Lizards: Their diversity and abundance in dryland habitats

An update from the Landcare Research Sustaining and restoring biodiversity programme funded by the Foundation for Research, Science and Technology.

Landcare Research’s dryland research programme aims to improve the understanding, protection and conservation management of dryland biodiversity.

Dryland environments cover 19% of New Zealand and contain some of our least protected and most threatened native ecosystems; less than 3% of the dryland zone is legally protected.

QEII covenants potentially have a key role in protecting biodiversity in these under-represented environments.

Trees (podocarps and beech) and a diversity of shrubs and vines (Coprosma, Olearia, Myrsine, Pseudopanax and Rubus) were once widespread over interior South Island drylands and remnants of woody vegetation remain.

Nowadays, mixtures of introduced and native grasses dominate. However, with reductions in fire and grazing, many habitats will naturally succeed back to a variety of woody states.

To understand and predict some of the changes in biodiversity that will occur as woody succession proceeds, Landcare Research scientists Deb Wilson and Grant Norbury lead a team surveying and quantifying bird, lizard and plant biodiversity associated with dryland ecological communities.

Biodiversity can be measured at multiple scales (from a single ecological community to a region or landscape), and diversity measures can describe both the number of species and their relative abundance.

‘By systematically assessing the species diversity and relative abundance of native skinks and geckos in dryland regions, we are trying to answer questions such as: What species of lizards are found in different dryland communities? Do some habitats support markedly more individuals than others? How will changes in the vegetation cover affect lizard diversity measured at different scales, from small patches to landscapes?’ says Deb.

‘Lizards are a primary focus because of their diversity and persistence in dryland environments. For example, will lizard biodiversity change if we intervene to accelerate succession to woody habitats in some reserves? Conversely, how will it change if scrub or tussock is cleared for development?’

The team has surveyed biodiversity intensively in several dryland sites in Central Otago, and are now using what they’ve learned to design a more extensive survey.

Measuring vegetation characteristics in a dryland habitat

Above: Preparing to measure vegetation characteristics in a dryland habitat dominated by native grasses and shrubs and (in the distant lowlands) exotic grasses and trees.

Measuring lizard populations in the field presents challenges. To assess the lizard populations, the researchers recorded numbers found in non-lethal pitfall traps.

‘The most thorough way is to mark every animal found and go back day after day’, explains Deb. ‘Then a mathematical model is used to estimate the population size.

‘This method requires consecutive days of warm or sunny weather when the animals are active and likely to encounter traps, and it can be costly.

‘So for the extensive survey, we’re using a basic method of counting how many lizards are captured in a 24-hour period.

'It’s a quick index of population size for species such as common skinks and McCann’s skinks and common (brown) geckos. Unfortunately, we’re unlikely to detect less abundant species such as green skinks, cryptic skinks or jewelled geckos.’

Discussing drylands survey plot locations

 

Left: Steph Hicks, Kev Drew and Kate Ladley discuss drylands survey plot locations.

 

 

 

 

 

 

 

 

 

 

Deb adds that it is too early to give final results.

‘So far, we have found skinks in many grassy and shrubby habitats, whereas geckos have been more often associated with rocks or woody cover.

'We’ve also found some big differences between sites in the abundance of lizards.

'These differences may be related to vegetation or simply reflect different site histories or the size of surrounding source populations.’

Open SpaceTM Magazine No. 75, March 2009 © QEII National Trust

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