LECTURE OUTLINES EXAM 3
updated 24 November 2003
LECTURE 20 - 10 NOV
LECTURE 21 - 12 NOV
LECTURE 22- 17 NOV
LECTURE 23 - 19 NOV
LECTURE 24 - 24 NOV
LECTURE 25- 26 NOV - CLASS CANCELLED
LECTURE 26- 1 DEC
LECTURE 27- 3 DEC
***Writing Assignment Pt 4 due 19 NOV 2003****
****EXAM 3 - 10 DEC 2003****
***EXAM 3 WILL BE 50 MULTIPLE CHOICE QUESTIONS***
***EXAM 3 STARTS AT 3:30-6:15***
LECTURE 20 - 10 NOV 2003
Chapter 20 - Continued
it is difficult to locate the genetic basis of co-evolution. competition has a genetic basis and competitive ability can change in laboratory settings (house flies and blowflies)
lichens are mutualisic organisms of fungi and algae.
three categories of mutualisms: tropic, defensive, and dispersive.
trophic mutualisms involve specializations associated with nutrient exchange. lichens are an example of a trophic mutualism. bacteria form nodules on the roots of plants in the pea family (legumes); the nodules fix nitrogen and the plant provides the fungus with carbohydrates. bacteria in rumens of ruminates digest cellulose.
defensive mutualisms involve species that receive food or shelter for defense against herbivores, predators, or parasites (cleaning symbiosis is an example). The ant acacia (Acacia) and ant (Pseudomyrmex) mutualism is a defensive mutualism.
dispersive mutualisms involve animals that move pollen between flowers for a food reward. seed dispersal by animals is also a dispersive mutualism. the relationship between plants and pollinators tends to be more specific than the relationship between plant and dispersal agent.
yucca-moth (Tegeticula) is a member of the moth family Prodoxidae and all members of the family mate on the yucca. two species pollinate the plan and egg laying in the flowers has evolved three times.
community = assemblage of species that occur in the same place; organisms in communities interact through competitive interactions, through consumer-resource interactions or through mutualistic interactions.
some believe communities are like superorganisms. some argue that communities are loose assemblages of organisms that tolerate the conditions found in any location.
Clement argued that communities are like superorganisms and community structure was strongly tied to vegetation type. Gleason, argued that a community is a fortuitous association of species.
interactions in communities govern flow of energy and cycling of elements in ecosystem. interactions among community members can influence population processes and therefore relative abundance.
individualistic view of communities gives them no organization and species all try to maximize heir reproductive output. community structure difficult to define & measure.
LECTURE 21 - 12 NOV 2003
species richness is a fundamental aspect of community structure. species diversity is incredibly high in the tropics and in the case of trees, individuals may be separated by kilometers; land conversion in the tropics is difficult because species can experience mate limitation, if their nearest reproductive neighbors are killed during deforestation. most communities are made up of a few common species and several rare species.
community structure can be defined based on trophic relationships and within each trophic level, organisms can be grouped into guilds.
community has been used to denote the assemblage of plants, animals and other organisms living in a particular locality. Sky islands are defined by the mountains and desert; riparian communities are defined by streams; stream communities are defined by their substrates.
communities are linked by movements of animals (migrating birds; amphibians with biphasic life cycles). direct and indirect effects are important in communities.
holistic vs. individualistic concepts of community organization differ. In the holistic view, communities are closed and from the individualistic concept, communities are open.
ecotones occur where two communities meet; several attributes change along ecotones (temperature, soil moisture, light intensity, and fire frequency; ecotones are blurry when environmental change is gradual.
Continuum concept of communities.
Feeding relationships organize communities in food webs. species occur in similar functional groups whose members are in the same trophic position. is a complex food web more stable than a simple food web?; keystone predators change the nature of communities.
LECTURE 22 - 17 NOV 2003
three types of food webs: connectedness food webs, energy flow food webs and functional food webs.
omnivory occurs when an organisms feeds at more than one trophic level; number of species and number of feeding links per species are important attributes of food webs.
trophic cascades occur when there are indirect interactions in food webs; some argue they can only occur in closed ecosystems like lakes; food webs ignore unique roles of species.
plot of species abundance data results in reverse-J shaped curve;
LECTURE 23 - 19 NOV 2003
species area relationships; species richness includes the number of species and their evenness. Shannon-Wiener diversity index. Rarefaction is a way to make comparisons that involves discarding data to equalize the comparisons.
Krakatau explosion provided an opportunity to study succession. The first plants to arrive were carried by ocean currents; these were followed by wind-dispersed plants. Once plants established, birds visited the island and deposited seeds which increased the types of plants found on the islands.
communities are in flux because organisms are dynamic; especially when they respond to disturbance. When a community is disturbed, it rebuilds slowly. Pioneers can tolerate harsh conditions.
succession is the sequence of changes that follows disturbance. climax community is the ultimate association of species. Pioneers change the environment once they arrive by shading soil and contributing to detritus.
studies of "old fields" have been important in understanding succession. The agricultural fields are followed until grasslands are replaced by shrubs and shrubs are replaced by trees.
climax communities are the ultimate stage in the successional process. Each stage in succession is called a sere and each type of community has a unique process of succession.
Lake Michigan dune example.
Primary succession in newly formed habitats. Primary succession also occurs when ponds become bogs.
LECTURE 24- 24 NOV 2003
Treefall gaps are a different type of disturbance. Succession takes place but there is a seedbank and surrounding trees and this is secondary succession.
Weeds are species that are adapted to disturbances.
Clements (believed communities were superorganisms) recognized 14 climax communities in the United States. Succession can be altered by facilitation, inhibition, and tolerance.
successional rates vary depending on the starting point (bare rock vs. tornado blowing through a forest).
some climax communities are maintained by extreme environmental conditions. many factors affect composition of the climax community. fire is an important feature in many climax communities.
succession can also occur on dead animals.
dry plant biomass production is 224 billion tons/yr; 59% terrestrial production and 35-40% of that total is used by humans as food, fiber crops or feed for animals. Oceans major source of food for population. early 1980s global fish catch = 75 million tons/yr and it has increased.
two marine ecologists tried to estimate the level of production required to sustain fisheries. They assumed that for each step in the chain leading from algae to fish, 90% of the consumed energy is used for maintenance leaving 10% for growth, reproduction, and contribution to the exploited fishery. The inshore fisheries required 1/3 of the total energy produced by the marine ecosystem which suggests that these fisheries may be at the upper limit.
Food web concept was operationally defined by Charles Elton in the 1920s; food web participants were regarded as an ecological unit and this was a novel concept during Elton's time.
an English plant ecologist AG Tansley provided an operational definition for ecosystem by considering organisms, and their physical surroundings as ecological systems. Tansley regarded ecosystems as the fundamental unit of ecological organization.
Alfred Lotka considered organisms in communities as energy transforming systems and that these systems could be described by a series of equations that represent changes of energy and matter (including photosynthesis, consumption of resources). Lotka thought that the size of the system and rates of energy and material transformations obeyed thermodynamics.
Lotka's notions were difficult and ignored until 1942 when Ray Lindeman at the University of Minnesota brought the concepts to light. Lindeman thought Tansley's idea of the ecosystem as the fundamental ecological unit and Elton's food web concept to be the most useful expressions of ecosystem structure.
food chain is the sequence of feeding relationships by which energy passes through the ecosystem. Lindeman visualized a pyramid of energy with less energy reaching each higher trophic level. Energy is lost at conversion to the next level because of work and inefficiency of biological energy transformations.
by 1950s ecosystem ecology emerged as a discipline and cycling of matter and energy were the basis for describing ecosystem structure and function. Carbon is a currency that ecologists could use to compare structure and function of different ecosystems in terms of energy and matter residing in and transferred among plants, animals, microbes, and abiotic components of the ecosystem.
ecologists started measuring energy flow and the cycling of nutrients using the paradigm of the thermodynamic concept of the ecosystem. Eugene Odum was a proponent of this approach. Odum pioneered the use of energy flow diagrams.
energy enters ecosystems as light and leaves as heat; nutrients are regenerated and retained in system. Plants take up inorganic forms, convert them to biomass and are returned to inorganic forms following decomposition. production of carbon dioxide by respiration and the use of carbon dioxide by plants. in ecosystem energetics, studies of nutrient cycling are as important as studies of energy flow which is very difficult to measure accurately.
understanding how carbon moves through the ecosystem gives us an index of how the energy in sunlight is transmitted through plants to the rest of the ecosystem components.
Primary Production - assimilation of light energy and production of organic matter by photosynthesis. plants, algae, and some bacteria capture light energy and transform it to the energy formed in chemical bonds in carbohydrates. primary productivity is the rate of primary production. photosynthesis combines water and carbon dioxide to make glucose with the release of oxygen.
Photosynthesis transforms carbon from an oxidized (low energy) state in carbon dioxide to a reduced (high energy) state in carbohydrates. Work is performed to increase the energy levels of carbon so energy is required and it is provided by visible light. For each gram of carbon assimilated a plant transfers 39 kilojoules (kJ) of energy from sunlight to the chemical energy of carbon in carbohydrates.
photosynthesis provides the energy needed for a plant to build tissues and grow. glucose is modified to become fats, starches, oils, and cellulose.
plants and other photosynthetic autotrophs form the base of all food chains and are the primary producers of the ecosystem. total energy assimilated by photosynthesis is gross primary production. Of the energy that comes in, some is used, some lost to respiration.
plant production involves fluxes of carbon dioxide, oxygen, minerals, and water and the accumulation of biomass. Net productivity can be measured as grams of carbon assimilated, dry weight of plant tissue or their energy equivalents. these variables are highly correlated. the energy equivalent of an organic compound depends on how much carbon it has. organic compounds have about 39 kJ of metabolizable energy per gram of carbon.
in terrestrial ecosystems, folks measure annual aboveground net primary productivity (AANP) and this value is used to compare terrestrial communities.
Production of plants can be measured at the leaf level by placing the leaf in a cuvette and measuring rates of carbon fixation using infrared gas analyzers. Once folks get leaf-level measurements, they can extrapolate from the tree and on to the entire forest (in simple forest systems). To determine gross primary production one must measure total carbon dioxide uptake and dark respiration to get carbon dioxide output to determine what the net uptake is.
Radioactive isotope of carbon-14 provides a tool for measuring productivity.
in aquatic systems measuring carbon dioxide is difficult. to estimate primary production, water with phytoplankton is put into light and dark bottles to measure NPP and dark respiration using oxygen levels.
primary production is sensitive to variations in light and temperature. light can be limiting. leaves do not always operate at the maximum photosynthetic rates.
Photosynthetic efficiency = percentage of energy in sunlight that is converted to NPP during the growing season.
rate of photosynthesis increases with temperature up to a point. net production depends on rate of respiration and it also increases with temperature.
stomata are leaf openings across which carbon dioxide and oxygen are exchanged with atmosphere. water also leaves during transpiration. rate of photosynthesis depends on soil moisture.
transpiration efficiency is a measure of drought resistance in crop plants expressed as number of grams of dry weight produced/kg water transpired.
fertilizers stimulate growth in most environments. plants are variable in their responses to fertilization.
nutrients limit primary production in aquatic environments, particularly in open ocean where scarcity of dissolved minerals reduces production below terrestrial levels. in shallow coastal waters where vertical mixing, upwelling, and run-off from land maintain high levels of nutrients, the addition of fertilizers (often in form of pollutants) upsets the natural balance of the aquatic ecosystems.
highest terrestrial productivity on earth in humid tropics. within a given latitude belt, net production is related to temperature and annual precipitation.
Swamp and marsh ecosystems which occupy the interface of terrestrial and aquatic habitats can produce more than tropical forests.
in open ocean, scarcity of mineral nutrients limits productivity. production is higher in freshwater environments than it is in the ocean.
primary production by plants, algae, and bacteria form base of ecological food chains. animals, fungi, and microorganisms obtain energy from plants, animals, or dead remains of either. with each step in food chain, 80-95% of energy is lost.
food chain efficiency.
organisms uses energy to maintain itself, fuel activities, grow, and reproduce. the assimilated energy is what is digested and absorbed. animals excrete some of the assimilated energy in form of nitrogen containing wastes.
assimilated energy = ingested energy - egested energy
production = assimilated energy - respiration - excretion
assimilation efficiency is the ratio of assimilation to ingestion expressed as a percentage. Energy value of plants depends on food quality. food of animal origin is more easily digested than plant products.
most active animals have lowest net production efficiencies. ratio of energy in production relative to the total assimilated energy is the net production efficiency with is expressed as a percentage.
production efficiency can be based on total energy ingested rather than on energy assimilated = gross production efficiency.
gross production efficiency = (assimilation/ingestion) x (production/assimilation) x 100 = (production/ingestion) x 100.
gross production efficiency represents the overall energetic efficiency of biomass production within a trophic level. Gross production efficiencies of warm-blooded terrestrial animals rarely exceed 5%. For insects, efficiencies lie within range of 5 to 15% and some aquatic animals exceed 30%.
detritus food chains: most of production of terrestrial plants consumed as detritus.. two parallel food webs run in terrestrial communities. the first originates when large animals feed on leafy vegetation, fruits and seeds and the second originates when small animals and microorganisms consume detritus in litter and soil.
importance of herbivore-based and detritivore-based food chains varies greatly among communities.
exploitation efficiency: little energy accumulates at any trophic level. the efficiency of a link in the food chain is equivalent to gross production efficiency.
ecological efficiency = exploitation efficiency x gross production efficiency
energy moves through ecosystems at different rates. for a given rate of production, the residence time of energy and the storage of energy in living biomass and detritus are directly related:
the average residence time of energy at a particular trophic level equals the energy stored divided by the rate at which energy is converted to biomass:
residence time (yr) = energy stored in biomass (in kJ/sq m)/net productivity (in kJ/sq m/year).
we can calculate the residence time defined by this equation in terms of mass instead of energy which is the biomass accumulation ratio:
biomass accumulation ratio (yr) = biomass (kg per sq m)/rate of biomassproduction (kg per/sq m/yr).
biomass accumulation ratios for primary producers may average from more than 20 years (forested terrestrial environments) to less than 20 days (aquatic phytoplankton based communities).
residence time of energy in accumulated litter can be determined by the following:
residence time (yr) = litter accumulation (g/sq m)/rate of litter fall (g/sq m/yr).
For forested ecosystems the value varies from 3 mo in the humid tropics to 1 to 2 years in dry and montane tropical habitats, 4-16 years in the SE US and more than 100 years in mtns and boreal regions.
flux of energy and efficiency of its transfer describe certain aspects of the structure of the ecosystem: number of trophic levels, importance of detritus feeding and herbivory, steady-state values for biomass and accumulated detritus and turnover rates of organic matter.
Lindeman constructed the first energy budget for an entire biological community - Cedar Bog Lake in Minnesota.
autochthonous production predominates in large rivers, lakes, and most marine ecosystems. allochthonous imports make up largest part of energy flux in small streams and springs under closed canopies of forests. caves and abyssal depths of the ocean subsist on energy transported in from the outside.
Lindeman's findings showed that herbivores
consumed 20% net primary production and carnivores consumed 33%
of net production of herbivores. Cedar Bog Lake ecosystem achieved
a 12% overall ecological efficiency of energy transfer between
LECTURE 25 - 26 NOV2003 - CLASS CANCELLED
LECTURE 26- 1 DEC 2003
LECTURE 27 - 3 DEC 2003