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MBEA Activity: Frequency distributions
1. Dr. Mark A. McGinley Texas Tech University BIOL 5311 Summer 2011 MBEA Activity:Frequency Distributions
2. Importance of Body Size Body size of an organism is an important factor that can influence population dynamics, reproduction, interspecific interactions, etc. Body size can vary between species (interspecific variation) and within species (intraspecific variation) Both types of variation can be important and interesting to study.
3. How Should You Measure Body Size? There is not one single right way to measure the body size of organisms. Let’s think about humans. How could you measure body size in humans. Height Weight
5. Measuring Body Size Ecologists measure body size differently in different organisms. Snout-vent length in lizards Snout-tail length in snakes Body mass in rodents Wing length in bats Head width in ants Best choice is influenced both by need and practicality. Sometimes they might take multiple measurements.
6. How Do They Determine Body Size in Rainforest Bats? Forearm length Body mass
7. How Does the Size of Individuals Very Within A Species? You can examine size variation within a species by constructing a frequency distribution. Let’s construct a frequency distribution for forearm length in the Malaysian bat, Hipposideroscervinous.
8. Hipposideroscervinous Physical DescriptionNose: Like all roundleaf bats Hipposideroscervinus has a very distinctive noseleaf, which in this case is a pinkish grey color. Ears: The ears are rather triangular at the tips in HipposideroscervinusHipposideroscervinus hanging from a small branch Wings: The wings are a dark brown, broad and rounded, so this species can fly with great manoevurability in the forest. Tail: Like all Hipposideros, a small tail membrane stretches between the legs, but doesn’t go much beyond the ankle. The tail itself is fully enclosed by the membrane, with maybe just a mm or two of the tail poking out beyond the edgeSize: This is one of our medium-sized bats, with an average forearm of about 50 mm, and average weight of about 10g.
9. Hipposideroscervinous This is a common bat often found roosting in large colonies in caves that can include more than 100,000 individuals. They also use smaller caves and crevices among boulders and sometimes roost in association with Hipposideros bicolor species. Where they can be foundHipposideroscervinus has a very large range; from Peninsular Malaysia, Sumatra, Philippines through to Vanuatu, and NE Australia.
10. Frequency Distribution In order to create the frequency distribution for the forearm length of H. cervinousI 1) divided the forearm length into 1 mm wide categories (e.g. 48.0 – 48.99 mm) (the 1mm wide categories just seemed to make sense) 2) counted the number of individuals with forearm lengths that fell into each category
13. As Always….. Start off by writing down a few sentences that describe all of the information held in the graph.
14. Interpret the Graph There is variation in the forearm (FA) length of H. cervinous The minimum FA length is < 46 mm and the maximum FA length is > 51 mm The most common FA length is between 49.0 and 49.99 mm As you move farther from the most common value the number of individuals with each FA length increases.
15. Activity Choose a common bat species from the MBEA data set (>25 individuals) and construct a frequency distribution for this species Do this by hand Describe all of the information in that graph Compare the frequency distribution of your species with that of H. cervinous
16. Interspecific variation in body size Discuss with members of your learning circle how you would produce a frequency distribution examining interspecific variation in body size. After you have agreed on the protocol, work together to construct the graph Interpret the graph
