Back to index of herpetofauna studies

SEXUAL DIMORPHISM AND HABITAT USE OF A FOREST SKINK, MABUYA RUDIS

It has been recognised for a number of years that tropical rainforests are areas of great biodiversity. Unfortunately it is also recognised that these highly specialised habitats have become subject to increasing destruction. My incentives for taking part in this particular project were not only to witness first hand the herpetofauna of the rainforest and experience another culture; but also to assist with vital research which will be used to help conserve the biodiversity of Buton Island.

• To identify and define the differences in morphology between the males and females of Mabuya rudis.

• To identify and define the presence or absence of any microhabitat partitioning between Mabuya rudis and Sphenomorphis textum.

• To identify and define the presence or absence of any macro-habitat partitioning between Mabuya rudis and Sphenomorphus textum.

Sexual dimorphism

The following measurements were taken from M. rudis individuals caught in the pit-fall traps set up in the Kakenawe reserve and La Pago base camp:

1. Sex
2. Mass
3. Snout to vent
4. Tail length (if not regenerated)
5. Head depth
6. Tympanum to snout
7. Forelimb length
8. Forelimb girth
9. Length of dorsal stripe (scale count)
10. Length of lateral stripe (scale count)
11. Depth of lateral stripe (scale count)
12. Colour of lateral stripe
13. Colour of throat
14. Number of ocelli

Micro-habitat partitioning

A series of 100 metre transects were marked running approximately parallel to the pit lines. The transects were then walked the following day between 11am and 2pm (optimal activity time for both species) with the intention of spotting skinks. The following measurements were taken at the point of each siting:

1. Species
2. Sex (only possible with M. rudis due to colouration differences between the sexes)
3. Distance along transect
4. Activity (basking, perched, walking, running, eating)
5. Percentage light cover (determined using a 0.5m² quadrat and counting the crosshairs illuminated by sunlight)
6. Number of stems at a height of 30cm within the quadrat area and their diameters
7. Vegetation density at 30, 100 and 150cm. (determined by holding a 1m yellow pole marked every 1cm with a black stripe, at those heights and counting the number of whole stripes still visable from a distance of 2m)
8. Vertical vegetation density (determined by placing the same pole on the ground within the quadrat area and looking down on it from a height of 1.5m counting whole stripes visable)
9. Percentage logs (using the quadrat and counting the crosshairs over dead wood)
10. Percentage leaf litter (same method as above)
11. Average depth of leaf litter (5 measurements- 4 corners and the centre of the quadrat area)
12. Percentage rock cover (leaf litter removed then same method as above)
13. Distance to nearest log with diameter greater than 10cm
14. Average diameter of log (3 measurements- ends and middle)
15. Length of log
16. Distance to nearest tree with diameter greater than 50cm (at breast height)
17. Circumference of tree (at breast height)
18. Number and circumferences of trees with diameter (at breast height) less than 50cm but taller than 4m, within a 2.5m radius of the centre of the quadrat

Macro-habitat partitioning

At each of the pit sites a 5m² area was roped off at both ends and the following measurements were taken:

1. GPS
2. Aspect
3. Distance to nearest stream
4. Distance to nearest gully
5. Distance to nearest ridge
6. Vegetation density at 100 and 150cm (done as micro-habitat but using a white pole 2m long marked every 2cm counting lines which are either wholly or partially visable)
7. Circumference of every tree
8. Circumference of every vine
9. Length of any logs with diameter greater than 10cm
10. Average diameter (3 measurements- as above)
11. Distance to tree with diameter greater than 50cm (at breast height)
12. Circumference of tree (at breast height)
13. Average depth of leaf litter (9 measurements- corners, middle of each side and centre)
14. Exposed rock coverage (m²)

After the end of the wet season, the number of M. rudis caught in the pit-fall traps declined dramatically. This has resulted in very few individuals being measured for the sexual dimorphism study – the data for this is insufficient and will not be included in my Honours project. The data collected for the microhabitat study has also been disappointing as very few M. rudis were seen (although much data has been collected for S. textum.) and so a comparative study may not be possible. However, it should be possible to analyse the data for S. textum and look for niche partitioning between the adults and juveniles of this species. The macro-habitat assessments will be analysed in conjunction with the pit-fall data (which includes numbers and sexes of M. rudis and S. textum ) to look for habitat partitioning between the two species.

Report

A report entitled Sexual dimorphism and habitat use of a forest skink Mabuya rudis was produced by Pamela Minto, University of Glasgow in May 2002.