What Processes Create Mosaics

We have already discussed the origin and communality of mosaics. In general, a mosaic is created by the limited capacity of abiotic or biotic actors to spread everywhere. If we consider that every biological organism has a limited neighboring area in which to live and in which to influence the surroundings, we immediately understand that a mosaic is the result of such intrinsic character.

Every species lives in a restricted space and this produces "local" heterogeneity. If we add the tendency for every species to enter into contact with individuals of the same species, the clump effect is per se a mosaic. We can give an example by discussing phytophagous larvae such as caterpillars. Such larvae develop from eggs laid on the bottom side of a leaf and spread onto the upper part, biting the leaf surface according to a design that is strictly linked with the growing size of their body.

In this way it is possible to observe many irregular holes in the leaves that can be interpreted as a foraging mosaic. Every patch, which is in reality a hole in the leaf, is the result of destructive interaction with the host plant and the presence in the leaves of less-palatable parts, such as the vascular and sustaining system. Such a mosaic that has an irreversible effect on the attacked leaf is very similar to the one created by the macro-herbivore in grasslands (Fig. 3.9).

The mosaic is spatially distributed, with patches of irregular shape and size that reflect different behavior, different growing stage of larvae and also different climatic conditions (cold, hot, dry, wet, windy, etc.) that has favored or discouraged larvae to forage. The pattern created by these larvae is (apparently) easy to analyze because only one actor is involved. Nevertheless, the choice of the part of the leaf and the spatial arrangement of each foraging patch are not clearly understood by

Fig. 3.9 Holes created by the feeding habits of caterpillar larvae can be considered patches in a system in which the vascular and skeletal system represents the landscape constraint around which animals try to optimize their grazing activity (leaf from a Beech forest, Northern Apennines). From (A) to (C) different levels of patch density show the increase of the "landscape" constraint in vascular and sustaining systems

Fig. 3.9 Holes created by the feeding habits of caterpillar larvae can be considered patches in a system in which the vascular and skeletal system represents the landscape constraint around which animals try to optimize their grazing activity (leaf from a Beech forest, Northern Apennines). From (A) to (C) different levels of patch density show the increase of the "landscape" constraint in vascular and sustaining systems just observing the behavior of larvae. And also in such a simple system based on the destruction of the resource a complex mechanism should act. Under conditions of abundance of resources, few holes appear and the distribution of foraging patches could be random, but, moving toward the reduction of resources, the location of foraging patches is more and more deterministic and finally is the main vascular and sustaining systems that form a constrained mosaic.

The same story can be observed when you are picking grapes in a vineyard. You move from one bunch to another after you have picked a grape. We can explain this in terms of instinctive anxiety under predatory pressure, but whatever is the cause of such behavior at the end you move from one patch to another, and you create unintentionally a mosaic of partially harvested bunches.

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