Individual study: Heteropteran faunas of sheep grazed and ungrazed chalk grassland, Barton Hills, Bedfordshire, England
Morris M.G. (1969) Differences between the invertebrate faunas of grazed and ungrazed chalk grassland. III. The heteropterous fauna. Journal of Applied Ecology, 6, 475-487
This study assessed the differences between Heteropteran faunas of sheep grazed and ungrazed chalk grassland at Barton Hills (Nat. Grid ref. TL 090297), Bedfordshire, southern England. The Heteroptera within exclosures (ungrazed for 3-4 years) and grazed plots were compared.
Experimental design: Ungrazed exclosures and grazed areas measured 40 x 25 m, one of each established in March 1965 on two adjacent sites about 50 m apart, on upright brome Zerna (= Bromopsis/Bromus) erecta-dominated grassland.
Grazing regime: The experimental area was intensively, but not continuously, grazed by sheep throughout the experimental period (1965-1968). Following relatively low intensity stocking in 1967, the area was more heavily grazed in 1968.
Sampling: Sweep-net sampling used in 1965 (August-September) and 1966 (May-September). This was superseded in 1967 and 1968-69 by sampling with a vacuum net (back-pack model D-Vac). Two standard samples from 24 ft² (2 m²) of vegetation were taken from each plot at 2 to 4 week intervals from June to November 1967 and April1968 to March 1969. Turf samples were also taken.
A maximum of nine species occurred regularly on the grazed grassland (Zicrona caerulea, Stygnocoris pedestris, Berytinus signoreti, Campylosteira verna, Acalypta parvula, Tingis cardui, Agramma laeta, Mirid sp. and Leptopterna ferrugata). Only one of these (the Mirid sp.) was unrecorded in the exclosures; six species showed a significant positive response to cessation of grazing, occurring in higher numbers on the ungrazed grassland.
Sixteen species occurred regularly in the exclosures. Increased numbers of several species were recorded in the fourth season following erection. The population of Agramma laeta increased markedly within the exclosures in the first three seasons but crashed in the fourth; populations of two other species declined to a lesser extent.
Conclusions: The intensively sheep-grazed chalk grassland supported a sparse Heteropteran fauna; nine species appeared to be the maximum number breeding regularly but the actual number was possibly lower. In contrast, larvae of 16 species were found regularly in the ungrazed areas. Of the species occurring regularly on the grazed grassland, all but Campylosteira verna and Trigonotylus ruficornis were found in greater numbers in the exclosures during at least part of the study period.