Conservation Biology

Thursday, August 17, 2006


Biological Invasion Risks and the Public Good: an Economic Perspective.
Charles Perrings, Mark Williamson, Edward B. Barbier, Doriana Delfino, Silvana Dalmazzone, Jason Shogren, Peter Simmons, & Andrew Watkinson (2002).
Conservation Ecology 6(1) 1, online at:

This paper suggests that the cause of the problem of alien invasives are economic and therefore require solutions which are also economic.

Four reasons are given for the increasing concern of alien invasives:

1) Alien invasive introductions are increasing at an alarming rate, added to, the addition of the weakening or scaling down of measures of eradication and control.
2) With an increase in alien invasives comes an associated increase in the cost of alien invasions.
3) Invasions are associated with a relatively “high degree of uncertainty because the risks they pose are both ‘endogenous, ‘ and because alien invasions often involve novel interactions.”
4) The “weakest-link” is the control and the exclusion of alien invasives.

The argument put forward is: An economic solution to the alien invasives problem has two facets. Incentives must be used to change our behaviour, and by so doing, prevent alien species introductions, establishment and their spread, and, develop institutions to effectively enforce and control the exclusion of invasives.

The definition of ‘endogenous’ is “the origination or production within an organism or cell”, “being produced or grown within,” i.e., this definition suggests that point no. 3 refers to the difficulty is discerning the suitable treatment and action to take for, and how to label alien invasives, or categorise them, to facilitate the most successful exclusion or control strategies.

The paper indicates that under the Convention on Biological Diversity, the definition of alien invasive species is those organisms which are introduced, can become established, can become naturalised and spread outside of their native range, but also that their impacts are significantly harmful, and therefore negative.

Apart from the common understanding of the economic impacts of alien invasives, such as the cost involved in associated costs to control weeds, invasives and pathogens, economics also incorporates the “understanding of the interactions between our behaviour which can be seen as the causative action, and natural processes, as well as seeking solutions at both institutional and behavioural levels.”

The authors specifically label the control of alien invasive species as “A public good of a very particular kind,” however, they also point out that the level of control of invasive species in one area or country, has a direct influence on the risk faced by other areas because of the movement of people and trade. An important point made is that due to the fact that the control of invasive species is an international and global responsibility, it is left to “uncoordinated efforts of different countries,” where there is insufficient control to protect the public interest over other hidden agendas (Sound familiar Richard…?…how green is the UWC roof indeed!).

A starting realisation which is put forward in this paper, and one which rings loud for South Africa and other developing African nations, is there will be (and is) ineffective and limited levels of protection against infectious diseases associated with the direct constraints of available resources. Biological invasion hot potato is and will remain HIV in Southern Africa, and the authors suggest that economics can help to identify the social causes of the problem and develop solutions through institutions. A powerful statement made suggests that in the conditions indicated above, invasive alien species control is the “weakest-link” of public good, and, the solutions required must be less politically motivated. (personal interpretation of “black-lists, white-lists, quarantine, and ad-hoc eradication programmes.”)

“The cost of biological invasions.”

Apart from the discussion on relative costs of invasive species on a national level in the USA, the paper indicates that the complete costs of biological invasions include more than just the control of the invasives or the cost of their control. The cost to the host ecosystem must be included, as well as the cost to human populations dependant upon the host ecosystem.

There are no global estimates of the widespread effects of invasions in general, though invasives are suggested to be one of the main causes of organism extinction, be it in local or total populations, the economic implications of which are yet to be experienced. This could occur through a number of factors including competition and superior exploitation of resources.

“Social & Economic cause of Biological invasions.”

The authors indicate that little research has been undertaken regarding the study of the “social as well as the economic causes of biological invasions” external to the more important and seemingly prioritised set of selected biological invasions of agricultural pests etc. It is directly suggested that invasions are the consequence of decisions made to use exotic species as sources of food, for habitat fragmentation (which could include dune stability?), and the “general movement of goods and people.” These decisions are aligned with not only social customs, but also what the paper labels as “incentive effects.” Incentive effects lead ultimately to wealth-creation. An important indication is that the response of people to invasive species and the spread thereof is generally slow. The relevant example of HIV is a good example. What is not indicated here is that culture in addition to economics plays an important role, and the ignorance of education, where education is a luxury in most developing nations, the lack of knowledge is the fuel supplying energy to the “weakest-link” as mentioned earlier. Generally people ignore the changes in the cost of their behaviour. Is this an attitude of shifted responsibility, or a total lack thereof?

The point made: Human behaviour is the cause for the spread of alien invasive species, however, a response of adaptation or mitigation can change the outcome to either curbing the spread of alien invasives to reducing the impacts of such an invasion. Better actions would be designed to factor in the value of such an affect.

Interestingly, when biological invasions directly impact individuals, their behaviour towards the invasion can change. The example is given of infectious diseases, which people respond to as a threat and therefore seek out immediate solutions to, relative to the “constraints imposed by their general socio-economic conditions.”

Small islands are predisposed to invasions. This is partly due to their general size and associated native biodiversity, which can be unique and therefore vulnerable and affected in smaller spaces of time. The importance of agriculture, tourism and the links of trade including the production of primary products commonly associated with small countries or islands (like sugar etc.) can lead to largely open economies and higher potentials therefore for imported (and exported) invasions. Ecosystems must be seen as varying in their risk and vulnerability to invasions, since some will be more predisposed for certain invasions than others, since invasive organisms do need to follow a general path of acceptable establishment which includes habitat and food resource and climate. Ecosystems with low natural diversity as for some island states, where predators may be lacking, may be more vulnerable to invasion than those of higher diversity, where it could also be argued that competition and niche-reservation is at a higher overall level. Vulnerability is also directly related to the way the land is used, and to the implementation of specific control measures for the prevention of invasions.

Would you believe that habitat conservation, through habitat fragmentation, as suggested by Richard Knight in one of his lectures, and the authors of this paper, can be blamed for the increased susceptibility of ecosystems to invasions. This makes sense if the fragmentation of an ecosystem restricts or excludes the functioning of micro-variables and ecological links of organisms within it, however, this is generally not seen as a concern over the theory of “Feel Good” that is often associated with macro-conservation. Without total habitat conservation and an understanding of the complex workings within an ecosystem, conservation efforts could be to none.

Trade and travel has a major impact on the frequency and method of invasion facilitation (also see the paper on the invasive marine species of South Africa by Robinson et al. 2005, which I reviewed and posted on the Invasion Biology Blog as an example using the European shore crab and its movement between Table Bay Harbour and Hout Bay Harbour.) There is also a higher probability for the introduction of purposeful invasive species through a need for their use and adaptability or survivability over native available or lack of alternatives.

The overall risk of invasions is suggested to be related to the people’s use of the invasive species, or transportation thereof, the use of their predators or competitors, or lack thereof, and the effects of the dependence of trade on the invasive organism if it is of specific value or not.

Interestingly the authors include that the cost of the invasive species in terms of market price, is not usually reflective of the cost to society in the long term, and the damage as a result is external to the same market. Economic policies including income-related policies in agriculture, supports the increase in susceptibility of ecosystems to invasions with agriculture promotion through subsidised land use and export promotion of what are known as cash crops, has resulted in higher buses of pesticides and the destruction or replacement of general-area plant diversity. Ironically property rights are also indicated as inhibiting in the fight to control invasives.

Are the authors taking it a step too far when they suggest that species introductions can be used strategically as instruments of bio-terrorism and warfare, or is this a possibility we may encounter in the future?

“The control of invasive species is a ‘weakest-link’ public good…”

Quarantine, my favourite subject! Quarantine policies, though somewhat lacking in this country, if affective, reduces the risk to all people in the country to biological invasions. Unfortunately where human attitudes are concerned, because public goods and services, such as quarantine processes, are non-exclusive and seen as a right rather than a privilege, there is an incentive to take advantage of a “free ride” on the efforts of others, and in the process, the control of invasives is undersupplied. Again, a classic example of perceived responsibility, and the attitude often described as “NMP,” or “Not My Problem.” Unfortunate but true is the fact of quarantine failure if only one facility, be it private or public, fails to contain an invasive pathogen for example, and the same applies for riparian land-owners and the control or eradication of invasive plant species from their properties.

Commitment of resources, time and funding to the risk of invasions will not necessarily be reflected in the demographics of the people, be them rich or poor, though their reaction to high-profile biological invasions will usually be the same.

It is therefore the benefits of the prevention of alien invasive species to all peoples regardless of demographics or culture or level of education, determined by efforts of the weakest, since the weakest link in the complete chain determines its ultimate strength.

I have purposefully left out the section “What is to be done” in the hopes that the above message will spark your own ideas and sentiments to which you can add to this posting.

A most interesting paper indeed!

David Vaughan
Senior aquarist, Quarantine
Two Oceans Aquarium
Cape Town, South Africa