Ecosystems, Sustainability, and Global Change

Definition: Coined by Sir Arthur Tansley in 1935, an ecosystem is the whole community of living organisms interacting with non-living environmental components such as air, water, and soil.
Core Connectivity: Biotic and abiotic components are linked through continuous nutrient cycles and energy flows.
Hierarchy of Scale: Scientific understanding generally decreases as the scale moves from cells and molecules up to organisms, populations, communities, ecosystems, and finally biomes.

Water Cycling: Involves the movement of water through the atmosphere, oceans, and land via precipitation, evapotranspiration, infiltration, and runoff.
Mineral Cycling: Explicitly demonstrated by the nitrogen cycle, which includes nitrogen-fixing bacteria in root nodules, ammonification ( $NH_4^+$ ), nitrification ( $NO_2^-$ and $NO_3^-$ ), and denitrification ( $N_2$ ).
Succession: The dynamic process of community change over time (e.g., moving from annual plants and grasses to shrubs, softwoods, and hardwood trees).
Energy Flow: The directional flow of energy from the sun to primary producers, consumers, and detritivores, often visualized as an energy pyramid.

Pollination: The transfer of pollen to female reproductive organs, classified by the transfer agent: * Anemophily: Wind. * Hydrophily: Water. * Entomophily: Insects. * Ornithophily: Birds. * Chiropterophily: Bats.
Pest Regulation: Control of pests through predators (e.g., Spined soldier bug), parasitoids (e.g., wasps), pathogens (e.g., fungi), and weed eaters (e.g., weevils).

Primary Productivity: The rate of new biomass production per unit of input.
Latitudinal Trends: Estimates of Gross Primary Productivity (GPP) show higher averages in tropical rainforests ( $3249\,g\,C\,m^{-2}\,year^{-1}$ ) compared to boreal coniferous forests ( $1019\,g\,C\,m^{-2}\,year^{-1}$ ).
Energy Sources: * Autochthonous: Organic matter produced within the ecosystem boundaries via photosynthesis. * Allochthonous: Organic matter imported from external sources.
Productivity to Biomass Ratio: Highly variable across systems, with aquatic systems showing a much higher ratio ( $17\,kg_{dry}\,kg_{standing}^{-1}$ ) than forest systems ( $0.042\,kg_{dry}\,kg_{standing}^{-1}$ ).

Environmental Constraints: Efficiency of solar energy interception, water and temperature (NPP increases with mean temperature and precipitation), soil texture/drainage, and growing season length.
Carbon Nutrient Balance Model (CNBM): Explains chemical plant defenses as a response to nutrient levels. Plants in nitrogen-poor soils implement carbon-based defenses, while higher nutrient levels shift resources toward growth instead of defense.

Decomposer System: Responsible for the majority of secondary production and respiratory heat loss in nearly every community.
Grazer System: Plays its greatest role in plankton communities where large proportions of NPP are consumed alive and assimilated efficiently; it is of low importance in terrestrial communities.
Aquatic System Trends: In stream communities, primary productivity often declines during summer due to canopy shading; energy is frequently derived from dead organic matter imported from terrestrial catchments.