99–107 — ECOLOGICAL ENERGY-TRANSFER ROLE
The Ecological Energy-Transfer Roles layer classifies organisms and biological systems according to their position and functional action within networks of biomass production, consumption, decomposition, nutrient release, and environmental modification.
Operational definition
Layer type: Food-web and ecosystem-function layer Governs: Items 99–107
Governing question
What does this system do within the larger ecological movement of matter and usable free energy?
Included roles
- primary producer;
- consumer;
- parasite or parasitoid;
- scavenger;
- detritivore;
- decomposer;
- mineralizer;
- trophic bridge;
- ecosystem engineer.
Inclusion rule
A role belongs here when it is defined by a relationship between the focal system and:
- a resource population;
- another organism;
- dead organic material;
- a trophic network;
- an elemental cycle;
- an environmental structure.
Relational rule
Ecological role is not an intrinsic metabolic property in isolation.
An organism may be:
- a consumer in relation to one resource;
- prey in relation to another organism;
- a host to a parasite;
- a decomposer of one substrate;
- an ecosystem engineer through its physical activity.
The same species may therefore hold several roles simultaneously.
Identity-versus-role distinction
“Chemoorganoheterotroph” is a nutritional identity.
“Decomposer” is an ecological role.
Many animals, fungi, bacteria, and protists may share the first identity while occupying very different ecological positions.
Producer rule
A primary producer must add newly fixed organic carbon to the system.
Using light does not by itself establish primary production. A photoheterotroph may use light for energy while remaining dependent on preexisting organic carbon.
Engineer rule
An ecosystem engineer is classified by the environmental consequence of its activity, whereas Niche Construction under Part XII records the focal organism’s energetic investment in creating that consequence.
99. Primary producer
Fixes inorganic carbon into biomass using:
99.1 Photoautotrophy
External input:
light
99.2 Chemoautotrophy
chemical/geochemical free energy
A phototroph is not automatically a primary producer; a photoheterotroph uses light but still depends upon organic carbon.
100. Consumer
100.1 Primary consumer
Consumes primary producers.
100.2 Secondary or higher consumer
Consumes other consumers.
100.3 Omnivore
Acquires resources across multiple trophic positions.
100.4 Microbial consumer
Consumes cells, dissolved metabolites, or particulate organic matter.
101. Parasite or parasitoid
- host remains alive during much or all resource extraction
- host is eventually killed
- host metabolism subsidizes parasite reproduction
102. Scavenger
Consumes relatively large dead organisms or tissues.
103. Detritivore
Ingests particulate dead organic matter.
104. Decomposer
Chemically breaks down organic material, commonly through extracellular enzymes followed by absorption.
105. Mineralizer
Converts organic nutrients into inorganic forms that reenter biogeochemical cycles.
106. Trophic bridge
Transfers production between otherwise weakly linked channels.
Examples:
- mixotroph connecting primary production and predation
- microbial loop organisms
- filter feeders
- host–symbiont complexes
107. Ecosystem engineer
Changes the future availability or distribution of energy and matter by altering the environment.