Local and biogeographic determinants and stochasticity of tree population demography

Abstract

Demographic events such as the birth and death of organisms are ubiquitous in nature. Disentangling the processes that underlie the demographic dynamics of species is fundamental to understanding how biodiversity is organized and will be re-organized at multiple scales. To provide new insights on multispecies demographic dynamics, I designed the present study to focus on local and biogeographic influences on mortality and recruitment rates for tree populations in forest biomes throughout the Japanese archipelago. Most populations exhibited mortality that fell within the 95% confidence intervals of a neutral model (i.e. the expectation of demographic stochasticity). However, there were also important determinants that make population dynamics to deviate from the neutral expectation. Interspecific niche differentiation was important to reduce the mortality rate, regardless of the local rarity or ubiquity of a species. Although intraspecific aggregation that caused density-dependent mortality was only significant for locally abundant species, the degree of isolation from a species’ central or optimal range determined mortality only for locally rare species. These differences between rare and common species provide important empirical quantification of aspects of population dynamics that have been less accounted for in ecology and biogeography studies. Synthesis. Unifying different theories such as those rooted in local-scale community ecology and macro-scale biogeography is important. At this juncture, this study emphasizes that disentangling the interactive roles of demographic stochasticity and determinism that operate at different scales would be a clue to advance the field of ecology both in theory and practice.