About Ecological Niche and Habitat

The "niche theory" in ecology describes the main functional and structural characteristics recognized by a species (Grinnell 1917, Hutchinson 1957), and represents a foundation of modern ecology. This paradigm has been extraordinarily useful for understanding the evolutionary and adaptive mechanisms by which a species interacts with the environment; nevertheless, this paradigm is unable to account for the mechanisms acting to transfer the information of the life trait into the "real world" and vice versa.

The impressive advancement in information science during the Twentieth Century has emphasized the concept of information itself, which is necessarily associated with its emission, transport, and reception (Shannon and Weaver 1949, Brillouin 2004, Battail 1997). In an evolutionary perspective a large amount of information is carried by resources, which, defined in a broad sense, refers to any environmental variable necessary for the survival of the species, and does not exclusively refer to food and nutrients. Resources can thus include temperature, humidity, and refuges from predators or light for photosynthesis, mental and spiritual elements as well.

The same resource may be used in different ways by different organisms, thus leading to a new definition of "niche" in topological terms according to functional traits that become the niche axes. In such a metric of functional traits, the niche is delimited by the intersection of species environment with the functional circle of resources (von Uexkull 1982 (1940)). Resources can be intercepted at different times and at different scales. This concept emphasizes the dynamics of the resources. Resources are characterized by their temporal availability and their spatial arrangement: generally are not abundant and are heterogeneous in time and space.

In general, the habitat of a species is a physical space under environmental constraints, in which to find food, mating places, refuges, etc. (see Mitchell and Powell 2002 for a discussion and criticism on the habitat definition). There are species that have a broad foraging niche and contemporarily have habitat type restrictions. The classic "habitat" definition based on binary logic (habitat, nonhabitat) can be modified using fuzzy logic to range from a fully suitable to an adverse environment, moving across a broad spectrum of intermediate conditions characterized by different spatio-temporal patterns. These patterns must carry information that is perceived by functional trait sensors. The Umwelt (the "external world" following von Uexkull 1982 (1940)) becomes a subjective representation of the environment according to one organism's mind (Noth 1998). The different suitability of habitats recall the source-sink model (Pulliam 1988, 1996).

In a way similar to what happens in living organisms, which detect the energy of the physical world through sensory systems that transform sensation into perception via a cognitive process, we assume that functional trait sensors are characterized by specific cognitive properties beyond the "structural pairing" proposed by Maturana (1975). This framework allows us to complete the niche concept by assuming that organisms "perceive" their environment according to a species-specific scale that depends on the functional trait active at a specific time.

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