Lecture 19 Flashcards
Ecological Roles
- Determined by their trophic interactions
- Determines the influence of an organism on the movement of energy and nutrients through an ecosystem
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)
Detritus
- part of the first level
Detrivores
- 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
- Second law of thermodynamics states that during any transfer of energy, some is dispersed and becomes unusable:
- 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
- Common where productivity is lowest (nutrient poor regions of the open ocean)
- Ex. Phytoplankton turnover is high, associated with high growth rate and short life span compared with phytoplankton of nutrient-rich waters
Positive Relationship Between Net Primary Production and Amount of Biomass Consumed by Herbivore
- suggests that herbivore production is limited by the amount of food available
- Biomass is proportional to NPP and what gets consumed above it ( more stuff = more ability to consume)
Herbivores on Land
- 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 reachh carrying capacity
- Predator removal experiments support this
Autotrophs have defenses against herbivory
- such as secondary compounds, spines, etc
- Plants of resource-poor environments tend to have stronger defenses 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
- Higher in aquatic ecosystems than in terrestrial ecosystems
- Tends to be higher for carnivores than herbivores
Assimilation Efficiency
- 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
Animals Have a Carbon: Nutrient Ratio
- Will be similar to the animals consuming them
Assimilation Efficiencies of herbivores and Detritivores
20-50%