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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.
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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).