ECOLOGY

Definition of Terms•Ecosystem- the interactions between all

the organisms, and their environment, in a particular area

•Habitat-a place where an organism lives•Niche-the role of an organism in an

ecosystem, the effects that it has on other components of the ecosystem and the effects that they have on it

Definition of Terms•Ecology•Population•Community•Biotic factor•Abiotic factor•Producer•Consumer-primary, secondary, tertiary•Herbivore•Omnivore

Definition of Terms•Trophic level•Food chain•Food web

Energy Flow in Ecosystem•Study of energy flow in ecosystem-

ecological energetics•Sun-ultimate source of energy•40% of sun’s energy reflected by clouds,

dust, earth’s atmos•15% absorbed, converted to heat energy

in atmos•Remaining 45% reaches earth’s surface-

only half of which is in the photosynthetically active range(PAR)

Energy Flow in Ecosystem•10% of PAR converted into gross

primary productivity (GPP)-actual amt of light energy from the sun that is utilized in photosynthesis

•Net primary productivity (the net gain of organic material in photosynthesis after allowing for losses due to respiration) varies between 50-80%of GPP

•Total radiant energy captured by green plants is only about 0.1%

Food Chains•A simplified sequence used to illustrate

the flow of energy from one organism to another in a community

•Producers are first organisms in food chain-capable of making sugars from simple raw materials utilizing solar energy eg. green plants, cyanobacteria-autotrophs

•Heterotrophs-consume other organisms, cannot make own food eg. all animals, fungi

Food Chains•Primary consumers (herbivores) -feed on

producers•Carnivores- feed on herbivores

(secondary consumers); if they feed on other carnivores (tertiary consumers)

•Trophic level-feeding level•Only a small portion of available energy is

transferred from one trophic level to the next

•Some energy lost as heat during respiration

Food Chains•This loss of energy limits the number of

organisms in a food chain•Some energy remains locked up in the

bodies of producers and consumers upon death

•Decomposers and detitivores-recycle nutrients by breaking down complex organic materials into simple compounds

•Detritivores are larger than decomposers, they digest food internally and not externally

Food Chains•Energy used by organisms for movement,

growth, excretion, reproduction, digestion, tissue repair

Food Webs

Food Webs•An interconnection of various food chains

where a single species may form part of many different food chains, not always occupying the same trophic level in each chain

•Feeding relationship more complex than a food chain

•Unlike a food chain-most organisms have multiple food sources

Food Webs•Omnivores feed at all trophic levels

Advantages of Food Webs1. Organisms feed on a variety of food

sources2. If one population dies, the organism can

survive on another food source3. Energy transfer is more efficient –as

food chains ascend energy loss is greater

Trophic Efficiency•Percentage of energy at one trophic level

which is incorporated into the next trophic level

•measured in a given area over a defined period of time, units usually kJ m-2 year-1

•The rate at which producers convert light energy from the sun into chemical energy is called the primary productivity.

Trophic Efficiency• Gross primary productivity (GPP) is defined as

the total amount of chemical energy that is extracted from the light energy to which the producers are exposed to.

• Only about 1-5% of the incident light radiation is converted to chemical energy by plants the rest is reflected or not absorbed, or in the form of heat. This value takes into consideration the position of the sun, the time of the day, the exposure of a plant to it and the location of the plant on the earth’s surface.

Trophic Efficiency• The net primary productivity (NPP) is defined as

the total amount of energy that is made available by the producers to the next trophic level, which is after they have respired and undergone photorespiration. The amount thus available is 20-25% of the GPP of the producers.

• Even from this amount consideration must be given at each subsequent level to the energy needs by the organism in the production of sweat, waste and the conversion to storage molecules.

Ecological Pyramids•important to study the efficiency of energy

transfers within an ecosystem •tell us how much energy is available to an

organism and subsequently how many organisms an ecosystem can support

•Pyramids used as representations of the energy made available to organisms at every trophic level by the measurement of the area in each box which constitutes the pyramid

Ecological Pyramids•Pyramid diagrams allow for comparison of 1. Different ecosystems2. Seasonal variation within a particular

ecosystem3. Change in an ecosystem

Ecological PyramidsThree types:

1. Pyramids of numbers-based on counting the number of organisms at each trophic level

2. Pyramids of biomass-monitors the energy content of the organisms at each trophic level

3. Pyramids of energy- notes the dry wieght of organisms at each trophic level, considered the most important as they deal directly with the flow of energy in a food chain

Pyramid of Numbers•Organisms of a given area are first

counted and grouped into their trophic levels

•Bar diagram drawn to indicate the relative number of individuals at each trophic level

•Length or area of each bar is proportional to the number of organisms in a given area or volume

•Progressive decrease in the number of organisms at each successive trophic level

Pyramid of Numbers

Pyramid of Numbers-Limitations1. Trophich level difficult to ascertain2. Doesn’t give a realistic picture of energy

transfer because it only takes into consideration the number of organisms and not the size of them. Eg a tree is given the same status as a grass plant. Pyramid shape often not obtained

3. Number of organisms too large to be represented accurately on the same scale as others in a food chain

4. No account made for juveniles whose dietary (energy) requirement vary from adults

Pyramid of Numbers

Pyramid of Biomass•the obstacle of size: number is overcome

by measuring the dry mass of the living tissues of the organisms at each trophic level

•It suggests that biomass is related to energy transferred at each trophic level.

Pyramid of Biomass

Pyramid of Biomass-Limitations1. Obtaining the dry mass of an organism involves

driving of all the water from that organism by heating it in an oven (destructive method)

2. Individuals have to be weighed and counted-laborious and time consuming

3. Impossible to measure exactly the biomass of all individuals in a population

4. Standing crop-seasonal variation in mass, gives no indication of total productivity eg. phytoplankton and tree may have the same productivity but significantly different mass

Pyramid of Energy•Each bar represents the amount of energy

per unit area or volume that flows through the trophic level in a given time period

•the energy made available to each subsequent trophic level is determined by calorimetry of individual tissues

•It is the most accurate measurement of the efficiency of energy transfer within an ecosystem

Pyramids of Energy-Limitations•Data is very difficult and time consuming

to collect as it involves burning the tissue of an organism and measuring the amount heat that is released to raise the temperature of water.

Pyramid of Energy-Advantages•Takes into account the rate of production•Allows different ecosystems to be

compared•Inverted pyramids are not obtained•Weight for weight, two species do not

necessarily have the same energy content•Solar energy can be added as an extra

rectangle at the base of the pyramid

Nitrogen Fixation•Opposite of denitrification•Conversion of gaseous nitrogen into

organic nitrogen-containing chemicals•Carried out by 1. free-living nitrogen fixing bacteria eg.

Azotobacter and Clostridium-contribute to soil fertility

2. Organisms living in symbiotic association with leguminous plants eg. Rhizobium

Nitrification•Series of rxns involved in the oxidation of

ammonium to nitrates•Process carried out in two stages:1. The oxidation of ammonium compounds

to nitrites by free-living bacteria eg. Nitrosomonas

2. The oxidation of the nitrite by other free-living bacteria eg. Nitrobacter

Denitrification •Nitrate in the soil is converted into

gaseous nitrogen, unavailable to many plants

•Process carried out by anaerobic bacteria eg. Pseudomonas denitrificans

•Bacteria thrive under anaerobic conditions eg. waterlogged soil

•Reduce soil fertility by converting nitrates to atmos. nitrogen

Energy flow through an Ecosystem•Energy enters ecosystem from sun via

photosynthesis•Producers use light energy to make

carbohydrates, proteins, fats•These substances serve as chemical

energy for consumers

Nutrient cycling•Unlike energy, matter tends to be

recycled through the ecosystem•Organisms bodies are used as nutrients

by decomposers that break down organic molecules and liberate atoms/ions

•Decomposers return used materials to the ecosystem for use by other organisms