Species-species and species-habitat interactions have been demonstrated to be important in influencing diversity across a variety of ecosystems. Despite generalities in the importance of these interactions, appropriate mechanisms to explain them are absent in many systems. In sandhill systems of the southeast U.S., gopher tortoises have been hypothesized to be a crucial species in the maintenance of diversity and function. However, the mechanisms and magnitude in which they influence their communities and habitats have rarely been empirically quantified. I examined how habitat structure influences tortoise abandonment of burrows and how tortoise densities influence nonvolant vertebrate community diversity. Tortoise burrow abandonment is directly influenced by canopy closure, with each percent increase in canopy cover relating to a ~2% increase in the probability of burrow abandonment. In addition, tortoise burrow density was positively correlated with diversity and evenness, but not species richness. This influence was directly proportional to burrow density, supporting a dominance role for this species and rejecting the commonly asserted keystone species mechanism. I also quantified the influence of tortoises in influencing diversity relative to other environmental and habitat variables. Through this research, I have demonstrated that disturbance and habitat structure are important, but diversity responds most to density of burrows in the habitat. These findings demonstrate the intricate relationships interacting to maintaining diversity in sandhill systems. In particular, habitat change leading to declines of gopher tortoises may have drastic negative impacts on vertebrate species diversity.

This master's thesis deals with a symbolism of tortoise in fine art. The text is limited to the European art only, to keep the range of the thesis sustainable. The thesis is devided into three parts. The first chapter focuses on literature, as a source of meanings for fine art. There are in detail described beginnings of literature about turtles and development of the dominant lines of their symbolism until 17th century. It is about "Tortoise-Lady", "Tortoise-Beast & Heretic" and "Slow Tortoise". Within the second part there are briefly mentioned the shades of turtle meanings that were not specified in the previous chapter due to the time period limitation. The third section includes a case study of the painting "Bathers with a Turtle" by Henry Matisse. It contains also occurrence of "Tortoise-Lady" within the history of art.

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