Perlid Stoneflies Research Articles

Prey Preference of Stoneflies: Sedentary vs Mobile Prey

We investigated the effects of prey size and type (sedentary vs mobile) on prey preference in a predaceous stonefly, based on choice experiments and observations of the predator-prey interaction. We presented three size classes of black fly larvae (Prosimulium) to various sizes of the perlid stonefly Hesperoperla pacifica in laboratory experiments. Analysis by preference indices (a, e) indicated that small predators preferred small prey, large predators preferred large prey, and H. pacifica of intermediate size exhibited a weak, non-significant trend toward preferring prey of intermediate size. These results using sedentary prey, black fly larvae, are compared to previous results using a mobile prey, the mayfly Baetis. Encounter, attack, capture rates and handling times differ as a function of predator size, prey size, and prey type. The results of preference trials generally can be predicted from differential encounter, attack and capture rates, and similar preference curves may have different underlying causes. Small H. pacifica preferred small prey, mainly due to a much higher capture success. Large H. pacifica preferred large prey, due principally to higher encounter and attack rates. Offered a choice between Baetis and Prosimulium, stoneflies exhibited lower encounter and attack rates with Prosimulium, but much higher capture success, resulting in a net preference for black fly larvae. We suggest that laboratory results for attacks, captures and handling time can reasonably be extrapolated to animals in nature, thus lending insight into preference estimates based on gut analysis. However, encounter rates inevitably are influenced by details of the laboratory design and may bear little relation to nature.

Factors Influencing the Microdistribution of Two Sympatric Species of Plecoptera: An Experimental Study

The responses of nymphs of two species of perlid stoneflies to manipulation of some important features of their microhabitats were studied in laboratory stream tanks fitted with an infrared beam interruption system. The activity of both Paragnetina media (Walker) and Phasganophora capitata (Pictet) was significantly affected by current speed and substrate size, and by an interaction between the two. Regression analysis showed that activity for P. capitata was highest at 15 and 75 cm/s and minimal between 25 and 50 cm/s, while that for P. media was highest at 15 cm/s and lowest at 25 cm/s and above. For P. media there was a significant negative relationship between substrate size and activity at a current speed of 15 cm/s. The relationship between the activity of P. capitata and substrate size was not linear. Addition of trout skin mucus to the stream tanks caused an increase in the levels of activity of P. media but a decrease in the activity of P. capitata. Addition of nymphs of the mayfly Ephemerella subvaria to the tank containing P. media produced no effect. These findings suggest mechanisms that establish different microdistributions for sympatric species.

Perlid Stoneflies (Plecoptera) in an Appalachian Drainage: A Multivariate Approach to Mapping Stream Communities

Perlids were collected at 56 sites in the Little River drainage, Great Smoky Mountains National Park, Tennessee. Distributions were correlated with habitat variables (elevation, stream linkage number, gradient) which could be determined from topographic maps. Habitat amplitudes (elevation, stream number) of the five common species were: Acroneuria abnormis (300-1000 m, 1-310), A. carolinensis (500-700 m, 16-118), Beloneuria (600-1150 m, 1-8), Eccoptura xanthenes (500-1100 m, 1-118), Paragnetina immarginata (300-700 m, 64-310). Perlids were absent above 1150 m. A monothetic, divisive cluster analysis identified groups of associated species. Discriminant analysis using the habitat variables separated the three-group split with 75 % reliability and six groups at 55 o. The classification functions were used to predict the fauna of unsampled sites. Potential uses of the procedure include watershed mapping, sampling design, management prescription and impact evaluation.

Food habits and dietary overlap of perlid stoneflies (Plecoptera) in a tributary of Lake Ontario

Food habit studies were conducted on the nymphs of three species of sympatric perlid stoneflies from May to September 1979 in Orwell Brook, New York. A total of 1106 specimens were examined, which included 744 Phasganophora capitata, 251 Paragnetina immarginata, and 111 Acroneuria abnormis. Chironomids, trichopterans, and ephemeropterans were generally the principal, prey of all three species. Using Horn's measure of overlap, the monthly diets of P. immarginata and P. capitata were most similar [Formula: see text] and the diets of A. abnormis and P. immarginata[Formula: see text] least similar. Diel trends in food consumption during July indicated that the feeding intensity of both P. immarginata and P. capitata was the greatest from 2100 to 0500 hours. Examination of the guts of P. immarginata and P. capitata at 4-h intervals over a 24-h period showed that there was considerable variation in the diel diet composition of these species.

Resource division by perlid stoneflies (Plecoptera) in a lake outlet ecosystem

In a stream draining a productive lake, two abundant (250/m2) stoneflies Calineuria californica and Hesperoperla pacifica differed in population size structure, habitat use and food although overlap in resource use was extensive. Life cycles of two (Calineuria) and three years (Hesperoperla) were indicated. A multivariate analysis of habitat use demonstrated size dependent habitat selection in both species and between species habitat differences. Feeding habits differed although only the largest Hesperoperla had a food refuge. Diets of individual nymphs represented an interaction of species, size and habitat.