90 



LUGO 



Recycling 



Total 

 Respiration 



Fig. 8 Model illustrating energy flows associated with the develop- 

 ment and maintenance of structural complexity in ecosystems. (For 

 identification of symbols, see Fig. 2, and, for a discussion of the 

 figure, see the text.) The gross energy flow of the system (i.e., all 

 incoming energies that contribute to order) can be allocated to 

 overcome disordering energies (flow 1), to develop the initial 

 amount of structure required for survival (flow 2) and/or to develop 

 additional complexity and species diversity (flow 3). Each of the 

 state variables feeds back positive work that increases the ability of 

 the system to process more energy and to use resources more 

 efficiently. Energy allocation for structural development and com- 

 plexity increases if there is net energy and if the energy investment 

 in the feedbacks (flows 4 to 6) are offset by the increase in the 

 energy capture and conversion efficiency of the system. As the net 

 energy of the gross energy conversion increases (flows 1 to 3 minus 

 flows 4 to 6), the capacity to develop more complexity and diversity 

 also increases. Ultimately the balance between all energy sources and 

 all stressors will determine ecosystem complexity. 



A second assumption is that ecosystem complexity pays off by 

 allowing higher efficiency in the use of energy resources and in the 

 recycling of matter. This widely held working principle of ecology 

 has been discussed many times (e.g., E. P. Odum, 1969; Margalef, 

 1969; 1975) and still makes sense to me. 



