Scientific progress is frequently triggered by new methodological developments. Often new tools adopted from unrelated scientific areas lead to a breakthrough and cause strong activity in a certain field and new paradigms. For example, quantitative phytoplankton research became possible in the early 1930s when H. Utermohl proposed the use of the inverted microscope to enumerate algal cells. This was the beginning of a new era of phyto-plankton studies relating phytoplankton abundance and composition to environmental variables, e g. nutrients. The method is still being used, and Utermohl's (1958) detailed description of the technique is still frequently cited.
The availability of radioisotopes, in particular phosphorus-32, carbon-14 and tritium after World War II made it possible to measure to uptake rates and turnover as well as nutrient concentrations. This caused a boom in studies of nutrient dynamics and productivity. Although measuring techniques for radioisotopes have become more sensitive and safer with time, the basic procedures of measuring primary and bacterial production are still the same (see Box 4.3). Satellite imaging opened the door for large-scale monitoring by remote sensing. Another recent example is the renaissance of food-web studies since techniques for measuring stable isotopes have become affordable (see Box 7.1).
Like many disciplines of biology, ecology has recently been revolutionized by the introduction of techniques from molecular biology. This process is still going on, and it will certainly become more and more important. There is already a subdiscipline called molecular ecology that uses molecular methods to study ecological questions. Studies of the structure of DNA and DNA products (genomics, prote-omics) can be used to identify genes indicating an organism's possible role in ecological processes, and the measurement of gene expression can give insights into its activity. Genetically engineered organisms have been constructed to serve as "bioreporters" that indicate environmental properties (e.g., iron availability).
By far the most important application of molecular genetic techniques in evolutionary ecology is presently the use of molecular markers (Avise 2004). Since the development of the polymerase chain reaction (PCR) to amplify traces of DNA, molecular genetic data have been integrated in various areas, in particular population genetics, phyl-ogeny, species identification, phenotypic and genotypic diversity, kinship and parental analyses, hybridization, dispersal and gene flow, speciation and many more. A large variety of methods has been developed to determine the base sequence of defined sections of the DNA, or to generate DNA fragment patterns (amplified fragment length polymorphism, microsatellites) like bar codes for the identification of genotypes. The common principle is a comparison of the similarity of certain portions of DNA or DNA products (RNA, proteins) to estimate the genetic relationships between organisms, either individuals (population genetics), or taxa (phylogeny and systematics). Technological developments in this field are extremely rapid. Examples of applications have been summarized in various books (e.g., Moya and Font 2004). We will mention various examples in the following chapters.
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