Alterations in activities of acid phosphatase, alkaline phosphatase, ATPase and ATP content in response to seasonally varying Pi status in okra (Abelmoschus esculentus)

Phosphorus (P) is the second most important macronutrient for plant growth. Plants exhibit numerous physiological and metabolic adaptations in response to seasonal variations in phosphorus content. Activities of acid and alkaline phosphatases, ATPase and ATP content were studied in summer, rainy and winter seasons at two different developmental stages (28 and 58 days after sowing) in Okra. Activities of both acid and alkaline phosphatases increased manifold in winter to cope up with low phosphorus content. ATP content and ATPase activity were high in summer signifying an active metabolic period. Phosphorus deficiency is characterized by low ATP content and ATPase activity (which are in turn partly responsible for a drastic reduction in growth and yield) and enhanced activities of acid and alkaline phosphatases which increase the availability of P in P-deficient seasons.     

Biomass of suspended bacteria over coral reefs

The biomass of bacteria suspended in water flowing over coral reefs at Lizard Island and Yonge Reef (Northern Great Barrier Reef) was estimated by measurement of muramic acid. Values ranged from 20 mg C m^-3 in the open water up to about 60 mg C m^-3 over the reef flat. Direct counts of total numbers of free bacteria were made for comparison. Values of around 2.0x10⁹ cells g^-1 muramic acid showed that there was a good agreement between direct counts and muramic acid content of free bacteria in the open water. In samples containing suspended particulate matter, ratios of direct counts to muramic acid concentration were lower, because bacteria on particles could not be counted. Thus, these ratios were used to indicate the proportions of bacteria attached to particles. Changes in the biomass and numbers of bacteria were determined in water masses identified either by a drogue or fluorescein, as they moved across the reefs. In the zone on the outside of the reef, the number of free bacteria decreased compared to open sea water, but total biomass increased, showing that particulate matter containing bacteria was thrown up into suspension. About 50% of bacteria were attached to particles. Water flowing over the reef flats contained much particulate material with bacteria attached. Bacteria constituted between about 5 and 20% of particulate organic carbon.     

Amphi-Atlantic phylogeography of direct-developing lineages of Lasaea, a genus of brooding bivalves

Direct-developing intertidal Lasaea spp. occur in the North Atlantic as both continental margin and oceanic island populations. We conducted a molecular phylogenetic analysis of representative populations in order to test colonization hypotheses for North Atlantic oceanic islands. Thirty individuals each were collected in 1995 and 1996 from two continental putative source populations (Florida, Iberia) and two oceanic island populations (Bermuda, Azores). They were sequenced for a 462 nucleotide portion of the mitochondrial large ribosomal subunit (16S) gene. No amphi-Atlantic genotypes were detected: Bermudan lineages co-clustered exclusively with Floridian congeners, and Azorean samples formed an exclusive clade with Iberian haplotypes. Our data indicate that geographical proximity to continental source populations is a better predictor of phylogenetic relationships in North Atlantic Lasaea spp. than present-day oceanic surface circulation patterns. The phylogenetic trees generated are not consistent with colonization of oceanic islands by indirect-developing ancestral lineages or by truly trans-oceanic rafting events. However, they are consistent with predicted topologies resulting from limited (≤ 2000 km), long-distance colonization by rafting (against present-day circulation patterns in the case of the Azores) and from anthropogenic introductions. Received: 17 December 1998 / Accepted: 7 June 1999     

Microbial populations in surface films and subsurface waters: Amino acid metabolism and growth

Sea surface microlayer (film) and subsurface microbial populations (biomass and activities) were studied in the Damariscotta (Maine) estuary in May and September, 1987. Dissolved free and combined amino acids (DFAA, DCAA), bacterial numbers, microbial ATP, bacterial and microbial DNA synthesis (via³H-thymidine and³H-adenine), and amino acid (³H-glutamic acid) metabolism were measured. DFAA and DCAA were typically enriched in the surface microlayers relative to surface waters, although utilization of glutamic acid was usually more rapid in subsurface waters, as was incorporation of thymidine. Bacteria represented 12 to 40% of the microbial biomass as determined by ATP, except during microalgal blooms in the microlayer. Bacteria were generally not enriched in the surface films, although ATP usually was enriched. Rain input appeared to deplete population densities but stimulated population activities. Two stations which contained similar microbial populations (as estimated by bacterial counts, chlorophylla and ATP) showed very different microbial activities, apparently due to the effects of a substantial rainstorm on one of the stations. The bacterially-dominated processes utilizing thymidine and glutamic acid were enhanced approx five-fold after the rain. Autotrophic carbon production increased approx two-fold, while total microbal community DNA synthesis (as estimated by adenine incorporation into DNA) increased nearly tenfold. The observations of this study indicate that surface microlayers in the temperate waters off the coast of Maine contain highly active heterotrophic and autotrophic populations. The microbial community responds rapidly to changes in nutrient and dissolved organic matter concentrations resulting from both seasonal and temporal effects, including rain and runoff.     

Modelling growth forms of the spongeHaliclona oculata (Porifera,Demospongiae) using fractal techniques

The radiate-accretive growth process of the spongeHaliclona oculata, under different environmental conditions, is simulated in a two-dimensional model with fractal modelling techniques. In this model material is added in layers to the object, and growth velocities attain highest values at its protrusions. With this model some aspects of the growth process can be explained. It is possible to simulate thin-branching growth forms, which are normally found under sheltered conditions, and plate-like forms, which are typical for sites more exposed to water movement. These simulated forms are compared with actual growth forms in order to test the validity of the model.     

Influence of habitat quality, population size, patch size, and connectivity on patch-occupancy dynamics of the middle spotted woodpecker

Despite extensive research on the effects of habitat fragmentation, the ecological mechanisms underlying colonization and extinction processes are poorly known, but knowledge of these mechanisms is essential to understanding the distribution and persistence of populations in fragmented habitats. We examined these mechanisms through multiseason occupancy models that elucidated patch-occupancy dynamics of Middle Spotted Woodpeckers (Dendrocopos medius) in northwestern Spain. The number of occupied patches was relatively stable from 2000 to 2010 (15-24% of 101 patches occupied every year) because extinction was balanced by recolonization. Larger and higher quality patches (i.e., higher density of oaks >37 cm dbh [diameter at breast height]) were more likely to be occupied. Habitat quality (i.e., density of large oaks) explained more variation in patch colonization and extinction than did patch size and connectivity, which were both weakly associated with probabilities of turnover. Patches of higher quality were more likely to be colonized than patches of lower quality. Populations in high-quality patches were less likely to become extinct. In addition, extinction in a patch was strongly associated with local population size but not with patch size, which means the latter may not be a good surrogate of population size in assessments of extinction probability. Our results suggest that habitat quality may be a primary driver of patch-occupancy dynamics and may increase the accuracy of models of population survival. We encourage comparisons of competing models that assess occupancy, colonization, and extinction probabilities in a single analytical framework (e.g., dynamic occupancy models) so as to shed light on the association of habitat quality and patch geometry with colonization and extinction processes in different settings and species.     

Securing the Demographic and Genetic Future of Tuatara through Assisted Colonization

Abstract: Climate change poses a particular threat to species with fragmented distributions and little or no capacity to migrate. Assisted colonization, moving species into regions where they have not previously occurred, aims to establish populations where they are expected to survive as climatic envelopes shift. However, adaptation to the source environment may affect whether species successfully establish in new regions. Assisted colonization has spurred debate among conservation biologists and ecologists over whether the potential benefits to the threatened species outweigh the potential disruption to recipient communities. In our opinion, the debate has been distracted by controversial examples, rather than cases where assisted colonization may be a viable strategy. We present a strategic plan for the assisted migration of tuatara (Sphenodon punctatus), an endemic New Zealand reptile. The plan includes use of extant populations as reference points for comparisons with assisted‐colonization populations with respect to demography, phenotypic plasticity, and phenology; optimization of genetic variation; research to fill knowledge gaps; consideration of host and recipient communities; and inclusion of stakeholders in the planning stage. When strategically planned and monitored, assisted colonization could meet conservation and research goals and ultimately result in the establishment of long‐term sustainable populations capable of persisting during rapid changes in climate.     

A general two-species competition model with time-varying rates

The classical mathematical model for the behaviour of the populations of two competing biological species has previously been generalized by the author, by assuming that the coefficients of intrinsic growth, self-inhibition and interaction were all functions of time and, for a certain class of the governing differential equations, the exact solutions were obtained: an example was given in which the coefficients were periodic functions. In the differential equations of this model (as well as in the autonomous Lotka-Volterra equations), each of the Malthusian growth-rates was assumed to be diminished by a linear function of the populations of the two species, without there being any rigorous justification for this assumption. We here generalize the differential equations by assuming for these diminution functions general nonlinear forms having time-varying coefficients. The exact solutions are given for four classes of the resulting strongly nonlinear non-autonomous differential equations. Various conclusions about the growth modes of the two populations and their asymptotic behaviour are drawn, both when specific and when arbitrary forms are assumed for the coefficient functions. Cases are examined in which the Competitive Exclusion Principle holds and others in which it does not.     

Variations de la concentration bactérienne dans les eaux et les sédiments littoraux

Bacterial counts, carried out bi-mouthly over 2 years, at diverse localities on the Provence shores (France), revealed that the bottom-water microflora is not dependent on chemical and biological characteristics of the upper sediment layer. Freshwater inflow, polluted or non-polluted, and high concentrations of suspended particulate matter usually induce the highest bacterial counts. The concentration of microflora in marine muds and sands is connected with their organic content. There is no apparent correlation with water microflora concentration or macrobenthos density. The area of highest bacterial concentration is restricted to a narrow, thin belt of littoral sediment. Bacterial transformation is probably more important in the water mass as a whole than in marine deposits. The annual range of variations in microflora distribution is higher than the range which was encountered when testing the validity of the bacterial count method with the sampling technique employed. Certain bacterial concentrations, appearing simultaneously in different sediment layers and at different stations seem to be related to ecological factors. Such variations seem to realize a true annual cycle. The highest counts occur during the warm season, unlike the phytoplankter populations. Bacterial proliferation in water masses usually succeeds to phytoplankton blooms.     

Genetic structure of green turtle (Chelonia mydas) peripheral populations nesting in the northwestern Pacific rookeries: evidence for northern refugia and postglacial colonization

Several green turtle (Chelonia mydas) nesting populations have been reported in the northwestern Pacific region, the northernmost limit of its distribution range. However, the population history in this region as a whole is not well understood. To clarify how the green turtle nesting populations have evolved in the northwestern Pacific region, the genetic composition of mitochondrial DNA control region sequences in the northwestern Pacific was compared with that of the other Pacific populations. We analyzed 302 samples from the northwestern Pacific rookeries, including 78 newly collected samples from rookeries in the Ryukyu Archipelago, Japan (from 24.27°N, 123.76°E to 28.45°N, 129.61°E). Our results revealed that the northwestern Pacific populations consisted of one highly endemic lineage (Clade IV) in the northwestern Pacific rookeries and two other lineages (Clades I and V) which were widely observed in other Pacific populations. We concluded that the highly endemic lineage indicated that a refugial population existed in this region during the Last Glacial Maximum, and the other two lineages indicated that colonization from populations at lower latitudes occurred during interglacial periods. The green turtle nesting populations in the present periphery of their distribution range had been thought to have their origin in colonization from lower latitudes, which served as refugia during glacial periods. However, the present results indicated that the northwestern Pacific peripheral populations have been maintained on the evolutionary timescale of this species and should be treated as long-term conservation resources.     

Geometrical Factors and Metapopulation Dynamics of the Bush Cricket, Metrioptera bicolor Philippi (Orthoptera: Tettigoniidae)

This paper presents a metapopulation study of the bush cricket, Metrioptera bicolor , living in a recently fragmented landscape. The species inhabits grass and heathland patches of varying area and isolation. Analyses are made of how these geometrical factors affect local population size and density, distribution pattern, and the probability of local extinction and colonization. The proportion of available patches occupied varied between 72 and 79% during 1985–1990. Unoccupied patches were smaller and more isolated than those that were occupied. Patches where populations became extinct during this period were smaller than those with persisting populations. Since local population size was well correlated with patch area, it was clear that stochastic extinctions only occurred in small populations. Critical patch size for population extinction was approximately half a hectare. Colonized patches were less isolated than those that had not been colonized. Critical inter-patch distance for colonization was about 100 meters. The turnover was restricted to an identifiable share of the available patches. Only 33% of the patches were so small that extinction due to stochastic causes could be considered highly probable. This metapopulation will therefore most likely persist over a considerable period in its present spatial structure. There are apparent threats of further fragmentation, however, and nothing is known about the likelihood of large-scale extinctions resulting from extremely unfavorable weather conditions. Nevertheless, our results show that it is appropriate to include geometrical factors in metapopulation models.     

Divergence in ectomycorrhizal communities with foreign Douglas-fir populations and implications for assisted migration

Assisted migration of forest trees has been widely proposed as a climate change adaptation strategy, but moving tree populations to match anticipated future climates may disrupt the geographically based, coevolved association suggested to exist between host trees and ectomycorrhizal fungal (EMF) communities. We explored this issue by examining the consistency of EMF communities among populations of 40 year-old Douglas-fir (Pseudotsuga menziesii var. menziesii) trees in a common-garden field trial using four provenances from contrasting coastal climates in southwestern British Columbia. Considerable variation in EMF community composition within test sites was found, ranging from 0.38 to 0.65 in the mean similarity index, and the divergence in EMF communities from local populations increased with site productivity. Clinal patterns in colonization success were detected for generalist and specialist EMF species on only the two productive test sites. Host population effects were limited to EMF species abundance rather than species loss, as richness per site averaged 15.0 among provenances and did not differ by transfer extent (up to 450 km), while Shannon's diversity index declined slightly. Large differences in colonization rates of specialist fungi, such as Tomentella stuposa and Clavulina cristata, raise the possibility that EMF communities maladapted to soil conditions contributed to the inferior growth of some host populations on productive sites. The results of the study suggest locally based specificity in host-fungal communities is likely a contributing factor in the outcome of provenance trials, and should be a consideration in analyzing seed-transfer effects and developing strategies for assisted migration.     

Conserving Slow-Growing, Long-Lived Tree Species: Input from the Demography of a Rare Understory Conifer, Taxus floridana

Abstract:  Although land preservation and promotion of successful regeneration are important conservation actions, their ability to increase population growth rates of slow-growing, long-lived trees is limited. We investigated the demography of Taxus floridana Nutt., a rare understory conifer, in three populations in different ravine forests spanning its entire geographic range along the Apalachicola River Bluffs in northern Florida (U.S.A.). We examined spatial and temporal patterns in demographic parameters and projected population growth rates by using four years of data on the recruitment and survival of seedlings and established stems, and on diameter growth from cross-sections of dead stems. All populations experienced a roughly 10-fold increase in seedling recruitment in 1996 compared with other years. The fates of seedlings and stems between 8 and 16 mm differed among populations. The fates of stems in two other size classes (the 2- to 4-mm class and the 4- to 8-mm class) differed among both populations and years. Individual stems in all populations exhibited similarly slow growth rates. Stochastic matrix models projected declines in all populations. Stochastic matrix analysis revealed the high elasticity of a measure of stochastic population growth rate to perturbations in the stasis of large reproductive stems for all populations. Additional analyses also indicated that occasional episodes of high recruitment do not greatly affect population growth rates. Conservation efforts directed at long-lived, slow-growing rare plants like Taxus floridana should both protect established reproductive individuals and further enhance survival of individuals in other life-history stages, such as juveniles, that often do not appear to contribute greatly to population growth rates.     

Past,present, and future of a freshwater fish metapopulation in a threatened landscape

It is well documented that hydropower plants can affect the dynamics of fish populations through landscape alterations and the creation of new barriers. Less emphasis has been placed on the examination of the genetic consequences for fish populations of the construction of dams. The relatively few studies that focus on genetics often do not consider colonization history and even fewer tend to use this information for conservation purposes. As a case study, we used a 3‐pronged approach to study the influence of historical processes, contemporary landscape features, and potential future anthropogenic changes in landscape on the genetic diversity of a fish metapopulation. Our goal was to identify the metapopulation's main attributes, detect priority areas for conservation, and assess the consequences of the construction of hydropower plants for the persistence of the metapopulation. We used microsatellite markers and coalescent approaches to examine historical colonization processes, traditional population genetics, and simulations of future populations under alternate scenarios of population size reduction and gene flow. Historical gene flow appeared to have declined relatively recently and contemporary populations appeared highly susceptible to changes in landscape. Gene flow is critical for population persistence. We found that hydropower plants could lead to a rapid reduction in number of alleles and to population extirpation 50–80 years after their construction. More generally, our 3‐pronged approach for the analyses of empirical genetic data can provide policy makers with information on the potential impacts of landscape changes and thus lead to more robust conservation efforts.     

Long-term drivers of persistence and colonization dynamics in spatially structured amphibian populations

Many organisms live in networks of local populations connected by dispersing individuals, called spatially structured populations (SSPs), where the long-term persistence of the entire network is determined by the balance between 2 processes acting at the scale of local populations: extinction and colonization. When multiple threats act on an SSP, a comparison of the different factors determining local extinctions and colonizations is essential to plan sound conservation actions. We assessed the drivers of long-term population dynamics of multiple amphibian species at the regional scale. We used dynamic occupancy models within a Bayesian framework to identify the factors determining persistence and colonization of local populations. Because connectivity among patches is fundamental to SSPs dynamics, we considered 2 measures of connectivity acting on each focal patch: incidence of the focal species and incidence of invasive crayfish. We used meta-analysis to summarize the effect of different drivers at the community level. Persistence and colonization of local populations were jointly determined by factors acting at different scales. Persistence probability was positively related to the area and the permanence of wetlands, whereas it was negatively related to occurrence of fish. Colonization probability was highest in semipermanent wetlands and in sites with a high incidence of the focal species in nearby sites, whereas it showed a negative relationship with the incidence of invasive crayfish in the landscape. By analyzing long-term data on amphibian population dynamics, we found a strong effect of some classic features commonly used in SSP studies, such as patch area and focal species incidence. The presence of an invasive non-native species at the landscape scale emerged as one of the strongest drivers of colonization dynamics, suggesting that studies on SSPs should consider different connectivity measures more frequently, such as the incidence of predators, especially when dealing with biological invasions.     

Photosynthetic responses and daily carbon balance ofColpomenia peregrina: Seasonal variations and differences between intertidal and subtidal populations

The seasonal photosynthetic responses and daily carbon gain of upper intertidal, low intertidal and subtidal (3 to 4 m depth) populations ofColpomenia peregrina were examined over a 2 yr period (1986–1988) in Santa Catalina Island, California, USA. The populations showed significant differences in their photosynthetic responses, daily carbon balance and carbon-specific growth rates when normalized to tissue area or to chlorophyll content. The substantial plasticity with respect to photosynthetic responses shown byC. peregrina is considered to be an important factor in facilitating the colonization of both intertidal and subtidal habitats. This species appears to have a cellular carbon metabolism influenced by responses to season and tidal elevation. Highest net daily carbon balance, predicted carbonspecific growth rates and net growth efficiency were achieved in upper intertidal habitats during summer. These parameters decreased in winter and progressively declined with increasing depth as plants become increasingly exposed to low-light regimes. The diminishing net daily carbon balance and predicted carbon-specific field growth rates found during winter suggest that standing stock and lower subtidal limits of distribution ofC. peregrina are at least partly controlled by these two factors.     

Extinction, Colonization, and Metapopulations: Environmental Tracking by Rare Species

Extinction and metapopulation theories emphasize that stochastic fluctuations in local populations cause extinction and that local extinctions generate empty habitat patches that are then available for recolonization. Metapopulation persistence depends on the balance of extinction and colonization in a static environment. For many rare and declining species, I argue (1) that extinction is usually the deterministic consequence of the local environment becoming unsuitable (through habitat loss or modification, introduction of a predator, etc.); (2) that the local environment usually remains unsuitable following local extinction, so extinctions only rarely generate empty patches of suitable habitat; and (3) that colonization usually follows improvement of the local environment for a particular species (or long-distance transfer by humans). Thus, persistence depends predominantly on whether organisms are able to track the shifting spatial mosaic of suitable environmental conditions or on maintainance of good conditions locally.     

New insight on population genetic connectivity of widespread amphidromous prawn Macrobrachium lar (Fabricius, 1798) (Crustacea: Decapoda: Palaemonidae)

Due to the sparse and unstable nature of insular freshwater habitats, marine larval dispersal of amphidromous species is considered a critical element of population persistence. We assessed population genetic structure of freshwater prawn Macrobrachium lar across its range that encompasses two biogeographic barriers: the vast open ocean separating Western and Central Pacific regions and the Indo-Malay archipelago separating Indian and Pacific oceans. A total of 173 samples collected from 21 islands throughout the Indo-Pacific were sequenced at 16S and 28S rDNA. We observed distinct genetic isolation of populations located at the eastern and southwestern edge of the species range but no evidence of an effect of the Indo-Pacific barrier. Differentiation patterns are consistent with a stepping-stone model of dispersal. Genetic differences of Central Pacific populations may reflect founder events associated with colonization of isolated islands, or be a signature of a past bottleneck after population depletion caused by drastic climatic events.     

Phylogeography and demographic history of <Emphasis Type="Italic">Atherina presbyter</Emphasis> (Pisces: Atherinidae) in the North-eastern Atlantic based on mitochondrial DNA

A fragment of the mitochondrial control region was used to assess phylogeographic patterns and historical demography of the sand-smelt Atherina presbyter in the North-eastern Atlantic, covering its geographical range. A striking result is the highly marked differentiation between the Canary Islands population and western European ones. A genetic structure among European populations of A. presbyter was revealed, with a pattern of isolation-by-distance or a gradient effect at a scale of hundreds kilometres, an uncommon pattern likely related to the biological and life-history traits of the sand-smelt. The northern European populations present a much lower genetic diversity when compared to southern populations, which is consistent with a recent colonization from southern populations. The results showed signs of Pleistocene signatures, with the population age estimates for the European populations being clearly older than the Last Glacial Maximum (18,000 years bp). Nevertheless, paleotemperature reconstructions show that the sand-smelt could not have inhabited the western European shores during the last glacial phase. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Impact of anaerobically treated and untreated (raw) distillery effluent irrigation on soil microflora, growth, total chlorophyll and protein contents of Phaseolus aureus L

Impact of distillery effluent (untreated and treated) irrigation on soil microflora of the pots used for growing Phaseolus aureus L. was investigated. The growth of the P. aureus plants as affected by distillery effluent irrigation was also evaluated. The irrigation of the pots by 1-10% distillery effluent (anaerobically treated) stimulated the growth of the soil microflora (increased number of bacteria, fungi and actinomycetes) and P. aureus plants (increased shoot and root lengths, biomass, chlorophyll and protein contents). Further, 15-20% distillery effluent (anaerobically treated) had toxic effect on soil micro flora as indicated by reduced number of bacteria, fungi and actinomycetes. Reduction in shoot, root, lengths, biomass, chlorophyll, protein contents of P. aureus was also observed when irrigated by 15-20% treated distillery effluent. All the concentrations of raw distillery effluent reduced the bacterial population. However, the treated distillery effluent concentrations <10% had stimulatory effect on fungal and actinomycetes population. However, raw effluent concentrations >5% reduced the same. Raw distillery effluent was more toxic to P. aureus than treated distillery effluent as concentrations >5%, had reduced the growth (shoot, root length and biomass) of the test plant. Raw distillery effluent had adverse effect to total chlorophyll contents and all the test concentrations reduced the total chlorophyll level. However, untreated (raw) distillery effluent stimulated the protein content initially. It has been concluded from-present study that lower concentrations of the raw distillery effluent (1-5%) and treated distillery effluent (1-10%) had stimulated the growth of P. aureus and soil microflora except soil bacteria (inhibited by all the concentration of the raw effluent). However, higher concentrations (raw effluent: 10-20%; treated effluent 15-20%) had toxicity to test parameters.