Background/Question/Methods Previous studies have shown that a gleaner-opportunist trade-off between the minimum resource requirement (R*) and the maximum growth rate is a key for fluctuation-dependent coexistence of competing consumers. On the other hand, by conducting a meta-analysis of functional responses, a recent study suggested that the gleaner-opportunist trade-off may be uncommon in nature (Kiørboe and Thomas 2020). Rather, their results indicate a slow-fast continuum, where a consumption rate of a fast species is always higher than that of a slow species irrespective of resource density. In response, Letten and Yamamichi (2021) pointed out that population growth rates need to be examined instead of functional responses for understanding coexistence due to the gleaner-opportunist trade-off. Here, we analyze mathematical conditions for species-specific conversion efficiencies and mortality rates to change the slow-fast continuum in functional responses to the gleaner-opportunist trade-off in population growth rates.
Results/Conclusions When functional responses of two species exhibit the slow-fast continuum, we derived conditions for conversion efficiencies and mortality rates of the two species to produce the gleaner-opportunist trade-off. When the two species have the same conversion efficiency, a fast species needs to have a higher mortality rate than that of a slow species. In such a case, depending on parameter combinations, there are two types of the gleaner-opportunist trade-off: (i) the fast species is a gleaner and the slow species is an opportunist; (ii) The fast species is an opportunist and the slow species is a gleaner. We clarified that species-specific conversion efficiencies can produce the two types of gleaner-opportunist trade-off as well. We further explored the effects of the Holling type III functional response, resource-dependent mortality rates and conversion efficiencies, and a shared predator on a gleaner-opportunist trade-off (with P* instead of R*). This will be an important step for future meta-analyses for understanding the prevalence of the gleaner-opportunist trade-off in the wild.
