The Living World – Part 2 AP Env Sci 2011-2012

All Ecosystems Have a Similar Biotic Structure In Summary All Ecosystems Have a Similar Biotic Structure

Food Chains and Food Webs

Food Chain or Food Web ? Food Chain: Squirrel eats the nut, fox eats the squirrel. Caterpillar eats the leaf, warbler eats the caterpillar, hawk eats the warbler. Food Chain is a specific pathway. Food Web: Collection of all food chains Interconnected pathways

A Food Web

How Many Trophic Levels? Usually no more than three or four in terrestrial ecosystems. Sometimes five in marine ecosystems. Why? Heterotrophs are not as “efficient” as autotrophs At each higher trophic level, biomass is 90% less than level before Biomass: total combined mass of all organisms at given trophic level

The Biomass Pyramid

Why a Pyramid Instead of a Rectangle? Much food consumed by heterotrophs is not converted to body mass. Much of the biomass of the producer goes directly to decomposers. Consumers that eat consumers must be larger than what they are eating. Sets Limits.

Energy Flow Pyramid Similar to Biomass Pyramid (matter is NOT energy) Average 90% Loss at each level Ecological Efficiency

Non-Feeding Relationships Mutually Supportive: Mutualism: benefit to both species Example: flower/pollinating insects Symbiotic: Symbiotic relationships can be mutualistic or parasitic Flea: not mutualistic

Non-Feeding Relationships: Competitive All-Out competition is rare – each species occupies own habitat or ecological niche Ecological Niche: What animal feeds on Where it feeds When it feeds Where it finds shelter Response to abiotic factors Nesting

Non-Feeding Relationships: Competitive Resource Partitioning Both Competitors Can Thrive Apparent Competitors Occupy Different Niches: Bats vs. Swallows Both eat flying insects Bats: night-flying insects Swallows: day-flying insects Competitive Exclusion Principle Direct Competition Eliminates One Competitor Example: European rabbit in Australia -> demise of several marsupial species