Examination of ecological networks

Using an ecological food web model, we examine the change in exergy storage and energy throughflow (power) as a consequence of eight network changes including (1) increased input, (2) removal of food chain links, (3) addition of new pathways (links) from producers to herbivores, (4) addition of new pathways (links) from herbivores to carnivores, (5) food chain prolongation, (6) increased flow rates in the food chains, (7) transfer of energy from one food chain to another, and, (8) reduced loss as detritus. It has been shown previously that exergy storage and energy throughflow increase during stages of ecosystem growth and development. We hypothesis that network changes yielding the highest exergy storage and throughflow will have a selective advantage and would be more favorable to the overall system organization. This hypothesis could be used to explain the selective criterion for changes that occur in an ecological network. Here, we investigate which changes, in general, lead to these more favorable conditions. Model results demonstrate the following six rules regarding network effects on exergy and power: I. Increased input gives proportional increase of exergy and power; II. Additional links only affect power and exergy when they increase the overall network throughflow, thus the connection placement is important; III. Food chain prolongation has a positive effect on the power and exergy of the network; IV. Reduction of loss of exergy to the environment or as detritus (with a 0 value of 1 only) yields a higher power and exergy of the network; V Faster cycling-detritus is decomposed faster or the transfer rates between two tropic levels are increased-implies higher power and exergy; and, VI. Input of additional exergy or energy recycling flows has bigger effect the earlier in the food chain the addition takes place. (c) 2006 Elsevier B.V All rights reserved.