Circannual rhythm in spatial distribution of burrows of freshwater crab, Barytelphusa cunicularis (Westwood, 1836)

Abstract

Ecologists use a number of techniques to quantify and statistically analyse patterns of spatial distribution. The present study deals with the temporal distribution and nature of the burrows of the crab Barytelphusa cunicularis, found at Maroda Sector, Bhilai, India. All the burrows present in an area of 112 m² were examined, during a span of 24 consecutive months. The number and pattern of burrows were observed every month in the study area. The data were subjected to nearest neighbour analysis. Rn values were computed to ascertain whether the distributions are clustered, random or regular. The burrows are considered more randomly spaced when Rn gets closer to 1.0. Time series data on Rn values, number of the total, single- and double-mouthed burrows were analysed by cosinor rhythmometry. The pattern of burrow distributions becomes more random in the early September with a spread between the beginnings of July and November. The timing of the peak in the burrows follows the peak in Rn values suggesting a post-reproductive increase in burrowing activities. The chronobiological analyses of Rn values add a new dimension to the interpretation of spatial distribution of crab burrows. This paper documents rhythm as an ecological phenomenon.

Keywords:

• circannual rhythm
• freshwater crabs
• burrow distribution
• nearest neighbour distance
• patterns of burrows

Acknowledgements

We thank the Head, School of Life Sciences, Pt. Ravishankar Shukla University, Raipur, India, for providing us with the research facilities. Thanks to the Head, Department, Zoology, Kalyan College, Bhilai, India. This work was partially funded by the UGC under the DRS-SAP sanctioned to the School of Life Sciences.