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Umbrella, Icon and Keystone Species
Use of the single species concepts of umbrella, icon and keystone species in environmental managementWe can all recognise and appreciate the richness of the natural environment around us. This richness is displayed in diversity on so many different levels including:
This diversity and its associated biochemical and physical processes are known to drive the earth's biochemical processes. Faced with massive pressure from development, forestry and agriculture the number of species that have become extinct in Australia in the past 200 years is considerable. Twenty mammal species; 10 species and subspecies of birds and 97 vascular plants have known to have become extinct. Also, our temperate grasslands and other ecosystems such as the Cumberland Plain Woodland are facing possible extinction. It is likely that other species have disappeared too, without our knowledge.
Biologists have now listed all those plants and animals that they know are at risk of extinction in Australia. These are called endangered species. The list includes 10 species of fish, 12 frogs, 13 reptiles, 32 birds, 33 mammals and 209 plants. In addition, there are many more species that are listed as vulnerable and some that are classified as rare.
It is necessary in order to met the challenge of this loss in biological diversity to define the spatial, compositional and functional attributes that are required to ensure the needs of species present are met and to maintain the integrity of the system.
Within the scientific community there is considerable debate on the best approach when developing management plans to maintain a healthy ecosystem. One approach is through analysis of patterns and processes at higher levels of organisation such as the ecosystem or landscape. The other is management based on a single species approach.
In taking a landscape or ecosystem approach emphasis is placed on relationships such as species richness and diversity and a measure of productivity, soil nutrient retention (nitrogen availability) or respiration (carbon dioxide production). Such an approach helps to identify elements required within the landscape or ecosystem to obtain a more integrated knowledge of natural processes.
Experiments performed on primary productivity in grassland communities in California (Tilman & Downing, 1994) reveal that communities with greater diversity are more resistant to and recover more quickly from drought with drought resistance becoming essentially independent of plant species richness in communities with greater then eight species. This suggests that certain species play a crucial role in the maintenance of ecosystem processes, beyond which additional species are have no influence. The role of a greater diversity of species in this case may ensure the presence of those species fundamental to the maintenance of an ecosystem during that time. For example, in the experiment on Californian grassland, greater species diversity increases the possibility of the presence of drought hardy species which supports the ecosystem until conditions change to favour other sets of species.
Such a broad approach to landscape management is however, unable to define the appropriate quantity and distribution of the crucial components it identifies. Consequently, the role of certain species and their needs must be ascertained within the landscape to develop an effective management plan.
In the past a species based approach has commonly been taken. Species may be chosen based on the concept of an umbrella species whose requirements are believed to incorporate the needs of other species (Lambeck, 1996). That is, decisions concerning land management, for example habitat size, distance from other communities and risk from threatening processes are based primarily on one species and in doing so the needs of other species present are automatically met.
How then are umbrella species chosen? Priority is often given to those species considered endangered or threatened, often those we know the most about. This identifies the species most sensitive due to habitat destruction or fragmentation and weed or pest invasion and can be used to define the minimum acceptable level at which that threat can occur. Legislation such as the Environmental Planning and Assessment Act (1979) and the Threatened Species Conservation Act (1995) provide a vehicle for action to be taken incorporating management into planning and development decisions. It also attempts to address the insistent problem our country faces concerning of loss of species.
The umbrella species concept has been demonstrated as an effective tool in the conservation of habitat (Launer & Murphy, 1993) and is considered valuable to decision makers. Doubts still exist however, concerning the extent of protection given to species under the 'umbrella' which is difficult to monitor and often assumed rather then proven. It difficult to justify concentrating on one species within a single ecosystem not knowing its role in ecosystem functioning. It may be unlikely to be of value in the larger scheme of things. Ensuring one nail is hammered in will not guarantee the house will remain standing.
The single species based approach is often criticised due to the immense cost absorbed in the conservation of a single species. Consider the economic consequences of focusing on, for example, the hairy nosed wombat under threat from competition from introduced grazers, destruction of habitat, shooting and poisoning. Conservation planning in South Australia included the purchase of 1215 ha of land and the erection of a fence at a considerable cost (White, 1997).
This has led to a situation where emphasis is placed upon species that are most able to raise the funds required to develop and implement conservation strategies. These include whales, elephants, frogs, butterflies, koalas etc. and are referred to as icon or flagship species, and typically evoke interest and investment from the community. Whilst this approach can be quite successful due to the fact that icon species are usually large invertebrates who require large tracts of land thus providing the 'umbrella' under which other species may persist, once again the exact value of the species is unknown. Further more, the conservation of two flagship species may conflict.
Further ecological research has lead to the understanding that certain organisms play a more vital role in the creation, modification and maintenance of habitats. These species are referred to as keystone species. Examples include pollinators and seed dispersers such as the cassowary that feeds on a number of seeds from different rainforest plant species which, by passing through the birds digestive tract are triggered to germinate. Others may include environmental engineers such as earthworms, which alter the physical environment making it more suitable for other organisms to live. Accordingly, any adverse effect on these species could change the functioning on the ecosystem dramatically. Another example provided by Kitching (1994) is the strangler fig that supports a myriad of species birds, insects and crabs.
The phrase keystone species was coined 25 years ago and has grown in popularity over the years as a possible tool for environmental managers, as it brings together the best of both the ecosystem and species based approaches to management. The natural system or environment is viewed in terms of one central species and priorities are set accordingly with the integrity of the entire system in mind.
Due to the inherent complexities of natural systems it is sometimes very difficult to identify species that may play such a role. A recent conference held in 1994 as part of the Global Biodiversity Assessment (GBA) sponsored by the United Nations Environmental Program (UNEP) attempted to determine whether a keystone species may be identified a priori (before experiment) by distinguishing traits (Power & Mills, 1995).
An important indicator was the fact that a species considered to be a keystone often exerted an influence on the associated assemblage out of proportion to its biomass or abundance such as the tortoise Gopherus poluphemus, whose burrows provide homes for up to 332 other species. Another clue suggested was that keystone species may preferentially consume or hold in check another species that would otherwise dominate the system. A keystone may also be identified through comparison from history where a species has intentionally or unintentionally been removed or a system altered providing insight into the influence a species may have within that system.
With the considerable difficulties in identifying a possible keystone species there is potential danger mistaking the exact influence that species may have. It is possible that several species may each play a crucial role in ecosystem function or perhaps a certain combination is required. This could result in management decisions being completely baseless and economic pain.
It is important to keep in mind that the distribution and abundance of an umbrella or keystone species upon which decisions are based may exist only temporarily and are dependent on so many other components, such as physical conditions, for instance cyclical weather events with the changing seasons along with droughts, also migration of other species. There is a good deal of uncertainty involved due to this spatial and temporal variation, and management decisions need to incorporate this in ways of a thorough knowledge base, flexibility and long-term monitoring.
The use of the icon, umbrella and keystone species concepts are without a
doubt extremely useful tools, potentially providing means to achieve
biodiversity conservation strategies. Research into the most suitable
species is vital and will result in the greatest benefit and most effective
allocation of conservation funds in the long-term. References Kitching R. (1994). Biodiversity political responsibilities and agendas for research and conservation. Pacific Conservation Biology 1: 279 83.
Lambeck R. (1996). Focal Species: A Multi Species Umbrella for Nature Conservation. Conservation Biology 11(4): 849 56.
Launer A. & Murphy D. (1993). Umbrella Species and the Conservation of Habitat Fragments: A Case of a Threatened Butterfly and a Vanishing Grassland Ecosystem. Biological Conservation 69: 145 53.
Power M. & Mills L. (1995). The Keystone cops meet in Hilo. TREE 10(5): 182 4.
Tilman D. & Downing J. (1994). Biodiversity and stability in grasslands. Nature 367: 363 365.
White M. (1997) LISTEN... Our Land is Crying. Australia's environment: problems and solutions. Kangaroo Press, Dural. Back to Technical Reports
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