Changes in vertical and horizontal diversities mediated by the size structure of introduced fish collectively shape food-web stability

Species introductions can alter local food-web structure by changing the
vertical or horizontal diversity within communities, largely driven by
their body size distributions. Increasing vertical and horizontal
diversities is predicted to have opposing effects on stability. However,
their interactive effects remain largely overlooked. We investigated the
independent and collective effects of vertical and horizontal diversities
on food-web stability in alpine lakes stocked with variable body size
distributions of introduced fish species. Introduced predators destabilize
food-webs by increasing vertical diversity through food chain lengthening.
Alternatively, increasing horizontal diversity results in more stable
food-web topologies. A non-linear interaction between vertical and
horizontal diversities suggests that increasing vertical diversity is most
destabilizing when horizontal diversity is low. Our findings suggest that
the size structure of introduced predators drives their impacts on
stability by modifying the structure of food-webs, and highlights the
interactive effects of vertical and horizontal diversities on stability.