Community ecology examines how species interact and relate to one another within biological communities. Ecologists represent feeding interactions through food chains and complex food webs. Organisms are classified based on trophic levels according to their position in the food web. Communities experience natural and human-caused disturbances and undergo succession over time. Some species have outsized impacts on community structure as keystone species, ecosystem engineers, or foundation species. Community ecologists study how communities resist or recover from disturbances.

1. Ecology I Community Ecology

2. Questions asked by Community Ecologists How do species coexist? How do they relate to each other? How do communities change with time?

3. Food chains and webs Food chain = simplified linear diagram of who eats whom Food web = complex network of who eats whom We can represent feeding interactions (and thus energy transfer) in a community:

4. Classification based on trophic level Trophic level : all organisms that share the same general type of food. Unit 2: Ecology 1: Principles of Matter, Energy and LIfe

5. Aquatic examples Terrestrial examples Detritivores and decomposers Crayfish Water mold Aquatic bacteria Tertiary consumers Cormorant Hawk Secondary consumers Fish Rodent Primary consumers Zooplankton Grasshopper Producers Phytoplankton Grass Detritivores and decomposers Earthworm Shelf fungus Soil bacteria

6. White oak Caterpillar and other insects on leaves Spider Eastern chipmunk Cedar waxwing Beetles and other insects Blackberry Ticks Eastern cottontail White-tailed deer Rat snake Red-bellied woodpecker Shelf fungus Deer mouse Grasses Earthworm Soil bacteria American toad

7. Community Disturbance Natural vs. Human Caused

8. “ Natural” Changes Catastrophic: Drought, flood, fire, volcano, earthquake, hurricane, disease Gradual Climate change, immigration and emigration, ecological succession, evolution

9. Human-caused Changes Catastrophic: Deforestation, overgrazing, soil erosion, pesticides, urbanization, mining, toxic releases, etc. Gradual Habitat loss, introduced species, overharvesting, pest control, salinization, waterlogging, compaction

10. Community Succession … ..a series of directional, predictable, quantifiable changes that communities go through following a disturbance • Primary succession: Pioneer species colonize a newly exposed area (lava flows, glacial retreat, dried lake bed). • Secondary succession: The community changes following a disturbance (fire, hurricane, logging). Early successional stages  late successional stages Pioneer stage  intermediate stage  climax community

12. Secondary terrestrial succession Grasses, herbs, forbs Shrubs, seedlings Shrubs, poplar trees Pines Oaks, hardwoods LE 5-7

14. Community Stability Resistance A community that remains stable despite disturbance is showing resistance to the disturbance. Resilience A community shows resilience when it changes in response to disturbance but later returns to its original state.

15. Community Organizers Keystone species Ecosystem Engineer Foundation Species

16. Keystone species … are species that have especially great impacts on other community structure and identity despite low numbers or biomass. If keystone species are removed, communities change greatly. A “keystone” holds an arch together.

17. Keystone species When the keystone sea otter is removed, sea urchins overgraze kelp and destroy the kelp forest community.

18. Ecosystem Engineer … a species that exerts influence on ecosystem or community by changing the physical environment If ecosystem engineer is removed, communities change greatly. Termite mound in Australia Termites play a vital role in recycling nutrients by building mounds from sub-surface soils With the aid of bacteria which live in termite guts, they can digest otherwise indigestable cellulose from the plant matter that they eat

19. Foundation species … a species that strongly influences community structure by creating environments suitable for other species and by major effects on ecosystem processes If a foundation species is removed, communities change greatly. Example: dominant forest tree such as Ponderosa Pine

20. What have community ecologists learned? When we try to pick out anything by itself we find that it is bound fast by a thousand invisible cords that cannot be broken, to everything in the universe. John Muir, Journal, July 27, 1869