Fast-slow traits predict competition network structure and its response to resources and enemies

Plants interact in complex networks but how network structure depends on
resources, natural enemies, and species resource-use strategy remains
poorly understood. Here, we quantified competition networks among 18
plants varying in fast-slow strategy, by testing how increased nutrient
availability and reduced foliar pathogens affected intra- and
inter-specific interactions. Our results show that nitrogen and pathogens
altered several aspects of network structure, often in unexpected ways due
to fast and slow-growing species responding differently. Nitrogen addition
increased competition asymmetry in slow-growing networks, as expected, but
decreased it in fast-growing networks. Pathogen reduction made networks
more even and less skewed because pathogens targeted weaker competitors.
Surprisingly, pathogens and nitrogen dampened each other’s effect. Our
results show that plant growth strategy is key to understanding how
competition responds to resources and enemies, a prediction from classic
theories that has rarely been tested by linking functional traits to
competition networks.