Ecological Observations on the Critically Endangered Tobago Endemic Frog Mannophryne Olmonae
Total Page：16
File Type：pdf, Size：1020Kb
Ecological observations on the Critically Endangered Tobago endemic frog Mannophryne olmonae Jahson B. Alemu I1,2, Michelle N.E. Cazabon1, Lena Dempewolf1, Adrian Hailey3, Richard M. Lehtinen4, Ryan P. Mannette1, Kerrie T. Naranjit1, Alicia C.J. Roach1 1 Project L.E.A.P., c/o Department of Life Sciences, University of the West Indies, St. Augustine, Trinidad and Tobago 2 Present address: School of Biological Sciences, University of Wales, Bangor, Gwynedd LL57 2UW, United Kingdom. Corresponding author; e-mail: [email protected] 3 Department of Life Sciences, University of the West Indies, St. Augustine, Trinidad and Tobago 4 Department of Biology, 931 College Mall, The College of Wooster, Wooster, OH 44691, USA Abstract. No previous ecological study has addressed the Critically Endangered (IUCN Red List) Tobago endemic frog Mannophryne olmonae (Aromobatidae) since its initial description in 1983. The species was found in six rivers and 15 first-order streams in northeastern Tobago in 2006. Snout-vent lengths of 126 measured individuals ranged from 9.6-25.7 mm, and the sexes were distinguishable at a length of 18.5 mm. Maximum size was similar in males and females — unlike M. trinitatis from Trinidad, which shows greater sexual size dimorphism. Frogs were found close to streams in forested areas, with a mean distance of 2.0 m from the water’s edge, but only calling males were found within the forest itself. Juveniles made up a much larger proportion of the sample than in M. trinitatis. Calling group size averaged 1.9 males, and large choruses were infrequent. Tadpoles were found in isolated pools close to streams, but not in the stream itself; separate size classes suggest multiple deposition by males. There potential listing of M. olmonae as an Environmentally Sensitive Species in the Republic of Trinidad and Tobago is discussed. Key words: Aromobatidae; Bloody Bay frog; Critically Endangered; Mannophryne olmonae; Mannophryne trinitatis; sexual size dimorphism; stream frog; tadpole; Tobago; West Indies. Introduction Schwartz and Henderson (1991) noted that very little was known of the ecology of 95% of the West Indies herpetofauna. Despite some studies in the intervening years, increased knowledge of the basic ecology of amphibian and reptile species is still a requirement for herpetological conservation in the Caribbean region (Wilson et al., 2006). The Bloody Bay frog Mannophryne olmonae was described by Hardy © Koninklijke Brill NV, Leiden, 2007 APPLIED HERPETOLOGY 4: 377-386 Also available online - www.brill.nl/ah 378 J.B. Alemu I et al. (1983), who distinguished the populations on Tobago from M. trinitatis of Trinidad and Venezuela, in which it was formerly included. Subsequently the Venezuelan populations of these aromobatid (formerly dendrobatid; Grant et al., 2006) stream frogs also have been separated into a new species (Barrio-Amorós et al., 2006; M.J. Jowers, pers. comm.), resulting in recognition of endemic Mannophryne species on both Trinidad and Tobago. Nevertheless, Murphy (1997) noted the close similarity in external morphology between stream frogs in Trinidad and in Tobago, and suggested that they were conspecific. Murphy (1997) also interpreted the distinctive call of M. olmonae described by Hardy (1983) as perhaps being from a different social situation, as M. trinitatis are known to produce at least three types of call (Wells, 1980). Several studies have addressed the ecology of M. trinitatis (e.g., Cummins and Swan, 1995; Downie et al., 2001, 2005; Jowers and Downie, 2004, 2005) but no scientific study has concerned M. olmonae since its initial description, which included only physical appearance, maximum size, and call characteristics. This species is listed as Critically Endangered in the 2006 IUCN Red List, based on the criteria of an estimated population decline of more than 80% over the previous three years (presumably 2001-2004), limited geographic range (restricted to northeastern Tobago), a severely fragmented distribution, and continuing decline in the number of mature individuals (Hardy, 2004). A study of the present distribution and population density of this species was undertaken between May and September 2006 (during the wet season). This paper reports general ecological observations on M. olmonae in Tobago, especially to contrast findings with those pertaining to the well-studied M. trinitatis. Methods Observations were made in six rivers in northeastern Tobago (Argyle River, Bloody Bay River, Doctor’s River, King’s Bay River, Louis d’Or River, Roxborough River), some of their tributary streams, and in 21 first-order streams on the northern coast along the Northside Road between Bloody Bay and Charlotteville. These were typically clear-water rivers, fast flowing in the higher reaches, with substrates of stones, gravel, or silt, and banks (defined by lack of persistent vegetation) of boulders and gravel. Riverside vegetation above the bank was secondary riparian woodland, scrub (often of giant bamboo, Bambosa vulgaris), or grazing land. The primary woodland of the Rain Forest Association that covers the Main Ridge (Beard, 1944) was found at higher levels along the upper reaches of some rivers and their tributaries. Sampling was in daylight for this diurnal frog, mostly at the frogs’ peak activity times from 0600-1200 h and 1500-1830 h. Some physical characteristics of the rivers, streams and nearby pools were measured with: YSI EcoSense pH 10 (YSI Inc., Yellow Springs, Ohio, USA — pH and water temperature); YSI DO 200 (dissolved oxygen DO, and water temperature); 25-m × 1 cm tape rule (width of.