Stress resistance strategy in an arid land shrub: interactions between developmental instability and fractal dimension

This paper investigates allocation of energy to mechanisms that generate an d preserve architectural forms (i.e. developmental stability, complexity of branching patterns) and productivity (growth and reproduction) in response to environmental disturbances (i.e. grazing and resource availability). Th e statistical error in translational symmetry was used to detect random int ra-individual variability during development. This can be thought of as a m easure of developmental instability caused by stress. Additionally, we use changes in fractal complexity and shoot distribution of branch structures a s an alternate indicator of stress. These methods were applied to Anthyllis cytisoides L., a semi-arid environment shrub, to ascertain the effect of g razing and slope exposure on developmental traits in a 2 x 2 factorial desi gn. The results show that A. cytisoides maintains developmental stability a t the expense of productivity. Anthyllis cytisoides was developmentally mor e stable when grazed and when on south-facing, as opposed to north-facing s lopes. On the contrary, shoot length, leaf area, fractal dimension and repr oductive-to-vegetative allocation ratio were larger in north-than in south- facing slopes. As a consequence, under extreme xeric conditions, shrub mort ality increased in north-facing slopes, especially when not grazed. The rem oval of transpiring area and the reduction of plant competition favoured de velopmental stability and survival in grazed plants. Differences between gr azed and ungrazed plants were most evident in more mesic (north-facing) are as. (C) 2000 Academic Press.