44-1 copyright 2010 mcgraw-hill australia pty ltd powerpoint slides to accompany biology: an...
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44-1Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Chapter 44: Ecosystems
44-2Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Feeding relationships shape ecosystems
• Ecosystems are dynamic systems consisting of interacting biotic and abiotic components
• The boundaries are seldom fixed or precise• Ecosystems are structured by trophic relationships
– autotrophs synthesise complex molecules using sunlight (photosynthesis) or chemical energy (chemosynthesis)
– heterotrophs cannot synthesise organic matter, just reorganise it
these include herbivores, carnivores, parasites, scavengers, detritivores and decomposers
44-3Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Fig. 44.2: Flow of energy and materials through an ecosystem: although energy flows through the system, materials are recycled
44-4Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Food chains and food webs• Grazer chains occur when consumers depend on
living plants for food– rocky shores, grasslands
• Detritus chains are those where consumers eat decaying matter (detritus) and debris– mangroves, forests
• The distinction of the two types may not be clear– termites consume both living and detrital plant matter
• Chains are over-simplified: webs more realistic
44-5Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Fig. 44.4: Simplified food web
44-6Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Basic patterns of food webs• Usually only 3 to 4 trophic levels• Omnivores (i.e. organisms that feed on >1 trophic
level) are scarce• Insect- and detritus-based webs are often
exceptions to the above patterns• Trophic interactions may be compartmentalised• The number of trophic levels limits web complexity
44-7Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Ecological pyramids
‘Why are big, fierce animals rare?’ (Colinvaux, 1993)
• Pyramids of numbers do not work (e.g. termites and cattle both eat grass)
• Pyramids of biomass do not take into account the rate of biomass production (e.g. phytoplankton)
• Pyramids of energy flowing between trophic levels conform best to Elton’s classic ascending pyramid
Fig. 44.6: Ecological pyramids
44-8Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
44-9Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Why food chains are shortIs it because of reduction of energy up the trophicscale?• Usually only 10–20 per cent of energy is
transferred to next level above• Energy base of different ecosystems ranges widely
so expect wide variation in length of food chains
BUT the observed number of levels is uniformly small
length cannot be controlled just by energy input
44-10Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Other models to explain food chain length
• Ecosystem stability models– persistent ecosystems are those able to recover stability
after disturbance, so simpler ones best
• Cascading hierarchy in feeding links– a species can only feed on those below it, and be fed on
by those above it in the hierarchy
• Manipulative ecological experiments are needed to test these hypotheses
44-11Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Potted food webs• Experiments were performed in rainforests to test
the hypothesis that the amount of energy at bottom of chain limits the chain length
• Artificial ‘tree holes’ were supplied with three different amounts of detritus, as food
• Food supply was shown to be a minor factor compared with the length of time the pots were left
• Only unnaturally small food supplies had a significant and limiting effect on food web structure
44-12Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Biomass, energy and productivity
• Biomass is expressed as energy equivalents, e.g. kJ per kg
• Net primary productivity of an ecosystem is rate of change of biomass per unit area, e.g. gm-2yr-1, after respiratory losses of plants are accounted for
• Some primary production may– be ‘lost’
as shed structures, e.g. leaves, branches; carapace, cuticle
– be eaten e.g. fruit, flowers
– die during senescence
44-13Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Productivity of different ecosystems
• Production of plant communities varies with rainfall, temperature, nutrients
• Marine communities are usually nutrient-limited except in areas of upwelling and in coastal areas
• Biomass can be misleading as an indicator of productivity: it is the rate of change of biomass that matters
44-14Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Fig. 44.10: World ecosystems
44-15Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Fig. 44.11: Upwelling
44-16Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Productivity in ecosystems may change through time• Young ecosystems have more actively growing
tissue, but older systems have more biomass• If resources are limited, regeneration of the original
ecosystem may be impossible—cleared rainforest may revert to open grassland (see Fig. 44.13)
44-17Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Fig. 44.13: Grasslands
Question 1:
Biological communities change because:
a) Each stage modifies the environment and adapts for a later stage.
b) The soil is depleted and food gives out.
c) Old species move out and new species move in.
d) Old species evolve into new species.
e) New species move in, displacing old species.
44-18Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
44-19Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Biogeochemical cycles• Whereas energy flows through the biosphere,
materials are recycled• Ecosystem productivity is controlled by efficiency
of recycling as well as by energy available• Materials transported in the atmosphere (water,
carbon, nitrogen and sulphur) global cycles• Phosphorus, potassium, calcium and magnesium
move through soil local ecosystem cycles
44-20Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
The water cycle• 97% of water on earth is in the oceans• Processes of convection, precipitation,
transpiration and respiration move water around the cycle
• Approx. 3% of total water is relatively inaccessible, in icecaps, glaciers and as deep groundwater
• Within the scale of local ecosystems, water behaves more like energy because it effectively flows through and is not recycled
44-21Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Fig. 44.15: Global water cycle
44-22Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Australian conditions• Two-thirds of mainland Australia is desert• Rainfall has high variability• Desert ecosystems are productive in pulses when
rain falls, or from utilisation of reserves (seeds, lignotubers) at other times
• Consumers must – adopt a pulse and reserve pattern, e.g. grasshoppers– eat reserves of other organisms, e.g. seed or wood-
eaters; or – adopt opportunistic feeding habits
44-23Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Fig. 44.16: Desert areas of the world
44-24Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Fig. 44.17: Water flows through a desert ecosystem
44-25Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Effects of clearing trees• Rainfall is no longer taken up by deep tree roots
Groundwater is recharged, water table rises (e.g. Lemon catchment in WA—water table rose 20 m after clearing)
• Salt from subsoil rises in groundwater and discharges at surface
Degrades land because vegetation cannot grow in salty conditions
44-26Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
The carbon cycle• Most carbon is locked up in earth’s rocks as
carbonate (and also fossil fuels)• The most active pool is carbon dioxide, 0.03 per
cent of the atmosphere
• CO2 is withdrawn by photosynthesis and replaced during respiration
• Large amounts of CO2 are dissolved in the ocean
• Burning of fossil fuels returns CO2 to the atmosphere faster than it can be cycled
This contributes to global warming
44-27Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Fig. 44.19: Global carbon cycle
Question 2:Which of the following is not a major positive feedback mechanism in which the activity of humans to increase global climate temperatures leads to an even further increase?
a) Tropical deforestation causes warming and drying so that remaining forests begin to decline
b) Global warming causes snow to melt in polar regions and therefore increases global albedo
c) Global warming causes increased CO2 release from biomass decomposition
d) Global warming causes increased rainfall, plant growth and photosynthesis
44-28Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
44-29Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Nitrogen cycle• Abundant in atmosphere, 78%• Plants cannot absorb atmospheric nitrogen• Absorbed as ammonium or nitrate after fixation of
nitrogen by symbiotic bacteria, or in soil solution• Denitrifying bacteria convert nitrate back to
gaseous nitrogen• Electrical storms also fix nitrogen• Nitrogen becomes limiting if microbial activity is
inhibited
44-30Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Fig. 44.20: Cycle of nitrogen
44-31Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Nitrogen and tree dieback• Tree dieback results from long or repeated periods
of sublethal stress• Effects of increased stocking rates, growing exotic
pasture species, adding fertilisers and land-clearing combine to cause rural dieback
• Insect damage to leaves is worse where soil fertility is high
• Stock congregate under few remaining shade trees, both damaging saplings and enriching the soil
44-32Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Fig. B44.4b: Rural dieback
44-33Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Phosphorus cycle• Essential to all life, in ATP• Not common in earth’s crust or in atmosphere• Taken up by plants as phosphate from sparingly
soluble soil storage pool• Australian flora are well adapted to low P, and
efficient at recycling phosphorus• Symbiosis between plant roots and mycorrhizal
fungi enhances the phosphorus supply
44-34Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Fig. 44.22a: Local cycle of phosphorous
Summary• Organisms can be considered as either autotrophs
or heterotrophs• Feeding interactions are important relationships in
determining ecosystem structure and function• Both biotic and abiotic factors play a role in cycling
nutrients and water through ecosystems and the biosphere
• Biogeochemical cycles can operate at the global and local scales
44-35Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University