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Ecological Modelling
An ecosystem is defined as a relatively discrete unit within which
energy and nutrients are fixed and cir culate with only minor transfers
across the ecosystem boundaries. To begin modelling an ecosystem, our
main objective was to locate the important parameters and components
that define an ecosystem. Based on multiple references, the main
constituents of an ecosystem include the following: geography structure
and relief, climate, soils, hydrology, producers and consumers,
decomposition and soil processes, energy and nutrient cycling, and
interaction between terrestrial and aquatic communities (if relevant to
the area of study). By developing a descriptive and quantitative model
for each constituent we can compile the information for the structure
and function of the ANWR ecosystem.
**On using physiological ecology to predict
ecosystem response to environmental change:
- Ecosystem response to environmental change is often predicted
from simple physiological responses of organisms
(e.g., estimation of
plant production from temperature and light responses of photosynthesis). In the long term, however, feedbacks
among processes often govern performance under natural circumstances more
strongly than do short-term, kinetic responses of individual processes. For
Example, even though photosynthesis always responds to CO2 concentration in the
short term, compensatory changes in photosynthetic potential when plants are
grown under different CO2 concentrations may counteract these short-term
effects. Consequently, environmental
factors that exert strong short-term effects may6 not be influential over
longer time scales. To predict
ecosystem responses, we must study feedbacks as well as direct environmental effects
on plants.
Simulation modeling based on physiological studies can incorporate many of the feedbacks
that operate in natural ecosystems. Experience
suggests, however, that modeling predictions cannot be usefully extrapolated
beyond two levels of organization. For this reason, the types of controls studied at one level of organization may not be fully relevant at other levels. Most past ecophysiological work has
emphasized the direct effect of environment on physiology. Yet we need to know the nature, strength, and timing of the feedbacks and time lags that control resource supply and,
indirectly, the growth of organisms.
This will require an integrated, whole-plant approach to physiological
ecology. Ecosystem and community
ecology may provide the criteria for deciding which feedbacks are important at
these higher levels of organization.
Ecosystem response to environment has been predicted
from comparisons of current performance in two different environments
(e.g.,
latitudinal comparisons). A
comparison of two ecosystems under equilibrium condition says nothing about the
trajectory an ecosystem might follow in going from one equilibrium state to
another. Moreover, a new environment
will be occupied by different combinations of species than those co-occurring
at present. If the dynamics of the present
community are strongly influenced by specific competitive interactions, we may
have difficulty predicting how new combinations of species will interact. Forecasting such interactions is particularly
difficult because there are no present analogs of future climate, such
as increased atmospheric CO2.?Latitudinal
gradients in temperature, which might provide some insight into vegetation
response to a changing thermal regime, are complicated by differences in day length
and soils that will not be mimicked by climate change. Simulation modeling and whole-ecosystem
experiments may enable us to test novel combinations of factors.
Source: CHAPIN, F.S., JEFFERIES, R.L., REYNOLDS, J.F., SHAVER, G.R. Arctic Ecosystem in a Changing Climate: An Ecophysiological Perspective, 1991
>>>>>>>
Ecosystem and Change
- how change in ecological
complexity will affect ecosystem function
- relationship between
ecological complexity and ecosystem -- > needs to be investigated
- “Ecological complexity rather
than biodiversity because more than just the number of species
- => spatial patterns of
species and communities
- influence population
dynamics and landscape and regional scale processes
(less known about the relationship
and how affected by rapid environmental change
arctic terrestrial ecosystem
appear to be relatively stable over time and may have little resilience to
disturbance effects
one approach: reciprocal
experiment biological composition
(structure) and abiotic environment (factors
affecting physiological function) are separately altered
-
=> effects on each other
measured (details of experiment yet to be determined)
Source: OECHEL, W.C., CALLAGHAN, T., GILMANOV, T., HOLTEN, J.I., MAXWELL, B.,MOLAU, U., SVEINBJORNSSON, B., Global Change and Arctic Terrestrail Ecosystems
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