Declining species are the focus of conservation biology. Gaining an understanding of the historical processes that led to contemporary patterns of genetic variation can be of great value to implement effective management strategies.
The Kea (Nestor notabilis), is an alpine and endemic parrot of New Zealand. The bird is well known for its intelligence and ability to adapt to various environments. In contrast to the majority of avian species of New Zealand, Kea have presumably undergone an important population growth and possible range expansion upon the arrival of Europeans. However, because of the frequent Kea attacks on sheep, the species was persecuted from the 1870s until the 1970s and it has been estimated that some 150,000 birds were killed during that period. Because Kea are highly mobile, patchily distributed and live in rugged and remote areas, it is difficult to obtain an accurate estimate of contemporary population size using traditional monitoring approaches. Despite the uncertainty on the contemporary population size, it is estimated that the population numbers between 1000-5000 birds, which suggests that the population only represents a fraction of its historical size. The historical Kea abundance was not well documented prior to Europeans, therefore the effect of the recent decline on Kea genetics is unclear. Indeed, it is uncertain whether the species has now returned to its pre-European population size or whether it has fallen below its historical abundance.
Using molecular genetics provides a useful alternative to estimate historical and contemporary population size, loss of genetic diversity and to unravel the species history and phylogeography. A total of 410 contemporary samples were genotyped at 17 microsatellite loci and 91 samples were sequenced for the mitochondrial Control Region. Genetic diversity for these markers was also examined in 15 museum samples to investigate the loss of genetic diversity caused by the recent population decline.
Our results showed that despite the Kea’s dispersal capabilities, the species exhibited a pattern of isolation by distance and population substructure. Testing two contrasting models of post-glacial expansion showed that the species recolonized its former range from a single refugium and that the contemporary population structure was most likely due to this pattern of recolonization. Additionally, neither classical methods of population contraction detection (Heterozygote excess, M-ratio) nor comparison of historical and contemporary samples (allelic and haplotypic diversity) showed a loss of genetic diversity in Kea. However, there was evidence that the contemporary population structure was locally not representative of the historical one of the late 1800s. Comparison of short- and long-term population effective size suggested that Kea had been through at least one population decline. It is very likely that a population decline occurred since European settlement in New Zealand, but older population contractions linked to habitat modification or older unaccounted events could not be excluded.
This study highlights the importance of using molecular genetics to unravel past demography and phylogeograhy when little data on past population trends are available. Also, the results obtained will also be used to help develop appropriate management strategies for a species of conservation concern.
