Energy Dynamics

What factors govern energy capture, allocation, storage, and transfer between producers and consumers in a terrestrial ecosystem?

BACKGROUND
Almost all life on this planet is powered, either directly or indirectly, by sunlight. Energy captured from sunlight drives the production of energy-rich organic compounds during the process of photosynthesis. These organic compounds create biomass. The net amount of energy captured and stored by the producers in a system is the system’s net productivity. Gross productivity is a measure of the total energy captured. In terrestrial systems, plants play the role of producers. Plants allocate that biomass (energy) to power
their life processes or to store energy. Different plants have different strategies of energy allocation that reflect their role in various ecosystems. For example, annual weedy plants allocate a larger percentage of their biomass production to reproductive processes and seeds than do slower growing perennials. As plants, the producers are consumed or decomposed, and their stored chemical energy powers additional individuals, the
consumers, or trophic levels of the biotic community. Biotic systems run on energy much as economic systems run on money. Energy is generally in limited supply in most communities. Energy dynamics in a biotic community is fundamental to understanding ecological interactions.
To model ecosystem energy dynamics, you will estimate the net primary productivity (NPP) of seeds growing under lights and the flow of energy from plants to butterfly larvae (the consumers) as the larvae eat plants.
The following exercises describe skills and methods for estimating energy flow in a terrestrial ecosystem. Note and record any questions that occur to you as you work through this activity.
 
Questions might include the following:
• What kinds of things affect plant productivity, the growth of cabbage white butterfly larvae, or the interactions of these organisms?
• How do you keep track of energy as it moves through the biological system? Can the techniques used for tracking energy be improved?
• What is the role of energy in ecosystems?

One or more of these questions will help guide you through the final part of this laboratory, where you are expected to carry out your own research project based on one of your questions.