Ecosystem Dynamics

Ecosystem Dynamics

Ecosystem dynamics is the study of how ecosystems change over time. Ecosystems are dynamic in nature, subject to regular micro and macro disturbances, both internal and external. Ecosystem dynamics identifies positive and negative feedback loops as the basic mechanism through which biological creatures and whole ecosystems regulate themselves and change over time. The processes through which organisms regulate themselves and their environment in order to maintain a stable state is recognized as one of the defining characteristics of life. It is understood today that all organisms survive by transforming energy and by regulating their internal environment in order to maintain a stable condition conducive to that functionality and this regulation process is central to the dynamics of the organism or ecosystem as it goes through both stable linear and rapid nonlinear processes of change.

Linear & Nonlinear

Within any system, we can identify two qualitatively different types of development, linear and nonlinear. Linear processes of development are bound within some set of parameters that enable the system to function and develop in a semi-stable pattern. Linear processes of development are driven by negative feedback loops, where two things balance each other out, where for every source of energy or resource within the system there is a sink, for every anabolic process there is a catabolic process within that overall system. These negative feedback loops form closed cycles, giving us an oscillatory pattern of development. Nonlinear processes of development, in contrast, are driven by positive feedback where two variables change in the same direction; more begets more. These positive feedback loops drive the system in one direction over time. As positive feedback loops have a compounding effect upon themselves the net result is often a radical process of exponential growth or decay, that can drive the system outside of its normal operating parameters.

Homeostasis

All living organisms, whether unicellular or multicellular or even whole ecosystems, exhibit homeostasis. To maintain dynamic equilibrium and effectively carry out certain functions, a system must detect and respond to perturbations. After the detection of a perturbation, a biological system normally responds through negative feedback. This means stabilizing conditions by either reducing or increasing the activity of an organ or system. Examples of homeostasis within the human body include the regulation of temperature, the balance between acidity and alkalinity, or release of glucagon when sugar levels are too low. On the micro-level of a single organism, this process is often done through a centralized regulatory system, such as the hypothalamus in the human body.

Homeostasis requires a sensor to detect changes in the condition to be regulated, an effector mechanism that can vary that condition, and a negative feedback connection between the two. Although macro-level systems like ecosystems typically do not have centralized control systems, they do have distributed mechanisms for regulatory. Ecosystems also manage to keep their physical conditions within some set of limits. For example, biotic and abiotic processes regulate the quantity of water in the soil. Plants function best when there is neither too much nor too little water. Too much water can push out air needed by microorganisms and plant roots; too little water restricts plant growth. If there is too much water in the soil after heavy rain, plants consume large quantities, and excess water percolates downward through the soil. If there is too little water during periods of lesser rainfall, plants reduce their water consumption, and clay and soil organic matter store water for use by plants and soil microorganisms.

This is an example of homeostasis on the level of a local ecosystem. But the Gaia hypothesis posits the concept of ecosystem homeostasis for the whole macro level biosphere. For example, the global carbon cycle maintains atmospheric oxygen and carbon dioxide at concentrations required by the plants and animals in earth's biosphere. This is accomplished by a variety of processes including photosynthesis, respiration and the carbonate buffer system in the oceans. This hypothesis sees global ecosystem homeostasis as a consequence of homeostasis in a large number of distributed local, but mutually interacting ecosystems across the planet. Ecosystems, like the biosphere, are then complex systems composed of many distributed feedback loops that regulate their dynamics. As scientists discover more about Earth, vast numbers of positive and negative feedback loops are being discovered on an ongoing basis, that, together, maintain a metastable condition, sometimes within a very broad range of environmental conditions. But this stable state to the ecosystem enables a gradual and prolonged incremental pattern of development.

Succession

This stable state of development can be understood as ecological succession. Where succession is a phenomenon or process by which an ecological community undergoes more or less orderly and predictable changes following an initial disturbance. Succession was one of the first theories advanced in ecology and the study of succession remains at the core of ecological science today. During succession, biotic and abiotic conditions change. Pioneer and intermediate communities alter conditions so much so that they promote the growth of new communities that eventually replace them. Succession is the natural evolution or progression of an ecosystem