Photosynthetic oxygen exchange in C4 grasses: the role of oxygen as electron acceptor

C₄ grasses of the NAD‐ME type (Astrebla lappacea, Eleusine coracana, Eragrostis superba, Leptochloa dubia, Panicum coloratum, Panicum decompositum) and the NADP‐ME type (Bothriochloa bladhii, Cenchrus ciliaris, Dichanthium sericeum, Panicum antidotale, Paspalum notatum, Pennisetum alopecuroides, Sorghum bicolor) were used to investigate the role of O₂ as an electron acceptor during C₄ photosynthesis. Mass spectrometric measurements of gross O₂ evolution and uptake were made concurrently with measurements of net CO₂ uptake and chlorophyll fluorescence at different irradiances and leaf temperatures of 30 and 40 °C. In all C₄ grasses gross O₂ uptake increased with increasing irradiance at very high CO₂ partial pressures (pCO₂) and was on average 18% of gross O₂ evolution. Gross O₂ uptake at high irradiance and high pCO₂ was on average 3.8 times greater than gross O₂ uptake in the dark. Furthermore, gross O₂ uptake in the light increased with O₂ concentration at both high CO₂ and the compensation point, whereas gross O₂ uptake in the dark was insensitive to O₂ concentration. This suggests that a significant amount of O₂ uptake may be associated with the Mehler reaction, and that the Mehler reaction varies with irradiance and O₂ concentration. O₂ exchange characteristics at high pCO₂ were similar for NAD‐ME and NADP‐ME species. NAD‐ME species had significantly greater O₂ uptake and evolution at the compensation point particularly at low irradiance compared to NADP‐ME species, which could be related to different rates of photorespiratory O₂ uptake. There was a good correlation between electron transport rates estimated from chlorophyll fluorescence and gross O₂ evolution at high light and high pCO₂.     

Genetic diversity in the Eurasian otter, Lutra lutra, in Scotland. Evidence from microsatellite polymorphism

The relationship between microsatellite diversity and geographical fragmentation and isolation was studied in Scottish populations of the Eurasian otter, Lutra lutra. The geographic range of the study encompassed isolated archipelagos, islands adjacent to the Scottish mainland and both fragmented and continuous mainland populations. Tissue samples of 496 individuals from across Scotland were assayed for polymorphism at ten microsatellites. The isolation of populations on Shetland, and to a lesser degree on Orkney, was associated with reduced levels of microsatellite diversity. Most of the remaining island and fragmented mainland populations contained levels of microsatellite diversity similar to the high levels observed in die continuous mainland populations. Unexpectedly, both island and continuous mainland populations showed similar rates of departures from mutation-drift equilibrium. Such departures could have arisen from a variety of local demographic processes besides population bottlenecks. Gene flow appeared to be a major factor maintaining microsatellite diversity in all of these populations except the one on Shedand.     

Contrasting responses of Peromyscus mice of Yosemite National Park to recent climate change

Accurately predicting the response of species to climate change is crucial for the preservation of contemporary species diversity. In the current study, we analyze the response of two congeneric small mammal species (Peromyscus maniculatus and Peromyscus truei) to recent climate change in the region of Yosemite National Park (California, USA). The generalist P. maniculatus did not change its distribution in response to climate change while the specialist P. truei substantially changed its geographic and elevational distribution in the region, expanding into Yosemite. Using molecular genetic techniques we found that a cryptic geographic shift in genetic variation may have occurred within the geographically stable P. maniculatus distribution. Using a combination of morphometric and molecular genetic techniques we confirmed that a P. truei subspecies previously identified as a habitat specialist expanded into new habitat types, suggesting that this subspecies is not in fact a habitat specialist. Instead, we propose that the range of this subspecies is instead limited by climatic variables currently varying in response to contemporary climate change. These results underscore the importance of verifying the natural‐history‐based assumptions used to develop predictive models of species' response to climate change.     

Building Hierarchical Models of Avian Distributions for the State of Georgia

Abstract To predict the distributions of breeding birds in the state of Georgia, USA, we built hierarchical models consisting of 4 levels of nested mapping units of decreasing area: 90,000 ha, 3,600 ha, 144 ha, and 5.76 ha. We used the Partners in Flight database of point counts to generate presence and absence data at locations across the state of Georgia for 9 avian species: Acadian flycatcher (Empidonax virescens), brown-headed nuthatch (Sitta pusilla), Carolina wren (Thryothorus ludovicianus), indigo bunting (Passerina cyanea), northern cardinal (Cardinalis cardinalis), prairie warbler (Dendroica discolor), yellow-billed cuckoo (Coccyzus americanus), white-eyed vireo (Vireo griseus), and wood thrush (Hylocichla mustelina). At each location, we estimated hierarchical-level-specific habitat measurements using the Georgia GAP Analysis18 class land cover and other Geographic Information System sources. We created candidate, species-specific occupancy models based on previously reported relationships, and fit these using Markov chain Monte Carlo procedures implemented in OpenBugs. We then created a confidence model set for each species based on Akaike's Information Criterion. We found hierarchical habitat relationships for all species. Three-fold cross-validation estimates of model accuracy indicated an average overall correct classification rate of 60.5%. Comparisons with existing Georgia GAP Analysis models indicated that our models were more accurate overall. Our results provide guidance to wildlife scientists and managers seeking predict avian occurrence as a function of local and landscape-level habitat attributes.     

Evaluating the influence of land use,drought and reach isolation on the occurrence of freshwater mussel species in the lower Flint River Basin,Georgia (U.S.A.)

1. North American freshwater mussels have been subjected to multiple stressors in recent decades that have contributed to declines in the status and distribution of many species. However, considerable uncertainty exists regarding the relative influence of these factors on observed population declines. 2. We used an occupancy modelling approach to quantify relationships between mussel species occurrence and various site‐ and catchment‐level factors, including land cover, stream size, the occurrence of drought and reach isolation due to impoundment for 21 mussel species native to the lower Flint River Basin, Georgia, U.S.A. 3. Our modelling approach accounted for potential biases associated with both incomplete detection and misidentification of species, which are frequently not accommodated as sources of bias in freshwater mussel studies. 4. Modelling results suggested that mussel species were, on average, four times less likely to be present following severe drought, but the negative effects of drought declined rapidly with increasing stream size. Similarly, mussel species were 15 times less likely to occupy small streams that were isolated from mainstem tributaries by impoundments. 5. This study provides insight into the effects of natural and anthropogenic factors on freshwater mussel species. Our findings add to a growing body of literature aimed at improving understanding of the predominant factors influencing freshwater mussel populations and fostering the development of more informed and effective conservation strategies.     

The history of the Eurasian Beaver Castor fiber in Scotland

In 1995 Scottish Natural Heritage proposed a feasibility study to examine the case for reintroducing the Eurasian Beaver Castor fiber to Scotland. Following IUCN guidelines, an important first step is to demonstrate that the Beaver was once a native of Scotland and that the causes of its extinction no longer pose any threat to reintroduced animals. Therefore, palaeontological, archaeological and historical evidence for the former existence of the Beaver in Scotland and the causes of its extinction are reviewed.
Palaeontological and archaeological evidence suggest that the Eurasian Beaver was once widely distributed throughout mainland Scotland. Historical evidence suggests that although it was once probably fairly common, it became extinct between the twelfth and sixteenth centuries, most probably towards the latter. The main cause of its decline and extinction was probably hunting for its pelt, meat and castoreum, but habitat destruction may have been important in the loss of some small isolated populations.
Given that the causes of extinction of the Beaver in Scotland now no longer exist or can be effectively controlled, there is no reason why a feasibility study cannot proceed to assess the practicalities of a reintroduction.