1. Species Interactions and Community Ecology
Chapter 4

2. Species Interactions Competition Occurs when Resources Limited:
Competition – relationship where multiple organisms seek same limited resources
Interspecific – between different species
Intraspecific – between same species
Niche – functional role of species in a community
Fundamental niche – full niche species occupies
Realized niche – part of the niche organism actually fills

4. Exploitive Relationships:
Predation – one species hunts, captures, kills, and consumes another species
Top-down control – predator controls prey population
Bottom-up control – prey controls predator population
Both have effect on size of each other population
Parasitism – one species depends on another species for sustenance
When parasite is a disease it’s called a pathogen

5. Other Symbiotic Relationships:
Symbiosis – relationship between species that live in close proximity
Mutualism – both species benefit
Honey bee and flower
Commensalism – one species benefits, other species neither helped nor harmed
Cattle egret and cow
Amensalism – one species is harmed, other species unaffected
Cattle creating trails in grass

6. Ecological Communities
Energy and Trophic Levels:
Some of the most important interactions are feeding relationships, and matter and energy movement between trophic levels
Trophic level – rank in feeding order
Autotrophs/producers convert solar into chemical energy through photosynthesis, 1st trophic level
Small % of autotrophs use geothermal energy, called chemosynthesis

7. Primary consumer – eats producers, 2nd trophic level, herbivores
Secondary consumers – eats primary consumers, 3rd trophic level
Carnivores – meat eaters
Tertiary consumer – predators on highest trophic levels, consume secondary consumers, 4th trophic level
Omnivores – eat everything
All except autotrophs are heterotrophs

8. Some organisms consume nonliving organic matter
Detritivores - scavenge waste products or dead bodies
Millipedes, soil insects
Decomposers - break down organic litter, other nonliving matter into simpler chemicals to be used by plants
Fungi, bacteria

9. Energy, Biomass, and Numbers decrease at Higher trophic Levels:
Energy is used inefficiently and most is lost as heat
Each trophic level has only about 10% of the energy of the level under it
There is less biomass (mass of living matter) with each higher trophic level

11. Food Webs Show Feeding Relationships and Energy Flow:
Food chain - linear series of feeding relationships
Food web - visual map of feeding relationships and energy flow

13. Some Species Have More Impact:
Keystone species - species that has wide-reaching impact far out of proportion to its abundance
Removal of a keystone species has substantial ripple effects
Significantly alters the food web
Trophic cascade - phenomenon in which predators at high trophic levels indirectly affect populations at low trophic levels
Disturbance - event that causes rapid changes in the environment that alters the community or ecosystem

14. Disturbance and Succession:
Succession - predictable series of changes in a community following a disturbance
Primary succession - disturbance removes all vegetation and soil life
Community is built from scratch
Pioneer species - the first species to arrive in a primary succession area (e.g., lichens, mosses)
Secondary succession - disturbance dramatically alters, but does not destroy, all local organisms