The Concepts of Vulnerability and Resilience
|
All ecosystems experience periods of stress which reduce their normal functioning. These stresses may be natural or anthropogenic (man-made).
The rate of change of a stress may also be quite catastrophic or very gradual. Stress may even be so gradual as to encourage the evolution of an ecosystem or a migration of its location. Vulnerability refers to how susceptible an ecosystem is to stress. Resilience on the other hand, refers to how quickly an ecosystem can restore normal functioning after a stress. The vulnerability of an ecosystem is determined by its location, its extent, its biodiversity and the number of linkages within its food web. The resilience of an ecosystem refers to the ability to adapt to change and restore normal functioning after a period of stress. Ecosystems with high biodiversity often have many pioneer species that can colonise areas damage by stress. Ecosystems may be very elastic with some stress events but very vulnerable to others. For example, Grassland ecosystems are very resilient to fire and quickly regrow from underground roots, however, they are highly vulnerable to ploughing. |
|
|
|
Impacts Due to Natural Stress.
Natural stresses are usually better accommodated by ecosystems. If an ecosystem was unable to respond to a natural stress in a given area, it would not have evolved in that location.
Coral reefs are frequently damaged by tropical cyclone activity, however, they have many pioneer species that perform colonising functions after damage. Mangroves are also strong colonising species.
Coral reefs are frequently damaged by tropical cyclone activity, however, they have many pioneer species that perform colonising functions after damage. Mangroves are also strong colonising species.
Impacts due to human induced modifications
Humans alter ecosystems in various ways and these cause stress on ecosystem functioning. For centuries this has taken place as humans take resources from the Earth without understanding the delicate equilibriums in which ecosystems operate. Climate change and overpopulation are now the most significant threats as they operate at a global scale.
Ecosystems are degraded, simplified or destroyed. The most common example of this is land clearing and cropping, whereby the ecosystem is replaced either by urban land uses or monoculture cropping. In both of these cases a simplified ecosystem is installed. An urban ecosystem for example contains very few plant species and encourages only pest species such as rats and ibis.
Human activities can also alter the hydrology of an location. For example, the removal of trees from cropland in Australia has caused the water table to rise and bought salinity issues. The changing of coastlines along rivers and bays alters the wave energy and tidal flows.
Ecosystems are degraded, simplified or destroyed. The most common example of this is land clearing and cropping, whereby the ecosystem is replaced either by urban land uses or monoculture cropping. In both of these cases a simplified ecosystem is installed. An urban ecosystem for example contains very few plant species and encourages only pest species such as rats and ibis.
Human activities can also alter the hydrology of an location. For example, the removal of trees from cropland in Australia has caused the water table to rise and bought salinity issues. The changing of coastlines along rivers and bays alters the wave energy and tidal flows.
Through hunting, fishing and habitat destruction key predator and pest populations are put out of equilibrium. Apex predators, such as lions, wolves, sharks and birds of prey are particularly vulnerable due to the low numbers and large requirements for range. The loss of such species creates a tropic cascade which can degrade ecosystems and strengthen pest numbers.
Ecosystems are also disturbed by various forms of pollutant. Plastic litter is highly visible and creates serious problems in coastal ecosystems. Similarly, toxic chemical inputs into ecosystems can have detrimental effects such as the DDT pesticide which reduced the breeding potential of higher tropic species. Bioaccumulation occurs with chemicals that are not biodegradable further weakening predator species. Noise, heat and light pollution are all common in urban environments and can alter ecosystems beyond their range of tolerance.
Ecosystems are also disturbed by various forms of pollutant. Plastic litter is highly visible and creates serious problems in coastal ecosystems. Similarly, toxic chemical inputs into ecosystems can have detrimental effects such as the DDT pesticide which reduced the breeding potential of higher tropic species. Bioaccumulation occurs with chemicals that are not biodegradable further weakening predator species. Noise, heat and light pollution are all common in urban environments and can alter ecosystems beyond their range of tolerance.
The increased movement of people and goods globally has resulted in greater exposure to exotic species. Exotic species often alter energy flows and food webs and have no predator species to limit their growth. Introductions from ballast water are a common transmission route for marine species. Introductions for sport or failed attempts at biological control have been common in Australian environments. On land, foxes are a common Australian pest which require constant management.