Our Livins; Rfsoiines — Inverrehrales 



I7.i 



based on a priori knowledge of species richness 

 and patterns of endemic species occurrence. 



The number of resident butterflies was deter- 

 mined by counting the number of species 

 recorded for each state or region. Species 

 i^nown to be nonresidents (vagrants or sporadic 

 residents) in a particular state or region were 

 excluded. For the three moth families, all 

 species recorded in a particular state or region, 

 including vagrants, were included in the counts. 



The reader should be aware that the quantity 

 and quality of the data are not sufficient to ana- 

 lyze temporal trends for individual species. In 

 addition, all geographic units have not been 

 sampled with equal intensity. 



Status and Trends 



In the 17 western states. 915 species of but- 

 terflies and moths in the studied groups are 

 recorded. The number of species ranges from 

 181 (20% of total species count) for North 

 Dakota to 520 (57% of total species count) for 

 Texas (Table 1). In general, there are fewer 

 species of butterflies and moths in more north- 

 em states and in states with less topographic 

 diversity, which creates less variety in tenain. 

 Of course, larger states tend to have more 

 species than smaller states, since large states, on 

 average, have more diverse habitats and topog- 

 raphy. These trends are similar to those of other 

 organisms as well. 



The patterns for butterflies and the three 

 moth families are similar, except that species 

 richness of hawkmoths is unexpectedly high in 

 Nebraska and Oklahoma (Table 1 ). most likely 

 because of the immigration of nonbreeding 

 tropical species (Smith 1993). 



Each of the five subregions is smaller than 

 Washington, the smallest western state, yet 

 species richness is greater in all subregions 

 (except the Lower Rio Grande) than in nearly 



Table 1. Number of species of selected Lepidoplera by 

 state. 



State 



Area 

 km^ (mi^) 



Hawk- 

 moths 



Silk- Tiger Bulter- 

 motlis moths flies 



Total 



two-thirds (11 out of 17) of the states studied 

 (Table 2). The richest subregion. with 273 

 species, is the sky islands of southeastern 

 Arizona and southwestern New Mexico. 

 Species richness is second highest in the Front 

 Range of Colorado, which straddles the 

 Continental Divide and includes a large eleva- 

 tional range and diverse habitats ranging from 

 prairie to alpine tundra. The relatively small 

 Lower Rio Grande Valley has the fewest species 

 of the five subregions, but still has more species 

 than some states that are almost 15 fimes as 

 large. Moreover, the best remaining native 

 habitats in this subregion amount to only a few 

 thousand hectares. Sampling intensity is rela- 

 tively high for the Front Range, sky islands, and 

 southern California, but increased sampling 

 efforts in the Lower Rio Grande Valley and Big 

 Bend might add significant numbers of species. 

 Each subregion has a distinct butterfly and 

 moth fauna that includes many endemics — 20 

 or more are potential candidates for listing as 

 endangered species. Each of the four subregions 

 that adjoin the Mexican border also hosts from 

 a few to many Mexican species that occur 

 nowhere else in the United States. 



^Lower Rio Grande Valley includes all of Cameron. Hidalgo, Willacy, and 



Starr counties, TX 



''Big Bend includes ail ol Brewster, Jeff Davis, and Presidio counties, TX 



■^The Colorado Front Range includes all ol Boulder, Clear Creek, Custer, 



Douglas, El Paso, Fremont, Gilpin, Grand, Huerfano, Jackson. 



Jefferson, Larimer, Park, Pueblo, Summit, and Teller counties. 



''Sky islands include all ol Cochise and Santa Cruz counties, the eastern 



half of Pima County, AZ, and all of Hidalgo County, NM 



'^Southern California includes all of Imperial, Los Angeles, Orange, 



Riverside, San Bernardino, and San Diego counties. 



The highest species richness of western 

 Lepidoptera is in the Southwest, usually in 

 areas that adjoin the Mexican border. 

 Invertebrates are seldom considered in manage- 

 ment plans for parks, preserves, or refuges, and 

 their management needs are often not the same 

 as those for vertebrate wildlife or plants. 

 Processes unfavorable to Lepidoptera diversity 

 include overgrazing, overuse of controlled 

 bums, urbanizafion, and excessive modification 

 or recreational use of selected specialized 

 ecosystems such as wetlands and dunes. 

 Because invertebrates account for more than 

 90% of animal species, it makes good sense for 

 managers to address the health and populations 

 of these species in planning and in making man- 

 agement decisions. Management which favors 

 high Lepidoptera species richness is usually 

 similar to that which favors natural ecosystem 

 processes and the maintenance of extensive 

 native plant populations. 



1 , Lower Rio Grande Valley, Texas 



2, Big Bend, Texas 



3, From Range, Colorado 



4 Sky islands, Anzona and New Mexico 



5 Southern California 



■^ 



Fig. 1. Western United States 

 showing five subregions of fiigh 

 species richness. 



Table 2. Number of species of 

 selected Lepidoptera by subregion. 



Two tailed swallow-tail [Papilio 

 nmlticaudata). 



Tiger moth [Gnopluiela venmcula- 

 ta). 



