The Influence of Rainfall, Evaporation and Atmospheric Temperature on Fluctuations in the Size of a Natural Population of Thrips imaginis (Thysanoptera)

Abstract

other ("correlation" of log N with A log N) indicates density-disturbance (as defined by Nicholson 1954). Both cannot be right.The method followed by Davidson and Andrewartha is clearly set out in their two papers and in Andrewartha and Birch (p. 587). We certainly did not, and we stated clearly that we did not, infer causal relationships from our regressions. On the contrary, our independent variates were chosen to represent causal relationships which we had inferred from a prior knowledge of the biology of Thrips imaginis. If we had overlooked a causal relationship, then, because the regression accounted for a high proportion of the variance, the neglected variable would, of necessity, be highly correlated with at least one of the variables included in the regression. From the nature of the variates that were included, it seems unlikely that a substitute could be found for any of them that would be consistent with the idea of "density-dependent factors."We did not include an independent variate to represent a density-dependent factor .because we could not find one. Our study of the biology of T. imaginis established, with reasonable certainty, that shortage of food was not operating as a density-dependent factor. We searched for evidence that predators, parasites or diseases were influential but failed to find it. Nor could we find any other component of environment that might be said to act like a density-dependent factor. SUMMARY Davidson and Andrewartha (1948b) concluded that the results of their study of a population of Thrips imaginis provided no confirmation of the theory of density-dependent factors. Smith (1961) re-analyzed some of their results and reached the opposite conclusions. This paper suggests that Smith's conclusions are not acceptable because:(a) He made the logical error of inferring a causal relationship from a statistical correlation. (b) He made the statistical mistake of "correlating'' two variables that were not ascertained independently. (c) He retained two criteria that gave opposite answers to the same question.

Independent and Competing Disease Risks: Implications for Host Populations in Variable Environments

“…Our modeling results suggest an alternative explanation: the same pattern would emerge if disease effects usually functioned as competing risks in both groups, but invertebrate population dynamics were driven primarily by density-independent factors, whereas vertebrate populations were typically regulated by density-dependent factors. Predicting disease impacts on host population dynamics can thus not be divorced from the long-standing debate over density-dependent versus density-independent population regulation (Davidson and Andrewartha 1948;Nicholson 1954).…”

Species with more volatile population dynamics are differentially impacted by weather

“…[1][2][3][4]). This dialogue has resulted in widespread appreciation of the importance of both classes of processes.…”

“…[2,4,5]). Inferences made from these analyses, while informative, are necessarily limited to the taxon under examination.…”

Impact of Trap Design, Windbreaks, and Weather on Captures of European Corn Borer (Lepidoptera: Crambidae) in Pheromone-Baited Traps

“…The dependent variable in the model was the number of moths collected per Julian date, and the initial Þxed effects were a linear term for Julian date, a quadratic term for Julian date, year, ßight, nightly mean air temperature (Celsius), nightly mean relative humidity (percentage), nightly mean wind speed (kilometers per hour), nightly precipitation (millimeters), the interactions of linear Julian date with the weather parameters, and the interactions of ßight with the weather parameters. The orthogonal polynomial functions of Julian date helped model the natural rise and fall cycle of moth populations over time (Davidson and Andrewartha 1948). Model construction was conducted in a stepwise manner.…”

“…The location or surroundings of insect traps inßu-ences their efÞciency (Wellington and Trimble 1984, Lee 1988, Mason et al 1997, Sappington and Spurgeon 2000, Kavallieratos et al 2005, and insect responsiveness to traps is often a function of weather (Davidson and Andrewartha 1948, Vogt 1986, Gregg et al 1994, Mohamed-Ahmed and Wynholds 1997, Butler et al 1999. Windbreaks such as tree lines modulate air movement, airborne chemicals, and airborne insects (Lewis and Dibley 1970), and an insectÕs ability to control ßight is a function of wind speed.…”