Riparian Taxa Research Articles

Organic-walled dinoflagellate cyst assemblages in surface sediments of the Ría de Vigo (Atlantic margin of NW Iberia) in relation to environmental gradients

Organic-walled dinoflagellate cyst assemblages were analysed in 31 surface sediment samples from the Ría de Vigo (NW Iberia) to obtain supporting evidence for the interpretation of past environmental signals from sediment cores. Complementarily, the totals of pollen (and pollen from riparian taxa), foraminiferal linings and freshwater algae were also considered to test their value as (palaeo)environmental indicators in fluvio-marine sedimentary environments. Abundances of foraminiferal linings gradually increased towards the ría's mouth, which supports its use as a proxy to infer the degree of marine influence in the sediment record. The ratio of dinoflagellate cysts to pollen and spores (D/P) increased with distance to the main river's mouth (and water depth) in the inner (<7 m water depth) and the outer (>20 m) parts of the ría. Total pollen concentrations decreased with water depth in the outer part but did not show any clear trend in the rest of the ría. No clear pattern in the distributions of pollen from riparian plants and spores from freshwater microalgae was detected. Multivariate analyses (clustering and RDA) performed on dinoflagellate cyst records and environmental data reflected a marked inshore-offshore distribution pattern mainly controlled by a fluvio-marine environmental gradient. Increasing abundances of cysts of Gymnodinium species and heterotrophic cysts as well as higher cyst diversity characterised the deeper environments of the outer ría. These observations suggest a relationship with increased shelf influence and are compatible with the heterotroph upwelling signal described in previous works. A very different cyst association with a predominance of autotrophic cysts characterised the intermediate and inner parts of ría, where exceptionally high cyst abundances of Lingulodinium polyedra (~56–99% and ~ 200–114,000 cysts.g−1) were reported. Abundances of cysts of L. polyedra positively correlated with shallower and higher river-influenced environments characterised by higher sea-surface temperature. Our results agree with previous studies and reinforce the value of this species as an indicator of warmer and stratified conditions. Moreover, cysts of L. polyedra positively correlated with winter sea-surface nitrate contents, which is compatible with the nutrient enrichment signal (natural or anthropogenic) that has already been described in other deep and stratified estuarine environments and is consistent with historical cyst records obtained in the Ría de Vigo. However, further research is needed to disentangle the nutrient enrichment signal from the influence of other environmental factors.

Subfossil Coleoptera from Eifel maar sediments as indicators of the environmental evolution in Central Europe over the last 60,000 years

A reconstruction of landscape and paleotemperatures is presented from a composite drill core from the Eifel maar lakes of Auel and Holzmaar, Germany. The compositecore is 112 m long and covers the last 60,000 years (Marine Isotope Stages MIS 3, 2, and 1) based on the new ELSA-20 stratigraphy. Findings are based on an analysis of arthropod remains, with moisture-dependent, riparian or (semi)aquatic Staphylinidae representing the majority of beetle sclerites in the assemblages, especially during cold intervals. Assemblages change corresponding to climate and vegetation, with a greater variety of taxa during the woodland phases (60,000–44,000 yr b2k, i.e. years before 2,000 CE) versus cold adapted taxa during late MIS 3 and early MIS 2 (28,500–23,500 yr b2k). Beetles that inhabit damp, moist or wet locations, as well as aquatic or riparian taxa are present throughout the record. The assemblage corresponding to a period of tundra-like vegetation (29,000–24,000 yr b2k), contained three taxa suitable for temperature calculation (Arpedium brachypterum, Bembidion fellmanni, and Boreaphilus henningianus), all of which are found only in cold phases (Greenland Stadial 2 and 4, and Heinrich Event 2). Paleotemperatures were reconstructed via the Mutual Climatic Range method giving the following results. Mean temperature for the early tundra phase (28,500–27,800 yr b2k) is −32 to −2 °C for the coldest month, and 6 to 9.5 °C for the warmest month. Mean temperature for the later tundra phase (27,000–24,000 yr b2k) is −30 to −20 °C for the coldest month and 6 to 9.5 °C for the warmest month. This shift indicates an increase in seasonality towards the Last Glacial Maximum. Paleotemperature calculations are in good agreement with other European records and indicate a major decline in median winter temperatures towards the Last Glacial Maximum, whereas the summer temperatures remained relatively stable throughout Europe, resulting in an increase in seasonality and continentality.

The use of umbrella fish species to provide a more comprehensive approach for freshwater conservation management

Abstract Where freshwater species populations are in decline, conservation management requires rapid, cost‐effective approaches to develop recommendations, particularly at broad geographical scales or where species‐specific information is lacking. The umbrella species approach, typically applied to terrestrial taxa, is one potentially useful option to inform large‐scale freshwater management efforts. A quantitative, integrated approach is proposed for selecting suites of umbrella fish species over diverse spatial scales using a combination of species ranges, life‐history traits, and species vulnerability scores. The approach also uses expert opinion to validate methods and results. This approach was applied to native fishes in California, and results for two river basins are explored in the context of instream flow management. These examples illustrate how the results could help address two common instream flow management challenges in California: (i) the lack of information related to species‐specific flow requirements in basins with many species; and (ii) the need to move beyond a single species approach to flow management. In addition, the results indicate that the protection of native fishes in California would provide co‐benefits for other aquatic and riparian taxa. A key benefit of this approach is that the data used to select suites of umbrella species (e.g. species ranges, life‐history traits, climate vulnerabilities) are widely available at varying degrees of specificity for most freshwater fishes. Therefore, this flexible approach could be applied in other regions to aid managers in making freshwater conservation decisions, such as for instream flow strategies, in an efficient and cost‐effective manner.

Is bat guano a potential pollen trap? A comparative assessment from conventional soil and moss substrates from Eraaning Cave of Meghalaya, India

This study examines the pattern of preservation of pollen and non-pollen palynomorphs on bat guano samples in Eraaning Cave in relation to the current vegetation of the surrounding Garo hills of Meghalaya. It is observed that, the recorded pollen data does reflect the tropical mixed deciduous forest with an admixture of riparian and evergreen plant taxa from the local and regional vegetation. The presence of evergreen and riparian taxa namely, Mesua, Schima, Duabanga, and Syzygium in the pollen assemblage is strongly indicative of the high rainfall in the region. The recovery of fern and fungal spores in the pollen assemblage also reflects the warm and humid climatic condition in this region. The forestland and open-land samples from the vicinity of the cave were also studied to understand the nature of pollen preservation in relation to the bat guano samples. The presence of cereal, Areca, Psidium, and Citrus along with Melastoma pollen in both bat guano and open-land samples is indicative of the anthropogenic activities in and around the study area. Multivariate principal component analysis (PCA) and box plot were applied to the quantified data obtained from pollen frequency analyses which clearly revealed a significant variation and similarity in vegetation types among the surface samples collected in and around Eraaning Cave. The generated pollen data from the bat guano, forestland, and open-land samples reveals that, bat guano in cave sediments provides a reliable substrate to understand the modern pollen and vegetation relationship and can fruitfully be utilized as a baseline for the reconstruction of the palaeoecology in the Garo hills of Meghalaya. The study also suggested that the bat species utilized the mixed vegetation composition and different landforms as their preferred habitats as demonstrated by the pollen data from the bat guano samples.

Riparian plant guilds of ephemeral, intermittent and perennial rivers

Summary Plant functional types (or guilds) increasingly are being used to predict vegetation response to global changes. Continued human population growth coupled with projected warmer and drier climate will alter the hydrologic regimes of many arid‐zone rivers, including intermittent rivers. We aimed to identify (i) woody plant guilds associated with distinct stream types of an arid region and (ii) plant traits indicating adaptation to the selective pressures of water availability and fluvial disturbance. We used hierarchical clustering to identify 11 plant guilds from floodplains, terraces and uplands of eight Arizona rivers that vary in surface flow permanence, depth to ground water and intensity of fluvial disturbance. Six guilds were riparian pioneers with small, wind‐dispersed seeds, three guilds were late‐seral, shade‐tolerant riparian taxa with large animal‐dispersed seeds, and two guilds were composed of desert xerophytes. Within the riparian pioneer and seral groups, guilds varied in water acquisition and productivity traits including wood density and rooting depth. The community‐weighted traits varied or covaried with water availability and fluvial disturbance. Root: shoot ratio, canopy height and leaf area were influenced strongly by water availability, with the latter two showing a nonlinear response to changes in water table depth. Leaf length increased, and wood density decreased, as sites become wetter and more fluvially disturbed. Community‐weighted seed mass, seed dispersal and spinesence varied most strongly with elevation above thalweg (an indicator of decreasing fluvial disturbance). These analyses will enable prediction of changes in the relative abundance of plant types and plant traits in response to changes in stream flow regimes, such as shifts towards greater intermittency. The distribution patterns of guilds among riparian habitat types emphasise the importance of focusing conservation efforts not only on the limited number of perennial rivers remaining in arid regions, but also on intermittent and ephemeral rivers with shallow water tables.

Provincial and cosmopolitan: floristic composition of a dryland urban river

High rates of intercontinental exchange of plant species have caused scientists to ask whether floristic areas with similar environments are undergoing global homogenization. We focused on riparian forests of the urban Salt River (Sonoran Desert, USA) to ask: (1) Is the forest dominated by cosmopolitan or provincial elements? (2) Which trees planted in the irrigated cityscape have established along the river? (3) Which types of restoration interventions have favored provincial species? We surveyed tree abundance, size and vigor in belt transects among five reaches that differed in degree of restoration, and obtained data on tree species composition of the urban landscape and pre-development riparian zone. Our results reveal the urban riparian forest to have many cosmopolitan elements, owing in part to spillover of trees from the cultivated cityscape (e.g., Acacia stenophylla, Vitex agnus-castus). Global spread of some regional (Neotropical) riparian taxa (e.g., Parkinsonia aculeata, Prosopis) also has contributed to the cosmopolitan status. Yet, the forests retain a distinct regional signature. Unintentional restoration of winter floods has allowed for regeneration of Salix gooddingii, a vernally-adapted provincial pioneer, although its long-term survivorship is restricted to limited micro-sites (storm drain outfalls). Urbanization-related changes in stream hydrogeomorphology explain increases in some regional species (e.g., Washingtonia spp.) that historically were excluded from the river.

Coexistence among large predators during the Lower Paleolithic at the site of La Mina (Barranc de la Boella, Tarragona, Spain)

Barranc de la Boella is made up of several open-air late Early Pleistocene archaeological sites (Pit 1, La Mina and El Forn) the formation of which is related to a deltaic sedimentary environment. Its age makes it a key site for studying the behavior of the early hominin groups of the Iberian Peninsula and western Europe and the ecological context in which they developed.At La Mina locality, three archaeostratigraphic levels have been identified, with level 2 being the richest in terms of the archaeological remains recovered. It exhibits high taxonomic diversity, with the most common taxa belonging to open and partially open habitats, although aquatic and riparian taxa have also been identified. Carnivore remains are present, although scarce. Coprolites from a hyaenid have also been found.Both hominin and carnivore activity has been documented at the site. Evidence of carnivore activity suggests at least one bone-cracking carnivore had access to the assemblage. The anatomical ratios employed suggest that La Mina was formed at a time of high competition (intra and/or inter-specific), with a high number of predators in this ecological context. Anthropic activity in a highly competitive context might suggest that these hominin groups had a high degree of control over the environment and over local resources, as has been shown at other Early Pleistocene sites.

Modern Pollen Record on Bat Guano Deposit from Siju Cave and its Implication to Palaeoecological Study in South Garo Hills of Meghalaya, India

Meghalaya is well known for its rich tropical biodiversity and numerous natural caves. The Siju Cave of Meghalaya, also known as cave of the bat, is among the longest caves on the Indian subcontinent. The palynological study of fifty bat-guano samples from Siju Cave and of thirty surface soil and moss cushion from the area immediate surrounding the cave reflects the close similarity between the modern pollen and vegetation in the region in the two areas sampled. The resulting palynodata comprise mainly the native flora, dominated by riparian taxa like Duabanga, Syzygium, Careya, and Ficus, along with evergreen and deciduous elements in the region. The evergreen taxa Mesua, Elaeocarpus ,a ndGarcinia, along with Impatiens, reflect the high precipitation in the region. The climate of the region and the vegetation are strongly influenced by the Simsang River, and the heavy rainfall results in the dominance of riparian taxa and other high-rainfall indicator taxa. The occurrence of pollen from Nepenthes khasiana ,a n endemic and endangered plant of Meghalaya, in bat guano is significant and may be due to its insectivorous and entomophilous nature. However, medicinal plants like Swertia chirata, Cinchona, and Rauvolfia are not encountered in the bat-guano sediments, despite their luxuriant growth around the cave, and these species could be avoided by the insects due to their alkaloid contain and bitter taste. The presence of highland taxa such as Pinus, Abies, Picea, and Larix in the bat guano deposit is significant and suggestive of high winds from higher altitudes, or the pollen may be introduced by the return of migratory Siberian birds during winter to the nearby Siju wildlife and bird sanctuary. The recovery of cerealia along with Areca catechu and Citrus pollen indicate the human activity in the region. The abundance of fungal remains, namely Meliola, Glomus, and Microthyriaceae along with degraded palynomorphs are suggestive of strong microbial activity under warm and humid conditions during sedimentation in the region. The main objective of this study is to identify the potential of bat guano for palaeoecological research and as supportive data for surface and sedimentary soil profiles in the South Garo Hills of Meghalaya. The palynodata from the bat guano of the Siju Cave provides a useful source for palaeoecological information for the South Garo Hills, where intensive natural and human-caused forest fires, heavy rainfall, and soil erosion occur every year and there is a relative scarcity of the lake, wetland, and swamp habitats that normally preserve pollen.

Water surface locomotion in tropical canopy ants.

Upon falling onto the water surface, most terrestrial arthropods helplessly struggle and are quickly eaten by aquatic predators. Exceptions to this outcome mostly occur among riparian taxa that escape by walking or swimming at the water surface. Here we document sustained, directional, neustonic locomotion (i.e. surface swimming) in tropical arboreal ants. We dropped 35 species of ants into natural and artificial aquatic settings in Peru and Panama to assess their swimming ability. Ten species showed directed surface swimming at speeds >3 body lengths s(-1), with some swimming at absolute speeds >10 cm s(-1). Ten other species exhibited partial swimming ability characterized by relatively slow but directed movement. The remaining species showed no locomotory control at the surface. The phylogenetic distribution of swimming among ant genera indicates parallel evolution and a trend toward negative association with directed aerial descent behavior. Experiments with workers of Odontomachus bauri showed that they escape from the water by directing their swimming toward dark emergent objects (i.e. skototaxis). Analyses of high-speed video images indicate that Pachycondyla spp. and O. bauri use a modified alternating tripod gait when swimming; they generate thrust at the water surface via synchronized treading and rowing motions of the contralateral fore and mid legs, respectively, while the hind legs provide roll stability. These results expand the list of facultatively neustonic terrestrial taxa to include various species of tropical arboreal ants.

Rainfall variability and vegetation dynamics of the lower Limpopo Valley, Southern Africa, 500 AD to present

The long‐term responses of vegetation to climate variability are of relevance for predicting present and future vegetation change, and have implications for the management of savanna and riparian ecosystems. This paper explores the links between regional rainfall, hydrology and vegetation dynamics in the savannas and riverine forests of the lower Limpopo Valley, southern Africa, from 800AD to the present, reviewing palaeoecological data (fossil pollen, spores, diatoms and lithology) from several hydrological systems in Kruger National Park (KNP), South Africa and Limpopo National Park (PNL), Mozambique. The PNL–KNP records show that riverine arboreal taxa expanded during wetter periods, including 800–1400AD and after 1800AD. Between 1400 and 1800AD, grasses, savanna taxa and generalist taxa were favored over riparian taxa, a change that is linked with the onset of dry spells in the region (corresponding to the so-called Little Ice Age). The most extreme drought events around 1700AD resulted in a marked decline of riparian forest taxa near Lake Mapimbi, KNP. In contrast, many water-scarce sequences away from the riverine environment, such as Radio Pan, Mafayeni Pan, Malahlapanga Pan and Lake Makwadzi show stable grassland vegetation throughout the last 1200years. The results demonstrate the resilience of the grassland–savanna ecosystems to projected climate change with warmer and overall drier climate. The riverine forests are predicted to be more vulnerable especially as more extreme weather events are projected.

Paleoecology of an Interglacial Peat Deposit, Nuyakuk, Southwestern Alaska, U.S.A.

This paper reports the presence of interglacial beetle and pollen assemblages within a Pleistocene peat deposit exposed along the Nuyakuk River of southwestern Alaska. The fossil beetle assemblages contain a number of species not previously identified from eastern Beringian fossil assemblages. The Nuyakuk interglacial deposits are exposed within a 6-m-high terrace along the river, about 4 km beyond the moraine of the penultimate glaciation. Interglacial peat lies within the lowermost meter of the bluff and is overlain by fluvial gravel and loess. Insect fossils were extracted from five peat samples, yielding sixty-seven identified beetle taxa. The insect faunal diversity of the Nuyakuk assemblages is comparable to that found in regional Holocene peat samples. In contrast to assemblages of similar age from interior eastern Beringia, the Nuyakuk fauna contains significant numbers of aquatic, hygrophilous and riparian taxa. Four pollen samples from the Nuyakuk site were analyzed, providing spectra dominated by a few taxa, notably Alnus, Betula, Picea, Gramineae, Cyperaceae, Filicales, and Sphagnum, suggesting a rich alder-birch shrub tundra not much different from the modern regional vegetation. The pollen and insect fossil records also suggest climatic conditions similar to modern.

Mechanisms Associated With Decline of Woody Species in Riparian Ecosystems of the Southwestern U.S.

Throughout western North America, riparian ecosystem function has been transformed by anthropogenic influences on riverine environments. Modified flood frequency, duration, or intensity; depressed floodplain water tables; and increased alluvium salinity have contributed to change in riparian forest communities formerly dominated by Populus fremontii and Salix gooddingii. The invasion of the naturalized arborescent shrub, Tamarix ramosissima, potentially alters competitive hierarchies and disturbance regimes in these riparian ecosystems. We evaluated the structure and function of two southwestern riparian communities that differed in the degree of streamflow perturbation to which they had been subjected: the highly regulated lower Colorado River and the less tightly regulated Bill Williams River. Ordination analyses provided evidence that these riparian communities are structured along gradients relating to moisture, salinity, disturbance from fire, and community maturity, with Colorado River sites being more xeric and saline than those on the Bill Williams River. Foliar elemental analyses revealed high sodium concentrations in Tamarix (Na:K ratio = 1.87) and in the native shrub Tessaria sericea (Na:K = 1.56). Evaluation of tissue water relations parameters showed that Tamarix had lower osmotic potentials than sympatric woody taxa, helping to confirm that Tamarix is halophytic and probably capable of greater osmotic adjustment than native species. Carbon isotopic discrimination (△) provided evidence for higher water use efficiency in Tamaris than in Populus, Salix, and Tessaria. Tamarix △ averaged over 1% less than that of the other riparian taxa. Experimental removal of Tamarix from stands where Salix was codominant resulted in growth augmentation, less negative water potentials, and higher leaf conductance in Salix, all providing evidence of interspecific competition. The persistence of Salix, but not Populus, on the Colorado River appears to be due to greater water— and salinity stress tolerance in Salix than in Populus. A preponderance of senescent Populus along the Colorado River is an indication that this formerly dominant species is effectively approaching local extinction in parts of this ecosystem.