Globalisation and Invasive Species: Economic Insights from Theoretical Ecology

1. Globalisation and Invasive Species: Economic Insights from Theoretical Ecology Charles Perrings University of York Washington DC August 2004

2. Globalisation • Globalisation is widely understood to mean the closer integration of the world's economic systems, systems of governance and cultures. • This interpretation of the term is reflected in the 2003 World Development Report's reference to the world ‘coming to resemble a single community' (World Bank, 2002).

3. Globalisation and the dispersion of species • Globalisation has increased both the speed with which new species are dispersed, and the extent of their dispersion. • The widening and deepening of trade links has • connected previously unconnected ecosystems, • created new pathways between those ecosystems and • increased the rate of dispersion of species along those pathways. • The dispersion of new species includes both deliberate introductions (new crops, livestock strains, biocontrol agents and so on) and accidental introductions.

4. Biodiversity trends • At the same time successive environmental assessments (most recently the MEA) have shown a number of trends, including: • that the number of exotic species in many managed and impacted systems has increased; • that the diversity of native species within ecosystems has fallen; • that the diversity of all species across ecosystems has fallen. • How are these things connected?

5. Intermediate dispersion theory • Loreau M., Mouquet N. and Gonzalez A. 2003. Biodiversity as spatial insurance in heterogeneous landscapes, PNAS 100 (22): 12765-12770. • The paper explores the functional significance of biodiversity change across space. • Species that are functionally redundant in one place may not be functionally redundant in other places if environmental conditions vary across space, and asynchronously over time. • The dispersion rate determines local biodiversity.

6. The spatial insurance model • If different communities experience different environmental conditions, and if these conditions fluctuate asynchronously over time, then different species will thrive in each of the communities at different points in time. • Differences in dispersion rates between communities will affect the level of biodiversity in those communities.

7. The model The model comprises equations of motion for biomass and the limiting natural resource:

8. Variables and parameters Nij(t) is biomass of species I in community j at time t Rj(t) is amount of limiting resource in community j M is the number of communities Sis number of species cij(t) is rate at which species i consumes the resource in j eij(t) is efficiency with which the limiting resource in j is converted into biomass by species i mij(t) is mortality of species I in community j Ij is renewal rate of the limiting resource in j ljis decay/loss rate of the limiting resource in j a is dispersal rate of all species

9. Consumption • Consumption rates are responsive to; • environmental fluctuations and • species traits • They give species responses to environmental fluctuations where: • Hiis the ‘trait value’ of species i (i.e. a measure of its best performance along an environmental gradient) • Ej (t) is the environmental value of community j

10. Ecosystem productivity • Ecosystem productivity is production of new biomass per unit of time averaged across the metacommunity

11. Environmental fluctuations • Environmental values are assumed to exhibit autocorrelated sinusoidal fluctuations with period T :

12. Impact on local biodiversity • Dispersal of species between communities has non-monotonic effects. • Low and high rates of dispersal are both associated with low local biodiversity. • Intermediate rates of dispersal are associated with high levels of local biodiversity.

13. Impact of dispersion rate on diversity (a = 0) The species with initial competitive advantage excludes others. Biomass varies with environmental conditions. Regional diversity is high. Time

14. Impact of dispersion rate on diversity (a = 0.001) Source-sink effects begin to increase local diversity.Regional diversity begins to fall. Time

15. Impact of dispersion rate on diversity (a = 0.02) Source-sink effects allow local (and regional)coexistence of large numbers of species. Time

16. Impact of dispersion rate on diversity (a = 0.2) The metacommunity begins to behave as a single community, and species with average traits begin to dominate. Time

17. Impact of dispersion rate on diversity (a = 0.4) The community behaves like a single community. The species with the average trait competititively excludes others. Local and regional diversity falls. Time

18. Impact on productivity • If there is a positive relation between local biodiversity and either productivity or resilience, this implies that: • very low and very high rates of dispersion may be expected to be associated with low levels of productivity/resilience and • intermediate rates of dispersion with high levels of productivity/resilience.

19. Impact of dispersion rate on productivity (a = 0 to 0.2) Time

20. Impact of dispersion rate on productivity (a = 0.2 to 0.4) Time

21. Ecological conclusions • Biodiversity can affect ecosystem functioning in ways that cannot be detected by small-scale experiments. • Changes in ‘connectivity’ between communities at the landscape level can alter both species diversity and ecosystem processes. • Beyond a certain point increasing landscape ‘connectivity’ will decrease species diversity, and will increase the variability of productivity at the local level.

22. Ecological conclusions (cont) • The intermediate-type species that dominate when dispersal is high have lower variability than the species that dominate local communities when dispersal is low. • More connected metacommunities experience lower variability in productivity than unconnected communities.

23. Economic implications • How does this help us to think about the implications of globalisation? • What are the connections between trade and dispersion? • What are the connections between dispersion and exotic species? • What does competitive exclusion mean in ecological-economic communities? • What are the implications for invasive species?

24. How does this help us to think about the implications of globalisation? • The spatial insurance model is a model of the behaviour of more or less strongly linked members of an ecological metacommunity. • An economic analogue to the closed community within a metacommunity is the autarkic state. • An economic analogue to a metacommunity that behaves as a single community is the fully integrated world economy.

25. The economic implications • The dispersion of new products, processes, technologies and management strategies has changed both the nature and management of local risks. • As production systems have become more homogeneous, the risks associated with those systems have become more highly correlated, e.g: • vulnerability to external stresses and shocks, • vulnerability to pests and pathogens) • The portfolio of natural capital stocks has been reduced

26. What are the connections between trade and dispersion? • The rate of dispersion in ecology is driven both by the characteristics of the species and environmental conditions. • In an ecological-economic system environmental conditions include the pattern and volume of trade. • The dispersion of species depends on the direction and volume of trade: • the direction of trade determines the distribution of propagules • the volume of trade determines propagule pressure

27. What are the connections between dispersion and exotic species? • Trade involves the dispersion of species of many kinds • Crops (flora providing foods, fibres and construction materials) • Ornamentals (flora providing decoration or amenity) • Livestock (fauna providing foods, fibres and draught power) • Pets (fauna providing amenity) • Biocontrol agents • Pests • Pathogens • 1 - 5 are typically deliberately introduced through trade, and may depend on repeated introduction, cultivation or management. • 6-7 are typically the unintended consequence of trade or travel

28. What does competitive exclusion mean in ecological-economic communities? • Species introduced via trade may competitively exclude others either ecologically or economically. • Ecological competitive exclusion implies that the species best adapted to local conditions out-competes others in accessing resources. • Economic competitive exclusion implies that dominant products/firms out-compete others in accessing markets and hence resources, e.g.: • high yielding varieties of rice • BT cotton

29. What are the implications for invasive species? • Invasive species are introduced species that spread (usually following establishment and naturalisation), with either more or less significant consequences for ecosystem processes and functioning. • The probability that any species will become invasive is depends on its invasiveness (including propagule pressure) and the invasibility of the host system (affected by disturbance, fragmentation etc). • Pests, pathogens and cultivated alien species can all have similar effects, competitively excluding native species and affecting the production of ecological goods and services.

30. What are the implications for invasive species? • By convention, alien species that persist only because of domestication are not considered invasive. But they may have equivalent ecological effects, and these should be taken into account. • The risks of successful introductions of alien invasive species increase with the volume of trade in the species itself, or in the goods and services on which it is a passenger.

31. The world as a single community • The advantages of moving from autarky to trade are well-understood. • It is argued that trade should benefit the environment by: • improving the efficiency of activities that use natural resources, • reducing the environmental impact of activities, • improving security of land tenure by assigning private property which promotes investment in land conservation and environmental stewardship, • induce greater macroeconomic stability which encourages investment in conservation activities, • reducing poverty and hence pressure on open-access resources, • lowering the costs of environmental protection, and • helping diffusion of environmental protection technologies.

32. Implications of the intermediate dispersion hypothesis • The intermediate dispersion hypothesis suggests that • the impact on local species diversity of the move from autarky to trade should initially be positive, but that • the impact on local species diversity of the further growth of trade might be expected to become negative at some point. • Both have consequences for productivity and resilience. • There may also be economic analogues to this…..

33. Implications for the research problem • What is the nature of the problem? • Historically, research on invasive species has focused on pest species - those whose spread is somewhat independent of human behaviour, and whose impacts inflict appreciable harm • These are part of a spectrum of exotic species whose introduction and spread has transformed local ecosystems and the goods and services derived from those systems. • The spectrum stretches from pests and pathogens, through bio-control agents to cultivated crops.

34. Implications for the research problem (cont) • In all cases the generic research questions are the same. • At the micro level (of individual species) they are: • What is the opportunity cost of the introduction and spread of new species (in terms of forgone ecosystem services)? • Is this compensated by the net benefits offered by the actions that lead to the introduction and spread of new species, taking all other effects into account?

35. Implications for the research problem (cont) • At the macro level they are: • What are the consequences of the change in the mix of species (induced by globalisation) for the functioning of ecosystems? • What effects does this have on the production of goods and services and human well-being. • These questions apply as much to species whose spread depends wholly on human action as to those whose spread is independent of human action.

36. Implications for the research problem (cont) • We should be taking a fresh look at problems that have previously been in the domain of health and epidemiology, agriculture, forestry. • We should be asking what the net consequences of changes in the species mix have been in terms of the capacity of local systems • to support the production of valuable goods and services • to function over a range of environmental conditions

37. Implications for the research problem (final) • The micro question has been posed by adding environmental externalities to quite standard production theory. • The macro question has been dealt with far less satisfactorily, although it is beginning to be posed in questions about the optimal mix of production and conservation activities in the landscape. • We need to consider the impact of changes in species mix at the same level.