A BASAL MIXOSAURID ICHTHYOSAUR FROM THE MIDDLE TRIASSIC OF CHINA

Abstract:  New specimens of a mixosaurid ichthyosaur are described from the People's Republic of China. They consist of an almost complete skull, forefin and shoulder girdle of a single individual, and a second partial skull from the Anisian Guanling Formation of Guizhou Province that belongs to the same taxon. A phylogenetic analysis shows this species to be the sister-taxon of all other mixosaurids. It is distinguished from Mixosaurus , Contecotpalatus and Phalarodon by features of its dentition and cranial morphology. There is only one maxillary tooth row. The posterior maxillary teeth are blunt and rounded, and much wider than the premaxillary teeth, but they are not strongly elongated anteroposteriorly. The teeth are subthecodontously implanted. The postorbital skull segment is long. The jugal-quadratojugal notch is deep and these two elements remain separated externally. The postorbital separates supratemporal and postfrontal. There are no postaxial ossifications of the forefin. Autapomorphies include a long ventral process of the postorbital lamina of the postorbital as well as characteristic morphologies of the coracoid and humerus. The material is therefore clearly distinguished from other known mixosaurids. It can be referred, on the basis of the features of the humerus and coracoid, to Mixosaurus maotaiensis Young, 1965. As it is generically distinct from Mixosaurus , a new generic name, Barracudasaurus gen. nov. is proposed. The phylogenetic relevance of the external separation of jugal and quadratojugal in some Triassic ichthyosaurs is discussed and it is concluded that it does not demonstrate the initial presence of a lower temporal fenestra in ichthyosaurs. The new material suggests that mixosaurids could have also originated in the Eastern rather than the Western Tethys, as previously assumed.     

Lake responses to reduced nutrient loading – an analysis of contemporary long-term data from 35 case studies

1. This synthesis examines 35 long‐term (5–35 years, mean: 16 years) lake re‐oligotrophication studies. It covers lakes ranging from shallow (mean depth <5 m and/or polymictic) to deep (mean depth up to 177 m), oligotrophic to hypertrophic (summer mean total phosphorus concentration from 7.5 to 3500 μg L^?1 before loading reduction), subtropical to temperate (latitude: 28–65°), and lowland to upland (altitude: 0–481 m). Shallow north‐temperate lakes were most abundant. 2. Reduction of external total phosphorus (TP) loading resulted in lower in‐lake TP concentration, lower chlorophyll a (chl a) concentration and higher Secchi depth in most lakes. Internal loading delayed the recovery, but in most lakes a new equilibrium for TP was reached after 10–15 years, which was only marginally influenced by the hydraulic retention time of the lakes. With decreasing TP concentration, the concentration of soluble reactive phosphorus (SRP) also declined substantially. 3. Decreases (if any) in total nitrogen (TN) loading were lower than for TP in most lakes. As a result, the TN : TP ratio in lake water increased in 80% of the lakes. In lakes where the TN loading was reduced, the annual mean in‐lake TN concentration responded rapidly. Concentrations largely followed predictions derived from an empirical model developed earlier for Danish lakes, which includes external TN loading, hydraulic retention time and mean depth as explanatory variables. 4. Phytoplankton clearly responded to reduced nutrient loading, mainly reflecting declining TP concentrations. Declines in phytoplankton biomass were accompanied by shifts in community structure. In deep lakes, chrysophytes and dinophytes assumed greater importance at the expense of cyanobacteria. Diatoms, cryptophytes and chrysophytes became more dominant in shallow lakes, while no significant change was seen for cyanobacteria. 5. The observed declines in phytoplankton biomass and chl a may have been further augmented by enhanced zooplankton grazing, as indicated by increases in the zooplankton : phytoplankton biomass ratio and declines in the chl a : TP ratio at a summer mean TP concentration of <100–150 μg L^?1. This effect was strongest in shallow lakes. This implies potentially higher rates of zooplankton grazing and may be ascribed to the observed large changes in fish community structure and biomass with decreasing TP contribution. In 82% of the lakes for which data on fish are available, fish biomass declined with TP. The percentage of piscivores increased in 80% of those lakes and often a shift occurred towards dominance by fish species characteristic of less eutrophic waters. 6. Data on macrophytes were available only for a small subsample of lakes. In several of those lakes, abundance, coverage, plant volume inhabited or depth distribution of submerged macrophytes increased during oligotrophication, but in others no changes were observed despite greater water clarity. 7. Recovery of lakes after nutrient loading reduction may be confounded by concomitant environmental changes such as global warming. However, effects of global change are likely to run counter to reductions in nutrient loading rather than reinforcing re‐oligotrophication.     

Habitat shifts of endangered species under altered climate conditions: importance of biotic interactions

Predicting changes in potential habitat for endangered species as a result of global warming requires considering more than future climate conditions; it is also necessary to evaluate biotic associations. Most distribution models predicting species responses to climate change include climate variables and occasionally topographic and edaphic parameters, rarely are biotic interactions included. Here, we incorporate biotic interactions into niche models to predict suitable habitat for species under altered climates. We constructed and evaluated niche models for an endangered butterfly and a threatened bird species, both are habitat specialists restricted to semiarid shrublands of southern California. To incorporate their dependency on shrubs, we first developed climate‐based niche models for shrubland vegetation and individual shrub species. We also developed models for the butterfly's larval host plants. Outputs from these models were included in the environmental variable dataset used to create butterfly and bird niche models. For both animal species, abiotic–biotic models outperformed the climate‐only model, with climate‐only models over‐predicting suitable habitat under current climate conditions. We used the climate‐only and abiotic–biotic models to calculate amounts of suitable habitat under altered climates and to evaluate species' sensitivities to climate change. We varied temperature (+0.6, +1.7, and +2.8 °C) and precipitation (50%, 90%, 100%, 110%, and 150%) relative to current climate averages and within ranges predicted by global climate change models. Suitable habitat for each species was reduced at all levels of temperature increase. Both species were sensitive to precipitation changes, particularly increases. Under altered climates, including biotic variables reduced habitat by 68–100% relative to the climate‐only model. To design reserve systems conserving sensitive species under global warming, it is important to consider biotic interactions, particularly for habitat specialists and species with strong dependencies on other species.     

Environmental indicator potential of the dominant litter decomposer,Talitriator africana (Crustacea,Amphipoda) in Afrotemperate forests

Abstract Environmental disturbance and condition are complex concepts to define and measure in forested landscapes. The highly fragmented Afrotemperate forests in South Africa are under increasing pressure from the agricultural matrix and resource harvesting. Rapid assessment of forest condition and disturbance would aid their conservation management. The terrestrial amphipod, Talitriator africana, dominates the decomposer guild of Afrotemperate forests and has been previously identified as a potential indicator of forest condition. Using four published studies, we further evaluate this species' suitability as an environmental indicator of forest disturbance and condition. Amphipods were consistently more abundant at highly disturbed forest edges compared to less disturbed interiors, and less abundant in deep litter compared to shallow litter. High amphipod numbers in shallow litter was correlated with low predator abundance. Shallow litter may in turn be caused by more efficient breakdown of litter by amphipods at forest edges. Numbers varied considerably between sites and years, but showed a consistent trend of high abundance with increasing forest disturbance. The latter, and the ease with which it can be surveyed and identified, make a compelling case for the use of T. africana as a single‐species environmental indicator of forest disturbance. However, relatively broad tolerances and the difficulty of calibrating the abundance‐disturbance relationship over a wide region limits the indicator value of this species to the local landscape, where disturbance effects vary only in their intensity (as opposed to type) across forests.     

Comparative anatomy and morphology of fertile complexes of Prumnopitys and Afrocarpus species (Podocarpaceae) as revealed by histology and NMR imaging, and their relevance to systematics

Fertile complexes (individual reproductive units of ovulate cones) of three Prumnopitys species and Afrocarpus falcatus (Podocarpaceae) were subjected to histological examination and non-destructive NMR imaging. The latter technique allowed the display, frame-by-frame analysis and electronic 'dissection' of internal structures such as the number and courses of vascular traces and resin canals and their morphology. Characters of these internal structures distinguished all three Prumnopitys species from each other and thus were shown to be taxonomically diagnostic. Fertile complexes of Prumnopitys andina and P. taxifolia were most similar, possessing simple vascular traces and few unbranched resin canals. Those of P. ferruginea were very different and possessed an interconnected network of resin ducts within the sarcotesta. These findings are congruent with relationships inferred from molecular phylogenetic studies, in which two subclades were recovered within Prumnopitys . The anatomy of the female fertile complexes of Afrocarpus falcatus was very distinct from all Prumnopitys species analysed. Its most distinctive feature was the existence of a complex network of radial vascular strands originating from within the outer layers of the sarcotesta and penetrating the inner layers of the fertile complex. The surface texture and morphology of the sclerotesta of the seed was also unique to each species.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 145 , 295–316.     

Landscape genetics, historical isolation and cross-Andean gene flow in the wax palm, Ceroxylon echinulatum (Arecaceae)

Knowledge of the role of landscapes in shaping genetic connectivity and divergence is essential for understanding patterns of biogeography and diversity. This is particularly relevant for the Andes region, a major biodiversity hotspot of relatively recent origin. We examined the phylogeography and landscape genetics of the Andean wax palm Ceroxylon echinulatum (Arecaceae) that occurs in two narrow bands of montane forests on each side of the Andes in Ecuador and northeastern Peru. First, we tested the hypothesis of C. echinulatum being a geographic cline species crossing the Andes in the Amotape–Huancabamba zone (AHZ) of southern Ecuador/northern Peru, as indicated by observations on fruit morphology. Second, we assessed the timeframe of cross-Andean divergence, and third, we investigated the impact of contemporary and historical landscape features on observed spatio-genetic patterns. Individual-based Bayesian clustering (BC) identified a northeastern, southeastern, southwestern, and northwestern cluster, with areas of genetic discontinuity coinciding with the Andes and the Giron–Paute deflection. F -statistics derived from BC suggested an east-to-west dispersal history. Population-based analyses revealed strong genetic structuring at both small and large geographic scales. Interpopulation relationships and Mantel tests strongly supported the cline model with cross-Andean dispersal in the AHZ. Along the cline, gene flow measured as F _ST was mainly limited by distance, with less but significant impact of climatic friction. Coalescent analysis revealed that cross-Andean divergence took place during the Quaternary. Significant historical isolation ( R _ST >  F _ST) was found in the southwestern population. The current study illustrates a joint effect of founder dynamics, divergence by distance and historical isolation on patterns of Andean diversity and distribution.     

The evolution of sexual and parthenogenetic Warramaba: a window onto Plio–Pleistocene diversification processes in an arid biome

Environmental changes over the Plio‐Pleistocene have been key drivers of speciation patterns and genetic diversification in high‐latitude and mesic environments, yet comparatively little is known about the evolutionary history of species in arid environments. We applied phylogenetic and phylogeographic analyses to understand the evolutionary history of Warramaba grasshoppers from the Australian arid zone, a group including sexual and parthenogenetic lineages. Sequence data (mitochondrial COI) showed that the four major sexual lineages within Warramaba most likely diverged in the Pliocene, around 2–7 million years ago. All sexual lineages exhibited considerable phylogenetic structure. Detailed analyses of the hybrid parthenogenetic species W. virgo and its sexual progenitors showed a pattern of high phylogenetic diversity and phylogeographic structure in northern lineages, and low diversity and evidence for recent expansion in southern lineages. Northern sexual lineages persisted in localized refugia over the Pleistocene, with sustained barriers promoting divergence over this period. Southern parts of the present range became periodically unsuitable during the Pleistocene, and it is into this region that parthenogenetic lineages have expanded. Our results strongly parallel those for sexual and parthenogenetic lineages of the gecko Heteronotia from the same region, indicating a highly general effect of Plio‐Pleistocene environmental change on diversification processes in arid Australia.     

Use of Occupancy Models to Estimate the Influence of Previous Live Captures on DNA-Based Detection Probabilities of Grizzly Bears

Abstract: Large carnivores potentially change their behavior following physical capture, becoming less responsive to the attractants that resulted in their capture, which can bias population estimates where the change in behavior is not appropriately modeled. We applied occupancy models to efficiently estimate and compare detection probabilities of previously collared grizzly bears (Ursus arctos) with bears captured at DNA hair-snag sites that were not previously collared. We found that previously captured bears had lower detection probabilities, although their detection probabilities were still >0, implying that they were still visible to be sampled via the DNA hair-snag grid, which was able to detect finer differences in capture probabilities of previously collared bears compared with Huggins closed-captures population models. To obtain relatively unbiased population estimates for DNA surveys, heterogeneity caused by previous live capture should be accounted for in the population estimator. (JOURNAL OF WILDLIFE MANAGEMENT 72(3):589–595; 2008)     

Analysis of Covariance Models for Data From Observational Field Studies

Abstract We outline the features of a general class of statistical models (i.e., analysis of covariance [ANCOVA] models) that has proven to be effective for the analysis of data from observational studies. In observational studies, treatments are assigned by Nature in a decidedly nonrandom manner; consequently, many of the crucial assumptions and safeguards of the classic experimental design either fail or are absent. Hence, inferences (causal or associative) are more difficult to justify. Typically, investigators can expect the primary factors of interest, which are usually called environmental exposures rather than treatments, to be involved in complex interactions with each other and with other factors, and these factors will be confounded with still other factors. We provide examples illustrating the application of ANCOVA models to adjust for confounding factors and complex interactions, thereby providing relatively clean estimates of association between exposure and response. We summarize information on available software and supporting literature for implementing ANCOVA models for the analysis of cross-sectional and longitudinal observational field data. We conclude with a brief discussion of critical model fitting issues, including proper specification of the functional form of continuous covariates and problems associated with overfitted models and misspecified models that lack important covariates.