WRL reference M04 D03 M04 Ecosystems Tropical Rainforests D03 The effect of altitude on dung beetle community structure

Transcription

1 WRL reference M04 D03 Module M04 Ecosystems Tropical Rainforests Data set D03 The effect of altitude on dung beetle community structure Data collection methods: 123 sites across Cusuco National Park were sampled using four dung baited pitfall traps (see the photos in the resources folder) in a 10x10m square. These traps were filled with a mixture of water, propylene glycol and a small amount of detergent. Propylene was used as it does not evaporate and detergent breaks the surface tension allowing small insects to go into the liquid and drown quickly. The square of traps is used as a control for microhabitat variation within a site. Each trap was baited with 25g of fresh horse or mule dung which was used because of its availability and similarity to dung produced by natural forest herbivores. The traps were left out for 3-5 days (previous work has shown no difference in catch after 5 days, the dung having lost its attractiveness!). Dung beetles were collected between 3 and 5 times from each site using this method to allow for fluctuations in weather conditions. The beetles were then extracted and identified using a specially produced ID guide (see DATA folder). In total dung beetles were captured and identified in The standardised abundance was then calculated by summing the total number of all species found at each site and then dividing this by the number of times that site was sampled: this is then multiplied by three to remove recurring decimals.

2 Species Richness was also calculated by adding up the number of different species found at each site. Also for interest and further study, the abundance of the guilds or types of beetles found at each site was determined. This involved defining two example guilds or groups of beetles based on their behaviour. One guild were the paracoprids (tunnellers) who dig tunnels beneath the dung pile and deposit the dung at the end of the tunnel for consumption and egg incubation and the telecoprids or rollers that roll balls of dung away from the original site before eating or burying it. These different strategies often avoid interspecific competition between species. The GPS location of each site was taken and this was used to extract environmental data from WorldClim ( Elevation was extracted from a Digital Elevation Model. And further habitat data was collected from a 20x20m square which surrounded the pitfall traps: the data collected followed the standard habitat protocol for Cusuco National Park see M04 D02 data set. The complete dataset can be viewed by opening M04 D03 DATA COMPLETED in the data folder but ONLY do this if you want to see just how much data has been collected. Also in the data folder is M04 D03 DATA reduced set which will be used to answer some of the research questions you are going to investigate. Dung balls ready for the traps.

3 Research Question 1: How do you identify the different species of dung beetle? Identifying Dung beetles accurately is very important for this type of research and there is now an ID guide that has been produced specifically for Cusuco National Park. This ID guide uses a dichotomous key method to identify specimens. These keys consist of a list of numbered dichotomies or pairs of mutually exclusive morphological characters for a specimen to be compared against. The keys are based solely on the morphological characteristics of a specimen and technical morphological terms are used in order to be unequivocal and concise these are explained in the glossary section of the ID guide. The names of the parts of a beetle can be very confusing but you do NOT have to learn them as you provided with a number of diagrams to help. In Honduras this year one activity was sorting and identifying Dung beetles and students found that with patience and practice, specimens could be identified successfully. In this exercise you are going to identify a number of beetles down to Genus level. You can then check out how successful you have been and the answers can be found in the Research Question folder but please only access this when your supervisor says so! 1. Open the ID guide which can be found in the Data Folder. Load ID-Guide-Cusuco-Dung- Beetle Genus only.pdf The full species guide can be found in the Full Guide folder. 2. Have a good look at the guide and read as much of the background information as you can but DO NOT WORRY about the large number of technical terms especially those describing the different parts of a beetle. 3. Look at the diagram on page 12 and if you have access to a printer, make a copy. 4. Now load the question sheet which you can find in the Data folder and begin to identify the specimens: Beetle I has been done for you. Fill in the answers in the spaces provided ID Genus Question sheet. 5. In Cusuco National Park there are 33+ species of dung beetle found within 12 Genera and 33+ species

4 Research Question 2: What is the effect of altitude on dung beetle community structure? To answer this question you are going to plot elevation (altitude) for each site sampled against the dung beetle total abundance and then species richness. This will then help you to see if there is any correlation between the altitude of the site and the structure of the dung beetle community. Instructions: 1. Open M04 D03 DATA reduced set using Excel or a suitable spread sheet program found in the Data folder. 2. Column A gives the elevation of the site in metres and column B the coding for each site e.g. BA1_SS3 is the third Sample Site along transect route 1 that originates near the mountain village of Buenes Aires. 3. Columns AM to AY give calculated data for Dung Beetles. You will notice that a number of columns have been hidden to make the table clearer - if you want to see this data go to the Format-Column-unhide tab - altering data here will alter the data in columns AM-AY so be careful. Re-hide the columns. 4. This data is all continuous data (i.e. not categories), so is well suited for graphical analysis. Use MS Excel to plot a scatter plot with altitude on the X-axis and Total abundance on the Y axis. Since the abundance data is skewed towards 0, it may be preferable to switch the Y-axis to a log axis (right click axis in plot, click format, tick log - ask your supervisor to explain the value of log scales or 5. This plot shows a slight downward trend, but with a lot of variation. Add a best fit line by right clicking on any point and clicking add trendline. This will be curved if the Y-axis is logged. 6. Display the equation and the R 2 value by right clicking on the line, clicking format and checking the two boxes at the bottom. R 2 value is a measure of fit of the data to the line, and gives a value between 0 and 1, 1 being perfect fit and 0 being no fit. In this sort of ecology, 0.12 is acceptable, and it suggests that there is a relationship between abundance and altitude. However, the data varies considerably around the line which suggests that other variables are affecting dung beetle abundance, not just altitude.

5 7. Abundance is important for the total functioning of dung beetles, but species richness is important for ensuring the dung beetles will be able to process a wide range of resources. To look at species richness instead of abundance replot the graph using Column AW. The graph still suggests a trend but the fit is less good and R suggests no significant relationship or trend so it seems that other variables are more important in determining the distribution of overall species richness. 8. Look at M04 D03 DATA reduced set completed to see these plots - label the axes and tidy up the presentation. 9. In addition to this you can also investigate the guild distribution for each site related to elevation 10. Be aware that with complex data sets such as this, patterns and trends in the data aren t always as clear as they can be with smaller more specific ones, so make sure you look carefully at the results! Research Question 3: What other environmental and habitat variables might affect dung beetles? If you open the original full dataset (M04 D03 DATA COMPLETED) you will see that a large number of other data items are present for each site such as the number of tree types, cut stumps, precipitation, canopy height, depth of litter layer etc. Some of these may well give a clue to why the dung beetles vary so much in their distribution and community structure. 1. Open this table M04 D03 variable table found in the Data folder and look at the variables that have been measured for each site. In the comment column suggest how this variable might affect the number of dung beetles found at a site and even what type (guild) it might favour. e.g. Dead trees and cut stumps might indicate an unhealthy habitat where dungproducers are not found or where leaf litter and soil density might affect the dung beetles ability to roll or tunnel dung. You may need to do some research by reading the papers in the resource folder or by accessing the internet. There is also a very good introduction at the start of the full ID guide for the Dung Beetles of Cusuco National Park. Some of the columns have been filled in for you with some suggestions. 2. Once you have completed the table, write a short summary on the factors that you think might affect the abundance and structure of Dung beetle communities. 3. How would you support your conclusions about important variables if you were going to Cusuco national park next year?

6 Dung beetle pitfall trap