Lecture 19: Energy Flow and Food Webs Flashcards
Trophic Interactions
- what they eat and what eats them
- Can change over time
Trophic Levels
- Describe the feeding positions of groups of organisms in ecosystems
- All organisms are either consumed by other organisms or enter the pool of dead organic matter (detritus)
- First (primary producers - autotrophs), second (primary consumers - herbivores), third (secondary consumers - primary carnivores), fourth (tertiary consumers - secondary carnivores)
Detritus (dead organic matter)
- part of the first level
Detrivores (equivalent to herbivores)
- part of the second level
Allochthonous
- external energy inputs
- Found in water systems
- Inputs can be important in stream ecosystems (99.8%)
Autochthonous
- Energy produced by autotrophs within the system
- Energy input increases from the headwaters toward the lower reaches of a river
As you Go Downstream
- velocity decreases
- nutrient concentrations increase
Energy flow among Trophic Levels
- Amount of energy transferred from one trophic level to the next depends on food quality and consumer abundance and physiology
- Energy will decrease with each trophic level
Trophic Pyramid
- Portrays the relative amounts of energy or biomass of each trophic level
- Very large at base and gets smaller as you go to the top
- Due to some of the biomass at each level not being consumed, so it is dispersed in the transfer to the next level
Terrestrial Ecosystems
- Energy and biomass pyramids are similar
- Biomass is closely associated with energy production
Aquatic Ecosystems
- Biomass pyramid inverted
- Live and die quickly, energy is produced and then leaves the ecosystem
Inverted biomass pyramids
- more common where productivity is lowest, such as nutrient-poor regions of the open ocean.
- Low productivity system = inverted pyramid
terrestrial vs aquatic biomass
- terresteral consume a much lower proportion of autotroph biomass than herbivores in most aquatic ecosystems
- On average 13% of terrestrial NPP is consumed
- Aquatic ecosystems average of 35% NPP is consumed
Herbivores are Constrained by Predators
- never reach carrying capacity
- Predator removal experiments support this
Autotrophs have defences against herbivory
- such as secondary compounds, spines, etc
- Plants of resource-poor environments tend to have stronger defences than plants from resource-rich environments
Phytoplankton are more nutritious for herbivores than terrestrial plants
- Terrestrial plants have structural components such wood (with few nutrients)
- Freshwater phytoplankton have carbon
- nutrient ratios closer to those of herbivores than to those of terrestrial plants
Trophic Efficiency
amount of energy at on trophic level divided by the amount of energy at the trophic level immediately below it
Trophic Efficiency incorporates three types of efficiency
- Consumption efficiency
- Assimilation efficiency
- Production efficiency
Consumption Efficiency
-Proportion of available energy that is consumed
- Higher in aquatic ecosystems than in terrestrial ecosystems
- Tends to be higher for carnivores than herbivores
Assimilation efficiency
- Proportion of ingested food that is assimilated
- Determined by food quality and the physiology of the consumer
- Food quality of plants and detritus is low because of complex compounds such as cellulose, lignins, and humic acids that are not easily digested and low concentrations of nutrients such as nitrogen and phosphorus
Production efficiency
- Proportion of assimilated food that goes into new consumer biomass
- Is strongly related to the thermal physiology and size of the consumer
Assimilation Efficiencies of herbivores and Detritivores
20-50%
Assimilation Efficiency of Carnivores
80%
Endotherms
- Digest food more completely than ectotherms
- Thus have higher assimilation efficiencies
- Allocate more energy to heat production
- Have less for growth and replication than ectotherms
- Body size affects heat loss ( as body size increases, the surface area-tovolume ratio decreases)