lecture 41 - ecosystems, biomes and diversity Flashcards
What are primary producers?
(photosynthetic and chemosynthetic organisms) take up
inorganic carbon, nitrogen, phosphorus and other compounds from the environment and convert them into proteins, nucleic acids, lipids and more
What are consumers?
(heterotrophic organisms) consume either primary producers directly or consumers of primary producers.
Describe ecosystem energy
• Energy does not cycle but must be continually harvested from the environment
to sustain the community.
• Photosynthesis is the key producer of energy.
• Energy stored in organic molecules is
available to consumers on the next trophic level.
What are trophic pyramids?
• Only about 10% of the energy and biomass available at each trophic level can be passed on to the next.
What is Liebig’s Law of the Minimum?
Primary production is limited by the nutrient that is least available relative to its use by primary producers.
Describe Species richness and stability
Charles Elton first suggested a link existed between species richness and stability. His main arguments were:
Elton, C.S. (1958) The ecology of invasions by animals and plants.
Islands are vulnerable to invasions.
Continent (Australia) are also vulnerable to invasion.
Cultivated land is susceptible to pest outbreaks.
Many monocultures (bracken) appear stable.
Rainforests do not show outbreaks.
Outbreaks do occur in rainforests.
Population cycles occur primarily in species poor areas (Arctic).
Describe laboratory tests
Two species of Paramecium predators with 1-3 bacterial
prey species
Lawler (1993): Paramecium feeding on bacteria
Microcosm experiments
Similar set-up, which was stable if there were only 2
trophic levels
but unstable when top predators were introduced.
Species identity was an important variable.
describe field tests
McNaughton's experiment I Gnu exclusion in the Serengeti: (McNaughton 1985) Gnus were allowed in some areas, excluded from others. Plant biomass was monitored. Biomass changed more in the species poor system when grazed by gnus. McNaughton's experiment II Yellowstone grasslands: (Frank & McNaughton 1991) Severe drought occurred in 1988. Vegetation abundance was monitored before and after the drought. The most diverse systems showed the least change (resistance)
Tilman’s long-term diversity
experiment in Minnesota
200 plots were seeded with up to 22 grassland species. Water, nutrient availability and carbon dioxide was controlled, different disturbance regimes followed, and primary production was measured annually for 23 years. A major drought perturbed the system in 1987-1988. Resistance to drought Species rich plots saw their biomass reduced less by drought than in species poor plots Resistance after drought After 4 years, species rich plots had returned closer to pre-drought biomass than species poor plants. Plots with more species had greater plant biomass. In the grassland experiment, species diversity promotes primary production.
What is the portfolio effect?
• By analogy to a portfolio of shares – a
portfolio tends to be less volatile than any
single share.
• Diversity increases variability at the species
level.
• Biological insurance: more opportunity for the
demise of one species to be compensated for
by another species in a diverse community.
Species richness & invasion success
Which is easier to invade – a low- or high-diversity community?
• Invaders must survive and grow on whatever levels of
resources are left unconsumed
• Levels of unconsumed resources decline as diversity increases
• Invader success declines with diversity
Naeem et al (2000)
– invader success decreased with increasing plant diversity
– High diversity plots had lower soil nitrate & light availability
Describe resistance to invasion
Sessile marine invertebrates
Invaders are less successful in species rich plots because space is more fully occupied.
Describe difference between species rich and species poor communities
• Species rich communities are more stable
than species poor communities (biological
insurance)
• They are also harder to invade (lower levels of
unused resources for invader to monopolize)
What are dynamic systems?
• Individuals are dynamic: they are born, move and
die.
• Populations are dynamic: increasing and decreasing
in response to local physical and biological
interactions of individuals.
• Communities and ecosystems may be dynamic, with
species arriving and departing as a result of invasion,
disturbance and succession.
• Biomes are stable: distinctive assemblages of species
found over broad regions of the Earth.
What are biomes?
Terrestrial biomes have characteristic vegetation reflecting evolutionary adaptations to climate.
Oceanic biomes are less well understood.
• The distribution of biomes reflects local
climate.
• Solar radiation, precipitation and wind vary
with latitude and altitude.
• Plants need to balance CO2 intake with water
loss by means of adaptations in shape and
physiology.
