20 Jan 2008, 6:50pm
by admin

Anthropogenic Fire and the Quino Butterfly

By Dr. Greg Brenner, consulting entomologist

Regarding a recent news article concerning Quino butterflies [here],

The Quino checkerspot butterfly (Euphydryas editha quino) is part of the Euphydryas editha species complex that has diverged phenotypically into geographical set of populations, each recognized as a separate subspecies among Lepidopterists. Subspecies are erected because, to the trained eye, there are consistent differences between populations. The differences are often difficult to distinguish, and at times appear to be imaginary. However, whether or not subspecies should be designated as endangered when the species complex occurs over a larger area and is surviving quite well is discussion for another post.

Conservation of the Quino checkerspot and its sister species will depend largely on the continued existence of their larval host plants. These butterflies inhabit openings within or in the vicinity of shrublands, grasslands, meadows, and lake margins. Their presence is closely tied to their larval host plant, dwarf plantain (Plantago erecta) that inhabits chaparral, coastal sage scrub and valley grassland plant communities. These plant communities are fire-adapted vegetation types and many of their component species require fire to regenerate new growth or allow seeds to germinate.

Fires in chaparral often result in a mosaic of various-aged habitats, with different plant species dominating the landscape over time as post-fire vegetation dynamics occur. Very recently burned areas of chaparral may be devoid of any surface vegetation, but these areas typically support resprouting shrubs, as well as species that principally reseed only after a fire, and particularly if adequate rainfall occurs.

In areas where fires do not occur over a long period of time, the structures of these communities typically become tall and dense, with relatively few species compared to the period immediately after a fire. This leads to a reduced number of ecological niches in unburned areas, and the less diverse habitat supports a less diverse range of wildlife species. Fires open up habitats, and thus support a greater diversity of wildlife in a given area.

Studies have shown that fire enhances native species richness (see Harrison, Inouye, and Safford (2003) Ecological Heterogeneity in the Effects of Grazing and Fire on Grassland Diversity. Conservation Biology 17 (3), 837­845). This suggests that fire can be used to manage native species diversity.

Entomologists have recognized fire as a management tool, and have recommended episodic disturbances such as fire and light grazing to create and maintain suitable habitat for species like the Quino checkerspot butterfly (QCB). In their study of the endangered Quino checkerspot butterfly, Mattoni, Pratt, Longcore, Emme and George (1997 Journal of Research on the Lepidoptera 34:99­118) found:

Areas on the western side of Otay Mountain occupied by QCB in 1997 were in early post-burn succession. Adult QCB, Plantago erecta, and ample nectar sources were found throughout recently burned areas. QCB distribution was limited by the edge of the burn, which was marked by dense, mature chaparral. Although in some areas P. erecta distribution is stable, it can also be found tracking disturbance, with a distribution variable in both space and time. Like other “fire-followers,” P. erecta grows well following disturbance (usually fire, but also other one-time events), sets large amounts of seed, and then thins out as the canopy is closed by the regenerating shrub layer. The regionally dynamic metapopulation structure of the QCB is adapted to such geographic and temporal variation in foodplant distribution.

If Downey is correct that “the black-and-orange-checkered insect once numbered in the millions” it is because it thrived in a landscape inhabited by American Indians who managed their environment using fire. They unlocked the dense chaparral and tended plants that would enhance their own survival. The result was the survival of other plants on which wildlife fed, including dwarf plantain, the larval host plant of QCB.

This is also true of thousands of insect species. The most rare are those associated with open habitats, once maintained by fire, but now lost to encroaching overstory. Strong evidence suggests that anthropogenic fire, not “natural” fire, engendered extensive prairies and other frequent disturbance environments throughout the West.

Concrete is not what is limiting Quino checkerspot butterfly populations; it’s the lack of food plants that is the problem. The butterflies need frequent, regular, seasonal anthropogenic fire to unlock the chaparral and allow their host plant species to regenerate and thrive.



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