... point.¹

Of course, I'm a population geneticist, so this way of thinking about the world comes naturally to me. If it doesn't come naturally to you and you don't find this analogy useful, feel free to ignore it.

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... diversity,²

You can find a brief survey of them in the Appendix if you're interested.

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... components.³

If you happen to have run across $F$-statistics in population genetics, you know what I'm referring to. If you haven't, don't worry about it.

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... Circle:⁴

This section draws heavily from [11, pp. 73-89].

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... islands.⁵

I don't find this argument particularly convincing. The biotas of temperate (e.g., Juan Fernandez, New Zealand), subtropical (e.g., Canary) and tropical (e.g., Hawaii) islands have all been dramatically altered through species introductions. It is, however, difficult to be certain that this is because island communities are more ``open.'' It could reflect habitat alterations that make them more suitable for aliens than natives.

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... communities.⁶

Again, it is difficult to be certain the low diversity of agricultural systems causes their susceptibility to invasion by exotics. Changes in the biotic and abiotic environment associated with agriculture might simply make it a more suitable habitat for new introductions than native species.

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... resistant⁷

Is this the same as stable?

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... effects⁸

functional effect: the effects that a species has on some aspect of ecosystem function.

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... response⁹

functional response: the way in which a species responds to changes in the ecosystem.

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... any?¹⁰

Even the earth's ecosystem taken as a single unit doesn't satisfy this definition. It depends critically on continual energy input from the sun. Perhaps the way to say it is that there is no variation in relevant external inputs to the system.

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... components.¹¹

It's not entirely circular because, as the example of the gyroscope makes clear, it's also possible for simple systems to be dynamically stable.

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... perturbed¹²

We'll see a good example of this when we talk about changes associated with some plant invasions later in the course.

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... rates.''¹³

Angermeier and Karr, BioScience 44:690-697; 1994

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... Taillie¹⁴

Patil, G. P., and C. Taillie. 1979. An overview of diversity. In Ecological diversity in theory and practice, ed. J. F. Grassle, G. P. Patil, W. K. Smith, and C. Taille, pp. 3-27. Intl. Co-operative Publ. House, Fairland, MD.

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... community.¹⁵

Note: this approach does not take account of either ecological or evolutionary distinctiveness.

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