Species coexist in communities according to interspecific trade-offs in ecological function. Trade-offs can be exhibited locally, when negative functional interactions among species’ traits emerge within habitats at small spatial scales, and regionally, when these negative interactions emerge among habitats at larger spatial scales. When independent of one another, these trade-offs at different spatial scales are predicted to lead to species coexistence at different spatial scales; however, when these local and regional trade-offs interact, the scale of species coexistence becomes more complicated. Despite this potential for interaction, theoretical and empirical studies have largely examined trade-offs for one spatial scale or the other. Here, we explored the potential interaction among local (competitive ability vs. disturbance tolerance) and regional (competitive ability vs. colonization rate) trade-offs for 10 common freshwater protozoan species using a suite of pair-wise species competition experiments and disturbance tolerance and colonization trials. 

Results/Conclusions

Protozoan species exhibited a regional trade-off (negative correlation) in competitive ability and colonization rate, but no local trade-off (no correlation) in competitive ability and disturbance tolerance when local and regional scale trade-offs were investigated separately. However, when investigated simultaneously, these trade-offs were shown to be linked producing a three-way trade-off (competitive ability vs. disturbance tolerance vs. colonization rate). These results suggest that some ‘local’ trade-offs might only be realized through a linkage with ‘regional’ trade-offs, which complicates the use of such scale-dependent terminology. Additionally, the extent to which such trade-offs linked across spatial scales are common in nature is unknown, highlighting the need for further research on trade-offs permitting species coexistence at multiple spatial scales.