Hongyu Guo, Yihui Zhang , Zhenjiang Lan, Steven C. Pennings.Global Change Biology,2013. 19: 2765–2774.

Many species are expanding their distributions to higher latitudes due to global warming. Understanding the mechanismsunderlying these distribution shifts is critical for better understanding the impacts of climate changes. Theclimate envelope approach is widely used to model and predict species distribution shifts with changing climates.Biotic interactions between species, however, may also influence species distributions, and a better understanding ofbiotic interactions could improve predictions based solely on climate envelope models. Along the northern Gulf ofMexico coast, USA, subtropical black mangrove (Avicennia germinans) at the northern limit of its distribution growssympatrically with temperate salt marsh plants in Florida, Louisiana, and Texas. In recent decades, freeze-freewinters have led to an expansion of black mangrove into salt marshes. We examined how biotic interactions betweenblack mangrove and salt marsh vegetation along the Texas coast varied across (i) a latitudinal gradient (associatedwith a winter-temperature gradient); (ii) the elevational gradient within each marsh (which creates different marshhabitats); and (iii) different life history stages of black mangroves (seedlings vs. juvenile trees). Each of these variablesaffected the strength or nature of biotic interactions between black mangrove and salt marsh vegetation: (i) Salt marshvegetation facilitated black mangrove seedlings at their high-latitude distribution limit, but inhibited black mangroveseedlings at lower latitudes; (ii) mangroves performed well at intermediate elevations, but grew and survived poorlyin high- and low-marsh habitats; and (iii) the effect of salt marsh vegetation on black mangroves switched from negativeto neutral as black mangroves grew from seedlings into juvenile trees. These results indicate that the expansionof black mangroves is mediated by complex biotic interactions. A better understanding of the impacts of climatechange on ecological communities requires incorporating context-dependent biotic interactions into species rangemodels.