BIOL 314 Chapter 20-23
Describe three factors that might affect the number of trophic levels in an ecosystem.
1. The amount of energy entering an ecosystem through primary production has been proposed as a determinant of the number of trophic levels. 2. The frequency of disturbances or other agents of change, such as disease outbreaks, can determine whether populations of higher-level predators can be sustained. Because lower trophic levels are required to sustain higher trophic levels, there is a longer time lag for the reestablishment of the higher trophic levels following a disturbance. 3. Physical size of an ecosystem can influence the number of trophic levels. Larger ecosystems support larger population sizes, which are less prone to local extinction. Larger ecosystems also have more habitat heterogeneity, and thus tend to have higher species diversity.
How is community or ecosystem stability affected by food web complexity?
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What is meant by the "background" extinction rate? And how do contemporary rates of extinction compare to the long-term background rate?
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Define allochthonous and autochthonous inputs to ecosystems, give an example of each.
Allochthonous inputs - external energy inputs Ex// in awuatic ecosystems plant leaves, stems, wood, and dissolved organic matter. Autochthonous inputs - energy produced by autotrophs within the system Ex//green plants, algae Ex// Bear Brook, head water stream receives 99.8% of its energy as allochthonous inputs. In contrast, autochthonous energy accounts for almost 80% of the energy in nearby Mirror Lake.
What is the difference between "bottom-up" and "top-down" control of trophic cascades?
Bottom up: amount of energy that flows through trophic levels may be determined by how much energy enters an ecosystem via NPP, which in turn is related to the supply of resources. The greater the NPP entering the ecosystem, the more energy can be passed on to higher trophic levels. It holds that the resources that limit NPP determine energy flow through an ecosystem. Top down: energy flow may be governed by rates of consumption at the highest trophic levels, which influence abundances and species composition at multiple trophic levels below them. Both bottom-up and top-down controls are operating simultaneously in ecosystems, bot the top-down view has important implications for the effects of trophic interactions on energy flow in ecosystems.
What is meant by a "nutrient spiral" in an aquatic ecosystem?
Cycling of nutrients as the water moves downstream results in repeated spirals of nutrient uptake and release.
Define gross primary production (GPP) and net primary production (NPP).
Gross primary production is the amount of energy that autotrophs capture by photosynthesis and chemosynthesis per unit of time. Net primary production is the amount of energy per unit of time that producers capture by photosynthesis and chemosynthesis minus the amount they use in cellular respiration.
How is that biomass pyramids can be inverted in aquatic ecosystems?
In aquatic ecosystems, the high consumption rates and the relatively short life spans of the primary producers (phytoplankton) result in a biomass pyramid that is inverted relative to the energy pyramid. The biomass of heterotrophs may be greater at any give time than the biomass of autotrophs. However, the energy produced by the autotrophs is still greater than that produced by the heterotrophs. The tendency toward inversion is greatest where productivity is lowest, such as nutrient poor regions of the open ocean.
What does it mean to say that conservation biology is a value-based discipline?
Science is not free of human values, and it inevitably takes place within a larger social context. Conservation biologists have had to come to terms with the implicit and explicit values that are part of their work.
What is "secondary production" and how is it related to heterotroph physiology?
Secondary production is energy that is derived from the consumption of organic compounds produced by other organisms. Organisms that obtain their energy in this manner are known as heterotrophs, and are classified according to the type of food they consume.
What is meant by "net interaction strength"?
interaction strength is a measure of the effect of one species' population on the size of another species' population. Determining interaction strengths is an important goal of ecologists because it helps us simplify the "spaghetti" in a complex food web by focusing attention on those links that are most important for basic research and conservation. **The net effect of a predator of a predator on a target prey species includes all possible indirect effects of the predator on other species in the community that interact with the target prey species as well as the direct effect of consumption.
What is a nutrient cycle? And why do different nutrients cycle at different rates?
is the movement and exchange of organic and inorganic matter back into the production of living matter. The process is regulated by food web pathways that decompose matter into mineral nutrients. Nutrient cycles occur within ecosystems. Different nutrients cycle at different rates depending on the element in question and the ecosystem where the cycle is occurring. In general, nutrients that limit primary production are cycled more rapidly than nonlimiting nutrients. Rates also vary with with climate due to the effects of temperature and moisture on the metabolic rates of the organisms associated with production, decomposition, and chemical transformations of nutrients. Rates of nutrient cycling by estimating the mean residence times. mean residence time = total pool of element/rate of input.
What is "taxonomic homogenization"?
the worldwide reduction of biodiversity resulting from the spread of non-native and native generalists couple with declining abundances and distributions of native specialists and endemics.
Define: nitrification and denitrification.
Nitrification: a process by which certain chemoautotrophic bacteria, known as nitrifying bacteria, convert ammonia (NH3) and ammonium (NH4+) into nitrate (NO3-) under aerobic conditions. Denitrification: a process by which certain bacteria convert nitrate (NO3-) into nitrogen gas (N2) and nitrous oxide (N20) under hypoxic conditions
How does NPP vary with latitude? how does it vary with global patterns in temperature and precipitation? and how is it measured?
Terrestrial NPP is highest in the tropics and declines in the north and south. PAGE 455 NPP varies tremendously over space and time. Year-to-year variation in NPP provides a metric for examining ecosystem health because changes in primary productivity can be symptomatic of stresses such as drought or acid rain. NPP is intimately associated with the global carbon cycle.
What is a trophic pyramid? And what is "trophic efficiency"?
Trophic pyramid is a common approach to conceptualizing trophic relationships in an ecosystem in which a stack of rectangles is constructed, each of which represents the amount of energy or biomass within one trophic level. These pyramids portray the relative amounts of energy or biomass at each level showing us how energy flows through the ecosystem. In studies of energy transfer in trophic systems the concept of trophic efficiency is used, defined as the amount of energy at one trophic level divided by the amount of energy at the trophic level immediately below it. Trophic efficiency incorporates the proportion of available energy that is consumed, the proportion of ingested food that is assimilated by the consumer, and the proportion of assimilated food that goes into producing new consumer biomass.
