Overview

Brief Summary

Biology

This species is terrestrial and nocturnal, and feeds on small invertebrates (6). Unlike most frogs, which lay their eggs in water, this species lays its eggs in small clumps on moist ground. The young do not hatch as tadpoles, but as fully formed small adult frogs. In other Sooglossidae species, tadpoles are carried on the female's or male's back until they metamorphose (7).
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Description

The Gardiner's tree frog is one of the smallest frogs in the world, growing to only 11 mm in length (2). This species is endemic to the Seychelles, as its other common name (Seychelles frog) suggests (3). In colour, it is green to brown, and has a distinctive dark band extending from the mouth and below the eye to the hind legs. The fore-limbs are small, while the hind-limbs are long and muscular (3).
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Distribution

Range Description

This species occurs on Mahé and Silhouette islands in the Seychelles, from 150-991 m asl (J. Gerlach pers. comm. March 2012). Its extent of occurrence (EOO) is estimated to be 116-120 km2, while its area of occupancy (AOO) is estimated at 33 km2 based on area polygons for occupied habitat for each mapped subpopulation (J. Gerlach pers. comm. March 2012). There are five known subpopulations (J. Gerlach pers. comm. March 2012), which are herein aggregated into three threat-defined locations: one location in Silhouette comprising one subpopulation, and two locations in Mahé comprising four subpopulations; of these two locations one is comprised of higher elevations (two subpopulations) and the second one of lower elevations (two subpopulations) (J. Gerlach pers. comm. March 2012).
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Range

This family of frogs is endemic to the Seychelles, a large group of islands in the Indian Ocean (4).
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Ecology

Habitat

Habitat and Ecology

Habitat and Ecology
It lives both on the ground in forest leaf litter and on low vegetation in leaf axils, in disturbed and undisturbed rainforest. It also occurs in degraded primary forest areas dominated by introduced trees such as cinnamon. It is rarely recorded in areas of secondary forest and the edges of highly degraded forests. It breeds by direct development, the eggs being laid on the ground, with clutch size ranges from 8-16 eggs (J. Gerlach pers. comm. March 2012).

Systems
  • Terrestrial
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Most members of the Sooglossidae family are restricted to high altitudes, but the Gardiner's tree frog is more adaptable and occurs in a wide variety of high and mid-altitude sites, favouring moist and deep littered rocky areas (2) (5).
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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
EN
Endangered

Red List Criteria
B1ab(ii,iii,v)+2ab(ii,iii,v)

Version
3.1

Year Assessed
2013

Assessor/s
IUCN SSC Amphibian Specialist Group,

Reviewer/s
Catenazzi, A.

Contributor/s
Gerlach, J. & Nussbaum, R.

Justification
Listed as Endangered given that its extent of occurrence (EOO) is estimated to be 116-120 km2, its area of occupancy (AOO) is estimated at 33 km2, it is known from three threat-defined locations, its population is considered to be severely fragmented, and there is a continuing decline in the number of mature individuals, its area of occupancy and quality of its habitat due to projected changes in rainfall patterns in the Seychelles and the loss of suitable habitat to invasive plants.

History
  • 2004
    Vulnerable
  • 1996
    Vulnerable
  • 1994
    Rare
    (Groombridge 1994)
  • 1990
    Rare
    (IUCN 1990)
  • 1988
    Rare
    (IUCN Conservation Monitoring Centre 1988)
  • 1986
    Indeterminate
    (IUCN Conservation Monitoring Centre 1986)
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Status

Classified as Vulnerable (VU) on the IUCN Red List (1).
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Population

Population
It is common at many sites in both disturbed and relatively undisturbed rainforest, occurring at densities of up to 2,000 animals per hectare in the best habitat. Population monitoring from 1994-2010 recorded declines in population density in lower altitude sites of over 67% over 16 years, while high altitude sites retained stable populations over this time (Gerlach 2011; J. Gerlach pers. comm. March 2012). These low altitude population declines have been associated with changes in rainfall patterns, which are in turn attributed to climate change (J. Gerlach pers. comm. March 2012). Furthermore, the projected effects of climate change suggest significant future population declines for all Seychelles Sooglossid frogs (Gerlach 2011). The global population is considered to be severely fragmented i.e., it occurs in fragmented habitat patches, the species has poor dispersal ability, such that it is not possible for animals to move between fragments, and it is believed that 50% or more of its individuals occur in isolated and fragmented habitat patches (J. Gerlach pers. comm. March 2012).

Population Trend
Decreasing
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Threats

Major Threats
The main threats are considered to be climate change and habitat degradation. Habitats are deteriorating mainly due to the increased frequency of fires and invasive species (principally the tree Cinnamomum verum), but this frog is somewhat adaptable to secondary habitats (J. Gerlach pers. comm. March 2012). Logging and small-scale agriculture are too localized to have a significant impact on this species (J. Gerlach pers. comm. March 2012). Cinnamon was established in plantations on Mahé in the 18-19th centuries (J. Gerlach pers. comm. March 2012). While this species has been identified as being more tolerant of dry conditions relative to other Sooglossid frogs, climate change is projected to lead to a 10% decline in area of occupancy within ten years, and a range contraction of 60% by 2100 for Seychelles Sooglossid frogs (Gerlach 2011; J. Gerlach pers. comm. March 2012).
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Land clearance for agriculture, human settlement, timber and tourism are the main threats on the Seychelle Islands. The majority of the lowland forests have been disturbed or destroyed, and coconut, vanilla and cinnamon plantations now occupy most of the coastal plateaus (6). This habitat loss has contributed to the decline in numbers of this species in recent years. This species is now classified as Vulnerable by the IUCN (1).
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Management

Conservation Actions

Conservation Actions
It occurs in the Morne Seychellois National Park, and in the site of a conservation project on Silhouette. There is a need for close monitoring of the population status of this species; this was initiated in 1996 but was forcibly terminated in 2011 (J. Gerlach pers. comm. March 2012). Captive colonies have been successfully maintained, although successful captive breeding has yet to be recorded for this species (J. Gerlach pers. comm. March 2012). The development of captive breeding techniques is recommended for this species, as well as improved habitat management to minimize the impact of invasive species (J. Gerlach pers. comm. March 2012).


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Conservation

The Seychelles Islands are considered as some of the most beautiful places on Earth and are extremely rich in terms of biodiversity. Many small reserves on the islands have been set up by the Seychelles Government and independent agencies to protect specific species and general habitat areas (3) (4). These efforts are important in the protection of the islands' wildlife, though many species, including the Gardiner's tree frog, still remain threatened (7) (8). Much of the range on Mahé fall within the Morne Seychellois National Park and conservation of Silhouette island is managed by the Nature Protection Trust of Seychelles (9).
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Wikipedia

Gardiner's Seychelles frog

Gardiner's frog (Sooglossus gardineri) is a small frog of the Sooglossidae family and endemic to the Seychelles.

Physical description[edit source | edit]

Gardiner's frog is one of the smallest frogs in the world, reaching a maximum length of 11 millimetres (0.4 in). Newly hatched frogs measure only 3 millimetres (0.1 in) in length. Adult males are only 8mm long. It is brown in color, and has a dark stripe running from its mouth to its legs. A relative comparison of the world's smallest frogs

Gardiner's frog is notable for its ability to hear despite the absence of a middle ear cavity. Research has shown that the species is able to use its mouth cavity to amplify sound and transmit it to the inner ear.[1]

Ecology and behavior[edit source | edit]

Gardiner's frog is a terrestrial frog, feeding on small invertebrates including mites, sciarid larvae, ants, and amphipods. It is restricted to the high- and mid-altitude areas of Mahé and Silhouette Islands of the Seychelles group. This is unusual among the Sooglossidae, as most are restricted to the high latitudes, which have a stable climate due to constant mist. Although Gardiner's frog is secure in the regions in which it is found, it is classified as vulnerable by the IUCN Red List because it is restricted to only five localities.

References[edit source | edit]

  1. ^ Renaud Boistel et al., How minute sooglossid frogs hear without a middle ear, Advance Online Publication PNAS Early Edition 2 September 2013.
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