Tropical Dry Forests Challenge Macroecological Rules of Positive Relationships Between Species' Niche Breadth, Range Size and Abundance

Abstract

Aim Niche theory has played a central role in explaining species spatial distribution, to the point that the niche breadth ‐ range and range‐abundance relationships are often cited as macroecological rules. We test the generality of these rules by evaluating the interdependencies between species niche breadth, range and abundance in tropical dry forests (TDF), a disjunct ecosystem known to harbour many locally dominant, range‐restricted species. Location Colombia. Time Period 2013–2015. Mayo'r Taxa Studied Trees. Methods We used a dataset encompassing 456 tree species derived from 458 floristic inventories and a network of 15–1 ha plots, located in five biogeographical regions in Colombia. Niche breadth was calculated based on edaphic and climatic variables using the Hurlbert index. We tested the relationship between abundance and frequency, and explored how locally dominant species influenced this pattern. Then, we evaluated the relationship between species niche breadth and both frequency and abundance at national and regional levels. Results Species abundance and frequency were significantly positively related, yet the explanatory power of the model was low ( R 2 = 0.06), likely due to the presence of locally dominant, range‐restricted species. Of the 456 tree species, 65% were confined to a single region, including many abundant species. Niche breadth was a strong predictor of species frequency ( R 2 = 0.78), but its relationship with abundance was weak ( R 2 = 0.10) and idiosyncratic across regions. Main Conclusions The patterns observed in these disjunct TDF challenge the commonly reported frequency–abundance relationship in many ecosystems. Most range‐restricted, locally dominant species exhibited narrow niches, indicating some degree of specialisation, while other species exhibited wide niches. This latter pattern is unlikely to result from niche processes, suggesting that biogeographic contingencies are also important. Further studies integrating biogeographical and niche‐based perspectives are needed, with particular attention on species responses to environmental limiting factors.

Bibliographic Information