Structure and diversity of stream invertebrate assemblages: the influence of temperature with altitude and latitude

1. Structure and diversity of the macroinvertebrate fauna were studied in relation to altitude and latitude among three groups of streams from Ecuador (lowland: 100–600 m, Central Valley: 2600–3100 m, páramo: 3500–4000 m), and one group from the temperate lowland region of Denmark. The streams in the four regions were comparable with regard to physical characteristics such as size, current and substratum.
2. In terms of faunal composition the Ecuadorian highland streams bore more resemblance to the Danish lowland streams than the Ecuadorian lowland streams. The greater similarity between the Ecuadorian highland and the Danish streams, however, was due to the large number of insect families in the Ecuadorian lowlands, many of which were not found in the other regions. Of ten physico-chemical parameters measured, maximum stream temperature explained by far the most variability in faunal composition.
3. The number of insect orders and families increased linearly with maximum stream temperature and therefore decreased with altitude and latitude. A compilation of literature data on insect richness and maximum water temperature from streams around the world confirmed this pattern, yielding a common linear relation for both temperate and tropical streams. This pattern may arise due to a direct temperature effect on speciation but is probably also related to geological history and the influence of climatic changes on stream ecosystems. We estimate that small, tropical, lowland streams have, on average, a two- to fourfold higher species richness than temperate lowland streams.     

Phylogenomic species delimitation and host‐symbiont coevolution in the fungus‐farming ant genus Sericomyrmex Mayr (Hymenoptera: Formicidae): ultraconserved elements (UCEs) resolve a recent radiation

Ants in the Neotropical genus Sericomyrmex Mayr cultivate fungi for food. Both ants and fungi are obligate, coevolved symbionts. The taxonomy of Sericomyrmex is problematic because the morphology of the worker caste is generally homogeneous across all of the species within the genus, species limits are vague, and the relationships between them are unknown. We used ultraconserved elements (UCEs) as genome‐scale markers to reconstruct evolutionary history and to infer species boundaries in Sericomyrmex. We recovered an average of ～990 UCE loci for 88 Sericomyrmex samples from across the geographical range of the genus as well as for five outgroup taxa. Using maximum likelihood and species‐tree approaches, we recovered nearly identical topologies across datasets with 50–95% matrix completeness. We identify nine species‐level lineages in Sericomyrmex, including two new species. This is less than the previously described 19 species, even accounting for two species for which we had no UCE samples, which brings the total number of Sericomyrmex species to 11. Divergence‐dating analyses recovered 4.3 Ma as the crown‐group age estimates for Sericomyrmex, indicating a recent, rapid radiation. We also sequenced mitochondrial cytochrome oxidase subunit I (COI) for 125 specimens. Resolution and support for clades in our COI phylogeny are weak, indicating that COI is not an appropriate species‐delimitation tool. However, taxa within species consistently cluster together, suggesting that COI is useful as a species identification (‘DNA barcoding’) tool. We also sequenced internal transcribed spacer (ITS) and large subunit (LSU) for 32 Sericomyrmex fungal cultivars. The fungal phylogeny confirms that Sericomyrmex fungi are generalized higher‐attine cultivars, interspersed with Trachymyrmex‐associated fungal species, indicating cultivar sharing and horizontal transfer between these two genera. Our results indicate that UCEs offer immense potential for delimiting and resolving relationships of problematic, recently diverged species.     

Modeling Historical Ecology, Thinking about Contemporary Systems

One way to make archaeological trajectories compelling to contemporary audiences is through detailed computer simulation with graphical interfaces that allow students or researchers to explore historical sequences and ask "what if" questions of them. We discuss progress on modeling coupled human systems and ecosystems over long periods in the Mesa Verde region of the U.S. Southwest, a project developed with both research and educational products in mind. The project has many foci, but here we concentrate on fuel-wood availability and its pre-Hispanic use in the pygmy forests of this region. Our preliminary results tend to indicate that wood for fuels became sufficiently limited in this sequence to become a factor of considerable importance in decisions about where to live, how to build, and even whether to remain in the region. The same logic of modeling can be used to study problems of contemporary forest use in other parts of the world.     

Methane bubbles in surface peat cores: in situ measurements

The quantification of greenhouse gas sources and sinks is important to understanding the impact of climate change. Methane (CH₄) is a potent greenhouse gas, which, on a global scale, is released largely as a product of anaerobic microbial decomposition and predominantly from wetlands. A zone of intense CH₄ production just below the water table is thought to contribute significantly to the overall flux from peat bogs. We describe the use of membrane inlet quadrupole mass spectrometry (QMS) to confirm the existence of bubbles, their gaseous concentrations and their localization at a fine spatial resolution within intact peat cores. We use the distribution of the noble gas argon (Ar) and the distinct QMS responses to dissolved and gaseous (bubble) phases to identify trapped bubbles with a resolution of 0.6 mm. Bubbles with CH₄ concentrations of up to 20 kPa were widely distributed in the upper 300 mm of the cores with ～11% of all profiles comprising bubbles. The dissolved concentrations responsible for the bubbles were on average 83±80 μm , indicating lower concentrations relative to other QMS studies. We suggest that if the distinction between dissolved and gaseous phases is not made in studies of CH₄ within peat profiles then the prominence of bubbles is likely to result in overestimates of dissolved CH₄ concentrations. Fluxes of CH₄ from peat as a result of drawdown or other perturbation are likely to be large, rapid and short lived because of bubble burst, and also larger than from peat without bubbles. We suggest that the dynamics of fluxes need to be modelled taking into account both gaseous and dissolved phases. Estimates of potential fluxes that assume CH₄ is dissolved are likely to overestimate fluxes if the gaseous phase has not been taken into account.     

Declining coral calcification in massive Porites in two nearshore regions of the northern Great Barrier Reef

Temporal and spatial variation in the growth parameters skeletal density, linear extension and calcification rate in massive Porites from two nearshore regions of the northern Great Barrier Reef (GBR) were examined over a 16‐year study period. Calcification rates in massive Porites have declined by approximately 21% in two regions on the GBR ～450 km apart. This is a function primarily of a decrease in linear extension (～16%) with a smaller decline in skeletal density (～6%) and contrasts with previous studies on the environmental controls on growth of massive Porites on the GBR. Changes in the growth parameters were linear over time. Averaged across colonies, skeletal density declined over time from 1.32 g cm^?3 (SE = 0.017) in 1988 to 1.25 g cm^?3 (0.013) in 2003, equivalent to 0.36% yr^?1 (0.13). Annual extension declined from 1.52 cm yr^?1 (0.035) to 1.28 cm yr^?1 (0.026), equivalent to 1.02% yr^?1 (0.39). Calcification rates (the product of skeletal density and annual extension) declined from 1.96 g cm^?2 yr^?1 (0.049) to 1.59 g cm^?2 yr^?1 (0.041), equivalent to 1.29% yr^?1 (0.30). Mean annual seawater temperatures had no effect on skeletal density, but a modal effect on annual extension and calcification with maxima at ～26.7 °C. There were minor differences in the growth parameters between regions. A decline in coral calcification of this magnitude with increasing seawater temperatures is unprecedented in recent centuries based on analysis of growth records from long cores of massive Porites. We discuss the decline in calcification within the context of known environmental controls on coral growth. Although our findings are consistent with studies of the synergistic effect of elevated seawater temperatures and pCO₂ on coral calcification, we conclude that further data on seawater chemistry of the GBR are required to better understand the links between environmental change and effects on coral growth.     

Wood density predicts plant damage and vegetative recovery rates caused by cyclone disturbance in tropical rainforest tree species of North Queensland,Australia

Abstract The ability to withstand disturbance (resistance) and the ability to recover biomass following disturbance (resilience) were investigated in Australian wet tropical rainforest tree species. These two attributes are expected to be negatively correlated, because investment of biomass in structural support (conferring resistance) results in trees exhibiting high wood densities and slow growth rates, and vice versa. We examined species’ responses to disturbance caused by a severe tropical cyclone to test this hypothesized trade‐off. We assessed cyclone damage in six species in three Mabi rainforest fragments on the Atherton Tablelands. Species differed in the proportion of individuals within four damage categories (minor damage, severe branch damage, snapped, uprooted). Resistance was positively related to wood density. We found a positive correlation between the proportion of trees experiencing minor damage only and wood density, supporting the hypothesized association between resistance and mechanical strength. Among the subset of trees in which stems snapped, rates of resprouting differed between species and were highest in low wood density species and lowest in species with highest wood density. Resilience, characterized as the ability to recover biomass following disturbance and estimated as growth rate standardized for stem diameter at breast height (g day^?1 · mm^?1), was negatively related to wood density. Thus, species with low wood densities were more likely to suffer stem and branch damage owing to cyclonic winds, but also demonstrated highest resprouting and fastest responses in terms of redeveloping biomass in the 8 months following disturbance. This suggests that a species’ position along the resistance–resilience spectrum can be predicted by mean wood density, which may allow managers to predict species’ responses to future cyclones. Our findings also provide mechanistic evidence for the ‘direct regeneration’ model of post‐cyclone succession, where response is characterized by resprouting and species composition is unchanged.     

Sources of plant-derived carbon and stability of organic matter in soil: implications for global change

Alterations in forest productivity and changes in the relative proportion of above‐ and belowground biomass may have nonlinear effects on soil organic matter (SOM) storage. To study the influence of plant litter inputs on SOM accumulation, the Detritus Input Removal and Transfer (DIRT) Experiment continuously alters above‐ and belowground plant inputs to soil by a combination of trenching, screening, and litter addition. Here, we used biogeochemical indicators [i.e., cupric oxide extractable lignin‐derived phenols and suberin/cutin‐derived substituted fatty acids (SFA)] to identify the dominant sources of plant biopolymers in SOM and various measures [i.e., soil density fractionation, laboratory incubation, and radiocarbon‐based mean residence time (MRT)] to assess the stability of SOM in two contrasting forests within the DIRT Experiment: an aggrading deciduous forest and an old‐growth coniferous forest. In the deciduous forest, removal of both above‐ and belowground inputs increased the total amount of SFA over threefold compared with the control, and shifted the SFA signature towards a root‐dominated source. Concurrently, light fraction MRT increased by 101 years and C mineralization during incubation decreased compared with the control. Together, these data suggest that root‐derived aliphatic compounds are a source of SOM with greater relative stability than leaf inputs at this site. In the coniferous forest, roots were an important source of soil lignin‐derived phenols but needle‐derived, rather than root‐derived, aliphatic compounds were preferentially preserved in soil. Fresh wood additions elevated the amount of soil C recovered as light fraction material but also elevated mineralization during incubation compared with other DIRT treatments, suggesting that not all of the added soil C is directly stabilized. Aboveground needle litter additions, which are more N‐rich than wood debris, resulted in accelerated mineralization of previously stored soil carbon. In summary, our work demonstrates that the dominant plant sources of SOM differed substantially between forest types. Furthermore, inputs to and losses from soil C pools likely will not be altered uniformly by changes in litter input rates.     

Factors Influencing Reporting and Harvest Probabilities in North American Geese

ABSTRACT We assessed variation in reporting probabilities of standard bands among species, populations, harvest locations, and size classes of North American geese to enable estimation of unbiased harvest probabilities. We included reward (US$10, $20, $30, $50, or $100) and control ($0) banded geese from 16 recognized goose populations of 4 species: Canada (Branta canadensis), cackling (B. hutchinsii), Ross's (Chen rossii), and snow geese (C. caerulescens). We incorporated spatially explicit direct recoveries and live recaptures into a multinomial model to estimate reporting, harvest, and band-retention probabilities. We compared various models for estimating harvest probabilities at country (United States vs. Canada), flyway (5 administrative regions), and harvest area (i.e., flyways divided into northern and southern sections) scales. Mean reporting probability of standard bands was 0.73 (95% CI = 0.69–0.77). Point estimates of reporting probabilities for goose populations or spatial units varied from 0.52 to 0.93, but confidence intervals for individual estimates overlapped and model selection indicated that models with species, population, or spatial effects were less parsimonious than those without these effects. Our estimates were similar to recently reported estimates for mallards (Anas platyrhynchos). We provide current harvest probability estimates for these populations using our direct measures of reporting probability, improving the accuracy of previous estimates obtained from recovery probabilities alone. Goose managers and researchers throughout North America can use our reporting probabilities to correct recovery probabilities estimated from standard banding operations for deriving spatially explicit harvest probabilities.     

Phylogeny‐based species delimitations and the evolution of host associations in symbiotic zoanthids (Anthozoa,Zoanthidea) of the wider Caribbean region

Zoanthids are marine cnidarians with simple morphologies that challenge our ability to delineate species. Phylogenetic analyses of internal transcribed spacer (ITS) sequences are consistent with six morphologically described species from the wider Caribbean region, and reveal four additional species that were not previously recognized. Histological examinations of unidentified species reveal cryptic Isozoanthus and Edwardsiidae (Actiniaria) species. Observations of zoanthids in situ reveal geographic distributions that range from regional to trans‐Atlantic. ITS and 16S data are consistent with hypotheses of paraphyly in some higher taxa of zoanthids; however, the clades of zoanthids recovered in both analyses can largely be defined by their host associations, thereby supporting phylogenetic conservatism in zoanthid–host association evolution. The single clear example of a zoanthid switching hosts was accompanied by a compensatory loss of endosymbiosis, which maintained the match in photosynthetic symbioses between zoanthids and sponge hosts. © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2009, 156 , 223–238.     

Regional examination shows potential for native feedstock options for cellulosic biofuel production

Kentucky, as with many regions around the globe, has a relatively long growing season with significant rainfall that could produce sizeable quantities of perennial herbaceous and woody biomass on land that does not compete with food crops. Additionally, there are limited options for renewable power production from low carbon sources such as solar-photovoltaic, wind and hydroelectric. Recent studies have shown that producing renewable energy from perennial cellulosic crops, as opposed to starch-based biofuel crops, will have a carbon-mitigating outcome. Currently, there is a lack of data regarding regionally suitable genotypes. Herein, we establish baseline values for multiple entry selections of three native C4 grass species, switchgrass (SW) ( Panicum virgatum L.), eastern gamagrass (EG) (Trispicum dactyloides L. ) and big bluestem (BB) (Andropogon gerardii Vitman ) . Yield potential examined over 7 years showed that environment, species and entries had a significant impact on yield, but EG had higher total yield over the duration of the study. Cellulosic biofuel potential was examined by measurement of saccharification efficiency, relative lignocellulosic energy density, cellulose content and lignin content during three growing seasons. EG had significantly higher digestibility rate than SW and BB. Underlying this was a negative correlation between lignification and saccharification efficiency. However, higher lignin content and higher cellulose content among SW entries resulted in higher energy density relative to EG and BB. These data reveal that locally bred EG varieties were most suited to cellulosic ethanol production under the growing conditions of central Kentucky, USA, compared with SW and BB and suggest the importance of regional examination.