Ch. 2— Importance of Biological Diversity • 41 



of the Charles River wetlands would have re- 

 sulted in an average of $17 million per year in 

 flood damage (80,88,90). (Data on wetlands eco- 

 system losses are given in chapter 3,) 



Species Diversity 



Some species play such an important role in 

 particular ecosystems that the ecosystems are 

 named after them. Zambezi Teak Forest and 

 Longleaf-Slash Pine Forest are examples. But 

 the ecological processes that maintain domi- 

 nant species often depend on other species. For 

 example, elephants and buffaloes make a cru- 

 cial contribution to regeneration of Zambezi 

 teak by burying seeds, providing manure, and 

 destroying competing thicket species (72). 



Depletion of species can have a devastating 

 impact higher up the food chain. For example, 

 catches of common carp in the Illinois River 

 are one-tenth of what they were in the early 

 1950s. This decrease appears to be the result 

 of pollution-caused die-off in the 1950s of fin- 



gernail clams, mayfly larvae, and other river- 

 bottom macro-invertebrates. These macro-inver- 

 tebrates are still scarce, for river-bottom sedi- 

 ment is slow to recover from pollution, much 

 slower than water quality, for example (44). 



Certain species have a greater effect on pro- 

 ductive processes than is indicated by their po- 

 sition in a food web (figure 2-1). Earthworms, 

 for instance, improve the mixing of soil, in- 

 crease the amount of mineralized nitrogen 

 available for plant growth, aerate the soil, and 

 improve its water-holding capacity (98). Ants 

 also contribute to soil formation in temperate 

 regions and the tropics. They contribute to the 

 aeration, drainage, humidification, and enrich- 

 ment of both forest and grassland soils (99). 



In East Africa, species diversity increases the 

 productivity of grasslands. For example, graz- 

 ing by wildebeest promotes the lush regrowth 

 eaten by gazelles (59,60). Similar interactions 

 have been observed in North American grass- 

 lands between prairie dogs and bison. Although 

 the standing crop of grass in prairie dog towns 



hi. 



Photo credit: National Park Service. Department at ttie Interior 



Wind Cave National Park, South Dakota, contains a variety of w/ildlife including bison, elk, prairie dogs, pronghorn, and 

 deer. Interactions betvi^een species such as prairie dogs and bison increase the productivity of grasslands. 



