Ecological stability
[3] Stable ecological systems abound in nature, and the scientific literature has documented them to a great extent.
[4] Nevertheless, it is important to mention that not every community or ecosystem in nature is stable (for example, wolves and moose on Isle Royale).
Also, noise plays an important role on biological systems and, in some scenarios, it can fully determine their temporal dynamics.
With the advancement of theoretical ecology in the 1970s, the usage of the term has expanded to a wide variety of scenarios.
[3] In 1997, Grimm and Wissel made an inventory of 167 definitions used in the literature and found 70 different stability concepts.
[5] One of the strategies that these two authors proposed to clarify the subject is to replace ecological stability with more specific terms, such as constancy, resilience and persistence.
In order to fully describe and put meaning to a specific kind of stability, it must be looked at more carefully.
[6] Following this strategy, an ecosystem which oscillates cyclically around a fixed point, such as the one delineated by the predator-prey equations, would be described as persistent and resilient, but not as constant.
Some authors, however, see good reason for the abundance of definitions, because they reflect the extensive variety of real and mathematical systems.
[8] To analyze the stability of large ecosystems, May drew on ideas from statistical mechanics, including Eugene Wigner's work successfully predicting the properties of Uranium by assuming that its Hamiltonian could be approximated as a random matrix, leading to properties that were independent of the system's exact interactions.
It implies that dynamical stability is limited by diversity, and the strictness of this tradeoff is related to the magnitude of fluctuations in interactions.
Although the characteristics of any ecological system are susceptible to changes, during a defined period of time, some remain constant, oscillate, reach a fixed point or present other type of behavior that can be described as stable.
In the sense of perturbation amplitude, local stability indicates that a system is stable over small short-lived disturbances, while global stability indicates a system highly resistant to change in species composition and/or food web dynamics.
[14] Observational studies of ecosystems use constancy to describe living systems that can remain unchanged.
A perturbation is any externally imposed change in conditions, usually happening in a short time period.
Resistance is a measure of how little the variable of interest changes in response to external pressures.
Pielou remarked at the outset of her overview, "It obviously takes considerable time for mature vegetation to become established on newly exposed ice scoured rocks or glacial till...it also takes considerable time for whole ecosystems to change, with their numerous interdependent plant species, the habitats these create, and the animals that live in the habitats.
"[15]Resilience is the tendency of a system to retain its functional and organizational structure and the ability to recover after a perturbation or disturbance.
Ecology borrows the idea of neighborhood stability and a domain of attraction from dynamical system theory.
[18][19] Focusing on the biotic components of an ecosystem, a population, or a community possesses numerical stability if the number of individuals is constant or resilient.
The effect of diversity on stability in food-web models can be either positive or negative, depending on the trophic coherence of the network.
[24] At the level of landscapes, environmental heterogeneity across locations has been shown to increase the stability of ecosystem functions.
[25] A stability diversity tradeoff has also been recently observed in microbial communities from human and sponge host environments.
[26] In the context of large and heterogeneous ecological networks, stability can be modeled using dynamic Jacobian ensembles.
[27] These show that scale and heterogeneity can stabilize specific states of the system in the face of environmental perturbations.
Ecology as a science was developed further during the late 19th and the early 20th century, and increasing attention was directed toward the connection between diversity and stability.
[28] Frederic Clements and Henry Gleason contributed knowledge of community structure; among other things, these two scientists introduced the opposing ideas that a community can either reach a stable climax or that it is largely coincidental and variable.
Robert MacArthur proposed a mathematical description of stability in the number of individuals in a food web in 1955.
[29] After much progress made with experimental studies in the 60's, Robert May advanced the field of theoretical ecology and refuted the idea that diversity begets stability.
[8] Many definitions of ecological stability have emerged in the last decades while the concept continues to gain attention.
