When in doubt, keep collecting data

I shouldn’t have built anticipation by waiting so long since posting about collecting data on lizards in the museums. I closed with a teaser that I’d soon post results of my data analysis. Well, here they are and unfortunately the short of it is, the data don’t look too great. Luckily, as I’ve an hour to spare, I’ll bombard you with the long of it as well.

Over the course of my visits to the Yale, Harvard and NYC natural history museums, I collected morphological data on 72 lizards. I decided on these measurements after a review of some 50 studies, all measuring these features of lizards and relating them to physical performance. Remember “functional traits?” These morphological characteristics all have, in some species of lizard, a connection to function. We don’t have any previous data on Podarcis erhardii, so I decided to measure all of them to see if any varied between islands.

Ecolunch 2013.046

The 72 lizards I measured were from a wide array of islands in the Aegean. Too wide an array actually; 22 of them labeled P. erhardii have actually since been split into other species based on molecular data. Still, with 50 lizards from some 10 islands, I forged boldly on to start testing for relationships across islands.

My first effort was to look for patterns between body size and island area; a relationship quite common for many species. I found a slight positive trend but there was so much noise in the data I couldn’t detect a significant pattern. Not worrying overmuch, I continued analyzing data, testing for patterns between the various morphological features and their islands of origin. Time after time the answer came back negative, I was a little discouraged.


Now, it could very well be that my hypotheses are completely wrong and that these lizards do not in fact vary consistently in different ecological contexts, but I have a few qualms with the data that make me want to keep investigating further. First, as you’ll see, my sample sizes were fairly small (usually between 4 and 10 lizards per island) and those samples were collected over many decades. Second, unfortunately we cannot know where these lizards were caught on the island, what context they were found in, and whether they truly reflected the population of the island as a whole. I am hypothesizing that all of these factors are important, and so missing data about them may be obscuring significant trends. Finally, there’s a great deal of variability in all of the traits on each island. While this makes finding a statistically significant relationship between X and Y nearly impossible, it does give me hope that perhaps these morphological traits have enough variability in them that they might contain patterns and stories to be told with the help of a bit more background information.

There is my impetus for this summer. I am going to head out onto some of these islands, measure these lizards, and measure as many variables to do with their ecological surroundings as I can so as to begin to explore which might be important in explaining that morphological variation. Stay tuned, hopefully the next graphs I post will be prettier!

One thought on “When in doubt, keep collecting data

  1. I am looking forward to hearing how you find the lizards in greece these days. a lot has changed in the years between the lizard’s collection and your measuring – if i am remembering your last post correctly. Anyway- forge on MacDuff!!

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