Energy transfer Through Communities

Energy Pyramids 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/m2/year SALT MARSHES

What can be inferred from just the shape alone? More biomass at lowest level Biomass decreases at every level Numbers of species decrease Sizes of populations decrease WHY? Available energy decreases!

What happens to the energy? 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 LOST AS HEAT; Cellular respiration releases heat energy; this energy is not available to the next level. Endotherms convert faster, more heat Ectotherms convert slower, less heat STORED AS CHEMICAL ENERGY in the tissues of plants (as starch) and fat (as glycogen) in animals; this is the only source of energy available to the next trophic level in the food chain…

Step by Step…from the bottom-up! 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. UNUSEABLE ENERGY PHOTOSYNTHESIS PRODUCERS 100% converted and stored as carbohydrates and is available to the next trophic level…

Primary Consumers Remember; at each trophic level consumers use, loose, and store energy. The question is how much of each? STORED: 10% LOST: 80% USED: 10% 1ST Level: Primary Consumer 100% stored as carbohydrates A whopping 90% of the available energy is gone at the 1st level!

Secondary Consumers A this level there is only 10% available energy stored in each mouse's tissues. So, how many mice does the fox need to eat to get 100% of the energy it needs? 10 STORED: 1% LOST: 8% USED: 1% 2ND LEVEL 10% STORED 100% stored as carbohydrates 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.

Tertiary Consumers (Apex Carnivores) At this level there is only 1% stored energy available to support the apex carnivore. Which is why, they are constantly on the hunt! STORED: 0.1%, not enough to support another trophic level LOST: 0.8% USED: 0.1% 1% STORED 90% ENERGY GONE! 10% STORED PEANUTS 100% stored as carbohydrates Now we understand why population sizes and numbers of species decrease the higher they are, and why eventually all food chains end.

Let’s look at one in terms of biomass…

Apex carnivores instinctively know when to break off the hunt…. 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!

Endothermic vs Ectothermic, 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!

BIOLOGICAL MAGNIFICATION 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/pollutants in the tissues of organisms at each trophic level in a food chain

Rachel Carson 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.

How it works… Many pesticides and herbicides do not break down in the ecosystem. Grasshoppers consume the leaves covered with herbicide… Mice consume the grasshoppers. 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…

DDT: it killed more than mosquitoes 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 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

How biomagnification affects you…