Conservation status and demographics of the Galapagos land iguana (Conolophus subcristatus) in the Galapagos Islands, Ecuador : a thesis presented in partial fulfilment of the requirements for the degree of Masters of Natural Science in Conservation Biology, Massey University, New Zealand
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Date
2019
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Massey University
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Abstract
In conservation biology, understanding the basic demography of populations across their range,
provides opportunities to identify and prioritise management actions to improve the conservation of
both, populations and of the species as a whole. The Galapagos land iguana or land iguana (Conolophus
subcristatus) (endemic to the Galapagos Islands), is an ideal model to explore these ideas and to
generate information that can assist its conservation. Currently, the species is classified as IUCN:
Vulnerable. Land iguana populations are threatened by introduced species and habitat loss but the
intensity of these threats varies between populations. The population sizes across the species range are
partially known and suspected to relate to the presence/absence of introduced predators. Although
demographic trends are virtually unknown, it is suspected that populations in disturbed areas have a
lower recruitment of juveniles and limited population growth. Overall, these gaps in knowledge
represent a challenge to a formal evaluation of the species’ conservation status. Historically,
translocation of land iguanas to predator-free or predator-managed sites in the Galapagos Islands has
played an important role for its conservation. Since the 1970s there have been calls for translocating
land iguanas to Santiago Island, considered to harbour one of the largest land iguana populations until
the early 1900s. Although the mechanism for the extinction of the Santiago Island population is not
understood, it is most likely linked to habitat changes driven by humans and the effects of introduced
predators, which are common denominators in significant iguana population declines on other islands
around the world. Since the early 2000s, introduced predators have been eradicated on Santiago Island,
and the possibility of reintroducing land iguanas there has resurfaced with greater intensity. While the
habitat on Santiago Island is considered suitable for land iguanas, and the expertise to handle and
transfer these organisms exists there are missing gaps in knowledge in particular: is the size of
historically translocated populations comparable to undisturbed populations? What are the current
population sizes of land iguana populations? and what are the effects of introduced predators on land
iguana populations?
This thesis addresses these gaps in land iguana demography by providing an update of the
current conservation status, estimates of population size and an analysis of the effects of feral cats using
historical data. I examined the effects of feral cats on two populations by comparing historical demographic data from cat-absent and cat-present populations. I found cat-present populations
exhibited significantly different population structure and morphology to cat-absent populations,
including significantly lower juvenile percentage indicating reduced juvenile recruitment as a result of
juvenile depredation . Further, I studied a translocated population of land iguanas (North Seymour) and
the most undisturbed land iguana population in one of the most active volcanoes worldwide; Fernandina
Island. I estimate and compare population size to assist the planning of a reintroduction of the species
to Santiago Island. Finally, I review the IUCN status of the species and conclude that the Vulnerable
status is justified, primarily due to its limited geographic range and projected population decline. Four
weeks before the completion of this thesis, the Directorate of the Galapagos National Park, Island
Conservation and Massey University completed a transfer of over 2000 land iguanas to Santiago Island
based on the information provided in this document. Although I could not incorporate the posttranslocation
monitoring of land iguanas as part of my thesis, I discuss future research needs that will
contribute to the restoration of Santiago Island, and the conservation of land iguanas across their range.
Description
Keywords
Iguanas, Animal populations, Endangered species, Wildlife conservation, Wildlife relocation, Galapagos Islands