Nature Notes

Volume XXVI - 1995

Mimicry Among the Pines?
By Ron and Joy Mastrogiuseppe

The deep blue of Crater Lake is enhanced by the verdure of the coniferous forest around it. Splashes of green unite in harmony with multicolored volcanic bluffs in the caldera landscape. Distance masks the variety of species in these green areas. There is a certain pleasure in recognizing species by name, but even with a close view, walking among the noble conifers, there are striking similarities in the appearance of different members of a genus such as Abies, the true firs.

Sometimes these similarities obscure their differences. Such difficulty in distinguishing species is more challenging if seed cones are unavailable at the time identification is made. Since seed cones of the true firs disintegrate at maturity, features such as cone shape, cone scales, bracts, and seeds may not be available for inspection. This lack of essential diagnostic features can frustrate a desire to classify and distinguish a species by name.

Even when the important diagnostic features are present, species distinction may be confusing at times. In the late 1970s it was reported that Jeffrey pine, Pinus jeffreyi, occurs in the forested panhandle of Crater Lake National Park. The most northerly known natural populations of this tree occur, however, on serpentine substrates near the Illinois Valley southwest of Grants Pass. The biologists reporting Jeffrey pine in the panhandle (some 100 miles northeast of those Illinois Valley populations) based their determination primarily on seed cones which did not appear like cones of typical ponderosa pine, P. ponderosa. Apparently those biologists were unaware of another contender, P. washoensis, a rare pine similar to ponderosa but with smaller cones. As it turned out, the ponderosa variants in the panhandle are actually closer to Washoe pine than to Jeffrey pine based on cone length and diameter. There still is the need, however, for additional study of local populations as one part toward understanding variation on a larger geographic scale because the widely-distributed variants of ponderosa pine are so difficult to interpret.

If we shift our attention from three-needled pines to members of the genus whose needles are borne in clusters of five, each life zone (a concept which largely corresponds to elevation in this part of the Cascade Range) within Crater Lake National Park may be characterized by a different species. Sugar pine, P. lambertiana, of the mixed conifer forest bears foliage which resembles that of western white pine, P. monticola, which typically grows in association with more high elevation true firs such as red and noble fir within the A. magnifica/procera complex. When sugar pine and western white pine occur in overlapping habitats, younger trees of both species look alike. We can also find species very distinct taxonomically but adapted to similar habitats and displaying an amazing degree of similarity in a number of characteristics during each life stage. For example, whitebark pine, P. albicaulis, of the upper caldera rim area is strikingly similar to limber pine, P. flexilis. Although limber pine is absent at Crater Lake today, it typically occurs in subalpine habitats in the northern Rocky Mountains, much of the Great Basin, and the eastern Sierra Nevada, where there are some areas that whitebark and limber pine grow together. Strangely enough, limber pine is Oregon's rarest conifer, with the state's only known populations occurring in the Wallowa Mountains some 300 miles northeast of the park.

In asserting that many species look much alike, we may wonder what is a species? It is generally regarded as a group of similar individuals which are reproductively isolated from other groups. Although members of a species share many characteristics, variation is inherent. Hidden within the forest canopy are many seed cones nurturing potential trees. Formed through the genetic mystery of reproduction, the seeds bear an awesome responsibility in perpetuating their kind in all its variation. In conifers, the messenger of similarity and difference becomes the wind as it carries vast quantities of pollen to receptive young cones. Differences in timing of pollen release and of conelet receptivity act as barriers to cross-pollination between different species.

Recognition of species is not only rewarding, but also crucial to understanding interactions among trees, their physical environment, and the creatures that depend on the trees. Coevolution is the reciprocal evolution of two species, in that one species adapts to evolution in the other. If, for example, we have a specific insect and a plant on which it depends for food, an evolutionary change in the chemistry of the plant might make it less digestible by the insect species. Those individuals of the insect species which are still able to digest the plant tissues survive and reproduce. Thus the evolutionary change in the plant has led to an evolutionary change in the insect.

Sometimes coevolution or coadaptation results in mimicry. This is the close resemblance of one species to another, stemming from pressures acting to select for those individuals in the "mimicking" species which resemble the "mimicked" species. Mimicry may have various advantages to a species, including protection from predation, thereby favoring their survival. But is this the case in conifers? Pines are subject to predation by a multitude of herbivorous insects which, at least in some cases, identify pine species based on the unique chemistry of their resins. It is unknown at present if there are any cases where resins of one conifer species have, over time, come to include a certain compound or compounds which cause insects to avoid another species. This would happen through the chance occurrence of the compounds in individuals which would then be more likely to survive and reproduce.

In some cases, experts may be faced with perceived differences which do not justify separation into distinct species. This is the challenge facing the biosystematist in evaluating the degree of difference necessary to separate species. The classification of organisms necessarily includes some subjective evaluation because lumping all similar species into one group on some "objective" basis (thereby ignoring their interesting differences) would compromise our understanding of the species' respective ecological roles and the limits of their environmental ranges. With the term "species diversity" becoming increasingly important in discourse about the biological conservation of organisms, it seems obvious that careful thinking and humility are needed when trying to assess ecological quandaries posed by forces difficult to quantify. Those who oversimplify and arrogantly generalize about our world do so at their peril, as Alexander Pope noted almost three centuries ago:

Go, wond 'rous creature! mount where Science guides,
Go, measure earth, weigh air, and state the tides;
Instruct the planets in what orbs to run,
Correct old Time, and regulate the Sun;
Go, soar with Plato to th' empyreal sphere,
To the first good, first perfect, and first fair;
Or tread the mazy round his follow 'rs trod,
And quitting sense call imitating God;
As Eastern priests in giddy circles run,
And turn their heads to imitate the Sun.
Go, teach Eternal Wisdom how to rule -
Then drop into thyself, and be a fool!

Ron and Joy Mastrogiuseppe are former seasonal employees at Crater Lake. They are now based in Burns, Oregon, where he is an ecologist and she works as a botanist.

sketch of trees
Amy Mark, NPS files.

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