Changing attitudes to nature conservation: The National Trust

The National Trust was founded in 1895 to preserve land and its associated flora, fauna and buildings. The Trust's land holding has since increased to over 220000 ha, of which almost one-third is of high nature conservation value. The protection provided by Trust ownership is particularly important for certain species. In recent years land management for nature conservation has been transferred from volunteers to professional staff and links with other conservation bodies have been developed. A special programme began in 1979 to survey the wildlife of Trust properties. Research is encouraged where it will benefit management. In some areas where traditional management has lapsed the Trust has invested considerable resources into restoring former regimes.     

Hybridization studies in the Schistocerca americana complex. I. The specific status of the Central American Locust

The Central American Locust has previously been identified as Schistocerca paranensis (Burmeister), the Argentinian Locust, and it has been suggested that S. americana of North America represents its solitarious phase. Hybrids of locusts from the Yucatan peninsula of Mexico with locusts from Argentina and Florida were reared, their fertility measured and meiosis in the males examined. It was found that: (1) sex ratios in the F, hybrids were distorted; (2) hybrids had reduced fertility; (3) female hybrids were more fertile than male hybrids; (4) meiosis in hybrid males was disturbed; (5) these effects were more pronounced in die hybrids with the Argentinian Locust than in those with Florida locusts.
These results are discussed in relation to Haldane's rule and the biogeography of die group. It is concluded that the Central American and Argentinian Locusts are separate species, but that the relationship of the former to S. americana americana requires further investigation.     

The Structure and Permeability of Integument

SYNOPSIS. The skin is a heterogeneous, multimembrane systemwith multiple diffusion pathways and potentially numerous rate-limitingbarriers for specific molecules that are exchanged with theenvironment. A broad survey of animals indicates that integumentarycoverings are morphologically, biochemically and embryologicallydiverse but with common themes of adaptation. The evolutionaryproliferation of intercellular junctions, fibrous or mineralizedprotective barriers, and lipoid waterproofing barriers emphasizethe generality of diffusion limitations. However, the regulationof specific exchange processes such as the flux rates of respiratorygases entails a complex interaction of multiple factors affectingboth diffusion and perfusion limitations. Consideration of specificpathways and rate limitations for diffusion of various substancessuggests that the permeation of skin by specific molecules canbe partially independent of other exchange processes. Our understandingof regulated permeability is, however, lacking in mechanisticand integrated analysis in most cases. Comprehensive understandingof the integument as a regulatory pathway of communication withthe environment will require comparative studies of specifictransport pathways, their rate-limiting resistances, and theinteractions as well as individual regulation of transportedmolecules.     

Some Observations on the Effects of Salinity on Ion Distributions and Cell Ultrastructure in Wheat Leaf Mesophyll Cells

The distribution of ions within wheat leaf mesophyll cells fromplants grown in the presence of 100 mol m^–3 NaCl werestudied by X-ray micro-analysis, and the volume fractions occupiedby the analysed compartments were determined stereologically.Generally, the cells did not accumulate high ion concentrationsin their vacuoles, and the much higher Na⁺ and Cl^– concentrationsin the cell walls would produce an imbalance of cell water relations.The Na⁺, K⁺ and Cl^– concentrations in the cytoplasm wereoften too high to be compatible with biochemical activity. Inresponse to saline growth conditions, the volume fractions occupiedby the cytoplasm and chloroplasts increased. Correspondence to: Institut für Botanik, Fachbereich Biologie,Technische Hochschule Darmstadt, 3–5 Schnittspahnstr.F.R.G. Key words: Salinity sensitivity, X-ray micro-analysis, stereology     

A modified photogrammetric technique for assessing age-structures of elephant populations and its use in Kidepo National Park

(1) A modification of an aerial photographic technique for assessing the age-structure of African elephant populations is introduced. (2) The method is quick, inexpensive, and provides important population dynamics information relevant to one of the most serious wildlife management problems in Africa–namely, the interaction of elephants and their habitats. (3) The method consists of photographing elephant breeding herd groups vertically, measuring their relative lengths, and then relating the lengths to a mean breeding herd growth-curve. (4) An example of the application of the technique is given in an assessment of the age-structure of two elephant populations in the Kidepo Valley National Park, Uganda. (5) The Kidepo populations are similar in age-structure and are in general healthy. The similarities probably represent allopatric responses to the same climatic regime. (6) Peaks and troughs in the age-structures are related to local rainfall, which indirectly aifects conception and mortality of young animals. (7) There are some obvious differences between the two populations, the home-ranges of which exhibit differences in rainfall and habitat characteristics. The differences between the populations reaffirm the sensitivity of elephant population regulating mechanisms to local variations in climate and rainfall. (8) The relative roles of post-mortem and observational techniques in elephant studies and the need for long-term research are discussed.