Advantages of Living in a Mosaic Like System

If a mosaic is a common pattern in the distribution of energy, resources, and organisms evolutionary and adaptive forces should be involved. The advantages for a species of living in a mosaic may depend on:

1. The optimization of the resources that are distributed in patches.

2. The reduction of the hostility of unfavorable habitat (with patches of a mosaic being considered islands in a sea).

There are species that live in one type of patch and species that utilize a mosaic to live and to maintain different functions. We call the first specialists and the second generalists. But this is only one part of the story because there are species that use different patches to find the same type of food, and other species that collect a very heterogeneous category of food in the same patch. But considering different living traits and not only the feeding, for instance roosting, breeding, migrating and different periods of the year, we often can observe a very different reaction to environmental patchiness, and the number of cognitive mosaics intercepted by a species can be very high.

The border of functional patches is strictly regulated by the capacity of the biological sensor of species.

It is not easy to demonstrate that mosaics are patterns perceived by organisms and included in their genetic memory. Some examples are offered to discuss this interesting topic.

1. Many organisms cope with the mosaic-like pattern. For instance, animals living in flocks probably reduce the cost of individual anti-predatory behavior. Individuals that are at the border of the flocks may be the strongest, or may be males with redundant reproductive functions. The close vicinity of individuals such as in a shoal of fish or a pack of gnu encourages the exchange of information about direction and source of food or predatory vicinity.

2. The environmental mosaic is perceived by animals in different ways but many species have utilized the mosaic design to become mimetic.

3. Patches of suitable quality are often distributed at random. One good example is from the foraging behavior of white stork (Ciconia ciconia) by Johst et al. (2001) (Fig. 3.10). Studies in central Europe of this central-place forager have demonstrated the high sensitivity of white stork to the dynamics of foraging patches under human stewardship. Distance of patches from the nest, time after the mowing and asynchronous mowing are important components. The relationship between two different strategies of patch selection - by random or active decision in patch selection - is also important. Increasing the dynamics and the heterogeneity of mowing, we can expect an increase in patch-selection strategy against a random strategy. Strategies to manage patchy landscape can produce advantages for some species, for instance, changing harvesting practices from a simultaneous to a sequential mowing.

et al. 2001, with permission)

Fig. 3.10 Representation of spatial structure of landscape and availability of patches around the white stork nest. Food availability decreases following a logistic shape after mowing (from Johst

Fig. 3.10 Representation of spatial structure of landscape

Fig. 3.11 A hypothetical population (AB) in which A is the component exposed to an external constraint and B is "protected" and isolated from the hostile context C

4. Patch position in a mosaic. At the border of the patches the uncertainty is higher than in the central part of the patches. Such uncertainty offers organisms new choices and the chance to become the driver of a system. But at the border the resources are more abundant and the competition is reduced.

Borders are for "pioneers," and the "frontier" is the place in which uncertainty is very high and far from self-organizing. In Fig. 3.11 we present a very simple model composed of three zones - A: interior, B: bordering, C: hostile. We can imagine that the flux of information in A is quite low if compared with B but system A is more stable than B and able to self-organize. In B the uncertainty is very high and the hostility of the matrix reduces the "attribute" efficiency that can be found in A. But in B individual variability can be used to cope with uncertainty and to find new strategies to expand and to dominate.

The thinness of a subpopulation shape is necessary to "penetrate" into the matrix by the occupation of small gaps existing in the hostile matrix.

The expansion front is composed of narrow propagules. This pattern can be observed either in plants (root systems) or in animal flocks.

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