The impact of grazing on plant fractal architecture and fitness of a Mediterranean shrub Anthyllis cytisoides L.

Abstract

Summary1. We examined natural grazing by livestock (sheep and goats) on Albaida Anthyllis cytisoides L. with the aim of determining whether variation in the allometric relationships between plant parts provides a sensitive indicator of the impact of grazing. 2. The intra-individual variation in translatory symmetry with scale and increased complexity of fractal structures reflect environmental disturbance under heavy grazing pressure and lack of grazing. 3. Fitness consequences of grazing were also investigated. Grazing promotes growth and adult survival, and a drop in seed production as a consequence of consumption. In spite of that, total inclusive fitness (population rate of change) tends to increase with grazing. 4. Moderate grazing, while promoting growth, also enhances stability of vegetative structures. The favourable effect of moderate levels of herbivory on A. cytisoides is reflected in the homeostatic maintenance of its translatory symmetry and in the increased complexity of its fractal structures.

Instability of development and fractal architecture in dryland plants as an index of grazing pressure

“…What differs is the nature of the stress. This points out one of the unique advantages of developmental instability as a measure of stress; it can be used to resolve the controversy over whether light to moderate grazing enhances the fitness of grazed plants directly (see McNaughton, 1977(see McNaughton, , 1979(see McNaughton, , 1983Collins, 1987;Escós et al, 1997) or, alternately, arises indirectly from a release from competition (see Belsky, 1986Belsky, , 1987. Our results support the contention that grazing reduces competition.…”

“…However, bilateral symmetry is only one of many measures of developmental instability. Other kinds of symmetry in development -radial symmetry, translational symmetry, and symmetry of spatial scale Graham et al, 1993a;Alados et al, 1994, in press;Escós et al, 1995bEscós et al, , 1997 -have also proven useful in detecting and assessing the biological effects of stress.…”

“…Until recently most studies concerned animals with bilateral symmetry, though studies have now revealed that plants also are suitable subjects to detect developmental instability caused by environmental disturbance Alados et al, 1994, in press;Møller & Eriksson, 1994Escós et al, 1995bEscós et al, , 1997Møller, 1995a;Tracy et al, 1995;Sherry & Lord, 1996).…”

Human–landscape interactions in the Conquezuela–Ambrona Valley (Soria, continental Iberia): From the early Neolithic land use to the origin of the current oak woodland

“…Emlen et al (1993) and Watson and Thornhill (1994) argued that symmetries of complex traits may be more sensitive indicators of stress because such traits are under the control of higher organized processes; i.e., allometric growth implies the coordination of size and shape relationships. Thus, in addition to FA, other methods have been used in order to estimate developmental instability by measuring the within-plant variation, such as frequency of phenodeviants and deviations from radial, spiral, translational, and fractal dimensions of plant structures Graham et al 1993b;Alados et al 1994Alados et al , 1998aEscó s et al 1995Escó s et al , 1997Sherry and Lord 1996). In addition, the relationship between different indices of developmental instability and fitness is largely unknown.…”

“…The parameter k represents the starting conditions of shoot enlargement (length of the first internode), a represents the exponential growth, and b represents the inhibition process of growth. This relation has been used to calculate developmental instability in several plant species (Alados et al 1994(Alados et al , 1998a(Alados et al , 1998b(Alados et al , 1999Escó s et al 1995Escó s et al , 1997Sherry and Lord 1996;Anne et al 1998). This equation has two parts.…”