1998/10/01 by Derek J. Lactin, Dan L. Johnson
Environmental Science · #Ecology and Vegetation Dynamics Studies #Fire effects on ecosystems #Species Distribution and Climate Change
paper · doi:10.4039/ent130551-5
Abstract We describe a model which estimates grasshopper body temperature ( T b ) by linking energy-flow equations with empirical descriptions of aboveground gradients of air temperature ( T a ) and wind speed. The model was tested using restrained grasshopper nymphs; estimated and observed T b agreed well ( r 2 > 0.81). At a rangeland site near Lethbridge, Alberta, Canada (49 °42′N, 112 °48′W), we observed 315 free-living grasshoppers. We recorded the shadow each cast on a horizontal surface, then reconstructed their orientation to the sun by geometric analysis. We used the model to estimate their T b and the range and frequency of possible T b within their environment. Modelled T b exceeded T a , and was generally lower than the modelled maximum possible T b , but was well correlated with T b of insects on top of the dense layer of vegetation which pervaded the site. This observation suggests that behaviours which elevate T b are constrained by environmental barriers. T b exceeded the value expected if insects were located and oriented randomly within their environment (mean difference = 3.95 °C, SE = 0.115); this is unequivocal evidence for behavioural thermoregulation. Heuristic simulations using temperature-dependent developmental- and feeding-rate equations for Melanoplus sanguinipes (Fabricius) suggest that thermoregulatory behaviour increased these rates by 30–40% compared with those for insects located and oriented randomly within their environment. During this study, population processes were never inhibited by excess heat; therefore any climatic warming at the experimental site will probably accelerate the phenology of these grasshopper species. Effects at other sites may differ; the model can be applied to test this possibility.