Patterns Of Environmental Variation Research Articles

Hydrological Regime and Fish Predation Regulate the Zooplankton Community Size Structure in a Tropical Floodplain Lake

Floodplain ecosystems are characterised by alternating flood and drought periods that can affect the structure of the aquatic community. Dynamic changes in the hydrological regimes from flooding to dry periods influence the migration and dispersal of aquatic fauna and the exchange of particulate matter and nutrients. Riverine floodplains are among the most productive ecosystems; however, increasing pressure from anthropogenic activities has altered the hydrological regimes, threatening aquatic biodiversity. In this study, we examined the temporal patterns of zooplankton community size structure and fish density during three distinct hydrological events in a tropical floodplain lake, Lake Tempe, Indonesia. We included fish density data and three contrasting hydrological conditions, moderate-, high-, and low-water periods, as the environmental factors regulating zooplankton community structure. In high- and low-water conditions, the ecosystem heterogeneity was characterised by high chlorophyll-a, total nitrogen, and total phosphorus concentrations; high fish density; and high zooplankton abundance and biomass. During the early flood period, the ecosystem was characterised by lower concentrations of trophic indicators and significant decreases in zooplankton abundance and biomass, as well as decreased fish density. While there was no clear association between hydrological conditions and zooplankton size structure, our findings indicate that fish predation probably suppressed zooplankton size diversity in Lake Tempe, shown by the dominant contribution of small-sized zooplankton towards total abundance and biomass under all hydrological conditions. Our results indicate that the patterns of environmental variables, zooplankton community, and fish density are affected by hydrological conditions, highlighting the role of water level fluctuation as the driving factor for zooplankton community structure. Our results also indicated that fish predation led to the development of a small-sized population of zooplankton in Lake Tempe.

Inter-annual variability in breeding census data across species and regions

There is an intense interest in long-term trends of species abundance that may reflect, for example, climate change or conservation actions. Less well studied are patterns in the magnitude of inter-annual variability in abundance across large spatial scales. We collated abundance time-series for 133 nesting sites across the globe of the seven sea turtle species. Inter-annual variability in nest numbers was lowest in loggerhead turtles (Caretta caretta), Kemp’s ridley (Lepidochelys kempii) and flatback turtle (Natator depressus) and highest in green turtles (Chelonia mydas), likely reflecting their lower trophic position compared to other species and hence tighter coupling of food availability to environmental conditions each year. The annual number of nests in green turtles could vary by 60-fold between successive years. We identified regional patterns in the magnitude of inter-annual variability in green turtle nest numbers, variability being highest for nesting beaches around Australia and lowest in the western Indian Ocean and equatorial Atlantic. These regional patterns are likely linked to corresponding patterns of environmental variability with, for example, areas subjected environmental extremes as part of the El Nino Southern Oscillation (ENSO) showing high inter-annual variability in nest numbers.

A landscape-scale framework to identify refugiafrom multiple stressors.

From a conservation perspective, quantifying potential refugial capacity has been predominantly focused on climate refugia, which is critical for maintaining the persistence of species and ecosystems. However, protection from other stressors, such as human‐induced changes in fire and hydrology, that cause habitat loss, degradation, and fragmentation is also necessary to ensure that conservation efforts focused on climate are not undermined by other threats. Thus, conceptual and methodological advances for quantifying potential refugia from multiple anthropogenic stressors are important to support conservation efforts. We devised a new conceptual approach, the domains of refugia, for assessing refugial capacity that identifies areas where exposure to multiple stressors is low. In our framework, patterns of environmental variability (e.g., increased frequency of warm summers), thresholds of resilience, and extent and intensity of stressors are used to identify areas of potential refugia from a suite of ongoing anthropogenic stressors (e.g., changes in fire regime). To demonstrate its utility, we applied the framework to a Southern California landscape. Sites with high refugial capacity (super‐refugia sites) had on average 30% fewer extremely warm summers, 20% fewer fire events, 10% less exposure to altered river channels and riparian areas, and 50% fewer recreational trails than the surrounding landscape. Our results suggest that super‐refugia sites (∼8200 km2) for some natural communities are underrepresented in the existing protected area network, a finding that can inform efforts to expand protected areas. Our case study highlights how considering exposure to multiple stressors can inform planning and practice to conserve biodiversity in a changing world.

Memory shapes microbial populations.

Correct decision making is fundamental for all living organisms to thrive under environmental changes. The patterns of environmental variation and the quality of available information define the most favourable strategy among multiple options, from randomly adopting a phenotypic state to sensing and reacting to environmental cues. Cellular memory-the ability to track and condition the time to switch to a different phenotypic state-can help withstand environmental fluctuations. How does memory manifest itself in unicellular organisms? We describe the population-wide consequences of phenotypic memory in microbes through a combination of deterministic modelling and stochastic simulations. Moving beyond binary switching models, our work highlights the need to consider a broader range of switching behaviours when describing microbial adaptive strategies. We show that memory in individual cells generates patterns at the population level coherent with overshoots and non-exponential lag times distributions experimentally observed in phenotypically heterogeneous populations. We emphasise the implications of our work in understanding antibiotic tolerance and, in general, bacterial survival under fluctuating environments.

Modelling Soil Greenhouse Gas Fluxes from a Broad-Leaved Korean Pine Forest in Changbai Mountain: Forest-DNDC Model Validation

Fluctuations in soil greenhouse gas (GHG) are an important part of the terrestrial ecosystem carbon-nitrogen cycle, but uncertainties remain about the dynamic change and budget assessment of soil GHG flux. Using high frequency and consecutive soil GHG fluxes measured with an automatic dynamic chamber system, we tested the applicability of the current Forest-DNDC model in simulating soil CH4, CO2 and N2O fluxes in a temperate broad-leaved Korean pine forest at Changbai Mountain. The results showed that the Forest-DNDC model reproduced general patterns of environmental variables, however, simulated seasonal variation in soil temperature, snow melt processes and soil moisture partly deviated from measured variables, especially during the non-growing season. The modeled CH4 flux was close to the field measurement and co-varied mainly with soil temperature and snowpack. The modeled soil CO2 flux had the same seasonal trend to that of the observation along with variation in temperature, however, simulated CO2 flux in the growing season was underestimated. The modeled N2O flux attained a peak in summer due to the influence of temperature, which was apparently different from the observed peak of N2O flux in the freeze-thaw period. Meanwhile, both modeled CO2 flux and N2O flux were dampened by rainfall events. Apart from consistent estimation of annual soil CH4 flux, the annual accumulation of CO2 and N2O was underestimated. It is still necessary to further optimize model parameters and processes using long-term high-frequency observation data, especially transference of heat and water in soil and GHG producing mechanism. Continues work will improve modeling, ecosystem carbon-nitrogen budget assessment and estimation of soil GHGs flux from the site to the region.

The genetics of phenotypic plasticity. XVI. Interactions among traits and the flow of information.

Although the environment varies, adaptive trait plasticity is uncommon, which can be due to either costs or limitations. Currently there is little evidence for costs of plasticity; limitations are a more promising explanation, including information reliability. A possible cause for a decrease in information reliability is the channeling of environmental information through one trait that then affects the phenotype of a second trait, the information path. Using an individual-based simulation model, I explored the ways in which configurations of trait interactions and patterns of environmental variation in space and time affect the evolution of phenotypic plasticity. I found that genotypes and phenotypes evolved to shorten and simplify the information path from the environment to fitness. A shortened path was characterized by a decrease in the amount of plasticity for traits that had a less direct connection between the environment of development and fitness. A simplified path was characterized by a decrease in the amount of plasticity for traits that had multiple paths between the environment and their phenotype. These results suggest that an eighth proposition be added to the theory of the evolution of phenotypic plasticity: Trait plasticity will evolve to minimize the information path between the environment and fitness.

The genetics of phenotypic plasticity. XV. Genetic assimilation, the Baldwin effect, and evolutionary rescue.

We used an individual‐based simulation model to examine the role of phenotypic plasticity on persistence and adaptation to two patterns of environmental variation, a single, abrupt step change and continual, linear change. Our model tested the assumptions and predictions of the theory of genetic assimilation, explored the evolutionary dynamics of the Baldwin effect, and provided expectations for the evolutionary response to climate change. We found that genetic assimilation as originally postulated is not likely to occur because the replacement of plasticity by fixed genetic effects takes much longer than the environment is likely to remain stable. On the other hand, trait plasticity as an enhancement to continual evolutionary change may be an important evolutionary mechanism as long as plasticity has little or no costs. Whether or not plasticity helps or hinders evolutionary rescue following a step change in the environment depends on whether plasticity is costly. For linear environmental change, noncostly plasticity always decreases extinction rates, while costly plasticity can create a fitness drag and increase the chance of extinction. Thus, with changing climates plasticity can enhance adaptation and prevent extinction under some conditions, but not others.

Harvested populations are more variable only in more variable environments.

The interaction between environmental variation and population dynamics is of major importance, particularly for managed and economically important species, and especially given contemporary changes in climate variability. Recent analyses of exploited animal populations contested whether exploitation or environmental variation has the greatest influence on the stability of population dynamics, with consequences for variation in yield and extinction risk. Theoretical studies however have shown that harvesting can increase or decrease population variability depending on environmental variation, and requested controlled empirical studies to test predictions. Here, we use an invertebrate model species in experimental microcosms to explore the interaction between selective harvesting and environmental variation in food availability in affecting the variability of stage‐structured animal populations over 20 generations. In a constant food environment, harvesting adults had negligible impact on population variability or population size, but in the variable food environments, harvesting adults increased population variability and reduced its size. The impact of harvesting on population variability differed between proportional and threshold harvesting, between randomly and periodically varying environments, and at different points of the time series. Our study suggests that predicting the responses to selective harvesting is sensitive to the demographic structures and processes that emerge in environments with different patterns of environmental variation.

Temporal patterns in the intertidal faunal community at the mouth of a tropical estuary.

The use of intertidal sandy beaches by fish and macrocrustaceans was studied at different temporal scales at the mouth of a tropical estuary. Samples were taken along the lunar and diel cycles in the late dry and rainy seasons. Fish assemblage (number of species, density and biomass), crustaceans and wrack biomass, showed significant interactions among all studied factors, and the combination of moon phase and diel cycle, resulting in different patterns of environmental variables (depth, water temperature and dissolved oxygen), affected habitat use by the different species. Variances in faunal community were detected between seasons, stimulated by salinity fluctuations from freshwater input during the rainy season. These differences suggest an important cycling of habitats and an increase in connectivity between adjacent habitats (estuary and coastal waters). Moreover, the results showed that this intertidal sandy beach also provides an alternative nursery and protected shallow-water area for the initial development phase of many marine and estuarine species. In addition, this intertidal habitat plays an important role in the maintenance of the ecological functioning of the estuarine-coastal ecosystem continuum.

Processes underlying tidal variability of carbon dioxide in the Tagus Estuary (Portugal)

Tidal variation of CO2 system parameters was evaluated in the Tagus Estuary (SW Portugal) based on field observations performed in 2007 in the lower estuary under low river discharge conditions, during spring and autumn. Differences were found in the distribution patterns of environmental variables along a tidal cycle and at neap and spring tides essentially due to tide amplitude effects and tidal asymmetric behavior. A dominant east-westbound current was detected transporting CO2 enriched estuarine water offshore mainly during the ebb, and the reverse tidal current transporting more oxygenated marine water and with high chlorophyll a concentration during the flood. Distinct seasonal features were observed in terms of CO2 water properties and productivity. Regarding the tidal variability of the CO2 system parameters, besides the key processes controlling the variability, such as tidal advection and horizontal mixing of the two water masses present (estuarine and oceanic), specific biogeochemical processes emerged as playing an important role. Data obtained indicate that photosynthesis (in spring), aerobic respiration, and CaCO3 precipitation/dissolution (mainly in autumn) processes co-occur and control short-scale variations of CO2, reflecting the complexity of CO2 chemistry in the Tagus Estuary.

Achieving higher heritabilities through improved design and analysis of clonal trials

Clonal testing was studied under different environmental patterns and experimental designs through simulation with the criteria of maximizing broad-sense heritability estimates and genetic gain from clonal selection. Several experimental designs were studied together with three patterns of environmental variability. In addition, empirical 95% confidence intervals for heritability estimates were compared with Dickerson's approximate method. Other elements studied included (i) conditions under which different environmental patterns yield high or low heritabilities and (ii) effects of varying the number of ramets per clone. Row-column designs produced the highest mean individual broad- sense heritability, but these designs were only slightly more efficient than incomplete block designs with small block sizes. For all experimental designs, Dickerson's approximate method for estimating the variance of heritability estimates produced reasonable 95% confidence intervals but overestimated the upper confidence limit of complex designs. Larger heritabilities were found with higher tree-to-tree spatial correlations and lower amounts of microsite residual variance, and varying gradients had negligible influence. The effect of implementing Latinization was significant on increasing heritability, but small in practical terms, and was more important for patchy surfaces. Experiments with more ramets per clone yielded higher clonal mean heritabilities, and using between four and six ramets per clone per site is recommended.

Comparison of Experimental Designs for Clonal Forestry Using Simulated Data

Abstract Various alternatives for the design of clonal field trials in forestry were studied using simulated data to identify “optimal𠇍 or “near-optimal𠇍 scenarios for the estimation of genetic parameters. The simulated field site consisted of a rectangular grid on which 256 clones with 8 ramets each were installed. Estimates of genetic parameters were compared for (1) single-tree and four-tree row plots; (2) several experimental designs (completely randomized, randomized complete block, incomplete blocks of various sizes, and row–column); (3) no mortality versus 257% mortality; and (4) different patterns of environmental variability (only patches, only gradients, and both patches and gradients). Use of single-tree plots, on average, increased the correlations between true and predicted clonal values by 57% over four-tree row plots and increased genetic gain from selection. Starting with a parametric broad-sense heritability (H B 2) of 0.25 for a completely randomized design, the experimental designs resulting in the highest H B 2 were row–column designs for single-tree plots and incomplete blocks with 32 blocks per replication when four-tree row plots were used. These designs increased average heritability 107% and 147% over a randomized complete block design, respectively. The only effect of 257% mortality was an increase in the variability of some variance component estimates.

A test of Brown's principle in the intertidal limpet Collisella scabra (Gould, 1846)

AbstractAim Brown's principle predicts that a species will peak in density near its range centre, and decline gradually towards the margins of its geographical distribution. The decline is assumed to reflect a decrease in individual performance near range margins. I test this abundance–performance hypothesis by comparing patterns in density and size across the northern half of the geographical distribution of the marine patellogastropod Collisella scabra (Gould, 1846).Location Collisella scabra is a high intertidal patellogastropod species distributed along the Pacific coast of North America from Cape Mendocino (CA, USA) to southern Baja California (Mexico). I surveyed 11 research sites spanning c. 36–44° N.Methods In each of the 11 research sites I surveyed four distinct microhabitats, and compared spatial patterns in density and in the size of solitary limpets.Results Both density and size were highly variable across the species range. Density peaked near the northern range margin, and showed greater variance at small spatial scales (< 10 km) than at large scales (> 100 km). In contrast, large size occurred uniformly across the survey area, and size was strongly associated with microhabitat.Main conclusion Collisella scabra does not show spatial patterns of density or performance that are consistent with Brown's principle. The underlying assumptions of Brown's principle may conflict with specific characteristics of C. scabra's life history and/or patterns of environmental variation across its range. Because such conflicts may be common in a large number of marine and terrestrial species, the generality of Brown's principle is questioned.

Human impacts in Antartic marine soft-sediment assemblages: correlations between multivariate biological patterns and environmental variables at Casey Station

Correlations between the spatial distribution of soft-sediment assemblages and environmental variables were evaluated at a number of control and potentially impacted locations (waste dumps, a sewage outfall and a wharf) at Casey Station, East Antarctica. Patterns of assemblage composition were compared with patterns of environmental variables using univariate and multivariate techniques. The utility of these methods, however, is uncertain in areas of significant habitat heterogeneity (at scales <10 m), such as at Casey Station. A number of environmental variables were measured to determine their potential influence on assemblage structure including sediment heavy metal concentrations, total organic carbon (TOC), grain size and depth. Soft-sediment assemblages clustered strongly into two groups and this pattern was found to be most highly correlated with concentrations of heavy metals of anthropogenic origin: cadmium, copper, lead, tin and zinc. The relationship, however, is complex and is likely to be further influenced by variables affecting the bioavailability of metals such as grain size, TOC and sediment anoxia. Impacted locations were characterised by fewer taxa, lower diversity and lower species richness. One of the control locations was found to have naturally high levels of cadmium, nickel and zinc and had assemblages very similar to those at the potentially impacted, polluted locations. One of the potentially impacted locations had coarse sediments and low levels of heavy metals but had assemblages very similar to other impacted locations. Problems of sampling design for human impacts detection in real world situations are discussed in relation to this study. This study provides evidence that these multivariate statistical methods are useful in heterogeneous environments and across pollution gradients where pollutants have the potential to act as a primary cause of spatial variation in assemblage structure.

The evolution of Daphnia pulex in a temporally varying environment

We investigated three aspects of adaptation to variable environments in Daphnia pulex (Cladocera: Crustacea): (1) effects of temporal variation on the evolution of phenotypic plasticity ; (2) plasticity in sexual versus asexual lineages; (3) maintenance of genetic variation in variable environments. We performed a 72-day quasi-natural selection experiment comparing three patterns of variation: constant temperatures, varying but predictable temperature change, and unpredictable temperature change. All populations were begun with an identical array of 34 clones. During selection clonal variation declined in all populations and different patterns of environmental variation had little effect on amounts of genetic variation. Sexual and asexual lineages differed in size and growth rate, but did not differ in amounts of plasticity or in adaptation to variable environments. The primary target of selection was the Malthusian parameter (r) and life history traits of development time, offspring size and offspring number. The heritability of plasticity was generally lower than trait heritability. Because of this difference, the selection response on the mean of the traits overwhelmed the selection response on plasticity. Lower heritabilities of plasticity are very typical, suggesting that our results will be typical of responses to selection in nature. Our results suggest that selection will act mostly on trait means within environments and that plasticity will evolve often as a correlated trait. Because selection on plasticity is based on its across-deme, global fitness, this process will usually be slow. Comparative studies need to shift from closely related, local population differences to those of more distantly related populations or even different species.

Phenology and mortality of common woody plants during and after severe drought in south-eastern Zimbabwe.

The phenological patterns of 14 woody species that are common components of deciduous woodland in a southern African lowveld region were studied in the Gonarezhou National Park, Zimbabwe. Biweekly assessments of the number of leaf buds, young, mature and dead leaves, flower buds, open flowers, unripe and ripe fruits showed a gradual deterioration in the food supply in a season of low rainfall. Production of vegetation followed a simila, but less marked, pattern of environmental variation. The tree population in the major vegetation types declined because a large proportion of the woody species was killed during the 1991-92 drought. This suggests that climatic extremes are more important to plants than the average conditions. Transactions of the Zimbabwe Scientific Association Volume 72 1998, pp. 1-6

Reproductive Ecology of Tetraphis pellucida. I. Population Density and Reproductive Mode

Reproductive Ecology of Tetraphis pellucida. I. Population Density and Reproductive Mode

THE INFLUENCE OF ENVIRONMENTAL VARIATION ON GROUP AND INDIVIDUAL SELECTION IN A CRESS.

An experimental study of group and individual selection for leaf area under different patterns of environmental variation is presented. This study, which uses the cress Arabidopsis thaliana, demonstrates that group selection can occur in plants. The response to group selection was always in the expected direction, but surprisingly, the response to individual selection was not. Furthermore the interaction between group and individual selection was significant. Individual selection interfered with the response to group selection whether the two forces were acting in concert or were opposed. The effects of the environmental variation treatments were detected mainly as three-way interactions with group and individual selection. Group selection was more effective in environments that interfered with individual selection, as well as in environments that did not interfere with group selection. These results suggest that the ability of a character to respond to group selection, individual selection, or both will depend on a great many factors and that the relative importance of the different levels of selection can only be determined empirically.

ADAPTATION AT SPECIFIC LOCI. III. FIELD BEHAVIOR AND SURVIVORSHIP DIFFERENCES AMONG COLIAS PGI GENOTYPES ARE PREDICTABLE FROM IN VITRO BIOCHEMISTRY

Previous work on the phosphoglucose isomerase (PGI) polymorphism of Colias butterflies led to predictions concerning aspects of differential survivorship and fecundity among the polymorphic genotypes in the wild. Explicit assumptions underlying these predictions were that functional differences among genotypes at the in vitro biochemical level reflected roughly corresponding differences in vivo, and that the interaction of such differences with the thermal dependence of flight capacity was correctly understood. All those predictions tested were confirmed. We now report experimental designs for testing three more of these predictions. They concern both differential survivorship and the flight activity component of differential fecundity. We find, as predicted: (1) certain heterozygotes, kinetically most effective at low temperature, begin flight earlier in the day than do other genotypes (six replicates); (2) among the three most common genotypes, the order of kinetic effectiveness, i.e., 3/4 > 3/3 >> 4/4, is reflected in asymmetric order of heterotic advantage, 3/4 > 3/3 >> 4/4, in time of flight initiation, breadth of flight time and/or overall flight density through the day (six replicates); (3) under high temperature stress, the usual survivorship advantage of kinetically favored genotypes is reversed, and the three most thermally stable genotypes show better survivorship.--These results strengthen further the case for direct natural selection on this locus. Implications for population sampling practices, for studies of the adaptive organization of metabolism, and for studies of the interaction of genetic variation with patterns of environmental variability are discussed.

Genetic variation in varying environments

SUMMARYIn order to assess the relationship between genetic and environmental variability, a large natural population ofDrosophila melanogasterwas replicated as eight subpopulations, which were subjected to four different patterns of environmental variation. The environmental variable imposed was presence of 15% ethanol in the culture medium. Experimental treatments of the populations were intended to simulate constant environmental conditions, spatial heterogeneity in the environment, and two patterns of temporal environmental variation with different periodicity (long- and short-term temporal variation). Additive genetic and phenotypic variation in sternopleural and abdominal chaeta number, and body weight, were estimated in two successive years, and measurements were taken of the genotype–environment correlation of body weight and sternopleural bristle score with medium type.Additive genetic variance of sternopleural chaeta number and of body weight was significantly greater in the three populations experiencing environmental heterogeneity than in the control population, but additive genetic variance of abdominal bristle score was not clearly affected by exposing populations to varying environments. Temporal environmental variation was equally, if not more, efficient in promoting the maintenance of genetic variation than spatial heterogeneity, but the cycle length of the temporal variation was of no consequence. Specific genotype–environment interactions were not present, therefore adaptation to heterogeneous environments is by selection of heterozygosityper se, rather than by differential survival of genotypes in the alternate niches.