The Remnant Leiopelma Pakeka (Anura: Leiopelmatidae) Population on Maud Island: Population Size, Distribution and Morphology
Leiopelma pakeka is an archaic frog native to New Zealand, and until recently was restricted to a 15ha forest remnant on the south-east face of Maud Island. The L.pakeka population appears to be growing and spreading out from the forest remnant. This study investigated the population size, structure, and distribution of L. pakeka on Maud Island in 2006. The forest remnant was searched using 106 randomly placed 25m2 plots. Population size was estimated using a bootstrap method repeated 10,000 times, adjusted for likelihood of emergence, likely maximum plot population size, and area. The average population size was 34,449 frogs, which is much higher than a 1994 minimum number alive estimate of 19,312. The new figure, however, is similar to another recent estimate of 39,563, based on an update of the 1994 figure. Distributional patterns within the forest remnant were similar to the 1994 study, with most frogs between 90-170m above sea level. The comparability of the population size estimates indicates that L. pakeka numbers have reached the carrying capacity of the forest remnant. The distribution of the remnant L. pakeka population was determined by thoroughly searching the south-east face of Maud Island, thereby minimising the possibility of missing frogs. A total of 232 frogs were found. Frogs generally colonised areas within 50m of the remnant; movement was greater in regenerating forest (75m in the southwest and 100m in the north east) than in pastoral areas (<25m). The size of frogs increased with distance from the forest remnant (weight, girth, condition index, and average snout-vent and tibio-fibula lengths). The size increases may be indications of competitive release, as frog density decreased with distance from the forest remnant. The size range of Leiopelma pakeka was extended by the current study from 50.5mm to at least 52mm snout-vent length. A total of 15 L. pakeka were found on Fort Road, approximately 350m from the remnant. These frogs were most likely in the area before 1994. The Fort Road frogs were compared to the forest remnant L. pakeka, and were not morphologically distinct as only patterning differed significantly. Fort Road L. pakeka may belong to a separate subpopulation. L. pakeka distribution was significantly affected by habitat. Important variables were vegetation type, and rock, canopy, sub-canopy, and leaf litter cover. The size of emergent frogs (tibio-fibula length) was significantly and positively correlated with relative humidity.