Basic Information

I understand that the course of ESS can be divided into 3 parts: one directed to explain the nature of the environment; the second one in which we study the basic activity of humans in the environment; and the third one and most important for me: the way we are linked to the environment considering the correlations between humans and nature.

In order to go to the third part, we must remember some basic information that has to do with the nature of the environment:

• A system is a set of biotic and abiotic factors that are interrelated between them. It is important to emphasize that the system also includes the relations between all those factors. 
• Some examples of ecosystems are the tundra, taiga, rainforest, desert, estuary, etc. Here in our city we have a lot of ecosystems: 

Decidious forest in Chipinque

Aquatic ecosystem of Presa de la Boca

The steppe in the northern side of the city (García, N.L.) 

• Inside an ecosystems, the biotic factors (which involve all animals, plants, bacterias and microorganisms) can be arranged in trophic levels, which are the position that an organism (representing the entire population of that same organism) occupies inside a food chain. So for example, in the ecosystem of the steppe of García N.L. there are population of short bushes, roadrunners and coyotes. Since the coyotes eat roadrunners, and the roadrunners feed from the bushes, we can state that each population occupies a different trophic level: the bushes represent the first trophic level (producers); the roadrunners represent the second trophic level (herbivores) and the coyotes represent the third trophic level (carnivores).

• Another characteristic of an ecosystem, as it was stated previously, it includes the interrelation between the factors that form it. Two of the most important interrelations are the energy and mass flow: 

In the savanna, the trophic level from a population of sequoias represent the producers organisms because they through photosynthesis can assimilate the energy from the sun light and store it to be available to the next trophic level; the same happens with the mass, as well as the energy, it is transfer from the fist trophic levels to the last one. One interesting issue is that, as the second law of thermodynamics state, only the 10% of the energy from one trophic level will be used by the upper trophic level, and it is reflected in the mass of an organism of the upper trophic levels must eat in order to get all the energy it need: since there is less energy available, an upper trophic level eat more amount of mass. So in this specific ecosystem, the savanna, a large population of producers feed a medium population of giraffes, which are eaten by just a few lions, which, at the top of the food chain, store a large amount of mass, but a small amount of energy.