An assessment of macrophyte community metrics in the determination of the ecological condition and total phosphorus concentration of Mediterranean ponds

The macrophyte vegetation of 51 ponds situated in the Duero river basin on the Northern Iberian Plateau was studied with the aim of selecting metrics that responded clearly to perturbation and that should be included in a multimetric index for assessing the ecological condition (expression of the quality of the structure and functioning of aquatic ecosystems associated with surface waters) of Mediterranean ponds. Furthermore, the specific response of metrics to the total phosphorus (TP) concentration was also investigated because of agricultural activities, which usually increase the concentration of nutrients in aquatic systems, are one of the principal types of impairment affecting ponds in the Duero basin.A total of 19 metrics representing several aspects of the structure of macrophyte communities (cover, richness, diversity) were selected as potential metrics.The strong overlap which was observed for macrophyte metrics between classes of ecological conditions (bad, poor, moderate, good, best available) and TP concentrations (>600, 600-300, 300-100, 100-50, <50 μg L⁻¹ TP) constitutes a major problem in defining and separating these classes. For this reason, Mann-Whitney U-test and discrimination efficiency were carried out to determine which of the measures best discriminated between slightly impaired sites (ponds in good or best available condition) and perturbed ponds (ponds in moderate, poor or bad condition). Most of the metrics showed significant differences (p < 0.05) between slightly impaired and perturbed ponds. However, only total cover and hydrophyte richness, which had the highest discrimination efficiency (>78%), showed no inter-quartile overlap (25th-75th percentile) between the two ecological classes. For these reasons, both total cover and hydrophyte richness were selected for the implementation of a multimetric index able to discriminate between slightly impaired and degraded Mediterranean flatland ponds.Currently, eutrophication is considered the main pressure on lakes. However, macrophyte metrics were far less sensitive to TP concentration than to ecological condition changes. This shows that other pressures are also of considerable importance. Thus, the definition of the ecological condition of lakes using macrophytes should not be based only on responses to eutrophication pressure, as has been done in some European countries.     

Grazing with Galloway cattle for floodplain restoration in the Syr Valley, Luxembourg

Three years after a river restoration scheme in the Syr Valley (Luxembourg) we investigated habitat development and habitat use of Galloway cattle deployed in a low-intensity grazing system on a permanent floodplain pasture. Habitats were delimited with a mobile GPS/GIS mapping system and their spatial development was assessed over three consecutive years. During these three years, the patches of the six habitats decreased to 40% of mean initial size, and a rapid net area expansion of wetland habitats (large sedge swamps: +100%, marsh and tall forb grasslands: +43%) was observed. The behavioural patterns and grazing preferences of the cattle were observed directly during the vegetation period in June, August and November. These observations were complemented by a transect analysis of cattle impact indicators in June and November. The cattle grazed the different habitats very selectively, as they preferred the mesophilic, and ruderal grasslands 1.6, and 5.6 times more than expected respectively. During the growing season, the grazing niche breadth declined (3.92 in June to 2.68 in November), and less preferred forage habitats like large sedge swamps were grazed primarily in the autumn. We used bite and step rates to investigate grazing intensity by habitat type. During summer, grazing intensity correlated with forage quality in the different habitat patches, whereas in autumn it was obviously influenced by the effort required to access the desired forage plants in a given habitat. The impact indicators revealed a matter transfer from riparian areas to the valley edge. Here, we give a first insight into habitat development and habitat use of Galloway cattle in a recently restored floodplain area and derive recommendations for the adaptive management of future projects.     

Paleoenvironment of Ankilitelo Cave (late Holocene, southwestern Madagascar): implications for the extinction of giant lemurs

Following human arrival, Madagascar suffered well-documented megafaunal extinctions and widespread deforestation. Although humans are widely considered to be the primary cause of the extinctions, the relative contributions of climate change and human activities to this ecological transformation remain uncertain. Reconstructing the habitats of the giant lemurs of Madagascar can provide key information for understanding the evolutionary mechanisms involved in their extinction. In this study, I present a faunal analysis of the subfossil assemblage from Ankilitelo Cave, southwestern Madagascar. This assemblage documents the latest known occurrence of five species of extinct giant lemur, in association with abundant well-preserved small mammal remains. I compared the small mammal fauna at Ankilitelo with 27 extant Malagasy mammal communities spanning the range of Madagascar's habitat types. Similarities in species composition between modern communities and Ankilitelo were assessed using cluster analysis. Ecological similarities were examined by assigning each species to dietary, locomotor, activity pattern, and body size categories. Multiple discriminant analysis was then used to classify Ankilitelo relative to modern habitat types in Madagascar, based on the ecological structure of the subfossil fauna. Results indicate that the habitat surrounding Ankilitelo during the late Holocene was similar to the succulent woodlands of modern southwestern Madagascar. This suggests that approximately 500 yr BP, these semi-arid habitats supported a subfossil lemur community that included the highly-suspensory Palaeopropithecus, and deliberate slow-climber Megaladapis, as well as Archaeolemur, Pachylemur, and Daubentonia robusta. In such environments, these giant lemurs would likely have been highly vulnerable to increasing human pressure in southwestern Madagascar.     

Response of nitrogen dynamics in semi-natural and agricultural grassland soils to experimental variation in tide and salinity

In the framework of rehabilitation efforts to enhance the ecological value of closed-off estuaries, we studied the effects of restoring a tidal movement and seawater incursion on soil nitrogen conversion rates and vegetation response of semi-natural and agricultural grasslands in an outdoor mesocosm experiment. Intact soil monoliths including vegetation were collected in June 2004 on two locations on the shores of the Haringvliet lagoon in the south-western part of the Netherlands, which used to be a well-developed estuary before closure in 1970. For more than 1 year, soil monoliths were continuously subjected to a full-factorial combination of tidal treatment [stagnant/tidal (0.20 m amplitude)] and water type [(freshwater, oligohaline (salinity = 3)]. Soil, soil moisture and water nitrogen concentrations were monitored for a year, as well as vegetation response and nitrogen conversion rates in the soil. As expected, nitrogen mineralization rates were enhanced by the tidal treatment in comparison with the stagnant treatment. Denitrification rates however, were much less affected by tide and were even lower in the tidal treatments after 3 months in the agricultural grassland soils, implying that in general, soils were more oxic in the tidal treatments. Oligohaline treatments had virtually no effect on soil nitrogen conversion rates compared to freshwater treatments. Vegetation performance, however, was lower under saline conditions, especially in the semi-natural grassland. No further significant differences in response to the tidal and oligohaline treatments were found between the two soils although they differed strongly in soil characteristics. We conclude that if the rehabilitation measures in the former Haringvliet estuary are carried out as planned, drastic changes in soil nitrogen processes and vegetation composition will not occur.     

Relationships between benthic macrofauna and biogeochemical properties of sediments at different spatial scales and among different habitats in mangrove forests

In muddy intertidal sediments, there are reported complex interactions between the biological, physical and chemical properties of the sediment and the benthos that live in and on it. These are expected to be reflected in strong relationships between benthic animals and particular properties of the sediment, although some research has shown these relationships to be relatively weak. This study investigates the relationships between benthic macrofauna and biogeochemical properties of sediments within and among different habitats in multiple mangrove forests in a temperate estuary, in order to address the generality of any such relationships. Matched samples of benthos and sediment were collected from three habitats, which differed with respect to shading, the amounts of algae and leaf litter and the presence of pneumatophores. The sediment was sampled for water content, grain size, organic matter, chlorophylls a and b and colloidal and total carbohydrate.Spatial variation in sediment and benthos were significantly correlated across habitats in two of the three bays, but the sediment properties that contributed to differences between habitats and those that best correlated with the benthos varied among bays. In all bays, the single taxon that best correlated with the sediment was spionid polychaetes, but correlations were generally weak. There was no generality in the patterns of variation among the benthos or sedimentary properties among habitats. The benthos differed significantly among bays in all habitats, with large variation within and among sites. The sediment varied significantly at small scales in all habitats, but significant differences among bays were only found in two habitats. All spatial scales contributed to the total amount of variability in the sediment and there was little predictability from the patterns shown in one habitat to those in other habitats, or from one component of sediment to other components. Such variability suggests that there may be structural redundancy in this fauna, with different components of the benthos contributing to similar functions in different places. Such variability must be considered in experiments designed to understand relationships between ecological structure and function in these complex habitats and in any sampling studies to identify environmental impacts in these habitats.     

Natural selection on ecophysiological traits of a fern species in a temperate rainforest

Unlike other species of the genus Blechnum, the fern Blechnum chilense occurs in a wide range of habitats in Chilean temperate rainforest, from shaded forest understories to abandoned clearings and large gaps. We asked if contrasting light environments can exert differential selection on ecophysiological traits of B. chilense. We measured phenotypic selection on functional traits related to carbon gain: photosynthetic capacity (A _max), dark respiration rate (R _d), water use efficiency (WUE), leaf size and leaf thickness in populations growing in gaps and understorey environments. We assessed survival until reproductive stage and fecundity (sporangia production) as fitness components. In order to determine the potential evolutionary response of traits under selection, we estimated the genetic variation of these traits from clonally propagated individuals in common garden experiments. In gaps, survival of B. chilense was positively correlated with WUE and negatively correlated with leaf size. In contrast, survival in shaded understories was positively correlated with leaf size. We found positive directional fecundity selection on WUE in gaps population. In understories, ferns of lower R _d and greater leaf size showed greater fecundity. Thus, whereas control of water loss was optimized in gaps, light capture and net carbon balance were optimized in shaded understories. We found a significant genetic component of variation in WUE, R _d and leaf size. This study shows the potential for evolutionary responses to heterogeneous light environments in functional traits of B. chilense, a unique fern species able to occupy a broad successional niche in Chilean temperate rainforest.     

Innate versus adaptive immunity in sticklebacks: evidence for trade-offs from a selection experiment

In vertebrates, the immune system consists of two arms of different characteristics: the innate and the acquired immune response. Parasites that are only shortly exposed to the immune system are most efficiently attacked by fast, constitutive innate immune mechanisms. Here, we experimentally selected within four fish families for high innate resistance versus susceptibility of three-spined sticklebacks (Gasterosteus aculeatus) against infection with the eye-fluke (Diplostomum pseudospathacaeum), a parasite whose metacercariae are protected from the immune system within the eye lens. We predicted that in families with high susceptibility, the adaptive immune system would be upregulated when challenged with infection. In accordance, we found that MHC class IIB expression is increased by approximately 50% in those lines selected for higher parasite load (i.e. low innate response). This suggests extensive genetic correlations between innate and adaptive immune system and/or crosstalk between both lines of defense. An efficient, specific innate immune response might reduce overall activation of the immune system and potentially alleviate associated effects of immunopathology.