Community Ecology Chapter 41

Community Interactions Community: populations of different species living in the same area. 1. Interspecific competition: members of different species compete for resources (food, space, water, sun, etc). Gause’s competitive exclusion principle: the niches of two species can’t overlap significantly for very long.

Gause’s Experiment

Fundamental vs. Realized Niches

Species Interactions cont. 3. Predation/Herbivory – members of one species feed directly on another species, without living in or on the prey. Symbiosis: 4. Parasitism -- one species lives in or on another species, causing harm to the host. 5. Mutualism – two closely associated species benefit each other. 6. Commensalism – one species benefits; other species not harmed nor helped.

“Extra important” species Dominant species – often the most abundant, highest biomass in the community; shapes the habitat for other species (often vegetation). It’s not uncommon for invasive species to take over, pushing out native species, and changing the entire community. Keystone species – may not be abundant, but control community structure (otters).

Ecosystems Chapter 42

Solar Energy Most solar energy that reaches Earth is reflected or absorbed by atmosphere. What reaches us: Visible light Infrared radiation (heat) Ultraviolet radiation (UV) What it does for us: Warms troposphere and land (w/ help of greenhouse effect). Drives the water cycle. Fuels photosynthesis

Greenhouse Effect http://www.earthguide.ucsd.edu/earthguide/diagrams/greenhouse/

Living Components of Ecosystems Producers (autotrophs) – photosynthetic organisms that convert light, water, and carbon dioxide into glucose and oxygen. (Chemosynthesizers use heat and H2S.) Ex: plants, algae, phytoplankton, some bacteria.

Classification of Consumers Consumers (heterotrophs) – get energy by feeding on other organisms or their wastes. Primary consumers (herbivores) – feed on producers. Secondary/Tertiary consumers (carnivores) – feed on consumers. Omnivores – eat plants and animals. Scavengers – feed on dead organisms. Detritivores – feed on dead organisms and wastes. (detritus feeders, decomposers)

Energy/Matter Flow in Ecosystems About 1% of solar energy reaching earth is harnessed by producers and converted to chemical energy (Gross Primary Productivity). About 90% of that energy is used by the producer and lost as heat, leaving 10% available for the next trophic level (Net Primary Productivity). Limits to productivity include amounts of light, water, and nutrients.

Ecological Pyramids Ecological efficiency is % usable energy transferred from one level to the next in the form of matter (usually about 10%). For most land ecosystems, amount of biomass decreases with each higher trophic level. Also, number of organisms at each higher level decreases.

Pyramid of Biomass

Primary Productivity Gross primary productivity – rate at which producers convert light energy into biomass. (greatest in shallow ocean and coral reefs; lowest in deserts and open ocean) Net primary productivity – rate at which producers store biomass for use by consumers.

Nutrients cycle through ecosystems Biogeochemical processes recycle chemical elements essential to life. Water cycle Carbon cycle Nitrogen cycle Phosphorus cycle

Keystone species and trophic cascades