ELEMENTS OF OCEANOGRAPHY

 

TOPIC 17 - TROPHIC RELATIONSHIPS, FOOD CHAINS, AND WEBS

Overheads:

Biological Producers (autotrophs)
Organisms that generate their own food (carbohydrates) through photosynthesis or chemosynthesis
Metaphytes, algae, diatoms, bacteria
These organisms are mostly limited to the photic zone of the world's oceans (bacteria mostly live in aphotic zone)

Biological Consumers (heterotrophs)
All other organisms feed on producers, other consumers, decaying remains (carrion), or detritus
herbivores - eat plants
carnivores - eat other animals
scavengers - eat organic detritus and carrion
decomposers - like scavengers (fungi, bacteria)
omnivores - do two or more ofthe above

Consumer Feeding Strategies
filter feeders - sweep through the water column capturing any organism in their path that is not too large
browsers - scrape food offsurfaces or feed on plant or sessile benthic organisms
deposit feeders - eat sediment and extract organic materia lor small organisms from sediment
predators or scavengers - actively pursue other living or dead organisms

Simple Food Chains
A food chain is a sequence of animals and plants that feed on each other in sequence
Each level in the feeding sequence is called a trophic level
Plants always originate each food chain and represent the (lowest) producer trophic state
Animals occupy high trophic states feeding on plants and each other

An Example Food Chain
Lowest trophic level
Producer = Diatom
Herbivore = Copepod
Primary Carnivore = Anchovy
Secondary Carnivore = Tuna
Tertiary Carnivore = Human
Highest tropic level

Transfer of Energy and Mass in a Food Chain
In biological systems, energy flows one way only, even though nutrients may recycle
Biomass, the amount of matter per unit volume in an ecosystem, is a measure of stored energy
As one organism eats another, it uses the food (biomass) to generate energy for several functions - living, waste removal, growth
About 10% of the energy goes into growth
This shows out in a biomass pyramid associated with any food chain

Food Webs
Food chains are an overly simplified view of the true multidimensional food chains that occur in real communities
Individual organisms may occupy different trophic states with regard to other animals and food chains
The resulting view is really a Food Web of interconnected trophic states

Ecosystem Stability

Communities survive due to a set of checks and balances between species.

Population variation is a key factor - birthrate, recruitment, and death rate.

Environmental resistance defines the combinaiton of biotic and abiotic factors that limit a species populaiton.

Ecological succession shows the natural (and sometimes unnatural) evolution of ecosystems

 

Trace-Element Concentration in Food Webs
As part of photosynthesis or chemosynthesis, plants will absorb a variety of organic chemicals and trace elements which are added to the plant biomass
In most cases, these materials will be biologically neutral to the host organism
As consumers eat producers and are eaten in turn, the concentrations of these materials will increase
Eventually, their concentration will be high enough that they may become hazardous to health

 

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