74 



LUGO 



Table 2 (Cont.) 



Stressor 



Pushing effect 



Pulling effect 



Eutrophi- 

 cation 



Fire 



Herbicides, 

 oil, and 

 other 

 poisons 



Heavy 

 rains 



High tem- 

 perature 



Low tem- 

 perature 



Temperature 

 amplitude 



Hurricanes 



Insecticide 



Stimulates primary productivity 

 and growth of consumers 

 (E. P. Odum, 1971) 



Makes nutrients and moisture 

 more available; reduces 

 competition (Wright, 1976) 



Select for certain life forms over 

 others, survivors grow faster 

 (Wein and Bliss, 1973; 

 Niering and Goodwin, 1974; 

 Burk, 1977) 



Act as a clue for starting pheno- 

 logical events in deserts 

 (Beatley, 1974); relieve 

 salinity in coastal situations 

 and redistribute nutrients 

 (Chabreck and Palmisano, 

 1973) 



Accelerates processes, particu- 

 larly respiration and recycling 

 (Smith et al., 1974) 



By slowing down processes, 

 allows for conservation of 

 storages (Mooney and 

 Billings, 1965) 



If short-term, fluctuations may 

 stimulate metabolism 

 (Sweeney and Schnack, 1977); 

 increases resistance to thermal 

 shock (Hubbs, 1964) 



Bring water, nutrients, sedi- 

 ments, and propagules 

 (Chabreck and Palmisano, 1973) 



DDT (5 — 10 ppm) enhances 

 resistance to X-ray radiation 

 (Erdman, 1966) 



Shifts species composition, 

 causes anoxic conditions, 

 and eventually reduces 

 species diversity and 

 complexity (E. P. Odum, 

 1971) 



Removes structure 

 (Wright, 1976) 



Reduce productivity by 

 altering behavior and 

 physiology, poisoning, 

 and killing organisms 

 (Krebs and Burns, 1977); 

 lowers species diversity 

 (Tomkins and Grant, 1977) 



Remove structure and may 

 cause other stresses, such 

 as flooding, which affect 

 gas exchange of wetlands 

 sediments and the 

 turbidity in aquatic 

 systems (Hoopes, 1974) 



Can be lethal; reduces 

 species diversity 

 (KuUberg, 1968) 



Freezes can be lethal 



If amplitude is wide and 

 change is rapid, it can be 

 lethal (Hubbs, 1964; 

 Sastry, 1976) 



Structure is removed 

 (Craighead, 1964) 



Eventually lethal (Erdman, 

 1966) 



*Literature citations are not intended to imply that these are the only or the 

 most significant documentations of the example. 



