Community Ecology Chapter 41

What you need to know The role of competitive exclusion in interspecific competition The symbiotic relationships How energy flows through the ecosystem via food chains and food webs The role of habitat and niche as part of an organism’s life The difference between primary and secondary succession

Community Relationships Producer/consumer Predator/prey relationship Symbiosis Parasitism: One + One – Commensalism One negligible Mutualism Both +

Habitats and Niches Habitats are the part of the environment an organism lives (home address) Niche is the role the organism plays in the habitat (job/profession; how it fits in) Ecological niche: sum total of biotic and abiotic factors used by species Fundamental niche: niche a species will normally occupy Realized niche: niche the species actually occupies as a result of competition

Competitive Exclusion Principle G.F. Gause Grew protists separately with success Put them together and one drove the other to extinction Two species cannot coexist in a community if their niches are identical One species will use the resources more efficiently

Resource Partitioning Competitive exclusion does not always lead to the extinction of a species Sometimes a species will modify its fundamental niche into a realized niche to survive

Important Species Dominant species: most abundant species Keystone species: exert strong control on food web Robert Paine – University of Washington

Wolves change Rivers https://www.youtube.com/watch?v=ysa5OBhXz-Q Which one is it? http://www.naturefootage.com/video_clips/NZ47_018 http://www.animalplanet.com/tv-shows/animal-planet-presents/videos/top-10-odd-animal-couples-tree-ants-caterpillars/

Diversity Species diversity is often used to measure the health of an ecosystem Increased diversity = increased survivability

Ecological Succession Colonization of barren environments Sequence of specific steps Primary Succession Colonization of new, previously uninhabited placed (new islands, lava deposits) Secondary succession Recolonization of previously inhabited, but destroyed environments (wildfires, floods, vast storms)

Primary Succession Erosion of rock by water/weather leading to thin layer of soil (nutrient poor) Pioneer species arrive Lichens, mosses, and fungus: cause further erosion, organic matter (detritus) Hardy, low growing plants and grasses Larger plants, larger animals

Primary Succession Shrubs, pine trees, and predators Climax community: biome that is expected according to climate. Pioneer species are replaced Timeline = hundreds of years

Secondary Succession Presence of soil and surviving roots Fire-activated seeds germinate, root balls sprout Fast growth and recovery Climax community similar to old one Invasive species Timeline: 1-2 years

Secondary Succession

Food Chain Linear feeding relationship between several organisms

Food Web Interconnected feeding relationships in an ecosystem among many organisms (multiple food chains)

The Pyramids Divided into trophic levels which represent individual organisms/populations Energy Pyramid Biomass Pyramid Pyramid of Numbers

Energy Pyramid Producers trophic level (bottom): most energy stored Primary consumers: less energy Secondary consumers: less energy Energy is lost in the daily function of organisms

Biomass Pyramid Biomass: amount of living matter at each trophic level Usually expressed as grams/unit area Highest biomass is always at the bottom (producers)

Pyramid of Numbers Number of individuals at each trophic level Meadow 1,000 grasses 200 caterpillars 10 birds 1 hawk Forest 10 trees