Leaf Damage is Not the Answer! Reduced Herbivore Pressure Does Not Underpin Either Downhill or Uphill Range Shifts

Many organisms are observed shifting their ranges uphill or toward the poles in response to climate change. However, recent studies suggest that 20%-37% of species are exhibiting shifts in counterintuitive directions, that is, downhill or toward the equator. The Interaction Opportunists Hypothesis suggests that counterintuitive shifts might be induced by climate change-driven decreases in enemy pressure at species' warm range edges. To test this hypothesis, we estimated the amount of leaf damage and the number of damage types in nine alpine plant species native to Kosciuszko National Park, Australia, that have shifted their ranges uphill, downhill, or remained stable. Contrary to our prediction, the amount of leaf damage and the number of damage types experienced at species' warm edge versus distribution core did not differ between downhill, uphill, and non-shifting species. These results do not support the idea that reduced enemy pressure drives downhill range shifts. However, counterintuitive range shifts may be underpinned by changes in other biotic interactions, such as soil pathogen attacks, competition, or seed predation. Currently, it remains unclear why species are shifting their ranges toward warmer climates. Advancing understanding of counterintuitive shifts is critical for accurately predicting the likely impact of climate change on species, the composition and reorganisation of ecological communities, and ecosystem functioning into the future.