Raw data: Direct and insect-mediated effects of pathogens on plant growth and fitness

1. Plants are attacked by a large diversity of pathogens. These pathogens
can affect plant growth and fitness directly, but also indirectly by
inducing changes in the host plant that affect interactions with
beneficial and antagonistic insects. Yet, we lack insights into the
relative importance of direct and indirect effects of pathogens on their
host plants, and how these effects differ among pathogen species. 2. In
this study, we examined four fungal pathogens on the wood anemone (Anemone
nemorosa). We used field observations to record the impacts of each
pathogen species on plant growth and fitness throughout the season, and
experimental hand-pollination and insect feeding trials to assess whether
fitness impacts were mediated by pathogen-induced changes in
plant-pollinator and plant-herbivore interactions. 3. Three out of four
pathogens negatively affected plant size, and pathogens differed strongly
in their effect on plant architecture. Infected plants had lower fitness,
but this effect was not mediated by pollinators or herbivores. Even so,
two out of four pathogens reduced herbivory on anemones in the field, and
we found negative effects of pathogen infection on herbivore preference
and performance in feeding trials. 4. Synthesis. Our results are of
broader significance in two main respects. First, we demonstrated that
pathogens negatively affected plant growth and fitness, and that the
magnitude of these effects varied among pathogen species, suggesting that
pathogens constitute important selective agents that differ in strength.
Second, direct effects on plant fitness were more important than effects
mediated by beneficial and antagonistic insects. In addition, even though
we did not detect insect-mediated effects on plant fitness, the negative
effects of some pathogens on herbivore preference and performance indicate
that pathogen communities influence the distribution and abundance of
herbivores.