Species

• Biologists use species numbers to measure biodiversity, and look for changes in species to help us monitor the effect of both natural environment changes and changes that result from human activity. Biologists look for both adaptations within a species and for changes in the numbers or types of species in an environment
• The definition of species that Linnaeus originally developed was a morphological species model, which was based solely on the appearance of the organisms be observed. However, the appearance of an organism can be affected by many factors, and they’re can be a huge amount of variation within a group of closely related organisms, for example species that show sexual dimorphism (great difference between males and females)
• The definition of species ‘a group of organisms with similar characteristics that interbreed to produce fertile offspring has many limitations. For example all organisms in a species cannot attempt to interbreed because they do not love in the same area.
• To overcome previous limitations, two other definitions were made:

  • a group of organisms with similar characteristics that are all potentially capable of breeding to produce fertile offspring
  • a group of organisms in which genes can flow between individuals
• Scientists use molecular phylogeny which is the analysis of the genetic material of organisms to establish their evolutionary relationships.
• The ecological species model is based on the ecological niche occupied by an organism
• The mate-recognition species model is a concept based on unique fertilisation systems, including mating behaviour. The difficulty is that many species will mate or cross-pollinate with other species and still produce fertile offspring
• The genetic species model is based on DNA evidence and is the most reliable and ultimate method of determining species. However, scientists have to decide how much genetic difference is needed for two organisms to be members of different species. Before DNA was difficult to collect and it took a lot of money to analyse, but now it is getting faster and cheaper.
• Limitations of species model:

  • finding evidence - many living species have not been observed mating
  • plants of different species frequently interbreed and produce fertile offspring
  • many organisms do not reproduce sexually
  • fossil organisms cannot reproduce and do not usually have any accessible DNA, but they still need to be classified
• In DNA sequencing, the base sequences of all or part of the genome of an organism is revealed. DNA sequencing leads to DNA profiling, which looks at the non-coding areas of DNA to identify patterns. These patterns are unique to individuals, but the similarity of patterns can be used to identify relationships between individuals.