Climatic forcing and larval dispersal capabilities shape the replenishment of fishes and their habitat‐forming biota on a tropical coral reef

Fluctuations in marine populations often relate to the supply of recruits by oceanic currents. Variation in these currents is typically driven by large‐scale changes in climate, in particular ENSO (El Nino Southern Oscillation). The dependence on large‐scale climatic changes may, however, be modified by early life history traits of marine taxa. Based on eight years of annual surveys, along 150 km of coastline, we examined how ENSO influenced abundance of juvenile fish, coral spat, and canopy‐forming macroalgae. We then investigated what traits make populations of some fish families more reliant on the ENSO relationship than others. Abundance of juvenile fish and coral recruits was generally positively correlated with the Southern Oscillation Index (SOI), higher densities recorded during La Niña years, when the ENSO‐influenced Leeuwin Current is stronger and sea surface temperature higher. The relationship is typically positive and stronger among fish families with shorter pelagic larval durations and stronger swimming abilities. The relationship is also stronger at sites on the coral back reef, although the strongest of all relationships were among the lethrinids (r = .9), siganids (r = .9), and mullids (r = .8), which recruit to macroalgal meadows in the lagoon. ENSO effects on habitat seem to moderate SOI–juvenile abundance relationship. Macroalgal canopies are higher during La Niña years, providing more favorable habitat for juvenile fish and strengthening the SOI effect on juvenile abundance. Conversely, loss of coral following a La Niña‐related heat wave may have compromised postsettlement survival of coral dependent species, weakening the influence of SOI on their abundance. This assessment of ENSO effects on tropical fish and habitat‐forming biota and how it is mediated by functional ecology improves our ability to predict and manage changes in the replenishment of marine populations.     

Contrasting patterns of density‐dependent selection at different life stages can create more than one fast–slow axis of life‐history variation

There has been much recent research interest in the existence of a major axis of life‐history variation along a fast–slow continuum within almost all major taxonomic groups. Eco‐evolutionary models of density‐dependent selection provide a general explanation for such observations of interspecific variation in the "pace of life." One issue, however, is that some large‐bodied long‐lived “slow” species (e.g., trees and large fish) often show an explosive “fast” type of reproduction with many small offspring, and species with “fast” adult life stages can have comparatively “slow” offspring life stages (e.g., mayflies). We attempt to explain such life‐history evolution using the same eco‐evolutionary modeling approach but with two life stages, separating adult reproductive strategies from offspring survival strategies. When the population dynamics in the two life stages are closely linked and affect each other, density‐dependent selection occurs in parallel on both reproduction and survival, producing the usual one‐dimensional fast–slow continuum (e.g., houseflies to blue whales). However, strong density dependence at either the adult reproduction or offspring survival life stage creates quasi‐independent population dynamics, allowing fast‐type reproduction alongside slow‐type survival (e.g., trees and large fish), or the perhaps rarer slow‐type reproduction alongside fast‐type survival (e.g., mayflies—short‐lived adults producing few long‐lived offspring). Therefore, most types of species life histories in nature can potentially be explained via the eco‐evolutionary consequences of density‐dependent selection given the possible separation of demographic effects at different life stages.     

Individual-based model of spatio-temporal dynamics of mixed forest stands

This research presents the results of constructing and parameterizing an individual-based model of spatiotemporal dynamics of mixed forest stands. The model facilitates computerized experiments with forest stands having different combinations of species and age structures. These forest stands grow on temperate areas where light is the main system-forming factor that shapes and develops forest ecosystems. The model TEMFORM (TEMperate FORests Model) is developed with few equations and parameters, most of which can be estimated using standard forest inventory data. Parameterization of the model used the growth tables of a set of basic forest-forming species in Far East Russia. Simulation results of the development of the natural single- and mixed-species stands and the effects of different types of disturbances on the stand dynamics and compositions are presented.     

SOCIAL SELECTION AND THE EVOLUTION OF ANIMAL SIGNALS

Social selection is presented here as a parallel theory to sexual selection and is defined as a selective force that occurs when individuals change their own social behaviors, responding to signals sent by conspecifics in a way to influence the other individuals' fitness. I analyze the joint evolution of a social signal and behavioral responsiveness to the signal by a quantitative-genetic model. The equilibria of average phenotypes maintained by a balance of social selection and natural selection and their stability are examined for two alternative assumptions on behavioral responsiveness, neutral and adaptive. When behavioral responsiveness is neutral on fitness, a rapid evolution by runaway selection occurs only with enough genetic covariance between the signal and responsiveness. The condition for rapid evolution also depends on natural selection and the number of interacting individuals. When signals convey some information on signalers (e.g., fighting ability), behavioral responsiveness is adaptive such that a receiver's fitness is also influenced by the signal. Here there is a single point of equilibrium. The equilibrium point and its stability do not depend on the genetic correlation. The condition needed for evolution is that the signal is beneficial for receivers, which results from reliability of the signal. Frequency-dependent selection on responsiveness has almost no influence on the equilibrium and the rate of evolution.     

Size-dependent mortality in a Neotropical savanna tree: the role of height-related adjustments in hydraulic architecture and carbon allocation

Size-related changes in hydraulic architecture, carbon allocation and gas exchange of Sclerolobium paniculatum (Leguminosae), a dominant tree species in Neotropical savannas of central Brazil (Cerrado), were investigated to assess their potential role in the dieback of tall individuals. Trees greater than ∼6-m-tall exhibited more branch damage, larger numbers of dead individuals, higher wood density, greater leaf mass per area, lower leaf area to sapwood area ratio (LA/SA), lower stomatal conductance and lower net CO₂ assimilation than small trees. Stem-specific hydraulic conductivity decreased, while leaf-specific hydraulic conductivity remained nearly constant, with increasing tree size because of lower LA/SA in larger trees. Leaves were substantially more vulnerable to embolism than stems. Large trees had lower maximum leaf hydraulic conductance ( K _leaf) than small trees and all tree sizes exhibited lower K _leaf at midday than at dawn. These size-related adjustments in hydraulic architecture and carbon allocation apparently incurred a large physiological cost: large trees received a lower return in carbon gain from their investment in stem and leaf biomass compared with small trees. Additionally, large trees may experience more severe water deficits in dry years due to lower capacity for buffering the effects of hydraulic path-length and soil water deficits.     

Consumer pressure, seed versus safe-site limitation, and plant population dynamics

Plants often suffer reductions in fecundity due to insect herbivory. Whether this loss of seeds has population-level consequences is much debated and often unknown. For many plants, particularly those with long-lived seedbanks, it is frequently asserted that herbivores have minimal impacts on plant abundance because safe-site availability rather than absolute seed number determines the magnitude of future plant recruitment and hence population abundance. However, empirical tests of this assertion are generally lacking and the interplay between herbivory, spatio-temporal variability in seed- or safe-site-limited recruitment, and seedbank dynamics is likely to be complex. Here we use a stochastic simulation model to explore how changes in the spatial and temporal frequency of seed-limited recruitment, the strength of density-dependent seedling survival, and longevity of seeds in the soil influence the population response to herbivory. Model output reveals several surprising results. First, given a seedbank, herbivores can have substantial effects on mean population abundance even if recruitment is primarily safe-site-limited in either time or space. Second, increasing seedbank longevity increases the population effects of herbivory, because annual reductions in seed input due to herbivory are accumulated in the seedbank. Third, population impacts of herbivory are robust even in the face of moderately strong density-dependent seedling mortality. These results imply that the conditions under which herbivores influence plant population dynamics may be more widespread than heretofore expected. Experiments are now needed to test these predictions. Received: 3 November 1999 / Accepted: 15 February 2000     

Adsorption and immobilisation of human insulin on graphene monoxide,silicon carbide and boron nitride nanosheets investigated by molecular dynamics simulation

The adsorption and immobilisation of human insulin onto the bio-compatible nanosheets including graphene monoxide, silicon carbide and boron nitride nanosheets were studied by molecular dynamics simulation at the temperature of 310 K. After equilibration, heating and 100 ns production molecular dynamic runs, it was found that the insulin was adsorbed and immobilised onto the considered surfaces in a native folded state. The structural parameters, including root-mean-square deviation and fluctuation, surface accessible solvent area, radius of gyration (R_g) and the distance between the centre of the mass of immobilised protein and the surface of the considered nanosheets, were measured, analysed and discussed. The energetics of the studied systems such as the interaction energy between protein and nanosheet was also measured and addressed. The discussions were centred on the structural and energetic parameters of the protein and nanosheets, including charge density, hydrophobicity, hydrophilicity and residue polarity. The results also showed that the active site of C-termini of chain B played an important role in the adsorption process and this could be helpful in the protection of insulin in its smart delivery and release applications.