Best-fit Linear Model Research Articles

Between-group differences in the Iberian dung beetle species-area relationship (Coleoptera: Scarabaeidae)

Abstract Between-group α- and β-diversity differences were derived from species-area relationships fitted to field data. The accuracy of spatial richness variation predictions based on area size was also checked. The log-log model (log S = c + z log A ) was found to be the best-fit linear model, with slopes ( z ) ranging from 0.089 to 0.142. Between-group comparisons of z (slope) and q (intercept) parameters, using the S = q + cA z curvilinear regression model, corroborated early results, indicating a lower β-diversity (slope) for Scarabaeinae than for Geotrupinae and Aphodiinae. The latter group, probably more sensitive to environmental heterogeneity, should contribute more to species richness in large areas. α-Diversity is greater for Aphodiinae, more relevant to local diversity (1 km 2 ), than for Scarabaeinae and considerably greater for these two groups than for Geotrupinae. As earlier results show that the richness of a single dung pat is rather more a function of the Scarabaeinae species pool, richness on dung pat scales is probably due more to the between-dropping mobile Scarabaeinae, while Aphodiinae contribute mainly to local and regional pool richness. Nearly 88 % of the total richness variance is explained by area size. This percentage decreases to 37 % when the spatial structure of area size and species number are extracted. The corresponding figures for Scarabaeinae, Aphodiinae and Geotrupinae are 44, 22 and 31 %, respectively.

Fine-root parameters as indicators of sustainability of forest ecosystems

The potential of fine roots as indicators of forest sustainability is discussed. In 10 oak ( Quercus petraea, Q. robur) trials, where moderate doses of lime had been applied up to 27 years ago, the effects on soil, root and foliar chemical parameters were compared with above- and below-ground growth. The effects of liming on growth appeared positive and sustained for ca. 25 years after application, whereas effects on soil, root, and foliar chemical parameters only lasted for 10–25 years. Fine-root biomass or length appeared to be significantly increased by liming and comparable to the effects on above-ground tree growth, but were considered to be too time-consuming for use as indicators of ecosystem function. A combination of soil and root chemical parameters predicted fine-root mass and length the best – and thus tree growth – with foliar chemical parameters being of minor importance. When this best-fitting linear regression model was applied, separately for both the lime treatment and the control, the contribution of root chemical parameters in the model decreased in the lime treatment as compared to the control, while that of foliar chemical parameters increased. Consequently, root as well as soil chemical parameters appeared to be more sensitive to changes in the chemical status of the site. In general it is recommended, that studies aiming to define useful indicators, should start with a feasibility study (e.g. comparing the utility of soil, root and foliar chemical parameters) before defining a smaller set of most sensitive parameters. For the sites examined, a combination of parameters such as fine-root Ca, Al, Mg, Ca/Al, Mg/Al, soil exchangeable Ca, Al, and Mg gave a good insight into the actual uptake capacity of roots or constraints on that capacity.

Smooth Amaranth Interference with Watermelon and Muskmelon Production

Studies were conducted to determine the critical period of smooth amaranth interference in watermelon (Citrullus lunatus L.) and muskmelon (Cucumis melo L. var. reticulatus). Best-fit linear or exponential regression models were used to predict the maximum period of competition and the minimum weed-free period for 10% yield loss. The maximum period of competition and minimum weed-free period was 0.50 and 2.97 weeks after watermelon emergence, respectively, and 1.0 and 3.9 weeks after muskmelon emergence, respectively. The critical periods of smooth amaranth interference for the crops were between those intervals. In both crops, late emerging smooth amaranth had little effect on total yield. Smooth amaranth introduced at crop emergence reduced total yield. The effect of competition on yield components, i.e., fruit number per hectare and fruit mass, varied by crop. Muskmelon fruit count was more sensitive to smooth amaranth competition than was watermelon fruit count. Conversely, mass per fruit of muskmelon was less sensitive to this competition than was mass per fruit of watermelon.