Ecological Complexity and Mosaics

Ecological complexity is the result of several processes that are determined by at least four main properties that behave differently: invariance, density, diversity, and spatial arrangement (Fig. 3.1).



Fig. 3.1 Ordination of invariance, density, diversity, and spatial arrangement according to self-control and variability

Invariance means the capacity of individuals to maintain constant forms from one generation to another and at the same time the capacity to adapt to a changing world. This factor is largely controlled by genetic mechanisms acting in an evolutionary fashion.

Density represents the quantity of individuals necessary to maintain populations under the numerical fluctuations by natural stressors and environmental unpredictability. Density means populations and their emergent characteristics that regulate the number of individuals and their behavior.

Diversity assures the coalescence of different species into communities with beneficial effects on single species by multiple uses of available resources. Diversity allows the optimal use of resources by the creation of complex trophic linkages, interspecific competition avoidance, and mutual reinforcement.

Finally, spatial arrangement provides the ability to cope with the environmental variability in the physical space. The different arrangement of patches in a mosaic greatly contributes to the creation of new conditions for species, populations, and communities. The spatial arrangement of environmental patches presents the highest level of spatial arrays, which contributes in great measure to "creating" new possibilities for communities and populations. The complexity of ecological systems is created by the processes activated by the above-mentioned factors.

Every factor is sensitive to the environmental constraints. The self-control of each of these factors changes greatly. Invariance is controlled by the same individual through distinct genetically driven mechanisms. Moving from populations to spatial arrangement, the internal control decreases in terms of importance and the external factors become more and more important. Finally, the spatial arrangement of patches becomes the level at which human activity manipulates, but only indirectly, diversity, populations, and genomes.

Variability increases as it moves from the first factor (invariance) to the last (the spatial arrangement) and this emergent property plays a fundamental role in assuring new opportunities for species adaptation. We recognize in the spatial arrangement of the objects (communities, populations, individuals) one of the most important sources of variability and unpredictability that largely contributes to self-maintenance of the ecological complexity.

If the mosaic is a universally recognized pattern of living and nonliving entities, a common ontogenesis should be recognized. If a horse is introduced to a new paddock and we observe the modification of the paddock through grazing and trampling (disturbances strictly associated with the horse), this introduction gradually produces more and more disturbed areas connected by pathways. Finally, after a few days the horse will have transformed the paddock, initially homogeneous in terms of grass cover, into a mosaic of differently grazed patches, connected by trails. What lesson can we learn from this? A mosaic is not per se generated like the pattern is observed, but by a differentiated intensity in local disturbance associated with a strong investment in memory. The reaction of the grass cover is not manipulated by an explicit goal-function of the horse but by the frequency of return of the disturbance and the direction from which the disturbance is coming. The system apparently is driven by external factors (e.g. grass species preferred by a horse), but progressively the external factors are associated with an internal dynamic of grass cover that reacts to disturbance, favors species more resistant to trampling, and generates a less diverse grass cover with the appearance of more homogeneous patches: the mosaic appears and progressively these mechanisms are reinforced! The disturbance intensity produces a mosaic that can survive, when created, for a long time by an intrinsic reinforcement.

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