Unlike the grassland or woodland, which are relatively resistant to short- 

 term environmental fluctuations, the brush-grass ecotone is more responsive to 

 changes in the magnitude or timing of critical regulating factors. Slight 

 changes can enhance or suppress the competitive advantage of either component 

 and will determine the final dominant. Fire is the most critical regulating 

 factor, and its timing, frequency, and intensity determine the successional 

 direction of the community (Daubenmire, 1968; Weaver, 1954). Under most circum- 

 stances, grazing will cause the same ecological effects as fire suppression in 

 reducing the competitive advantage of grasses and favoring woody plant expansion 

 (Ellison, 1960). 



Primary producers include perennial grasses, hardwood shrubs (brush), peren- 

 nial herbs, and to a lesser extent annual herbs and grasses and mature trees. 

 Either brush or perennial grasses will dominate, depending on the stage of tran- 

 sition and current fire and grazing regime. Plant competition for soil moisture 

 operates through the same mechanism as previously discussed. The effects of 

 shading still regulate the complex interactions involved with the competition 

 for soil water. 



Primary consumers include the hoofed mammals (white-tailed deer, javelina, 

 and feral swine), small mammals (rats, mice, and rabbits), granivorous song 

 and ganiebirds (turkey, dove, quail, sparrow, etc.), and the diverse insect group. 

 The shrubs, particularly if not too dense, and perennial herbs are of great 

 food and cover value to many wildlife species (Blakey, 1947). The high degree 

 of cover-type interspersion produces a diverse environment in terms of life 

 forms and species composition. Consumer groups reflect the desirable conditions 

 and high primary productivity by n.aintaining elevated population levels. White- 

 tailed deer have maintained population levels of 1 deer per 2 to 4 ha (5 to 10 

 acres), and turkeys reached densities of 1 bird per 16 ha (10 acres) on Aransas 

 Refuge; both are extremely high productivity levels (Blakey, 1947), Overall 

 consumer diversity is greater than productivity levels (Blakey, 1947). Overall 

 consumer diversity is greater than in either the grassland or woodlands. 



Secondary consumers include the predatory memmals (coyote, bobcat, grey 

 fox, raccoon, and others); raptors such as the red-tailed hawk ( Buteo 

 jamaicensis ), Harris' hawk ( Parabuteo unicinctus ), and great horned owl; and 

 insectivorous songbirds such as vireos~ TVi'"eo spp. ), Carolina chickadee ( Parus 

 carol inensis ), and warblers. These species may forage in the grassland or mari- 

 time woodland periodically, but most of the hunting activity for rodents, 

 rabbits, and insects occurs in the ecotone. On occasion, some of the secondary 

 consumers shift trophic levels by feeding extensively on seasonally abundant 

 fruits. 



The whooping crane ( Grus americana ) uses portions of the community that 

 adjoin the marsh for protection from severe northerly winds and as an occasional 

 feeding area (Allen, 1952). 



System outputs to the abiotic system are similar to those described for 

 the woodland and grassland systems. 



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