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  • Level: GCSE
  • Subject: Maths
  • Word count: 5264

Investigation into the shapes of limpets on sheltered and exposed rocky shores.

Extracts from this document...

Introduction

Title: Investigation into the shapes of limpets on sheltered and exposed rocky shores.

Aim:

   The objective of this investigation is to determine whether there is any statistically significant difference between the dimensions, or shape, of limpets on sheltered and exposed rocky shores.

Scientific Background:

The seashore

   Classified as a unique habitat, the seashore provides a good opportunity to study the diverse adaptations boasted by the various plant and animal life found there. Perhaps the most influential feature of the seashore on local organisms is the rise and fall of the tide. Tides are the vertical and periodical oscillations of the sea caused by the gravitational forces exerted upon the earth by the sun and moon. On the shores of Western - Europe the tides are semi-diurnal, meaning there are two high and two low tides each day as illustrated in the diagram below.

Figure 1- tides due to the rotation of the earth about its axis

Although the above diagram shows that tides are due to the earth rotating on its own axis, completing a full cycle every 24 hours, their overall pattern, or behaviour, is also affected by the relative position of the earth, moon and sun such that there are four specific tidal levels along the shore during a lunar month (28 days), as shown by the diagram below:

Figure 2- shore profile showing tidal levels during the year

   These tidal levels are very useful as they represent different environmental conditions to which organisms must adapt in order to survive. For example, organisms living at EHWS are only submerged for a relatively brief period of time during a given month while organisms living at ELWS are nearly permanently submerged.

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Middle

   As mentioned in the scientific background, the growth rate of limpets is faster on the sheltered shore compared to that of the limpets on the exposed shore due to the presence of more algae on the sheltered shore. We would therefore expect to find larger limpets on the sheltered shore, see predictions. However, this should have no affect upon the width:height ratio as both the width and height should grow by the same amount.

Preliminary Work:

   Before any practical work directly relating to this investigation was done, some preliminary work on species distribution on exposed and sheltered rocky shores was carried out.

   The data sheets on pages 6 – 9 show the types of species found at different vertical heights along a sheltered shore (Sawdern point) and along an exposed shore (Manor Bier). In this experiment, ¼ m² quadrats were used to define a sampling area at a certain height. The numbers and types of species found within that area were then recorded in the previously mentioned data sheets. The Kite diagrams on pages 10 and 11 illustrate the results obtained.

Hypothesis:

   There will be a statistically significant difference between the width:height ratios of limpets found on the exposed rocky shore and on the sheltered rocky shore.

Null Hypothesis:

   There will be no statistically significant difference between the width:height ratios of limpets found on the exposed rocky shore and on the sheltered rocky shore.

Method:

Rough method:

   Before the experiment that would obtain the necessary data for this investigation was actually carried out, a brief plan was written out, see page 13. Note that the procedure outlined in the rough method is not exactly the same as the one written below.

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Conclusion

   If there is a similar change in allele frequency in a population of limpets, then there should also be limpets with larger width:height ratios found on the sheltered shore. Indeed, there are three limpets of greater width:height ratio than the mean width:height ratio of limpets found on the exposed shore (3.29). These are limpet numbers 2, 21 and 27 with width:height ratios of 3.41, 3.40 and 3.48 respectively  – see table 1, page 19. One could also argue that limpet numbers 5 and 19 also have relatively large width:height ratio (more than 3.00) similar to those found on the exposed shore. This data suggests that there is an allele responsible for a larger width:height ratio, either by reducing the height or increasing the width or both, that is always present in population of limpets. However, we cannot be certain of this without further investigation. It may be the case that there is no allele coding for a large width:height ratio. Rather the conditions on the shore to which the limpets are exposed, cause them to grow a larger width:height ratio.

   In conclusion, the evidence collected suggests that there is a statistically significant difference between the shapes of limpets found on sheltered rocky shores and those found on exposed rocky shores. Therefore we accept the hypothesis made earlier on page 5. The evidence also shows that the width:height ratios of limpets found on exposed rocky shores are in fact on average greater than the width:height ratios of limpets found on sheltered rocky shores.                

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