The critical thermal maximum (CTMax) of Peucetia viridans Hentz 1832 adult spiders was determined in the laboratory. Mean temperature at death was higher for gravid spiders (49.4° C) than for postparturient females (47.2° C) and males (46.9° C). Painted copper spider models placed in the environment to examine available temperatures predicted that spider body temperatures would rarely exceed 40° C thus making it unlikely for P. viridans to naturally reach CTMax, at least in the climate of central Tennessee.
The striped lynx spider, Oxyopes salticus Hentz, is found in high abundances in agricultural fields where it forages on many agricultural pests. Pesticides are applied to these fields and can therefore impact these natural pest predators. Researchers have examined the effects of a number of pesticides on this spider and other pest predators, but many of these studies only examine how these pesticides affect mortality. More recently, researchers have begun to examine the sublethal effects of these chemicals. We examined both the lethal and sublethal effects of three common pesticides with the active ingredients bifenthrin, carbaryl and malathion. We found that only malathion significantly reduced the post-exposure lifespan of these spiders; however, each pesticide had sublethal effects on behaviour. Exposure to malathion reduced jumping, likely an important foraging and escape behaviour. Spiders exposed to bifenthrin spent increased time grooming, which can reduce the time spent performing other important behaviours. Finally, spiders that were exposed to carbaryl surprisingly increased their prey capture rate. We show here that pesticides can not only directly affect the lifespan of the striped lynx spider but that each pesticide can cause different sublethal effects that likely impact the survival and ecology of these important pest predators.
When forested riparian zones are cleared for agriculture or development, major changes can occur in the stream temperature regime and consequently in ecosystem structure and function. Our main objective was to compare the summer temperature regimes of streams with and without forest canopy cover at multiple sites. The secondary objective was to identify the components of the stream heat budget that had the greatest influence on the stream temperature regime. Paired stream reaches (one forested and one non-forested or 'open') were identified at 11 sites distributed across the USA and Canada. Stream temperature was monitored at the upstream and downstream ends of 80 to 130-m-long reaches during summer, and five variables were calculated to describe the stream temperature regime. Overall, compared with forested reaches, open reaches tended to have significantly higher daily mean (mean difference = 0.33 ± 1.1°C) and daily maximum (mean difference = 1.0 ± 1.7°C) temperatures and wider daily ranges (mean difference = 1.1 ± 1.7°C). Mean and maximum daily net heat fluxes in open reaches tended to be greater (or less negative) than those in forested reaches. However, certain sites showed the opposite trends in some variables because of the following: (i) Daily mean and maximum temperatures were biased by differences in inflow temperature between paired reaches and (ii) inputs of cold groundwater exerted a strong influence on temperature. Modelling and regression results suggested that within sites, differences in direct solar radiation were mainly responsible for the observed differences in stream temperature variables at the daily scale.
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