Ecological significance rating and degree of remnant-dependency

    Two different measures of the degree to which each butterfly species is associated with, or indicative of, undisturbed natural habitat are given here:  the "environmental significance", as formulated by John K. Bousemann and James G. Sternburg in the "Field Guide to Butterflies of Illinois",1 and the degree of "remnant dependency" as described by Ron Panzer, et. al. in "Prevalence of Remnant Dependence Among the Prairie- and Savanna-inhabiting Insects of the Chicago Region".2

    The "environmental significance" of each butterfly is ranked on scale from 1 to 10 by Bousemann and Sternburg.  The definitions for the numerical rankings are as follows:

1.  An introduced species.
2.  A rare vagrant.
3.  A migrant that rarely breeds in Illinois.
4.  A migrant that regularly breeds in Illinois.
5.  A species with weedy larval hosts, found in waste areas, old fields, pastures, roadsides.
6.  A species of urban forests and woodlands, as well as forests.
7.  A common species restricted to forests.
8.  A local species of forests.
9.  A local species of prairies and open grasslands.
10.  A very local species of marshes, dunes, and other restricted habitats.
    One can see that roughly as the number increases from 1 to 10, the value of the butterfly as an indicator of the quality of the habitat in which it is found increases.  Migratory butterflies like the Monarch, although they are magnificent butterflies, travel extensively throughout the US and feed on a common varieties of milkweed as caterpillars.  So the presence of Monarchs in a natural area does not tell us much about the quality of the habitat.  (Monarchs get a 4.)  On the other hand, Eyed Browns feed as caterpillars only on native sedges in wetlands, and the adults rarely stray from the wetland habitat in which they developed.  Eyed Browns tend to be found only in relatively undisturbed wetlands, so their presence tells us something about the quality of the wetland. (Eyed Browns get a 10.)  Since "Field Guide to Illinois Butterflies" does not include skippers, I do not have an environmental significance rank for the skippers.

    The degree of "remnant dependency" is indicated here as "R" for remnant-dependent and "r" for remnant-associated.  "Remnant-dependent" refers to a species which is found almost only in natural area remnants.  "Remnant-associated" means a species is mostly found in natural area remnants but may also be found in somewhat disturbed environments.  A discussion of these concepts and some of the research that underlies the determination of remnant dependency may be found in "Prevalence of Remnant Dependence Among the Prairie- and Savanna-inhabiting Insects of the Chicago Region", by Ron Panzer, et. al.2  The degree of remnant-dependence ascribed to these species in the Fermilab butterfly list is taken from "Butterfly Monitoring Network's Guide to the Butterflies of Illinois", compiled by Doug Taron and edited by Mel Manner3.  Quoting from the latter source, "The remnant reliancy refers to how reliant a species is on high quality natural areas to survive. If it is highly remnant reliant, it will only be found in the proper natural habitat.  If it is somewhat remnant reliant, it may be able to tolerate some disturbance and loss of quality to its habitats."

    I include both of these ecological ratings since the judgments by these authors of the degree to which a butterfly is restricted to natural areas differ from one another in a few cases.

1.  John K. Bouseman and James G. Sternburg, "Field Guide to Butterflies of Illinois," Illinois Natural History Survey, Champaign, Illinois, 2001.
2.  Ron Panzer, et. al., "Prevalence of Remnant Dependence Among the Prairie- and Savanna-inhabiting Insects of the Chicago Region",  Natural Areas Journal 15:101-116, 1995.
3.  Doug Taron and Mel Manner (editor), "Butterfly Monitoring Network's Guide to the Butterflies of Illinois", published privately.