Semiempirical modeling of abiotic and biotic factors controlling ecosystem respiration across eddy covariance sites

In this study we examined ecosystem respiration (R_ECO) data from 104 sites belonging to FLUXNET, the global network of eddy covariance flux measurements. The goal was to identify the main factors involved in the variability of R_ECO: temporally and between sites as affected by climate, vegetation structure and plant functional type (PFT) (evergreen needleleaf, grasslands, etc.). We demonstrated that a model using only climate drivers as predictors of R_ECO failed to describe part of the temporal variability in the data and that the dependency on gross primary production (GPP) needed to be included as an additional driver of R_ECO. The maximum seasonal leaf area index (LAI_MAX) had an additional effect that explained the spatial variability of reference respiration (the respiration at reference temperature T_ref=15 °C, without stimulation introduced by photosynthetic activity and without water limitations), with a statistically significant linear relationship (r²=0.52, P<0.001, n=104) even within each PFT. Besides LAI_MAX, we found that reference respiration may be explained partially by total soil carbon content (SoilC). For undisturbed temperate and boreal forests a negative control of total nitrogen deposition (N_depo) on reference respiration was also identified. We developed a new semiempirical model incorporating abiotic factors (climate), recent productivity (daily GPP), general site productivity and canopy structure (LAI_MAX) which performed well in predicting the spatio‐temporal variability of R_ECO, explaining >70% of the variance for most vegetation types. Exceptions include tropical and Mediterranean broadleaf forests and deciduous broadleaf forests. Part of the variability in respiration that could not be described by our model may be attributed to a series of factors, including phenology in deciduous broadleaf forests and management practices in grasslands and croplands.     

Fitness of insularia morphs of the peppered moth Biston betularia

In recent years the industrial melanic carbonaria morph in the moth Biston betularia (L.) has decreased rapidly in frequency in Britain as air pollution has decreased. The intermediate melanic insularia has shown a variable response. We have estimated the fitness of insularia, compared with the other two morphs, for several data sets. As a rule its fitness lies between that of carbonaria and typical, but nearer to typical and sometimes very close to it. The intermediate position is expected if fitness relates directly to phenotype. The results suggest that insularia may continue polymorphic while carbonaria is likely to disappear. The past high frequency of insularia in South Wales may have been due to an initial increase in insularia frequency before carbonaria reached the region. Differences in dynamics of frequency change in insularia and carbonaria are evidence against induction, which has sometimes been invoked to explain the spread of melanism in this species.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 82 , 359–366.     

Determining parentage and relatedness from genetic markers sheds light on patterns of marine larval dispersal

Population connectivity, the extent to which geographically separated subpopulations exchange individuals and are demographically linked, is important to the scientific management of marine living resources. In theory, the design of a marine protected area, for example, depends on an explicit understanding of how dispersal of planktonic larvae affects metapopulation structure and dynamics ( Botsford et al. 2001 ). In practice, for most marine metazoans with planktonic larvae, the mean and variance of the distances that larvae disperse are unobservable quantities, owing to the small sizes of larvae and the very large volumes through which they are distributed. Simulation of dispersal kernels with models that incorporate oceanography and limited aspects of larval biology and behaviour, coupled with field studies of larval distribution, abundance, and settlement, have provided the best available approaches to date for understanding connectivity of marine populations ( Cowen et al. 2006 ). On the other hand, marine population connectivity has often been judged by spatial variation in the frequencies of alleles and genotypes, although the inherent limitations of this indirect approach to measuring larval dispersal have often been overlooked ( Hedgecock et al. 2007 ). More recently, researchers have turned to genetic methods and highly polymorphic markers that can provide direct evidence of population connectivity in the form of parentage or relatedness of recruits (e.g. Jones et al. 2005 ). In this issue, Christie et al. (2010) provide a particularly elegant example, in which both indirect and novel direct genetic methods are used to determine the major ecological processes shaping dispersal patterns of larval bicolour damselfish Stegastes partitus, a common and widespread reef fish species in the Caribbean Basin ( Fig. 1 ).

Figure 1 Open in figure viewer PowerPoint The bicolour damselfish Stegastes partitus shows substantial self‐recruitment of juveniles to their natal coral reef habitat. Below, a male guarding an artificial nest made from PVC pipe; differential reproductive success of parents or differential survival of egg clutches or the larvae that hatch from them may account for signals of sweepstakes reproductive success in this species (photo credits: top, Bill Harward; bottom, Darren Johnson).     

Ecological partitioning among parapatric cryptic species

Geographic range differences among species may result from differences in their physiological tolerances. In the intertidal zone, marine and terrestrial environments intersect to create a unique habitat, across which physiological tolerance strongly influences range. Traits to cope with environmental extremes are particularly important here because many species live near their physiological limits and environmental gradients can be steep. The snail Melampus bidentatus occurs in coastal salt marshes in the western Atlantic and the Gulf of Mexico. We used sequence data from one mitochondrial (COI) and two nuclear markers (histone H3 and a mitochondrial carrier protein, MCP) to identify three cryptic species within this broad‐ranging nominal species, two of which have partially overlapping geographic ranges. High genetic diversity, low population structure, and high levels of migration within these two overlapping species suggest that historical range limitations do not entirely explain their different ranges. To identify microhabitat differences between these two species, we modelled their distributions using data from both marine and terrestrial environments. Although temperature was the largest factor setting range limits, other environmental components explained features of the ranges that temperature alone could not. In particular, the interaction of precipitation and salinity likely sets physiological limits that lead to range differences between these two cryptic species. This suggests that the response to climatic change in these snails will be mediated by changes to multiple environmental factors, and not just to temperature alone.