Biological Foundations 112, Lecture 37


The Ecosystem and its Functioning

Chapter 48, pages 1118-1134
Chapter 49, pages 1145-1165
Ecology-1 0:00-13:17
Ecology-2 0:00-15:10
Ecology-3 0:00-16:03


I.   Ecosystems

     A.   Definitions

            1.   A network consisting of organisms, their environment, and all of the interactions that  
                  exist in that environment

            2.   An interdependent and dynamic biological, physical, and chemical system

     B.   Examples

            1.   Simple ecosystem - rock with lichens growing on it

            2.   Complex ecosystem - pond or tropical rainforest

     C.   Ecotones - regions of overlap between ecosystems

     D.   Factors characterizing an ecosystem

           1.   Abiotic Factors

                 a.   Physical and chemical factors

                       (1)  Precipitation

                       (2)  Temperature

                       (3)  Sunlight

                       (4)  Humidity levels

                       (5)  Availability of oxygen

                       (6)  Carbon dioxide

                       (7)  Phosphorus

                       (8)  Nitrogen

                 b.   Range of tolerance

                       (1)  Organism is fine-tuned genetically to the environment

                       (2)  Zone of Physiological Stress - zone where the organism is uncomfortable

                       (3)  Zone of Intolerance - zone where organism will die

                 c.   Limiting factors

                       (1)  Limits or inhibits physical growth of the organism

                       (2)  Falls outside the range of tolerance and into the zone of intolerance

                       (3)  Environmental factors are bad enough that whole populations of organisms    
                             do not survive and the organism becomes extinct in that geographic area

           2.   Biotic Factors

                 a.   The living components of the ecosystem - the organisms

                 b.   Organization of the biotic factors

                       (1)  Species - different kinds of organisms that live together in a given geographic
                                               region

                       (2)  Populations - the number of individuals of a given species living in the given  
                                                     geographic region

                       (3)  Communities - The populations of species that are living together in the      
                                                       given geographic region

                 c.   Niche and Habitat

                       (1)  Habitat

                             (a)  The actual real estate that the organism owns

                             (b)  The kind of neighborhood the organism lives in

                       (2)  Niche

                             (a)  What the organism does for a living

                             (b)  How the organism gets its energy

                                    i)   Interspecific competition - competition between different species  
                                                                                      for food

                                    ii)  Intraspecific competition - competition between members of the    
                                                                                      same species for food

                             (c)  Examples of niches:

                                   i)   Predation

                                   ii)  Commensalism

                                   iii) Mutualism

                                   iv) Parasitism

II.  Functioning of Ecosystems

     A.   Food chains and food webs

            1.   Food Chains - order in which organisms in an ecosystem are consumed

            2.   Types of food chains:

                  a.   Grazer food chain

                  b.   Decomposer or detritus food chain

            3.   Two major parts to the grazer food chain:

                  a.   Producers - those organisms that photosynthesize and store more energy in        
                                            food than they consume

                  b.   Consumers - those organisms that do not photosynthesize and must eat other    
                                              organisms for energy

            4.   Types of consumers:

                  a.   Heterotrophs - organisms that must eat other organisms for food

                  b.   Herbivores - plant eaters

                  c.   Carnivores - flesh eaters

                  d.   Omnivores - both plant and flesh eaters

     B.   Classifying consumers by their position in the food chain

            1.   Primary consumers eat producers

            2.   Secondary consumers eat primary consumers, etc.

            3.   Trophic level - level the organism occupies in the food chain

                  a.   First trophic level - producer

                  b.   Second trophic level - primary consumer

     C.   Thus, the Food Web - all feeding interactions in the ecosystem

     D.   Flow of energy and matter through the ecosystem

            1.   Energy flow in the ecosystem

                  a.   Energy - the capacity to do work

                  b.   Laws of Thermodynamics

                        (1)  First Law - Conservation of Energy

                                     Energy can neither be created nor destroyed but only transformed from
                                      one form to another.

                        (2)  Second Law - Entropy

                                     As energy is lost, matter becomes more and more disorganized with less
                                     energy trapped within.

                        (3)  Third Law - energy is degraded (lost) when it changes form (never 100%  
                                                   of  energy is transformed)

                  c.   Conclusion about energy flow in the ecosystem:  The total amount of energy in  
                        any given trophic level of the food chain gets smaller and smaller as one              
                        progresses up the food chain.

            2.   Biomass flow in the ecosystem

                  a.   Biomass - the dry weight of all the living organisms at any given trophic level

                  b.   Each trophic level contains less and less biomass as one proceeds up the food    
                        chain

            3.   Flow of numbers of individuals in the ecosystem - the number of individual organisms
                  decreases at each trophic level as one progresses up the food chain   

     E.   Ecological Pyramids

            1.   Three pyramids can be visualized as it relates to the trophic levels of the food web

                  a.   Pyramid of Energy

                  b.   Pyramid of Biomass

                  c.   Pyramid of Numbers

            2.   As the trophic level increases in number the amount of energy, amount of biomass,    
                  and the number of individual organisms decrease

     F.   Productivity

           1.   Definition - rate of conversion of sunlight to chemical energy (sugar)

           2.   Definition of units of energy:

                 a.   Calorie - amount of heat energy it takes to warm one gram of water one degree  
                                       centigrade

                 b.   Kilocalorie

                       (1)  1000 calories

                       (2)  The unit of energy used in biological systems

           3.   Productivity measured three different ways:

                 a.   Gross Primary Productivity - GPP

                       (1)  Rate at which sunlight is converted to chemical energy

                       (2)  Kilocalories/square meter/year

                 b.   Respiration rate of producers - R

                       (1)  Energy used by producers for metabolism

                       (2)  This is the energy necessary to maintain life for the producer

                 c.   Net Primary Productivity - NPP

                       (1)  Amount of energy stored by plants

                       (2)  GPP - R = NPP

III. Nutrient Cycles

     A.   Carbon cycle

     B.   Nitrogen cycle

     C.   Phosphorus cycle

     D.   Water cycle


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