SummaryPlant function requires effective mechanisms to regulate water transport at a variety of scales. Here, we develop a new theoretical framework describing plant responses to drying soil, based on the relationship between midday and predawn leaf water potentials. The intercept of the relationship (Λ) characterizes the maximum transpiration rate per unit of hydraulic transport capacity, whereas the slope (r) measures the relative sensitivity of the transpiration rate and plant hydraulic conductance to declining water availability.This framework was applied to a newly compiled global database of leaf water potentials to estimate the values of Λ and r for 102 plant species.Our results show that our characterization of drought responses is largely consistent within species, and that the parameters Λ and r show meaningful associations with climate across species. Parameter r was ≤1 in most species, indicating a tight coordination between the gas and liquid phases of water transport, in which canopy transpiration tended to decline faster than hydraulic conductance during drought, thus reducing the pressure drop through the plant.The quantitative framework presented here offers a new way of characterizing water transport regulation in plants that can be used to assess their vulnerability to drought under current and future climatic conditions.

Although many taxa show a latitudinal gradient in richness, the relationship between latitude and species richness is often asymmetrical between the northern and southern hemispheres. Here we examine the latitudinal pattern of species richness across 1003 local ant assemblages. We find latitudinal asymmetry, with southern hemisphere sites being more diverse than northern hemisphere sites. Most of this asymmetry could be explained statistically by differences in contemporary climate. Local ant species richness was positively associated with temperature, but negatively (although weakly) associated with temperature range and precipitation. After contemporary climate was accounted for, a modest difference in diversity between hemispheres persisted, suggesting that factors other than contemporary climate contributed to the hemispherical asymmetry. The most parsimonious explanation for this remaining asymmetry is that greater climate change since the Eocene in the northern than in the southern hemisphere has led to more extinctions in the northern hemisphere with consequent effects on local ant species richness.

Summary1. In Mediterranean ant communities, a close relationship has been found between activity rhythm in the period of maximum activity and position in the dominance hierarchy: subordinate species are active during the day, when conditions are more severe, while dominants are active during the afternoon and the night. 2. Results obtained in this study confirmed that the species foraging at higher temperatures were closer to their critical thermal limits than the species foraging at lower temperatures. 3. This enabled two extreme strategies of foraging in relation to temperature to be distinguished: (1) heat-intolerant ant species behaved as risk-averse species, foraging at temperatures very far from their critical thermal limits; and (2) heat-tolerant ant species behaved as risk-prone species, foraging very near their critical thermal limits and running a high heat mortality risk. 4. Heat-tolerant species benefited from this strategy by having better foraging performance at high temperatures. 5. This wide range of thermal niches may be one reason why Mediterranean ant faunas are so diverse in the face of limited diversity in vegetation and habitat structure: the daily range of temperature may be sufficiently great to meet the requirement both of heat-adapted and cold-adapted species as well as a spectrum of intermediate forms.