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Endangered organisms receive varying levels and labels of severity for their plight, depending on the categories of the labeling agency.  However, the endangered organisms all bear high risk for total disappearance due to altered habitat, diminishing population, and increasingly unsuitable form.

My own scheme (NOT formally recognized) for grouping specific causes of endangerment and extinction has four basic classes; natural, over-exploitation, habitat modification, and introduction.  All species will eventually disappear upon replacement by new creatures having better adaptations to changing environments.  This is natural.   It also is not a uniform process; losses and replacements tend to occur in clusters both in time and space.  At present, however, there is an ongoing acceleration of this process much exceeding the "geologic average", and a relatively new environmental factor is responsible--humans.  Below are just eight North American examples illustrating the variety of endangerment causes.

[NOT YET FUNCTIONAL]

PLEISTOCENE EXTINCTIONS

There are significant obstacles to explaining the mass disappearance of organisms.  One is that they do not often coincide well with the timing of major environmental changes.   The graph below shows a peak of large mammal extinctions, yet the peak does not coincide closely with the last glacial maximum, the Bering land bridge, or the arrival and development of human societies.  A second problem (not evident in this graph) is the selectivity of extinctions; only large carnivorous and scavenging birds suffered similar losses--few plants, smaller mammals, reptiles, fish, insects, or small birds disappeared at the peak of mammal extinctions.

[still looking for the various references...]

A third challenge to explanation is the apparent discrepancy between extinction waves that occurred in disparate locations.  The timing map below indicates that apparent peaks of disappearance times for large mammals differed between continents, and implies regional (or realm-centered) rather than global triggers.

compiled from Pielou 1991and others

And as if explanation is not elusive enough, there is also the discrepancy between the origin of the survivors versus the lost.  Among North American Pleistocene large mammals, the listing below suggests that enormous inequity existed for the likelihood of becoming extinct, and high incidence appears strongly associated with North American origin or presence exceeding one million years.  Few Old World origin newcomers disappeared; many New World mammals did.

compiled from Pielou 1991and others

HISTORICAL-ERA EXTINCTIONS

NOTE!!!  Updates with many revisions and additions are under development at:

• http://www.uwsp.edu/geo/faculty/heywood/Geog358/endangr/HistExti.htm

• http://www.uwsp.edu/geo/faculty/heywood/Geog358/endangr/extinctb/extinctb.htm

• http://www.uwsp.edu/geo/faculty/heywood/Geog358/endangr/extinctm/extinctm.htm

We run into a problem with what constitutes "historical era".  Arbitrarily, I present this as since the advent of "modern" technology, or basically since about 1500 AD.  There are, however, a few instances of earlier extinctions preceeding this date that I include and still attribute to human capability (especially in landscape modification).

More importantly, escalating human populations and their capacity to modify their surroundings are a significant influence on modern rates of extinction and endangerment.   As examples I focus here on the "cute and cuddlies", particularly birds and mammals, because they are noticeable, imaginable, and therefore better documented than other organisms.  However, other classes of organisms face similar levels of threat, regardless of our emotional affinity towards them.

These examples and inventories are symptomatic, but not inclusive.  My primary interest is to demonstrate spatial patterns of loss, not resolve taxonomic arguments.  That is the realm of biologists, ornithologists, and zoologists; my one remark on the taxonomy issue is that the vast majority of these extinctions are of subspecies, not full species.   Be aware that the dot hotspots are only what I can find docimentation for at present; I have little doubt that there are many more.

The spatial patterns are remarkable, however.  Note the concentrations on islands, at lower latitudes, and in proximity to the oceans.   These tendencies are not coincidence.  Note also that, for the most part, the concentrations of extinction do NOT coincide with the spatial concentrations of human occupancy; it is the fringe areas of recent or occasional human contact where the losses are greatest.

Of the several hundred historically extinct creatures below, nearly all had several of the following characteristics that rendered them helpless:

• few defensive traits (often because of few natural enemies)

• low mobility (flightlessness, slow motions, few dispersal mechanisms, etc.)

• high visibility (large size, vivid colors or patterns, attractive motions, etc.)

• docile nature (tame, fearlessness, inquisitive)

• small population (often dictated by small available area)

• small or unique habitat area

• isolation, especially over long periods of time

• slow reproductive and maturation rates

• extreme niche specialization

• low resiliance to disturbance

There are now two additional threats, both largely due to human actions.  The first is importation of disturbance-adapted foreign competitors.  The second, only recently receiving much recognition, is genetic alteration and hybridization.   Either of these poses the prospect for pushing even more endangered organisms, which somehow survived the direct exploitation and habitat modification, over the brink of extinction.

BIRD EXTINCTIONS

NOTE!!!  Updates with many revisions and additions are under development at:

• http://www.uwsp.edu/geo/faculty/heywood/Geog358/endangr/HistExti.htm

• http://www.uwsp.edu/geo/faculty/heywood/Geog358/endangr/extinctb/extinctb.htm

• http://www.uwsp.edu/geo/faculty/heywood/Geog358/endangr/extinctm/extinctm.htm

MAMMAL EXTINCTIONS

NOTE!!!  Updates with many revisions and additions are under development at:

• http://www.uwsp.edu/geo/faculty/heywood/Geog358/endangr/HistExti.htm

• http://www.uwsp.edu/geo/faculty/heywood/Geog358/endangr/extinctb/extinctb.htm

• http://www.uwsp.edu/geo/faculty/heywood/Geog358/endangr/extinctm/extinctm.htm

Be aware that mammal extinction details tend to have less secure documentation.  The "indeterminate" cases here probably reflect reporting biases, and have particularly weak literature support.   As before, however, it is less the veracity of any single case, than a cumulative pattern, that is noteworthy.

adapted from Nillson (1983) and UNESCO data

REFERENCES

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N. C. Heywood maintains this page, last updated 08AUG00.