
• Limits: need enough size, funding, enforcement, and the right habitat inside boundaries
• Unintended issue: conflicts with local communities, or climate change may shift habitat outside the protected area

Habitat corridors

Corridors connect isolated patches and improve movement and gene flow. Wildlife crossings are part of this.

Example:

• Banff National Park overpasses and underpasses with fencing

Drawbacks include cost, poor design, and possible spread of invasive species, disease, or fire.

Sustainable land use

Examples:

• selective logging
• streamside buffer zones
• agroforestry and shade-grown crops
• rotational grazing
• clustered development
• road placement that avoids critical habitat

These reduce damage, but they usually do not preserve original biodiversity completely.

Habitat restoration

This can include replanting natives, removing invasives, restoring hydrology, reconnecting floodplains, rebuilding dunes or reefs, and reintroducing species. It can improve function, but it is slow, expensive, and uncertain.