Conservation Biology and Global Change

Core Explanation

Biodiversity

Biodiversity encompasses the variety of life at multiple levels:

1. Genetic diversity: Variation in genes within a population or species. Low genetic diversity reduces a population's capacity to adapt to environmental change and increases extinction risk.
2. Species diversity: The variety of species in an ecosystem or across the biosphere. ~1.8 million species have been described; estimates of total species range from 5–30+ million.
3. Ecosystem diversity: The variety of ecosystems — forests, grasslands, wetlands, coral reefs, deserts, etc. Each provides distinct ecological services.

Threats to Biodiversity

Habitat Destruction and Fragmentation

The single greatest threat to biodiversity is habitat loss. When habitats are destroyed or fragmented:

• Total available habitat area decreases.
• Remaining patches become smaller and more isolated → populations within them are smaller, more vulnerable to extinction, and less likely to be recolonized.
• Edge effects increase: the boundary between habitat and altered land exposes organisms to different microclimates, predators, and invasive species.

Habitat fragmentation reduces connectivity, impedes migration and dispersal, and can lead to inbreeding depression in isolated populations. Wildlife corridors — strips of habitat connecting larger patches — can partially mitigate these effects.

Invasive Species

Invasive species are organisms introduced (intentionally or accidentally) outside their native range that establish, spread, and cause ecological or economic harm. They often thrive because they have escaped their native predators, pathogens, and competitors. Examples: kudzu vine in the southeastern US, zebra mussels in the Great Lakes, brown tree snakes in Guam, cane toads in Australia.

Overharvesting

Unsustainable hunting, fishing, and collection have driven many species to extinction or severe decline. Examples: passenger pigeon (extinct), Atlantic cod fisheries collapse, overharvesting of tropical hardwoods, rhino and elephant poaching for horns/ivory.

Pollution

Pollutants affect ecosystems through multiple pathways: nutrient runoff (eutrophication), toxic chemicals, oil spills, plastics, and atmospheric pollutants (acid rain from SO₂ and NOₓ emissions).

Climate Change

Climate change is reshaping ecosystems globally. Key mechanisms:

• Shifting ranges: Species distributions are moving poleward and to higher elevations as temperatures rise. Species unable to move fast enough — or blocked by habitat fragmentation — face extinction.
• Phenological mismatch: The timing of biological events (flowering, migration, breeding) is shifting. When interdependent species respond at different rates (e.g., birds arriving after their insect prey has already peaked), population declines can result.
• Ocean warming and acidification: Increasing atmospheric CO₂ is absorbed by oceans, forming carbonic acid and lowering pH (~0.1 pH unit decrease since pre-industrial times). Acidification impairs calcification in corals, mollusks, and some plankton — organisms that form the base of marine food webs.
• Sea-level rise: Threatens coastal ecosystems (salt marshes, mangroves) and low-lying islands through inundation and saltwater intrusion.

The Greenhouse Effect

The greenhouse effect is a natural phenomenon essential for life: greenhouse gases (CO₂, CH₄, N₂O, H₂O vapor) in the atmosphere absorb infrared radiation emitted by Earth's surface and re-radiate it, warming the planet. Without it, Earth's average temperature would be approximately −18°C instead of the current ~15°C.

The problem is the enhanced greenhouse effect: human activities — primarily fossil fuel combustion, deforestation, and agriculture — have dramatically increased atmospheric greenhouse gas concentrations:

• CO₂: ~280 ppm (pre-industrial) → ~420 ppm (2024)
• CH₄: ~700 ppb → ~1,900 ppb
• N₂O: ~270 ppb → ~335 ppb

Stratospheric Ozone Depletion (Distinct from Climate Change)

Critical distinction: Stratospheric ozone depletion and climate change are SEPARATE environmental issues with different causes and mechanisms:

CFCs are chemically stable in the lower atmosphere, allowing them to drift into the stratosphere where UV radiation breaks them apart, releasing chlorine atoms. A single Cl atom can destroy ~100,000 ozone molecules before being removed — a catalytic cycle of extraordinary efficiency. The Montreal Protocol phased out CFCs, and the ozone layer is projected to recover to 1980 levels by ~2060-2075.

Bioaccumulation and Biomagnification

Bioaccumulation is the buildup of a substance (typically a fat-soluble, persistent pollutant) in an organism's tissues over time. Biomagnification is the increase in concentration of that substance at successively higher trophic levels.

Example: DDT (dichlorodiphenyltrichloroethane)

• DDT is fat-soluble and resistant to metabolic breakdown.
• In aquatic ecosystems: water → phytoplankton (absorb DDT) → zooplankton → small fish → large fish → fish-eating birds.
• At each step, predators consume many prey organisms, concentrating DDT in their tissues. Concentrations in top predators may be 10,000–100,000× higher than in water.
• In birds, DDT interferes with calcium metabolism, causing thin eggshells that break during incubation. Bald eagles, peregrine falcons, and brown pelicans were driven to the brink of extinction before DDT was banned in the US (1972).

Mercury similarly biomagnifies: atmospheric mercury from coal combustion and industrial sources deposits in water, is converted to methylmercury by bacteria, and concentrates up aquatic food chains — posing neurological risks to humans (particularly developing fetuses) who consume large predatory fish.

How It Works — Conservation Strategies

• Protected areas: National parks, wildlife refuges, and marine protected areas preserve habitat. About 15% of Earth's land surface and ~8% of oceans are currently protected.
• Habitat restoration: Active restoration of degraded ecosystems (reforestation, wetland restoration, dam removal).
• Wildlife corridors: Connecting habitat fragments to allow gene flow and migration.
• Captive breeding and reintroduction: Programs for critically endangered species (California condor, black-footed ferret, Arabian oryx).
• Sustainable management: Regulating harvests (fishing quotas, forestry certification), managing invasive species, and reducing pollution.
• Ex situ conservation: Seed banks, botanical gardens, and zoos preserve genetic material outside natural habitats as an insurance policy.