9530

• UCREFRP Catalog Number: 9530
• Author: Nelson, S. M. and D. C. Andersen
• Title: Butterfly ‎(Papilionoidea and Hesperioidea)‎ Assemblages Associated with Natural, Exotic, and Restored Riarian Habitats along the Lower Colorado River, USA
• USFW Year: 1999
• USFW - Doc Type: Regulated Rivers
• Copyright Material: YES

486
S.M. NELSON AND D.C. ANDERSEN
described by early investigators as `jungle' (Grinnell, 1914; Brown, 1923). In areas of near-surface ground
water, salt grass (Distichlis spicata) was common (Brown, 1923). Lagoons and marshes, formed from
abandoned. stream channels, were often present at some distance from the river and usually replenished
with flood waters every year (Brown, 1923). The rarely flooded Second Bottom was characterized by
mesquite (Prosopis spp.), saltbush (Atriplex spp.); and creosote bush (Larrea tridentata) (Grinnell, 1914).
River regulation and trans-basin diversion has promoted both invasion of exotic plants and conversion
of floodplain landscapes to irrigated agriculture. Exotic tamarisk (Tamarix ramosissima) now often
dominates non-agricultural riparian areas along the lower Colorado River, and areas of original
vegetation types, especially those associated with the First Bottom, are very rare (Ohmart et al., 1988).
The prediction by Sykes (1937) that river regulation and agriculture would cause the `luxuriant vegetation'
along the river to become desert-like has in large part come true. In response to these changes, attempts
are being made to restore some tamarisk-dominated sites to a condition more like that of the historic
riparian ecosystem.
Assessment of the environmental quality of revegetated areas relative to that of the historic riparian
ecosystem is difficult, in part because baseline data on the structure and dynamics of desert riparian
assemblages maintained by a highly irregular flow regime are either limited or lacking. Despite these
limitations,. butterfly assemblages may be useful for. investigating these riparian ecosystems., Collection. is
practical, natural histories-are relatively well-known, and taxa richness is. high in most areas. Sensitivity
of butterfly species to environmental. perturbations varies from sensitive to resilient; with various species
sensitive'td vegetation changes, fragmentation of habitat; and pesticides: Although direct measurement" of
vegetation"'can provide insight into the effects of altered flows, vegetation °may be slow to respond fo
environmental change. For example, cottonwood and willow may persist for many .years in a " non-
functioning ecosystem: Because of their rapid response to environmental perturbation, butterfly assem-
blages," particularly in this situation, can. serve to integrate riparian vegetation, fragmentation, and
ecological processes and provide a responsive measure of biodiversity (i.e., .composition,. structure, and
function). -
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The purpose. of this study was to determine whether the structure of the butterfly assemblage associated
with revegei'ated sites tends towad-that'assbciated~wlth "natural'riparianxlaridsca`pes as plantings~mature
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Figure 1. Comparison of non-regulated (1904-1935, n = 32) and regulated (1936-1964, n = 29) flows in the Colorado River at
Yuma, Arizona. Values shown are averages of mean daily discharge by month. Vertical bars around averages enclose the middle half
of the data (25th to 75th quartiles). Data from US Geological Survey 1954, 1964 and 1970
Copyright ©1999 John Wiley & Sons, Ltd. Regut. Rivers: Res. Mgmt. 15: 485-504 (1999)