Notes on Ecosystems

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Topic 1: Ecosystems at Risk

A. Ecosystems and Their Management

2. Vulnerability and Resilience of Ecosystems

* Vunerability is the sensitivity of an ecosystem to cope with stress.

* Resilience is the ability of an ecosystem (or a component of an ecosystem) to adapt to a changing environment and to restore function and structure following an episode of natural or human-induced stress.

* All ecosystems function in a state of dynamic equilibrium or a continual state of balanced change. * This state of dynamic equilibrium is the product of the interrelationship of the elements in the ecosystem: the atmosphere, lithosphere, hydrosphere and biosphere. * Change occurs because the interrelationship between minerals, energy and communities varies over time. * It is also the interdependence of these four elements that makes an ecosystem vulnerable. * A change beyond the limits of the equilibrium, in any of these elements, means that the system as a whole cannot exist in its original state. * All ecosystems are, in a sense, vulnerable, but the level of vulnerability depends on how small a change is needed in any element to upset the equilibrium. * Ecosystems, are therefore, not equally at risk – some are more resilient than others.

Which ecosystems have greater resilience?
Resilience is the ability of an ecosystem (or component of an ecosystem) to adapt to a changing environment and to restore function and structure following an episode of natural or human- induced stress. Ecosystems rich in biodiversity generally have greater resilience than those with little diversity. They are able to recover more readily from naturally induced stress (including drought and fire) and human- induced habitat destruction.

2. Under what conditions does long-term degradation occur? Long-term degeneration occurs when the magnitude and duration of the stress exceed the ability of the component to repair itself. 3.Explain the process shown in Fig 1.1.28.

Figure 1.1.28 shows the impact of stress on the functioning of ecosystems. It shows the Elasticity and the rate of recovery of an ecosystem property following disturbance. It also shows the rate of amplitude and the threshold level of strain beyond. The intensity and duration of stress is important in terms of the effect it has on ecosystems.

4. Outline how natural sources of stress can play an important role in the functioning of ecosystems. These changes could be in response to changes in the availability of water, average temperature or many other natural events. In nature, these changes usually take place very slowly. The biome gradually adapts as animals and plant species that have characteristics unsuited to the change die out and those more suited the environment remains alive to breed and pass on their characteristics to successive generations. This process is known as natural selection.

Causes of Ecosystem Vulnerability

* All ecosystems have some ability to withstand stress.
* They tend to resist being disturbed or altered and will restore themselves to their original condition if not disturbed too dramatically. * In other words, ecosystems maintain themselves within a tolerable range of conditions. * A number of factors are relevant to the vulnerability of ecosystems to stress, including location, extent, biodiversity and linkages.

a) Location
* Where an ecosystem is will affect its functioning.
* At a global scale, latitude, distance from the sea, and altitude play decisive roles in determining climate and ultimately the nature of particular ecosystems. * The microclimatic features of a location can be significant enough to create a range of distinctive ecosystem types within relatively small areas e.g. aspect. * Some ecosystems are located in environments that are extreme e.g. deserts, polar, hypersaline lagoons. * Organisms capable of living in such conditions are highly specialised. * The greater the degree...
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