Hello again! As the weather has become colder, we are spending much more time in the office than out in the field, which means there has been plenty of time to process some of the data we have collected so far. I am heading to the Tennessee Academy of Sciences conference in Clarksville, TN tomorrow (Nov. 17th), so I thought I would share some of the findings that I will be presenting there on this blog.

Behold, a map of some individual Hellbender home ranges! I made this figure using my new found GIS skills, thanks to the Intro to GIS course I am enrolled in this semester.

As you can see, there are a wide variety of sizes in the home ranges of these Hellbenders. Most hellbenders stayed within the same small areas, often located under the same rock for multiple weeks in a row. However, as I discussed last week – there were some big moves that we detected in the fall. For example, individual #3 moved way up stream, and then returned to where it was the week before.

We used minimum convex polygons (MCPs) to calculate a rough estimate of the home range sizes of these individuals. Essentially, this means just forming a polygon from the outer points in their range. This does tend to over estimate the size of the areas used by the animals, and it doesn’t help draw attention to which areas an animal uses more. A different method, known as kernel densities can help us to do that. For my poster presentation I chose to use MCPs because our data is still preliminary and it would allow us to easily make comparisons across the individuals and between the two streams.

I was also interested to see if there was any effect of size, sex, or site on their home range sizes. Below is a quick plot that I used to analyze the effects of these variables.

Based on this chart, it is hard to conclusively say if size or sex have an impact on the home range sizes of the individuals. It’s important to keep in mind that our sample size is relatively small – only 10 animals in Tumbling Creek, and 17 in the Hiwassee River (now 14 due to predation events).

I removed the female from Tumbling Creek that moved over 2 miles from this chart, because her point was a huge outlier that greatly influenced the scale of this graph. It seems as though there may be a slight trend towards larger animals having larger home ranges, but this clearly is not the only explanation for the patterns we have observed here. There does not seem to be an effect of sex on the size of the home range, although previous literature has shown that females tend to have larger home ranges (Burgmeier et al. 2011).

It will be interesting to see what folks at the Tennessee Academy of Sciences have to say about our results so far! I look forward to getting some valuable feedback on our methods and advice on how to further analyze our data for trends. Follow this link for  an image of the poster that we are presenting tomorrow: TAS Poster. 

 

Wish us luck!

-Brad