Abstract
This study aims to analyze how the vegetation structure (physiognomy) and seasonal changes between seasons (wet and dry) influence richness, diversity and composition of ant species of arboreal and shrubby Caatinga environments. The vegetation structure was significantly different among the three strata for all parameters (mean diameter of vegetation, level of herbaceous cover, degree of coverage and thickness of litter and percentage of canopy cover). We collected 127 ant species. The mean number of species was approximately two times higher in the rainy season than in the dry season. There was no difference in species richness between the arboreal and shrubby Caatinga physiognomies nor interaction between season and physiognomy. Despite the similarity in richness, species composition differed between physiognomies, however we found no difference in composition between seasons. The seasonal differentiation may be mainly related to the variation in the overall numbers of individuals circulating in the environment, since the enhancement of resource availability during rainy season allows the colony to grow or expand foraging activities, which increases local diversity. Water restriction explains the limited diversity in both environments, while the occurrence of species with greater resource specificity may determine differences in ant composition. Differences in composition of each of Caatinga's physiognomy enhance beta diversity, therefore, raising the overall diversity in the Caatinga Domain.
Highlights
It is common that communities suffer changes in species composition and richness in seasonal environments, such as tropical dry forests (Murphy & Lugo, 1986)
The vegetation structure of arboreal and shrubby Caatinga were different in all traits, with the arboreal physiognomy presenting a CBH 1.4 times greater than in shrubby Caatinga, herbaceous cover twice as large, larger leaf litter coverage (U = 122.5; n = 90; P
There was no difference in species richness among the Caatinga physiognomies (χ2 = 0.4796; d.f.=1; P = 0.49) nor interaction between physiognomy and season (χ2 = 6.95; d.f. = 3; P = 0.07) (Fig. 1)
Summary
It is common that communities suffer changes in species composition and richness in seasonal environments, such as tropical dry forests (Murphy & Lugo, 1986). The ecological prediction states that the occurrence of more species in a community is seen as a response to the greater complexity of vegetation structure (Pacheco et al, 2009; Corrêa et al, 2006), which provides a greater amount of realizable niches by species of animals and a greater number of species in a given community (Tews et al, 2004) To test this hypothesis, several studies involving the comparison of areas with distinct physiognomies have been done throughout the world, using ant communities, such as Armbrecht and Ulloa-Chacón (1999) in Colombia; Fisher and Robertson (2002) in Madagascar; Wilkie et al (2009) in peruvian Amazonic Forest; Lindsey and Shinner (2001) in South Africa. In Brazil we highlight the studies of Fowler et al (2000) comparing forests from Bahia and Pará States; Corrêa et al (2006) in forest patches from Mato Grosso do Sul and Delabie et al (2007) comparing shaded cocoa agroecosystem developed under Atlantic Forest vegetation or other native vegetation in Bahia State
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