Two Species Whose Ranges Are Shifting Uphill Are Not Pollen Limited, But Are More Successful Selfers Than Two Non-Shifting Species.

Abstract

Many species are expected to shift their ranges uphill in response to climate change and shifts to new ranges can be associated with changes in both positive and negative biotic interactions. We asked whether two uphill shifting species are more pollen limited at the upper range edge versus distribution core than are two non-shifting species and whether the two uphill shifting species reproduce more successfully through self-fertilisation (selfing) than the non-shifting species. We performed pollinator exclusion, open pollination and pollen supplementation experiments and counted pollen grains deposited on the stigmas of six alpine plant species native to Kosciuszko National Park, NSW, Australia. Counter to our hypothesis, the uphill shifting species in our study did not experience pollen limitation in any part of their distribution, while non-shifting species were more pollen limited in the core of their distribution than at range edges. However, the two uphill-shifting species did show higher selfing rates than did non-shifting species. Our results suggest that reproductive mechanisms may be non-uniform across species ranges, although the spatial variability of traits is seldom taken into account in predictive models. Although plant-pollinator interactions are often predicted to alter in the face of climate change, our study shows that some uphill-shifting plants may be able to maintain sufficient pollinator services.