Resilience with Multiple Domains

The term 'resilience with multiple domains' takes into account more general dynamic behavior that allows for alternative stable states, that is, the system passing to more than one stability domain. Resilience is the marginal energy or disturbance size that can be absorbed by the system before it changes its stability domain. This is referred to as ecological resilience. Ecological resilience assumes multiple stable states and an overall tolerance of the system to disturbances that shift among different domains. The presence of multiple stable states is more meaningful in ecology than one global equilibrium, and is much more common in natural systems. Examples include many cases of successional dynamics, for example, the transition from grass to woody vegetation in semiarid rangelands, where the states are represented in a successional manner, and the main disturbance is grazing pressure. Also the shallow lake dynamic transition from clear water to turbid patterns, and the array of stable states in the community structure among primary producers is an appropriate example. Here, the sources of disturbance are varying physical conditions (such as light intensity, nutrient concentrations, and temperature) that affect the system.

A heuristic of a ball in a cup is presented in order to help clarify the differences between the different types of resilience (Figure 1). The ball represents the dynamical system and the cup represents the domain of stability. The arrows represent perturbations from the equilibrium.

Figure 1 Ball and cup heuristic of system stability. Valleys represent stability domains, balls represent the system, and arrows represent disturbances. Engineering resilience is determined by the slopes in the stability landscapes, whereas ecological resilience is described as the width. Adaptive capacity refers to the ability of the system to remain in a stability domain, as the shape of the domain changes (as shown by the three slices or landscapes).

Figure 1 Ball and cup heuristic of system stability. Valleys represent stability domains, balls represent the system, and arrows represent disturbances. Engineering resilience is determined by the slopes in the stability landscapes, whereas ecological resilience is described as the width. Adaptive capacity refers to the ability of the system to remain in a stability domain, as the shape of the domain changes (as shown by the three slices or landscapes).

Gravity pulls the ball downward, and therefore pits in the surface of the landscape are assumed to be stable states. The deeper a pit, the more stable it is, because it takes strong disturbances in order to move an ecological state away from the bottom of the pit. The steepness of the sides of a stability pit corresponds to the strength of the negative feedback processes maintaining an ecosystem near its stable state, and consequently engineering resilience increases with the slope of the sides of a pit. The marble is perturbed from the bottom of the cup and depending on the shape of the valley it either returns to the previous equilibrium position (engineering definition) or it visits a different valley with an array of different scenarios for stability (ecological definition). The latter has to do a lot more with the characteristics ofthe shape of the region. A third and even more important view of resilience has to do with the possibility of the nonstatic terrain ofthe stability domain. This means that the system may gradually change its characteristics, and thus the domain of its shape as a result of changing environmental conditions (global change) or anthropogenic impacts to the stability landscape. The same can happen if, for example, a population stays longer in the valleys of stability but makes resource conditions worse by prolonged exploitation, thus raising the bottom of the cup to cause dynamics more complicated, as, for example, in ecological succession. Examples of gradual change in systems include nutrients in lakes and wetlands, and community changes in rangelands.

Project Earth Conservation

Project Earth Conservation

Get All The Support And Guidance You Need To Be A Success At Helping Save The Earth. This Book Is One Of The Most Valuable Resources In The World When It Comes To How To Recycle to Create a Better Future for Our Children.

Get My Free Ebook


Post a comment