The life-histories of seven species of Nemouridae and two of Leuctridae have been investigated in Southern Ontario . Eleven sampling stations were chosen to illustrate the range of temperature conditions found in local streams .The Nemouridae and Leuctridae make up most of the stonefly fauna of the upstream cooler stations, but their numerical importance decreases considerably downstream .There is a definite seasonal succession of the species : Soyedina vallicularia, Prostoia completa and Shipsa rotunda appear in late spring, Nemoura trispinosa, Amphinemura delosa and A . nigritta in early summer, Leuctra tenuis in midsummer and A . linda in late summer. L . ferruginea emerges throughout most of the summer, at least in the headwater streams .All the species are univoltine, except La ferruginea which is usually semivoltine . Most Nemouridae, A . spp ., P. completa and S. rotunda undergo a long embryonic diapause, whereas N. trispinosa and S. vallicularia develop directly. The nymphal development of N. trispinosa was compared in three streams ; although the general pattern is similar, the growth is much more synchronized in the warmest station . There appears to be 16 nymphal instars in this species .L . ferruginea was common in seven stations ; in the coolest, the life-cycle lasts two years, but in the warmest, many specimens succeed in completing their cycle in one year .
1986. Microhabitat-preference curves of biackfly larvae (Biptera: Simuliidae): a comparison of three estimation methods. Can. J. Fish. Aquat. Sci. 43: 1235-1241.Three analytical techniques are available to describe the observed response of stream-dwelling organisms to variations in their physicochemical environment: the incremental method, polynomial regression on a single factor, and multiple regression. The efficacy of these tools as descriptors of the responses has not been compared. We used the three methods to describe density and microhabitat-preference curves for Pacssimulium rnixturnjfuuscum, Stegopterna mutata, and Sirnudiurn aureum in response to distance from the lake, current velocity, and water depth in a stream draining a Laurentian lake. The incremental method yielded the least precise estimates of density and biased estimates of optimal current velocity for two of the three species; multiple regression yielded the most precise estimates sf density and unbiased estimates of optimal conditions, whereas polynomial regression on a single factor was intermediate. From this comparison, we suggest that the multipleregression approach to estimate microhabitat-preference curves be used in developing optimal management stategies. Further, we suggest that rare species should be excluded From such analysis because of the low precision of density estimates for rare organisms.Trois techniques d'analyse sont disponibles pour dkcrire la reaction qu'on observe chez les organismes qui habitent les cours d'eau face aux variations de leur milieu physico-chimique : la methode des charges croissantes, la r6gression polynorniafe a un seul facteur et la regression multiple. On nfa pas compare I'efficacite de ces outils comme descripteurs des reactions. Nsus avons utilise les trois methodes afin de decrire les courbes de densit6 et de pr6ference en matiere de rricrohabitat pour Paosirnuliurn rnixt~rnjfuuscum, Stegopteana rnutata et Sirnulium awreurn en reponse 5 la distance par rapport au lac, 5 la vitesse du courant et a la profondeur de &'eau dans un ccsurs d'eau qui draine un lac de la region laurentienne. La rnethde des charges croissantes a donne les estimations Bes moins prkcises de la densitk et des estimations faussees de la vitesse sptimale du courant pour deux des trois especes; la regression multiple a donne les estimations les plus precises de la densite et des estimations non fausskes des ,conditions optimales tandis que la regresson polyncsmiale 2 uw seul facteur a donne des resultats interrnediaires. A partir de cette corn paraison, nous propssons d'utii iser I'apprsche de la rkgression multiple pour estirner les courks de preference en matiere de microhabitat lors de I'klaboration des strategies de gestion optirnale. En outre, nous estimons qu'il faut exclure lles especes rares de ce type d'analyse en raison de la prkcision peu elevee des estimations de la densit6 pour ce qui est des organismes rares.
The nymphs of several winter stoneflies, Taeniopteryx burksi, T. nivalis, Brachyptera fasciata, Capnia manitoba, Allocapnia granulata, A. pygmaea, and A. vivipara, undergo a diapause during the summer. The diapause determines external morphological changes, which are described. This adaptation enables the species to inhabit streams that reach high temperatures or dry up during the summer; its advantages over the more common embryonic diapause are that it permits the nymphs to grow in both spring and fall and to seek a convenient site in which to aestivate.
The drifting of invertebrates was sampled for six 24-
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