EcosystemEcosystem EffectsEffects ofof OverfishingOverfishing OutlineOutline • Human exploitation: Land vs Sea • Altered Food webs • Escalating Human Impacts, from hunter gatherer to Globalization. American bison New Zealand Moas Australian diprotodont Sirenia But our exploitation of the sea is different • On the land, we replaced wild species with domestic species, and rebuilt the structure of terrestrial ecosystems • In the sea, we made important species functionally extinct and did not replace them Coral reefs Coral reefs Prehistoric Stock Depletion 1200 St. Thomas 1000 St. Martin 800 600 Saba 400 Nevis 200 Puerto Rico Average reef fish weight (g) 0 2000 1500 1000 500 0 Years before present Fishing Down the Food Chain 3.8 St. Thomas 3.7 Puerto Rico 3.6 Saba 3.5 St. Martin Trophic level index Nevis 3.4 2000 1500 1000 500 0 Years before present The working hypothesis: Three distinct transitions Three distinct transitions 1. Loss of macrofauna 2. Loss of structure 3. Rise of “pests” Human Impacts on Ecosystems 5 Climate change 4 Introductions 3 Human Mechanical population habitat Altered growth destruction ecosystems 2 Pollution 1 Fishing Then Now Global Demand Roving Bandits Expansion of the live fish trade Serial expansion and depletion of live fish trade ContributionContribution ofof fourfour speciesspecies toto thethe livelive fishfish tradetrade overover timetime 8 7 Plectropomus leopardus 6 Lepoard Coral Trout Epinephelus coioides Green Grouper 5 Plectropomus maculatus Coral Trout Epinephelus lanceolatus 4 Giant Qld Grouper kg/year) 6 Cheilinus undulatus Humphead Wrasse (10 3 2 Mass of live fish imported to Hong Kong Mass of live fish imported to Hong 1 0 1998 2000 2002 Year Summary • Human exploitation of the Land and Sea has altered foodwebs. • Even early human societies had an impact. • Population growth and emerging technologies have escalated the problem to a global scale Produced by For.