The global diversity and status of both amphibians and reptiles at the end of the 20th century were described in thorough detail in the previous edition of the current volume (McDiarmid and Mitchell 2000). During the 1990s, however, it became clear that the diversity and status of amphibians were changing rapidly, with substantial declines in amphibian populations in many regions (Alford and Richards1999). There has also been widespread concern regarding possible increases in the prevalence of developmental abnormalities and malformations in amphibians (Johnson et al. 2003). Great advances have been made in understanding these problems since 1999. This chapter concentrates on defining the problems, illustrating and interpreting our understanding of their causes, and developing ideas regarding how the problems can be managed.

Declines and the Global Status of Amphibians

Indonesia is one of the world’s largest exporters of frogs’ legs for consumption as food. The majority of the frogs are
caught in natural habitat on the island of Java - predominantly the Crab-eating Frog Fejervarya cancrivora (75%), and the Giant Javan Frog Limnonectes macrodon (19%). While the greater number of frogs taken is for local consumption, the available data show increasing numbers of frogs’ legs have been exported from Indonesia over time - from around 28 t in 1969, rising to around 5600 t in 1992 and then declining to around 3800 t in 2002. A strong increase in exports after 1985 corresponded with the banning in that year of exports of edible frogs from India and Pakistan - formerly the principal exporters of frogs’ legs. This paper examines the trade in Indonesia based on export data covering 34 years (1969 to 2002) and market surveys and interviews conducted in 2001 to 2003. Although some concern has been raised about the trade, this paper discusses the possibility that the current level of harvest has not depleted Indonesia’s population of edible frogs. However, it is not possible at the moment to state that current harvest levels are not a problem as insufficient information is available on production for the substantial domestic market.

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Indonesia's exports of frogs' legs

Human activities have fragmented amphibian habitats and affected amphibian diversity and distribution, but the ecology is poorly known. A four-year study assessed the diversity and distribution of amphibians in undisturbed and disturbed sites of the Kudremukh National Park (KNP), India. Iron-ore mining and associated activities in the KNP have induced habitat fragmentation. The disturbed sites had ranges of habitat variables clearly distinguishable from undisturbed sites. Thirty-six species of anurans and six species of caecilians have been recorded in the KNP and the total amphibian species richness represents 20% of the whole Indian amphibian fauna. Among these, 20 species were distributed in both disturbed and undisturbed sites, while 22 were found only in undisturbed sites indicating they may be threatened by further habitat fragmentation. Species diversity and richness formed two distinct groups clearly associated with disturbed and undisturbed habitats, respectively.

Amphibian assemblages in undisturbed and disturbed areas of Kudremukh National Park, central Western Ghats, India

Frogs are harvested in Indonesia for both domestic consumption and export
Concerns have been expressed about the extent of this harvest, but there have been no
detailed studies on the edible frog trade in Indonesia, or on the status or population
dynamics of the harvested species To investigate the possible impact of this practise, I
collected data on harvesting and trading of frog legs in Java, Indonesia I also
investigated the ecology and population dynamics of the three species that are most
heavily harvested: Fejervarya limnocharis-iskandari complex, F cancrivora and
Limnonectes macrodon
The first step of the study quantified the extent of the Indonesian edible frog leg
trade for export and domestic purposes Harvesting is an unskilled job and serves as
livelihood for many people There is no regulation of this harvest, and species taken and
size limits are governed by market demand The most harvested species in Java are F
cancrivora and L macrodon Harvests occur all year long The number of frogs
harvested fluctuates and is controlled by natural forces such as dry/wet seasons, moon
phase, and planting seasons Records of the international trade in Indonesian frog legs
are available from 1969 to 2002; the mass of frozen frog legs exported has increased
over the years I used data on the relative weights of frogs and their legs to estimate how
many frogs were represented by the export records In 1999-2002 an average of
3,830,601 kg of frozen frog legs were exported annually; this represents an export
harvest of approximately 28 to 142 million frogs, all with masses greater than 80 g, the
minimum size of animals that have legs considered suitable for export I used data
collected by following frog hunters in the field to assess their capture rates and the
numbers and sizes of frogs captured I found that only about one-eighth of frogs captured are of sizes acceptable for export, and therefore estimate that the domestic
market is approximately 7 times as large as the export market
In the second step of the study, I used field data on F limnocharis-iskandari
complex, F cancrivora and L macrodon to gain greater understanding of the
population biology and dynamics of the harvested species Populations of F
limnocharis-iskandari complex and F cancrivora were studied in six rice fields in West
Java during the planting seasons of 2002 and 2003 Both F limnocharis-iskandari
complex and F cancrivora were abundant in the rice fields, with estimated overall
mean densities of 19371 and 3976 per hectare The mean density of F cancrivora was
very similar to that of unharvested populations in Malaysia (86 – 912 per hectare)
(Jaafar, 1994) and was much higher than the mean density (07 frogs/ha) found for Rana
tigerina, the larger species of edible Indian paddy field frog investigated by Dash and
Mahanta (1993) These comparisons suggest that densities of F cancrivora in Javan
rice fields are relatively high, despite ongoing harvesting pressure F limnocharisiskandari
complex and F cancrivora were able to breed continuously all year without
an apparent season Both species showed sexual size dimorphism, with females larger
than males Both appear to be short lived
The population dynamics of L macrocodon were observed at two stream sites
West Java: Cilember and Ciapus Leutik The habitat at Ciapus Leutik is relatively
heavily modified bu human activity, while Cilember is in a nature reserve and ls less
disturbed A mark recapture study was conducted once a month between June 2002 and
May 2003 (a continuous 12 month sampling period), and in January, April and July
2004 Skeletochronological analysis of phalanges removed during toe clipping suggests
that this species lives longer than F cancrivora or F limnocharis-iskandari complex
Recapture rates of L macrodon in both locations were low and more frogs were observed during periods of higher rainfall In this study, more L macrodon were found
at Cilember than at Ciapus Leutik stream It is unclear whether the low number of frogs
at Ciapus Leutik was caused by over-harvesting or by other factors There is a need for
further monitoring to obtain a greater understanding of the population dynamics of this
species
In conjunction with my field work, I measured a number of parameters to
determine the type and extent of pesticide residues present in rice fields, and to attempt
to determine whether those and another potential stressor, drought, might be affecting
the morphology, body condition, or developmental stability of frogs I also surveyed
populations of the rice field frogs and L macrodon for the emerging disease
chytridiomycosis, which could strongly affect the population dynamics of the frogs
Two types of pesticide residues were detected in water and soil: organochlorine
(lindane, aldrin, heptachlor, dieldrin and endosulfan) and organophospate (chlorpyrifos
and diazinon) Six organochlorines type (BHC, lindane, aldrin, heptachlor, dieldrin and
endosulfan) and three organophosphates (propenofos, chlorpyrifos and diazinon) were
detected in the livers and leg muscles of both frog species Almost all pesticide residues
were low compared to the Maximum Residue Limit set by WHO and the Government
of Indonesia although a few individuals showed higher pesticide residues contents
Pesticide residue levels did not appear to be related to any measure of frog condition or
stress Both species of rice field frogs exhibited relatively low percentages of
abnormalities, probably within the normal range Only F limnocharis-iskandari
complex consistently exhibited levels of fluctuating asymmetry in excess of
measurement error Levels of asymmetry differed between characters Higher limb
asymmetries were elevated in 2002 compared to 2003, whilst body condition was lower
in 2003 It is possible that the lower body condition in 2003 was caused by stress from an environmental factor, in this case the drought in that year It is clear that for both F
limnocharis-iskandari complex and F cancrivora, fluctuating asymmetry is not a
powerful indicator of stress There was no sign of chytrid infection in any samples of
the three species
To assess the impact of harvesting, I used two approaches I developed a model
of the population dynamics of F cancrivora and ran simulations for ranges of
parameters including harvesting rate The simulation indicated that current levels of
harvest may be near the maximum level sustainable by the population My second
approach was to compare data on the population biology and distribution of both
Fejervarya species to criteria for assessing the conservation status of the species, ie
IUCN Red Categories and the CITES Res Conf 924 on the Criteria for Amendment of
Appendices I and II
My assessment using listing criteria showed that neither F limnocharisiskandari
complex or F cancrivora are qualified for inclusion into any IUCN Red List
and CITES Appendices On the other hand, more consideration needs to be given to L
macrodon This frog is not qualified for inclusion in CITES Appendix I At present, it
is not possible to determine whether this species could be listed as vulnerable or in
CITES Appendix II due to a lack of data, such as survivorship among stages, and
habitat size, on the population biology of this species
Recommendations for management of the harvest include: 1) regular monitoring
of this trade especially in other islands such as Sumatra by the scientific authority of
CITES (The Indonesian Institute of Science or Lembaga Ilmu Pengetahuan Indonesia,
LIPI), 2) regular monitoring of the numbers of export companies and their middleman,
3) developing a simple identification key and distributing it to the middlemen to ensure
correct identifications, 4) assessing the possibility of breeding local frogs for this trade to replace the farming of the exotic frog Rana catesbeiana, and 5) ensuring that harvest
is limited to species that are not adversely impacted

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Edible frog harvesting in Indonesia: evaluating its impact and ecological context

As a group amphibians are the vertebrates most affected by anthropic activity, particularly by agriculture. The rapid advance of the agricultural frontier makes it important to identify the role of agroecosystems as habitat supply for amphibians. We analyzed the differences in amphibian assemblages and populations between habitats with different plant covers and different degrees of human intervention in northwestern Argentina. For three years we conducted 114 high frequency trap samplings to quantify abundance, specific composition and species richness of amphibian assemblages in three habitat types (lemon and sugarcane crops and secondary forest) of a piedmont agroecosystem of Tucuman province. Crops hosted more species and individuals than secondary forests, but the specific composition of forest was different from that of crops suggesting that they could be complementary. Although the assemblage abundance of every observation responded to climate, the strong effect of sampling year was not related to climatic factors suggesting that there might be long term fluctuations that were not analyzed. We also found that responses to agricultural practices were species specific, so no generalizations about these practices should be done. Our study shows that cultivated areas are not hostile environments for amphibians since they can lodge huge amphibian populations and that the occurrence of disturbances associated to agricultural practices is not necessarily reflected in a decrease in the abundance and richness of amphibians in the short term. However, our results also show that forested lands are necessary to lodge some specialist species which are very rare in the croplands. This suggests that environmental heterogeneity generated by the combination of natural and cultivated patches can increase biodiversity at landscape scale because this allows the coexistence of species related to either kind of environment.

Amphibian diversity increases in an heterogeneous agricultural landscape

Amphibian community structure in five tropical sites was studied using dominance, diversity, evenness indices, niche breadth and overlapping scores and association analysis. Ten species of amphibians with average density/ha varying from 8 to 49 in different sites were collected. Rana limnocharis and Bufo melanostictus were respectively the dominant amphibia in paddy fields and other sites. Niche breadth scores indicated Rana limnocharis, Bufo melanostictus and Rana cyanophlyctis as habitat generalists indicating wide tolerance to environmental gradients. Five frog species i.e. Rana tigerina, Microhyla ornata, Ramanella variegata, Uperedon systoma and Polypedates maculatus were considered habitat specialists indicating narrow tolerance to environmental gradients. Niche breadth scores were found to be a function of the cumulative relative abundance value of different species. The niches of Rana limnocharis and Rana cyanophlyctis, Bufo melanostictus and Bufo stomaticus showed maximum overlapping. Rana tigerina showed maximum niche overlapping with Rana variegata in paddy fields and with Microhyla ornata when all sites were taken together. The coefficient of community index was maximum between the paddy fields and minimum between the paddy fields and forest site. Rana tigerina occurred very sparsely and analysis of data indicates that its population are threatened and require conservation measure.

J. K. Mahanta

Papers

Quantitative analysis of the community structure of tropical amphibian assemblages and its significance to conservation

Morphometric relationships in tropical anurans and their relationship to some life history parameters