Rucete ✏ Campbell Biology In a Nutshell
Unit 8 ECOLOGY — Concept 56.2 Population Conservation Focuses on Population Size, Genetic Diversity, and Critical Habitat
Conservation biologists work at the population level to prevent extinction by addressing genetic variation, effective population size, and habitat quality. They use case studies, models, and interventions to stabilize small populations and recover endangered species.
1. Extinction Risks in Small Populations
- Small populations are vulnerable to inbreeding, genetic drift, and environmental change
- These lead to an extinction vortex: loss of genetic diversity → lower fitness → reduced survival and reproduction
- Example: Northern elephant seals survived a bottleneck but still have low genetic diversity
2. Case Study: Greater Prairie Chicken
- Habitat fragmentation dropped Illinois population below 50 by 1993
- Genetic analysis revealed low variation and reduced fertility
- 271 birds translocated from other states → genetic diversity and hatching success improved
- Demonstrated genetic rescue can reverse extinction vortex
3. Minimum Viable Population (MVP)
- MVP = smallest population size needed for long-term survival
- Estimated via population viability analysis (PVA): models probability of survival (e.g., 95% over 100 years)
- Example: Yellowstone grizzly bears
- MVP = 70–90 bears for 95% survival
- Actual population ≈ 700, but effective population size (Ne) ≈ 175 due to breeding limits
4. Effective Population Size (Ne)
- Ne = number of breeding individuals contributing genes
- Formula: Ne = 4NfNm / (Nf + Nm)
- Ne is lower than total due to sex ratios, age, or social structure
- To increase Ne: promote gene flow by introducing unrelated individuals
5. Case Study: Red-Cockaded Woodpecker
- Endangered in Southeast U.S.; relies on mature longleaf pine forests
- Threats: fire suppression and logging
- Conservation efforts:
- Controlled burns to manage undergrowth
- Artificial nest cavities installed → 18 of 20 colonized
- Habitat restoration helped recovery
6. Weighing Conflicting Demands
- Must balance ecological goals with economic and social needs
- Examples:
- Ranchers vs wolf reintroduction in Yellowstone
- Shade-grown coffee supports bird biodiversity
- Best solutions are “win-win” strategies for nature and people
In a Nutshell
Population conservation focuses on maintaining viable, genetically diverse populations in suitable habitats. By understanding extinction dynamics and using strategies like gene flow and habitat restoration, conservationists can stabilize endangered species. But lasting solutions require balancing science with society’s needs and protecting the ecosystems that support biodiversity.