Ecology Unit 4 Chapter 2

What is a food web?

A network showing the feeding relationships and energy transfers between organisms in an ecosystem.

Why do ecologists use food webs?

They provide basic but useful information about community structure and how organisms obtain energy.

What is a trophic level?

A group of organisms that obtain their energy in similar ways.

What determines an organism's trophic level?

The source of its energy and nutrients within the food web.

How does energy flow begin in an ecosystem?

Radiant energy from sunlight is converted into chemical energy through primary production.

What is primary productivity?

The rate at which autotrophs produce new biomass.

What are primary producers?

Autotrophs, such as algae and phytoplankton, that produce their own organic matter.

What are primary consumers?

Herbivores that obtain energy by eating primary producers.

What are secondary consumers?

Organisms that obtain energy by eating primary consumers.

What are tertiary consumers?

Organisms that obtain energy by eating secondary consumers.

What are herbivores in a trophic pyramid?

Primary consumers that feed directly on producers.

What are planktivores?

Organisms that eat plankton, positioned above herbivorous primary consumers in the trophic pyramid.

What are piscivores?

Fish-eating predators that occupy higher trophic levels.

What does the direction of arrows in a food web indicate?

Arrows point from the organism being eaten toward the organism consuming it, showing the direction of energy transfer.

What is an example of a four-level aquatic food chain?

Phytoplankton → zooplankton → small planktivorous fish → piscivorous fish.

Why can an organism occupy multiple trophic levels?

Some organisms eat food from different trophic levels, so their position can vary depending on what they consume.

What is the role of bacteria and benthic detritivores in a food web?

They process dead organisms and organic waste from multiple trophic levels, helping recycle nutrients.

What is the microbial loop?

A process where microorganisms consume dissolved organic matter and transfer some of that energy back into the aquatic food web.

What is the epilimnion?

The upper layer of lake water, where the microbial loop occurs.

What is dissolved organic matter (DOM)?

Organic material dissolved in water that can be consumed and processed by microorganisms.

What is dissolved organic carbon (DOC)?

The carbon-containing portion of dissolved organic matter.

What organisms are involved in the microbial loop?

Bacteria, viruses, protists, and fungi.

What is the role of bacteria in the microbial loop?

Bacteria consume dissolved organic matter.

What is the role of protozoa in the microbial loop?

Protozoa consume bacteria, transferring energy to another level of the food web.

What is the role of zooplankton in the microbial loop?

Zooplankton consume protozoa and can release organic material through sloppy feeding.

What is the role of fish in the microbial loop?

Fish consume zooplankton and release nutrients and organic matter through waste.

What is the first pathway of the microbial loop?

DOM → bacteria → protozoa → zooplankton.

What is the second pathway of the microbial loop?

DOM → bacteria → protozoa → zooplankton → fish.

How do terrestrial inputs contribute to DOM?

Organic material from land enters aquatic ecosystems and contributes to dissolved organic matter.

What is sloppy feeding?

When organisms release part of their food into the surrounding water while eating.

How do shredders contribute to DOM?

Shredders break down coarse woody debris and increase its surface area, helping microorganisms process the material.

How does zooplankton feeding on phytoplankton release DOC?

Zooplankton release some organic carbon into the water while consuming phytoplankton.

What is viral cell lysis?

The breaking open of cells caused by viruses, releasing their organic contents into the water.

How does phytoplankton death contribute to DOM?

Dead phytoplankton release organic material that microorganisms can process.

How does excrement contribute to the microbial loop?

Waste products release nutrients and organic matter that can be recycled.

What is the protozoan clearance rate?

The rate at which protozoa capture or remove suspended food particles from water.

What does the six-protozoa clearance rate graph demonstrate?

Different protozoa capture particles of different sizes at different rates.

What is particle-size niche partitioning?

Different organisms consume different particle sizes, potentially reducing competition for food.

How does energy return to the food web through the microbial loop?

Microorganisms consume dissolved organic matter and are then eaten by larger consumers.

What are dinoflagellates in the microbial loop diagram?

Shown as primary producers.

What are copepods in the microbial loop diagram?

Zooplankton shown as primary consumers.

What is a young anchovy in the microbial loop diagram?

Shown as a secondary consumer.

What is a mackerel in the microbial loop diagram?

Shown as a tertiary consumer.

What is the first law of thermodynamics?

Energy cannot be created or destroyed; it can only be transferred or transformed.

What is the second law of thermodynamics?

Energy transfers are not 100% efficient; some usable energy is degraded and released as heat.

How is energy lost during trophic transfers?

Energy is lost through respiration, heat, waste, and material that is not consumed or assimilated.

What is the 10% rule of energy transfer?

On average, approximately 10% of the energy or production at one trophic level is transferred to the next.

Why is the 10% rule only an average?

Different organisms have different assimilation efficiencies, metabolic rates, growth efficiencies, and feeding behaviors.

How much energy is lost between trophic levels?

Approximately 90% energy loss per transfer, emphasizing heat loss.

If producers have 10,000 energy units, how much reaches primary consumers?

Approximately 1,000 energy units.

If producers have 10,000 energy units, how much reaches secondary consumers?

Approximately 100 energy units.

If producers have 10,000 energy units, how much reaches tertiary consumers?

Approximately 10 energy units.

If producers have 20,000 energy units, how much reaches the second trophic level?

Approximately 2,000 energy units.

If producers have 20,000 energy units, how much reaches the third trophic level?

Approximately 200 energy units.

What is a productivity pyramid?

A diagram showing how biomass or energy production decreases as you move upward through trophic levels.

Why do productivity pyramids become narrower at higher trophic levels?

Energy is lost during each transfer, leaving less energy available for production at higher levels.

Which trophic level has the highest productivity?

The first trophic level, consisting of primary producers.

What is biomass?

The mass of living material present at one time within a specified area.

What is primary production?

The change in biomass of autotrophs over a specified period and area.

What is gross primary production (GPP)?

The total amount of production by autotrophs before subtracting the energy they use in respiration.

What is net primary production (NPP)?

Gross primary production minus the energy used by autotrophs in respiration.

What is secondary production?

The production of new biomass by heterotrophs consuming plants, animals, microorganisms, fungi, or detritus.

What is the difference between primary and secondary production?

Primary production is performed by autotrophs, while secondary production is performed by heterotrophic consumers.

What is a biomass pyramid?

A diagram showing the amount of living biomass present at each trophic level.

What is an inverted biomass pyramid?

A situation where primary consumers have more standing biomass than primary producers.

How can an aquatic biomass pyramid be inverted?

Phytoplankton reproduce rapidly and are consumed quickly, allowing them to support large consumer populations despite low standing biomass.

What is the phytoplankton turnover rate?

The rate at which phytoplankton biomass is replaced through growth and reproduction.

What is energy ingested (I)?

The total amount of energy consumed by an organism through food.

What is energy assimilated (A)?

The portion of ingested energy that is absorbed into the organism's body.

What is energy egested?

Energy contained in undigested material that leaves the organism as waste.

What is respiration in terms of energy?

Assimilated energy used for metabolism and released as heat.

What is production in ecological terms?

The portion of assimilated energy converted into new consumer biomass.

What is the equation for energy budget?

I = A + egested energy; A = P + R.

What does assimilation efficiency measure?

The proportion of ingested energy that an organism successfully absorbs.

How is assimilation efficiency calculated?

Formula: A/I × 100%.

What does growth efficiency measure?

The proportion of ingested energy converted into new biomass.

How is growth efficiency calculated?

Formula: P/I × 100%.

What is the assimilation efficiency if I = 100 and A = 60?

60%.

What is the growth efficiency if I = 100 and P = 15?

15%.

What indicates high assimilation efficiency?

Most of the energy consumed by an organism is absorbed into its body.

What indicates low assimilation efficiency?

Much of the ingested material cannot be digested and leaves the organism as waste.

Which animal has the highest assimilation efficiency in the lecture's table?

Weasel, at 95%.

Which animal has the lowest assimilation efficiency in the lecture's table?

Grasshopper, at 37%.

Which animal has the highest growth efficiency in the lecture's table?

Weasel, at 20%.

Which animal has the lowest growth efficiency in the lecture's table?

Sparrow, at less than 0.1%.

What is the most important control on primary productivity?

Energy availability and the first and second laws of thermodynamics.

What are secondary controls on primary productivity?

Temperature, nutrient availability, predation, competition, and disturbance.

What controls secondary production?

The amount of primary production and the efficiency with which consumers assimilate and transfer energy.

Why does primary production vary between habitats?

Habitats differ in available energy, temperature, nutrients, and other biological and physical conditions.

Why do less productive ecosystems generally support fewer trophic levels?

Less energy enters the food web, leaving even less available to support higher-level consumers.

What nutrient most commonly limits freshwater productivity?

Phosphorus (P).

What did Dillon and Rigler (1974) study?

The relationship between available phosphorus and algal biomass in North American lakes.

How is algal biomass measured in phosphorus studies?

Using chlorophyll a concentration, measured in mg/m³.

What units are used for available phosphorus in the lecture graph?

Milligrams of phosphorus per cubic meter (mg/m³).

What was the result of the Findlay and Kasian (1987) experiment?

Phytoplankton biomass increased substantially in the fertilized lake.

What is eutrophication?

Nutrient enrichment of an aquatic ecosystem that increases primary productivity and can lead to excessive algal growth.

What is bottom-up control?

The availability of resources such as nutrients and energy regulates primary productivity.

What is top-down control?

Predators and consumers regulate the abundance of organisms at lower trophic levels.

What is a trophic cascade?

An indirect interaction where predators influence organisms at lower trophic levels.

What can cause primary producer biomass to differ from its nutrient-based potential?

Predation and other food-web interactions can change producer abundance.