ABSTRACT
Like all animals, we Homo sapiens evolved within a web of relationships among species, some of which constitute our food, others are our predators, others recycle our wastes, others provide us with shelter or with resources, and still others compete with us for those same resources or services. Such communities of species (also called biotic communities), together with their abiotic environment, make up ecosystems of all sizes throughout the Earth’s biosphere. An ecosystem is a dynamic complex of plant, animal, and microorganism communities and their non-living environment interacting as a functional system (Alcamo et al. 2003 ). All ecosystems share several characteristics: they contain living and non-living elements; they show a measurable degree of diversity (species, genes, epigenetics); they have a degree of resilience (defi ned as the system’s ability to maintain relationships between system elements in the presence of disturbances.); a net fl ow of energy follows a one-way path from outside to inside to heat; they have a carrying capacity for particular kinds and numbers of organisms; they exist in a state of non-equilibrium (i.e., they change over time); changes are irreversible (i.e., ecosystems do not return to a previous state, but develop to a new form) (Bosselmann 2010 ; Molles and Cahill 2008 ).
