The effect of forest degradation on the
density, dominance and relative abundance
of herpetofauna in the spiny forests
of the Mandrare River Valley,
southern Madagascar.
by
Elise Damstra
An Extended Essay submitted in partial fulfillment of the requirements
for the International Baccalaureate Diploma Programme.
May 2012.
ABSTRACT
The globally unique spiny forests of southern Madagascar have many endemic species
but are threatened by forest degradation due to the need for cultivation and grazing. The
research question of this study asks ‘What is the effect of forest degradation on the density,
dominance and relative abundance of herpetofauna in the spiny forests of the Mandrare River
Valley, southern Madagascar?’ The independent variable is forest degradation. Three levels
were selected: highly degraded, moderately degraded and forest that was not degraded. In
each site a transect 250 m x 10 m was set up and the number and species of herpetofauna (the
dependent variables) were recorded on three different occasions in July 2011. Nineteen species
of reptiles were sighted totaling 282 animals. Other variables were controlled as much as
possible.
Degradation was shown to have a negative effect on the density of herpetofaunal
species. The species density in the forest that was not degraded is 15 per transect. This is
reduced by almost a half in the moderately degraded and two thirds in the highly degraded
forest. Species dominance was measured using the Simpson Index where a low index indicates
high biodiversity. The Simpson Index of the highly degraded transect is more than double that
of the other two sites, reflecting greater dominance by a single species. The changes in relative
abundance link forest degradation to a decrease in the ecosystem health. The community of
species also changes with degradation: ten species were restricted to forest that is not
degraded but four species were only found in areas with some degradation.
This research contributes to developing an effective management plan for the spiny
forests that may result in the degradation being reduced, halted or possibly reversed.
2
CONTENTS
Abstract .............................................................................................. 2
Research Question ............................................................................. 5
Introduction ....................................................................................... 5
Hypothesis ......................................................................................... 9
Investigation ...................................................................................... 9
Discussion .......................................................................................... 12
Evaluation .......................................................................................... 17
Conclusions ........................................................................................ 17
Extension ............................................................................................ 18
Bibliography ........................................................................................ 19
Appendix A: Raw Data ....................................................................... 22
Appendix B: Processed Data .............................................................. 30
Appendix C: Statistics ………………………………………..…………………………… 34
Acknowledgements ………………………………………………………………………. 36
3
Ifotaka
Figure 1: Map of Madagascar showing the remaining primary vegetation (Moat and Du Puy,
1997). The study site, Ifotaka in the Mandrare River Valley, is marked in the south in an area
of deciduous dry southern forest and scrubland (the spiny forests).
4
RESEARCH QUESTION
What is the effect of forest degradation on the density, dominance and relative
abundance of herpetofauna in the spiny forests of the Mandrare River Valley, southern
Madagascar?
INTRODUCTION
On finding out that there was a possibility of going to Madagascar with Operation
Wallacea to do my Extended Essay, I immediately began researching the reptiles and
amphibians, together called herpetofauna. Madagascar is a biodiversity hotspot1 where almost
all the amphibians and 92% of the reptiles are endemic2. The trip was in the dry season (July
2011, see Appendix A.4) so we were unlikely to find Amphibia that aestivate until the rains. So I
concentrated on reptiles although I was advised that sightings could not be guaranteed. As a
child on holiday in Cape Town, I found Cape dwarf chameleons in garden hedges and was
excited at the opportunity of visiting Madagascar which is the ‘centre of diversity’ of
chameleons3. I have seen skinks and geckos in Africa, and iguanas in zoos, although the species
in Madagascar would be new to me. I was keen to find plated lizards about which I had only
heard.
The semi-arid spiny forests of southern Madagascar are under threat from forest
degradation. They are such a unique environment which is so rich in endemic species that they
have been suggested as a UNESCO World Heritage Site. WWF include the spiny forests as one of
the Global 200 Priority Ecoregions for Global Conservation stating: ‘they are globally unique in
terms of structure and taxa’4. Their distribution is shown on Figure 1. Appropriately, this
research falls in the UN International Year of Forests 2011, a global celebration of people’s
action for sustainable forest management5.
I was travelling to the village of Ifotaka (24o 48’06”S, 46o 08’03”E) on the southern bank
of the Mandrare River (Figure 1). The study area lies across the river in the Ifotaka-North
Protected Area (Figure 2). A co-ordinated team of researchers is working on a baseline survey to
allow the spiny forest to be managed effectively. A detailed environmental monitoring plan for
this area has been drafted6. The first phase includes research on the herpetofauna, in
collaboration with Ole Theisinger from the University of Hamburg7.
All of this research is ‘to establish a sound scientific basis for understanding the
effectiveness of the management of the protected area’8. The aim is to encourage conservation
1
Conservation International, 2011.
Glaw and Vences, 2007: 46 & 77.
3
Ibid.: 266.
4
Olson and Dinerstein, 2002: 213.
2
5
UN International Year of Forests, 2011
Ferguson, 2011.
Theisinger, 2011.
8
Ferguson, 2011: 1.
6
7
5
Mahavelo
Mandrare
River
5 km
Sisal
plantation
Figure 2: Aerial photo of the study area showing the three transects in the spiny forest
north of the Mandrare River in the vicinity of Ifotaka and Mahavelo Field Camps (Google
Earth, imagery date 8/9/2005).
Transect 1 (T1, yellow) is highly degraded; Transect 2 (T2, green) is moderately degraded;
and Transect 3 (T3, red) is not degraded (for exact co-ordinates see Appendix A.1).
6
by working with the local villagers who traditionally use the area to cultivate crops (often by
clearing), as grazing for their cattle, and for harvesting products for food, fuel, shelter and cash9.
This causes forest degradation. A small area of 540 hectares is considered sacred by the
locals . It is only used for grazing cattle and as a burial ground. Just outside this area, there is a
great deal of logging for firewood and timber which is the main building material because bricks,
cement and other materials are expensive. Both logging and collecting dead wood reduces the
habitat available for reptiles. Can the needs of the community be met without degrading the
environment? This question can be answered when we have a greater understanding of the
effect of forest degradation.
10
There are different reasons for sampling herpetofauna. Besides finding species of
‘special conservation concern’, ‘other species might be indicators of ecological conditions’11.
'Interest in using amphibians and reptiles as indicators of forested ecosystem health has
increased'12. Herpetofauna may be more important indicators of degradation by cattle in arid
habitats, like Arizona13 and the Kalahari14. Theisinger suggests this is because they are highly
abundant and ‘often specialised concerning habitat requirements’15. Scott et al. found that
clearance of the spiny forests 30 km east of Ifotaka significantly reduced the species richness
and abundance of lizards but not of birds and small mammals16. They suggest that of these
three groups lizards ‘may be the most sensitive to habitat modification’17.
It was this concept of using herpetofauna as an indicator to measuring the overall
impact of human activity on the spiny forest that attracted me to this project. I decided to
investigate the effect of forest degradation on the density, dominance and relative abundance
of the herpetofauna in the Mandrare River Valley.
9
Ibid.: 5; WWF, 2011
Miller, 2008.
11
Bonar, et al., 2011: 12.
12
Bury and Corn, 1988.
13
Castellone and Valone, 2006.
14
Wasiolka and Blaum, 2011.
15
Theisinger, 2011.
16
Scott et al., 2006.
17
Ibid.: 82.
10
7
Figure 3: Spiny forest of the
highly degraded Transect 1.
The stony area marks a family
tomb and tall Alluaudia procera
protrude above the canopy
(Photo: E. Damstra, July 2011).
Figure 4: Zebu cattle grazing in the sacred area near the highly degraded Transect 1 with prickly
pear to the far right (Photo: A. McBride, July 2011).
8
HYPOTHESIS
I hypothesize that increased degradation of the spiny forest will result in both a smaller
variety of species and a lower density of herpetofauna.
INVESTIGATION
The fieldwork on herpetofauna needs to match the data collected on lemurs, birds and
vegetation so the selection of suitable transect sites was prepared by the Ifotaka Ecological
Monitoring Technical Advisory Panel and is outlined by Ferguson18. No detailed vegetation
maps exist. The sites have been placed in different management zones and reflect different
levels of forest degradation. So the independent variable in this study is the state of
degradation of the forest and three levels were selected: highly degraded, moderately
degraded, and forest that is not degraded. The dependent variables are the number and species
of herpetofauna sampled. Technical advice was provided by Ole Theisinger. Fieldwork was
undertaken together with local guides and help from fellow pupils of Sevenoaks School. I
prepared for the work by being able to classify the different lizard families and having an
illustrated list of the local species. Local guides helped with classification. Herpetofauna can be
sampled using transects, pitfall traps and cover-boards19.
Transects: The most successful quantitative method is day-time transects with a team
counting the number of reptiles of each species found in a fixed area. This allows us to observe
their behaviour in their natural environment with minimal damage to the forest. Transects have
to be done when reptiles are active. Most reptiles emerge once the sun has started to heat the
ground. They bask in direct sunlight to increase their body temperature so they have energy to
move around. This variable was controlled by completing the transects between 09.00 and
14.00. Another controlled variable is the size of each transect which was 250 m by 10 m. This
was considered large enough to represent the species composition of the area. Everyone
collecting data (a group of about 8 people) spreads out along the width of the transect (10 m)
and walks slowly in a straight line. The path of each transect was marked by small flags on trees.
While walking and looking, we routinely turned over rocks or scraped back bark on trees as
these are popular shelters for reptiles. In order to conduct the search as thoroughly as possible,
it was necessary to take time, as each reptile seen has to be classified, which can be difficult
when they are only glimpsed. Some species needed to be caught because they can only be told
apart by counting certain scales. Different types of scale counts are used in different reptile
families. In snakes, the number of ventral scales is counted and in many lizards, mental and
postmental scales (scales located under the mouth) are used to differentiate between species.
Transects were carried out every day, but in different places. Each transect was inspected on
three different days to even out slight differences in weather conditions.
The three transects representing the highly degraded, moderately degraded, and not
degraded forests were selected about 2 km apart from each other as shown on Figure 2 (the coordinates are included in Appendix A.1). No significant climatic or geological difference exists
18
19
Ferguson, 2011.
Ibid.: 38-40.
9
Figure 5: The high spiny forest of the moderately degraded Transect 2 with a person to show the
scale. Alluaudia procera protrude above the shrub layer that contains succulent Euphorbia
(Photo: E. Damstra, July 2011).
Figure 6: The spiny forest of Transect 3 which is not degraded (Photo: A. Dudney, July 2011).
10
between the sites. On each visit to a transect we were accompanied by at least one local guide
and the work took approximately one hour to complete.
Transect 1 (highly degraded) is a 10-minute walk from the river, to the north of Ifotaka village.
It is an area with a high level of human activity with a well-used path nearby. Family tombs are
covered in large rocks (Figure 3). Most of the transect is flat. Cattle were seen grazing in the
surrounding area and there was evidence (dung) that they had been grazing within the transect
(Figure 4). There are few particularly big trees, which indicates that there has been
deforestation. There was no dead wood in the transect which means that it had been removed
for firewood or other purposes. The invasive prickly pear is common (Figure 4). The trees that
are present are scattered and it is easy to walk through the area.
Transect 2 (moderately degraded) is a 40-minute walk from the river, located off a path that
seemed to be well-used. It has more shrubs and low bushes than Transect 1 as well as more
dead wood, a few rotting tree trunks, almost no prickly pear and a few tall trees (Figure 5).
Much of the forest is relatively open, and it is mostly easy to walk through, though there are
several bushes and dead tree trunks that have to be walked around or stepped over. The
majority of this transect is flat and there are no tombs. There was no obvious sign of cattle
grazing, but there was evidence of logging.
Transect 3 (intact forest, not degraded) is north-east of Mahavelo Field Camp, a 90-minute walk
from the Mandrare River. It is in a dry river bed, with slopes on either side. It is located about
100 m off the closest path, which is not a main path. There are some big trees on either bank
and almost no prickly pear (Figure 6). It is a lot more difficult to walk in a straight line along this
transect. There are many branches to be ducked under and more shrubs to step over. There
was a lot of dead wood.
Pitfall traps in lines sample species that hide from people or are present at night. These traps
were also set up to sample small mammals20. It was considered disrespectful to dig pitfall traps
in the sacred forest (the highly degraded area of Transect 1). As a result the data does not allow
a complete quantitative comparison in the three areas. Each trap was a 10 litre bucket buried
flush with the ground. A pitfall line consists of 10 buckets in a line 10 m apart with a piece of
black plastic marking out the line. The function of this plastic is to lure in, or guide in nocturnal
animals that scavenged on the forest floor for food. However some animals are able to crawl
out of the traps.
Cover-boards include ground cover objects (such as pieces of corrugated iron placed on the
ground which heat up in the sun to attract lizards and snakes) and tree cover objects (pieces of
foam wrapped around tree trunks as artificial bark to attract geckos).
20
Ferguson, 2011: 40.
11
DISCUSSION
An annotated list of all the species of herpetofauna found during this survey is included
in Appendix A.2. The three transects provide the best quantitative data for analysis (the raw
data is shown in Appendix A.3). However Bonar et al. highlight the problem of having a
sampling technique that could exclude species that may be present ‘at different times of the
day’21. The pitfall-traps and cover-boards therefore provide qualitative data on species that may
not be seen in transects. The pitfall traps at Transects 2 and 3 mainly trapped pygmy musk
shrews, spiders and scorpions. The herpetofauna included only a few ground geckos and a
single specimen of the microhylid frog, Scaphiophryne brevis, which moves around at night22. If
there had been a lot of species in these traps that were not seen in the transects this would
mean that the transects were not sampling the herpetofauna well. But this was not the case
which supports the idea that transects are a reliable sampling method for herpetofauna in the
spiny forest. Species found in the pitfall traps and beneath cover-boards are included in
Appendix A.2.
I will start by comparing the total number of herpetofaunal species present in each of
the three levels of forest degradation. This is called the species richness of that area. With any
sampling technique we cannot find everything in the habitat, we can only find the observed
species richness which is called the species density. The more samples we take and the more
Cumulative number of species found
16
14
12
10
8
Highly degraded
Moderately degraded
6
Not degraded
4
2
0
0
1
2
3
Transect repeat number
Figure 7: Graph to show the cumulative number of species found in each transect with each
repeat. This is a measure of species density in the transect (processed data in Appendix B.1).
21
22
Bonar et al., 2011: 13.
Glaw and Vences, 2007: 110.
12
complete our survey then the closer the observed species density reflects the real species
richness. Figure 7 shows the cumulative number of species found for the three repeat samples
in each transect. Each curve shows the species density that has been observed approaching the
species richness for that transect. Initially the slope rises steeply as most of the species in the
area are sampled. Then the slope forms a plateau which in theory will flatten out at the species
richness. The height of the plateau is different for each transect. For the highly degraded
transect the plateau may not be much above the 5 species found. The curve for the moderately
degraded forest is forming a gently rising plateau when it reaches 8 species on the third repeat
sample. In the forest that is not degraded the curve has also passed the steep slope. After
three repeat samples the plateau is still rising steadily. The shape of the curve implies that the
species richness may be over the 15 species that were sampled. These results match those
found 30 km east where the spiny forests that was not degraded had 13 species of lizard but
areas which had previously been cleared had only 7 species23.
This clearly demonstrates that in spiny forest the level of degradation affects the density
of different species in the area. By comparison with forest that is not degraded, the species
density is reduced by almost a half in the moderately degraded and two thirds in the highly
degraded forest.
But species richness is only part of biodiversity. Two areas can have the same number
of species but in one area a few species are dominant and the rest are rare whereas in the other
area all species are present in equal numbers. The second area is considered to have a greater
biodiversity. There are many calculations that try to measure this. Buckland et al. discuss which
of these is best and suggest that the Simpson Index ‘performs well’24, although for ideal
comparison the samples should have the same number of individuals. The calculation is shown
in Appendices C.1 & B.2 and the results in Figure 8. Simpson’s diversity index measures
dominance25. It answers the question: What is the probability that, when you take two
specimens out of the habitat at random, they will both be the same species? The index is on a
scale from zero to 1. It is 1 when all individuals belong to the same species and there is no
diversity. Zero means there is maximum evenness of the different species. Evenness is a
measure of how equally abundant each of the species are: high evenness indicates ecosystem
health26.
Figure 8 clearly shows that the highly degraded forest has a high level of dominance
with the mean Simpson Index more than double the value of that in either of the other two
transects. Looking at the raw data this can be accounted for by the high frequency of
Trachylepis elegans in the highly degraded forest. These skinks are ‘common in disturbed open
landscape’27 and frequently found in human influenced habitat28. This high dominance suggests
a poorer biodiversity and is not considered favourable in a habitat. The Simpson Indices for the
Scott et al., 2006: 78.
Buckland et al., 2011: 27.
25
Simpson, 1949.
26
Danoff-Burg, 2003b.
27
Boumans et al., 2007: 833.
28
Gandola, 2011.
23
24
13
Simpson Index = 1:
no diversity, all
species belong to one
dominant species,
indicates poor
biodiversity.
1,0
0,9
0,8
Simpson Index
0,7
0,6
0,5
0,4
0,3
0,2
0,1
0,0
0
20
40
60
80
Total number of specimens recorded in transect
100
Simpson Index = 0:
maximum evenness
of the different
species, usually
indicates high
biodiversity.
Figure 8: The Simpson Index relative to sample size in spiny forest that is not degraded (red),
moderately degraded (green) and highly degraded (yellow). Processed data in Appendix B.2.
other two transects are not very different but with the moderately degraded forest having a
lower value, which indicates that it has a higher evenness. This can be explained by the low
number of individuals found in this transect. The lowest Simpson Index (0.07, see Appendix B.2)
occurs in the second repeat in the moderately degraded forest where the fewest specimens
were seen: only 6 individuals representing 5 species. Although the index provides information
on dominance it needs to be understood in relation to the sample size (Figure 8).
Interestingly the community of herpetofauna also changes with forest degradation (see
Appendix A.3). Ten species were found exclusively in the forest that was not degraded. To
conserve these rare species, forest that is not degraded needs to be protected. Three species
were only found in the moderately degraded forest, these include a chameleon ‘common in
disturbed areas’29, a snake abundant in ‘a wide variety of anthropogenic habitats’30 and a gecko.
Only one species, Trachylepis aureopunctata, was restricted to the degraded areas. This
indicates that some forest degradation may help to maintain a more diverse community of
herpetofauna.
29
30
Glaw and Vences, 2007: 302.
Ibid., 2007: 440
14
Relative abundance (log scale)
Highly degraded
Not degraded
Moderately degraded
100,0
100,0
10,0
10,0
1,0
0
0,1
5
10
Abundance rank
15
1,0
0
0,1
5
10
Abundance rank
Figure 9: The mean rank abundance plots for the three habitats (processed data shown in
Appendix B.3). The highly degraded transect in yellow is almost a straight line, the moderately
degraded transect is in green, and the transect in forest that is not degraded is in red.
The rank abundance plot is ‘one of the best known and the most informative method’ to
visualize the species diversity, species evenness and the relative abundance of species31.
McGill suggests that the interpretation is complicated because ‘the differences in species
richness quickly dominate all other patterns’32. To produce these graphs (Figure 9, Appendix
B.3), the species with the most individuals is ranked 1. This rank is plotted on the x-axis. The yaxis is the mean number of individuals of that species that are present in the sample. This is the
relative abundance and it is plotted on a log10 scale. The gradient of the curve represents the
species evenness: a steeper curve reflects greater differences in the numbers of the different
species. Theoretically there are four different curves on this type of graph (Figure 10).
Evenness, or ecosystem health, increases from a Geometric Series to a Log Series, to a LogNormal series, to the ‘Broken-Stick Model’33. Changing in the opposite direction would indicate
a reduction in the diversity of the community.
Figure 9 shows the mean rank abundance plots for all three transects. The highly degraded
transect (yellow) is dominated by one species and has only has five species in total. The graph is
close to a straight line which indicates a geometric series. This is low species evenness and low
species density. The moderately degraded transect (green) has greater species evenness, and
more species. It is less like a straight line than the highly degraded transect. The intact forest
that is not degraded (red) has the greatest evenness with the highest species density. The
pattern is least like a straight line and may possibly approach the log-normal curve. The pattern
31
Sohier, 2008.
McGill, 2011: 108.
33
Danoff-Burg, 2003b.
32
15
of the results therefore follows what we would expect if the health of the forest decreased as it
was increasingly degraded.
Although these results support my hypothesis because increased degradation of the
spiny forest reduces both the variety of species and the density of herpetofauna, the effect is
more subtle than I had imagined at the time. The community of species also alters and different
species exploit different levels of degraded forest.
Hypothetical Model Curves
100
10
Broken Stick Model
Per 1
Species
Abundance 0.1
Log-Normal Series
0.01
Log Series
0.001
Geometric Series
10
20
30
40
Species Addition Sequence
Lecture 3 – Evenness & Species Abundance Models
© 2003 Dr. James A. Danoff-Burg, [email protected]
Figure 10: Suggested interpretations of rank abundance plots. Data on a rank-abundance curve
could show one of four different patterns. Evenness (linked to ecosystem health) increases from
a Geometric Series (the straight line graph) to a Log Series, to a Log-Normal series, to the
‘Broken-Stick Model’ that has maximum evenness (from Danoff-Burg, 2003b).
16
EVALUATION
‘Sampling bias occurs when the sample does not include all groups of interest in the
population’34. Transects always include some sampling bias however in this study the pitfall
traps and cover-boards show that only a few species are not represented in the transect data.
But have sufficient samples been completed? To answer this we need to see how species
density changes as more samples are studied. Each successive sample should result in fewer
new species found. When this graph starts to plateau out then generally biologists suggest that
the sampling effort has been good enough35. This is shown on figure 7 where the transects are
levelling off, which indicates that sufficient samples were taken in order to measure the species
richness.
The data collected can be deemed as reliable in the sense that the same method was
used each time, but there are many limitations and problems with collecting transect data. The
thoroughness of searching depend on the research assistants, as some may have been more
perceptive than others. Also, less experienced assistants may not have been able to identify a
specimen before it ran away.
The weather on the day has a significant effect on the activity of reptiles. Reptiles are
cold blooded animals and heat up in the sun. If it is sunny they will sit in the open and bask, but
if it is overcast they will not expose themselves as much. Three repeats of each transect were
done on different days to counteract as many of these variables as possible.
CONCLUSIONS
The effect of forest degradation on the density, dominance and relative abundance of
herpetofauna in the spiny forests of the Mandrare River Valley was examined. Field work was
done in the dry season (July 2011). Three different levels of forest degradation were selected:
highly degraded, moderately degraded and forest that was not degraded. Three repeats of each
transect (250 m x 10 m) were examined.
Nineteen species of reptiles were sighted in the trasects totaling 282 animals. Results from
pitfall traps and cover-boards indicate that transects sample herpetofauna populations
efficiently.
Degradation was shown to have a negative effect on the density of herpetofaunal species.
Species density: A total of 15 different species were found within the transect in the forest that
was not degraded. This is reduced by almost a half in the moderately degraded and two thirds
in the highly degraded forest.
The Simpson Index of the highly degraded forest is double that of the other two sites reflecting a
greater dominance by a single species. This represents a reduced biodiversity.
34
35
Bonar et al., 2011: 14.
Danoff-Burg, 2003a.
17
Rank abundance curves reflect the relative abundance of herpetofauna. The curves link
increased forest degradation to a decrease in the ecosystem health.
The results emphasize the negative effects of degradation in these globally unique spiny forests
with their many endemic species. But the local villagers also need land for cultivation and
grazing. Understanding degradation is the first step in developing effective management and
promoting conservation. Limited human activity may even encourage some species. This
research project is part of the management plan to provide sustainable ‘livelihood alternatives
for the local people’36 which includes us making use of the Ifotaka Community Bungalows and
the Ifotaka Field Laboratory where the field guides are trained. If successful the forest
degradation may be reduced, halted, or possibly even reversed.
EXTENSION
Recent literature is critical of rank abundance curves even though they ‘offer a useful
and appealingly simple visual check of community structure’37. This research needs to be
extended by doing more complicated analyses of the data38.
This project examined the effect of degradation but did not ask why the reptile
population changes when the forest is degraded? Ole Theisinger39 suggests that reptiles are less
particular about the composition of the vegetation but are sensitive to the availability of
habitats in the form of dead wood where they seek food, shelter and protection from predators.
With increased human activity, dead wood is often removed and used for firewood. This
hypothesis could be tested.
Why are some species rare and others common? This question is posed by the
interesting Raunkiaer frequency distribution I found for Ifotaka reptiles (see Appendix C.2).
More work is needed to answer this question.
Ferguson, 2011: 5.
Dornelas et al. 2011: 243.
38
Magurran and McGill, 2011.
39
Pers. comm., July 2011.
36
37
18
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Danoff-Burg, James A. 2003a. Choosing Between Diversity Indices. Available at:
http://www.columbia.edu/itc/cerc/danoff-burg/MBD%205.ppt#256,1,Choosing Between
Diversity Indices [accessed 12 August 2011].
Danoff-Burg, James A. 2003b. Evenness and Abundance Models. Available at:
http://www.columbia.edu/itc/cerc/danoff-burg/MBD%203.ppt#256,1,Evenness and Abundance
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Magurran, Anne E., and Brian J. McGill (eds) Biological Diversity: Frontiers in measurement and
assessment. Oxford University Press, Oxford: 237-251.
19
Ferguson, Barry. 2011. Ifotaka-North Protected Area participatory environmental monitoring
plan 2011-2015. Third draft, 1st May 2011. Available at:
http://independent.academia.edu/BarryFerguson/Papers/597004/Ifotaka_Monitoring_Plan_Dr
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Madagascar. Available at:
http://www.opwall.com/Universities/Thesis/Dissertation_summaries/MN226%20Microhabitats
%20and%20niche%20partitioning%20in%20chameleons%20or%20skinks%20in%20Madagascar.
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Glaw, Frank and Miguel Vences. 2007. A field guide to the amphibians and reptiles of
Madagascar. Third edition. Vences & Glaw Verlag, Cologne: 496 pp.
IUCN Red List of Threatened Species. 2011. Available at:
http://www.iucnredlist.org/apps/redlist/details/9014/0 [accessed 29 October 2011].
McGill, Brian J. 2011. Species abundance distributions. In: Magurran, Anne E., and Brian J.
McGill (eds) Biological Diversity: Frontiers in measurement and assessment. Oxford University
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measurement and assessment. Oxford University Press, Oxford.
Miller, L. 2008. Walking amongst the sacred spines: Social and ecological investigation of the
Fenoaivo and Zanavo Sacred Forests in southern Madagascar. Independent study project for
the School of International training, 60pp. Available at:
http://digitalcollections.sit.edu/cgi/viewcontent.cgi?article=1572&context=isp_collection
[accessed 12 August 2011]
Moat, Justin and David Du Puy. 1997. GIS and Conservation for Madagascar. Available at:
http://www.kew.org/gis/projects/madagascar/primary_veg.html [accessed on 12 August 2011].
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August 2011].
Raunkiær, C. 1918. Über das biologische Normalspektrum. Biologiske Meddelelser / Kongelige
Danske Videnskabernes Selskab, 1 (4): 1-17. Reprinted in: Raunkiær, C. 1934. The life forms of
plants and statistical plant geography. Oxford University Press, Oxford: 425-434. Quoted in:
Colinvaux, Paul A. 1973. Introduction to Ecology. John Wiley & Sons, N.Y: 514-520.
Scott, Dawn M., Daniel Brown, Simon Mahood, Buck Denton, Anastasia Silburn and Felix
Rakotondraparany. 2006. The impacts of forest clearance on lizard, small mammal and bird
communities in the arid spiny forest, southern Madagascar. Biological Conservation 127: 72-87.
20
Simpson, Edward H. 1949. Measurement of diversity. Nature 163: 688. Available at:
http://people.wku.edu/charles.smith/biogeog/SIMP1949.htm [accessed 25 August 2011].
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[accessed 30 August 2011].
Sohier, Charlotte. 2008. Measurements of Biodiversity. Available at:
http://www.coastalwiki.org/coastalwiki/Measurements_of_biodiversity [accessed 30 August
2011].
Theisinger, Ole. 2011. The effect of degradation and land use on reptile communities in the spiny
forest of Ifotaka, southern Madagascar. Dissertation summary. Available at:
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munities%20of%20the%20spiny%20forest.pdf [accessed 25 October 2011].
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http://www.audleytravel.com/Destinations/Africa/Madagascar/Places-to-Go/Southern-Tip-ofMadagascar/Ifotaka-Community-Forest/Climate.aspx [accessed 23 October 2011].
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836-841.
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August 2011].
21
APPENDIX A: RAW DATA
Appendix A.1: Raw data on the transect lines with co-ordinates and vegetation
description.
Transect 1 (Ifotaka, at the first pitfall line):
S 24o 47.841’ E 46o 08.949’ to S 24o 47.808’ E 46o 08.808’
Vegetation highly degraded, no dead wood, no big trees, a lot of prickly pear, signs of current
logging.
Transect 2 (Ifotaka, at the second pitfall line):
S 24o 46.825’ E 46o 09.440’ to S 24o 46.952’ E 46o 09.409’
Vegetation moderately degraded, some dead wood, some rotting tree trunks, almost no prickly
pear, some bigger trees, relatively open, signs of current logging.
Transect 3 (Mahavelo, in the dry riverbed):
S 24o 45.460’ E 46o 09.561’ to S 24o 45.472’ E 46o 09.708’
Vegetation not degraded, a lot of dead wood/drift wood, some big trees, almost no prickly pear,
heterogeneous, no signs of current logging.
The occurrence of prickly pear (Opuntia spp.) is significant because it is an exotic
invasive species, particularly in disturbed areas. It was originally planted as food, but has spread
uncontrollably and taken over some of the spiny forest. However, the fact that it has not spread
to other areas shows that particular area's lack of degradation and how untouched it is. It is also
a source of food for the local zebu cattle and people collect the fruit to eat (Ferguson, 2011). In
the wild Opuntia are a favourite food plant for the endemic and critically endangered radiated
tortoise (Smithsonian National Zoological Park, [n.d.], IUCN Red List of Threatened Species,
2011).
22
Appendix A.2: List of species found during this survey.
Class: Reptilia
Family: Testudinidae (tortoises: distributed worldwide).
Figure A.1: The radiated tortoise
(Astrochelys radiata), which is endemic
to the spiny forest in the south of
Madagascar, is listed as critically
endangered on the IUCN Red List of
Threatened Species (2011) because it is
consumed for food and heavily poached
(Glaw and Vences, 2007). It is a
‘conservation target species’ in the
Ifotaka-North Protected Area
(Ferguson, 2011). I photographed this
specimen just off Transect 3, July 2011.
Family: Chamaeleonidae (chameleons: distributed in the Old World).
Furcifer verrucosus is endemic to Madagascar where it is “common in disturbed areas” (Glaw
and Vences, 2007).
Family: Iguanidae (iguanas: distributed in the Americas, Pacific islands and Madagascar,
not in Africa or Asia).
Genus: Oplurus (endemic to Madagascar and Comoros).
Figure A.2: Oplurus cyclurus is found in
dry areas of southern and western
Madagascar (Glaw and Vences, 2007.
Photo: A. Dudney, July 2011).
23
Oplurus saxicola is endemic to south-western Madagascar where it is relatively common in arid
areas (Glaw and Vences, 2007).
Figure A.3: Oplurus
quadrimaculatus is endemic to the
extremely arid south-west of
Madagascar (Glaw and Vences,
2007. Photo: A. McBride, July
2011).
Family: Gerrhosauridae (plated lizards: distributed in southern Africa and Madagascar)
Genus: Zonosaurus
Zonosaurus laticaudatus is endemic to Madagascar, common in open areas (Glaw and Vences,
2007).
Genus: Tracheloptychus (endemic and restricted to the arid regions of southern
Madagascar, Glaw and Vences, 2007).
Figure A.4: Tracheloptychus
madagascariensis is found in dry
forests, thornbush and dunes (Glaw
and Vences, 2007. Photo: E.
Damstra, July, 2011).
24
Family: Scincidae (skinks: distributed worldwide).
Genus: Trachylepis (distributed in the African-Malagasy region).
Trachylepis elegans is common and widespread in Madagascar (Glaw and Vences, 2007). These
skinks are ‘common in disturbed open landscape’ (Boumans et al., 2007: 833) and frequently
found in human influenced habitat (Gandola, 2011).
Trachylepis gravenhorstii is common and widespread in Madagascar (Glaw and Vences, 2007). A
specimen was found near Mahavelo.
Trachylepis aureopunctata is endemic to arid habitats of south-western Madagascar (Glaw and
Vences, 2007).
Trachylepis dumasi is endemic to spiny forests of Madagascar (Glaw and Vences, 2007).
Figure A.5: Trachylepis vato occurs in arid
areas of south-western Madagascar and the
southern part of the central highlands (Glaw
and Vences, 2007. Photo: A. McBride, July,
2011).
Genus: Madascincus (endemic to Madagascar).
Madagascincus igneocaudatusis is found in the arid south-west of Madagascar (Glaw and
Vences, 2007).
Genus: Voeltzkowia (legless skinks, endemic to Madagascar).
Voeltzkowia lineata is restricted to south-western Madagascar (Glaw and Vences, 2007).
25
Family: Gekkonidae (geckos, worldwide distribution).
Genus: Geckolepis (endemic to Madagascar).
Geckolepis typica is widespread in Madagascar (Glaw and Vences, 2007).
Genus: Hemidactylus (house geckos, worldwide distribution).
Figure A.6: Hemidactylus mercatorius is widespread
throughout Madagascar in villages, towns, degraded
areas and secondary forests (Glaw and Vences,
2007. Photo: A. McBride, July 2011).
Genus: Paroedura (endemic to Madagascar and Comoros)
Paroedura androyensis occurs in dry forests and dry coastal rocks in southern Madagascar (Glaw
and Vences, 2007.
Figure A.7: Paroedura picta is often in dry forest
or spiny scrub vegetation (Glaw and Vences,
2007. Photo: A. McBride, July 2011).
Genus: Lygodactylus (from Africa, Madagascar and South America).
Lygodactylus decaryi is a poorly known species endemic to dry areas of southern Madagascar
(Glaw and Vences, 2007).
Genus: Phelsuma (from Madagascar and other Indian Ocean islands).
Phelsuma mutabilis lives in the hot and dry west and south of Madagascar (Glaw and Vences,
2007). Found under a tree-cover object near Ifotaka.
26
Family: Colubridae (typical snakes, worldwide distribution)
Genus: Lycodryas (endemic to Madagascar).
Figure A.8: Lycodryas pseudogranuliceps is a
poorly known species from arid habitats. It
is in a genus of slender tree snakes with
distinct, broad heads (Glaw and Vences,
2007. Photo: A. Dudney, July 2011).
Genus: Mimophis (a monotypic genus endemic to Madagascar).
Figure A.9: Mimophis mahfalensis is
common in a wide variety of habitats across
Madagascar including disturbed areas. It is
so different from all other snakes in
Madagascar that it probably arrived from
Africa after the others (Glaw and Vences,
2007. Photo: D. Adeline, July 2011).
Class: Amphibia
Family: Microhylidae (distributed worldwide).
Figure A.10: Scaphiophryne brevis occurs
in dry open areas in southern and southwestern Madagascar. They are burrowing
frogs that move around at night (Glaw
and Vences, 2007). This specimen was
caught in a pitfall trap near Transect 2
(Photo: A. McBride, July 2011).
27
Transect 1 Highly Degraded
Species
Transect 2 Moderately Degraded
Transect 3 Not Degraded
Date
02/07/11
10/07/11
11/07/11
03/07/11
10/07/11
12/07/11
05/07/11
16/07/11
19/07/11
Time
09:19
10:45
10:45
09:15
09:00
09:18
11:25
12:56
11:40
Tracheloptychus madagascariensis
2
3
3
6
1
2
10
1
11
Trachylepis elegans
21
19
28
5
2
9
20
19
43
Trachylepis aureopunctata
1
1
2
1
3
14
22
Trachylepis vato
2
2
Hemidactylus mercatorius
1
1
1
Geckolepis typica
1
Paroedura androyensis
1
Mimophis mahfalensis
1
Furcifer verrucosus
1
1
1
Lygodactylus sp.
1
Trachylepis dumasi
1
1
Oplurus quadrimaculatus
1
2
Oplurus saxicola
1
Lygodactylus decaryi
1
Zonosaurus laticaudatus
1
2
3
Madascincus igneocaudatus
1
Oplurus cyclurus
2
1
Voeltzkowia lineata
1
Paroedura picta
1
Key:
Frequency of occurrence in transect:
1
2
3
4-9
10 - 19
20 +
Appendix A.3: Raw data showing how many individuals of each species were found in each repeat in the three transects.
28
Appendix A.4: Temperature and precipitation data for Ifotaka Community Forest.
The main rains are between January and March. July, when this data was collected, is
considered part of the cooler dry season. (From: Visit Ifotaka Community Forest, Southern Tip of
Madagascar, 2011)
29
APPENDIX B: PROCESSED DATA
Sample 1
Sample 2
Sample 3
Highly
degraded
3
4
5
Moderately
degraded
4
7
8
Not
degraded
9
13
15
Appendix B.1: The cumulative number of species found in each transect with each
repeat (data from Appendix A.3, used to construct Figure 7).
30
Species
Highly degraded
Moderately
degraded
Tracheloptychus madagascariensis
Trachylepis elegans
Trachylepis aureopunctata
Trachylepis vato
Hemidactylus mercatorius
Geckolepis typica
Paroedura androyensis
Mimophis mahfalensis
Furcifer verrucosus
Lygodactylus sp.
Trachylepis dumasi
Oplurus quadrimaculatus
Oplurus saxicola
Lygodactylus decaryi
Zonosaurus laticaudatus
Madascincus igneocaudatus
Oplurus cyclurus
Voeltzkowia lineata
Paroedura picta
Total number of specimens
Simpson Index
Mean Simpson Index
2
21
1
6
5
1
3
19
1
2
3
28
2
1
1
2
Not degraded
2
9
2
10
20
1
19
11
43
3
14
1
1
22
1
2
2
1
1
1
1
1
1
1
1
1
1
1
1
3
1
2
1
1
1
24
25
34
13
6
15
39
42
84
0.76
0.58
0.68
0.32
0.07
0.36
0.32
0.31
0.34
0.68
0.25
0.32
Appendix B.2: The total number of specimens and the Simpson Index for each sample as well as the mean Simpson Index
for each transect (data used to plot Figure 8). The raw data and colour key are the same as in Appendix A.3.
31
Status
Transect
Highly degraded
Moderately degraded
Intact forest, not degraded
T1.1 T1.2 T1.3 Mean Rank T2.1 T2.2 T2.3 Mean Rank T3.1 T3.2 T3.3 Mean Rank
Species
No.(n) No.(n) No.(n) No.(n)
No.(n) No.(n) No.(n) No.(n)
No.(n) No.(n) No.(n) No.(n)
Trachylepis elegans
21
19
28
22.7
1
5
2
9
5.3
1
20
19
43
27.3
1
T. madagascariensis
2
3
3
2.7
2
6
1
2
3
2
10
1
11
7.3
3
Trachylepis aureopunctata
1
1
2
1.3
3
1
2
1
3
Trachylepis vato
2
3
14
22
0.7
13
2
4
Oplurus saxicola
1
3
1.3
4
Trachylepis dumasi
1
1
2
1.3
5
Oplurus quadrimaculatus
1
2
1
6
Oplurus cyclurus
2
1
1
7
Mimophis mahfalensis
1
1
0.7
4
Hemidactylus mercatorius
1
0.3
5
1
1
0.3
5
0.3
8
Geckolepis typica
1
1
0.3
6
0.3
9
Paroedura androyensis
1
0.3
7
Furcifer verrucosus
1
0.3
8
Lygodactylus sp.
1
0.3
10
Lygodactylus decaryi
1
0.3
11
Zonosaurus laticaudatus
1
0.3
12
Madascincus igneocaudatus
1
0.3
13
Voeltzkowia lineata
1
0.3
14
Paroedura picta
1
0.3
15
Appendix B.3 (Processed Data): Data for the rank abundance curves (Figure 9).
For each transect the mean number of each species sampled is calculated and then ranked from most abundant to least abundant.
The rank is plotted on the x-axis, whereas the mean is plotted as the y-coordinate a log scale.
32
Status
Transect abbreviation
Species
Trachylepis elegans
Tracheloptychus madagascariensis
Trachylepis vato
Trachylepis aureopunctata
Oplurus quadrimaculatus
Hemidactylus mercatorius
Geckolepis typica
Paroedura androyensis
Mimophis mahfalensis
Furcifer verrucosus
Lygodactylus sp.
Oplurus saxicola
Trachylepis dumasi
Lygodactylus decaryi
Zonosaurus laticaudatus
Oplurus cyclurus
Madascincus igneocaudatus
Voeltzkowia lineata
Paroedura picta
Highly degraded
T1.1
T1.2
T1.3
P
P
A
P
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
P
P
P
P
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
P
P
A
P
A
P
A
A
A
A
A
A
A
A
A
A
A
A
A
P
A
Moderately degraded
T2.1
T2.2
T2.3
P
P
A
P
A
P
A
A
A
A
A
A
A
A
A
A
A
A
A
P
P
A
A
A
A
P
P
P
A
A
A
A
A
A
A
A
A
A
P
P
A
P
A
A
A
A
P
P
A
A
A
A
A
A
A
A
A
Not degraded
T3.1
T3.2
T3.3
P
P
P
A
P
A
A
A
A
A
P
P
P
P
P
A
A
A
A
P
P
P
A
P
P
P
A
A
A
A
A
P
A
A
P
P
A
A
P
P
P
A
A
A
A
A
A
A
A
P
P
A
A
P
A
P
P
Occurrence % Occurrence
9/9
100
9/9
100
4/9
44
5/9
55
2/9
22
3/9
33
2/9
22
1/9
11
2/9
22
1/9
11
1/9
11
2/9
22
3/9
33
1/9
11
1/9
11
2/9
22
1/9
11
1/9
11
1/9
11
Key:
Species present in this transect
Species absent in this transect
Appendix B.4 : Table to show percentage occurrence of each species in all transects used to construct the
Raunkiaer frequency distribution (Appendix C.2).
33
APPENDIX C: STATISTICS
Appendix C.1: The Simpson Index40.
The formula to work out the Simpson Index (D) is:
D=
ఀ௡(௡ିଵ)
ே (ே ିଵ)
where N is the sum of animals sighted and n is the total number of each species sighted.
Therefore N is the sum of all values of n.
To work out the mean Simpson Index for the highly degraded transect (Transect 1) using all repeats:
Species
Repeat 1 Repeat 2 Repeat 3 Number (n) n(n-1)
Tracheloptychus madagascariensis
2
3
3
8
56
Trachylepis elegans
21
19
28
68
4556
Trachylepis aureopunctata
1
1
2
4
12
Trachylepis vato
2
2
2
Hemidactylus mercatorius
1
1
0
83
Total (N)
4626
ᄿ n(n-1)
D=
ସ଺ଶ଺
଼ଷ(଼ଶ)
D = 0.68
Using this method, the mean Simpson Indices for moderately degraded (Transect 2) and not
degraded forest (Transect 3) are 0.25 and 0.32 respectively. The Simpson Index for each repeat is
shown in Appendix B.2 and Figure 8.
40
Simpson, 1949.
34
Appendix C.2: Raunkiaer’s Law of Frequency.
Many ecologists have asked the question: why are some species rare and others common?
In 1918 the Danish botanist Raunkiaer calculated the percentage frequency of all the species he
found in random quadrats41. He lumped the results into five classes (A to E) each of 20% so that
Group A (the rare species) occurred in 0 – 20% of the quadrats, Group B in 21-40%, etc., ending with
Group E (the common species) in 81 – 100%. When plotted as a histogram his data had a back-tofront J curve. Group A always had more species than B, which had more than C, which had more
than D, which had less than E. This is stated as A > B > C > D < E, which is known as Raunkiaer's Law
of Frequency. Since then biologists have found this pattern not only with plants but in birds and
moths at light traps42.
I decided to construct a Raunkiaer frequency distribution using the data from this study. The
percentage occurrence of all the herpetofaunal species found in the 9 samples was calculated
(Appendix B.4) and Raunkiaer’s frequency distribution was plotted (Figure C.1). The result follows
Raunkiaer's Law of Frequency exactly, A > B > C > D < E.
Graph to show the frequency of occurrence of each
species
10
Frequency
8
6
4
2
0
-2
0-20
21-40
41-60
61-80
81-100
Percentage occurence
Figure C.1: Raunkiaer’s frequency distribution using all herpetofauna found in all the repeats
from all transects (data shown in Appendix B.4).
There is much discussion about what Raunkiaer's Law of Frequency really means. It has
been suggested that whenever the rank abundance plot shows a clear log-normal curve then it will
give the back-to-front J pattern that Raunkiaer found43. This does not answer the question of why
some species are rare and others common.
Raunkiaer, 1918, quoted in Colinvaux, 1973.
Colinvaux, 1973.
43
Colinvaux, 1973.
41
42
35
ACKNOWLEDGEMENTS
It is a great pleasure to thank all of those whose support made this project possible. I would like to
thank Barry Ferguson for patiently answering all my e-mails in preparation for the trip and for
making my time in Ifotaka thoroughly enjoyable. I am inordinately grateful to Ole Theisinger for
helping me to finalise both my project and the data collection. I would also like to thank the
herpetofaunal team for their superb identification skills and for teaching me how to lasso a lizard
using dental floss. Special thanks go to my supervisor Mrs K. Pitcher. Not only did she organise the
incredible expedition, but she has been supportive and patient through to the preparation of the
final draft. Finally, I am exceedingly grateful to my friends Alex McBride, Dan Adeline and Alex
Dudney for being enthusiastic photographers during the trip and allowing me to use their shots.
36