Ecosystems

1. Ecosystems Energy and Nutrient Cycling

2. Outline I. Ecosystems A. Definition B. Energy Flow within Ecosystems 1. Trophic Relationships 2. Energy Budgets 3. Ecological Pyramids C. Nutrient Cycling 1. Biogeochemical Cycles 2. Nutrient Pollution

3. Ecosystem • All of the organisms living in a particular place as well as the chemical/physical factors with which they interact. • Range in size from small (like aquarium) to large (like forest) • E.g. desert ecosystem: organisms that live there (cacti, snakes, rodents), soil chemistry, average rainfall, temperatures etc.

4. Energy Flow • Energy flows through ecosystems, while matter cycles within them • Resources critical to human survival and welfare, ranging from the food we eat to the oxygen we breathe, are products of ecosystem processes

5. Energy Flow • Energy in ecosystems follows the rules of thermodynamics • Ecosystems are open systems where energy (generally from the sun) is input, is transformed, and is ultimately released as heat from organisms • Heat lost from organisms is disordered, unusable energy and therefore has increased entropy of the system • Energy transfers between organisms are not completely efficient • Without energy input (sun) ecosystems collapse

6. Trophic Relationships • Trophic level: how an organism gets it’s nutrition (energy) • All organisms at a particular trophic level are the same number of transfer steps away from the energy input into the system • Food Web: who eats whom in the ecosystem • Interconnected food chains • Energy flows through ecosystems via trophic levels within the food web

7. Trophic Levels • Primary producers: 1st trophic level-the autotrophs-capture sun energy (the initial energy source for almost all of earth’s ecosystems) • Primary consumers: heterotrophs-herbivores (caterpillars, cows etc), feed on primary producers • Secondary consumers: carnivores (birds, wolves etc), feed on primary consumers • Tertiary consumers: carnivores that feed on other carnivores

8. Decomposers • aka detritivores -consumers that get their energy from detritus-nonliving organic material • Dead organisms, feces, leaf litter, wood • Bacteria, fungi, animals which feed on detritus like earthworms • Decompose organic material in ecosystem and transfer chemical elements in inorganic forms to reservoirs such as soil, water, and air • Decomposition by bacteria and fungi accounts for most conversion of organic materials from all trophic levels to inorganic compounds usable by primary producers (thereby closing the loop of nutrient cycling)

10. Ecosystem Energy Budgets • Primary production: amount of light energy converted to chemical energy by autotrophs in a given time period. • Sets the “spending limit” for the energy budget of the ecosystem • Of the visible light that reaches the earth, only about 1% is converted to chemical energy by photosynthesis • Biomass: amount of biological material in a group of organisms in an ecosystem (ex. weight of all trees)

13. Ecological Pyramids • A good portion of the energy produced by primary producers is used to fuel their life functions-cellular respiration, growth, reproduction-this is true at every trophic level • General rule: only about 10% of the energy contained in a particular trophic level is available for transfer to the next trophic level

15. Ecological Pyramids • The only generalization in an ecosystem that always holds true: energy decreases with each successive trophic level • Some generalizations that are often true: • # of individuals decreases as you increase trophic level • Size of individuals increases as you increase trophic level

19. Nutrient Cycling in Ecosystems • Within an ecosystem nutrients are cycled internally, there are leaks (outputs) like erosion and timber/crop harvest • Must be replaced by nutrient inputs: • Weathering of rocks • Windblown dust • Precipitation • Decomposition into form available to plants

26. Nutrient Cycling in Ecosystems • Nutrients are carried from terrestrial ecosystems by movement of water and deposited in aquatic ecosystems and associated lowlands • If inputs exceed outputs, the nutrient cycle in the ecosystem becomes stressed or overloaded resulting in pollution (nutrient levels exceed capability of the ecosystem to process them)

27. Nutrient Cycling in Ecosystems • Nutrients eroded from agricultural lands, sewage, industrial wastes drain into streams, rivers, lakes and estuaries • These pollutants destroy plants and animals that cannot tolerate their presence or the changed environmental conditions caused by them