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.
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