Imagine a specific population of birds living in a forest. Forest is not a homogeneous area by definition, and resources are variously located in the forest. This distribution depends on several physical, biological, and ecological processes that have nonuniform distributions.
Perturbations originating external to the forest, such as hurricanes, logging, and fire can modify shape, history, and spatial aggregation of individual plants. Soil reflects differences in nutrient content, water availability, fungi, and bacteria. All these factors influence the distribution of plants, their individual history, and the collective shape of the forest. Now we investigate the distribution of individuals of a species of bird, for instance the European robin (Erithacus rubecula). The distribution of this species in the forest is not homogeneous. There are areas of high and low density. At first sight this pattern is the result of the distribution of resources, and a multitude of studies try to link resource distribution and birds. But if we try to define a resource, we immediately think of food and water. In reality, organisms need more types of "resources" from the environment. For a bird these could be: food, water, opportunity to acquire a mate, nesting site, singing place, resting place, anti-predatory refuge, roosting place, flying space, and feeding space.
It is evident that the meaning of "resource" has been enlarged, and, in addition to biomass availability, we have considered also environmental and social conditions like safety.
This list could be enlarged according to the species considered.
For every need an individual requires a specific "resource" that is intercepted by cognitive mechanisms mediated by specific sensors, such as the eye, ear, nose, tactile sensor, etc. or by "behavior" sensors, such as the choice of roosting place or by cultural and experiential tools.
Every function activated by a specific physiological requirement needs a space in which to find a "structural coupling" with the environment (Fig. 8.8). I have called this space the "eco-field." According to the meaning theory of von Uexkull, the eco-field could be considered "a spatial configuration carrier of meaning" (Fig. 8.4). By definition a space has borders and, consequently, a dimension. Inside the eco-field the conditions to perform that specific function are not isomorphic and heterogeneity creates conditions with a different quality inside a specific eco-field. But assuming that a final unique score can be attributed at every eco-field of a selected species, the quality of the environment in which an individual resides depends on the score of each eco-field. And in turn the score of each eco-field determines the fate of that individual. Let me present another example. If all eco-fields have high scores -except for predation susceptibility which is very high and registers as a low score -survival will be extremely low.
• Eco-field c "*- Function c ^ Need c y Eco-field d ^- Function d ^^ Need d
Fig. 8.8 The cognitive landscape is the combined perception and interpretation through the composing eco-fields. This is a unifying principle that can be applied to every species. The activation of a function is necessary to accomplish a need. Every function refers to a cognitive template (cognitive map) that is used for scanning the surroundings to find the corresponding spatial configuration carrier of meaning necessary to intercept the resource
For instance the tree pipit (Anthus trivialis) is a bird that, during the breeding season, requires open grassland in which to place the nest, but at the same time it needs a tree from which to jump and to perform a singing flight. If all other eco-fields have a high score but trees are absent, no birds will settle in such a condition. But if trees are present although the food resources are scarce, a pair can establish a territory. Finally, the total scores for all eco-fields will determine the functional condition for a specific individual. A fat individual can be unhappy, and a hungry individual happy. Adaptation mechanisms are active in a real space for precise functions with effects on the genetic selection of individuals in a population. The concept of eco-field demonstrates the possibility of coupling knowledge of the "habitat" with adaptability processes.
A double mechanism is in action for every individual: a priority in selecting a function according to the past history of the actions performed, as well as a differentiated effect according to the qualities of the distinct eco-fields (Table 8.1).
This vision has considerable implications for the management of species and for the reconnection of evolutionary biology to physiological ecology. A species can be resident for a long time in a place, and at a certain moment, can disappear
Table 8.1 The best sequence of food and water depends, for a horse, not only on individual preferences for a certain type of food but on the type of activity carried out before food selection. If the horse was mounted on a hot day, for a long time sequence A could be the best. Case B is for a horse with a moderate activity. Case C is for a horse not in activity. Case D is for a horse after a training set. The sequence can be established according to the memory of the previous actions. A priori action does not exist; the sequence depends on the history
Water Apple Hay Fodder
Fodder Fodder Fodder Water
Apple Water Apple Apple abruptly. This could be described in terms of ecological debt (Tilman et al. 1994). In this case low scores for some eco-fields have not caused any apparent effect on the population, but, when a threshold has been passed for an additional negative factor, the entire "family" of eco-fields no longer has the minimum requirements. As a result, species go extinct.
The sequence of functions (regulated by internal genetic and physiological mechanisms, and by external perturbations) and their eco-field score create a phase-space that delineates the border of the individual survival gradient. If you maintain a wild shrew in a small cage, in a short time it will die, even though you provide fresh food, water, and refuge in abundance. But if you enlarge the cage for instance by providing perforated bricks the shrew can move a lot inside and outside of the brick using the holes and brick tunnels. The shrew can then survive for a long time even if food is scarce. This is an example of different eco-field scores that make a difference. Survival is not the total sum of the eco-field scores, but it depends on the position in which the specified eco-field is ranked. We could define essential and complementary eco-fields, although this distinction can't be absolute only relative and strongly connected with other factors such as seasonality.
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