Evolution of Brain and Behavior in African Cichlid Fishes
HABITAT COMPLEXITY
How and Why Do We Quantify Habitat Complexity?
We are interested in how the habitat an animal lives in affects its brain and behavior. We want to know if an animal that lives in a complex environment has a more complex brain and behavior compared to animals from a simpler environment such as sand. To make that comparison, we need to quantify the habitat in some way. We quantify the habitat of our study species in two ways: 1) by measuring the rugosity of the substrate and 2) by measuring the optical intensity of the substrate, a new technique that we developed. This new measure, either alone, or used in conjunction with rugosity, should prove useful to researchers exploring habitat complexity in marine and freshwater systems alike. Furthermore, the method can be used to quantitatively compare habitat quality among candidate regions for protected areas.
In collaboration with Hans Hofmann of Harvard University.
Rugosity
Rugosity is a simple measurement of the surface roughness that has been used routinly by coral reef biologists. It is calculated by holding a rope of known length taut above the substrate. A chain that is attached at one end to the rope is draped across the substrate contours (see fig 1). The rugosity is the ratio of the chain length (A) to the rope length (B). The rugosity value was then normalized by calculating the z score using the equation z = X-µ/δ where X = the rugosity value, µ = the mean rugosity and δ = the standard deviation. The z score tells us how many standard deviations the value is from mean. We looked at three different habitats; rock, sand and intermediate, and found that the rugosity was significantly different in each of the habitats.
Publication: Pollen, A.A., A.P. Dobberfuhl, J.G. Scace, M.M. Igulu, S.C.P. Renn, , C.A. Shumway, and H.A. Hofmann. (2006, in revision). Environmental complexity and social organization sculpt the brain in Lake Tanganyikan cichlid fish. Brain Beh. Evol.
Optical Intensity
Intensity analysis is a purely visual, scale-independent, measure of habitat differences. A SCUBA diver videotapes a quadrate approximately 1 meter above the substrate using a digital video camera. Five images/quadrat are captured and converted to bitmaps. Subsequent intensity analysis of each image using Image Pro results in intensity values for each pixel in the image. The standard deviation of the intensity values is determined for each of the 5 images. The normalized mean standard deviation for each quadrat is subsequently calculated and used for statistical comparison between the quadrats. We found that sand habitats were significantly different from the intermediate and rock habitats.
Publication: Dobberfuhl, A.P., C.A. Shumway, and H.A. Hofmann. (2006, in revision). Quantifying Habitat Complexity in Aquatic Ecosystems. Freshwater Biology.
Figure 1. Demonstration of the optical intensity method. A) video frames of habitats. The numbers at the top indicate the mean variance for that particular frame.
B) Color representation of the bitmap analysis.
C) Location of the five video frames captured for analysis within the quadrat.
D) Color scale (0 to 255) used in the corresponding bitmap analysis. Bottom: Calibration, using a checkerboard. of the extreme intensities, 0 and 255.
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