Species Interactions and Community Ecology Chapter 4

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

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

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

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

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

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

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

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

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

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