Sea-level rise and drought interactions accelerate forest decline on the Gulf Coast of Florida, USA

Sea-level rise threatens low-lying coastal ecosystems globally. In Florida, USA, salinity stress due to increased tidal flooding contributes to the dramatic and well documented decline of species-rich coastal forest areas along the Gulf of Mexico. Here, we present the results of a study of coastal forest stand dynamics in thirteen 400 m² plots representing an elevation gradient of 0.58–1.1 m affected by tidal flooding and rising sea levels. We extended previously published data from 1992–2000 to 2005 to quantify the full magnitude of the 1998–2002 La Niña-associated drought. Populations of the dominant tree species, Sabal palmetto (cabbage palm), declined more rapidly during 2000–2005 than predicted from linear regressions based on the 1992–2000 data. Dramatic increases in Juniperus virginiana (Southern red cedar) and S. palmetto mortality during 2000–2005 as compared with 1995–2000 are apparently due to the combined effects of a major drought and ongoing sea-level rise. Additionally, coastal forest stands continued to decline in species richness with increased tidal flooding frequency and decreasing elevation. Stable isotope (H, O) analyses demonstrate that J. virginiana accesses fresher water sources more than S. palmetto . Carbon isotopes reveal increasing δ ¹³C enrichment of S. palmetto and J. virginiana with increased tidal flooding and decreased elevation, demonstrating increasing water stress in both species. Coastal forests with frequent tidal flooding are unable to support species-rich forests or support regeneration of the most salt-tolerant tree species over time. Given that rates of sea-level rise are predicted to increase and periodic droughts are expected to intensify in the future due to global climate change, coastal forest communities are in jeopardy if their inland retreat is restricted.     

Diurnal fluctuations of dissolved nitrous oxide (N2O) concentrations and estimates of N2O emissions from a spring-fed river: implications for IPCC methodology

There is uncertainty in the estimates of indirect nitrous oxide (N₂O) emissions as defined by the Intergovernmental Panel on Climate Change (IPCC). The uncertainty is due to the challenge and dearth of in situ measurements. Recent work in a subtropical stream system has shown the potential for diurnal variability to influence the downstream N transfer, N form, and estimates of in‐stream N₂O production. Studies in temperate stream systems have also shown diurnal changes in stream chemistry. The objectives of this study were to measure N₂O fluxes and dissolved N₂O concentrations from a spring‐fed temperate river to determine if diurnal cycles were occurring. The study was performed during a 72 h period, over a 180 m reach, using headspace chamber methodology. Significant diurnal cycles were observed in radiation, river temperature and chemistry including dissolved N₂O‐N concentrations. These data were used to further assess the IPCC methodology and experimental methodology used. River NO₃‐N and N₂O‐N concentrations averaged 3.0 mg L⁻¹ and 1.6 μg L⁻¹, respectively, with N₂O saturation reaching a maximum of 664%. The N₂O‐N fluxes, measured using chamber methodology, ranged from 52 to 140 μg m⁻² h⁻¹ while fluxes predicted using the dissolved N₂O concentration ranged from 13 to 25 μg m⁻² h⁻¹. The headspace chamber methodology may have enhanced the measured N₂O flux and this is discussed. Diurnal cycles in N₂O% saturation were not large enough to influence downstream N transfer or N form with variability in measured N₂O fluxes greater and more significant than diurnal variability in N₂O% saturation. The measured N₂O fluxes, extrapolated over the study reach area, represented only 6 × 10⁻⁴% of the NO₃‐N that passed through the study reach over a 72 h period. This is only 0.1% of the IPCC calculated flux.     

Community structure in some southern English streams: the influence of species interactions

SUMMARY. 1. The results of a survey of thirty-four stream sites, differing in pH and invertebrate species richness, indicated that the pool of locally available, suitably adapted species was smaller in the acid streams. This plays a part in determining the general pattern of lower species richness at more acid sites.
2. Diversity of feeding categories increased with species richness, indicating that a greater range of food resources was available in the less acid, more species-rich communities.
3. The pattern of predation varied with pH and species richness. The numbers of large insect predators were lower in the less acid, more species-rich communities and this was correlated with the presence of fish.
4. A detailed study of the guild of detritivorous stoneflies in four streams differing in species richness provided evidence that density compensation occurs, niche width decreases and niche overlap declines as species richness increases.
5. We discuss the roles that competition and predation play in determining the structure and richness of stream invertebrate communities.     

Cellulolytic decomposition in streams of contrasting pH and its relationship with invertebrate community structure

SUMMARY. 1. Ceilulolytic decomposition, measured by loss of tensile strength in strips of cellulose test cloth, was estimated in thirty-four stream sites in experiments in summer, autumn and winter.
2. The results of multiple regression analyses showed that strength loss was most closely related to temperature in summer, when the model accounted for only 38% of the variation, and to stream pH in autumn and winter, when the models accounted for 52% and 75% of the variation, respectively.
3. The relationship between decomposition rate and the structure of invertebrate communities in streams of dissimilar pH is discussed. We argue that a very rapid rate of decomposition of coarse particulate organic matter may profit consumers of fine particulate organic matter at the expense of coarse particle shredders.     

The use of artificial neural networks to predict the presence of small-bodied fish in a river

1. Discriminant factorial analysis (DFA) and artificial neural networks (ANN) were used to develop models of presence/absence for three species of small-bodied fish (minnow, Phoxinus phoxinus , gudgeon, Gobio gobio , and stone loach, Barbatula barbatula ).
2. Fish and ten environmental variables were sampled using point abundance sampling by electrofishing in the Ariège River (France) at 464 sampling points.
3. Using DFA, the percentage of correct assignments, expressed as the percentage of individuals correctly classified over the total number of examined individuals, was 62.5% for stone loach, 66.6% for gudgeon and 78% for minnow. With back-propagation of ANN, the recognition performance obtained after 500 iterations was: 82.1% for stone loach, 87.7% for gudgeon and 90.1% for minnow.
4. The better predictive performance of the artificial neural networks holds promise for other situations with non-linearly related variables.     

Some Observations on Invertase Activity in Roots of Vicia faba L.

Invertase activity has been determined at intervals along primaryroots of Vicia faba as they elongated from 0·5 to 8 cm.Little activity was evident in 0·5–1·0 cmlong primaries but in those 2–8 cm in length the mainpeak of enzyme activity was associated with the region of cellelongation. Changes took place in the pattern of invertase activityalong the primary roots as they lengthened and these changeshave been correlated with fluctuations in both the rate of rootelongation and the supply of sucrose to the root from the cotyledons.The presence of a root cap did not increase the activity ofthis enzyme in the apical 1 mm of these roots. Invertase activity was higher in lateral root primordia thanin most parts of the primary root basal to the meristem, presumablybecause of the presence of sucrose in the adjacent cavity inthe cortex of the primary root. The peaks of invertase activityfound basal to the region of cell elongation in 3–8 cmlong primary roots probably resulted from the development ofroot pnmordia in these parts of the root.     

Contrast Between Solitary and Clonal Lifestyles in the Sea Anemone Anthopleura elegantissima

The common intertidal sea anemone Anthopleura elegantissima(Brandt) occurs in two forms the clonal aggregating form andthe solitary form The obvious differences between the two apparentlyresult from the presence of asexual reproduction in the clonalaggregating form and its absence in the solitary form resultingdifferences in growth form suit the two anemones to differentlifestyles The clonal form is well suited to life higher inthe mid intertidal Asexual reproduction resulting in moderatelysmall individual size and close association with clonematesimproves its resistance to physical stress (drag and desiccation)and makes it a superior competitor in exposed habitats higherin the intertidal where species diversity and predator pressureare low The larger solitary animals live in more protected microhabitatslower in the intertidal and subtidal and are probably more resistantto predation and less able to withstand physical stress or intenseintraspecific competition The two forms also have differentbiogeographic ranges While the clonal aggregations are quitecommon at rocky sites at least as far north as Vancouver Islandin British Columbia populations of solitaries have not beenfound north of Point Reyes California Apparently the two formsare re productively isolated phenotype frequencies are verydifferent for clonals and solitaries living at the same locationswhile the between-sample variation within each form is relativelysmall These differences in phenotype frequencies biogeographicrange and microhabitat suggest that the clonal anemones andthe solitary anemones known as Anthopleura elegantissima areactually a sibling species pair.     

New role for majors in Atta leafcutter ants

Abstract.  1.  Atta (Hymenoptera: Formicidae) leafcutter ants display the most polymorphic worker caste system in ants, with different sizes specialising in different tasks. The largest workers (majors) have large, powerful mandibles and are mainly associated with colony defence.
2. Majors were observed cutting fallen fruit and this phenomenon was investigated in the field by placing mango fruit near natural Atta laevigata and Atta sexdens colonies in São Paulo State, Brazil.
3. Ants cutting the fruit were significantly heavier (mean = 49.1 mg, SD = 11.1 mg, n = 90) than the ants carrying the fruit back to the nest (mean = 20.9 mg, SD = 9.2 mg, n = 90).
4. Fruit pieces cut by majors were small (mean = 15.9 mg), approximately half the weight of leaf pieces (mean = 28.5 mg) cut and carried by media foragers. It is hypothesised that it is more difficult to cut large pieces from three-dimensional objects, like fruit, compared to two-dimensional objects, like leaves, and that majors, with their longer mandibles, can cut fruit into larger pieces than medias.
5. The study shows both a new role for Atta majors in foraging and a new example of task partitioning in the organisation of foraging.