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DisturbanceInitiatesSecondarySuccession Secondary Succession: Regeneration of climax community following disturbance (e.g., forest fire, clear-cut). FacilitationandInhibition Early successional colonists can facilitate OR inhibit growth and establishment of later successional species. Early successional species have no effect on later colonists, succession depends on dispersal capabilities and abiotic factors. KeystoneSpecies Keystone species have a much greater effect on community structure than their abundance (biomass) would suggest. Example: Pisaster (starfish) in the rocky intertidal Paine’sExperiment Removed Pisaster from one area: 8 Invertebrate Species Left adjacent area alone (control) 15 Invertebrate Species Starfish (predator) increased invertebrate diversity? DIRECT INDIRECT effects arise as a result of the interaction only between two species The effect on one species on a second species is routed through a third species. often a physical interaction, e.g., consumption can occur only in multi-species assemblages SpeciesInteractions Indirect Effect The effect on one species on a second species is routed through a third species. _ _ + Sea Otter State Urchin Barren State Estes et al. 1998 1) Energy Sources: Energy in ecosystems originates with primary production by autotrophs. 2) Energy Flow: Food webs and pyramids describe energy flow. 3) Global patterns in productivity indicate abiotic constraints. 4) Net primary productivity is also constrained by biotic factors: top-down versus bottom-up control. The most basic requirement for all organisms. Organisms obtain energy from sunlight, from inorganic chemical compounds, or through the consumption of organic compounds. All of these sources of energy are resources. 6CO2 + 6H2O + energy -> C6H12O6 + O2 C6H12O6 + 6O2 -> 6CO2 + 6H2O + energy Autotrophs are organisms that assimilate energy from sunlight (photosynthesis) or from inorganic compounds (chemosynthesis). The energy is converted into chemical energy stored in the carbon–carbon bonds of organic molecules. Autotrophs do not CREATE energy, they TRANSFORM it. Energy in ecosystems originates with primary production by autotrophs. Primary production by autotrophs Photosynthesis (most) Chemosynthesis (a little) Currency = Carbon NPP = GPP – R (net primary production) = (gross primary production) – (respiration) Net Primary Production is the total chemical potential energy input into the ecosystem (growth, consumption, storage of carbon) Temperate Forest: Hubbard Brook Experimental Forest (NH) Secondary production is generated through the consumption of organic matter by heterotrophs. Net Secondary Production ingestion – respiration – egestion Net Secondary Production << NPP Mostly detritivores (bacteria, fungi) Heterotrophs obtain their energy by consuming energy-rich organic compounds from other organisms. This energy ultimately originated with organic compounds synthesized by autotrophs. Charles Elton (1927) invented the food web concept. Carnivores2 Detritivores Carnivores1 Herbivores Detritus Plants Sunlight Hypothesis: more productivity à more trophic levels (Bottom-Up Control) But, why does biomass decrease at higher levels? (E Trophic LevelN+1) / (E Trophic LevelN) = ~10% Terrestrial NPP is highest in the wet/warm tropics due to climate. Marine NPP is highest along the coasts due to nutrient inputs from the coasts and from upwelling ocean currents. Net primary productivity is constrained by both abiotic and biotic factors. Nutrients: Nutrient availability can affect local productivity in terrestrial, freshwater, and marine ecosystems: N, P, K, Ca, Fe, Mg… Species Composition: Species vary in their capacity to respond to abiotic conditions and resources (e.g., fertilizer).