Chapter 3 Resources Introduction According to Tilman (1982), all things consumed by an organism are resources for it. But consumed does not simply mean ‘eaten’. Bees and squirrels do not eat holes, but a hole that is occupied is no longer available to another bee or squirrel | Chapter 3 Resources what are resources organisms may compete for resources Introduction According to Tilman 1982 all things consumed by an organism are resources for it. But consumed does not simply mean eaten . Bees and squirrels do not eat holes but a hole that is occupied is no longer available to another bee or squirrel just as an atom of nitrogen a sip of nectar or a mouthful of acorn are no longer available to other consumers. Similarly females that have already mated may be unavailable to other mates. All these things have been consumed in the sense that the stock or supply has been reduced. Thus resources are entities required by an organism the quantities of which can be reduced by the activity of the organism. Green plants photosynthesize and obtain both energy and matter for growth and reproduction from inorganic materials. Their resources are solar radiation carbon dioxide CO2 water and mineral nutrients. Chemosynthetic organisms such as many of the Archaebacteria obtain energy by oxidizing methane ammonium ions hydrogen sulfide or ferrous iron they live in environments such as hot springs and deep sea vents and use resources that were much more abundant during early phases of life on earth. All other organisms use as their food resource the bodies of other organisms. In each case what has been consumed is no longer available to another consumer. The rabbit eaten by an eagle is no longer available to another eagle. The quantum of solar radiation absorbed and photosynthesized by a leaf is no longer available to another leaf. This has an important consequence organisms may compete with each other to capture a share of a limited resource - a topic that will occupy us in Chapter 5. A large part of ecology is about the assembly of inorganic resources by green plants and the reassembly of these packages at each successive stage in a web of consumer-resource inter actions. In this chapter we start with the resources of plants and focus especially on those
