88 LUGO 



the volumes edited by Woodwell and Smith (1969) and Van Dobben 

 and Lowe-McConnell (1975) for summaries of the various theories 

 and arguments.] Sanders (1969), for example, listed the character- 

 istics of physically controlled and biologically accommodated com- 

 munities (Table 1). The idea that stressors have the effect of reducing 

 species diversity by increasing adaptation costs is probably correct, 

 because a stressor, by imposing energy barriers on a system, decreases 

 its ability to support complexity. Too much emphasis has been given 

 to the role of a stable environment, how^ever, without also acknowl- 

 edging the balance between energy subsidies and energy drains in a 

 given environment. All the energy flows entering the system and the 

 variety of possible ecosystem responses to stress have been ignored in 

 such efforts as that depicted at the top of Table 1. 



Slobodkin and Sanders (1969) suggested that short-term stability 

 (a duration of about five generations) in an otherwise unpredictable 

 environment decreased species diversity because opportunist species 

 would temporarily gain dominance over the normal animal com- 

 ponent of the system. If we assume that by "periods of predictable 

 conditions" they mean a relaxation of stress, then their conclusions 

 do not hold in theory or in practice. Theoretically, lower stress 

 (higher predictability?) should increase the carrying capacity of an 

 environment. Observations in rocky tidal shores (Connell, 1972; 

 Dayton, 1971) showed that removal of dominants by a stressor 

 results in a temporary increase in diversity. This also occurs in 

 high-salinity environments after a storm decreases salinity stress. At 

 these times species diversity increases for a short period but then 

 returns to its lower value as stressful conditions return to high 

 intensity. Thus a property of chronically stressed ecosystems is that, 

 during their successional patterns, species diversity may decrease 

 rather than increase (bottom of Table 1). 



Conflicting arguments about the causes of ecosystem complexity 

 can be clarified if analyses are based on the total energy flow 

 through the system. The productivity hypothesis of Connell and 

 Orias (1964) was criticized by Sanders (1969), who argued that 

 highly productive systems, such as marshes, are not necessarily 

 diverse, as inferred from the productivity theory of ecosystem 

 diversity. Others have argued that diverse systems are not necessarily 

 stable (e.g.. May, 1975). The argument can be restated by substituting 

 whole ecosystem analysis for generalizations based on population 

 studies and total energy flow per unit area (the energy signature 

 concept) for criteria of organic productivity. 



Ecosystem complexity is a function of the net energy available to 

 a system. Net energy is the balance between the energy expenditures 



