How are tree species distributed in climatic space? A simple and general pattern

Abstract

Aim Although many factors undoubtedly affect species geographic distributions, can a single, simple model nonetheless capture most of the spatial variation in the probability of presence/absence in a large set of species? For 482 North American tree species that occur east of the Rocky Mountains, we investigated the shape(s) of the relationship between the probability of occupancy of a given location and macroclimate, and its consistency among species and regions. Location North America. Methods Using Little's tree range maps, we tested four hypothetical shapes of response relating occupancy to climate: (1) high occupancy of all suitable climates; (2) threshold response (i.e. unsuitable climates exclude species, but within the thresholds, species presence is independent of climate); (3) occupancy is a bivariate normal function of annual temperature and precipitation; and (4) asymmetric limitation (i.e. abiotic factors set abrupt range limits in stressful climates only). Finally, we compared observed climatic niches with the occupancy of similar climates on off‐shore islands as well as west of the Rockies. Results (a) Species' distributions in climatic space do not have strong thresholds, nor are they systematically skewed towards less stressful climates. (b) Occupancy can generally be described by a bivariate normal function of temperature and precipitation, with little or no interaction between the two variables. This model, averaged over all species, accounts for 82% of the spatial variation in the probability of occupancy of a given area. (c) Occupied geographic ranges are typically ringed by unoccupied, but climatically suitable areas. (d) Observed climatic niche positions are largely conserved between regions. Main conclusions We conclude that, despite the complexities of species histories and biologies, to a first approximation most of the variation in their geographic distributions relates to climate, in similar ways for nearly all species.

Does climate limit species richness by limiting individual species’ ranges?

“…Regardless of their specific mechanism, top-down hypotheses of species richness predict that the richnessenvironment relationship is congruent through time and space because the mechanism operates independently of factors that vary spatially or temporally, other than climate [13]. In other words, these hypotheses require that the environment limits the number of species that can occur in a given region [13,14], or determines stochastic immigration and extinction rates [12,15].…”

Data-based modelling and environmental sensitivity of vegetation in China

“…The approach is innovative in combining a well-established technique in statistical niche modelling (multiple logistic regression, which is closely related to the popular maximum entropy method; Phillips et al, 2006) with algorithms used to estimate bioclimatic variables for dynamic vegetation and biogeochemistry modelling, and a process-based method to take account of CO 2 concentration effects. By fitting models with linear and quadratic (but not interaction) terms for each predictor, our modelling approach is consistent with Boucher-Lalonde et al (2012), who showed that the probabilities of occurrence of tree species in North America could be predicted with high efficiency from independent Gaussian functions of climate variables.…”

Historical distribution of Sundaland’s Dipterocarp rainforests at Quaternary glacial maxima

“…We were not able to include edaphic factors in our models because these are not known for the entire exposed Sunda Shelf. Nonetheless, plant distributions are primarily dictated by temperature and precipitation (31,42,43), within the climatic bounds modified by edaphic conditions. Even if the exposed region was fully covered by sandy soils, this still is no reason to assume that Dipterocarp rainforest was absent from central Sundaland.…”