Ecological threshold is the point at which a relatively small change or
disturbance in external conditions causes a rapid change in an
ecosystem
An ecosystem (or ecological system) is a system formed by Organism, organisms in interaction with their Biophysical environment, environment. The Biotic material, biotic and abiotic components are linked together through nutrient cycles and en ...
. When an ecological threshold has been passed, the ecosystem may no longer be able to return to its state by means of its inherent
resilience. Crossing an ecological threshold often leads to rapid change of
ecosystem health
Ecosystem health is a metaphor used to describe the condition of an ecosystem.Rapport, David (1998). "Defining ecosystem health." Pages 18-33 in Rapport, D.J. (ed.) (1998). ''Ecosystem Health.'' Blackwell Scientific. Ecosystem condition can vary a ...
. Ecological threshold represent a
non-linearity
In mathematics and science, a nonlinear system (or a non-linear system) is a system in which the change of the output is not proportional to the change of the input. Nonlinear problems are of interest to engineers, biologists, physicists, mathe ...
of the responses in ecological or biological systems to
pressures
Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and ev ...
caused by human activities or natural processes.
Critical load,
regime shift,
critical transition
Critical transitions are abrupt shifts in the state of ecosystems, the climate, financial and economic systems or other complex system, complex dynamical systems that may occur when changing conditions pass a critical or bifurcation theory, bifurca ...
and
tipping point are examples of other closely related terms.
Characteristics
Thresholds can be characterized as points or as zones. Zone-type thresholds imply a gradual shift or transition from one state to another rather than an abrupt change at a specific point. Ecological thresholds have caught attention because many cases of catastrophic worsening of conditions have proved to be difficult or nearly impossible to remedy (also known as points of no return).
Ecological extinction is an example of a definitive point of no return.
Ecological thresholds are often characterized by
hysteresis
Hysteresis is the dependence of the state of a system on its history. For example, a magnet may have more than one possible magnetic moment in a given magnetic field, depending on how the field changed in the past. Plots of a single component of ...
, which means the dependence of the state of a system on the history of its state. Even when the change is not irreversible, the return path from altered to original state can be drastically different from the development leading to the altered state.
Another related concept is
panarchy. Panarchy views coupled human-natural systems as a cross-scale set of adaptive cycles that reflect the dynamic nature of human and natural structures across time and space. Sudden shifts in ecosystem state can induce changes in human understanding of the way the systems need to be managed. These changes, in turn, may alter the institutions that carry out that management and as a result, some new changes occur in ecosystems.
Detection
There are many different types of thresholds and detecting the occurrence of a threshold is not always straightforward. One approach is to process
time series
In mathematics, a time series is a series of data points indexed (or listed or graphed) in time order. Most commonly, a time series is a sequence taken at successive equally spaced points in time. Thus it is a sequence of discrete-time data. ...
which are thought to display a shift in order to identify a possible jump. Methods have been developed to enhance and localize the jumps.
Examples
Some examples of ecological thresholds, such as clear lakes turning into turbid ones, are well documented but many more probably exist. The thresholds database
by
Resilience Alliance and
Santa Fe Institute
The Santa Fe Institute (SFI) is an independent, nonprofit theoretical research institute located in Santa Fe, New Mexico, United States and dedicated to the multidisciplinary study of the fundamental principles of complex adaptive systems, inc ...
includes over one hundred examples.
See also
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Carrying capacity
The carrying capacity of an ecosystem is the maximum population size of a biological species that can be sustained by that specific environment, given the food, habitat, water, and other resources available. The carrying capacity is defined as the ...
*
Catastrophe theory
In mathematics, catastrophe theory is a branch of bifurcation theory in the study of dynamical systems; it is also a particular special case of more general singularity theory in geometry.
Bifurcation theory studies and classifies phenomena chara ...
*
Dual-phase evolution suggests a mechanism underlying ecological thresholds and zones.
*
Inflection point
In differential calculus and differential geometry, an inflection point, point of inflection, flex, or inflection (rarely inflexion) is a point on a smooth plane curve at which the curvature changes sign. In particular, in the case of the graph ...
*
Tipping point (climatology)
In climate science, a tipping point is a critical threshold that, when crossed, leads to large, accelerating and often irreversible changes in the climate system. If tipping points are crossed, they are likely to have severe impacts on human ...
*
Gaia hypothesis
The Gaia hypothesis (), also known as the Gaia theory, Gaia paradigm, or the Gaia principle, proposes that living organisms interact with their Inorganic compound, inorganic surroundings on Earth to form a Synergy, synergistic and Homeostasis, s ...
References
External links
Resilience AllianceA multidisciplinary research group that explores the dynamics of complex adaptive systems
Thresholds of environmental sustainabilityA research project focusing on ecological thresholds
{{DEFAULTSORT:Ecological Threshold
Ecological economics
Ecology terminology