Low genetic variation in a Pacific cycad: conservation concerns for Cycas seemannii (Cycadaceae)

Abstract

The conservation status of Cycas seemannii, native to Vanuatu, New Caledonia, Fiji and Tonga, is assessed based on isozyme analysis, abundance estimates and factors affecting the survival of the species. Genetic variation in the species is low and genetic differentiation between populations is high, as compared to plants in general and to other cycads. Lower genetic variation was detected in a fragmented population as compared to less disturbed populations. Low gene flow was also detected, implying little contact between the various populations. A conservative estimate of 17,000 individuals remaining in the wild was obtained, with more than half of these located on the islands of Vanuatu. Accounts of past abundance suggest declining population sizes, most likely the result of repeated burning. Other factors that may be contributing to the decline are decreasing importance to and protection by humans, habitat alteration for agricultural and developmental purposes, and poor dispersal and recolonisation potential. An assessment based on the present estimated abundance and what is known of recent declines in numbers, indicates that the species should be categorised as Vulnerable on the IUCN Red List. On some of the densely populated islands, such as Viti Levu in Fiji and Nukualofa in Tonga, the species is locally Endangered or Critically Endangered. Possible conservation measures are suggested, and it is emphasised that populations on different islands must be considered separately because of their genetic differentiation.