Corixidae (Hemiptera) of an evolved Lake in the English lake District

Abstract

1. Lake District lakes have changed at different rates since their formation, according to the hardness of the rocks around them. They can, therefore, be arranged in an evolutionary series, three criteria for determining their position in the series being transparency of the water, percentage of drainage area cultivable, and percentage of lake shore rocky. The extent of reed-bed development is another criterion. 2. Previous work in lakes and tarns has shown that, as organic matter accumulates on the bottom, there is a succession of Corixid species: — % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqaqpepeea0xe9qqVa0l% b9peea0lb9Lq-JfrVkFHe9peea0dXdarVe0Fb9pgea0xa9W8qr0-vr% 0-viWZqaceaabiGaciaacaqabeaadaqaaqaaaOabaeqabqaq-laabc% cacaqGGaGaaeiiaiaabccacaqGGaGaaeiiaiaabccacaqGGaGaaeii% aiaabccacaqGGaGaaeiiaiaabccacaqGGaGaaeiiaiaabccacaqGGa% GaaeiiaiaabccacaqGGaGaaeiiaiaabccacaqGGaGaaeiiaiaabcca% caqGGaGaaeiiaiaabccacaqGGaGaaeiiaiaabccacaqGGaGaaeiiai% aabccacaqGGaGaaeiiaiaabccacaqGGaGaaeiiaiaabccacaqGGaGa% aeiiaiaabccacaqGGaGaaeiiaiaabccacaqGGaGaaeiiaiaabccaca% qGGaGaaeiiaiaabccacaqGGaGaaeiiaiaabccacaqGGaGaaeiiaiaa% bccacaqGGaGaaeiiaiaabccacaqGGaGaaeiiaiaabccacqGHsgIRca% qGGaGaaeiiaiaaboeacaqGUaGaaeiiaiaabsgacaqGPbGaae4Caiaa% bshacaqGPbGaaeOBaiaabogacaqG0bGaaeyyaiaabccacqGHsgIRca% WGdbGaaiOlaiaabccacaWGZbGaam4yaiaad+gacaWG0bGaamyAaiaa% bccacqGHsgIRcaqGGaGaae4qaiaab6cacaqGGaGaae4yaiaabggaca% qGZbGaaeiDaiaabggacaqGUbGaaeyzaiaabggacaqGGaGaaeiiaiaa% bccaaeaba9VaamytaiaadMgacaWGJbGaamOCaiaad+gacaWGUbGaam% yzaiaadogacaWG0bGaamyyaiaabccacaqGWbGaae4BaiaabEhacaqG% LbGaaeOCaiaabMgacaqGGaGaeyOKH4QaaeiiaiaaboeacaqGVbGaae% OCaiaabMgacaqG4bGaaeyyaiaabccacaqGZbGaaeiDaiaabkhacaqG% PbGaaeyyaiaabshacaqGHbGaaeiiaiaab2cacaqG8baabqaq-laabc% cacaqGGaGaaeiiaiaabccacaqGGaGaaeiiaiaabccacaqGGaGaaeii% aiaabccacaqGGaGaaeiiaiaabccacaqGGaGaaeiiaiaabccacaqGGa% GaaeiiaiaabccacaqGGaGaaeiiaiaabccacaqGGaGaaeiiaiaabcca% caqGGaGaaeiiaiaabccacaqGGaGaaeiiaiaabccacaqGGaGaaeiiai% aabccacaqGGaGaaeiiaiaabccacaqGGaGaaeiiaiaabccacaqGGaGa% aeiiaiaabccacaqGGaGaaeiiaiaabccacaqGGaGaaeiiaiaabccaca% qGGaGaaeiiaiaabccacaqGGaGaaeiiaiaabccacaqGGaGaaeiiaiaa% bccacaqGGaGaaeiiaiaabccacaqGGaGaaeiiaiaabccacqGHsgIRca% qGGaGaaeiiaiaaboeacaqGUaGaaeiiaiaabAgacaqGVbGaae4Caiaa% bohacaqGHbGaaeOCaiaabwhacaqGTbGaeyOKH4Qaae4qaiaab6caca% qGGaGaae4CaiaabggacaqGObGaaeiBaiaabkgacaqGLbGaaeOCaiaa% bEgacaqGPbGaaeiiaiaabccaaaaa!EECE!\[\begin{array}{l} {\rm{ }} \to {\rm{ C}}{\rm{. distincta }} \to C.{\rm{ }}scoti{\rm{ }} \to {\rm{ C}}{\rm{. castanea }} \\ Micronecta{\rm{ poweri }} \to {\rm{ Corixa striata - |}} \\ {\rm{ }} \to {\rm{ C}}{\rm{. fossarum}} \to {\rm{C}}{\rm{. sahlbergi }} \\ \end{array}\] The upper succession takes place when there is little decomposition and a consequent rapid rise in the percentage of organic matter, the lower when decomposition is rapid; botanically the successions correspond to the formation of bog and the formation of fen. 3. Blelham is a small lake representing an extreme stage of evolution; it is smaller than the other lakes which have been studied, and at some time in the past its level has been lowered about 60 cms. 4. Blelham Lake is almost completely fringed with reed-swamp growing on the wave-cut platform eroded when the level was higher. Presumably reed-swamp appeared first in sheltered bays, to which places it is confined in Windermere to-day, and last on the most exposed shores. Different parts of the lake therefore show vegetation at different stages of development. Development consists of the gradual encroachment into the reed-swamp of Carec elata and Salix fromm the shallow water, except on the poor coarse sediments of deltas where the chief plant is Carex rostrata. 5. 11 species of Corixid (table 2, p. 11) were collected by means of a pond-net. Results are expressed as catch per 30 minutes at each station. 6. 56 stations (fig. 3, p 7) were worked. They can be divided into those in the reed-swamp, those off the outer face of the Carex, and those in the Carex. The last two categories can be sub-divided. 7. The percentage of species in these five zones is shown in table 4 (p. 13) and fig. 4 (p. 12). 8. C. praeusta predominates in the reed-swamp and is associated with bays at the ends of the north shore (figs 5 and 6, p. 14 and 15). Its ecological relationships have defied analysis. 9. C. striata is common in the reed-swamp and off the Carex face, particularly at the exposed end of the lake (figs 5 and 6). C. fossarum replaces it in big reed-beds and at the sheltered end of the lake. Behind the Carex face C. fossarum is by far the preponderant species. C. sahlbergi is found with it where the reed-beds are wide and old. C. distincta is not found in the richer conditions where Carex elata grows, but is moderately important in the poorer condition where Carex rostrata grows. C. linnei is found at face stations where there is a good growth of Salix behind. C. falleni is associated with stream mouths. 10. There are no sandy shores in Blelham and correlated with this is the absence of Micronecta poweri and the reduced importance of C. striata when comparison is made with Windermere. In Blelham there are continuous reed-beds with a growth of Carex elata forming a distinct vertical face, and associated with this is the abundance of the carnivorous Cymatia bondsdorffi, very scarce in Windermere where reed-beds are few, small, and with little Carex elata. Other differences between these two lakes are presumed to be correlated with the richer silt and dissolved nutrient supply to Blelham and the fact that the smaller size of this lake means that they reach a greater proportion of shoreline. The differences are that in Blelham C. praeusta is an important species, C. fossarum is more important than C. distincta, and C. scotti is absent (table 2, p. 11).