Species with large local abundances tend to occupy more sites. One of the mechanisms proposed to explain this widely reported inter-specific relationship is a cross-scale hypothesis based on dynamics at the population level. Called the vital rates mechanism, it uses within-population demographic processes of population growth and density dependence to explain how positive inter-specific abundance-occupancy relationships can arise. Even though the vital rates mechanism is mathematically simple, it has never been tested directly because of the difficulty in estimating the demographic parameters involved. Here, using a recently introduced mark-recapture analysis method on 17 bird species, we show that inter-specific variability in density dependence strength can weaken both abundance-occupancy relationships and the expected corollaries of the vital rates mechanism. We demonstrate that one of the key assumptions of vital rates mechanism, that density dependence strength should be similar among species, is not met for these 17 species. Additionally, the mathematical structure of vital rates mechanism that relate population-level abundance and intrinsic growth rate is only weakly observed in our data. We argue that this mismatch of mathematical structure and data together with the violation of density dependence assumption weakens the expected positive abundance-occupancy association. Vital rates mechanism also predicts conditions under which positive abundance-occupancy association is weakened or even reversed; our results are consistent with these predictions. More generally, our findings support a cross-scale mechanism of macroecological abundance-occupancy relationship emerging from density-dependent dynamics at the population level.
Competing Interest Statement
The authors have declared no competing interest.