Ant-mediated expansion of an obligate seeder species during the first years after fire

Arnan X., Rodrigo A., Molowny-Horas R., Retana J. (2010) Ant-mediated expansion of an obligate seeder species during the first years after fire. Plant Biology. 12: 842-852.
Enllaç
Doi: 10.1111/j.1438-8677.2009.00294.x

Resum:

Most obligate seeder species build up a soil seed bank that is associated with massive seed germination in the year immediately after a fire. These species are also shade-intolerant and disappear when vegetation cover closes, creating unsuitable conditions for seedling recruitment. The only way for these plants to expand their populations is when habitats suitable for seedling recruitment arise (i.e. in years immediately after a fire). However, short primary seed dispersal of obligate seeders does not allow these plants to colonise the suitable habitats, and these habitats can only be colonised by secondary seed dispersion. We hypothesised that Fumana ericoides, an obligate-seeding small shrub, not only establishes abundantly in the first year after fire, but also expands its local range in the following years due to secondary dispersal by ants while suitable habitats are still available. We tested this hypothesis using experimental studies and a simulation model of potential population expansion in a recently burned area. Results showed that F. ericoides not only established prolifically in the year immediately after fire, but was also able to recruit new individuals and expand its population in the years following the fire, despite a low germination rate and short primary seed dispersal. Ant-mediated seed dispersal and availability of suitable habitats were key factors in this phenomenon: ants redistributed seeds in suitable habitats while they were available, which accelerated the expansion of F. ericoides because new plants established far away from the core population. © 2009 German Botanical Society and The Royal Botanical Society of the Netherlands.

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Analysis of decadal time series in wet N concentrations at five rural sites in NE Spain

Avila A., Molowny-Horas R., Gimeno B.S., Peñuelas J. (2010) Analysis of decadal time series in wet N concentrations at five rural sites in NE Spain. Water, Air, and Soil Pollution. 207: 123-138.
Enllaç
Doi: 10.1007/s11270-009-0124-7

Resum:

Nitrogen emissions have grown in Spain during the last 15 years. As precipitation scavenges gases and aerosols from the atmosphere, an effect on rainwater concentrations can be expected. However, time-series studies on wet N concentrations in the Iberian Peninsula are very scarce. This paper aims to fill this gap by analysing weekly rainfall N concentrations at a set of rural sites in Catalonia (NE Spain) from 1995/1996 to 2007 and a forest site monitored from 1983 to 2007. The sites encompass a range of rural environments and climate conditions, from the inland pre-Pyrenees (Sort) to the Mediterranean coast (Begur) and from north (Sort and Begur) to central (Palautordera and La Castanya) and south Catalonia (La Senia). We found a 1-year cycle for concentrations of NH 4 + and NO 3 - whereby higher values were reached at the end of spring-early summer, except at the easternmost coastal site of Begur. Weekly NH 4 + concentrations decreased with time at all sites (except at La Senia) whilst NO 3 - concentrations increased at all sites during the same period. Rainfall SO 4 2- concentrations decreased with time at all sites. The opposite trends in NO 3 - and SO 4 2- concentrations determined a shift in the relative acid contribution of those anions during the 12-13-year period. To interpret the increasing trend, mean annual NO 3 - concentrations were regressed against NO 2 Spanish emissions and to some indicators of local anthropogenic activity. The increase at Sort and Palautordera showed good correlation with local anthropogenic indicators. Wet inorganic N deposition ranged between 4.2 and 6.7 kg ha -1 year -1. When including estimates of dry deposition, total annual deposition rose up to 10-20 kg ha -1 year -1, values that have been found to initiate adverse effects on Mediterranean-type forest ecosystems. © 2009 Springer Science+Business Media B.V.

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Effect of temperature regime on diapause intensity in an adult-wintering Hymenopteran with obligate diapause

Sgolastra F., Bosch J., Molowny-Horas R., Maini S., Kemp W.P. (2010) Effect of temperature regime on diapause intensity in an adult-wintering Hymenopteran with obligate diapause. Journal of Insect Physiology. 56: 185-194.
Enllaç
Doi: 10.1016/j.jinsphys.2009.10.001

Resum:

Osmia lignaria is a solitary bee that over-winters as a fully eclosed, cocooned, unfed adult. Our objective is to understand the effect of wintering temperature on diapause maintenance and termination in this species. We measure respiration rates and weight loss in individuals exposed to various wintering temperatures (0, 4, 7, 22 °C, outdoors) and durations (28, 84, 140, 196, 252 days). We use time to emerge and respiration response (respiration rate measured at 22 °C) as indicators of diapause intensity. Adults spontaneously lower their respiration rates to ∼0.1 ml/g h within 1 month after adult eclosion, indicating obligatory diapause. Non-wintered individuals maintain low respiration rates, but lose weight rapidly and die by mid-winter. In wintered adults, two phases can be distinguished. First, respiration response undergoes a rapid increase and then reaches a plateau. This phase is similar in bees wintered at 0, 4 and 7 °C. In the second phase, respiration response undergoes an exponential increase, which is more pronounced at the warmer temperatures. Composite exponential functions provide a good fit to the observed respiration patterns. Adults whose respiration response has reached 0.45 ml/g h emerge promptly when exposed to 20 °C, indicating diapause completion. Individuals wintered for short periods do not reach such respiration levels. When exposed to 20 °C these individuals lower their metabolic rate, and their emergence time is extended. The relationship between respiration rates and emergence time follows a negative exponential function. We propose two alternative models of diapause termination to interpret these results. © 2009 Elsevier Ltd.

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Les pinedes de pi blanc. En: Manuals de gestió d’hàbitats.

Arnan X, Gràcia M, Molowny Horas R, Ordoñez JL, Retana J et al. (2010) Les pinedes de pi blanc. En: Manuals de gestió d’hàbitats. Diputació de Barcelona.