Water-energy Dynamics Research Articles

Plant species richness–environment relationships across the Subantarctic–Patagonian transition zone

AbstractAim To evaluate the relative importance of climate, productivity, environmental heterogeneity, biotic associations and habitat use by cattle to account for the species richness of trees, shrubs and herbs across the Subantarctic–Patagonian transition.Location An area of c. 150 × 150 km, within the transition zone between the Subantarctic and Patagonian subregions on the eastern slope of the Andes (c. 39–42° S, 70–72° W).Methods All vascular plants found at each one of 50 (10 × 10 m) sampling plots were counted to estimate the local tree, shrub and herb species richness. Path analysis was used to evaluate the relationship between the richness of the three life‐forms and plant cover, dried litter biomass, mean annual temperature, annual precipitation, daily temperature range, substrate heterogeneity and number of faecal pats. Principal coordinates of neighbour matrices was used to model the spatial autocorrelation of the data.Results Total plant species richness showed a unimodal pattern of spatial variation across the transition. Richness responded positively to indirect effects of precipitation mediated through plant cover, but there was a negative overall effect of precipitation on richness towards the west of the transition, most strongly for trees. An increase in substrate heterogeneity promoted a local increase in herb and shrub richness; the richness of trees increased in sites with steeper slopes. Canopy closure had a direct negative impact on herb richness; it also increased the local accumulation of litter, which negatively affected shrub and herb richness. The impact of habitat use by cattle negatively affected herb richness in areas to the east of the biogeographical transition.Main conclusions We suggest that the importance of indirect climatic effects mediated by vegetation cover can account for species richness patterns across this transition, most strongly for woody species, which supports the productivity hypothesis. The southern temperate forests towards the west may represent a deviation from the predictions of the water–energy dynamics hypothesis. Dissimilar spatial patterns of variation in the richness of woody and herbaceous species, and their different responses to climatic and heterogeneity variables across the transition, suggest that plant life‐form influences the plant species richness–environment relationships.

The global distribution of frugivory in birds

ABSTRACTAim To examine patterns of avian frugivory across clades, geography and environments.Location Global, including all six major biogeographical realms (Afrotropics, Australasia, Indo‐Malaya, Nearctic, Neotropics and Palaearctic).Methods First, we examine the taxonomic distribution of avian frugivory within orders and families. Second we evaluate, with traditional and spatial regression approaches, the geographical patterns of frugivore species richness and proportion. Third, we test the potential of contemporary climate (water–energy, productivity, seasonality), habitat heterogeneity (topography, habitat diversity) and biogeographical history (captured by realm membership) to explain geographical patterns of avian frugivory.Results Most frugivorous birds (50%) are found within the perching birds (Passeriformes), but the woodpeckers and allies (Piciformes), parrots (Psittaciformes) and pigeons (Columbiformes) also contain a significant number of frugivorous species (9–15%). Frugivore richness is highest in the Neotropics, but peaks in overall bird diversity in the Himalayan foothills, the East African mountains and in some areas of Brazil and Bolivia are not reflected by frugivores. Current climate explains more variance in species richness and proportion of frugivores than of non‐frugivores whereas it is the opposite for habitat heterogeneity. Actual evapotranspiration (AET) emerges as the best single climatic predictor variable of avian frugivory. Significant differences in frugivore richness and proportion between select biogeographical regions remain after differences in environment (i.e. AET) are accounted for.Main conclusions We present evidence that both environmental and historical constraints influence global patterns of avian frugivory. Whereas water–energy dynamics possibly constrain frugivore distribution via indirect effects on food plants, regional differences in avian frugivory most likely reflect historical contingencies related to the evolutionary history of fleshy fruited plant taxa, niche conservatism and past climate change. Overall our results support an important role of co‐diversification and environmental constraints on regional assembly over macroevolutionary time‐scales.

Patterns of woody plant species richness in the Iberian Peninsula: environmental range and spatial scale

AbstractAim Climate‐based models often explain most of the variation in species richness along broad‐scale geographical gradients. We aim to: (1) test predictions of woody plant species richness on a regional spatial extent deduced from macro‐scale models based on water–energy dynamics; (2) test if the length of the climate gradients will determine whether the relationship with woody species richness is monotonic or unimodal; and (3) evaluate the explanatory power of a previously proposed ‘water–energy’ model and regional models at two grain sizes.Location The Iberian Peninsula.Methods We estimated woody plant species richness on grid maps with c. 2500 and 22,500 km2 cell size, using geocoded data for the individual species. Generalized additive models were used to explore the relationships between richness and climatic, topographical and substrate variables. Ordinary least squares regression was used to compare regional and more general water–energy models in relation to grain size. Variation partitioning by partial regression was applied to find how much of the variation in richness was related to spatial variables, explanatory variables and the overlap between these two.Results Water–energy dynamics generate important underlying gradients that determine the woody species richness even over a short spatial extent. The relationships between richness and the energy variables were linear to curvilinear, whereas those with precipitation were nonlinear and non‐monotonic. Only a small fraction of the spatially structured variation in woody species richness cannot be accounted for by the fitted variables related to climate, substrate and topography. The regional models accounted for higher variation in species richness than the water–energy models, although the water–energy model including topography performed well at the larger grain size. Elevation range was the most important predictor at all scales, probably because it corrects for ‘climatic error’ due to the unrealistic assumption that mean climate values are evenly distributed in the large grid cells. Minimum monthly potential evapotranspiration was the best climatic predictor at the larger grain size, but actual evapotranspiration was best at the smaller grain size. Energy variables were more important than precipitation individually. Precipitation was not a significant variable at the larger grain size when examined on its own, but was highly significant when an interaction term between itself and substrate was included in the model.Main conclusions The significance of range in elevation is probably because it corresponds to several aspects that may influence species diversity, such as climatic variability within grid cells, enhanced surface area, and location for refugia. The relative explanatory power of energy and water variables was high, and was influenced by the length of the climate gradient, substrate and grain size of the analysis. Energy appeared to have more influence than precipitation, but water availability is also determined by energy, substrate and topographic relief.

Explaining the elevational diversity pattern of geometrid moths from Borneo: a test of five hypotheses

AbstractAim The aim of this study was to document quantitatively a hump‐shaped elevational distribution of diversity for the geometrid moths of northern Borneo. Furthermore, we aimed to test rigorously a number of hypotheses that were proposed as ‘general explanations’ for such patterns, namely (1) the mid‐domain effect, (2) overlap between lowland and montane (or endemic) fauna, (3) water and energy availability (i.e. temperature‐limitation at high elevations, water‐limitation at low elevations), (4) area size of elevational bands, and (5) determination by (host) plant diversity.Location Northern Borneo, Malaysia.Methods We used quantitative light‐trapping data across northern Borneo (from our own field work and published literature) for 52 sites (covering > 800 species) to quantify local diversity (as Fisher’s α). We used these data to test predictions of the five hypotheses in spatially explicit correlation analyses, using published data on climate, plant diversity and topography (Digital Elevation Model) as predictor variables.Results We documented a pronounced diversity peak at c. 650 m a.s.l. (breakpoint regression, r2 = 0.55). We observed additional effects of other habitat parameters, sampling methodology and time on diversity only for data below 655 m a.s.l. Furthermore, we did not find unequivocal support for any of the above‐stated hypotheses. The mid‐domain effect and faunal overlap can be ruled out as single explanations of observed patterns, whereas the data equally fit predictions from water–energy dynamics, area and plant diversity only at higher elevations, but not in the lower part of the gradient. Of those, only effects of energy (i.e. temperature) were expected a priori to be restricted to elevations above the breakpoint.Main conclusions We tentatively conclude that temperature (i.e. energy limitation) is the best explanation for decreasing diversity towards high elevations, but we did not find a compelling explanation of lowered diversity near sea level. We discuss and present some preliminary data on further possible explanations, i.e. niche conservatism of higher taxonomic groups.

The Canaries: an important biogeographical meeting place

The Canaries: an important biogeographical meeting place

Environmental determinants of amphibian and reptile species richness in China

Understanding the factors that regulate geographical variation in species richness has been one of the fundamental questions in ecology for decades, but our knowledge of the cause of geographical variation in species richness remains poor. This is particularly true for herpetofaunas (including amphibians and reptiles). Here, using correlation and regression analyses, we examine the relationship of herpetofaunal species richness in 245 localities across China with 30 environmental factors, which include nearly all major environmental factors that are considered to explain broad‐scale species richness gradients in such theories as ambient energy, water–energy dynamics, productivity, habitat heterogeneity, and climatic stability. We found that the species richness of amphibians and reptiles is moderately to strongly correlated with most of the environmental variables examined, and that the best fit models, which include explanatory variables of temperature, precipitation, net primary productivity, minimum elevation, and range in elevation, explain ca 70% the variance in species richness for both amphibians and reptiles after accounting for sample area. Although water and temperature are important explanatory variables to both amphibians and reptiles, water variables explain more variance in amphibian species richness than in reptile species richness whereas temperature variables explain more variance in reptile species richness than in amphibian species richness, which is consistent with different physiological requirements of the two groups of organisms.

Testing the impact of climate variability on European plant diversity: 320 000 years of water–energy dynamics and its long‐term influence on plant taxonomic richness

Models examining the present-day relationship between macro-scale patterns in terrestrial species richness and variables of water and energy demonstrate that a combined water-energy model is a good predictor of richness in mid-to-high latitude regions. However, the power of the individual water and energy variables to explain this richness through time has never been explored. Here, we assess how well energy and water can predict long-term variations in plant richness using a 320,000-year fossil pollen data set from Hungary. Results demonstrate that a combined water-energy model best explains the variation in plant diversity through time. However, this long temporal record also demonstrates that amplitude of energy variation appears to be a strong determinant of richness. Decreased richness correlates with increased climate variability and certain species appear to be more susceptible according to their ecological traits. These findings have important implications for predicting richness at times of increasing climate variability.

Global patterns and determinants of vascular plant diversity

Plants, with an estimated 300,000 species, provide crucial primary production and ecosystem structure. To date, our quantitative understanding of diversity gradients of megadiverse clades such as plants has been hampered by the paucity of distribution data. Here, we investigate the global-scale species-richness pattern of vascular plants and examine its environmental and potential historical determinants. Across 1,032 geographic regions worldwide, potential evapotranspiration, the number of wet days per year, and measurements of topographical and habitat heterogeneity emerge as core predictors of species richness. After accounting for environmental effects, the residual differences across the major floristic kingdoms are minor, with the exception of the uniquely diverse Cape Region, highlighting the important role of historical contingencies. Notably, the South African Cape region contains more than twice as many species as expected by the global environmental model, confirming its uniquely evolved flora. A combined multipredictor model explains approximately 70% of the global variation in species richness and fully accounts for the enigmatic latitudinal gradient in species richness. The models illustrate the geographic interplay of different environmental predictors of species richness. Our findings highlight that different hypotheses about the causes of diversity gradients are not mutually exclusive, but likely act synergistically with water-energy dynamics playing a dominant role. The presented geostatistical approach is likely to prove instrumental for identifying richness patterns of the many other taxa without single-species distribution data that still escape our understanding.

GLOBAL MODELS FOR PREDICTING WOODY PLANT RICHNESS FROM CLIMATE: REPLY

Hawkins et al. (2007) have provided strong and significant empirical support for water-energy dynamics, and thus climate, being a fundamental factor limiting the global distribution of terrestrial plant richness, as outlined in Field et al. (2005). Contrary to common expectations, Hawkins et al. find that rainfall, not energy, appears to be the most significant factor in the mid-to-high latitudes. In so doing they lend further empirical support to the global applicability of the Interim General Models (IGMs; O'Brien 1998, Field et al. 2005) and to the theoretical premise underlying this relationship: biological relativity to water-energy dy namics (O'Brien 2006). For a trans-scalar model of how spatial variation in water-energy dynamics might trans late into richness patterns, see Lavers and Field (2006). IGM-1 and IGM-2 of the climatic potential for richness are of the form

Biological relativity to water–energy dynamics: a potential unifying theory?

Climate has long been related to geographical differences in the distribution and diversity of life. What has eluded explanation is why this should be so. One emerging possibility is biological relativity to water-energy dynamics: the relative nature of biotic dynamics to changes in energy/matter conditions caused by changes in water (all states) while doing work, especially liquid water. The dynamic parameters involved - liquid water and optimal energy conditions - are independent of life, and have been shown to provide a simple, globally predictive explanation for co-variation between climate and the species richness of woody plants. Here I elaborate on what I mean by 'biological relativity to water-energy dynamics' and how it should relate to the geography and evolution of life in general (terrestrial, subterranean, marine/aquatic biota). Working through a natural hierarchy of physical, geographical, ecological and biological first principles, I outline the hierarchical, abiotic → biotic conceptual framework within which this idea operates. The implications of this idea include the following. First, the biosphere is better conceptualized as a 'subsphere' of the liquid hydrosphere -a system within a system, wherein 'life' has all the unique physical properties of liquid water, plus unique emergent properties of its own. Second, the fundamental capacity for life to exist and be dynamic in all biotic systems is determined by the abiotic capacity for liquid water to exist and be dynamic, which is always relative to the capacity for water-energy dynamics in general. Third, liquid water-energy dynamics acts as a fundamental mechanism of evolution, while being a constant mechanism of natural selection. Fourth, over space and time, there should be first-order predictable and/or systematic differences in the capacity for, operation and outcomes of, biotic dynamics globally (e.g. species richness), that necessarily dissolve into apparent chaos locally. Fifth, biological relativity to water-energy dynamics provides a fundamental and natural framework for operationalizing hierarchy theory and developing trans-scalar explanations for the geography and evolution of life's diversity.

Phytogeographical Analysis of Seed Plant Genera in China

A central goal of biogeography and ecology is to uncover and understand distributional patterns of organisms. China has long been a focus of attention because of its rich biota, especially with respect to plants. Using 290 floras from across China, this paper quantitatively characterizes the composition of floristic elements at multiple scales (i.e. national, provincial and local), and explores the extent to which climatic and geographical factors associated with each flora can jointly and independently explain the variation in floristic elements in local floras. A study was made of 261 local floras, 28 province-level floras and one national-level flora across China. Genera of seed plants in each flora were assigned to 14 floristic elements according to their worldwide geographical distributions. The composition of floristic elements was related to climatic and geographical factors. Variations in percentages of cosmopolitan, tropical and temperate genera among local floras tend to be greater at higher latitudes than at lower latitudes. Latitude is strongly correlated with the proportions of 13 of the 14 floristic elements. Correlations of the proportions of floristic elements with longitude are much weaker than those with latitude. Climate represented by the first principal component of a principal component analysis was strongly correlated with the proportions of floristic elements in local floras (|r| = 0.75 +/- 0.18). Geographical coordinates independently explained about four times as much variation in floristic elements as did climate. Further research is necessary to examine the roles of water-energy dynamics, geology, soils, biotic interactions, and historical factors such as land connections between continents in the past and at present in creating observed floristic patterns.

Biological relativity to water–energy dynamics

AbstractClimate has long been related to geographical differences in the distribution and diversity of life. What has eluded explanation is why this should be so. One emerging possibility is biological relativity to water–energy dynamics: the relative nature of biotic dynamics to changes in energy/matter conditions caused by changes in water (all states) while doing work, especially liquid water. The dynamic parameters involved – liquid water and optimal energy conditions – are independent of life, and have been shown to provide a simple, globally predictive explanation for co‐variation between climate and the species richness of woody plants. Here I elaborate on what I mean by ‘biological relativity to water–energy dynamics’ and how it should relate to the geography and evolution of life in general (terrestrial, subterranean, marine/aquatic biota). Working through a natural hierarchy of physical, geographical, ecological and biological first principles, I outline the hierarchical, abiotic → biotic conceptual framework within which this idea operates. The implications of this idea include the following. First, the biosphere is better conceptualized as a ‘subsphere’ of the liquid hydrosphere – a system within a system, wherein ‘life’ has all the unique physical properties of liquid water, plus unique emergent properties of its own. Second, the fundamental capacity for life to exist and be dynamic in all biotic systems is determined by the abiotic capacity for liquid water to exist and be dynamic, which is always relative to the capacity for water–energy dynamics in general. Third, liquid water–energy dynamics acts as a fundamental mechanism of evolution, while being a constant mechanism of natural selection. Fourth, over space and time, there should be first‐order predictable and/or systematic differences in the capacity for, operation and outcomes of, biotic dynamics globally (e.g. species richness), that necessarily dissolve into apparent chaos locally. Fifth, biological relativity to water–energy dynamics provides a fundamental and natural framework for operationalizing hierarchy theory and developing trans‐scalar explanations for the geography and evolution of life's diversity.

A resource‐based conceptual model of plant diversity that reassesses causality in the productivity–diversity relationship

ABSTRACTBiogeographical studies frequently reveal positive correlations between species richness and estimates of environmental water and/or energy. A popular interpretation of this relationship relates the supply of water and energy to productivity, and then, in turn, to richness. Productivity–diversity theories are now legion, yet none has proved sufficiently intuitive to gain broad acceptance. Like productivity, heterogeneity is known to influence diversity at fine spatial scales, yet the possibility that richness might relate to water–energy dynamics at coarse spatial scales via a heterogeneity‐generating mechanism has received little attention. In this paper we outline such a conceptual model for plants that is internally consistent and testable. We believe it may help to explain the capacity of environments receiving different inputs of water and energy to support variable numbers of species at a range of spatial scales, the pervasive correlation between productivity and richness, some exceptions to the productivity–diversity relationship, the form of productivity–diversity curves and the link between richness and environmental ‘harshness’. The model may also provide an answer to one of the most venerable puzzles in the field of diversity studies: why high inputs of water and energy correspond to more species rather than simply more individuals.

GLOBAL MODELS FOR PREDICTING WOODY PLANT RICHNESS FROM CLIMATE: DEVELOPMENT AND EVALUATION

There have been few attempts to generate global models of climate–richness relationships, and fewer still that aim to predict richness rather than fitting a model to data. One such model, grounded on theory (biological relativity to water–energy dynamics) is the interim general model (IGM1) of the climatic potential for woody plant richness. Here we present a second-generation model (IGM2), and genus and family versions of both models. IGM1 describes horizontal climate–richness relationships based on climate station data and systematic species range maps, with IGM2 additionally incorporating vertical changes in climate due to topographic relief. The IGMs are mathematical transformations of empirical relationships obtained for the southern subcontinent of Africa, whereby the re-described regression models apply to the full range of global variation in all independent climate parameters. We undertake preliminary validation of the new IGMs, first by mapping the distribution and relative spatial variation in forecasted richness (per 25 000 km2) across the continent of Africa, then by evaluating the precision of forecasted values (actual vs. predicted) for an independent study system, the woody plants of Kenya. We also compare the IGMs with a recent example of purely statistical regression models of climate–richness relationships; namely, the “global” model of A. P. Francis and D. J. Currie for angiosperm family richness. We conclude that the IGMs are globally applicable and can provide a fundamental baseline for systematically estimating differences in (woody) plant richness and for exploring the hierarchy of subordinate relationships that should also contribute to differences in realized richness (mostly at more discrete scales of analysis). Further, we found that the model of Francis and Currie is useful for predicting angiosperm richness in Africa, on a conditional basis (somewhere, sometime); we examined the relationship that it describes between climate and richness. Lastly, we found that indices of available soil water used in “water-budget” or “water-balance” analyses are not proxies for available liquid water as a function of climatological dynamics.

The environmental control of plant species density on a Himalayan elevation gradient

AbstractAim In eastern Nepal, forests occupy an elevation gradient of 4000 m with bioclimatic zones from near tropical to alpine. Understorey plants and trees were censused to measure species density and identify patterns of ecological change. By sampling in a manner robust against spurious mid‐domain effects, I aim to identify biologically valid controls on species density.Location The study area consists of land below 4250 m elevation between 27.1 and 27.8° N latitude, 86.5 and 88.0° E longitude on the southern slopes of the Himalaya Range in eastern Nepal. Sampling sites are limited to intact, natural forest with relatively little human impact.Methods Team members counted species of understorey plants and trees ≥ 10 cm d.b.h. in 0.04 ha plots throughout the study area. In addition, basal area, leafing phenology and species composition were determined for the trees in each plot. Estimates of regional species density were compiled for successive 250 m elevation bands from 250 to 4250 m elevation. Species density trends were identified and compared with the expectations of O'Brien's [Journal of Biogeography25 (1998) 379–398] climate‐based water–energy dynamics model.Results Stand basal area, tree leafing phenology and taxonomic composition (angiosperm vs. gymnosperm) show non‐random change with elevation. Understorey plant and tree species density both have a humped, unimodal trend with more species near the bottom of the gradient and fewest at the top. These trends are consistent with expected effects of the climatically active water and energy variables. After curve‐fitting, significant spatial structure in the residuals suggests that tree communities within the 1750–2250 m elevation range do not realize their climatic potential species richness.Main conclusions Neither mid‐domain effects nor biologically valid boundary effects like dispersal limitation explain the plant species density trends observed. Trends do fit a model in which species density is controlled by the same ‘active’ climatic variables that predict species richness on continental scales. Patterns of leafing phenology on the elevation gradient provide further support for the hypothesis of environmental control of species density. The productivity–diversity linkage that exists on continental scales may also apply on the smaller scale of a Himalayan elevation gradient. Human activity and possible competitive exclusion by Castanopsis tribuloides are the two best explanations for the observed decline in tree species density at 1750–2250 m elevation. Burning, lopping for fodder and livestock grazing might account for the decline, but this study does not assess the relative importance of these activities. The elevation richest for understorey plant and tree species (500–1500 m) also has the most severe reduction in forest cover. Local farmers deserve credit for sustaining plant biodiversity in forest enclaves, but further loss of forest at these elevations should be discouraged.

ENERGY, WATER, AND BROAD-SCALE GEOGRAPHIC PATTERNS OF SPECIES RICHNESS

It is often claimed that we do not understand the forces driving the global diversity gradient. However, an extensive literature suggests that contemporary climate constrains terrestrial taxonomic richness over broad geographic extents. Here, we review the empirical literature to examine the nature and form of the relationship between climate and richness. Our goals were to document the support for the climatically based energy hypothesis, and within the constraints imposed by correlative analyses, to evaluate two versions of the hypothesis: the productivity and ambient energy hypotheses. Focusing on studies extending over 800 km, we found that measures of energy, water, or water-energy balance explain spatial variation in richness better than other climatic and non-climatic variables in 82 of 85 cases. Even when considered individually and in isolation, water/ energy variables explain on average over 60% of the variation in the richness of a wide range of plant and animal groups. Further, water variables usually represent the strongest predictors in the tropics, subtropics, and warm temperate zones, whereas energy variables (for animals) or water-energy variables (for plants) dominate in high latitudes. We conclude that the interaction between water and energy, either directly or indirectly (via plant productivity), provides a strong explanation for globally extensive plant and animal diversity gradients, but for animals there also is a latitudinal shift in the relative importance of ambient energy vs. water moving from the poles to the equator. Although contemporary climate is not the only factor influencing species richness and may not explain the diversity pattern for all taxonomic groups, it is clear that understanding water-energy dynamics is critical to future biodiversity research. Analyses that do not include water-energy variables are missing a key component for explaining broad-scale patterns of diversity.

PRODUCTIVITY AND HISTORY AS PREDICTORS OF THE LATITUDINAL DIVERSITY GRADIENT OF TERRESTRIAL BIRDS

The latitudinal diversity gradient is the largest scale, and longest known, pattern in ecology. We examined the applicability of three versions of the energy hypothesis, the habitat heterogeneity hypothesis, and historical contingency to the gradient of terrestrial birds. The productivity version of the energy hypothesis, tested using actual evapotranspiration, a water–energy variable closely associated with plant productivity, accounted for 72% of the variance in a model of global extent. An historical contingency model based on biogeographic region explained 58% of the variance. A combined climate–region model accounted for 78% of the variance, but 52% comprised the overlap between these effects. This suggests that further resolution of contemporary vs. historical processes at the global level will require the inclusion of phylogenetic information. Regional-extent regression models suggest a latitudinal shift in constraints on diversity; measures of ambient energy (potential evapotranspiration and mean annual temperature) best predicted the diversity gradient at high latitudes, whereas water-related variables (actual evapotranspiration and annual rainfall) best predicted richness in low-latitude, high-energy regions. Intraregional spatial autocorrelation analysis confirmed that climatic models adequately describe geographic richness patterns at all but the smallest spatial scales resolved by the analysis. We conclude that the “water–energy dynamics” hypothesis, originally developed for plant diversity gradients, offers a parsimonious explanation for bird diversity patterns as well, presumably operating via plant productivity. However, more refined tests of historical factors are needed to fully resolve their influences on the gradient. Corresponding Editor: J. M. Ver Hoef.

Ecology's oldest pattern?

Ecology's oldest pattern?

Climate and woody plant diversity in southern Africa: relationships at species, genus and family levels

Woody plant richness across southern Africa was analysed and related to climate–based water–energy dynamics. The analyses, which were based on an equal–area grid system, were undertaken at the genus and family levels and compared with results previously obtained at the species level. In all cases– climate accounts for most of the variation in richness (74–79%,). with richness being a linear function of liquid water and a parabolic function of energy. There is some variation in the particulars of climate's relationship to richness between the three taxonomic levels considered. But, the overall similarity of the outcomes at all three taxonomic levels supports the view that independent and predictable geographic variation in water‐energy dynamics exerts a first‐order control on the realised distributional ranges, and thus richness, of surviving and evolving taxa.