• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

Evolutionary Arms Races.

Extracts from this document...

Introduction

Evolutionary Arms Races "...Thus I can understand how a flower and a bee might slowly become, either simultaneously or one after the other, modified and adapted in the most perfect manner to each other, by continual preservation of individuals presenting mutual and slightly favourable deviations of structure." (Origin of Species, 1857) Darwin was describing the interactions between organisms that result in reciprocal changes in traits (i.e. morphology, behaviour and physiology) over evolutionary time. He termed this phenomenon "co-adaptation". Over time, however, this term has become known as co-evolution, and the meaning of co-evolution has been refined. It defines an evolutionary change in trait(s) of the individuals in one population in response to a trait in the individuals of a second population, followed by an evolutionary response by the second population to the change in the first. This distinguishes coevolution from simple adaptations of organisms to their abiotic and biotic environment. For example, an insect herbivore that has the ability to detoxify certain secondary metabolites in the tissues of its host plant may not necessarily be "co-evolved" with that plant: the secondary metabolite might be present for a variety of reasons (i.e. ...read more.

Middle

seed in each cone; there has been an increase in the "fitness" of the seed coats, requiring the squirrels to spend more time and energy extracting each seed; there has been a trend of putting less energy into each seed, therefore requiring the squirrel to expend more energy; trees have shed their seeds from cones early, before the young squirrels of that year begin foraging, and finally, there have been periodic "cone failures". These reduce the squirrel population and the reproductive success drastically, hence reducing the intensity of predation during the next year. The fluctuations in cone crops from year to year have been shown to be an anti-squirrel strategy because even in optimum climatic conditions, this phenomenon still occurs. It is clear, therefore, that squirrels have had a profound evolutionary influence upon various reproductive characteristics of conifers including cone anatomy, location of cones, the number of seeds per cone, the time at which the cones are shed etc. These restrictions in turn placed on the squirrels have forced them to adapt in various ways, such as choosing cones carefully and stockpiling them. It is possible that the fruit fly (Drosophila pachea) ...read more.

Conclusion

This sort of adaptive radiation and co-evolutution is referred to as "diffuse coevolution", where an array of populations provides the selective pressure. Evidence of tight coevolutionary relationships, "paired coevolution", in which only two species are coevolved , are not common. This is because, when referring to co-evolution between plants and animals, many different organisms can attack plants (including bacteria, fungi, viruses, nematodes, molluscs, mammals, birds and reptiles). There might therefore not expect such perfect adaptation or coadaptation between insects and plants, when so many organisms are attacking plants. Secondly, different species of insects can exert selection pressures in different directions. For example, tannins deter leaf-chewing insects herbivores on Quercus rubra, while at the same time attracting gall-forming leaf-mining insects. Hence the advantages of leaf tannins may be dependent on the relative densities of leaf chewing or endophagous herbivores. Hence, in conclusion, predator-prey interactions very often lead to antagonistic evolution, known as evolutionary arms races. These arms races may in turn lead to adaptive radiation and the formation of new species of plants, insects and other organisms. However, whilst looking for any coevolutionary evidence in nature, it is important to consider all factors influencing the evolution of a species. Very often, what might appear to be coevolution between two species may in fact be evolution, but with selection pressures coming from a variety of directions , either abiotic or biotic. ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our University Degree Zoology section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related University Degree Zoology essays

  1. Analysis of Charles Darwin's theory of origin of the species

    Therefore it is most beneficial to have worker ants be neuter. Darwin has in my mind wholly and completely defended this point. He has combined his theory with an inescapable scientific fact. If a person releases a balloon it will float wherever the wind will take it.

  2. Free essay

    Explain, using evolutionary arguments, why social living is common among mammals

    Tinbergen, in his book 'Social Behaviour in Animals', suggests that parent-offspring groups develop into symbiotic relationships between families, before later developing into full scale communities. (4) This further concretes the concept of gene protection and inclusive fitness mentioned previously.

  1. Free essay

    Importance of correct identification of insect material.

    Stabulans is usually associated with urine and faeces - suggesting they were there before death. The absence of Lucilia flies was explained due to the lack of access to the flat - doors and windows firmly shut. PMI was estimated at 14 days (Benecke & Lessig 2001).

  2. Charles Darwin and his Theory of Natural Selection

    After a great number of generations, tortoises on the arid islands will have longer necks than those on the watered islands. And so one Species will have given rise to another. This concept did not become clear in Darwin mind until long after he had left the Galapagos Islands.

  1. Horse Evolution

    The ice age of that time occurred, spreading and receding five times (Wikipedia, 2007). The first Equus progressed from the Plesippus in Europe, roughly 4 - 2 million years ago. It crossed to North America; however, all horses that lived in North America became extinct approximately 11 000 years ago along with many other American mega fauna (Critters-2-Go, 2007).

  2. Evolution Essay

    In addition, genetic drift does not allow species to evolve to accommodate to their environment. The cause of this incapability occurs because genetic drift causes random changes in the cycle of characteristics. Over a long period of time, genetic drift is able to gradually alter the genetic features of a population.

  1. Invertebrate colonisation of leaf packs of different palatability in an upland river.

    Not all leaves breakdown at the same rate. For example Alder (Alnus glutinosa) leaves break down quicker than Oak (Quercus robur) leaves. This breakdown continuum means that a stream contains nutrients throughout the year, not just in autumn when the major input occurs.

  2. Comparing the Processes of Osmoregulation ...

    As such, this triggers a response in the insect that cause the spiracles to open. In some bigger insects the air sacs used for storage, through muscular contraction, can be used to forcibly expel air through the tracheae which creates a unidirectional air flow.

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work