Diagnosing and assessing uncertainties of terrestrial ecosystem models in a multimodel ensemble experiment: 2. Carbon balance

This paper examines carbon stocks and their relative balance in terrestrial ecosystems simulated by Biome‐BGC, LPJ, and CASA in an ensemble model experiment conducted using the Terrestrial Observation and Prediction System. We developed the Hierarchical Framework for Diagnosing Ecosystem Models to separate the simulated biogeochemistry into a cascade of functional tiers and examine their characteristics sequentially. The analyses indicate that the simulated biomass is usually two to three times higher in Biome‐BGC than LPJ or CASA. Such a discrepancy is mainly induced by differences in model parameters and algorithms that regulate the rates of biomass turnover. The mean residence time of biomass in Biome‐BGC is estimated to be 40–80 years in temperate/moist climate regions, while it mostly varies between 5 and 30 years in CASA and LPJ. A large range of values is also found in the simulated soil carbon. The mean residence time of soil carbon in Biome‐BGC and LPJ is ～200 years in cold regions, which decreases rapidly with increases of temperature at a rate of ～10 yr °C^?1. Because long‐term soil carbon pool is not simulated in CASA, its corresponding mean residence time is only about 10–20 years and less sensitive to temperature. Another key factor that influences the carbon balance of the simulated ecosystem is disturbance caused by wildfire, for which the algorithms vary among the models. Because fire emissions are balanced by net ecosystem production (NEP) at steady states, magnitudes, and spatial patterns of NEP vary significantly as well. Slight carbon imbalance may be left by the spin‐up algorithm of the models, which adds uncertainty to the estimated carbon sources or sinks. Although these results are only drawn on the tested model versions, the developed methodology has potential for other model exercises.     

Whole-body mechanics and kinematics of terrestrial locomotion in the Elegant-crested Tinamou Eudromia elegans

Whereas humans and certain birds experience an abrupt change in locomotor dynamics when shifting from walks to runs, a smooth walk–run transition characterizes many ground-dwelling birds. This study defines the biomechanical distinction between walks and runs in the Elegant-crested Tinamou Eudromia elegans using ground reaction forces. Three birds were filmed at 250 Hz from a lateral view as they moved over a force plate built into a trackway. Centre of mass mechanics and kinematic variables were analysed in 81 steady-speed trials that represented a speed range from 0.66 to 2.78 m/s. E. elegans undergoes two speed-related changes in locomotor mechanics. The first is a shift from walking strides that utilize vaulting mechanics to low-speed runs that exhibit bouncing mechanics; this transition occurs at Froude numbers between 0.4 and 0.6. Such low-speed runs exhibit duty factors exceeding 0.5 and, hence, lack an aerial phase between steps. The second transition, from grounded running to aerial running, occurs when duty factors decrease below 0.5. Grounded running in birds may enhance vision by stabilizing visual stimuli over the retina. The eventual incorporation of an aerial phase during running enables increased locomotor speeds primarily through longer stride lengths.     

Bennettitalean leaf cuticle fragments (here Anomozamites and Pterophyllum) can be used interchangeably in stomatal frequency‐based palaeo‐CO2 reconstructions

Abstract: Bennettites are an abundant and frequently well‐preserved component of many Mesozoic fossil floras, often playing an important ecological role in flood plain vegetation communities. During a recent study focusing on stomatal indices of Triassic–Jurassic fossil plants, it became evident that the leaf fragments of two bennettite genera Anomozamites Schimper (1870) emend. Harris (1969) and Pterophyllum Brongniart (1825) display a significant overlap of leaf shape as well as cuticular characters. Owing to the preference of recognition of single taxa (ideally species) for the stomatal method, we use a database of 70 leaf fragments of Anomozamites and Pterophyllum compressions from five isotaphonomic Late Triassic sedimentary beds of Astartekløft in East Greenland to test whether leaf and cuticle fragments of the two genera can be separated using a range of quantitative and qualitative morphological and statistical analyses. None of the observed characters – including stomatal frequencies – could be applied to separate the fragments of the two genera into well‐defined groups. Our results therefore indicate that fragmented material and dispersed cuticles cannot be utilized to distinguish between Anomozamites or Pterophyllum at the genus level, but that instead these cuticle fragments may be used interchangeably as stomatal proxies. Classification of fossil leaves into either of these genera is thus only possible given adequate preservation of macro‐morphology and is not possible based solely on cuticle morphology. We suggest that this large inter‐ and intra‐generic morphological variation in both leaf and cuticle traits within Anomozamites and Pterophyllum may be related to the bennettites’ role as understory plants, experiencing a range of micro‐environmental conditions, perhaps depending mainly on sun exposure. Based on the results obtained in this study, we conclude that Anomozamites and Pterophyllum cuticle fragments can be employed interchangeably in palaeo [CO₂] reconstructions based on the stomatal method, thus potentially annexing a plethora of bennettitalean fossil plant material as CO₂ proxies, including dispersed cuticles.     

Winter Habitat Selection by Canada Lynx in Maine: Prey Abundance or Accessibility?

Abstract: We related winter habitat selection by Canada lynx (Lynx canadensis), relative abundance of snowshoe hares (Lepus americanus), and understory stem densities to evaluate whether lynx select stands with the greatest snowshoe hare densities or the greatest prey accessibility. Lynx (3 F, 3 M) selected tall (4.4-7.3 m) regenerating clear-cuts (11-26 yr postharvest) and established partially harvested stands (11-21 yr postharvest) and selected against short (3.4-4.3 m) regenerating clear-cuts, recent partially harvested stands (1-10 yr), mature second-growth stands (>40 yr), and roads and their edges (30 m on either side of roads). Lynx selected stands that provided intermediate to high hare density and intermediate cover for hares (i.e., prey access) but exhibited lower relative preference for stand types with highest hare densities where coniferous saplings exceeded 14,000 stems/ha.     

Effects of Ear Removal on Photosynthesis, Carbohydrate Accumulation and on the Distribution of Assimilated 14C in Wheat

Removal of an ear from a tiller of a wheat plant growing inthe field did not result in any marked change in the net photosyntheticrate of the subtending flag leaf, even during the period whenthe ear would normally have received large amounts of assimilatefrom the flag leaf. Following ear removal, there was an increasein the amount of ethanol-soluble and ethanol-insoluble carbohydratesin the remaining organs of the tiller. ¹⁴C labelling studiesshowed that a new pattern of translocation was established within2–3 days of ear removal, and the tiller exported assimilateto other tillers on the plant, and possibly to the roots.     

Characterization of 16 highly variable tetranucleotide microsatellite loci for Oregon chub (Oregonichthys crameri) and cross amplification in Umpqua chub (O. kalawatseti)

We describe the isolation and development of 16 polymorphic tetranucleotide microsatellite loci for the endangered Oregon chub (Oregonichthys crameri). Two loci appear to be duplicated. For the remaining 14 loci, we observed between three and 19 alleles per locus in a sample of 42 fish. Thirteen of these loci were also polymorphic in the closely related Umpqua chub (O. kalawatseti). These loci will aid in our understanding of the molecular ecology and conservation of these two species.     

Do extraordinarily high growth rates in Permo‐Triassic dicynodonts (Therapsida,Anomodontia) explain their success before and after the end‐Permian extinction?

Dicynodonts were the most diverse and abundant herbivorous therapsids of the Permo‐Triassic. They include Lystrosaurus, one of the few taxa known to survive the end‐Permian extinction and the most abundant tetrapod during the Early Triassic postextinction recovery. Explanations for the success of Lystrosaurus and other dicynodonts remain controversial. This study presents an assessment of dicynodont growth patterns using bone histology, with special focus on taxa associated with the end‐Permian extinction event. Bone histological analysis reveals a high cortical thickness throughout the clade, perhaps reflecting a phylogenetic constraint. Growth rings are absent early in ontogeny, and combined with high vascular density, indicate rapid, sustained growth up to the subadult stage. Extraordinarily enlarged vascular channels are present in the midcortex of many dicynodonts, including adults, and may have facilitated a more efficient assimilation of nutrients and rapid bone growth compared to other therapsids. Both increased channel density and enlarged vascular channels evolved at or near the base of major radiations of dicynodonts, implying that the changes in growth and life history they represent may have been key to the success of dicynodonts. Furthermore, this exceptionally rapid growth to adulthood may have contributed to the survival of Lystrosaurus during the end‐Permian extinction and its dominance during the postextinction recovery period. © 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 160 , 341–365.     

Ecological patterns and genetic analysis of post‐dispersal seed predation in sunflower (Helianthus annuus) crop‐wild hybrids

Crop‐wild hybridization has been documented in many cultivated species, but the ecological and genetic factors that influence the likelihood or rate that cultivar alleles will introgress into wild populations are poorly understood. Seed predation is one factor that could mitigate the spread of otherwise advantageous cultivar alleles into the wild by reducing seedling recruitment of crop‐like individuals in hybrid populations. Seed predation has previously been linked to several seed characters that differ between cultivated and wild sunflower, such as seed size and oil content. In this study, seed morphological and nutritional characters were measured in a segregating population of sunflower crop‐wild hybrids and wild and cultivated lines. Seed predation rates among lines were then assessed in the field. The relationship between seed predation and seed characters was investigated and quantitative trait loci (QTL) were mapped for all traits. There was no effect of seed type (hybrid vs. parents) on seed predation, although a trend toward more early predation of wild seeds was observed. Within the hybrids, seed predators preferred seeds that contained more oil and energy but were lower in fibre. The relationship between seed predation and oil content was supported by co‐localized QTL for these traits on one linkage group. These results suggest that oil content may be a more important determinant of seed predation than seed size and provide molecular genetic evidence for this relationship. The cultivar allele was also found to increase predation at all QTL, indicating that post‐dispersal seed predation may mitigate the spread of cultivar alleles into wild populations.