Rucete ✏ Campbell Biology In a Nutshell
Unit 8 ECOLOGY — Concept 54.5 Pathogens Alter Community Structure Locally and Globally
Pathogens—disease-causing organisms like viruses, bacteria, protists, viroids, and prions—play powerful roles in shaping community structure. Their impacts are especially strong when introduced to new environments where hosts lack evolved resistance.
1. Pathogen Introduction and Virulence
- Pathogens can cause dramatic changes when introduced to new habitats
- Example: Chestnut blight fungus devastated American chestnuts but had mild effects on Asian trees
- Native populations often lack natural resistance, amplifying impacts
2. Coral Reefs and White-Band Disease
- White-band disease devastated Caribbean staghorn and elkhorn corals
- Fish habitats declined → algae took over → herbivorous fish became dominant
- Storms worsened reef collapse and biodiversity loss
3. Sudden Oak Death (SOD)
- Caused by Phytophthora ramorum, a protist
- Introduced from Europe → spread in California, killing over a million trees
- Impacted birds like acorn woodpeckers and oak titmice
- Genome sequencing is underway to find solutions
4. Human Disease and Global Spread
- Global travel spreads pathogens rapidly
- H1N1 (swine flu) spread globally in 2009, killed over 18,000 people
- True death toll likely higher due to underreporting
5. Zoonotic Diseases
- ~75% of emerging diseases are zoonotic (animal-origin)
- Often spread via vectors like ticks, mosquitoes, lice
- Lyme disease case:
- Once blamed on mice, but shrews were found to infect more ticks
- Correct host ID is key to disease control
6. Avian Flu (H5N1)
- Spread by wild birds through saliva and feces
- 2003–2006: Spread from Southeast Asia to Europe and Africa
- Ecologists monitor migratory birds in Alaska to detect transmission early
7. Ecosystem Perspective on Disease
- Pathogens affect physical and biological interactions in ecosystems
- Effective control needs understanding of host-pathogen-vector networks
- Must integrate ecology, evolution, and epidemiology for better management
In a Nutshell
Pathogens profoundly affect community composition and stability, particularly when introduced to new environments. Zoonotic diseases, coral epidemics, and tree-killing fungi demonstrate how tightly disease dynamics are linked to ecological interactions. Understanding these effects requires a broad ecosystem perspective—essential for both conservation and public health.