Ecosystem Tipping points

osystem Tipping Points
Ecosystem States
A tipping point is defined, as a situation in which an ecosystem experiences a shift to a new state, with significant changes to biodiversity and the services to people it underpins, at a regional or global scale. Tipping points are a major concern for scientists, managers and policy-makers, because of their potentially large impacts on ecosystem diversity, ecosystem services and species well-being.It can be extremely difficult for societies to adapt to rapid and potentially irreversible shifts in the functioning and character of an ecosystem on which they depend.
Tipping points also have at least one of the following four characteristics:
• The change becomes self-perpetuating through so-called positive feedbacks, for example deforestation reduces regional rainfall, which increases fire-risk, which causes forest dieback and further drying.
• There is a threshold beyond which an abrupt shift of ecological states occurs, although the threshold point can rarely be predicted with precision.
• The changes are long-lasting and hard to reverse.
• There is a significant time lag between the pressures driving the change and the appearance of impacts, creating great difficulties in ecological management.
Terrestrial Ecosystems
Land-use change continues as the main short-term threat to terrestrial ecosystems, with climate change, and the interactions between these two drivers, becoming progressively important. Tropical forests continue to be cleared, making way for crops and biofuels.Populations of wild species fall rapidly, with large impacts for equatorial Africa and parts of South and South-East Asia.Climate change causes boreal forests to extend northwards into tundra, and to die back at their southern margins giving way to temperate species.
For Example
The large-scale conversion of natural habitats to cropland or managed forests will come at the cost of degradation of biodiversity and the ecosystem services it underpins, such as nutrient retention, clean water supply, soil erosion control and ecosystem carbon storage, unless sustainable practices are used to prevent or reduce these losses.Climate-induced changes in the distribution of species and vegetation-types will have important impacts on the services available to people, such as reduced wood harvests and recreation opportunities.
In addition, there is a high risk of dramatic loss of biodiversity and degradation of services from terrestrial ecosystems if certain thresholds are crossed.
Due to the interaction of deforestation, fire and climate change, the amazon undergoes a widespread diebacks, changing from rainforest to savanna or seasonal forest over wide areas. The forest could move into a self-perpetuating cycle in which fires become more frequent, drought more intense and dieback accelerates. Die-back of the Amazon will have global impacts through increased carbon emissions, accelerating climate change and regional rainfall reductions.
Island ecosystems are afflicted by a cascading set of extinctions and ecosystem instabilities, due to the impact of invasive alien species. Islands are particularly vulnerable to such invasions as communities of species have evolved in isolation and often lack defences against predators and disease organisms.
The Sahel in Africa, under pressure from climate change and over-use of limited land resources, shifts to alternative, degraded states, further driving desertification. Severe impacts on biodiversity and agricultural productivity result. Continued degradation of the Sahel has caused and could continue to cause loss of biodiversity and shortages of food, fibre and water in Western Africa.
Avoiding biodiversity loss in terrestrial areas will involve new approaches to conservation, both inside designated protected areas and beyond their boundaries. In particular, greater attention must be given to the management of biodiversity in human-dominated landscapes, because of the increasingly important role these areas will play as biodiversity corridors as species and communities migrate due to climate change. For example, in the Amazon it is estimated that keeping deforestation below 20% of the original forest extent will greatly reduce the risk of widespread dieback.
Re-Wilding
There are also opportunities for re-wilding landscapes from farmland abandonment in some regions - in Europe, for example, about 200,000 square kilometers of land are expected to be freed up by 2050. Ecological restoration and reintroduction of large herbivores and carnivores will be important in creating self-sustaining ecosystems with minimal need for further human intervention.
Inland Water Ecosystems
Fish species unique to a single basin become especially vulnerable to climate change. One projection suggests fewer fish species in around 15% of rivers by 2100, from climate change and increased water withdrawals alone. River basins in developing countries face the introduction of a growing number of non-native organisms as a direct result of economic activity, increasing the risk of biodiversity loss from invasive species.
Inland freshwater ecosystems continue to be subjected to massive changes as a result of multiple pressures, and species biodiversity to be lost more rapidly than in other types of ecosystem. Challenges related to water availability and quality, multiply with increasing water demands. The introduction of alien species, pollution and dam construction, put further pressure on freshwater biodiversity and the services it provides.
Freshwater eutrophication caused by the build-up of phosphates and nitrates from agricultural fertilizers, sewage effluent and urban storm-water runoff shifts freshwater bodies, especially lakes, into an algae-dominated (eutrophic) state. As the algae decay, oxygen levels in the water are depleted, and there is widespread die-off of other aquatic life including fish.
Changing patterns of melting of snow and glaciers in mountain regions, due to climate change, cause irreversible changes to some freshwater ecosystems. Warmer water, greater run-off during a shortened melt-season and longer periods with low flows disrupt the natural functioning of rivers, and ecological processes. Impacts will include, loss of habitat, changes to the timing of seasonal responses (phenology), and changes to water chemistry.
Even with the most aggressive measures to mitigate climate change, significant changes to snow and glacier melt regimes are inevitable, and are already being observed. However, the impacts on ecosystems and species biodiversity can be reduced by minimizing other stresses such as pollution, habitat loss and water abstraction. Spatial planning and protected area networks can be adapted more specifically to the needs of freshwater systems, by safeguarding the essential processes in rivers and wetlands.
For Example
More integrated management of freshwater ecosystems will help reduce negative impacts from competing pressures. Restoration of disrupted processes such as reconnecting floodplains, managing dams to mimic natural flows and re-opening access to fish habitats blocked by dams, can help to reverse degradation. Payments for ecosystem services, such as the protection of upstream watersheds through conservation of riparian forests, can reward communities that ensure continued provision of those services to users of inland water resources in different parts of a basin.
Marine and Coastal Ecosystems
Wild fish stocks continue to come under pressure, as aquaculture expands. Progressively fishing down the marine food web comes at the expense of marine biodiversity. Climate change causes fish populations to redistribute towards the poles, and tropical oceans become comparatively less diverse. Sea level rise also threatens many coastal ecosystems. Ocean acidification threatens to undermine marine food webs as well as reef structures, while also increasing nutrient loads and pollution, which increase the incidence of coastal dead zones.
The decline of fish stocks and their redistribution towards the poles has major implications for food security and nutrition.In poor tropical regions, as communities often rely on fish protein to supplement their diet. The impact of sea level rise, by reducing the area of coastal ecosystems, will increase hazards to human settlements, and the degradation of coastal ecosystems and coral reefs will have very negative impacts on the tourism industry.
The combined impacts of ocean acidification and warmer sea temperatures make tropical coral reef systems vulnerable to collapse. More acidic water (brought about by higher carbon dioxide concentrations in the atmosphere) decreases the availability of the carbonate ions required to build coral skeletons. Together with the bleaching impact of warmer water, and human-induced stresses, reefs increasingly become algae-dominated with catastrophic loss of biodiversity.
Coastal wetland systems become reduced to narrow fringes or are lost entirely.This is due to sea level rise, exacerbated by coastal developments such as aquaculture ponds. The process is further reinforced by coastal erosion created by the weakened protection provided by tidal wetlands. Further deterioration of coastal ecosystems, including coral reefs, will also have wide-ranging consequences for millions of people whose livelihoods depend on the resources they provide.
The collapse of large predator species in the oceans, triggered by over exploitation, leads to an ecosystem shift towards the dominance of less desirable, more resilient species such as jellyfish.

Marine ecosystems under such a shift become much less able to provide the quantity and quality of food needed by people. Such changes could prove to be long-lasting and difficult to reverse.
The reduction of forms of stress on coral systems may make them less vulnerable to the impacts of acidification and warmer waters. Reducing coastal pollution will remove an added stimulus to the growth of algae, and reducing overexploitation of herbivorous fish will keep the coral/algae symbiosis in balance, increasing the resilience of the system. The development of low-impact aquaculture, dealing with the sustainability issues that have troubled some parts of the industry, would also help to meet the rising demand for fish without adding pressure on wild stocks.
Review
What can have large impacts on ecosystem diversity, ecosystem services and species well-being?

a. Spatial Planning , b. Deforestation, c. Tipping Point, d. Climate Change
Answer C) A tipping point is defined, as a situation in which an ecosystem experiences a shift to a new state, with significant changes to biodiversity and the services to people it underpins, at a regional or global scale.
What does the introduction of alien species, pollution and dam construction, put further pressure on?
a. Ocean Ecosystems, b. Coral Reefs, c. Coastal Wetlands, d. Freshwater Ecosystems
Answer D) Inland freshwater ecosystems continue to be subjected to massive changes as a result of multiple pressures, and species biodiversity to be lost more rapidly than in other types of ecosystem.
Keywords
acid rain corrosive rain caused by rainwater falling to the ground through sulfur dioxide gas, turning it into weak sulfuric acid; can damage structures and ecosystems
analytical model ecosystem model that is created with mathematical formulas to predict the effects of environmental disturbances on ecosystem structure and dynamics
apex consumer organism at the top of the food chain
chemoautotroph organism capable of synthesizing its own food using energy from inorganic molecules
conceptual model (also, compartment models) ecosystem model that consists of flow charts that show the interactions of different compartments of the living and non-living components of the ecosystem
detrital food web type of food web in which the primary consumers consist of decomposers; these are often associated with grazing food webs
ecosystem dynamics study of the changes in ecosystem structure caused by changes in the environment or internal forces
ecosystem community of living organisms and their interactions with their abiotic environment
equilibrium steady state of an ecosystem where all organisms are in balance with their environment and each other
food chain linear representation of a chain of primary producers, primary consumers, and higher- level consumers used to describe ecosystem structure and dynamics
food web graphic representation of a holistic, non-linear web of primary producers, primary consumers, and higher-level consumers used to describe ecosystem structure and dynamics
resilience (ecological) speed at which an ecosystem recovers equilibrium after being disturbed
resistance (ecological) ability of an ecosystem to remain at equilibrium in spite of disturbances
simulation model ecosystem model that is created with computer programs to holistically model ecosystems and to predict the effects of environmental disturbances on ecosystem structure and dynamics
trophic level position of a species or group of species in a food chain or a food web