Through Communities

 Used to illustrate the flow of energy at each trophic level within a community.  Measured in terms of BIOMASS: the amount of living, organic material that can be supported by a given community(ecosystem).  The abiotic limiting factors determine biomass. For example: deserts have low biomass, rainforests high…but not the highest!  Units of biomass are: Kcalories/m 2 /year SALT MARSHES

 More biomass at lowest level  Biomass decreases at every level  Available energy decreases  Numbers of species decrease WHY?

 At every trophic level in a community, energy is:  USED BY THE ORGANISM for metabolism to maintain life; this energy is not available to the next level  converted by organism’s metabolism and is LOST AS HEAT; this energy is not available to the next level. Endotherms convert more Ectotherms less  STORED AS CHEMICAL ENERGY in the tissues and fat; this is the only source of energy available to the next trophic level in the food chain…

PRODUCERS To simplify; we will assume that 100% of the sun’s unusable light energy is converted via photosynthesis into useable energy by PRODUCERS and stored as carbohydrates. 100% converted and stored as carbohydrates and is available to the next trophic level… PHOTOSYNTHESIS UNUSEABLE ENERGY

100% stored as carbohydrates Remember; at each trophic level consumers use, loose, and store energy. The question is how much of each? USED: LOST: STORED: 10% 80% 10% 1 ST LEVEL

100% stored as carbohydrates 10% STORED 2 ND LEVEL A this level there is only 10% available energy stored in each mouse's tissues. USED: 1% LOST: 8% STORED: 1% As you can see, again, only 10% of the energy is passed to the next trophic level, this ‘Rule of 10’s’ applies to most food chains. So, how many mice does the fox need to eat to get enough energy? 10

100% stored as carbohydrates 10% STORED 1% STORED At this level there is only 0.1% stored energy available to support the apex carnivore. Which is why, they are constantly on the hunt! Now we understand why population sizes and numbers of species decrease the higher they are, and why eventually all food chains end. USED: 0.1% LOST: 0.8% STORED: 0.1%, not enough to support another trophic level PARTY HAT

Because energy is at a premium at the top of the chain, if the chase uses more energy than will be gained back from the catch then they will stop and wait for a more opportunistic lunch!

Or, why is it better to eat the fish than the fox? Level for level: since ectotherms do not maintain a warm body temperature; more energy is conserved and stored so food chains that contain them can support more biomass! They are more energy efficient! And as we all know…. ` nature loves efficiency!

 Energy and biomass both decrease from producer through each consumer level in a community  However, some things do not decrease, but, actually increase from level to level…  BIOLOGICAL MAGNIFICATION refers to the increase in concentration of toxins and pollutants at each trophic level in a food chain

 Famous ecologist who first sounded the alarm regarding biological magnification in her book Silent Spring Her work marked the beginning of the modern ecological movement.

 Many pesticides and herbicides do not break down in the ecosystem.  A grasshopper may eat a non-lethal dose of a pesticide and then get eaten by a mouse…  The chemical gets stored in the fat and tissues of the mouse. Every contaminated grasshopper the mouse eats adds more toxins to its body  Snakes who eat the contaminated mice get larger amounts of toxins  Hawks who eat the snakes get the most bioaccumulation of toxins often with very detrimental effects

 Widely used globally as an insecticide in the 40’s and 50’s to control mosquitoes (malaria and yellow fever)  In 1960’s population numbers of birds of prey began to drop dramatically, so that by the 70’s most were on the endangered species list  It was found the egg shells were softer than normal so as the young grew the egg cracked killing the offspring…but what was causing it? Population sizes in lower levels of food chain were not showing any signs of a problem.  When the birds were tested levels of DDT were found to be upwards of 10 million times the levels sprayed into the environment  Since mosquitoes reproduce in the water those food chains were affected the most…also because those food chains tend to be longer magnification effects are more pronounced.  DDT was banned in the late 70’s and as of the year 2000 most birds of prey populations have recovered and have been removed from the endangered species list