Ecology Exam 2 Chapters 19, 20, 21 Flashcards
Why is the efficiency of energy transfer between grasses and gazelles quite low?
Blot: Because of the loss of heat through respiration. 10 percent of the total energy present in the producer trophic level will be found in primary consumers, like gazelles since the grass uses the 90% of energy for movement, growth, respiration and reproduction. As energy is often lost through heat and waste through consumption, assimilation and net productivity, each trophic level becomes smaller and ecological efficiency small with the organisms following the 10% rule.
Grass, a producer, uses the majority of its energy that it receives from sun for photosynthesis, which isn’t an efficient process. 99 percent of all solar light-energy that is available to producers reflects off them or passes through their tissues without being absorbed. Of the 1 percent of the solar energy that producers absorb and use for photosynthesis—that is, gross primary productivity—60 percent is used for respiration. Only 40 percent of absorbed solar energy is used for net primary productivity, which represents the growth and reproduction of producers. Also, 10 percent of the total energy present in the producer trophic level will be found in primary consumers, like gazelles since the grass uses the 90% of energy for movement, growth, respiration and reproduction. As energy is often lost through heat and waste through consumption, assimilation and net productivity, each trophic level becomes smaller and ecological efficiency small with the organisms following the 10% rule.
Compare and contrast the measurement of primary productivity in terrestrial versus aquatic ecosystems
In terrestrial ecosystems, primary productivity is measured through uptake and release of CO2 by plants. By placing a small plant into a sealed container with a highly sensitive CO2 sensor, When the container is placed in front of a light that simulates full sunlight, the plant consumes CO2 as it conducts photosynthesis. Since uptake from photosynthesis exceeds release from respiration. In aquatic ecosystems, net uptake of CO2 represents NPP in terrestrial ecosystems. quantifying changes in CO2 concentration is difficult to measure primary productivity because CO2 dissolved in water rapidly converts into bicarbonate ions. Since producers like algae release O2 during photosynthesis and take up O2 during respiration, NPP and GPP can be measured through uptake and release of O2. Similar to terrestrial ecosystems, in aquatic ecosystems, the uptake and release of O2 can be measured with light-dark bottle experiment.
Compare and contrast the factors that limit the net primary productivity in terrestrial versus aquatic ecosystems.
In both terrestrial ecosystems and aquatic ecosystems, nitrogen and phosphorus limit net primary productivity. Adding nitrogen and phosphorus together caused an NPP response much larger than adding either nutrient separately. Adding more of one nutrient causes the growth of producers to soon be limited by the other nutrient. However, in aquatic ecosystems, light availability, which declines within depth, also constrains the NPP. Also, even though nitrogen and phosphorus is abundant in open ocean where NPP is low, productivity is limited by other nutrients, like silicon and iron.
Why might assimilation efficiency be much higher for herbivores eating seeds than for herbivores eating leaves?
Assimilation energy is % of consumed energy that is assimilated by a consumer. herbivores that feed on seeds, such as many species of birds and rodents, have assimilation efficiencies as high as 80 percent. In contrast, herbivores, such as horses that feed on grasses and woody vegetation, have assimilation efficiencies of only 30 to 40 percent. Secondary consumers, which are predators on the herbivores, typically have high assimilation efficiencies ranging from 60 to 90 percent. These high assimilation efficiencies occur because consumed animal tissues from eating seeds are more digestible than consumed plant tissues from eating leaves.
What is the likely shape of the pyramid of biomass in a lake?
Pyramid of biomass represents the standing crop of organisms present in different trophic groups. The pyramid of biomass is inverted in a lake, an aquatic ecosystem due to shorter biomass residence time in aquatic ecosystems . The greatest amount of biomass occurs in tertiary consumers, with less biomass in secondary and primary consumers and lowest # in producers. This is because most of the energy is still found in the producers, but these producers are primarily tiny algae that do not live very long because they are rapidly consumed by herbivores. This continual rapid consumption results in a large biomass of consumers in these systems.
Why would you expect larger changes in stoichiometry between predators and prey to alter assimilation efficiencies?
BLOT: stoichiometry is the study of the balance of nutrients in ecological interactions, such as between an herbivore and a plant. We would expect larger changes in stoichiometry between predator and prey to alter assimilation efficiencies because When a nutrient-poor producer is consumed by an herbivore that requires a nutrient-rich diet, the herbivore consumes much less energy, further declining the ecological efficiency of predator’s trophic level.
The study of the balance of nutrients in ecological interactions, such as between an herbivore and a plant, is called ecological stoichiometry. If the stoichoioemtry significantly changes efficiency of energy transfer between trophic groups and prey ingest much less nutrients than which is necessary, the assimilation efficiency of the producer decreases. When a nutrient-poor producer is consumed by an herbivore that requires a nutrient-rich diet, the herbivore consumes much less energy, further declining the ecological efficiency of predator’s trophic level.
Why are residence times much longer in forest ecosystems than in aquatic phytoplankton-based ecosystems?
Blot: The rate of consumption from the next trophic level in forests is lower.
The energy residence time is the length of time that energy spends in a given trophic level. Energy residence time is directly related to the amount of energy that exists in a trophic level; the longer the residence time, the greater the accumulation of energy in that trophic level. The rate of consumption from the next trophic level in forests is lower than in aquatic phytoplankton-based ecosystems.
How might the carrying capacity for people in the United States change if we ate more plant products than animal products?
Blot: carrying capacity would increase because eating producers will make available 10x more energy than eating primary producers. Primary producers harvest their energy from the sun and the energy goes from one trophic level to the next, 10% of the energy from the previous trophic level is transferred, so if we eat them we will have more energy than eating primary producers.
The carrying capacity would increase. This is because eating producers will make available about 10 times more energy than eating primary consumers. Primary producers harvest their energy from the sun and the energy goes from one trophic level to the next, 10% of the energy from the previous trophic level is transferred. Therefore, the producers provide more energy than a primary consumer or secondary consumer would.
How does energy from the Sun drive the movement of water from the oceans to the continents and back to the oceans again?
Energy from the sun drives the hydrologic cycle. Solar energy provides the energy for the process of evaporation and evapotranspiration, which changes water from a liquid to a gas in the form of water vapor. There is a limit to the amount of water vapor that the atmosphere can contain. As additional water continues to evaporate, the water vapor in the atmosphere condenses into clouds that ultimately create precipitation in the form of rain, hail, sleet, or snow. To help maintain an overall balance, the excess water that is evaporated from aquatic ecosystems is transported by the atmosphere and falls onto continents. The excess water that falls on continents is transported in the form of runoff and groundwater into aquatic ecosystems.
Describe how methane gas is commonly produced in swamps.
In some habitats, such as the waterlogged sediments of swamps or marshes, oxygen is not available for respiration. Under such anaerobic conditions, some species of archaea use ethanol, (CH3OH) during respiration to produce CO2: 4 CH3OH -> CO2 + 2 H2O+ 3 CH4. Methane gas, a greenhouse gas, released from swamps is swamp gas, which is highly effective at absorbing and radiating infrared radiation back to Earth.
Given that the bottom of the ocean is anaerobic, what process in the nitrogen cycle is likely to be occurring in this location?
Denitrification, because under anaerobic conditions, the nitrate (NO3-) can be converted into nitrites (NO2-), which are converted to nitric oxide (NO), which is then converted to nitrous oxide (N2O), which is converted to nitrogen gas (N2), completing the nitrogen cycle. Denitrification is necessary for breaking down organic matter in oxygen-depleted soils and sediments.
How might nitrogen-fixing bacteria living in symbiosis with a plant affect the types of environments in which the plant could live?
The process of nitrogen fixation requires a high early-succession plants colonizing habitats that have little available nitrogen. The plant would not require much nitrogen to survive, and so would be able to adapt in environments with limited nitrogen availability.
Nitrogen fixing bacteria such as Rhizobium fix nitrogen by converting gaseous N2 into NH3 while living inside the roots of certain plants such as legumes. Plants then take in this fixed nitrogen source. This symbiotic relationship is extremely useful in environments that have areas left bare by glaciers or by lava from volcanoes. In fact, plants with nitrogen fixing bacteria tend to be the first types of plants to colonize such areas since nitrogen is crucial for plants.
Why is the weathering of bedrock in a New Hampshire forest responsible for such a small fraction of the nutrients available to plants?
Blot: slow process weathering, the bulk of nutrients available to plants comes from the breaking down of detritus and small organic molecules in soil.
Most calcium ions come from the decomposition of detritus (organic matter), while less than 10 percent of the calcium from weathering of bedrock. Although weathering of bedrock provides nutrients to the forest, it is a very slow process. This is because bedrock weathers slowly while the upper organic layer decomposes much faster.
Why do tropical and temperate soils have different rates of nutrient regeneration?
Organic matter does not fully decompose in temperate regions. Organic matter (detritus) in the tropics decomposes more rapidly because of warmer temperatures and higher amounts of precipitation. Temperature is low in temperate regions and so decomposition is also slow. Thus, more dead plant matter is left in temperate coniferous forests than in tropical rainforests.
How might global warming cause the release of CO2 from boreal forest soils?
Blot: As temperatures increase, it accelerates the nutrient cycle within the soil. An increase in temperatures in the soil of the boreal forests could causes microorganisms in the soil to metabolize faster. The microorganisms would metabolize much of the carbon in the soil. The product of carbon dioxide would then be released the into the atmosphere.
It would lead to excess release of CO2 in the atmosphere, increasing the temperature, thus increasing the rate of decomposition. Elevated temperature and CO2 levels would stimulate photosynthesis to result in an increase of CO2 uptake, while the temperature increase would promote decomposition of organic matter especially that stored in the soils to release CO2 to the atmosphere.
