Ecological niche modeling and principal component analysis of Krameria Loefl. (Krameriaceae)

Krameria plants are found in arid regions of the Americas and present a floral system that attracts oil-collecting bees. Niche modeling and multivariate tools were applied to examine ecological and geographical aspects of the 18 species of this genus, using occurrence data obtained from herbaria and literature. Niche modeling showed the potential areas of occurrence for each species and the analysis of climatic variables suggested that North American species occur mostly in deserted or xeric ecoregions with monthly precipitation below 140 mm and large temperature ranges. South American species are mainly found in deserted ecoregions and subtropical savannas where monthly precipitation often exceeds 150 mm and temperature ranges are smaller. Principal Component Analysis (PCA) performed with values of temperature and precipitation showed that the distribution limits of Krameria species are primarily associated with maximum and minimum temperatures. Modeling of Krameria species proved to be a useful tool for analyzing the influence of the ecological niche variables in the geographical distribution of species, providing new information to guide future investigations.     

Floral ecology and insect visitation in riparian Tamarix sp. (saltcedar)

Climate change projections for semiarid and arid North America include reductions in stream discharge that could adversely affect riparian plant species dependent on stream-derived ground water. In order to better understand this potential impact, we used a space-for-time substitution to test the hypotheses that increasing depth-to-groundwater (DGW) is inversely related to Tamarix sp. (saltcedar) flower abundance (F) and nectar production per flower (N). We also assessed whether DGW affected the richness or abundance of insects visiting flowers. We examined Tamarix floral attributes and insect visitation patterns during 2010 and 2011 at three locations along a deep DWG gradient (3.2–4.1 m) on a floodplain terrace adjacent to Las Vegas Wash, an effluent-dominated Mojave Desert stream. Flower abundance and insect visitation patterns differed between years, but no effect from DGW on either F or N was detected. An eruption of a novel non-native herbivore, the splendid tamarisk weevil (Coniatus splendidulus), likely reduced flower production in 2011.     

Effects of the abandonment of the burrowing mounds of fat sand rat (Psammomys obesus cretzschamar 1828) on vegetation and soil surface attributes along the coastal dunes of North Sinai,Egypt

Fat sand rats (Psammomys obesus) are strictly herbivorous and live in densely complex burrows in the desert of North Africa and the Middle East. Little is known however about the effect of their foraging and burrowing activities on surface morphology and plant community attributes. This study evaluated such effects by comparing burrow and mound surface morphology, canopy of the main host chenopod shrub Anabasis articulata, vegetation cover, and plant abundance and species richness on and off both active and abandoned colonies in the semi-stabilized sand dunes of the Northern Sinai. In general, active burrow systems were characterized by reduced A. articulata canopy area, and more soil disturbance, with higher and larger burrow mounds dominated by bare ground, dung, and dead and fresh litter. The abandonment of mounds for five years has resulted in significant increases of plant cover, canopy height, abundance and species richness. Vegetation structure and plant species assemblages differed between mound and non-mound patches of both active and abandoned sites. The results suggest that fat sand rats can have significant direct and indirect, short-term and long-term effects on vegetation dynamics and structure through their mound building and foraging.     

Comparative study of seed germination and growth of Kochia prostrata and Kochia scoparia (Chenopodiaceae) under salinity

Soils of arid regions of Central Asia contain salts of different types that may differentially affect seed germination and plant development. We studied effect of NaCl, Na₂SO₄, 2NaCl + KCl + CaCl₂ and 2Na₂SO₄+K₂SO₄+MgSO₄ on germination of Kochia prostrata and Kochia scoparia seeds under a range of concentrations from 0.5 to 5% and at two constant temperature regimes +22 °C and +6 °C. The observed salt tolerance limit of germination at constant temperature +22 °C for both species was 5-6%, while at low temperature (+6 °C) this limit was 2%. The salt tolerance of young plants (before flowering) was 3% for NaCl. Low concentrations of sulfuric and mixed salts had a stimulating effect on seed germination in K. prostrata. Despite similarity of salt-tolerance limits the studied species showed a significant difference in seed recovery ability, i.e. the ability of ungerminated, salt-soaked seeds to germinate after transfer to fresh water. K. scoparia demonstrated a full germination recovery after seed transfer to distilled water while K. prostrata showed only a partial recovery.     

Groundwater use by native plants in response to changes in precipitation in an intermountain basin

Many arid basins in western North America are likely to experience future changes in precipitation timing and amount. Where shallow water tables occur, plant acquisition of groundwater and soil water may be influenced by growing season precipitation. We conducted a rainfall manipulation experiment to investigate responses of four common native plant species to ambient, increased, and decreased summer monsoon rainfall. We measured plant xylem pressure potentials (Ψ) and stable oxygen isotope signatures (δ¹⁸O) to assess effects of altered precipitation on plant water relations and water acquisition patterns. Reduced rainfall decreased Ψ more in the grasses Sporobolus airoides and Distichlis spicata than the more deeply rooted shrubs Sarcobatus vermiculatus and Ericameria nauseosa. E. nauseosa had little response to natural or experimental differences in available soil water. Plant xylem water δ¹⁸O indicated that S. airoides and D. spicata are almost entirely dependent on rain-recharged soil water, while E. nauseosa is almost entirely groundwater-dependent. Sarcobatus vermiculatus used groundwater during dry periods, but utilized precipitation from soil layers after large rainfall events. Persistent changes in precipitation patterns could cause shifts in plant community composition that may alter basin-scale groundwater consumption by native plants, affecting water availability for human and ecosystem uses.     

Spatial patterning of Manta birostris in United States east coast offshore habitat

This study aims to identify patterns in spatial distribution of Manta birostris along American East Coast by analyzing presence data using a suite of geostatistical techniques. Analysis of data from 1979 to 2008 revealed that the spatial patterns exhibited by the M. birostris include a strong clustering zone off the North Carolina from (however, not all years are represented in that range), Virginia and Maryland coast. Their presence is high near the coastal shelf edge and along the edge of the Gulf Stream. The mix of warm water and high chlorophyll concentration throughout the year in the region seem to create an ideal environment for this clustering pattern. However, in seasons with warmer water temperature, manta rays spread further north and inshore, possibly to avoid competition for prey. The results of geographic weighted regression indicate the role of sea surface temperatures on Manta presence or absence off the main current of the Gulf Stream near North Carolina and Virginia. Knowledge of the spatial distribution of M. birostris can assist in further protecting the species especially from dangers of by-catch and habitat degradation.     

Dispersal of arbuscular mycorrhizal fungi and dark septate endophytes by Ctenomys cf. knighti (Rodentia) in the northern Monte Desert of Argentina

In arid and semi-arid environments, root-associated fungi may play a key role in plant communities (e.g., seedling establishment, nutrient acquisition, plant survival and heat tolerance). Several studies have shown the importance of small mammals as consumers and dispersal agents of mycorrhizal fungi spores in tropical and temperate ecosystems. However, little is known about the dispersal of infective propagules of endophytic fungi in arid and semi-arid ecosystems. This study analyzed the potential role of the subterranean rodent Ctenomys cf. knighti as a dispersal agent of root-associated fungi. In order to demonstrate this role, we analyzed: (1) the incidence of colonization of arbuscular mycorrhizae and dark septate endophytes on representative plant species of the Monte Desert; (2) the presence of fungal structures of arbuscular mycorrhizae and dark septate endophytes in C. cf. knighti fecal samples; and (3) the infectivity of the fungal propagules contained in the scat and their growth effects on nine native plant species. Data strongly suggest that this South American subterranean rodent may play a key role as a dispersal agent of arbuscular mycorrhizae and dark septate endophytes fungi in the arid environment of the northern Monte Desert of Argentina.     

Mesquite (Prosopis glandulosa) germination and survival in black-grama (Bouteloua eriopoda) grassland: relations between microsite and heteromyid rodent (Dipodomys spp.) impact

Prosopis pallida H.B.K. is one of the most economically and ecologically important tree species in the arid and semi-arid lands of the American continent. Sections of P. pallida were used to describe its wood anatomy and to determine whether annual rings were visible or not. Results showed that P. pallida has well-differentiated annual growth rings and is therefore suitable for dendrochronological studies. Tree ring chronologies correlate well with precipitation events related to El Niño Southern Oscillation phases. A master chronology for the northern area of Peru was built with these data, and some physiological derivations from the anatomy of P. pallida wood are discussed.     

Detecting ancient wild rice (Zizania spp. L.) using phytoliths: a taphonomic study of modern wild rice in Minnesota (USA) lake sediments

Wild rice (Zizania spp. L.) is a North American native grain with spiritual and dietary significance to many native people. Wild rice is also an important aquatic plant that provides critical habitat to wetland and aquatic wildlife. Past distribution of wild rice in North America is poorly understood, largely because of the limited taxonomic resolution of Poaceae pollen. A novel technique for detecting diagnostic Zizania silica phytoliths allows unambiguous identification of this taxon in lake sediments. We need to better understand modern depositional patterns of phytoliths in lake sediments, however, before attempting detailed paleoreconstructions. We analyzed distributions of diagnostic Zizania and other Poaceae phytoliths in modern sediments from three lakes with variable percent cover of wild rice and a non-wild rice control lake in central Minnesota. Absolute counts of phytoliths per gram sediment were achieved using an exotic diatom marker. Non-Zizania short-cell phytoliths, i.e. phytoliths from wetland grasses Phragmites australis and Muhlenbergia glomerata, dominate the assemblages in all lakes. Most Poaceae short-cell phytoliths appear to be derived locally, with little evidence for regional inheritance from eolian or alluvial processes. Because of anatomical differences in decay of plant debris and other taphonomic issues, Zizania inflorescence rondel phytoliths were most abundant, with morphotypes from other parts rarely encountered. Even in sediments under the densest wild rice stands, Zizania phytoliths contributed a maximum of 9 % to total Poaceae phytolith abundance. Lake morphology also affects the depositional pattern of phytoliths in modern sediments, so coring locations should be considered carefully. At least 500 phytoliths should be counted to detect a sufficient number of wild rice phytolith morphotypes. Diagnostic Zizania phytoliths are a reliable tool for wild rice detection in paleolake sediments.     

Host specificity, nutrient and water dynamics of the mistletoe Viscum rotundifolium and its potential host species in the Kalahari of South Africa

The mechanisms underpinning local host specificity in mistletoes remain elusive. We determined the degree of host specificity in the mistletoe Viscum rotundifolium at Pniel Estates, near Kimberley, South Africa. We found that V. rotundifolium parasitises only Ehretia rigida and Ziziphus mucronata at this site. Both commonly parasitised host species were not the most abundant trees, were not the tallest trees, and did not have the highest water or nutrient content of trees in the area, although these factors are good predictors for mistletoe parasitism. Mistletoe seeds deposited on branches of E. rigida and Z. mucronata have a greater chance of attachment and subsequent survival, compared with those seeds deposited on co-occurring Acacia and other potential host species. The mistletoes had higher water potential than their host trees and by doing so they can passively maintain the flow of nutrients. In addition, the mistletoes had a N:Ca ratio >1, indicating active uptake from host phloem. Thus, this mistletoe species uses both passive and active uptake, which may be a selective advantage in a nutrient-poor environment or on a nutrient-deficient host species.     

Report on species of Gyrodactylus Nordmann, 1832, distribution in polar regions

The aim of this study was to compare the Gyrodactylus fauna in the Arctic and Antarctic regions. Fish were collected from waters surrounding the South Shetland Islands in the Antarctic and from the Revelva River and Hornsund Fjord in south Spitsbergen in the Arctic. Eighty-two individual fish representing seven species from three families (Channichthyidae, Harpagiferidae, and Nototheniidae) were found in Antarctica and 2 Gyrodactylus infections with altogether 95 specimens were reported. Two new species were identified: Gyrodactylus sp. 1 Rokicka et al., 2009, from the gills of the black rock cod, Notothenia coriiceps Richardson, 1844, and Gyrodactylus sp. 2 Rokicka et al., 2009, from the gills of the gaudy notothen, Lepidonotothen nudifrons Lönnberg, 1905. No Gyrodactylus were found in the 95 Arctic fish examined, which represented four species from four families (Salmonidae, Gadidae, Cottidae, and Liparidae).     

Observations on the diet of the North African houbara bustard during the non-breeding season

The North African houbara bustard (Chlamydotis undulata undulata) is a medium-sized steppeland bird described as omnivorous and opportunistic. Its diet reflects the local abundances of plants and invertebrates. However, comprehensive studies based on both plant and animal materials are lacking to confirm or invalidate this characterization. The diet of the species during the non-breeding season was studied based on the contents of the stomachs of 42 adults collected during 2004, 2006 and 2007 in two regions of eastern Morocco. Taxa were identified to species or genus using a herbarium, a plant epidermis reference collection, an invertebrate reference collection, and an invertebrate fragment reference collection. We analyzed variation in the diet according to sex, region and year. The diet primarily included plant material (66 ± 25% of the dry weight of the stomach contents). The relative proportions of plants and invertebrates did not differ between the sexes but showed variations in space and time. The ingested plant and invertebrate assemblages differed between year and area but not between the sexes. These results suggest that both sexes forage in similar habitats and that their diet reflects spatial and temporal variations in plant and invertebrate availability, as expected for an opportunistic feeder.     

Allelopathic effects of VOCs of Artemisia frigida Willd. on the regeneration of pasture grasses in Inner Mongolia

Grassland of Inner Mongolia, the main grassland region of China and part of the Eurasia Steppe that stretches from East China to Hungary, is among the most seriously degraded grasslands in China. Previous studies on causes of grassland degradation in this region focused primarily on anthropogenic activities, such as rapid development, ranching, agricultural activities, and mining for mineral resources. Few studies have examined plant interactions during the processes of grassland degradation. In this study, using the thermal-desorption cold trap/gas chromatography/mass spectrometer technique (TCT/GC/MS) we examined the effects of volatile organic compounds (VOCs) of Artemisia frigida on the seed germination and seedling growth of 4 common grass species, Melitotus suaveolens, Sorghum sudanense, Elymus dahuricus and Agropyron cristatum, in the Inner Mongolian pastures. We found that the major constituents of the VOCs from natural A. frigida were 1,8-cineole, camphene, (E)-3-hexen-1-ol acetate, α-terpineol, β-Terpineol, (R)-(−)-p-Menth-1-en-4-ol, p-cymene, and camphor, whose relative content accounted for 96.0% of the 22 compounds identified for natural A. frigida. The content and amount of these VOCs varied when A. frigida was damaged artificially. The VOCs from A. frigida significantly decreased the seed germination and seedling growth of all the tested plant species. Our finding that artificially damaged plants of A. frigida released different types and amount of VOCs from undamaged ones under laboratory conditions indicate that grazing activity on natural pastures may influence the type and amount of VOCs released from A. frigida. However, more research is needed under field conditions to draw a conclusion if grazing activity has similar impacts on release of VOCs as under laboratory conditions.     

An assessment of revegetation treatments following removal of invasive Pennisetum ciliare (buffelgrass)

In semi-arid regions of North America and Australia, Pennisetum ciliare (L.) Link (syn. Cenchrus ciliaris; buffelgrass) is highly invasive and has the potential to introduce fire to fire-intolerant ecosystems. Major efforts to remove P. ciliare continue and it is essential that P. ciliare be prevented from recolonizing. This study investigated potential methods to revegetate with native herbaceous plants: sowing seeds; sowing seeds and mulching; sowing seeds and transplanting seedlings; and relying on natural revegetation from the seedbank. The treatments were applied in 2009 and 2010 at sites in the Sonoran Desert which had undergone P. ciliare removal. Monsoon precipitation was below average each year and seedling emergence and establishment rates were low. There are indications that soil disturbance associated with planting seedlings promoted P. ciliare emergence and increased mortality of brittlebush (Encelia farinosa A. Gray ex Torr.), a common native perennial forb. Addition of mulch may have promoted P. ciliare over native grasses, and seeding had no effect. We did not find competition between herbaceous seedlings. Rather, native and exotic grass seedling densities were positively correlated across sites. Under prevailing conditions, low precipitation appeared to limit herbaceous plant establishment and none of the treatments reduced P. ciliare abundance.     

Trophic preferences in an assemblage of mammal herbivores from Andean Puna (Northern Chile)

The patterns of plant consumption and preference were assessed for three mammal herbivores, the rodents Abrocoma cinerea and Chinchilla brevicaudata, and the camelid Vicugna vicugna, co-occurring in the Andean Puna (Chile). The plant proportion in the diet estimated from faeces epidermic materials was compared to transect plant cover. Although the harsh climatic conditions constrained plant availability (low vegetation, xerophytic species rich in secondary metabolites and structural carbohydrates) none of the mammals consumed plants according to their availability, displaying adaptations for efficient plant processing. V. vicugna, with a broad trophic niche, consumed short grasses and secondarily shrubs; C. brevicaudata also combined herbaceous plants and shrubs; and A. cinerea was specialised in shrub-eating. Although trophic overlap between the first two species was moderate, interactions were minimised by the mobility and low-impact grazing of V. vicugna. It is suggested that the diet of the three species differed due to their dissimilar abilities for responding to concentrations of secondary metabolites. The plants preferred by C. brevicaudata and V. vicugna did not carry high nutritional content but rather low content of secondary compounds. Conversely, A. cinerea was able to excrete terpenes, with metabolic costs compensated by the high energetic content of the plants eaten.     

The relation between accessibility,diversity and indigenous valuation of vegetation in the Bolivian Andes

A quantitative ethnobotanical study was conducted in the semi-arid Bolivian Andes community of Apillapampa to evaluate the impact of site accessibility on the diversity and perceived usefulness of (sub-)woody plants. Vegetation was sampled in thirty-six transects of 50 × 2 m², whereas data on plant uses were obtained from 13 local Quechua participants. Accessibility of sample sites correlated negatively with plant diversity, but positively with perceived usefulness. Hence, in spite of being less diverse, vegetation of more accessible sites was perceived as more useful to people than vegetation of more remote and also more diverse sites. This result contributes to the validity of the widely accepted notion that “more accessible plant resources are more useful to people”, not only at the level of individual plant species, but also for entire vegetation communities. In this respect, our finding that people attribute an equal usefulness to the vegetation of two local ecological zones (i.e. prepuna and puna) most likely reflects their similar accessibility from the village centre, which is located on the edge between both zones.     

Effects of fire and environmental variables on plant structure and composition in grazed salt desert shrublands of the Great Basin (USA)

Fire in shrub-dominated portions of the Great Basin, largely fueled by non-native annuals such as Bromus tectorum, has become an important structuring force altering vegetation composition and soil characteristics. The extent to which fire affects native species in drier portions of the Great Basin, termed salt desert, is poorly documented. We conducted a survey of grazed salt desert habitat in northwestern Nevada 5 years after wildfires burned 650,000 ha, with the goal of investigating community response to fire and factors correlating with post-fire recovery. We found that recruitment of a dominant shrub, Artemisia spinescens, is severely restricted following fire: it occurred in only 2 of the 24 burned sites. The co-dominant shrub, Atriplex confertifolia, occurred in most burned sites although on average its percent cover was one-third lower than adjacent unburned sites. Biotic soil crust cover was four times lower, and non-native species cover 5 times higher, in burned sites compared to unburned. Ordination analyses confirmed differences among plant communities in burned versus unburned sites, with environmental variables soil conductivity, plant litter, soil potassium (K⁺) and pH explaining 38% of the variance in community composition. However, we found no environmental predictors of recovery for native species in burned sites. Future recruitment is likely to be further limited, as fire frequency in the salt desert is expected to increase with invasion by non-native annual grasses and with global climate change.     

Post-fire plant recovery in the Mojave and Sonoran Deserts of western North America

Increasing wildfire activity is one of the most pressing management concerns in arid lands of the American West. To examine post-fire recovery of perennial vegetation in the Mojave and Sonoran Deserts, I analyzed data systematically synthesized from the literature. Post-fire sprouting by desert perennials is generally limited but varies among species. For example, only 3–37% of Larrea tridentata sprouted compared to 64–86% of Yucca schidigera. Four of five studies measuring recovery of perennial cover reported close relationships (r² = 0.67–0.99) between time since fire (TSF) and cover. In fact, three studies measuring the longest TSF (≥37 years) found that cover had returned to within 10% cover of unburned areas within approximately 40 years. Conversely, post-fire species composition exhibited little convergence with unburned composition in five of six studies even 47 years after fire. Sphaeralcea ambigua, Gutierrezia spp., Achnatherum speciosum, Encelia spp., Hymenoclea salsola, and Baileya multiradiata had the highest burned:unburned abundance ratios, although overall post-fire community composition differed between the Mojave and Sonoran Deserts. Analyzing the literature as a whole suggested some generalities (e.g., that perennial cover reestablishes faster than composition), but more work is required for improving specific knowledge about plant recovery among fires, sites, species, and climates.     

Acacia communities and species responses to soil and climate gradients in the Sudano-Sahelian zone of West Africa

Abiotic environmental factors have a major impact on the distribution and performance of plant species. In order to assess two major species–environmental relations in Sudano-Sahelian Acacia woodlands, we tested the relationship of soil and climate variables on plant diversity as well as on species responses.The indicator species values clustered in five vegetation units characterized by three to ten diagnostic species with woody species richness means varying from three to seven species per 0.09 ha. The NMS ordination explained 65% of the variation in species composition and revealed that soil properties, annual precipitations and temperature range structured the diversity of Acacia communities. Along the annual precipitations gradient, the response of Acacia polyacantha and Acacia hockii showed maxima in the wettest zone of our study area (more than 850 mm/year) whilst Acacia laeta showed a maximum response in the driest zone (below 500 mm/year). The unimodal response of A. hockii, Acacia gourmaensis and Acacia seyal to the soil available water gradient spanned their central borders, respectively from 13 to 18% (optimum 16%), 11–20% (optimum 15%) and 4–12% (optimum 7.5%).The response of Acacia communities and species to soil and climate gradients, makes them performant afforestation species in specific habitats of the Sudano-Sahelian zone.     

Three California annual forbs show little response to neighbor removal

In semi-arid systems, competition among plants has limited effects on performance compared to facilitative interactions and abiotic factors. However, the balance between competition and facilitation can change over the course of plant development. Determining when each interaction is important for plant productivity allows us to identify factors limiting plant growth. In this field study, neighbor removal mid-way through the growing season did not result in a size change for any species (Clarkia purpurea, Plantago erecta, and Micropus californicus) in the first year. In the second year, two species had greater biomass when neighbors were removed very early in the growing season, indicating a competitive effect. The third species neither benefited nor suffered from neighbor removal. In some years, P. erecta and M. californicus may be negatively affected by competition at early growth stages and are later unable to capitalize on newly-available resources after removals of competitors. This study shows that early-stage competition can drive biomass production in some annual plants, even in semi-arid systems.