Patterns of patch rejection in size-structured populations: beyond the ideal free distribution and size segregation

Journal ArticleWe examine optimal patch allocation strategies in a population structured by size or some other characteristic. By treating size-specific differences among patches as limiting factors, we create a single framework to analyse foraging for two resources, foraging in the presence of predators and foraging in the presence of competition. The ideal free distribution or size segregation are optimal only in restricted circumstances, among a range of other intermediate patterns of patch rejection. The predicted pattern can shift from an ideal free distribution to various forms of size segregation as resource renewal rates in patches become more different

Grazers and diggers: exploitation competition and coexistence among foragers with different feeding strategies on a single resource

A mathematical model is presented that describes a system where two consumer species compete exploitatively for a single renewable resource. The resource is distributed in a patchy but homogeneous environment; that is, all patches are intrinsically identical. The two consumer species are referred to as diggers and grazers, where diggers deplete the resource within a patch to lower densities than grazers. We show that the two distinct feeding strategies can produce a heterogeneous resource distribution that enables their coexistence. Coexistence requires that grazers must either move faster than diggers between patches or convert the resources to population growth much more efficiently than diggers. The model shows that the functional form of resource renewal within a patch is also important for coexistence. These results contrast with theory that considers exploitation competition for a single resource when the resource is assumed to be well mixed throughout the system.Shane A. Richards, Roger M. Nisbet, William G. Wilson, and Hugh P. Possingha

Topographical variation reduces phenological mismatch between a butterfly and its nectar source

© 2014, Springer International Publishing Switzerland. The timing of many biological events, including butterfly imago emergence, has advanced under climate change, with the rate of these phenological changes often differing among taxonomic groups. Such inter-taxa variability can lead to phenological mismatches. For example, the timing of a butterfly’s flight period may become misaligned with a key nectar resource, potentially increasing the extinction risk to both species. Here we fit statistical models to field data to determine how the phenology of the marbled white butterfly, Melanargia galathea, and its main nectar source, greater knapweed, Centaurea scabiosa, have changed over recent years at three sites across the UK. We also consider whether topographical diversity affects C. scabiosa’s flowering period. At our focal site, on the species’ northern range limit, we find that over a 13-year period the onset of C. scabiosa’s flowering period has become later whilst there is no obvious trend over time in the onset of M. galathea’s flight period. In recent years, butterflies have started to emerge before their key nectar source was available across most of the site. This raises the intriguing possibility that phenological mismatch could be an unrecognised determinant of range limits for some species. However, the presence of topographical diversity within the site decreased the chance of a mismatch occurring by increasing the length of the flowering period by up to 14days. We suggest that topographical diversity could be an important component in minimising phenological mismatches under future climate change

Recommendations for lung cancer screening in Southern Africa

Lung cancer remains the leading cause of cancer-related deaths in southern Africa. Early trials of chest radiograph-based screening in males at high risk for lung cancer found no mortality benefit of a radiograph alone, or a radiograph plus sputum cytology screening strategy. Large prospective studies, including the National Lung Screening Trial, have shown an all-cause mortality benefit when low-dose computed tomography (LDCT) was used as a screening modality in patients that are at high risk of developing lung cancer. The South African Thoracic Society, based on these findings, and those from several international guidelines, recommend that annual LDCT should be offered to patients between 55-74 years of age who are current or former smokers (having quit within the preceding 15 years), with at least a 30-pack year smoking history and with no history of lung cancer. Patients should be in general good health, fit for surgery, and willing to undergo further investigations if deemed necessary. Given the high local prevalence of tuberculosis (TB) infection and post-TB lung disease, which can radiographically mimic lung cancer, a conservative threshold (nodule size ?6 mm) should be used to determine whether the baseline LDCT screen is positive (thus nodules <6 mm require no action until the next annual screen). If a non-calcified, solid or partly solid nodule is ?6 mm, but <10 mm with no malignant features (e.g., distinct spiculated margins), the LDCT should be repeated in 6 months. If a solid nodule or the largest component of a non-solid nodule is ?10 or ?6 mm and enlarging or with additional malignant features present, definitive action to exclude lung cancer is warranted. Patients should be screened annually until 15 years have elapsed from date of smoking cessation, they turn 80, become unfit for a curative operation or significant changes are observed

Recommendations for lung cancer screening in Southern Africa

Lung cancer remains the leading cause of cancer-related deaths in southern Africa. Early trials of chest radiograph-based screening in males at high risk for lung cancer found no mortality benefit of a radiograph alone, or a radiograph plus sputum cytology screening strategy. Large prospective studies, including the National Lung Screening Trial, have shown an all-cause mortality benefit when lowdose computed tomography (LDCT) was used as a screening modality in patients that are at high risk of developing lung cancer. The South African Thoracic Society, based on these findings, and those from several international guidelines, recommend that annual LDCT should be offered to patients between 55–74 years of age who are current or former smokers (having quit within the preceding 15 years), with at least a 30-pack year smoking history and with no history of lung cancer. Patients should be in general good health, fit for surgery, and willing to undergo further investigations if deemed necessary. Given the high local prevalence of tuberculosis (TB) infection and post-TB lung disease, which can radiographically mimic lung cancer, a conservative threshold (nodule size ≥6 mm) should be used to determine whether the baseline LDCT screen is positive (thus nodules <6 mm require no action until the next annual screen). If a non-calcified, solid or partly solid nodule is ≥6 mm, but <10 mm with no malignant features (e.g., distinct spiculated margins), the LDCT should be repeated in 6 months. If a solid nodule or the largest component of a non-solid nodule is ≥10 or ≥6 mm and enlarging or with additional malignant features present, definitive action to exclude lung cancer is warranted. Patients should be screened annually until 15 years have elapsed from date of smoking cessation, they turn 80, become unfit for a curative operation or significant changes are observed.K Dheda is supported by the South African MRC (RFA-EMU-02-2017) and the EDCTP (TMA- 2015SF-1043 & TMA-1051-TESAII).http://jtd.amegroups.comam2020Cardiolog

Clinical, biochemical and genetic spectrum of low alkaline phosphatase levels in adults

Background: Low serum levels of alkaline phosphatase (ALP) are a hallmark of hypophosphatasia. However, the clinical significance and the underlying genetics of low ALP in unselected populations are unclear. Methods: In order to clarify this issue, we performed a clinical, biochemical and genetic study of 42 individuals (age range 20–77 yr) with unexplained low ALP levels. Results: Nine hadmild hyperphosphatemia and three hadmild hypercalcemia. ALP levelswere inversely correlated with serum calcium (r = -0.38, p = 0.012), pyridoxal phosphate (PLP; r = -0.51, p = 0.001) and urine phosphoethanolamine (PEA; r = -0.49, p = 0.001). Although many subjects experienced minor complaints, such as mild musculoskeletal pain, none hadmajor health problems.Mutations in ALPL were found in 21 subjects (50%), including six novelmutations. All but one,were heterozygousmutations.Missensemutations were themost common (present in 18 subjects; 86%) and themajority were predicted to have a damaging effect on protein activity. The presence of amutated allelewas associated with tooth loss (48% versus 12%; p=0.04), slightly lower levels of serumALP (p=0.002), higher levels of PLP (p b 0.0001) and PEA (p b 0.0001), aswell asmildly increased serum phosphate (p=0.03). Ten individuals (24%) had PLP levels above the reference range; all carried a mutated allele. Conclusion: One-half of adult individuals with unexplained low serum ALP carried an ALPL mutation. Although the associated clinicalmanifestations are usuallymild, in approximately 50% of the cases, enzyme activity is lowenough to cause substrate accumulation and may predispose to defects in calcified tissues

Typha (Cattail) Invasion in North American Wetlands: Biology, Regional Problems, Impacts, Ecosystem Services, and Management

Typha is an iconic wetland plant found worldwide. Hybridization and anthropogenic disturbances have resulted in large increases in Typha abundance in wetland ecosystems throughout North America at a cost to native floral and faunal biodiversity. As demonstrated by three regional case studies, Typha is capable of rapidly colonizing habitats and forming monodominant vegetation stands due to traits such as robust size, rapid growth rate, and rhizomatic expansion. Increased nutrient inputs into wetlands and altered hydrologic regimes are among the principal anthropogenic drivers of Typha invasion. Typha is associated with a wide range of negative ecological impacts to wetland and agricultural systems, but also is linked with a variety of ecosystem services such as bioremediation and provisioning of biomass, as well as an assortment of traditional cultural uses. Numerous physical, chemical, and hydrologic control methods are used to manage invasive Typha, but results are inconsistent and multiple methods and repeated treatments often are required. While this review focuses on invasive Typha in North America, the literature cited comes from research on Typha and other invasive species from around the world. As such, many of the underlying concepts in this review are relevant to invasive species in other wetland ecosystems worldwide

Ancient Lowland Maya neighborhoods: Average Nearest Neighbor analysis and kernel density models, environments, and urban scale

Many humans live in large, complex political centers, composed of multi-scalar communities including neighborhoods and districts. Both today and in the past, neighborhoods form a fundamental part of cities and are defined by their spatial, architectural, and material elements. Neighborhoods existed in ancient centers of various scales, and multiple methods have been employed to identify ancient neighborhoods in archaeological contexts. However, the use of different methods for neighborhood identification within the same spatiotemporal setting results in challenges for comparisons within and between ancient societies. Here, we focus on using a single method—combining Average Nearest Neighbor (ANN) and Kernel Density (KD) analyses of household groups—to identify potential neighborhoods based on clusters of households at 23 ancient centers across the Maya Lowlands. While a one-size-fits all model does not work for neighborhood identification everywhere, the ANN/KD method provides quantifiable data on the clustering of ancient households, which can be linked to environmental zones and urban scale. We found that centers in river valleys exhibited greater household clustering compared to centers in upland and escarpment environments. Settlement patterns on flat plains were more dispersed, with little discrete spatial clustering of households. Furthermore, we categorized the ancient Maya centers into discrete urban scales, finding that larger centers had greater variation in household spacing compared to medium-sized and smaller centers. Many larger political centers possess heterogeneity in household clustering between their civic-ceremonial cores, immediate hinterlands, and far peripheries. Smaller centers exhibit greater household clustering compared to larger ones. This paper quantitatively assesses household clustering among nearly two dozen centers across the Maya Lowlands, linking environment and urban scale to settlement patterns. The findings are applicable to ancient societies and modern cities alike; understanding how humans form multi-scalar social groupings, such as neighborhoods, is fundamental to human experience and social organization