morphological species concept PDF

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lecture notes on species and concepts...

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What is a species Biologists use species numbers to measure biodiversity, changes in species is also used to monitor the effect of both natural environment changes and for changes that result from human activity. Biologists look for both bath adaptations within a species and for changes in the numbers or types of species in an environment. The morphological species concept This definition was developed by Linnaeus, and was a morphological species concept, a species based solely on the appearance of the organism, the degree of difference or similarity of the physical characteristics was used to group them into species, genus etc. In many cases this approach still works and you can tell that just by looking at the organism what it is. However the appearance of an organism can be affected by many different things, and there can be huge amount of variation within a group of closely related organisms. In organisms that show sexual dimorphism- difference in appearance between males and females of a species, the different sexes could be thought of as being different species in a morphological species model. The reproductive or biological species concept For many years a morphological definition of a species was used but in time biologists moved to a basic model of species based on the reproductive behaviour of the organisms. One widely used definition of a species is: a group of organisms with similar characteristics that interbreed to produce fertile offspring. This definition overcomes issues such as sexual dimorphism and works for many animals’ species, but it has limitations. One limitation is that all of the organisms in a species cannot attempt to interbreed to produce fertile offspring because they don’t all live in the same area. So population of organisms of the same species may not interbreed simply because they are in different places, not because they ae different species. In this species model, if two individuals from different populations mate, they are considered the same species if the offspring produced are fertile and genes are combined or ‘flow’ from the parents to the offspring. For examples horses and donkeys look similar but if they reproduce, a mule is produces which is sterile. The genes cannot flow to the next generation so they are not the same species. However there are problems with this definition, for example, lions and tigers are different species but if they reproduce the offspring are fertile. To help overcome this there are two more definitions of species based on reproductive capabilities: • •

A group of organisms with similar characteristics that are all potentially able of breeding to produce fertile offspring A group of organisms in which genes can flow between individuals

A reproductive concept of species works for animals however is less useful in classifying plants. Other definitions of species Scientists are constantly developing the definition of a species. Some of the methods are more sophisticated than simple observation. Fundamentals chemicals such as DNA, RNA and proteins are almost universal. Whilst these chemicals are broadly similar across all species, differences are seen when the molecules broken down.

What is a species...