Drought is a normal, recurrent feature of climate. In order to understand the potential effect of increasing atmospheric CO2 concentration (Ca) on ecosystems, it is essential to determine the combined effects of drought and elevated Ca (EC) under field conditions. A severe drought occurred in Central Florida in 1998 when precipitation was 88 % less than the average between 1984 and 2002. We determined daytime net ecosystem CO2 exchange (NEE) before, during, and after the drought in the Florida scrub-oak ecosystem exposed to doubled Ca in open-top chamber since May 1996. We measured diurnal leaf net photosynthetic rate (PN) of Quercus myrtifolia Willd, the dominant species, during and after the drought. Drought caused a midday depression in NEE and PN at ambient CO2 concentration (AC) and EC. EC mitigated the midday depression in NEE by about 60 % compared to AC and the effect of EC on leaf PN was similar to its effect on NEE. Growth in EC lowered the sensitivity of NEE to air vapor pressure deficit under drought. Thus EC would help the scrub-oak ecosystem to survive the consequences of the effects of rising atmospheric CO2 on climate change, including increased frequency of drought, while simultaneously sequestering more anthropogenic carbon. and J. H. Li ... [et al.].
Although the Prisoner’s dilemma is a leading metaphor for the evolution of sociality, only a few studies demonstrate that this game indeed operates in nature. We offer an alternative perspective, in which parasites and their hosts are used as a model system, suggesting that Prisoner’s dilemma may be rare due to different individuals experiencing variation in the payoffs they receive from alternative strategies. Ectoparasites (such as fleas) move stochastically between hosts, causing differential parasite burdens. The resulting variance in the need for cooperation – in this case cooperative allogrooming – means that payoffs for different strategies (e.g. cooperate and defect) are not fixed. Our simulations revealed that due to parasite dynamics, cooperation among hosts conforms to a mixture of two games: Mutualism and Cruel Bind, both of which are more likely to coerce individuals into mutual cooperation than Prisoner’s dilemma. Though interesting, Prisoner’s dilemma is in fact the least likely scenario. If payoff variation is common, the dominance of the Prisoner’s dilemma paradigm may have made us unnecessarily puzzled by cooperation in nature.