1 Salt marshes in south-west Spain are being invaded by Spartina densi¯ora, a South American introduction, although the native S. maritima still dominates many lower marshes. A transplant experiment was used to investigate the means by which physical and chemical factors may determine lower vegetation limits in the tidal frame. Both species were transplanted from a mid-level marsh to lower, unvegetated tidal¯ats. 2 The survival and growth of transplanted clumps and their constituent tillers were monitored on an elevational gradient. The photosynthetic competence of transplants was assessed by measurements of leaf gas exchange and the fast kinetics of chlorophyll¯uorescence. Submergence period, salinity, redox potential and sulphide concentration in the sediment were also examined at the transplant sites. 3 Neither species survived for a year at the lowest transplant point ( 1.04 m relative to Spanish Hydrographic Zero). At 1.41 m elevation, S. maritima survived well but all clumps of S. densi¯ora died. At higher elevations ( 1.46±1.67 m), clumps of both species had high survival rates. Tiller growth rates in surviving clumps of both species increased with elevation, but that of S. densi¯ora was more sensitive to low elevation. 4 S. maritima showed no impairment of photosynthetic performance, even at the lowest elevation; its rates of gas exchange were independent of elevation, as were its chlorophyll¯uorescence parameters. In contrast, in S. densi¯ora the rate of CO 2 uptake declined and stress to photosystem II (Fv/Fp) increased at lower elevations; both of these photosynthetic measurements were linearly related to sediment redox potential. Stomatal conductance did not vary with elevation. 5 S. maritima has a potentially wide elevational tolerance and an absolute lower limit substantially below that of S. densi¯ora. The progressively reduced growth and survival of S. densi¯ora at lower levels appear to result primarily from impairment of photosynthesis when root conditions are hypoxic. This eect is mediated through eects on the photochemical apparatus rather than on stomatal resistance to CO 2 uptake. 6 These studies de®ne lower limits to the fundamental niches of the two species in a Mediterranean-type salt marsh and thus provide a basis for future investigations of interactions between them. The correlation between chlorophyll¯uorescence and long-term survival of S. densi¯ora suggests that this short-term measure may be a valuable tool.

Many animal species are living in urban areas, where they encounter human‐altered environmental conditions. Artificial light and traffic noise are two of the most prominent anthropogenic factors, both of which potentially affect animal life. Here we studied the changes in traffic noise conditions over the morning in the urban bird habitat of the city of Seville, Spain. We tested experimentally whether noise from human activities can cause a shift in the timing of birdsong activity. Our data revealed that noise conditions vary markedly among our replicate set of twelve streets. Relatively quiet streets show low base‐line amplitude levels early in the morning, with frequent events of brief noise bursts, followed by a strong rise in noise levels. Relatively noisy streets have high base‐line amplitude levels from a much earlier start in the morning. Experimental exposure data revealed a noise‐related earlier start of dawn singing for two out of six species: the spotless starling Sturnus unicolor and the house sparrow Passer domesticus. Our experiment did not cover earlier singing species and revealed no impact for species with more‐variable starting times of the dawn singing. Our study provides more insight into the intertwinings of bird and human behavior and confirms the potential for experimental approaches to successfully tackle questions related to the impact of anthropogenic factors on animal life in cities.

Sarcocornia fruticosa (L.) A.J. Scott is found in coastal marshes of south-west Spain, growing under a very wide range of interstitial soil salinity from 10 mM up to nearly 1000 mM. A glasshouse experiment was designed to investigate the effect of this range of salinities on the morphology and the photosynthetic apparatus of S. fruticosa by measuring growth rate, photosynthetic and non-photosynthetic area, atrophy of distal branch ends, water status, chlorophyll fluorescence parameters, gas exchange and photosynthetic pigment concentrations. The long-term effects of salinity on the growth of S. fruticosa were mainly determined by the extent of photosynthetic area rather than the variations in net photosynthetic rate. Photosynthetic area was reduced at 1030 mM as a result of a decrease in the length of the photosynthetic portions. This was induced by fewer internodes and, at salinities lower than 510 mM, smaller internode diameter. Net photosynthetic rate increased as the quantum efficiency of photosystem II decreased in the different salinity treatments, which means that the plant could be increasing photorespiration and/or using cyclic electron transport as additional photoprotective mechanisms. The recorded drop in net photosynthetic rate at higher salinities appeared to be due to a reduction in stomatal conductance. The results indicate that S. fruticosa is capable of tolerating very high and continued exposure to salt, showing its greatest growth rate at 510 mM NaCl.

Summary 1We examined salt marsh development over 17 years (1984)(1985)(1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001) in a rapidly accreting, well-drained lagoon of a macrotidal marsh in south-west Spain. Scattered, elevated tussocks of colonizing Spartina maritima expanded radially until they either coalesced or were separated only by narrow drainage channels. We recorded changes in elevation of the tussocks and investigated the cover and biomass of successive species invading them. 2 Sediment accretion produced a mean annual increase in tussock elevation of 3.5 cm. Sarcocornia perennis had begun to invade the raised centres of the tussocks by 1984, subsequently displacing Spartina maritima radially to become dominant by 1990. A hybrid form of Sarcocornia , which appeared on some of the tussocks occupied by S. perennis in 1997, also expanded radially and had achieved dominance on many of the invaded tussocks by 2001, by virtue of its more erect growth form and rapid accumulation of high above-and below-ground biomass. 3Tussocks not yet invaded by the hybrid remain dominated by S. perennis and have maintained sediment accretion rates and redox potentials similar to those that have been invaded. 4 Genetic analysis, using random amplified DNA (RAPD) markers, indicated that the hybrid was a cross between the diploid Sarcocornia perennis (2 n = 18) and the octaploid S. fruticosa (2 n = 72), a high-marsh species, and suggested that each hybrid individual may have resulted from a separate pollination of an indigenous S. perennis plant. 5 Invasion by the new hybrid thus probably occurred as a result of pollen flow from high-marsh S. fruticosa , some 1 km distant, to the stigmas of the established dominant S. perennis . Succession might therefore be facilitated genetically rather than simply by the enhanced sediment accretion, which ameliorated the effects of submersion and low sediment redox potentials that presumably exclude S. fruticosa from lower parts of the marsh.

• Premise of the study: Phenotypic acclimation of individual plants and genetic differentiation by natural selection within invasive populations are two potential mechanisms that may confer fitness advantages and allow plants to cope with environmental variation. The invasion of Spartina densiflora across a wide latitudinal gradient from California (USA) to British Columbia (Canada) provides a natural model system to study the potential mechanisms underlying the response of invasive populations to substantial variation in climate and other environmental variables. • Methods: We examined morphological and physiological leaf traits of Spartina densiflora plants in populations from invaded estuarine sites across broad latitudinal and climate gradients along the Pacific west coast of North America and in favorable conditions in a common garden experiment. • Key results: Our results show that key foliar traits varied widely among populations. Most foliar traits measured in the field were lower than would be expected under ideal growing conditions. Photosynthetic pigment concentrations at higher latitudes were lower than those observed at lower latitudes. Greater leaf rolling, reduced leaf lengths, and lower chlorophyll and higher carbon concentrations were observed with anoxic sediments. Lower chlorophyll to carotenoids ratios and reduced nitrogen concentrations were correlated with sediment salinity. Our results suggest that the variations of foliar traits recorded in the field are a plastic phenotypic response that was not sustained under common garden conditions. • Conclusions: Spartina densiflora shows wide differences in its foliar traits in response to environmental heterogeneity in salt marshes, which appears to be the result of phenotypic plasticity rather than genetic differentiation.