Independent Transects Research Articles

Bayesian geochemical correlation and tomography

To accurately reconstruct palaeoenvironmental change through time it is important to determine which rock samples were deposited contemporaneously at different sites or transects, as erroneous correlation may lead to incorrectly inferred processes and rates. To correlate samples, current practice interpolates geological age between datable units along each transect, then temporal signatures observed in geochemical logs are matched between transects. Unfortunately spatiotemporally variable and unknown rates of sedimentary deposition create highly nonlinear space-time transforms, significantly altering apparent geochemical signatures. The resulting correlational hypotheses are also untestable against independent transects, because correlations have no spatially-predictive power. Here we use geological process information stored within neural networks to correlate spatially offset logs nonlinearly and geologically. The same method creates tomographic images of geological age and geochemical signature across intervening rock volumes. Posterior tomographic images closely resemble the true depositional age throughout the inter-transect volume, even for scenarios with long hiatuses in preserved geochemical signals. Bayesian probability distributions describe data-consistent variations in the results, showing that centred summary statistics such as mean and variance do not adequately describe correlational uncertainties. Tomographic images demonstrate spatially predictive power away from geochemical transects, creating novel hypotheses attributable to each geochemical correlation which are testable against independent data.

Effects of habitat complexity and temporal variation in rocky reef fish communities in the Santos estuary (SP), Brazil

Abstract Rampant human activities within estuaries and adjacent areas lead to a significant loss of habitat for many fish species and decreases the quality of the remaining habitats. In this context, we investigated the effects of habitat complexity and temporal variation on the composition and diversity of rocky reef fishes in two coastal islands in southeastern Brazil, namely Ilha do Mato e Ilha das Palmas. We filmed seven independent transects of 400 m2 in each island in each of the four seasons during a year using remotely operated vehicle (ROV). Using the video records and accessories attached to the ROV, we collected information on environmental variables, habitat complexity, species richness, abundance and diversity. Our pooled data showed 13,993 individuals belonging to 56 species, 13 orders and 24 families of marine fish. Nineteen species (34%) occurred in all four seasons. Nine species (16%) were exclusive to spring, seven (12.5%) were exclusive to autumn, three (5.4%) occurred in summer, and only two species (3.5%) were exclusive to winter. Fish assemblages varied according to the habitat complexity. The environmental variables varied between islands and climatic seasons. Numerical abundance and species richness were positively associated with habitat complexity. The interaction between maximum depth and habitat complexity resulted in a greater abundance of individuals. In addition, species richness was negatively correlated to both salinity and maximum depth. However, increasing both variables simultaneously caused an increase in expected richness, due to interaction effects. Trophic diversity was positively correlated with temperature, whilst habitat diversity did not vary with any of the studied independent variables. Furthermore, we found significant differences between Ilha do Mato and Ilha das Palmas in abundance and in richness, which may be due to streams that present re-circulations bordering the latter and that carry organic matter from the Santos estuary. Finally, our non-destructive and non-sacrificial methodology allowed the successful assessment of fish assemblages in different environments and at different times and the description of important patterns, which may be useful for public policies and management.

Escape behavior in gravid and non-gravid females of Gonatodes albogularis (Squamata: Sphaerodactylidae)

Escape behavior in gravid and non-gravid females of Gonatodes albogularis (Squamata: Sphaerodactylidae). Theoretical models of predator-prey relationships describe tradeoffs between energetic and other costs of escape, effectiveness of escape behavior, and predation risk. These models predict that an animal will fee when the expected ftness cost due to risk of predation becomes equal to the the cost of the escape or post-encounter ftness is maximized, depending on the model. In this framework, several individual and ecological variables have been shown to affect escape patterns, but the effect of reproductive status has been studied in few species. We assess differences in escape behavior between gravid and non-gravid females of Gonatodes albogularis. Lizards were surveyed by applying a free search method along independent transects. For each lizard, we determined reproductive status as gravid or non-gravid and recorded several variables related to escape behavior. We made a discriminant function analysis to see whether the state of individuals affect escape behavior. Our results show that the escape variables distance fed, the fnal distance and the distance to refuge differ between gravid and non-gravid females. These fndings support predictions based on risk and cost, but do not support models of fight initiation distance. Such differences could be related to a physiological process known as behavioral compensation, through which some individuals (gravid females in our case) modify their behavior to offset predation risk. Further studies are needed to see if behavioral compensation can be explained in terms of adaptive processes in G. albogularis.

Hybrid zone formation and contrasting outcomes of secondary contact over transects in common toads.

Much progress in speciation research stems from documenting patterns of morphological and genetic variation in hybrid zones. Contrasting patterns of marker introgression in different sections of the contact can provide valuable insights on the relative importance of various evolutionary mechanisms maintaining species differences in the face of hybridization and gene flow and on hybrid zone temporal and spatial dynamics. We studied species interactions in the common toads Bufo bufo and B.spinosus in France and northwestern Italy using morphological and molecular data from the mitochondrial and nuclear genomes in an extensive survey, including two independent transects west and east of the Alps. At both, we found sharp, coincident and concordant nuclear genetic transitions. However, morphological clines were wider or absent and mtDNA introgression was asymmetric. We discuss alternative, nonexclusive hypotheses about evolutionary processes generating these patterns, including drift, selection, long-distance dispersal and spatial shifts in hybrid zone location and structure. The distribution of intraspecific mtDNA lineages supports a scenario in which B.bufo held a local refugium during the last glacial maximum. Present-day genetic profiles are best explained by an advance of B.spinosus from a nearby Iberian refugium, largely superseding the local B.bufo population, followed by an advance of B.bufo from the Balkans, with prongs north and south of the Alps, driving B.spinosus southwards. A pendulum moving hybrid zone, first northwards and then southwards, explains the wide areas of introgression at either side of the current position of the contact zones.

Clines Arc through Multivariate Morphospace.

Evolutionary biologists typically represent clines as spatial gradients in a univariate character (or a principal-component axis) whose mean changes as a function of location along a transect spanning an environmental gradient or ecotone. This univariate approach may obscure the multivariate nature of phenotypic evolution across a landscape. Clines might instead be plotted as a series of vectors in multidimensional morphospace, connecting sequential geographic sites. We present a model showing that clines may trace nonlinear paths that arc through morphospace rather than elongating along a single major trajectory. Arcing clines arise because different characters diverge at different rates or locations along a geographic transect. We empirically confirm that some clines arc through morphospace, using morphological data from threespine stickleback sampled along eight independent transects from lakes down their respective outlet streams. In all eight clines, successive vectors of lake-stream divergence fluctuate in direction and magnitude in trait space, rather than pointing along a single phenotypic axis. Most clines exhibit surprisingly irregular directions of divergence as one moves downstream, although a few clines exhibit more directional arcs through morphospace. Our results highlight the multivariate complexity of clines that cannot be captured with the traditional graphical framework. We discuss hypotheses regarding the causes, and implications, of such arcing multivariate clines.

Estimation accuracies of near infrared spectroscopy for general soil properties and enzyme activities for two forest sites along three transects

Visible and near infrared spectroscopy (vis-NIRS) is an established method for estimating the contents of soil organic carbon (SOC) and soil nitrogen (N). Recent studies have suggested that it may also be useful for estimating enzyme activities, however this potential has not been explored in detail. Objectives were to determine estimation accuracies of vis-NIRS for general soil properties (SOC, N, pH, texture) and nine enzyme activities for two forest sites, one on a sandy soil (Grinderwald) and the other on a loess soil (Rüdershausen). For each site, a calibration sample consisting of two transects sampled down to 185cm (Grinderwald: 128units, Rüdershausen: 64units) and an independent validation sample consisting of one transect (Grinderwald: 64units, Rüdershausen: 32units) was obtained and their absorbance spectra recorded. Chemometric approaches included the standard partial least squares (PLS) regression and PLS regression with a genetic algorithm (GA-PLS) for variable selection, which may improve estimation accuracies. This study confirmed the marked usefulness of vis-NIRS for an estimation of SOC and N contents in independent transects of a field scale. Estimation accuracy of soil pH and texture in independent transects was variable and mainly dependent on the range of measured data. GA-PLS markedly improved estimation accuracies compared to PLS in the cross-validation, but generally not in the validation transects. Few enzyme activities could be estimated in independent validation, but there was almost no additional benefit of vis-NIRS for their estimations compared to estimations using measured contents of main properties; however, these contents of main properties may also be estimated with vis-NIRS. Overall, for the studied sites, we do not see a benefit of vis-NIRS for a direct estimation of enzyme activities compared to laboratory methods, most likely due to a lack of sufficiently strong specific impacts on the measured spectral signals.

Heterogeneous genome divergence, differential introgression, and the origin and structure of hybrid zones.

Hybrid zones have been promoted as windows on the evolutionary process and as laboratories for studying divergence and speciation. Patterns of divergence between hybridizing species can now be characterized on a genomewide scale, and recent genome scans have focused on the presence of 'islands' of divergence. Patterns of heterogeneous genomic divergence may reflect differential introgression following secondary contact and provide insights into which genome regions contribute to local adaptation, hybrid unfitness and positive assortative mating. However, heterogeneous genome divergence can also arise in the absence of any gene flow, as a result of variation in selection and recombination across the genome. We suggest that to understand hybrid zone origins and dynamics, it is essential to distinguish between genome regions that are divergent between pure parental populations and regions that show restricted introgression where these populations interact in hybrid zones. The latter, more so than the former, reveal the likely genetic architecture of reproductive isolation. Mosaic hybrid zones, because of their complex structure and multiple contacts, are particularly good subjects for distinguishing primary intergradation from secondary contact. Comparisons among independent hybrid zones or transects that involve the 'same' species pair can also help to distinguish between divergence with gene flow and secondary contact. However, data from replicate hybrid zones or replicate transects do not reveal consistent patterns; in a few cases, patterns of introgression are similar across independent transects, but for many taxa, there is distinct lack of concordance, presumably due to variation in environmental context and/or variation in the genetics of the interacting populations.

Timeframe of speciation inferred from secondary contact zones in the European tree frog radiation (Hyla arborea group).

BackgroundHybridization between incipient species is expected to become progressively limited as their genetic divergence increases and reproductive isolation proceeds. Amphibian radiations and their secondary contact zones are useful models to infer the timeframes of speciation, but empirical data from natural systems remains extremely scarce. Here we follow this approach in the European radiation of tree frogs (Hyla arborea group). We investigated a natural hybrid zone between two lineages (Hyla arborea and Hyla orientalis) of Mio-Pliocene divergence (~5 My) for comparison with other hybrid systems from this group.ResultsWe found concordant geographic distributions of nuclear and mitochondrial gene pools, and replicated narrow transitions (~30 km) across two independent transects, indicating an advanced state of reproductive isolation and potential local barriers to dispersal. This result parallels the situation between H. arborea and H. intermedia, which share the same amount of divergence with H. orientalis. In contrast, younger lineages show much stronger admixture at secondary contacts.ConclusionsOur findings corroborate the negative relationship between hybridizability and divergence time in European tree frogs, where 5 My are necessary to achieve almost complete reproductive isolation. Speciation seems to progress homogeneously in this radiation, and might thus be driven by gradual genome-wide changes rather than single speciation genes. However, the timescale differs greatly from that of other well-studied amphibians. General assumptions on the time necessary for speciation based on evidence from unrelated taxa may thus be unreliable. In contrast, comparative hybrid zone analyses within single radiations such as our case study are useful to appreciate the advance of speciation in space and time.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0385-2) contains supplementary material, which is available to authorized users.

Small scale factors affect population size of the Wood Mouse (Apodemus sylvaticus) in a Mediterranean island (Sardinia)

The variation of population size of the Wood Mouse (Apodemus sylvaticus) was studied across 30 independent transects in Sardinia island (Italy), with emphasis on the relationships between population size and environmental variables (type of wood, litter depth, tree diversity, tree size, number of stumps, ground cover, shrub cover, dead wood). Studies were conducted through a capture-mark-recapture protocol with live traps placed along line transects, and surveyed in both spring and autumn. Seven environmental variables were contrasted to population size estimates in each transect, with estimates of population size being obtained from five distinct demography models for close populations. There were significant inter-seasonal differences in the number of captured specimens (peak in springtime), but the population size of the Wood Mouse, despite varying considerably by transect, did not differ significantly among types of forest habitats. Population size of this species was positively influenced by (i) ground cover, (ii) number of stumps, and (iii) % Erica arborea ; conversely, it was negatively influenced by (a) height of Rubus ulmifolius bushes and (b) by % Rubus ulmifolius. The possible reasons behind these patterns were explored and discussed.

Limited depth zonation among bathyal epibenthic megafauna of the Gully submarine canyon, northwest Atlantic

The Gully is a large submarine canyon incised into the Scotian Shelf, in the northwest Atlantic. A submersible-mounted camera was used to collect 17km of high resolution video imagery of the soft sediment flanks and floor of the canyon between 1000 and 2500m depth. A depth-stratified random survey design with two transects per stratum was followed. Depth strata were drawn at 1000–1500m, 1500–2000m and 2000–2500m reflecting global and regional faunal boundaries. The 47,614 individuals or colonies observed on the transects were identified into 49 unique taxa drawn from 7 phyla, while 21 additional taxa were observed between the transect lines. Cnidaria was the most diverse phylum (22 taxa) on the transects, followed by the Echinodermata (15 taxa). Most fauna were sessile or sedentary suspension feeders. A species of Xenophyophorida, likely Syringammina sp., was the most abundant taxon. Cluster analysis of transects based on a Bray–Curtis (BC) matrix of species abundance identified one cluster of five transects and one independent transect – the deepest transect (2406m average depth). A similarity profile test indicated that this structure is not random. There was a significant change in the megafaunal assemblage with depth over scales of 10s of kilometers, accounting for 65% of the variation in the BC matrix. Both total organic carbon and labile carbon were higher in cores from the 1000–1500m stratum than at greater depth, consistent with transport of food and sediments into the canyon from shallower waters. The first principal component calculated from species abundances separated the two transects from the 1000–1500m depth stratum from the others indicating that sediment food supply influences community structure and composition. Over small spatial scales (≤10m), eight groups of species associations were identified. However, the associations between the species within each group were not strong with the highest correlation between the Xenophyophorida and the Pennatulacea (ρ=0.66). At this spatial scale substrate type was an important factor, with hard and soft bottom species associations being identified.

Sex-specific clines support incipient speciation in a common European mammal

Hybrid zones provide excellent opportunities to study processes and mechanisms underlying reproductive isolation and speciation. Here we investigated sex-specific clines of molecular markers in hybrid zones of morphologically cryptic yet genetically highly-diverged evolutionary lineages of the European common vole (Microtus arvalis). We analyzed the position and width of four secondary contact zones along three independent transects in the region of the Alps using maternally (mitochondrial DNA) and paternally (Y-chromosome) inherited genetic markers. Given male-biased dispersal in the common vole, a selectively neutral secondary contact would show broader paternal marker clines than maternal ones. In a selective case, for example, involving a form of Haldane's rule, Y-chromosomal clines would not be expected to be broader than maternal markers because they are transmitted by the heterogametic sex and thus gene flow would be restricted. Consistent with the selective case, paternal clines were significantly narrower or at most equal in width to maternal clines in all contact zones. In addition, analyses using maximum likelihood cline-fitting detected a shift of paternal relative to maternal clines in three of four contact zones. These patterns suggest that processes at the contact zones in the common vole are not selectively neutral, and that partial reproductive isolation is already established between these evolutionary lineages. We conclude that hybrid zone movement, sexual selection and/or genetic incompatibilities are likely associated with an unusual unidirectional manifestation of Haldane's rule in this common European mammal.

Application of Recent Red Abalone HALIOTIS RUFESCENS Surveys to Management Decisions Outlined in the California Abalone Recovery and Management Plan

The management section of California's recently adopted Abalone Recovery and Management Plan (ARMP) uses results of fishery independent transect surveys at eight index sites to regulate total allowable catch (TAC) for the recreational red abalone, Haliotis rufescens (Swainson), fishery. The ARMP uses abalone densities over all depths, densities in deep water (8.4–19.7 m), and successful recruitment (>4,500 abalone/hectare in the 100–177 mm size class) to decide whether changes need to be made in the TAC (see Table 1 later). The catch is estimated from telephone surveys and returned abalone permit report cards. Recent surveys in 2003 and 2005 at four of the eight index sites show red abalone densities in the range of the baseline densities established by surveys in 1999 and 2000. Applying the results of the 2003 and 2005 surveys to the ARMP criteria indicates no change is needed in the current TAC. Two-way ANOVA showed there were no significant differences in density between sites (Van Damme and Salt Point; df = 1, F = 0.06, P > 0.8) and time periods (df = 1, F = 1.33, P > 0.25) for all depths combined. Likewise there were no significant differences at deep depths between the two sites (df = 1, F = 0.23, P > 0.63) and the two time periods (df = 1, F = 0.10, P > 0.75).

Increase in mate availability without loss of self‐incompatibility in the invasive species Senecio inaequidens (Asteraceae)

The evolution of the strength of self‐incompatibility in Senecio inaequidens, a native of South Africa was investigated in relation to its invasion in Europe. Levels of self‐incompatibility were estimated with hand‐pollinations in five populations in greenhouse conditions. One population came from the native range of the species and four populations were sampled in Europe from two independent transects of colonization with old and recent populations. Contrary to Baker's law predictions, our results suggest that the species has a sporophytic self‐incompatible system maintained in all populations. We suggest that the ability of S. inaequidens to colonize new sites with a self‐incompatibility system is promoted by its ecological characteristics (perenniality, extended reproductive period, massive seed production, generalist pollinators). In addition, we found that mate availability was increased (1) in the introduced range compared to the native range, (2) in marginal versus central European populations. Possible explanations for this surprising result are discussed.

Predicting interactions between wetland vegetation and the soil-water and surface-water environment using diversity, abundance and attribute values

This study investigated the response of freshwater wetland vegetation to hydrological driving factors by assessing collective vegetation variables, traits of dominant plant populations and hydrological and hydrochemical variables, repeat-sampled within wetland sites across Scotland and northern England. Sampling was conducted at 55 permanent sample stations located along 11 independent transects. Eco-hydrological interactions were investigated using a regression-based modelling approach. Facets of the water-table dynamic (e.g., level of drawdown, level of fluctuation), along with vegetation abundance (e.g., biomass, stem density) and diversity (e.g., species richness) values, were used to build predictive models. Of the models predicting vegetation characteristics, the greatest predictive power was R 2=0.67 (p < 0.001) for a model predicting stem density (m−2). Conversely, vegetation variables proved useful for predicting characteristics of the water-table environment. In this instance, the greatest predictive power was R 2=0.79 (p < 0.001) for a model predicting minimum water table level (i.e. maximum level of drawdown). The models were tested using data collected during 2000 from repeat sites and independent sites. This approach might be successfully applied for the purposes of integrated eco-hydrological management and monitoring of freshwater wetland vegetation.

Mitochondrial DNA in the hybrid zone between Mus musculus musculus and Mus musculus domesticus: a comparison of two transects

We studied mtDNA introgression across the contact zone between Mus musculus musculus and M. m. domesticus in two independent transects in the Czech Republic and Bavaria, Germany. A total of 1270 mice from 98 localities in the Czech transect and 456 mice from 41 localities in the Bavarian transect were examined for presence or absence of a BamHI restriction site in the mt-Ndl gene. Using this simple mtDNA marker, variants that belonged to the M. m. domesticus lineage (presence of restriction site) could be unequivocally distinguished from those belonging to the M. m. musculus lineage (absence of restriction site). The extent of introgression of mtDNA, three autosomal allozymes and the X chromosome was compared. The introgression of X markers was more limited than was that of the allozymes and mtDNA. In the Czech transect, the centre for the mtDNA dine was shifted about 3.6 km to the west relative to the X chromosome dine, with asymmetric introgression from M. m. musculus to M. m. domesticus. Interestingly, in the Bavarian transect, the centre of the mtDNA dine was shifted about 10.9 km to the east relative to the X chromosome dine, with asymmetric introgression from M. m. domesticus to M. m. musculus, opposite in direction to that observed in the Czech transect.

Scale dependency in spatial patterns of saturated hydraulic conductivity

This study investigates spatial patterns of Ks and tests the hypothesis of whether structural variance emerges from noise with increasing sampling precision. We analyzed point measurements of Ks along independent transects at sampling intervals of 25, 10, 1 and 0.25 m. The field area is a tropical rainforest catena (i.e. toposequence) characterized by systematic downslope changes in soil properties including color (red to yellow), mineralogy (kaolinite–illite to kaolinite) and texture (sandy clay to sand). Independent transects spanning the entire catena at lag intervals of 25 and 10 m reveal little to no spatial patterns in Ks; i.e. scatter plots are noisy and lack apparent spatial trends, and semivariograms suggest little to no autocorrelation in Ks. As sampling precision is increased ( h=1 and 0.25 m), spatial patterns emerge in Ks for the downslope areas, in which distinctive hydraulic boundaries in Ks correlate with relatively small-scale, topography-controlled soils with coarse textures (≥80% sand). For these areas, semivariograms of Ks and those of %sand and %clay exhibit similar spatial structure characterized by small nugget variances and large ranges, and nugget variance is reduced as sampling precision increases from 1 to 0.25 m. In the upslope, clay-rich locations along this toposequence, Ks exhibits few spatial patterns, irrespective of sampling scale. For these locations, scatter plots are noisy without apparent spatial trends, and semivariograms show almost complete nugget variance, suggesting little to no correlation in this hydraulic parameter at any scale. This study suggests that in the absence of coarse textures (≥80% sand), there is little predictability in Ks, even at sampling intervals of 0.25 m. We believe this lack of spatial structure is due to a predominance of small-scale processes such as biological activity that largely control Ks in this forested setting.

Spatial Patterns and Determinants of Winter Atmospheric Carbon Dioxide Concentrations in an Urban Environment

The purpose of this article is to describe determinants and spatial patterns of atmospheric carbon dioxide (CO2) in Phoenix, Arizona. Specifically, we use geographic information systems (GIS) and regression-based analyses to identify the human and biological factors that contribute to spatial and temporal variations in near-surface (2-meter height) atmospheric CO2 levels. We use these factors to create estimated surfaces of CO2 concentrations for the area. We evaluate the surfaces using records of CO2 from independent monitoring stations and transects. To investigate the temporal patterns and variations in CO2 concentrations, we estimate CO2 surfaces for the early mornings and the afternoons, on weekdays when traffic is heavy and spatially focused and on weekends when it is lighter and more spatially dispersed. Findings suggest there is a distinct relationship between the structure of Phoenix CO2 levels and spatial patterns of human activities and vegetation densities. Morning CO2 levels are higher than afternoon levels and correspond closely to the density of traffic, population, and employment. The spatial structure of human activity explains the pattern of CO2 better on weekdays than on weekends. CO2 surfaces reflect declining densities of human activity with distance from the city center, the pattern of irrigated agriculture in the Phoenix area, and riparian habitats on the urban fringe. Spatial and temporal patterns of CO2 concentrations are useful in understanding urban climate and ecosystem processes.

PREDICTION IN COMPLEX COMMUNITIES: ANALYSIS OF EMPIRICALLY DERIVED MARKOV MODELS

Understanding and predicting the effects of species extinction and other environmental impacts in natural ecosystems is difficult because of their inherent complexity. Successful prediction in complex systems requires empirically accessible theoretical frameworks to limit the range of possible outcomes. I explored the predictions of multispecies Markov models, based on transition probabilities derived from repeated censuses of fixed points in the middle intertidal community of Tatoosh Island, Washington, USA, under natural conditions and after altering the model to reflect species extinction and changes in size-structured processes. The unmanipulated model predicted a mussel-dominated community and quantitatively captured 98.7% of the variation in community composition in independent transects. Although model assumptions that transition probabilities did not vary over time and depended only on the state of a point at the previous census were violated, altering the model to account for these violations provided no improvement in model performance. The manipulated models indicated that most species and transitions had relatively weak effects on community composition, the strongest effects being associated with California mussels (Mytilus californianus), articulated coralline algae (Corallina vancouveriensis), and predatory birds. The manipulated models also predicted that extinction of several species, particularly predatory birds, affects the resilience of the system, as assessed by return time. The effects of species on composition and resilience were poorly correlated, suggesting that assessing the importance of species depends on the type of ecosystem response being considered. The model successfully predicted quantitative shifts in community composition and ecosystem dynamics under several novel conditions: on vertical walls where bird predation and adult mussel recruitment are absent, and in previously published experiments that excluded birds from horizontal benches. These results suggest that Markov models can provide a useful predictive framework for some types of environmental impacts on complex ecosystems.

Ecological controls on stromatolite development in a modern reef environment: A test of the ecological refuge paradigm

Paleontological and neontological studies suggest that stromatolite development may be limited to environments where ecological processes such as colonization (recruitment), growth, competition, and predation (herbivory) are low. We quantitatively tested this “ecological refuge paradigm” at a unique stromatolite-reef complex at Stocking Island, Bahamas where three contiguous zones grade in dominance from stromatolites in the back reef to a macroalgal turf in the reef flat to reef building corals and coralline algae and reef fishes in the fore reef. At two independent transects along this gradient, we quantified the distribution and abundance of the dominant organisms and measured the rates of the above-listed ecological processes and determined survival and growth of stromatolite, turf, and coralline algae transplanted to each of the three zones. We also measured both the sediment dynamics and temperature profiles along this gradient to determine if these may be controlling the ecological processes. Stromatolites dominate the back reef zone where species diversity (especially among eukaryotes) and associated ecological pressures were low. Measured rates of colonization from calcified (i.e., coralline) and noncalcified macroalgae and filamentous turf algae were lowest in the back reef (i.e., <5% substrate colonization/y) and highest in the fore reef (95% substrate colonization/y). This suggests that competition for space was lowest in the stromatolite zone. Growth and survival rates of transplanted coralline algae were low in both the back reef (3 mm/y and 20–40% annual survival rates) and reef flat (<2 mm/y, 0% surviving) and highest in the fore reef (about 10 mm/y, 80% surviving). Foraging activity from all fishes was lowest in the back reef (total 0.4 bites/m2/h) and reef flat (0 bites/m2/h) and highest in fore reef (900–2200 bites/m2/h, mostly from omnivorous wrasses). Herbivory from all potential sources was below detectable levels in the stromatolite zone and was highest in the fore reef. The ecological refuge found in the back reef stromatolite zone resulted primarily from periodic sediment inundation. Most eukaryotic reef-dwelling organisms cannot persist under as much as 700 mm of sediment for periods up to 100 days. Although the reef flat suffered both desiccation and thermal stress (averaging more than 5°C greater daily temperature fluctuation than the fore reef), natural and transplanted eukaryotic turf algae thrived there. Although transplanted stromatolites survived best in the back reef (about 80% of the original transplant surviving/y), they also persisted in the fore reef (about 40% surviving per year). Therefore,Schizothrix-dominated stromatolites can persist in fore reef environments but because of the presence of other organisms and associated ecological pressures, their laminated microbial-produced structure is lost or obscured. While the sediment and the organisms necessary for stromatolite formation exist in this and probably in other modern reef environments, their reef-building contribution will be low except in unusual habitats where abiotic stresses maintain an ecological refuge.

Population Fluctuations of the Monarch (Danaus plexippus) in the 4th of July Butterfly Count 1977-1994

-Monarchs reported in North America N of Mexico in the 4th ofJuly Butterfly Count (4JC) for 1977-1994 were analyzed for population fluctuations. From 1977 to 1986 the mean number of monarchs per hour in eastern North America varied significantly in only one of nine pairs of consecutive years. From 1986 to 1994, eastern monarchs varied significantly in five of eight year-pairs, with a nearly equal number of increases and decreases. However, the amount of variation within each year-pair was similar for 1977-1986 and 19861994 (median difference ca. a factor of 2). Although the Atlantic and midwestern subregions of the eastern population covaried in four of eight year-pairs from 1986-1994, differences between the two subregions sometimes damped fluctuations in the eastern population overall. Data from independent transect surveys in Wisconsin for 1990-1994 agreed with the direction of fluctuations in Wisconsin 4JCs. In 4JCs from 1987-1994 in the Pacific coastal states, monarchs varied less than the eastern population, with a significant increase in 1989 and significant decrease in 1988. However, a nonsignificant decline of an order of magnitude occurred in 1993, and a considerable but smaller increase occurred in 1994. Fluctuations in monarch abundance in eastern North America during 1977-1994 often, but not always, coincided with years affected by major widespread perturbations of typical weather such as the El Ninlo-Southern Oscillation, major volcanic eruptions, droughts and floods.