Life history,population dynamics and production of Pontoporeia hoyi (Crustacea,Amphipoda) in relation to the trophic gradient of Lake George,New York

The life history characteristics, population dynamics and production of Pontoporeia hoyi in Lake George, New York, were studied from May 1981 through October 1982. P. hoyi, in terms of both density and standing crop, is the most prevalent member of the deep water macrobenthos of Lake George. It reproduces in the winter, with young being released in the late winter-early spring. At the southernmost study site, young released in the spring grew to 6–7 mm in length and bred during their first winter. At the remaining sites, P. hoyi required two years to complete its life cycle. This difference in life history characteristics can be related to food availability and temperature differences. The open waters of the south end of Lake George are not only more productive but are also more closely associated with the littoral zone, providing a wealth of bacteria-rich detritus for benthic deposit feeders. The greater food availability in the south basin of Lake George is reflected in significantly larger brood sizes and smaller size at maturity for P. hoyi populations from the south end of the lake.The southernmost study site has significantly greater P. hoyi density and standing crop than all other sites. The cohort of the year dominated density and standing crop at the southern site while the cohort of the previous year dominated standing crop at the other sites. Peak abundance ranged from 600 · m^–2 at the north site to 2 900 · m^–2 at the south site. Cohort production ranged from 2g · m^–2 at the north site to 15g · m^–2 at the south site.     

Propagation in vitro of the apple rootstock M4: effect of phytohormones on shoot quality

The quality of shoots in cultures of the apple rootstock, M4, was used as a criterion for the selection of an optimum medium. The frequency of shoots in defined shoot clases was monitored for each of five media, which differed in the type and concentration of phytohormone. Media containing BA (1.15 mg l^-1) and IBA (either 0.15 or 0.20 mg l^-1) produced the maximum number of shoots that were desirable for transplantation and acclimatization.     

Observations on the seasonal and yearly occurrence and the distribution ofAtyaephyra desmaresti (Millet, 1831) (Crustacea,Decapoda, Natantia) in The Netherlands

Summary The seasonal occurrence ofAtyaephyra desmaresti in The Netherlands has been studied by sampling the cooling-water filtering screens of power stations situated along the rivers Rhine and Meuse. The shrimps were only found in large numbers at the two power stations with vegetation in the cooling-water intake areas. Fluctuations in the seasonal occurrence showed great similarity for these two localities. Highest numbers of shrimps were impinged in November. High numbers also occurred in September, while a lower peak in numbers was found in May.Changes in the numbers of records during the last 30 years in The Netherlands were compared with climatological fluctuations (severe or mild winters), indicating that this mainly southern-European species is living here at the limits of its ecological and geographical range.The distribution in The Netherlands reveals thatAtyaephyra desmaresti mainly occurs in freshwater habitats, although it tolerates higher chlorinities.     

Oxygen demand and long term changes of profundal zoobenthos

The paper attempts to combine the low oxygen content of the hypolimnion during stratification and the oxygen uptake of zoobenthos. Data of declining oxygen content in the hypolimnion and critical limits of respiration are combined for Chironomus anthracinus, Potamothrix hammoniensis and three species of Pisidium, P. casertanum, P. subtruncatum and P. henslowanum. The respiratory adaptation to low oxygen content influences both growth and population dynamics of the different species. The results have important bearing on eutrophication of the Lake Esrom ecosystem and temperate eutrophic lakes in general as well as the composition of profundal zoobenthos and its population dynamics.Publication No. 389 from Freshwater-Biological Laboratory, University of Copenhagen.     

Genetic structure of natural populations of the red-spotted newt,Notophthalmus viridescens

Genetic variation is described at 15 loci in 2 neotenic and 12 nonneotenic populations of red-spotted newts. Though high levels of genetic similarity (I=0.990) were found among all populations, allele frequencies at six of the eight most polymorphic loci show significant heterogeneity across populations. Change in allele frequencies at two of these loci (Pep-2 and Ldh-1) is significantly correlated with latitude. Interspecific homologies are established for newt peptidases based on substrate specificities and lactate dehydrogenases based on tissue distribution, thermal stability, and kinetic properties. Nonneotenic populations are highly variable (H=0.157) and neotenic populations are only slightly, but significantly, less variable (H=0.120). The high levels of heterozygosity detected in nonneotenic populations may result from large effective population size and/or environmental heterogeneity. The unexpectedly high heterozygosity values obtained for the neotenic populations may indicate adult dispersal or the presence of some previously undetected red efts at these localities. In any case, a major change in life history has apparently had little effect on the genetic structure of these populations.This research was supported by grants from the Blakeslee Fund of Smith College.     

Models for age structured populations with distributed maturation rates

In the use of age structured population models for agricultural applications such as the modeling of crop-pest interactions it is often essential that the model take into account the distribution in maturation rates present in some or all of the populations. The traditional method for incorporating distributed maturation rates into crop and pest models has been the so-called distributed delay method. In this paper we review the application of the distributed delay formalism to the McKendrick equation of an age structured population. We discuss the mathematical properties of the system of ordinary differential equations arising out of the distributed delay formalism. We then discuss an alternative method involving modification of the Leslie matrix.     

Temporal constancy in grasshopper assemblies (Orthoptera: Acrididae)

ABSTRACT.

• 1 Temporal constancy in the structure of grasshopper assemblies (about forty-five species each) from two types of North American grasslands was assessed; one site was followed 25 years and the other 7 years.
• 2 Densities and relative abundances varied but composition of assemblies based on ranks suggested significant structure when three or more species were included in the analysis.
• 3 Results compared favourably with other insect herbivore assemblies which have been examined; variability in population change was intermediate along the spectrum of organisms which have been studied.

     

Allozyme divergence between different gene arrangements in Drosophila subobscura

Allozyme and chromosomal polymorphism were analysed simultaneously in three population samples of Drosophila subobscura from Scotland, Germany and Italy. The study revealed significant genic divergence between the various chromosomal gene arrangements for the loci Acph, Lap and Pep, which are located inside inversions. No difference was found with the loci Me and Odh, which are both on the same chromosome but proximal to the structurally polymorphic region. Samples of a given gene arrangement taken from the different localities are genetically uniform. The data indicate that the observed non-random associations between enzyme genes and chromosomal inversions are the result of inhibited recombination in heterokaryotypes and gradual differentiation of the separated gene pools, rather than selection and coadaptation.     

Fertility interactions in Drosophila: Theoretical model and experimental tests

The results of 11 experiments with Drosophila species show that fertility is not a reducible property: the fertility of a mating pair cannot be predicted from the average fertility of the two genotypes involved. We propose a model of fertility selection that does not assume additivity (or multiplicativity) but assumes random mating and that the genotypic frequencies are in Hardy-Weinberg equilibrium. Numerical simulations show that removal of the assumption of Hardy-Weinberg frequencies does not significantly change the equilibrium frequencies predicted by the model.