Chapter 20 - Ecology
In most terrestrial and many aquatic ecosystems, the ________ food chain is the dominant pathway of energy flow.
detrital
Within any ecosystem, the two major food chains are the ________ food chain and the grazing food chain.
detrital
A(n) ________ chemical reaction must absorb energy in order to proceed.
endothermic
Which organism is most likely to have the highest assimilation efficiency?
endothermic carnivore, such as a lion
A chemical reaction requires energy to proceed. This would be
endothermic.
According to the first law of thermodynamics,
energy is neither created nor destroyed.
Where are the areas of highest NPP?
equator
Which of the following tree stands would you predict has the highest NPP?
30-60 years old
Detrital food chains contain all of the following except
herbivores.
NPP can be measured via satellite data because vegetation has
high reflectance in the NIR and low reflectance in VIS.
How does the open ocean have the highest relative net primary productivity while having one of the lowest mean biomass per unit area?
high turnover rate of plankton
Which group has the highest production efficiency?
insects
Why are there not seven or eight levels to a trophic food chain?
lack of trophic efficiency
Estimates of HANPP range around 20 percent, yet what percent of total heterotrophic biomass do humans make up?
less than 1 percent
Which factor is the primary control of productivity in aquatic systems?
light
What level of productivity would one predict with high levels of water supply but low temperatures?
low
In the surface waters of oceans, the two most limiting nutrients for primary productivity are
nitrogen and iron.
In which situation is the detrital food chain not more dominant than the grazing food chain?
open-water aquatic ecosystems
Which of the following has the highest assimilation efficiency?
spider
The amount of accumulated organic matter found in an area at a given time is the ________ crop biomass.
standing
For photosynthesis and productivity to occur, a plant must open its ________ to take in carbon dioxide.
stomata
Net primary productivity in an ecosystem increases as mean annual temperature
and mean annual rainfall increases.
Rates of herbivory are highest in
aquatic ecosystems dominated by phytoplankton.
If herbivores eat 1000 kcal of plant energy, approximately how much energy will be converted into the tissues of herbivores?
100 kcal
An ecologist studying productivity in a sample of grasses measures gross primary productivity as 1000 kcal/m2/yr and autotrophic respiration as 100 kcal/m2/yr. Based on these calculations, the net primary productivity would be
900 kcal/m2/yr.
(T/F) In a temperate rain forest, primary productivity remains relatively constant.
FALSE
(T/F) In all ecosystems, the biomass of primary producers is greater than the biomass of herbivores.
FALSE
(T/F) In all food chains, the flow of energy is unidirectional from the bottom to the top.
FALSE
(T/F) In most ecosystems, the biomass of carnivores is greater than the biomass of producers.
FALSE
(T/F) In terrestrial and shallow-water ecosystems, the grazing food chain is dominant over the detrital food chain.
FALSE
(T/F) Net primary productivity cannot be measured in aquatic ecosystems.
FALSE
(T/F) Net primary productivity is greater in temperate grasslands than in tropical rain forest.
FALSE
(T/F) Net primary productivity is greater in the open ocean than along the coast.
FALSE
(T/F) Primary producers form the base of all food chains.
FALSE
(T/F) The second law of thermodynamics is valid only in a closed system, such as a living organism.
FALSE
(T/F) Wealthy nations typically have lower rates of human appropriation of net primary productivity (HANPP) than developing nations.
FALSE
Which of the following formulas are correct regarding productivity?
GPP - R = NPP
________ primary productivity is the total rate of photosynthesis or energy assimilated by plants.
Gross
How do humans affect net primary productivity? Does the affluence of a society affect how humans appropriate net primary productivity?
Humans affect net primary productivity in various ways: • Land conversion into urban area • Land conversion into built-up land • Land conversion into agricultural land • Humans cause fires • Humans cause desertification • Causing long scale ecosystem degradation Human societies are part of Earth's NPP cycle but extend a disproportional influence in to. The extensive degree of human use of the planets resources, mostly via land use, results in various levels of impact on actual NPP. In the Nile Valley, irrigation had resulted in a considerable increase in primary production, but in most of the planet there is a notable trend of NPP reduction due to land changes. Reduction in NPP are also expected in the ocean as a result of climate change.
Which region represents the highest HANPP as a percentage of local NPP?
India
Describe the changes that might be expected to occur in allochthonous and autochthonous sources of carbon in the energy balance of flowing-water ecosystems from the smaller headwater streams to larger river systems.
It has been seen that the allochthonous from dissolved organic matter (DOM) and particulate organic matter (POM) is different every season (or it varies seasonally) according to the volume of water which flows from rivers and streams into the lake. whereas the allochthonous inputs are important in smaller lakes.
Describe the effects of temperature, moisture, length of photosynthetic period, and nutrient availability on net primary productivity in terrestrial ecosystems.
Net primary productivity is the rate of energy storage from organic matter resulting from respiration. Terrestrial net primary productivity increase with temperature, moisture, and nutrient availability. These factors are the ones which control the primary productions in terrestrial ecosystems. Let's take an example of temperature as one of basic factors. As temperature increase the NPP increase in terrestrial ecosystem thus greater variations of range. An increase in temperature results to an increase in dry matter productivity. If temperatures decrease, the rate of photosynthesis as well as productivity will be low so be it the NPP also decrease. NPP is high along the coast due to high temperatures compared to interior areas. Low temperatures also lead to reduction in moisture content thus increasing roots allocation. If evapotranspiration increase productivity also increase as well. Nutrient's availability nitrogen being a good example in the soil increase the NPP. Nutrients results to high productivity in ecosystems increasing the NPP. Length of growing season that is the photosynthesis periods increase leads to an increase in NPP.
Explain the difference between primary production and secondary production. How is secondary production affected by primary production?
Primary production - plants and autotrophs produce energy through photosynthesize. where they use sunlight and Carbon dioxide and releases oxygen and glucose (energy). In this way they form the first level of biomass in trophic cascade. Secondary production: - Primary consumer such as herbivores feeds on plants and stored 10 % of energy for the next trophic level. Since according to 10% energy transfer law: - energy transfer from one trophic level to next can stored only 10 % as a flesh/biomass. Since secondary production is exclusively depends on Primary production for foods/energy therefore any depletion or rise in primary production will results in depletion or rise in secondary production respectively. (Direct impact).
Define net primary productivity and describe an experiment for how it can be measured.
Primary productivity is the process by which organisms make their own food from inorganic sources. Most primary producers are terrestrial plants and microbial life, such as algae. Primary productivity due to photosynthesis is commonly measured by quantifying oxygen production or CO2 assimilation. One method of measuring the production of oxygen is the light and dark bottle method. In this method, sample water is placed into two BOD (biochemical oxygen demand) bottles. One bottle is stored in the dark and the other in a lighted area. Only respiration can occur in the bottle stored in the dark. Respiration rate is the decrease in dissolved oxygen (DO) in the dark bottle over time. Both photosynthesis and respiration can occur in the bottle exposed to light. The difference between the amount of oxygen produced through photosynthesis and that consumed through aerobic respiration is the net productivity. The difference in dissolved oxygen over time between the bottles stored in the light and in the dark is a measure of the total amount of oxygen produced by photosynthesis. The total amount of oxygen produced is called the gross productivity.
________ efficiency is the ratio of production to assimilation, which measures how efficiently the consumer incorporates assimilated energy into secondary production.
Production
(T/F) Consumption efficiency is the ratio of ingestion to production.
TRUE
(T/F) In endotherms, an increase in mass-specific metabolic rate lowers production efficiency.
TRUE
(T/F) In most marine ecosystems, autochthonous inputs of organic carbon are greater than allochthonous inputs of carbon.
TRUE
(T/F) In plants, low water availability favors the allocation of energy to the roots.
TRUE
(T/F) In stream and river ecosystems, the grazing food chain is of minor importance compared with the detrital food chain.
TRUE
(T/F) Net primary productivity is greater in areas with a long photosynthetic period than in areas with a short photosynthetic period.
TRUE
(T/F) Primary productivity in forests often increases during the early stages of stand development and then decreases again as the forest ages and standing biomass increases.
TRUE
(T/F) Productivity may be expressed in units of energy per unit area per unit time or in units of dry organic matter per unit area per unit time.
TRUE
(T/F) Secondary production in an ecosystem is always less than primary production.
TRUE
(T/F) When a chemical reaction results in the loss of energy from the system, the reaction is exothermic.
TRUE
What are the two main food chains of ecosystems? Which is more dominant in terrestrial ecosystems and why?
There are two crucial food chains: • The grazing food chain • The detrital food chain. In the grazing food chain, the energy source is living plant biomass or NPP (net primary production). In the detrital food chain, the energy source is dead organic matter or detritus. The grazing food chain is not an important or major one in most terrestrial and various aquatic ecosystems. Barely in several open-water aquatic ecosystems do the grazing herbivores play a prominent role in energy flow. Compared to other kinds of food chains, a detritus food chain has a much enormous energy flow in a terrestrial ecosystem. So, Detritus Food Chain is Major and Important. 6) Explain why energy is lost as it is transferred from one trophic level to another. What are the effects of energy loss on the biomass of different trophic levels? Energy goes on decreasing as it moves up trophic levels because energy is lost as metabolic heat. The metabolic heat is generated when the organisms from one trophic level are consumed by organisms from the next level trophic. About 10 percent of the energy at any trophic level is transferred to the next trophic level. The rest of the energy is lost largely through metabolic processes as heat as mentioned above. Take an example - Suppose a grassland ecosystem has 10,000 kilocalories of energy which is concentrated in vegetation of the 10,000 lcal only about 1,000 kcal will be transferred to primary consumers, and only about 10 kcal will make it to the tertiary level. This is called the rule of 10. So, only a fraction of the energy available at one of the trophic levels is transferred to the next trophic level. The rule of thumb is 10%, but this is very approximate. The numbers and biomass of organisms keeps on decreasing as one ascends the food chain. The amount of energy which is available to one trophic level is limited or determined by the amount stored by the level below. As energy is being lost in the transfer from one trophic level to the next, there is successively less total energy as you move up trophic levels. So, the higher trophic levels would have less total biomass than those below trophic, because less energy is available to them. The amount of energy at one level and amount of biomass are inversely proportional.
Which pathway leads to the detrital food chain?
W
The river continuum concept suggests that one of the following is higher in headwater streams.
allochthonous carbon
Organic carbon produced within an ecosystem is termed ________.
autochthonous
Why might secondary production be lower in grasslands than in forests?
because primary production is lower
Relative net primary productivity is the ratio of net primary productivity to standing ________.
biomass
In a body of water, the depth at which the availability of light is such that the rate of photosynthesis equals the rate of respiration is called the ________ depth.
compensation
The ratio of energy consumed at the next trophic level over what is produced is known as
consumption efficiency.
The base of the detrital food chain is formed by
dead organic matter.
The presence of which element is highly correlated with NPP?
phosphorus
Plants assimilate energy through the process of
photosynthesis.
Which ecosystem has the highest actual evapotranspiration?
pine forest
Secondary production is limited primarily by
primary production.
Net primary ________ is the energy available to the heterotrophic component of the ecosystem.
production
Low-moisture conditions favor allocation by a plant to
roots.
The ________ law of thermodynamics states that when energy is transferred or transformed, part of the energy assumes a form that cannot pass on any further.
second
The ratio of the productivity of one trophic level over what its organisms consume is known as
trophic efficiency.
Net primary productivity is generally greatest at
tropical latitudes near the equator.
