Ecology Chapter 24

You have a choice among leaves of a variety of different tree species to add to your compost heap. You are interested in rapid decomposition of the leaves because you wish to use the compost soon as an amendment for your garden. Which of the following kinds of leaves would you prefer to add to your compost? A) mulberry B) oak C) beech D) pine

Answer A Mulberry

While mycorrhizae assist plants in obtaining nutrients from soils, they may also provide an additional benefit to plants. What is it? A) protection from pathogenic organisms B) production of supplemental sugars C) creation of a fire‐retardant layer in the soil D) all of the above

Answer A Protection from pathogenic organisms.

In which of the following ecosystems would you expect to find litter on the forest floor contributing the largest percentage of total organic biomass? A) temperate needle‐leaved forest B) temperate hardwood forest C) tropical rain forest

Answer A temperate needle-leaved forest

During prolonged periods of vertical stratification, the sediments and adjacent bottom waters in temperate lakes become anaerobic because bacterial respiration depletes all available oxygen. Once oxygen has been depleted, can bacterial respiration continue? A) Yes, because bacteria can continue to use sulfate as an electron acceptor. B) No, because bacterial respiration is dependent on the presence of molecular oxygen.

Answer A) Yes, because bacteria can continue to use sulfate as an electron acceptor.

Which of the following elements was monitored to determine the rate of bedrock weathering in the Hubbard Brook Experimental Forest? A) calcium B) magnesium C) potassium D) nitrogen E) phosphorus

Answer A) calcium

Two situations in which high nutrient availability (and thus high productivity) occurs in the oceans are: A) shallow seas and coastal areas with upwelling of deeper water. B) shallow seas and coastal areas without upwelling of deeper water. C) deep seas and coastal areas with upwelling of deeper water. D) deep seas and coastal areas without upwelling of deeper water.

Answer A) shallow seas and coastal areas with upwelling of deeper water.

Areas in the Southern Ocean with relatively high productivity include those: A) throughout the entire area. B) downcurrent of Australia, New Zealand, South America, and the Antarctic Peninsula. C) west of southern South America between 40oS and 50oS latitude. D) close to the continent of Antarctica.

Answer B

Productivity in small lakes on the Canadian Shield increased dramatically upon experimental addition of this element, which has been shown to limit biological activity in many freshwater ecosystems A) nitrogen B) phosphorus C) potassium D) carbon E) silicon

Answer B

Research by Björn Lindahl and colleagues has shown that mycorrhizal fungi tend to be more active in which portion of the vertical profile of a forest soil? A) surface B) deep C) equally at both levels

Answer B

Under anaerobic conditions in lake sediments and adjacent bottom waters, which of the following forms of essential nutrients would you not expect to find? A) ferrous iron (Fe2+) B) nitrate (NO3 C) ammonia (NH3) D) phosphate (PO4 3+)

Answer B

Following passage of the Clean Air Act by the United States Congress in 1970, researchers working at the Hubbard Brook Experimental Forest found which of the following responses in forest growth? A) Forest growth rebounded quickly to pre‐industrial levels. B) Forest growth showed no immediate signs of recovery.

Answer B Forest growth showed no immediate signs of recovery.

Following passage of the Clean Air Act by the United States Congress in 1970, what happened to emissions of sulfur oxides and particulate matter emitted from factories and power plants? A) These emissions continued to increase. B) These emissions began to decline almost immediately. C) These emissions showed no change whatsoever.

Answer B These emissions began to decline almost immediately.

Thermal stratification of lakes during the summer months is most likely to happen at: A) high (polar) latitudes. B) intermediate (temperate) latitudes. C) low (tropical) latitudes.

Answer B intermediate (temperate) latitudes

Which of the following substances is an important precursor of acidified precipitation? A) lead emitted in automobile exhaust B) sulfur dioxide created from burning of fossil fuels C) dust particles carried into the atmosphere from agricultural fields D) sodium chloride and other salts from oceanic sources E) chlorofluorocarbons from industrial sources

Answer B) sulfur dioxide created from burning of fossil fuels

Michael Goulden and colleagues conducted a study of carbon evolution from boreal forest soils. One of the principal findings of this study was that: A) soil respiration was sensitive to fertilizer application. B) soil respiration was sensitive to depth of thawing. C) soil respiration was sensitive to acidified precipitation. D) there was no detectable respiration in these soils.

Answer B. Soil respiration was sensitive to depth of thawing.

In marine systems, peak productivity may occur in: A) stratified water B) unstratified water C) in areas of contact between stratified and unstratified water

Answer C

Leaves of different plant species decompose at different rates, depending largely on which of the following properties? A) size of the leaves B) manganese content of the leaves C) lignin content of the leaves D) moisture content of the leaves

Answer C

Under what conditions of available soil phosphorus are mycorrhizae most likely to benefit plants through uptake of phosphorus? A) high B) medium C) low D) equally at all levels

Answer C

Scientists monitoring acidified precipitation in the northeastern United States and Eastern Europe during the 1960s found that the pH of rainwater dropped to as low as A) 0.0 B) 2.0 C) 4.0 D) 6.0

Answer C 4.0

Traditional slash-and-burn agriculture in the humid tropics alternates 2-3 years of crop production with how many years of forest regeneration? A) 2-3 years B) 5-10 years C) 50-100 years D) 500-1000 years

Answer C 50-100 years

What did researchers estimate to be the rate of bedrock weathering (in terms of bedrock depth) in the Hubbard Brook Experimental Forest? A) 1 meter/yr B) 1 centimeter/yr C) 1 millimeter/yr D) 1 micrometer/yr E) zero

Answer C One millimeter per year

In thermally stratified temperate lakes, bottom waters become increasingly depleted of oxygen through the summer months. Anoxia results in increased concentrations of soluble reduced forms of several important nutrient elements in sediments and bottom waters. Following fall overturn, oxygen is replenished in deeper waters, resulting in production of oxidized insoluble forms of these elements. The only element in the list below with a soluble form under such conditions is __________, which can achieve relatively high concentrations of its oxidized form. A) phosphorus B) iron C) nitrogen

Answer C nitrogen

Acidified precipitation leaches various elements from forest soils. Heavy leaching of two elements in particular leads to poor growth and even mortality of trees. Which elements are these? A) aluminum and boron B) zinc and manganese C) chromium and nickel D) calcium and magnesium E) iron and silicon

Answer D

Although not always achieved, the Redfield ratio of 16:1 N:P characterizes the relative abundances of these two elements in deep waters of the open ocean. The reason for this consistent ratio, as proposed by Redfield, is: A) the relative supply of these two elements in runoff from terrestrial systems. B) the relative abundance of these elements in superheated waters emanating from deep‐sea hydrothermal vents. C) the relative solubilities of these two elements in seawater. D) the relative requirements for these two elements by phytoplankton.

Answer D

In an enormous experiment conducted in 1993, John H. Martin demonstrated that primary productivity by phytoplankton in the southern Pacific could be enhanced by addition of iron. However, increased primary production did not result in enhanced net uptake of CO2 by the system because A) CO2 was not limiting. B) other elements, such as silicon, were also limiting in this system. C) the added iron failed to complex with CO2. D) zooplankton populations also increased, regenerating CO2 through respiration.

Answer D

Regeneration of nutrients from aquatic sediments and from terrestrial soils differs in fundamental ways. Aquatic sediments are distinctive in that nutrient regeneration typically occurs: A) close to plant roots and under aerobic conditions. B) close to plant roots and under anaerobic conditions. C) far from plant roots and under aerobic conditions. D) far from plant roots and under anaerobic conditions.

Answer D

Salt marshes are considered by ecosystem ecologists to be particularly important habitats because: A) they are highly productive. B) they export substantial portions of their net production to surrounding marine ecosystems. C) they are important habitats for larval and immature stages of many marine fishes and invertebrates. D) All of the above are true.

Answer D

Unproductive "dead zones" can be found in the bottom waters of many estuaries and near the mouths of rivers. The ultimate cause of such zones is: A) influx of toxic organophosphates and other biocides from terrestrial sources. B) influx of toxic heavy metals from terrestrial sources. C) influx of inorganic and organic nutrients from terrestrial sources. D) All of the above are true.

Answer D

Where in the Neotropics would you expect to find oligotrophic soils A) Andes Mountains B) Central America C) West Indies D) Amazon Basin

Answer D

Which of the following elements is usually absent from soil parent material? A) calcium B) magnesium C) potassium D) nitrogen E) phosphorus

Answer D nitrogen

Vertical mixing in aquatic systems is inhibited when a layer of less dense water lies above a layer of denser water. This situation can arise when: A) sunlight heats surface water. B) fresh water from a river rides over denser saline water in an estuary. C) glacial ice melts in the ocean. D) precipitation is particularly high over the ocean. E) All of the above are correct

Answer E

Which of the following contribute to breakdown of litter on the forest floor? A) leaching of soluble components by water B) consumption of litter by large detritus‐feeding organisms C) activity of fungi D) activity of bacteria E) all of the above

Answer E

Primary production in the oceans may be limited by insufficient nitrogen and phosphorus. However, low oceanic productivity has been documented where both nitrogen and phosphorus occur in abundance. What other nutrient elements may have been limiting in these cases? A) aluminum and boron B) zinc and manganese C) chromium and nickel D) calcium and magnesium E) iron and silicon

Answer E iron and silicon

In a careful study conducted in "limnocorrals" in the Bay of Quinte, Lake Ontario, researchers found that uptake of nitrogen from the water column accelerated from early summer (June) to late summer (September). However, uptake of nitrogen by phytoplankton exceeded losses to zooplankton grazing and sedimentation in both periods. True or False

Answer True

The study by Goulden and colleagues (previous question) showed that the boreal forest ecosystem was not in equilibrium, as evidenced by a small net carbon loss from the system. True or False

Answer True