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Biosphere

The term BIOSPHERE refers to the totality of life on earth and its interdependency on abiotic environmental factors. It encompasses the interactions between the atmosphere, hydrosphere, and lithosphere to support the entirety of earth's organism through climate (temperature and precipitation), soil formation, hydrology (surface water, ground water, and soil moisture storage), solar energy input (variation in intensity and daily and seasonal accumulation with latitude), and the cycling of energy and nutrients through food webs. The biosphere is the highest level of the ecological hierarchy.

The lowest level of the ecological hierarchy focuses on individual species, with a single individual of a species at the lowest level of classification, and moving upward to a population of that species (the total number of individuals of a species in a given area) and metapopulations (the total number of individuals of a species across the total number of disjunctly distributed populations). Above the species level of classification is the community, which is concerned with the number of species co-occurring in a given location. Emphasis is placed strictly upon the species that are present and the nature of their competitive or mutualistic interactions in creating stable or unstable species compositions.

Above the community level, the ecosystem level is concerned with both the specific community composition in addition to environmental factors of nutrient and energy input as well as the cycling of these nutrients through food webs. At this level, both biotic and abiotic factors are considered to be components. At broader spatial scales, the abiotic inputs are grouped according to climatic patterns and their support of terrestrial ecosystems whose vegetation have similar physiognomic structure, giving the biome level of classification. For example, the tropical rainforest biome is characterized by high biomass and broadleaf evergreen trees forming multiple canopy layers, although the actual species composition and nutrient cycling specifics (i.e., ecosystems) will differ between the tropics of the various continents. Above the biome level is the globally inclusive classification of the biosphere, in which the interconnectedness of global climatic systems forms a principal analytical focus.

Human–Biosphere Interaction

Environmental concerns at the biosphere level focus on human–environment interactions, especially as these interactions contribute to global climate change and mass extinction of species. Ecologists consider the contemporary period of history, especially after the mid-20th century, to be unique in the history of the planet, in that human activity is altering the environment on a global scale. Furthermore, environmental management efforts are being targeted at the biosphere level as well.

Current extinction rates of known species exceed the background extinction rate by 40 times, but could be as high as 400 times the background rate based on estimates of total species. For this reason, many biologists consider these extinctions to be the beginning of a major extinction event. Ecologists have identified habitat loss as being the primary cause of these extinctions, as extractive activities (forest clearing for timber and agriculture, urban sprawl), with the introduction of nonnative species (either by direct human introduction or accidentally through transportation networks), pollution, and direct exploitation of species contributing greatly to these extinction rates. Regions of the world with highly specialized species and endemics are particularly at risk of extinctions, and identified as “biodiversity hotspots.” Due to high rates of endemism, many islands environments and Mediterranean shrubland ecosystems have been identified as biodiversity hotspots.

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