Aliens Among Us?

Slide 1: Title

Slide 2: Structure of the Talk

• Two Questions:
  • Scientific
  • Ethical
• Practical Philosophical Suggestions (!)
• Conclusion

Slide 3: The Four Horsemen of the Environmental Apocalypse

E. O. Wilson (1992) suggests there are at least four drivers or causes of the current loss of biodiversity:

• Habitat destruction
• Overhunting
• Disease
• Exotic species

Slide 4: Two Questions

Scientific question:

• What determines whether a species is exotic?

Ethical question:

• Under what conditions should an exotic species be killed, removed, or left alone?

Slide 5: Exotic Species Concepts

Different criteria:

• The human introduction criterion
• The evolutionary criterion
• The historical range criterion
• The community membership criterion

Slide 6: What is an Exotic Species?

• The human introduction criterion:
  • An exotic species is the result of direct or indirect, deliberate or accidental introduction of the species by humans.
• Counterfactual criterion:
  • If not for some human activity, then species X would not be in a given area.
• Criteria is used by National Park Service and Society for Restoration Ecology.

Sliide 7: What is an Exotic Species?

• Problems
  • Human activities have affected most of life on the planet; i.e. global climate change – most species are or will be exotics.
  • Suppose a species is introduced and there is a speciation event – are the daughter species native or exotic?
  • If a species migrates by traveling on a human by a its normal dispersal mechanisms why should it be thought of differently

Slide 8: What is an Invasive Species?

• An evolutionary criterion:
  • A species is an invasive to an area if it did not originally evolve in that area.
• For example, Darwin’s finches migrated to the Galapagos and subsequently speciated – the ancestral species is exotic and latter are native.

Slide 9: What is an Exotic Species?

• Problems:
  • How do we determine the area of origin? Forest ecologist Stephen Spurr writes, “all plants and animals are exotic except at the very point in space where the particular gene combination was constructed” (1980, 441).
  • Speciation events are “splayed out” in time and thus determining the area of origin is vague in time as well.

Slide 10: What is an Exotic Species?

• The historical range criterion:
  • A species is exotic if it occurs outside of its historical or natural range.
• Problems:
• How do we specify the historical range in space and time given the difficulties in reconstructing these biogeographical facts?

Slide 11: What is an Exotic Species?

• The community membership criterion:
  • The species is not an “integrated” member of the ecological community in which it finds itself – it is not participating in the relevant interspecific interactions.
• Problems:
  • Communities are arbitrary, individualistic assemblages.
  • Community composition is constantly changing in space and time.

Slide 12: What is an Exotic Species?

• Summary of proposals:
  • An invasive species is the result of direct or indirect, deliberate or accidental introduction of the species by humans.
  • A species is an invasive to an area if it did not originally evolve in that area.
  • A species is exotic if it occurs outside of its historical or natural range.
  • The species is not an “integrated” member of the ecological community in which it finds itself – it is not participating in the relevant interspecific interactions.

Slide 13: What is Exotic Species?

• Monism versus Pluralism about exotic species:
  • Monism: There is a single correct account of what an exotic species is; however, there are problems with each concept.
  • Pluralism: There is are variety of correct accounts of what an exotic species is though each may apply in different circumstances.

Slide 14: Are Exotics Bad?

• What values are at stake?
  • Ecosystem health: the persistence, stability, and resilience of communities.
  • Biodiversity: the variation with respect to genes, species, and ecosystems.
  • Naturalness: the degree to which a system exists independent of human interventions.
  • Animal welfare: the pleasure and pain of non-human animals.
  • Anthropocentric values: human-centered economic, recreational, and aesthetic values associated with ecological systems.

Slide 15: Are Exotics Bad?

• Exotic species are not necessarily harmful – on average, the number of successful colonization of an exotic species is greater the number of extinctions of natives.
• For example, after several centuries of European colonization, relatively few native plant species have gone extinct: whereas invading species have approximately doubled the size of island floras:
  • 2,000 to 4,000 on New Zealand;
  • 1,300 to 2,300 on Hawaii;
  • 221 to 421 on Lord Howe Island, Australia;
  • 50 to 111 on Easter Island;
  • and 44 to 80 on Pitcairn Island

Slide 16: Are Exotics Bad?

• Even if 90% of exotic species do not cause substantial ecological or economic impacts, still “10% of a large number is a large number” (Simberloff 2007).
  • Garry oak woodlands and meadows in the U.S. Pacific Northwest are now seas of Scotch broom.
  • Oaks have replaced the American chestnut in eastern North America.
  • Dead man's fingers, a Pacific alga, carpets much of the nearshore seafloor of the southern Gulf of Maine and the Nova Scotia coast where kelp forests once stood.
  • Massive monocultures of the Pacific "killer alga" smother sea-grass meadows off the coasts of Spain, France, Italy, and Croatia.

Slide 17: Are Exotics Bad?

• Simberloff suggests we should treat exotics as “guilty until proven innocent”.
• In ethics, this is a maximin strategy – when outcomes are uncertain, choose the best of worst

Slide 18: Are Exotics Bad?

• Precautionary principle:
  • If the appearance of exotics in a community might instigate a sequence of extinctions such that:
    • the harmful effects are irreversible, and
    • the benefits of their community membership are marginal,
  • then we should prevent the introduction of exotics and remove them when they appear.

Slide 19: What is Exotic Species?

• Application to Homo sapiens:
  • The criteria we have discussed apply to humans as well.
  • If we have reason to prevent species introductions, then we have the same reasons to prevent humans from invading.
  • Therefore, we have the same reasons to prevent humans from invading.

Slide 20: Practical Philosophical Suggestions

• Be clear/explicit with respect to how you use the terms ‘exotic’, ‘native’, and ‘invasive’.
  • Exotic – a species “introduced” into an area where it previously did not occur.
  • Endemic (Native) – a species that naturally occurs in an area.
  • Invasive – a species that tends to become abundant and expand into new areas and which is harmful.

Slide 21: Practical Philosophical Suggestions

• Do not define ‘exotic species’ as harmful.
  • Confuses facts and values and forces scientists to make unnecessary ethical judgments
  • Creates the impression that all exotics are harmful which we know to be false

Slide 22: Practical Philosophical Suggestions

• Determine which error is more risky – Type I or Type II?
  • False positive
  • True negative

Slide 23: Conclusion

• Two Questions:
  • What is an exotic?
  • Are exotics bad (harmful)?
• Practical philosophical suggestions:
  • Be explicit about terminology
  • Avoid confusing exotic and invasive
  • Even if some exotics are not invasives, the risks may be great

For more information contact jay@lclark.edu