Theory: Evolution / Ecology
1. Invasive Species and Extinction
Invasive species are among the leading causes of extinction globally (second only to habitat destruction). Introduced species may: outcompete native species for food/space, prey upon naive native species, introduce new diseases, hybridise with native species. Classic examples: Nile perch in Lake Victoria (caused extinction of ~200 endemic cichlid fish species), Brown tree snake in Guam (eliminated most native birds), Rabbits in Australia (massive ecological damage after introduction from Europe).
2. Galapagos Conservation
Galapagos Islands: home to many endemic species shaped by isolation and adaptive radiation. Giant tortoises: 13-15 subspecies/species, all endangered. Main threats: introduced species (goats, rats, cats, dogs), habitat modification, human settlement. Conservation successes: Project Isabela (largest island conservation effort) eliminated goats from northern islands using helicopters and hunting dogs (2006), allowing vegetation recovery and tortoise return.
3. Competitive Exclusion in Practice
Gause (1934) demonstrated competitive exclusion in lab with Paramecium species: P. aurelia and P. caudatum grown separately both survived; grown together, P. aurelia always outcompeted P. caudatum to extinction. However, in nature, complete competitive exclusion is rarer than expected because niches are rarely perfectly identical — resource partitioning allows coexistence.
4. Conservation Lessons
Key lessons from Abingdon tortoise case: Never introduce non-native species to isolated island ecosystems. Eradicate invasives early before populations establish. Captive breeding programs (attempted with Lonesome George) may be last resort but are costly. Genetic banking (preserving genetic material) for potentially extinct species. Small, isolated island species are disproportionately vulnerable to extinction.
Frequently Asked Questions
1. What is the story of the Abingdon Island tortoise? ⌄
The Pinta Island (Abingdon Island) giant tortoise (Chelonoidis abingdonii) was a subspecies of Galapagos giant tortoise. Goats were introduced to Pinta Island in the 1950s-1960s by humans. The goats rapidly multiplied and consumed the island's vegetation much more efficiently than the slow-growing, slow-reproducing tortoises. The last known Pinta tortoise, called "Lonesome George," was found alone in 1972. Despite attempts at conservation and breeding programs, Lonesome George produced no viable offspring. He died on June 24, 2012, marking the extinction of this subspecies.
2. What does this example illustrate ecologically? ⌄
This illustrates: Competitive exclusion: two species competing for the same resource cannot coexist — the more efficient competitor (goats) excluded the less efficient one (tortoises). Introduced/invasive species: goats (non-native) caused the extinction of a native species. Habitat destruction through overgrazing: removing vegetation affects the entire ecosystem. The "extinction vortex": small populations become increasingly vulnerable through inbreeding, demographic stochasticity.
3. What is competitive exclusion principle? ⌄
Gause's competitive exclusion principle: two species competing for exactly the same limited resource in the same niche cannot stably coexist indefinitely. The more efficient competitor will eventually exclude the other (outcompete it to extinction or reduce it to negligible numbers). Coexistence requires some ecological differentiation (niche partitioning).
4. What are other examples of extinction due to invasive species? ⌄
Classic cases: Dodo (Mauritius): extinct ~1681 due to habitat destruction + hunting + introduced predators (rats, cats, pigs eating eggs). Caribbean monk seal: extinct 2008, hunting + loss of habitat. Passenger pigeon: extinct 1914, massive hunting. Easter Island: native species eliminated by Polynesian settlers introducing rats and overexploiting resources.
5. What are the Galapagos Islands famous for? ⌄
Galapagos Islands (Ecuador): famous for Darwin's finches (adaptive radiation), Galapagos giant tortoises, marine iguanas, blue-footed boobies. Darwin visited in 1835 on HMS Beagle. Observations of beak variation in finches (14 species from one ancestor) across different islands contributed to his concept of natural selection. UNESCO World Heritage Site.