Regeneration of Carnegiea gigantea (Cactaceae) since 1850 in three populations in the northern Sonoran Desert

Saguaro cacti (Carnegiea gigantea) are long-lived and exhibit great variability in growth that makes age estimation problematic. A few single-site studies have focused on those locales where long-term data (e.g. 85 years) are available. Using a newly developed technique, 733 saguaros were sampled in three locales (Silverbell, Harcuvar, Kofa) across Arizona and their age structure reconstructed for the last 150 years based on a mathematical model of the heights of individuals. This is the first study to compare regeneration at multiple locations across the species' range. Regression analysis for each site (years and frequency of individuals established during that year) was run and residuals extracted to determine peaks and troughs in regeneration over time. Correlation was run on the residuals between sites, and chi-square analysis was employed to compare frequency of good and bad regeneration years between Kofa and Silverbell. Peaks and troughs represent regeneration as well as survivorship and mortality. Several large cohorts established at Kofa and Harcuvar since 1850, while at Silverbell well over 80% of sampled saguaros established after the late 1930s. This more recent recruitment at Silverbell may be related to the major freezing event of 1937 whose impact was likely greater at the cooler Silverbell site. Despite the widely different population structures at Silverbell and Kofa, recruitment trends in both populations were statistically linked as both locales often benefited from the same favorable periods for regeneration (P < 0.001). The Harcuvar population shares some common peaks and troughs in regeneration over time with Kofa and Silverbell, but its relationship to them is not statistically significant. Some trends overlap in some locales, such as the favorable regeneration period in the late 1800s and early 1900s, particularly at Silverbell and Kofa as well as at other known sites. However, each population has its own signature. Silverbell is a youthful population likely shaped by severe freezing events, while Kofa has many individuals representing regeneration at several different periods. Regeneration, mortality and subsequent population structure is shaped by both regional-scale influences as well as more localized conditions over the long and short terms.     

Analysis of the factors that affect the distribution and abundance of three Neobuxbaumia species (Cactaceae) that differ in their degree of rarity

We studied three species of columnar cacti in the genus Neobuxbaumia which differ in their degree of rarity: Neobuxbaumia macrocephala (the rarest), Neobuxbaumia tetetzo (intermediate), and Neobuxbaumia mezcalaensis (the most common). To investigate the ecological factors that limit their distribution and abundance, we surveyed 80 localities within the region of Tehuacan-Cuicatlán, in Central Mexico. At each locality we measured several environmental variables, and the density of the Neobuxbaumia populations present. We used a principal component analysis (PCA) to identify the factors that are associated to the presence/absence of each species. Additionally, we carried out multiple regressions between environmental variables and population density to test whether the variation in these variables was related to changes in abundance. The results show that factors significantly affecting the distribution of these species are mean annual temperature, altitude, rainfall, and soil properties such as texture and organic matter content. N. mezcalaensis reaches maximum population densities of 14,740 plants per ha (average density = 3943 plants per ha) and is associated with localities with relatively abundant rainfall. N. tetetzo shows maximum population densities of 14,060 plants per ha (average = 3070 plants per ha), and is associated with sites located at high latitudes and with high phosphorous content in the soil. The rarest species, N. macrocephala, shows maximum densities of 1180 plants per ha (average = 607 plants per ha) and is associated with localities with high soil calcium content. The distribution of this species is limited to sites with specific values of the environmental variables recorded, conferring it a high habitat specificity which accounts for its rarity.     

Stability of the spatio-temporal distribution and niche overlap in neotropical earthworm assemblages

The spatial distribution of soil invertebrates is aggregated with high-density patches alternating with low-density zones. A high degree of spatio-temporal organization generally exists with identified patches of specific species assemblages, in which species coexist according to assembly rules related to competitive mechanisms for spatial and trophic resources occur. However, these issues have seldom been addressed. The spatio-temporal structure of a native earthworm community in a natural savanna and a grass–legume pasture in the Colombian “Llanos” was studied during a 2-year-period. A spatially explicit sampling design (regular grid) was used to discern the distribution pattern of species assemblages in both systems. Earthworms were collected from small soil pits at three different sampling dates. Data collected from 1 m² soil monoliths were also used in the present study. Data were analyzed with the partial triadic analysis (PTA) and correlograms, while niche overlap was computed with the Pianka index. The PTA and correlogram analysis revealed that earthworm communities displayed a similar stable spatial structure in both systems during the 2-year study period. An alternation of population patches where different species' assemblages dominated was common to all sampling dates. The medium-sized Andiodrilus sp. and Glossodrilus sp. exhibited a clear spatial opposition in natural savanna and the grass–legume pasture for the duration of the study. The Pianka index showed a high degree of niche overlapping in several dimensions (vertical distribution, seasonality of population density) between both species. The inclusion of space-time data analysis tools as the PTA and the use of classical ecological indices (Pianka) in soil ecology studies may improve our knowledge of earthworm assemblages' dynamics.     

Assessing transpiration in the tussock grass Stipa tenacissima L.: the crucial role of the interplay between morphology and physiology

Plant transpiration has a key role on both plant performance and ecosystem functioning in arid zones, but realistic estimates at appropriate spatial-temporal scales are scarce. Leaf and tiller morphology and crown architecture were studied together with leaf physiology and whole plant water balance in four individual plants of Stipa tenacissima of different sizes to determine the relative influence of processes taking place at different spatial and temporal scales on whole plant transpiration. Transpiration was estimated in potted plants by leaf-level gas exchange techniques (infrared gas analyzer and porometer), by sap flow measurements, and by integrating leaf physiology and crown architecture with the 3-D computer model Yplant. Daily transpiration of each individual plant was monitored using a gravimetric method, which rendered the reference values. Leaves on each individual plant significantly varied in their physiological status. Young and green parts of the leaves showed five times higher chlorophyll concentration and greater photosynthetic capacity than the senescent parts of the foliage. Instantaneous leaf-level transpiration measurements should not be used to estimate plant transpiration, owing to the fact that extrapolations overestimated individual transpiration by more than 100%. Considering leaf age effects and scaling the estimates according to the relative amount of each foliage category reduced this difference to 46% though it was still significantly higher than gravimetric measurements. Sap flow calculations also overestimated tussock transpiration. However, 3-D reconstruction of plants with Yplant and transpiration estimates, considering both the physiological status and the daily pattern of radiation experienced by each individual leaf section within the crown, matched the gravimetric measurements (differences were only 4.4%). The complex interplay of leaf physiology and crown structure must be taken into account in scaling up plant transpiration from instantaneous, leaf-level measurements, and our study indicates that transpiration of complex crowns is easily overestimated.     

Adaptive settlement in sedge warblers Acrocephalus schoenobaenus—focus on the scale of individuals

Breeding site selection can be linked to population dynamics through pre-emptive site selection, by which an individual selects the best (in terms of fitness) available site, preventing others from sharing it. We examined the pattern of territorial settlement and its fitness consequences during a study of sedge warblers Acrocephalus schoenobaenus inhabiting two study plots in the Nida Wetlands (southern Poland). Throughout all 7 years of the study (1997–2003), male sedge warblers repeatedly occupied sites in sequence from best to worst, according to the amount of cover by reedmace and common reed on one plot, and the amount of common reed on the other plot. As individuals aged, they occupied sites with increasingly higher proportions of reedmace and common reed. On the first plot, where the within-habitat heterogeneity was greater, settlement date and consequently reedmace and common reed cover at the sites occupied by a male had a positive influence on that male's fitness components: the probability of mating, nesting success, and the number of offspring recruited to the breeding population in succeeding years. On the second plot, which was more homogenous, there was no such evident relationship between fitness and the proportion of cover by reeds.     

The effects of nutrient availability and removal of competing vegetation on resprouter capacity and nutrient accumulation in the shrub Erica multiflora

Nutrient availability is increasing in the Mediterranean Basin due to the great number and intensity of fires and higher levels of anthropomorphic pollution. In the experiment described in this paper, we aimed to determine the effects of N and P availability and of the removal of competing vegetation on resprouter capacity, biomass, and nutrient accumulation in Erica multiflora. Plants of the resprouter species E. multiflora were clipped to 0% of aerial biomass in a post-fire Mediterranean shrubland and fertilisation experiments and removal of competing vegetation were established in a factorial design. The resprouting of clipped plants was monitored during the first year after clipping and at the end of the year, all plant resprout populations were harvested and their resprout structure, biomass and N and P content measured. N fertilisation had no significant effect on leaf biomass either at plant level or on the total aerial biomass per stump unit area; however N concentration in resprout biomass did increased. P fertilisation slightly increased resprouting vigour and had a significant effect on P content of the leaf biomass. The removal of competing vegetation increased the ratio between leaf biomass and stem biomass, the lateral expansion of resprout, the hierarchy of resprouts branching, and the P content of stems, above all when P fertilisation was applied. These results show that as a response to decreased competition E. multiflora has the capacity to modify the relative proportions of the nutrients in the aerial biomass. All these characteristics allow E. multiflora to persist in increasingly disturbed Mediterranean ecosystems and contribute to the retention of nutrients in the ecosystem during early resprouting phases.     

Benthic foraminiferal assemblages of the Cretaceous platform carbonate succession in the Yavca area (Bolkar Mountains, S Turkey): biostratigraphy and paleoenvironments

The microbiostratigraphic analysis of the three outcrop sections from the Cretaceous inner platform carbonate succession in the Yavca area (Bolkar Mountains) allows to recognize the four local benthic foraminiferal zones. These are: (1) Voloshinoides murgensis and Praechrysalidina infracretacea Cenozone in the Lower Aptian; (2) Pseudorhapydionina dubia and Biconcava bentori Cenozone in the Middle-Upper Cenomanian; (3) Ostracoda and Miliolidae Interval Zone in the probable Turonian, represented by dolomitized limestones without any significant markers; (4) Moncharmontia compressa and Dicyclina schlumbergeri Cenozone in the Coniacian-Santonian. The benthic foraminiferal assemblages correspond to those in other areas of the Mediterranean realm, with the exception of a lack of alveolinids and orbitolinids due to unfavorable environmental conditions (inner platform, restricted shelf). After the regionally well-known emergence during the late Aptian, Albian and early Cenomanian, very shallow subtidal to intertidal conditions were re-established during the middle-late Cenomanian time. The Coniacian-Santonian benthic foraminiferal assemblage shows an increase in diversity and abundance as a result of open marine influence, confirmed by the presence of larger foraminifera (Dicyclina), Rotaliidae and radiolitid fragments. Thaumatoporella and Aeolisaccus-bearing wackestone intercalations still indicate the existence of sporadic restricted environment conditions. The Cretaceous shallow-water platform carbonate succession of the Yavca area is conformably overlain by gray pelagic limestones with calcispheres and planktonic foraminifera. The Campanian flooding of the Bolkar Da? carbonate platform resulted in drowning of the pre-existing biota and facies.     

Biostratigraphic control of the latest-Ordovician glaciogenic unconformity in Alnif (Eastern Anti-Atlas, Morocco), based on brachiopods

In the Alnif region of the Eastern Atlas (Morocco), seven fossiliferous horizons within the Lower-Ktaoua and Upper-Tiouririne formations (Ktaoua Group), as well as in the glaciomarine microconglomeratic shales of the Upper Formation of the Second-Bani Group have yielded biostratigraphically significant brachiopods and other taxa, such as trilobites and echinoderms. Several brachiopod species with short stratigraphic ranges, well-known in south-western Europe, allow a precise chronostratigraphic control of a succession that displays important lateral lithological and facies changes, when compared with the type sections in the Central Anti-Atlas. They have also permitted a better consensus between the macrofauna-determined age and that based on micropaleontological analyses. For the first time, the occurrence of a Hirnantia Fauna within the microconglomeratic shales of the Upper Formation of the Second Bani Group is reported. The biostratigraphic conclusions restrict the age of the Latest Ordovician glaciation to the early Hirnantian.     

The Radiolarian biotic response to Oceanic Anoxic Event 2 in the southern part of the Northern proto-Atlantic (Demerara Rise, ODP Leg 207)

Rare Radiolaria occur in the Upper Cenomanian-Lower Turonian part of finely laminated black shales recovered from Sites 1258 and 1261 of Demerara Rise (Ocean Drilling Program Leg 207, western tropical Atlantic, off Surinam). The observed fauna are of a low diversity, with up to 12 species co-occurring in a single sample and 49 species identified in total in both sites. Nassellarians and “Spumellarians” are equally represented in the assemblages. Diverse species of Stichomitra and Theocampe are particularly common, including the two new species described herein: Theocampe costata and T. demeraraense. Radiolarian preservation is on average moderate to poor, suggesting substantial influence of diagenetic alterations to species diversity. The few well-preserved assemblages can potentially provide better information about Cenomanian-Turonian Radiolarian biodiversity, but given their low abundance in the processed sediment samples, the diversity sampled during this study is considered to be an underestimate of the original Radiolarian diversity at Demerara. However, the abundance and diversity of Theocampe in Upper Cenomanian levels is noteworthy. Given the earliest known occurrence of the genus from Upper Albian sediments of the Deep Ivorian Basin it is likely that it originated and diversified in the opening Equatorial Atlantic Gateway. Based on the stable carbon isotope curve, the OAE-2 interval is clearly identified in the sedimentary sequence of both studied sites and helps to specify the known age range of three species (Acanthocircus hueyi, Archaeospongoprunum bipartitum and Rhopalosyringium hispidum). The most intriguing result of this study is the paucity of Radiolaria within the OAE-2 interval of the deeper site (1258) and the total absence of this micro-zooplankton group in the OAE-2 interval of the proximal site (1261). Radiolaria are the most abundant and diverse at the distal Site 1258, below OAE-2, while the proximal Site 1261 contains very few Radiolaria. The opposite pattern is observed above OAE-2 (few Radiolaria at site 1258, more abundant at site 1261). The paucity or absence of Radiolaria within the OAE-2 interval may be due to the upward excursion of the chemocline in the southern part of the Northern proto-Atlantic. Upwelling of deep warm waters may have fuelled primary productivity (sulfate-reducing bacteria) but prevented at the same time micro-zooplankton survival and proliferation after intensification of euxinic conditions in the surface waters.     

Habitat‐related variation in the plasticity of a UV‐sensitive photoreceptor over a small spatial scale in the palmate newt

Plastic phenotypes are expected to be favoured in heterogeneous environments compared with stable environments. Sensory systems are interesting to test this theory because they are costly to produce and support, and strong fitness costs are expected if they are not tuned to the local environment. Consistently, the visual system of several species changes with the conditions experienced during early development. However, there is little information on whether the amplitude of the change, that is the reaction norm, differs between visual environments. Given the rapid change of many ecosystems, especially eutrophication for aquatic habitats, it is crucial to determine down to which spatial scale, change in the reaction norm occurs. We addressed this issue by quantifying the between‐habitat variation in the expression of a UV‐sensitive opsin in a newt. In western France, this species breeds in ponds of small forest patches, where water filters out UV, and in agricultural ponds where UV transmission is variable. We raised larvae from both habitats with or without exposure to UV. Opsin expression was reduced in larvae from agricultural habitats when raised without UV, whereas it was low in larvae from forest ponds under all lighting conditions. Thus, the variation in the reaction norm of opsin expression was lower in stable filtering environments and higher in heterogeneous environments. Its variation occurred between habitats across a small spatial scale. We discuss the hypotheses for this pattern and for the maintenance of residual opsin expression in forest populations.     

Foraminiferal assemblages and the confinement index as tools for assessment of saline intrusion and human impact in the Mekong Delta and neighbouring areas (Vietnam)

Foraminiferal assemblages have been studied in 33 samples from the Can Gio region to the north of the Mekong Delta and from two regions of the Delta: the Tra Vinh province, in the middle part of the Delta; and the Ca Mau peninsula, to the south. Two plates, including 117 pictures, illustrate the species. These assemblages, either through the nature of the test or through the calculation of the confinement index Ic, clearly indicate differences in the balance between continental and marine influences, the Tra Vinh province being subject to the strongest freshwater influence. The decrease of calcareous specimens and the increase of Ic indicate the impact of deforestation in the Ca Mau peninsula, the influence of organic matter in shrimp ponds, and the impact of pollution in a tidal channel. The distribution of foraminiferal assemblages described in this study should be used as part of a reference point for further observations with a view to assessing environmental impacts of increasing human activities and/or global change.     

Plio-Pleistocene evolution of the genus Castor (Rodentia, Mammalia) in Europe: C. fiber plicidens of Pietrafitta (Perugia, Central Italy)

In the lignite sediments of Pietrafitta (Tiberino Basin, Umbria, Central Italy), a rich fossil assemblage of vertebrate, invertebrate and plant remains belonging to the Farneta Faunal Unit (Late Villafranchian, Early Pleistocene) was collected. Among them fossil beaver cranial remains are relatively abundant. Western-Central Europe Villafranchian beaver remains were assigned to C. plicidens by some authors because molar occlusal surface patterns show complex enamel crenulations. Several recent authors have classified them as C. fiber while analysing other morphological patterns. Our samples have been compared to Plio-Pleistocene fossil remains and to living European populations of the genus Castor. New morphometric parameters on molar occlusal surfaces have been defined and statistical analyses (One-Way MANOVA, Principal Component Analysis and Canonical Discriminant Analysis) have been performed on them. The results point out a subspecific separation between the Late Villafranchian beaver of Pietrafitta, Quarata and San Giovanni in Valdarno (Umbria and Tuscany) and C. fiber populations. St. Vallier (France) Late Pliocene and Mosbach 2 (Germany) Middle Pleistocene beavers classified respectively by Viret and Friant as C. plicidens, show a C. f. fiber molar teeth pattern. Therefore, C. fiber plicidens did not occur in Central-Western Europe and this subspecific name may be used only for the local populations of Valdarno and Tiberino Basin (San Giovanni in Valdarno, Quarata, Pietrafitta and a few localities of the same area), at that time peripheral populations, probably semi-isolated during the Late Villafranchian, and at the southern limit of the geographic range of C. fiber.     

Sexual and individual morphometric variation in Libycosaurus (Mammalia, Anthracotheriidae) from the Maghreb and Libya

Anthracotheres of late Middle Miocene and Late Miocene age have been described from several localities in northern Africa, all of them currently assigned to the genus Libycosaurus Bonarelli, although in several previous works they were assigned to Merycopotamus Falconer and Cautley, a considerably younger and specialised form from the Indian subcontinent which has quite different dental and cranial morphology. Three species of Libycosaurus have been named, but there has been some doubt about the morphometric variation within the various species, with some authors such as Gaziry (1987) placing the fossils from Sahabi (Latest Miocene, Libya) and Beglia (end Middle Miocene to basal Late Miocene, Tunisia) into the same species despite marked size differences, and others (Ducrocq et al., 2001) creating a species for a restricted sample of small specimens from Nementcha (Late Middle Miocene, Algeria), but which overlaps with the range of size variation of Beglia fossils. The aim of this paper is to examine the available samples in greater depth in order to understand the morphometric variation in these anthracotheres. It is confirmed that the Beglia sample is quite variable (Black, 1972), both morphologically and metrically, but it is concluded that it nevertheless belongs to a single species, because specimens from some of the localities within the Beglia Formation (e.g. Loc. 17 in the lower levels at Beglia) span the entire range of variation (Pickford, 1994). The sample from Nementcha cannot be distinguished from the Beglia sample on any consistent metric or morphological basis, but in general the specimens fall at the low end of the range of variation of the Beglia sample. It is thus likely that L. algeriensis is a synonym of L. anisae. The Sahabi and Chad samples (L. petrocchii), in contrast, fall above the known range of variation of the Beglia material in almost all metric features, but are close to it morphologically, and they are considered to represent a species distinct from the Beglia sample.     

Molecular parentage analysis in experimental newt populations: the response of mating system measures to variation in the operational sex ratio

Molecular studies of parentage have been extremely influential in the study of sexual selection in the last decade, but a consensus statistical method for the characterization of genetic mating systems has not yet emerged. Here we study the utility of alternative mating system measures by experimentally altering the intensity of sexual selection in laboratory-based breeding populations of the rough-skinned newt. Our experiment involved skewed sex ratio (high sexual selection) and even sex ratio (low sexual selection) treatments, and we assessed the mating system by assigning parentage with microsatellite markers. Our results show that mating system measures based on Bateman's principles accurately reflect the intensity of sexual selection. One key component of this way of quantifying mating systems is the Bateman gradient, which is currently underutilized in the study of genetic mating systems. We also compare inferences based on Bateman's principles with those obtained using two other mating system measures that have been advocated recently (Morisita's index and the index of resource monopolization), and our results produce no justification for the use of these alternative measures. Overall, our results show that Bateman's principles provide the best available method for the statistical characterization of mating systems in nature.     

Genetic variation in two populations of the rough‐skinned newt (Taricha granulosa) assessed using novel tetranucleotide microsatellite loci

Seven novel tetranucleotide microsatellite loci were identified from a partial genomic DNA library, enriched for GATA‐motif microsatellites, from the rough‐skinned newt (Taricha granulosa). All loci were polymorphic, and one displayed a high frequency null allele. A related species, T. rivularis, displays strong site fidelity and detectable population structure over small spatial scales, so we assessed genetic variation in two samples of T. granulosa separated by 16 km. Distributions of allele frequencies differ significantly between our two sites, but small values of F_ST and Rho_ST suggest that the populations are linked by a large amount of gene flow.     

Genetic structure of Schrenck newt <Emphasis Type="Italic">Salamandrella schrenckii</Emphasis> populations by mitochondrial cytochrome <Emphasis Type="Italic">b</Emphasis> variation

The nucleotide sequence variation of the mitochondrial cytochrome b gene was studied in Schrenck newt Salamandrella schrenckii (Strauch, 1870) from populations of Primorye and the Khabarovsk region. Phylogenetic analysis revealed two haplotype clusters, southern cluster 1 and northern cluster 2, with a divergence of 3%. Analysis of the mtDNA and cytochrome b amino acid sequence variations made it possible to assume that the modern range of Schrenck newt was colonized from south Primorye northwards. In contrast to the southern cluster, the northern one demonstrated all the signs of demographic expansion (a unimodal distribution of pairwise nucleotide differences, specific results of tests for selective neutrality of mtDNA variation, and a good correspondence of genetic parameters to those expected from demographic expansion models).     

Seasonal variation of immune response to heterologous erythrocytes in natural populations of red‐backed (Clethrionomys rutilus) and gray‐sided (C. rufocanus) voles in Western Siberia

We studied the seasonal variation of adaptive humoral immunity (AHI) in northern red‐backed vole (Clethrionomys rutilus Pallas, 1779, RBV) and gray‐sided vole (C. rufocanus Sundevall, 1846, GSV) in Tomsk region of Western Siberia. Immunoresponsiveness (IR) to sheep red blood cells was assessed by the number of antibody‐producing cells in the spleen. The use of a generalized linear model to analyze the effects of species, sex, year of research, and season of withdrawal of individuals from nature on IR showed a significant effect of species identity, season of animal capture, and the interaction of species with season. The RBV demonstrated higher immune responses during a year, and both species had higher IR in winter. Suppression of IR in spring was greater, started earlier, and lasted longer (March–May) in GSV. In RBV, immunosuppression was restricted to April. The significant negative within year correlations of IR with body mass and masses of reproductive organs in GSV indicated a trade‐off between AHI and growth and reproduction processes. A probable explanation for the difference between species in the seasonal variation of AHI may be related to the difference in tropho‐energetic requirements of each vole species. GSV is a predominantly herbivorous rodent and its thermoregulation seems less efficient than of RBV. The deeper spring immunosuppression in GSV may explain in part its higher mortality during the season of colds.