Emergence and Flight Activity of Alpine Stream Insects in Two Years with Contrasting Winter Snowpack

Figures & data

Figure 1 Hydrographs for 2002 (black diamonds, lines) and 2003 (gray circles, lines) during the peak runoff season on the Big Thompson River at 2400 m a.s.l. in Rocky Mountain National Park. Data from U.S. Geological Survey gage #402114105350101 (http://water.usgs.gov). Note that the use of black for 2002 and lighter colors for 2003 continues in all figures.

Figure 2 Cumulative proportions of the total catch of the six most common lotic species at different dates during the study period: (a) Asynarchus nigriculus, (b) Ameletus celer, (c) Cinygmula spp., (d) Stegopterna acra, (e) Alloperla pilosa, and (f) Zapada haysi. Parenthetic letters following species names indicate higher taxon: E  =  Ephemeroptera, P  =  Plecoptera, T  =  Trichoptera, S  =  Simuliidae. Black represents 2002 and white represents 2003 collections. Note that dates are not equally distributed and are more densely clustered in July, a peak emergence period for several species. In part f, 2002 collections began 8 July, after the Z. haysi emergence period had begun; hence the absence of 2002 data in the first two time categories.

Table 1 Total numbers of males (m) and females (f) collected for each higher-level taxonomic group and common species, and total species richness within higher-level groups across all traps in 2002 and 2003. Sex ratios marked with stars are significantly different from 1:1 (***p < 0.001; **p < 0.01; *p < 0.05).

Table 2 Lateral dispersal statistics for each major taxon and common species within each, along perpendicular transects in each of two years. R ², slope, and p-value are for the best-fit models for each order. ND  =  not decreasing (p-values > 0.2 for decreasing slope). P-values in bold are those significant at α  =  0.05.

Figure 3 Total numbers collected per year of each of the four major taxa as a function of trap distance from the stream. Filled diamonds are 2002 and open squares are 2003 values. Lines (solid—2002; broken—2003) are fitted functions as per Table 2 and are included only in cases of significant decrease.

Table 3 ANCOVA results summary. Note that ANCOVA was only assessed for taxa that showed significant decrease with distance according to regression of number collected on distance from stream for either or both 2002 and 2003. See Table 2 (“best model”) for transformations made to achieve linearity for the ANCOVA for each taxon. P-values in bold are those significant at α  =  0.05.