energy and trophic structure Flashcards
definition
the portioning of biomass between trophic levels
can be demonstrated as a trophic pyramid
with producers at base and secondary, tertiary, quaternary consumers on top
Chemical energy is transferred through feeding and stored as biomass
- Producers are autotrophs fixing energy from light or chemicals
- Energy is transferred between trophic levels through feeding
- Energy stored as biomass
- Determines trophic structure and the shape of the trophic pyramid
- Energy obtained from sources such as the sun
- Energy transfer efficiency ≈ 10%
*This limits the no. Of trophic levels an ecosystem can support and also means fewer organisms can be supported at higher trophic levels - Most lost as heat energy through cellular respiration
Trophic efficiency =
Energy in one trophic level/ Energy in trophic level immediately below
Nutrients
Healthy organisms require between 30 and 40 micro/macronutrients
These cycle through the trophic levels and abiotic components such as soil
Certain elements are also returned to the environment via gas exchange
Decomposers
Return nutrients in detritus to the environment making nutrients available to autotrophs and releasing carbon into the atmosphere
Autotrophs
Net primary productivity = gross primary production/ respiratory losses
NPP = GPP/R
Rate of primary production is relied on in many industries
Net secondary production
see diagram
Factors influencing transfer of biomass
- Efficiency of consumption
- Efficiency of assimilation – digestibility and ability to absorb
- Efficiency of production – proportion converted to waste compared to proportion used to produce biomass
^Hence causing only 10% transfer between levels
Endotherms have lower productivity than ectotherms as maintaining body temp increases energy demand
Top-down control
Biomass of lower trophic levels controlled by abundance of consumers
Bottom-up control
Nutrient availability to predators depends on producers abundance
Top-down control: biomass of lower trophic levels is controlled by the abundance and activity of consumers e.g. predator-prey interactions.
Bottom-up control: abundance and relative success of populations are controlled by biomass and productivity of populations in trophic levels below.
Factors influencing transfer in biomass
Source of energy:
e.g. hydrothermal vents
- Chemosynthesis: energy produced when inorganic nutrients are oxidised by archaea and bacteria
- Uptake of CO2 using energy from inorganic compounds
- CO2 used to produce carbohydrates
Trophic cascade
Trophic cascade
The effect of trophic interactions being propagated along a food web – bottom up or top-down
Possible through interconnections between trophic levels
e.g. direct through population or indirect through hydrological factors or vegetation cover
Factors influencing trophic cascade
Natural disaster e.g. wildfires wiping out primary producers or causing them to seek food elsewhere
Human activity e.g. over exploitation, proximity influence – such as wild boar consuming farmed palm fruit instead of foraging in Malaysia (aka a subsidy cascade is created)
Invasive species e.g. introduction of earthworms into boreal forest Great Lakes, Northern America – earthworms are non-native, they decompose the duff layer of leaf litter upsetting surface nutrient balance, and breaking down this carbon sink. Earthworms mix the acidic top layer of soil with their preferred more basic soil located below alkalising surface soil and damaging hyphal networks. This decreases boreal forest and allows other trees to colonise the area.
Great Lakes Worm watch citizen science campaign started 1999 to monitor earthworms and show citizens how to limit their spread – as the most common distribution is by tire treads. anticipating their spread is essential in future conservation
Modelling the niche and trophic structure
Using the Fossil Record
* Shows evolutionary trend of primary producers and consumers
* Highlights potential mass extinction events
* Life assemblages
Using Geological Principles:
* ‘Uniformitarianism
Using Facies Fossils:
Particular fossils show environmental conditions
* Rugosa corals found in Permo-Triassic beds.
* Foraminifera, a primary consumer shows abiotic factors
Fossil records can be used for paleoecological modelling
Environmental case studies: Tundra
Low productivity environment , Northern Canada, Alaska, Russia and Scandinavia
Fragile ecosystem depend on reliable repeated yearly temp cycles
Mosses, lichens, lemmings, hare, geese, arctic fox and snowy owl
Plant growth and all populations operates on a four year cycle rather than seasonally due to harsh habitat
e.g. it is possible to see a peak in lemming populations every 4 years on a population graph
The trophic web does not form a clear pyramid of trophic levels in this case (see notes for web)
^ A harsh habitat with generalist predators
Bottom up control from the 4 yearly plant cycle
Also top down evidence – no lemmings without predator presence as without predators they overconsume resources and cannot sustain their population, keystone species lemmings control both plant and predator abundance
Tundra: Arctic Fox conservation
Example: Norwegian Arctic fox captive breeding programme moving arctic fox from critically endangered to endangered
- A keystone predator and environmental engineer became endangered due to hunting
- A threatened species within the tundra ecosystem
Arctic Fox impacts on tundra trophic structure:
- Influences reproductive success and abundance of species at a lower trophic level (eg shorebirds and waterfowl)
- Denning behaviour- ecological hotspots
Threats:
* Global warming
* Loss of prey (eg lemmings)
* Slow replacement of the tundra habitat with boreal forest
Environmental case study: Hydrothermal vents
- Chemosynthetic energy base
- Extremely isolated populations
- Aseasonal, highly conserved
- Very limited and poorly understood distribution
Chemicals are fixed by bacteria held in symbioses with organisms higher up the food chain
chemosynthetic energy base
Isolated – independent from daylight world (do not rely on marine snow debris from above)
again the web does not form a clear pyramid
(see chemosynthesis diagram and food web)
Microbial loop a semi-independent food web which die forming a microbial mat
Hydrothermal vent conservation
Ecologically rare and vulnerable
O Rare habitat (approx 50km2) colonized by rare species
O Unpredictable reactions to a major change
O Natural variability of vents
O Scientific uncertainty (Recovery? Extinction?)
Methods:
O Protection laws ( eg Endeavour Hydrothermal Vents Marine Protected Area in Canada)
O Protection from disruptive activities
O Regulation of deep sea mining
Protection laws and regulation of deep sea mining essential to preserve hydrothermal vents
Human effects on trophic structure and biodiversity
Climate change – temp flux affects distribution and interaction of species
Urbanisation leads to habitat degredation and fragmentations – reconfiguring food webs decreasing biodiversity
The importance of apex predators
This group is most at risk of extinction
Loss has cascading effect through out trophic structure as it removes top down control
They limit prey density and control mesopredators
Loss of apex predators results in mesopredator release, increasing predation pressure and lowering biodiversity
*Trophic downgrading
Key-stone species
Role in determining community structure and their removal causes change in species composition
Example: Sea otters (Enhydra lutris)
*Removal -leads to a higher composition of sea urchins and therefore a rapid decline in kelp beds
*Consequences for inshore flora and fauna (grazing pressure)
*Reestablishment – decrease sea urchin populations and increase vegetational biomass
Trophic rewilding
Species reintroduction to re-establish trophic levels
Translocation of non-native species of tortoise to maintain biodiversity
*A strategy for the restoration of top-down trophic interactions and cascades, to raise biodiversity using species reintroduction
*Focus on the restoration of megafauna
*Trophic cascades (ecosystem function and biodiversity)
*Loss of megafauna causing trophic downgrading
Why?
*Biodiversity decline
*Species and ecosystem function loss
*Habitat loss
Trophic rewilding example: Tortoise reintroduction on Round Island Mauritius
The Mauritian Wildlife Foundation members aiding the Albabra giant tortoises on Round Island
((PDF) Reintroduction (MS version of entry in Encyclopedia of Ecology) (researchgate.net)
The translocation of nonnative Aldabra giant tortoise (Aldabrachaelys gigantea) and Radiated tortoise (Astrochylys radiata) to the Mauritian islands
*Translocation: the mediated movement of living organisms from one area to another
*Ecological replacement to increase ecosystem functioning
*Successful translocation based on survival, breeding success and health
Evidence:
- Restoring seed dispersal and grazing function on the islands
mitigating the human impact on trophic structure.
Control of invasive species
reintroduction of species
human education
habitat conservation
conservation of existing species
