C – Ecology and Conservation
C.2 Communities and ecosystems
Understandings:
 Trophic Levels – Most species occupy different levels in multiple food chains.
 Trophic level = feeding position in a food chain, because feeding relationships
are web-like, an organism can occupy more than 1
 Through pellet examination trophic levels of different species can be
identified
 When stating an organisms trophic level, reference must be made to a
specific food chain
 Food Webs – A food web shows all the possible food chains in a community.
 Trophic relationships = web-like b.c many consumers feed on more than 1
species and are fed on by more than one – food webs model this
 Organisms @ the same trophic level are drawn @ the same level in the web
when possible
 The Impact of Climate on Ecosystem Type – The type of stable ecosystem that will
emerge in an area is predictable based on climate.
 Climate depends on temperature and precipitation
 Temperature influences pop. distribution, rates of cell respiration,
photosynthesis, decomposition and transpiration, and productivity
 Precipitation impacts productivity by influencing rates of photosynthesis and
decomposition
 Info about combos of these 2 factors allows for predictions about what type
of stable ecosystem will exist in that area. (Ex. High rainfall = forest/
moderate or seasonal rains = grasslands/ little to no rain = a desert)
 Respiration Rates and Biomass Accumulation – The % of ingested energy
converted to biomass is dependent on the respiration rate.
 Production in plants happens when organic matter is synthesized by
photosynthesis/ in animals it occurs when food is absorbed after digestion
 Gross and net values can be calculated  net production = gross production
– respiration (gross = total produced/ net = total – amount used for
respiration)
 In early primary production there is lots of sunlight= high gross production
and little biomass, the total amount of respiration to support the small
biomass is low
 As succession proceed, biomass increases and respiration increases,
therefore gross production declines
 Once equilibrium is reached, total community production: community
respiration ratio = 1 @ this pt. the ecosystem is stable
 Secondary Succession – Disturbance influences the structure and rate of change
within ecosystems.
 Secondary succession occurs in areas with an ecosystem or that recently had
one. It is initiated by a change in conditions
 Close to disturbance, rates of respiration & productivity increase rapidly and
there is an accumulation of biomass, species diversity also increases
 @ the climax stages are slowing & the ecosystem is stable & resistant to
change
 Closed Ecosystems – In closed ecosystems energy but not matter is exchanged
with the surroundings.
 3 categories of systems that can be modeled  open systems: exchange
energy & matter/closed systems: exchange energy but not matter/ isolated
systems: exchange neither
 Ecological systems = a continuum, natural systems = open systems/
undisturbed systems the rate of exchange is due to the water cycle, human
interference increases the exchange of matter (harvesting of crops/addition
or depletion of nutrients
Applications:
 Food Conversion Ratio – Conversion ratio in sustainable food production
practices.
 Meat production requires animals to feed. / Feed conversion ratios =
quantity of dietary input (g) required to produce a certain amount of body
mass (ex. Ratio of 1.2 means it takes 120 g of food to get 100g of meat
 These ratios identify more sustainable dietary choices/ lower feed inputs
mean lower energy inputs for food production
 Avoiding meat consumption = lower energy losses due to feed conversion
Disruptions to Nutrient Cycling – Consideration of one example of how humans
interfere with nutrient cycling.
 Human activity can accelerate nutrient flows into and out of ecosystems
 Ex. Agriculture – the harvesting of crops & transport deplete nutrients in the
biomass of the crop, as a result fertilizer must be added
 Phosphate and nitrogen are both used in fertilizer – phosphate is mined,
converted to fertilizer and shipped/ nitrogen is produced from gaseous N
which increases input into the nitrogen cycle that wouldn’t naturally occur
 Runoff from fields results in build-up in waterways & = eutrophication
Skills:
 Interpreting a Whittaker Climograph – Analysis of a climograph showing the
relationship between temp., rainfall and ecosystem type.
 A climograph = a diagram showing relative combo. of temp. and precipitation
 Shows most likely stable ecosystem that will emerge under a certain climate

Dashed line reps. regions where the biome type is influenced by other factors
(fire, soil type)
 Comparison of Pyramids of Energy from Different Ecosystems
 Length of food chains is determined by the level of net primary productivity
 Higher productivity = longer food chain and broader trophic level
 Energy conversion efficiencies are affected by the organisms involved 
therefore pyramids of energy differ between ecosystems
 Gersmehl Nutrient Cycle Diagrams
 Modal of nutrient storage and flow for terrestrial ecosystems
 Has 3 storage compartments: biomass, litter, and soil (rep. by circles/ovals)
 Arrows rep. nutrient flows/fluxes & thickness rep. rates of nutrient flow (one
arrow can rep. more than one process)
 Primary Succession – Analysis of data showing primary succession.
 Ecological successions = changes that transform ecosystems over time, they
involve species & abiotic environments
 Abiotic factors set limits on organism distribution & organisms have an
affect on the abiotic factors
 Organisms can change abiotic factors such that the environment becomes
limiting to species & other better adapted species join the community
 2 Categories of succession: primary & secondary
 Primary: begins with an environment where living organisms haven’t
previously existed (@ the start only bacteria, lichens live)  then soil forms
& small herbs colonize, deeper soil develops & larger plants colonize (tall
herbs, shrubs, trees)  consumer pops. Will change with plant pops. , so will
decomposers and detritivores
 Secondary succession – Investigation into the effect of an environmental b
disturbance on an ecosystem.
 Can be studied in local areas (wooded areas/disused roads) by looking @ :
species diversity/ stem density/ above ground biomass/ leaf area index/ leaf
litter/ water cycle variables/ soil variables/ light levels/ soil density
Nature of Science:
 Pyramids of Energy as Models – Models are representations of the real world:
pyramids of energy model the flow of energy through ecosystems.
 Pyramid of energy = a bar chart used to show the relative amounts of energy
in each trophic level, bars = horizontal & symmetrically arranged. The lowest
pt. = production of producers (gross/net) each labeled & units indicated
KJm per year

Limitation: energy transfer rates can vary each season. Diet analysis is
necessary for organisms occupying diff. trophic levels in diff. food chains. %
Competition of their diets may vary according to season or opportuity
Abbreviations: B.c = because
Rep. = represent(ed)(s)
@ = At
= Means equals
Pops. = Population(s)
Pt. = point