Low structural complexity of non-native grassland habitat exposes prey to higher predation.

The structural complexity of vegetation can have profound effects on the hunting efficiency of predators, thereby affecting their intake rate of prey. While studies have shown that vegetation complexity can play an important role in managing unwanted impacts of predators, it is less clear how structural complexity of invasive vegetation affects the vulnerability of terrestrial prey. Short non-native pasture species, for example, bred for agricultural production are highly invasive and pervade grassland ecosystems worldwide. They generally have low structural complexity compared with taller native vegetation they often displace. We conducted controlled experiments to test whether non-native pastures expose fauna to greater predation risk. Survival of invertebrates (tethered locusts) subject to predation by invasive mammalian insectivores (European hedgehogs) in non-native pasture (0.10 per 24 hrs; 95% CI, 0.08-0.13) was less than half that in structurally complex native perennial tussock (bunch) grass (0.24; 95% binomial CI, 0.18-0.31). A significant positive relationship was apparent between structural complexity (grass dry stem density) surrounding each locust and their survival. In a second experiment, survival of locusts placed solely in tussock increased with decreasing locust density in tussock, presumably reflecting fewer resource-rich patches that predators could focus on. These results demonstrate that invasion by structurally simple non-native vegetation exposes prey to greater risk of predation. This is concerning from a global nature conservation perspective given that conversion of nearly half of the world's temperate grasslands to agriculture includes a range of invasive, structurally simple non-native plant species. Minimising invasion, and maintaining and restoring complex habitat structure may be a useful conservation option for reducing unwanted predation. This article is protected by copyright. All rights reserved.