A niche is a term describing the functional position of a species in its ecosystem. In nature there are predators and preys, generalist and specialist species, key species and so on. An invasive species is an exotic species that adversely affect the habitats they invade economically, environmentally or/and ecologically. Here you can find a good example in São Miguel Island (the Açores, Portugal).
On the other hand, on both sides of the commercial streets of most occidental cities, there are plenty of different niches. There is a niche filled by big book stores like Borders (US), Waterstones (UK) or La Casa del Libro (Spain). But it is possible as well observe McDonalds, IKEA or Zara everywhere. Because of Globalization, these sort of stores and restaurants are invading our urban ecosystems.
Three decades of research have established the field of complexity theories of cities (CTC) as a dominant approach to cities with urban simulation models (USM) as its major methodological tool. Now that the field has come of age, it is time to stop for a moment, look back at what has been achieved, with appreciation, but also with sober criticism and then look forward at potentials that have yet to be realized.
Cities are population aggregates that do not produce for themselves the means of subsistence. From their origins, the existence of cities is based on a technical, social and spatial division of production and involves exchanges of various kinds between those who produce subsistence and those who produce manufactured goods, symbolic goods, power and protection. Urbanization dynamics is linked to the potential interaction offered by cities, its urbanity, ie the power that produces the grouping of large number of people in the same place.
Les nouveaux principes de l'urbanisme. La fin des villes n'est pas à l'ordre du jour
James Lovelock and Andrew Watson published a short paper in 1983 to ilustrate a simple example of how the Gaia hypothesis works. This was based in a world with the following characteristics:
The model simulates a planet that is orbiting a sun whose radiant energy is slowly increasing (just like the Sun and the Earth). The planet’s soil is 5º C.
The world is seeded with two types of daisies: black and white. The black ones have an albedo of 0.25 (absorb light) and the white ones, on the other hand, 0.75 (reflect light).
Both flowers can live in a range of temperature (between 5º and 40º C), and their optimal point is 20º C.
According to these rules and variables, we run the model. The next figures simulate the partial coverage of daisies. Conversly, the result of the simulation is showed in the following graphic. In the model, the black and white daisies are represented as black and white features respectively, and the bare ground is red colored.
At the begining of the simulation, the sun's rays are weak and Daisyworld is too cold to support any life.
As the radiant energy of the sun increases, germination of black daisies becomes possible. The black variety is the first in making his apareance because they absorb light, as a result they are warm enough to survive. Eventually, they can spread over most part of the surface of the hypothetical planet. This provokes an increase of the global temperature and allows white daisies to show up.
Both communities can survive together in a dynamic equilibrium for a long time. In this phase, it is possible to achieve certain control of the levels of temperature: black daisies can increase them because they abosrb light and white ones can decrease them because they reflect light.
As the energy of the sun increases, white daisies become to be more adapted than black daisies in this new situation. White daisies can mantain a suitable temperature thanks to their key property: reflecting sun rays. The surface of the world becomes whiter day by day.
In the end, only white daisies can survive for a while in this hell. The sun's rays have grown so powerful that soon even the white daisies can no longer survive.
Daisyworld is a model very simple, but it is enough to show that our planet, the Earth, is in the middle of this simulation. We (human beings) must be there. Lovelock points out that life sustains life. But if something may go wrong, the new environmental conditions that the Earth system creates because of its own regulation, can be extremely damaging (but not for life).
As hard as they try humankind can not eliminate life. On the other hand, it can be very easy to kill themselves.
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