The article on the webpage titled "Keeping All the Parts" addressed the importance of maintaining biodiversity in naturally functioning park ecosystems and explained that many species are dependent on other species for their continued survival. In most cases, plants and animals depend on a wide range of species for their continued survival. For example, deer and elk depend on a wide range of species of plants for food, although they may prefer some foods over others. In situations where preferred food is not available, they switch to other plants.
Not all species are so lucky. Many plants and animals are dependent on one or a very few species for some aspect of their survival. Most of us realize that pandas would rapidly disappear if their only food, bamboo, were to go extinct. We don't realize this can be true for many species much closer to home. For example, the caterpillar stage of the Snow's skipper butterfly (Paratrytone snowi), known from Rocky Mountain National Park, has mountain muhly grass (Muhlenbergia montana) as its only food source (its host plant). Scientists estimate that for 99 species of plants that have gone extinct, 69 species of beetles and two species of butterflies that were dependent on them have also disappeared (Lian Pin Koh et al., Science 305, 1632 (2004)). It is called co-extinction when the species and its dependent associates all go extinct.
Further, we cannot forget that while plants and animals may appear to grow independently, most have much smaller species that may not be visible to us, but may be totally dependent on them. They may have even smaller species dependent on them. Ogden Nash best explained it in verse:
Big fleas have little fleas \ Upon their back to bite'em
And little fleas have lesser fleas \ And so ad infinitum.
Thus a multitude of species are dependent on one species we can see. Loss of this key species would result in loss of all its dependents. Endangerment of the key species would result in co-endangerment of its dependents.
Finally, many more species are dependent on only a very few foods, host plants, etc. and thus would be put at a severe disadvantage if one of their major food sources were to disappear. One park example is the Scudder's sulphur butterfly (Colias scudderi). Park researchers suspect the recent decline in Scudder's sulphur butterflies in some areas of the park may be related to the extensive browsing by elk on willows, a major host plant for the butterfly's larvae.
The issues of possible co-endangerment and co-extinction make the park's mandate to preserve the natural biodiversity even more challenging."Keeping all the parts" is not as easy as it sounds!