Abstract
Endozoochory (seed dispersal via frugivory) is a critical component of the reproductive strategy for many plant species, and the loss of indigenous seed dispersers can have cascading effects on community dynamics and ecosystem functions. While research is predominantly focused on birds and mammals, there is a growing understanding of the role lizards play as seed dispersers in many ecosystems, particularly on islands and in open, dry habitats. My research evaluated if, and to what extent, kōrero geckos (Woodworthia "Otago/Southland large") are important seed dispersers of mingimingi (Coprosma propinqua, Rubiaceae) in a rocky dryland ecosystem of inland Otago. This was answered by applying a seed dispersal effectiveness (SDE) framework to the potential seed dispersal relationship, consisting of quantitative and qualitative components.
The quantitative component of this research aimed to establish what contribution geckos made to fruit removal rates. Field-based exclusion experiments on mingimingi shrubs measured fruit removal rates over six weeks across four treatments (total exclusion, lizard-excluded, bird-excluded, and open access). Relative visitation rates observed on trail cameras indicated geckos were the predominant frugivore in the birdexcluded treatment. The bird-excluded treatment had significantly higher fruit removal (83%) than the lizard-excluded treatment (65.7%) and total exclusion treatment (0.9%). The high fruit removal in the lizard-excluded treatment raises questions about potential insect frugivory, although this figure could also be explained by limitations of the study design. Overall, these results suggest geckos are a major frugivore, capable of removing at least 17% and up to 83% of mingimingi fruit in the absence of larger taxa in the study area.
The qualitative component of this research aimed to estimate the impact of kōrero gecko gut passage on mingimingi seed germination – both overall and isolating the individual effects of disinhibition and scarification in a lab-based experiment. The majority (78%) of seeds from gecko scat germinated after 20 days, not significantly different from the 90% germination in the hand-cleaned (artificially disinhibited) control treatment. A further germination experiment found both artificial disinhibition and artificial scarification treatments led to higher germination rates than control seeds left in fruit after 35 days. The germination rate of total gut passage treatment (15%) was higher than the control (2.5%), although this difference was marginally nonsignificant. These results showed that seeds dispersed by kōrero geckos can successfully germinate at high rates.
Overall, I conclude that kōrero geckos are an effective seed disperser of mingimingi. Geckos removed a substantial quantity of fruit from mingimingi shrubs, and provided quality seed dispersal that increased the probability of germination when compared to experimental controls. These results add a new disperser species to the growing body of literature of lizard seed dispersal globally. It is notable that even small pockets of inland habitat can host these unique seed dispersal relationships. These results also represent another example of lizard seed dispersal of divaricate blue-white fruited Coprosma in New Zealand, furthering an ongoing discussion about potential co-evolution.