the extent of change (Weaver, 1954; Ellison, 1960). Overgrazing accelerates 

 the rate of grassland conversion to woody growth (Ellison, 1960). 



The primary consumers include insects, granivorous birds, such as the 

 eastern meadowlark ( Sturnel la magna ) and prairie chicken ( Tympanuchus sp. ), 

 and numerous small mammals (rodents). The grasses and other herbaceous species 

 of different stand densities and life forms provide food and cover for the con- 

 sumers. Aattwater's prairie chicken (T ympanuchus cupido attwateri ) is especially 

 dependent upon grassland presence and diversity. Loss of grasslands due to 

 agriculture, ranching, and brush encroachment has caused extensive population 

 reductions (Lehmann, 1941). 



Secondary consumers in the coastal grasslands include predatory mammals, 

 primarily the coyote ( Canis latrans ), and raptors such as the marsh hawk ( Circus 

 cyaneus ) that fly in from adjacent systems; reptiles; and insectivorous song- 

 birds. The predatory mammals and raptors hunt the rodent populations typically 

 associated with grasslands, such as the hispid cotton rat ( Sigmodon hispidus ). 

 The red wolf ( Canis rufus ) was formerly an important secondary consumer, but 

 its ecological role has since been assumed by the coyote. 



The limiting factors of the coastal grassland producers include the same 

 components as in the maritime woodland, with the addition of fire. Portions 

 of the system adjacent to the shoreline are subject to salt stress from periodic 

 storm-surge flooding and salt spray, which increases soil salinity. These sites 

 are rarely influenced by normal tidal action. Fire affects the consumer groups 

 by destroying nests and young, eliminating cover types and temporarily removing 

 or exposing food sources. Fire attracts several consumer groups to recently 

 burned sites to forage on new, succulent, and nutritious vegetation (Allen, 

 1952). 



System detritus is derived from the producers, primarily the perennial 

 grasses. Humification in the grasslands is rapid, but mineralization is slow 

 (Smith, 1966). System outputs include energy losses to the abiotic system 

 through detritus, surface-water outflows, and groundwater outflows. Sheetwater 

 flows carry nutrients into adjacent aquatic ecosystems, such as brackish and 

 fresh marshes, ponds, and swales. 



Brush-grass complex . An ecosystems diagram for the brush-grass complex 

 is presented in Figure 3-4. This ecotonal community represents the intermediate 

 stage in the successional transition from coastal grasslands to maritime wood- 

 land. In regions of low rainfall, as in south Texas, dense woody brush becomes 

 the climax community. As an interfacing system, this brush-grass complex func- 

 tions under all the previously described regulatory components. Community 

 structure and species composition are spatially and temporally variable. As a 

 transitional stage, the system is ^ery dynamic with respect to dominants, pro- 

 ducer composition, and structure. 



29 



