# Lecture 28: Conservation Biology and Global Change

## General Biology II — Organismal, Evolution & Ecology

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## Learning Objectives

By the end of this lecture, students will be able to:

1. Define biodiversity and describe its three levels (genetic, species, ecosystem)
2. Explain the major threats to biodiversity and their relative impacts
3. Describe the causes and consequences of habitat loss and fragmentation
4. Explain how invasive species, overexploitation, and pollution threaten species and ecosystems
5. Describe the causes and projected consequences of anthropogenic climate change
6. Explain the principles of conservation biology including small population dynamics, minimum viable population, and reserve design
7. Describe strategies for preserving biodiversity at the species, community, and landscape levels

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## Lecture Content

### I. Biodiversity and Its Value

**Biodiversity** — the variety of life at all levels of biological organization: **Genetic diversity** — variation in genes and alleles within and among populations; essential for adaptation to changing environments. **Species diversity** — the variety of species in an ecosystem or region (richness + relative abundance) **Ecosystem diversity** — the variety of ecosystems, habitats, and ecological processes in a region (forests, wetlands, coral reefs, grasslands) Current estimates: ~8.7 million eukaryotic species on Earth; only ~1.5-2 million described; vast microbial diversity largely uncharacterized. **Value of biodiversity**: **Ecosystem services** — processes provided by ecosystems that sustain human life: Provisioning: food, fiber, freshwater, timber, fuel, genetic resources. Regulating: climate regulation, water purification, flood control, pollination, disease regulation, carbon sequestration. Supporting: nutrient cycling, soil formation, primary production, oxygen generation. Cultural: recreation, aesthetics, spiritual value, education. **Economic value** — pharmaceuticals derived from natural products (~50% of drugs), agricultural genetic resources, ecotourism. **Intrinsic value** — every species has inherent worth independent of human utility.

### II. The Biodiversity Crisis

Earth is experiencing a **sixth mass extinction** — current extinction rates are estimated at 100-1,000 times the background extinction rate. IUCN Red List — the most comprehensive assessment of species conservation status: Categories: Least Concern, Near Threatened, Vulnerable, Endangered, Critically Endangered, Extinct in the Wild, Extinct. As of recent assessments: >40,000 species are threatened with extinction. Major taxonomic groups at risk: amphibians (~41% threatened), mammals (~26%), reef-building corals (~33%), conifers (~34%), sharks and rays (~37%).

### III. Major Threats to Biodiversity

#### A. Habitat Loss and Fragmentation

The **single greatest threat** to biodiversity worldwide. Causes: agriculture (largest driver), urbanization, logging, mining, infrastructure development. Tropical deforestation — ~10 million hectares of forest lost per year; tropical forests harbor >50% of terrestrial species. **Habitat fragmentation** — remaining habitat is broken into small, isolated patches: Reduces total habitat area. Increases edge effects — edge habitat has different abiotic conditions (more light, wind, temperature fluctuation) than interior → favors generalist and invasive species; detrimental to interior specialists. Reduces connectivity — impedes dispersal, gene flow, and migration → genetic isolation → inbreeding. **Island biogeography theory (MacArthur and Wilson)** — applied to habitat fragments: Species richness on an island (or fragment) is determined by the balance between immigration and extinction rates. Larger fragments support more species (lower extinction rate) Fragments closer to source populations receive more immigrants (higher immigration rate) Implications for reserve design: larger reserves and connected reserves support greater biodiversity.

#### B. Invasive (Introduced) Species

**Invasive species** — non-native organisms that establish, spread, and cause ecological or economic harm in a new environment. Often lack natural predators, parasites, and competitors in the new range → rapid population growth. Mechanisms of harm: predation on native species, competition, habitat alteration, disease introduction, hybridization. Examples: Brown tree snake (Boiga irregularis) in Guam — decimated native bird populations (many endemic species extinct or extirpated) Zebra mussels (Dreissena polymorpha) in North American Great Lakes — filter feeders that outcompete native mussels, clog water infrastructure. Cane toads (Rhinella marina) in Australia — toxic to native predators. Kudzu vine in southeastern United States — smothers native vegetation. Chytrid fungus (Batrachochytrium dendrobatidis) — caused amphibian declines and extinctions worldwide.

#### C. Overexploitation

Harvesting species faster than populations can replenish. Examples: overfishing (collapse of Atlantic cod stocks, bluefin tuna decline), bushmeat hunting, illegal wildlife trade (ivory, rhino horn, exotic pets), whaling. Particularly threatens large, slow-reproducing species (K-selected); species with high economic value; and species with small geographic ranges.

#### D. Pollution

Chemical contamination of air, water, and soil. **Nutrient pollution (eutrophication)** — excess nitrogen and phosphorus from agricultural runoff → algal blooms → decomposition consumes dissolved oxygen → hypoxic dead zones (e.g., Gulf of Mexico, Baltic Sea) **Acid rain** — SO2 and NOx from fossil fuel combustion → sulfuric and nitric acid in precipitation → damages forests, acidifies lakes, leaches soil nutrients. **Plastic pollution** — accumulation in marine environments; microplastics ingested by marine organisms; entanglement; enters food webs. **Persistent organic pollutants (POPs)** — DDT, PCBs, dioxins; bioaccumulate and biomagnify through food chains. **Heavy metals** — mercury, lead, cadmium; from industrial processes; neurotoxic; biomagnify. **Light and noise pollution** — disrupt animal behavior, migration, communication, and reproduction.

#### E. Disease

Emerging infectious diseases can devastate naive populations. Chytrid fungus — catastrophic amphibian declines on multiple continents. White-nose syndrome (Pseudogymnoascus destructans) — fungal disease killing millions of North American bats. Spread facilitated by climate change, habitat disturbance, and global trade/transport.

### IV. Climate Change

**Anthropogenic (human-caused) climate change** — driven primarily by greenhouse gas emissions from fossil fuel combustion, deforestation, agriculture, and industrial processes. **Greenhouse effect** — naturally occurring; greenhouse gases (CO2, CH4, N2O, H2O vapor) absorb and re-radiate infrared radiation → warms Earth's surface. Without the natural greenhouse effect, Earth's average temperature would be ~-18 degrees C instead of ~15 degrees C. **Enhanced greenhouse effect** — human activities have increased atmospheric concentrations of greenhouse gases: CO2: ~280 ppm (pre-industrial) → >420 ppm (current); primary driver. CH4 (methane): from livestock, rice paddies, landfills, fossil fuel extraction; ~80x more potent than CO2 over 20 years. N2O (nitrous oxide): from agriculture (fertilizer) and combustion. **Observed changes**: Global average temperature has risen ~1.1 degrees C above pre-industrial levels. Sea level rise (~20 cm since 1900; accelerating) — thermal expansion of seawater + melting of glaciers and ice sheets. Retreat of Arctic sea ice and glaciers worldwide. Ocean acidification — pH has decreased by ~0.1 units since pre-industrial (a ~30% increase in H+ concentration) Increased frequency and intensity of extreme weather events (heatwaves, droughts, hurricanes, floods) Shifts in precipitation patterns.

#### Consequences for Biodiversity:

**Range shifts** — species moving toward higher latitudes and elevations to track suitable climate conditions. Species that cannot migrate fast enough or lack suitable habitat face extinction. **Phenological mismatches** — changes in the timing of seasonal events (flowering, migration, breeding) may decouple species interactions (e.g., pollinators emerge before flowers bloom) **Coral bleaching** — elevated sea temperatures cause corals to expel their symbiotic zooxanthellae → whitening (bleaching) → if prolonged, coral death → reef ecosystem collapse. **Ocean acidification** — reduced carbonate ion availability → impairs shell and skeleton formation in mollusks, corals, echinoderms, and foraminifera. **Polar and alpine habitat loss** — ice-dependent species (polar bears, penguins, pikas) losing habitat. Synergistic effects — climate change exacerbates other threats (habitat loss, disease spread, invasive species expansion).

<image>A four-panel figure summarizing the causes and consequences of climate change. Panel A (Greenhouse effect): A diagram of Earth's atmosphere showing incoming solar radiation passing through the atmosphere and warming the surface. The surface emits infrared radiation, which is partially absorbed by greenhouse gas molecules (CO2, CH4, H2O, N2O shown as labeled molecular models) and re-radiated back toward the surface, trapping heat. An arrow shows excess greenhouse gases from factories, vehicles, deforestation, and livestock amplifying this effect. Panel B (CO2 trend): The Keeling Curve — a graph of atmospheric CO2 concentration from 1960 to 2025, showing the steady rise from approximately 315 ppm to over 420 ppm, with the characteristic seasonal sawtooth oscillation. A pre-industrial baseline at 280 ppm is marked. Panel C (Global temperature anomaly): A graph of global mean surface temperature anomaly from 1880 to 2025 relative to a 1951-1980 baseline, showing a clear upward trend especially from the 1970s onward, reaching approximately +1.1 degrees C. Panel D (Consequences collage): Four inset images arranged in a grid — upper left: a bleached white coral reef contrasted with a healthy colorful reef; upper right: a retreating glacier comparison (historical vs. present photograph of the same glacier); lower left: a map showing northward range shifts of species with arrows; lower right: a graph showing declining Arctic sea ice extent over the past four decades.</image>

### V. Conservation Biology Principles

**Conservation biology** — a goal-oriented, crisis discipline that applies ecology, genetics, evolution, and social science to preserve biodiversity.

#### A. Small Population Dynamics

Small populations are vulnerable to: **Genetic drift** — random fluctuations in allele frequencies have greater impact in small populations → loss of genetic diversity → reduced adaptive potential. **Inbreeding depression** — mating among close relatives increases homozygosity → expression of deleterious recessive alleles → reduced fitness (lower survival, reproduction) **Allee effects** — at very low population densities, per capita growth rate declines (difficulty finding mates, loss of cooperative benefits, predator swamping failure) **Demographic stochasticity** — random variation in birth and death rates can cause extinction in small populations. **Environmental stochasticity** — unpredictable environmental events (drought, disease outbreaks) disproportionately threaten small populations. **Extinction vortex** — a positive feedback loop: small population → reduced genetic diversity → lower fitness → smaller population → ... → extinction. **Minimum viable population (MVP)** — the smallest population size with a high probability (often defined as 95%) of persisting for a specified time (often 100 years) MVP estimates vary by species but are often in the hundreds to low thousands. **Population viability analysis (PVA)** — mathematical models that use demographic data to estimate extinction probability under various scenarios; used to guide management decisions.

#### B. Declining Population Approach

Focuses on threatened populations that are declining (not necessarily small yet) Diagnose the cause of decline → address the threat. Example: peregrine falcon decline was traced to DDT (eggshell thinning) → DDT banned → captive breeding and reintroduction → population recovery.

### VI. Conservation Strategies

#### A. Protected Areas

Nature reserves, national parks, marine protected areas (MPAs), wildlife refuges. Currently ~17% of terrestrial and ~8% of marine areas are protected (Kunming-Montreal Global Biodiversity Framework targets 30% by 2030) **Reserve design principles** (informed by island biogeography and landscape ecology): Larger reserves are better than smaller ones (support larger populations, more species) Connected reserves (wildlife corridors) are better than isolated ones (facilitate dispersal and gene flow) Single large reserve may be preferable to several small reserves (SLOSS debate), but multiple reserves can capture greater habitat diversity. Buffer zones around core protected areas reduce edge effects. Reserves should encompass biodiversity hotspots — regions with exceptionally high species richness and endemism that are under severe threat (e.g., tropical Andes, Mesoamerica, Madagascar, Sundaland, Mediterranean Basin).

#### B. Landscape and Ecosystem Management

**Wildlife corridors** — strips of habitat connecting isolated fragments; allow movement, migration, and gene flow (e.g., wildlife overpasses/underpasses, riparian corridors) **Restoration ecology** — re-establishing degraded ecosystems to a more natural state: Reforestation, wetland restoration, prairie restoration, coral reef restoration. Example: reintroduction of wolves to Yellowstone (1995) → trophic cascade → elk behavioral changes → riparian vegetation recovery → improved stream ecology. **Sustainable management** — managing resources (fisheries, forests, water) at rates that allow regeneration: maximum sustainable yield, ecosystem-based management.

#### C. Species-Level Conservation

**Ex situ conservation** — conservation outside natural habitat: zoos, botanical gardens, seed banks, captive breeding programs, cryopreservation of gametes/embryos. Captive breeding and reintroduction: California condor, Arabian oryx, black-footed ferret. **In situ conservation** — protection in natural habitat; preferred when possible. **Flagship species** — charismatic species used to promote conservation awareness and fundraising (e.g., giant panda, tiger, polar bear) **Umbrella species** — species whose protection confers protection on many co-occurring species due to large habitat requirements (e.g., grizzly bear) **Indicator species** — species whose health reflects the condition of the ecosystem (e.g., amphibians as indicators of water quality).

#### D. Addressing Climate Change

**Mitigation** — reducing greenhouse gas emissions: transition to renewable energy, energy efficiency, carbon capture, reforestation, methane reduction. **Adaptation** — adjusting human and ecological systems to cope with climate impacts: managed relocation of species, assisted gene flow, climate-resilient agriculture, coastal protection. International agreements: Paris Agreement (2015) — nations committed to limiting warming to well below 2 degrees C above pre-industrial levels, pursuing 1.5 degrees C target.

<image>A landscape-scale diagram illustrating conservation strategies and reserve design. The main image is a bird's-eye view of a region containing different land use types. In the center, a large core protected area (national park) is shown as a contiguous block of forest, labeled and color-coded green. Surrounding it is a buffer zone of managed land (lighter green). Two smaller reserve fragments are located to the north and south, connected to the core reserve by wildlife corridors (narrow green strips along rivers and ridgelines). Surrounding the reserves are agricultural lands (yellow), a city (gray), and a degraded area undergoing restoration (shown transitioning from bare ground to young trees). Arrows show animal movement through the corridors. Inset boxes around the margins illustrate key concepts: (1) edge effects — a cross-section diagram showing how temperature, light, humidity, and wind change from the forest edge to the interior, with invasive species and nest predators concentrated at edges; (2) species-area relationship — a log-log graph showing that larger areas support more species, with data points for islands or reserves; (3) the extinction vortex — a downward spiral diagram showing the cycle of small population to reduced genetic diversity to lower fitness to smaller population leading toward extinction.</image>

### VII. Moving Forward — The Future of Conservation

Biodiversity loss is accelerating, but conservation successes demonstrate that recovery is possible when threats are addressed. Key priorities: Expanding and connecting protected areas (30x30 initiative) Aggressive reduction of greenhouse gas emissions. Eliminating overexploitation (sustainable fisheries, combating wildlife trafficking) Controlling invasive species. Reducing pollution (especially nutrient pollution and plastics) Integrating conservation into land use planning and economic policy. Engaging local communities and indigenous peoples (who manage ~25% of Earth's land surface) in conservation decision-making. Conservation requires interdisciplinary collaboration — ecology, genetics, economics, policy, sociology, and ethics. The choices made in the coming decades will determine whether much of Earth's biodiversity survives the current century.

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