Source Habitats Research Articles

Patterns of dreissenid mussel invasions in western US lakes within an integrated gravity model framework

Freshwater invasive species, such as the quagga mussel (Dreissena rostriformis bugensis), are causing over $1 billion USD annually in damages to water infrastructure, recreation, and the environment. Once established, quagga and other dreissenid mussels are extremely difficult to eradicate. Preventing the spread of these invasives is critical and of high management concern. Invasive dreissenid establishment is predicated upon both successful dispersal from a source and suitable habitat in the uninfested waterbody to which they are transported. Recreational boaters have become predominant dispersal vectors making it possible to forecast the risk of invasion of waterbodies for more targeted management and prevention. We developed an integrated mussel dispersal model that couples a constrained gravity model and habitat suitability model to forecast future invasions. The model simulates boater movement between lakes, the likelihood of boats transporting mussels, and the likelihood that those mussels survive in the environmental conditions of the new lake. Model output was most sensitive to changes in boater threshold, then buffer zones, while not as sensitive to changes in habitat suitability. From an initial infested source pool of 11 among 402 Western inland US lakes, we forecast additional lakes infested in several possible simulation scenarios. Constraining movement reduced connectivity between waterbodies with amplifying effects at different distance levels. This model can be used to determine waterbodies most at risk for dreissenid mussel invasion and to highlight the importance of multifactor integrated models in environmental management.

Catchment‐scale applications of hydraulic habitat models: Climate change effects on fish

AbstractApproaches available for estimating the ecological impacts of climate change on aquatic communities in river networks range from detailed mechanistic models applicable locally to correlative approaches applicable globally. Among them, hydraulic habitat models (HABMs) link hydraulic models of streams with biological models that reflect how organisms select microhabitat hydraulics. Coarser but more general species distribution models (SDMs) predict changes in geographic distributions; they generally involve coarse predictors such as air temperature or distance to source but neglect proximate habitat descriptors such as microhabitat hydraulics. We propose an original application of HABM for predicting the ecological impacts of climate change at large scales, a comparison of their predictions with those of SDM and a linkage of the two modelling approaches. We showcase our approach in a large catchment (Rhône River) where an available distributed hydrological model estimates present and future unregulated daily flows over the whole river network. Despite large local uncertainties, simulations showed that climate change may strongly reduce low flow percentiles (e.g., a median reduction of 38.6% for a pessimistic climate scenario), inducing important alteration of fish hydraulic habitat suitability (e.g., a median loss of 3.9%–18.7% for three modelled fish species with contrasting habitat use: brown trout, barbel and sculpin). The HABM and SDM individually predicted consistent or opposite fish responses to climate change, depending on the species and their habitat requirements. Our results illustrate that accounting for ecological responses to proximate habitat variables such as hydraulics can strongly modify projections related to climate change.

Evaluation of Alfalfa Fields and Pastures as Sources of Spissistilus festinus (Hemiptera: Membracidae): Quantification of Reproductive and Nutritional Parameters.

The threecornered alfalfa hopper (Spissistilus festinus) is a pest of grapevine, with damage caused by transmission of grapevine red blotch virus. Because grapevine is not a preferred host of the threecornered alfalfa hopper, abundance in vineyards depends on proximity to source habitats and presence of preferred hosts in vineyard understories. The potential for alfalfa fields and pastures in the Central Valley of California to serve as sources of threecornered alfalfa hopper was evaluated by quantifying parameters associated with threecornered alfalfa hopper reproductive and nutritional status. Laboratory studies determined that the threecornered alfalfa hopper is synovigenic, emerging as an adult prior to initiation of oogenesis and that females have multiple rounds of egg production. Alfalfa fields, irrigated pastures, and vineyards were sampled monthly. Adults were observed year-round in alfalfa fields and pastures, with populations peaking in fall. Gravid females were observed from February through November. While rare, adult threecornered alfalfa hoppers were collected from 2 of 4 sampled vineyards. In spring, adults were observed in samples collected from vineyard ground cover. In fall, adults were observed in samples collected from vineyard ground cover and foliage samples. Samples collected from pastures and vineyards were male biased, whereas equal numbers of males and females were observed in alfalfa fields. Adults collected from alfalfa fields were larger, heavier, and had greater estimated energetic reserves than adults collected from pastures. Adults collected from vineyards were of above average size and had relatively high estimated energetic reserves. Results suggest that alfalfa fields are more likely to serve as sources of threecornered alfalfa hoppers than irrigated pastures and that differences in male and female behavior may affect rates of pathogen transmission.

Utilization of marine taxa within an artisanal shellcraft sector of the Indo-Pacific region

Sustainable utilization of marine taxa is critical for maximizing social and economic goals of livelihood development within the Indo-Pacific. Yet, despite an increasing importance of shellcraft as a livelihood activity within the Indo-Pacific, information on the taxa utilized within shellcraft sectors remains scant. To address this knowledge gap, our study examined diversity, in terms of composition and quantities, of marine taxa utilized by artisan households and, collectively, within an artisanal shellcraft sector of Papua New Guinea. For each taxon, critical source habitats were identified, and the geographic scale of exploitation established. Critically, presented data revealed 73 taxa, representing at least 77 species, were utilized within the studied sector. Many of the taxa utilized had not previously been linked to shellcraft sectors, demonstrating that a broader composition of taxa is utilized than previously acknowledged. In terms of quantity, annual utilization within the sector was close to 500,000 individuals, the majority being mollusks of either class Gastropoda (83.6%), represented by 37 genera, or class Bivalvia (9.6%), represented by four genera. There was a strong bias towards a particular species, Chrysostoma paradoxum (78.5% of all individuals), as indicated by indices for the diversity utilized (H′ = 1.23; D = 0.38). However, substantial variation was evident in the diversity of taxa utilized among households (n = 36) engaged in shellcraft (H′ = 1.09 ± 0.71; D = 0.43 ± 0.27), with each household utilizing a unique composition of 19.1 ± 10.6 taxa. Source habitats for taxa ranged from pelagic to benthic intertidal and subtidal substrates, with the geographic scale of exploitation extending to 34 discrete locations up to 417 km away. The array of sector, household, and taxon-specific information presented provides a basis for supporting greater sustainability within shellcraft sectors across the Indo-Pacific, which is discussed within a context of informing community-based resource management, further developing marine aquaculture, and strengthening existing governance.

Public and private economic benefits of adopting conservation tillage for cotton pollination

Enhancing pollinator communities and the services they provide within agricultural landscapes is a global priority. Despite the advantages of floral strips or hedgerows as part of pollinator habitat enhancement efforts, opportunity costs incurred by removing land from agricultural production can outweigh the benefits of enhanced pollination to remaining crops. Conservation tillage is a practice that has the potential to improve habitat while maintaining agricultural productivity. By leaving soil largely undisturbed, conservation tillage could improve nesting habitat for ground nesting bees within fields, as well as provide source habitat for pollinators foraging in neighboring habitat. Cotton, a crop of tremendous national and global value, benefits from insect pollination, but has the lowest adoption of conservation tillage of any major US crop. In this study, we focus on the cotton-growing community of Refugio County, Texas to estimate the effect of conservation tillage on key pollinators, quantify the resulting changes in pollination limitation, and partition benefits to private and external beneficiaries. We find that for every 1% adoption of conservation tillage, we see a county-wide benefit of roughly $16,000 USD. Assuming the costs of adopting conservation tillage are low, we demonstrate that the benefits are largely private, accruing collectively to owners instead of neighboring farms. Interestingly, even with 100% conservation tillage, our modeling shows that the county would still suffer lost revenue due to inadequate pollination, indicating a role for additional pollinator habitat enhancement efforts. Nevertheless, our findings suggest that growers can cost-effectively enhance habitat and alleviate pollen limitation, increasing crop yield and farmer income, without removing land from cultivation.

Extrapolating potential crop damage by insect pests based on land use data: examining inter-regional generality in agricultural landscapes

BackgroundInter-regional relationships between landscape factors and biological responses in natural conditions are important but difficult to predict because of the differences in each landscape context and local environment. To examine the inter-regional variability in relation to landscape factors and the biological response of an insect pest of rice, Stenotus rubrovittatus, we extrapolated a damage prediction model (the ‘original model’ of our previous study) for rice using land-use data. The ‘original model’ comprised as fixed factors the area of source habitat (i.e. pastures and graminoid-dominated fallow fields), soybean fields, and rice paddies within 300-m radii with research years as the random intercept. We hypothesized that the original model would be applicable to new regions, but the predictive accuracy would be reduced. We predicted that fitting a new extended model, adjusting the parameter coefficients of identical fixed factors of the ‘original model,’ and adding regional random intercepts would improve model performance (the ‘extended model’). A field experiment was conducted in two regions that had a similar landscape context with the original region, each in a different year of four years in total. The proportion of rice damage and surrounding land use within a 300-m radius was investigated, and the data were applied to the models and the applicability and accuracy of the models were examined.ResultsWhen the ‘original model’ was assigned to the combined data from the original and extrapolated regions, the relationship between the observed and the predicted values was statistically significant, suggesting that there was an inter-regional common relationship. The relationship was not statistically significant if the model was applied only to the new regions. The extended model accuracy improved by 14% compared with the original model and was applicable for unknown data within the examined regions as demonstrated by three-fold cross validation.ConclusionsThese results imply that in this pest–crop system, there is likely to be a common inter-regional biological response of arthropods because of landscape factors, although we need to consider local environmental factors. We should be able to apply such relationships to identify or prevent pest hazards by offering region-wide management options.

Genetic and Epigenetic Differentiation Across Intertidal Gradients in the Foundation Plant Spartina alterniflora

Ecological genomics approaches have informed us about the structure of genetic diversity in natural populations that might underlie patterns in trait variation. However, we still know surprisingly little about the mechanisms that permit organisms to adapt to variable environmental conditions. The salt marsh foundation plant Spartina alterniflora exhibits a dramatic range in phenotype that is associated with a pronounced intertidal environmental gradient across a narrow spatial scale. Both genetic and non-genetic molecular mechanisms might underlie this phenotypic variation. To investigate both, we used epigenotyping-by-sequencing (epiGBS) to evaluate the make-up of natural populations across the intertidal environmental gradient. Based on recent findings, we expected that both DNA sequence and DNA methylation diversity would be explained by source population and habitat within populations. However, we predicted that epigenetic variation might be more strongly associated with habitat since similar epigenetic modifications could be rapidly elicited across different genetic backgrounds by similar environmental conditions. Overall, with PERMANOVA we found that population of origin explained a significant amount of the genetic (8.6%) and epigenetic (3.2%) variance. In addition, we found that a small but significant amount of genetic and epigenetic variance (<1%) was explained by habitat within populations. The interaction of population and habitat explained an additional 2.9% of the genetic variance and 1.4% of the epigenetic variance. By examining genetic and epigenetic variation within the same fragments (variation in close-cis), we found that population explained epigenetic variation in 9.2% of 8,960 tested loci, even after accounting for differences in the DNA sequence of the fragment. Habitat alone explained very little (<0.1%) of the variation in these close-cis comparisons, but the interaction of population and habitat explained 2.1% of the epigenetic variation in these loci. Using multiple matrix regression with randomization (MMRR) we found that phenotypic differences in natural populations were correlated with epigenetic and environmental differences even when accounting for genetic differences. Our results support the contention that sequence variation explains most of the variation in DNA methylation, but we have provided evidence that DNA methylation distinctly contributes to plant responses in natural populations.

Functional and phylogenetic diversity of sharks in the Northeastern Pacific

AbstractAimThe expansive spatial scale of pelagic communities and the difficulty in acquiring pelagic species' functional traits have stymied an understanding of marine community dynamics. We assembled and analysed a shark trait database and community phylogeny to identify the major axes of trait variation that define shark functional groups. We tested whether membership to biophysical macroecological strata is related to these functional or phylogenetic relationships.LocationNortheastern Pacific, 180–255°E and 0–50°N.TaxonSharks (Class: Chondrichthyes, superorder: Selachimorpha).MethodsWe built a community phylogeny and collected habitat, reproductive, somatic growth, trophic and dentition traits. We used principal coordinates analyses to identify axes of trait variation and hierarchical clustering to classify functional groups. We tested whether functional or phylogenetic relatedness determined species' membership to strata from five macroecological gradients: latitude, habitat type, thermal, carbon source and bathymetry.ResultsWe assembled 38 traits from 1225 records from 130 sources, 260 pictographs from seven sources and 631 teeth from 79 jaw specimens. Life history, r versus K selection, was responsible for the biggest division in the functional dendrogram. Vertical habitat preference, growth rates, diet and dental morphology generated further divisions between r‐ or K‐selected species. Vertical habitat preference, carbon source and biochemical habitat type were significantly dispersed or clustered on the functional dendrogram or phylogram.Main ConclusionsHabitat and reproductive traits were the most important trait suites driving shark functional diversity. Through ordination and clustering, we were able to associate major axes of trait variation to the membership of shark functional groups. The phylogram approximated well the functional dendrogram's backbone but was a poor substitute for the trait diversity at the tips. Given the long evolutionary history of sharks and coincident expansive trait diversity, merging functional and phylogenetic approaches was necessary to capture the dimensions of shark biodiversity.

When a pest is not a pest: Birds indirectly increase defoliation but have no effect on yield of soybean crops.

Natural habitats near agricultural systems can be sources of both ecosystem services and disservices on farms. Ecosystem disservices, those aspects of an ecosystem that have negative impacts on humans, may disproportionately affect conservation decisions made by farmers. Birds, in particular, can have complex effects on crops, ranging from positive to neutral to negative. Therefore, it is important to quantify them in a meaningful way. Birds may be more abundant on farms near natural areas and may provide ecosystem services by consuming insect pests. However, when birds consume beneficial predatory arthropods rather than pest species (intraguild predation), they can provide a disservice to the farmer if the intraguild predation decreases crop yield. We studied bird intraguild predation in Illinois (USA) at six soybean fields adjacent to grasslands that provided source habitat for bird populations. We placed cages over soybean crops, which excluded birds but allowed access to arthropods, and measured differences in leaf damage and crop yield of plants in control and exclosure plots. We also conducted point counts at each site to quantify the bird communities. We found that plants within the bird exclosures had lower levels of leaf damage by pests than those in control plots, but there was no resulting effect on crop yield. We also found that sites with higher bird abundance had higher levels of leaf damage by pests, but bird species richness was not a significant predictor of leaf damage. These results suggest that although birds may have released pests through intraguild predation, there was no net disservice when considering crop yield, the variable most important to stakeholders.

Arthropod Communities on Young Vegetated Roofs Are More Similar to Each Other Than to Communities at Ground Level

Vegetated roofs are human-manufactured ecosystems and potentially promising conservation tools for various taxa and habitats. Focussing on arthropods, we conducted a 3 year study on newly constructed vegetated roofs with shallow substrates (up to 10 cm) and vegetation established with pre-grown mats, plug plants and seeds to describe pioneer arthropod communities on roofs and to compare them with ground level communities. We vacuum sampled arthropods from the roofs and nearby ground level sites with low, open vegetation, i.e., potential source habitats. We showed that the roofs and ground sites resembled each other for ordinal species richness but differed in community composition: with time the roofs started to resemble each other rather than their closest ground level habitats. Species richness increased with time on roofs and at ground level, but the roofs had consistently less species than the ground sites and only a few species were unique to the roofs. Also, the proportion of predators increased on roofs, while not at ground level. We conclude that vegetated roofs established with similar substrates and vegetation, filter arthropods in a way that produces novel communities that are different from those at ground level but similar to one another. The role of these insular communities in species networks and ecosystem function remains to be investigated.

Spatial and temporal patterns of Frankliniella fusca (Thysanoptera: Thripidae) in wheat agroecosystems

AbstractFrankliniella fusca Hinds (Thysanoptera: Thripidae) is an economically important pest of many cultivated crops including cotton, tomatoes, peppers and tobacco. Previous research has focused on the importance of non‐crop weeds for F. fusca populations when estimating crop infestation risk in the spring. Although weeds play an integral role in population development, early‐season cultivated hosts (e.g. wheat and sage) may also contribute and augment overall populations. Few studies have examined the role of early‐season crops as a source habitat for sensitive host crops later in the season. The goal of this study was to investigate the abiotic conditions and landscape components that are associated with F. fusca populations in winter wheat (Triticum aestivum L.). Exploring these relationships will provide insight into early‐season drivers of F. fusca. To do this, we conducted a 2 year study documenting F. fusca populations during an 8 weeks period each spring. We sampled immature thrips abundance on wheat heads while concurrently monitoring adult dispersal from the field using yellow sticky cards. Across both years, we found that immature thrips sampled during the milk and dough development stages best‐predicted adult dispersal 2 weeks later. Cumulative precipitation and the number of precipitation events beginning in the autumn of the prior year were the most important abiotic predictors of F. fusca abundance. At the landscape scale, adult F. fusca density was negatively related to the area of row crop agriculture, grasslands and amount of landscape fragmentation. Results of our study provide a basis to assess larval thrips and forecast dispersal of this pest from wheat using a head sampling method. At a landscape scale, we show that specific combinations of abiotic and landscape variables influence population abundance of F. fusca in North Carolina row crop agroecosystems.

Source or Sink? The Role of Residential Host Plants in Asian Citrus Psyllid Infestation of Commercial Citrus Groves.

Citriculture landscapes in the U.S. are typically habitat mosaics of commercial groves interspersed with residential areas supporting a variety of unmanaged citrus. Diaphorina citri the vector of Candidatus Liberibacter asiaticus, the causal agent of Huanglongbing feeds on citrus in both habitats. We postulated that residential citrus function as a 'source' of D. citri that infest groves, functioning as sinks. Here we report on an experimental mark-release-recapture study conducted at the interface of a residential neighborhood and groves. Adult D. citri marked with colored fluorescent powders were released in both habitats (n = 15,300) and their movement within and between milieus monitored. Although the recapture rate of marked psyllids was very low (0.23%), the results were instructive. Most of the recaptured psyllids in residential trees (84.6%) were released within that habitat. In contrast, approximately half of the marked psyllids recovered in groves were released in residential areas. Of all the recaptured psyllids, about 40% changed habitats, but the change was skewed toward movement from residential to grove habitat. These data strongly suggest that there is a constant exchange of D. citri adults between the two habitats, with residential citrus trees functioning as a source habitat of psyllids. The further the residential trees are located from groves, the less likely they will serve as sources of D. citri. Hence, to reduce the risks of citrus grove colonization by D. citri, new groves should be established away from residential habitats where possible, and psyllid management practices must also be implemented in residential habitats.

Unravelling the role of local and large-scale factors in structuring sandy beach populations: the wedge clam Donax hanleyanus

Changes in the structure and dynamics of sandy beach macrofaunal populations result from the simultaneous action of local and regional factors acting synergistically. This is particularly noticeable in transitional interfaces between freshwater and marine ecosystems, where large-scale gradients affect local beach morphodynamics and resident fauna. The wedge clam Donax hanleyanus occurs on beaches with contrasting morphodynamics along the salinity gradient generated by the Rio de la Plata estuary. We conducted sampling surveys to determine a fine-grained comprehensive coverage of the species’ distribution in Uruguay to assess the concurrent effects of large-scale variations in salinity and local beach morphodynamics on wedge clam populations along 400 km (16 sandy beaches) over 2 yr. The main factor controlling wedge clam occurrence was salinity, overriding the effects of local habitat features. On beaches where the species was present, total abundance was higher on oceanic dissipative shores, which also harbored a higher abundance and relative representation of recruits. Recruitment was almost lacking in reflective beaches. However, biomass of adults with larger body sizes prevailed on reflective beaches, suggesting a scaling of abundance to body size and potential density-dependent effects. In this metapopulation, estuarine beaches are sinks, whereas oceanic beaches act as source habitats. We concluded that large-scale gradients generated by salinity variations translated into local population patterns (distribution, abundance and population structure) and processes (recruitment), which were secondarily driven by local morphodynamics. The relative importance of pre- and post-settlement processes across the morphodynamic spectrum from reflective to dissipative beaches has yet to be elucidated.

Examining the production, export, and immediate fate of kelp detritus on open‐coast subtidal reefs in the Northeast Atlantic

AbstractKelp forests are highly productive coastal habitats and are emerging as important sources of organic matter for other ecosystems. Although their high rates of productivity and detritus release are expected to lead to substantial export of carbon, few studies have actually quantified rates of export or the persistence of detritus. We addressed this in eight subtidal kelp forests (Laminaria hyperborea) spanning the length (9° of latitude) of the United Kingdom. Specifically, we quantified detritus production, retention/export from source and adjacent habitats, and in situ decomposition rates. Detritus released via both dislodgment of whole plants and “May cast” shedding of old growth was highly variable between sites with greatest values recorded in our colder, northern sites. This was attributable to greater plant size biomass in northern regions, rather than plant density or dislodgement rates. On average, the annual production of kelp detritus was 4706 ± 700 g FW m−2 yr−1 or 301 g C m−2 yr−1. Low retention of detritus within the kelp forest and adjacent sedimentary habitats indicated very high rates of export (> 98% across the study). A litterbag experiment showed detritus may take > 4 months to decompose, suggesting great potential for long distance transport. Overall, our findings suggest that L. hyperborea forests export large amounts of detritus subsidies across their range, which can potentially shape the structure of distant benthic communities and constitute a relevant and largely overlooked flux in the coastal carbon cycle, which may represent an important component of natural carbon sequestration.

Direct and indirect effects of landscape and field management intensity on carabids through trophic resources and weeds

Abstract Carabids are important biological control agents of weeds and other pests in agricultural fields. The carabid community is built upon direct and indirect ecological effects of landscape complexity, field management intensity and biotic components that in interaction make any prediction of community size and composition challenging. We analyse a large‐scale sample of 60 European cereal fields using structural equation modelling to quantify the direct effects of field management intensity and the surrounding landscape, and their indirect effect via biotic components, on carabid diversity. Our results highlight that direct and indirect effects of increasing landscape complexity, mediated by trophic resources, mainly affect carabids positively. Field management intensity only ever affects carabids through indirect effects that are generally negative, by suppressing standing weeds and weed seeds. Indirect effects on granivore carabid species depended on weed seed availability, whereas omnivores depended on the availability of both weed seeds and animal prey. Synthesis and applications. A consideration of both the direct and indirect effects of landscape and field management is necessary for predicting carabid communities. These indirect effects, mediated via trophic resources, supports the diversity and abundance of carabid communities and their provision of ecosystem services. Our results show that promoting crop diversity and connectivity to semi‐natural habitats will directly enhance carabid communities in farmland by manipulating their migration from source habitats and indirectly by promoting the presence and diversity of their trophic resources. A reduction in field management intensity will preserve local standing weeds and weed seeds, and indirectly support carabid communities. These local and landscape modifications could contribute to improve the natural regulation of pests and weeds by carabids.

A sink host allows a specialist herbivore to persist in a seasonal source.

In seasonal environments, sinks that are more persistent than sources may serve as temporal stepping stones for specialists. However, this possibility has to our knowledge, not been demonstrated to date, as such environments are thought to select for generalists, and the role of sinks, both in the field and in the laboratory, is difficult to document. Here, we used laboratory experiments to show that herbivorous arthropods associated with seasonally absent main (source) habitats can endure on a suboptimal (sink) host for several generations, albeit with a negative growth rate. Additionally, they dispersed towards this host less often than towards the main host and accepted it less often than the main host. Finally, repeated experimental evolution attempts revealed no adaptation to the suboptimal host. Nevertheless, field observations showed that arthropods are found in suboptimal habitats when the main habitat is unavailable. Together, these results show that evolutionary rescue in the suboptimal habitat is not possible. Instead, the sink habitat functions as a temporal stepping stone, allowing for the persistence of a specialist when the source habitat is gone.

Coupled Source-Sink Habitats Produce Spatial and Temporal Variation of Cancer Cell Molecular Properties as an Alternative to Branched Clonal Evolution and Stem Cell Paradigms

Intratumoral molecular cancer cell heterogeneity is conventionally ascribed to the accumulation of random mutations that occasionally generate fitter phenotypes. This model is built upon the “mutation-selection” paradigm in which mutations drive ever-fitter cancer cells independent of environmental circumstances. An alternative model posits spatio-temporal variation (e.g., blood flow heterogeneity) drives speciation by selecting for cancer cells adapted to each different environment. Here, spatial genetic variation is the consequence rather than the cause of intratumoral evolution. In nature, spatially heterogenous environments are frequently coupled through migration. Drawing from ecological models, we investigate adjacent well-perfused and poorly-perfused tumor regions as “source” and “sink” habitats, respectively. The source habitat has a high carrying capacity resulting in more emigration than immigration. Sink habitats may support a small (“soft-sink”) or no (“hard-sink”) local population. Ecologically, sink habitats can reduce the population size of the source habitat so that, for example, the density of cancer cells directly around blood vessels may be lower than expected. Evolutionarily, sink habitats can exert a selective pressure favoring traits different from those in the source habitat so that, for example, cancer cells adjacent to blood vessels may be suboptimally adapted for that habitat. Soft sinks favor a generalist cancer cell type that moves between the environment but can, under some circumstances, produce speciation events forming source and sink habitat specialists resulting in significant molecular variation in cancer cells separated by small distances. Finally, sink habitats, with limited blood supply, may receive reduced concentrations of systemic drug treatments; and local hypoxia and acidosis may further decrease drug efficacy allowing cells to survive treatment and evolve resistance. In such cases, the sink transforms into the source habitat for resistant cancer cells, leading to treatment failure and tumor progression. We note these dynamics will result in spatial variations in molecular properties as an alternative to the conventional branched evolution model and will result in cellular migration as well as variation in cancer cell phenotype and proliferation currently described by the stem cell paradigm.

Variable coverage in an Autocidal Gravid Ovitrap intervention impacts efficacy of Aedes aegypti control.

Control of the arboviral disease vector Aedes aegypti has shown variable levels of efficacy around the globe. We evaluated an Autocidal Gravid Ovitrap (AGO) intervention as a stand‐alone control tool for population suppression of A. aegypti in US communities bordering Mexico.We conducted a cluster randomized crossover trial with weekly mosquito surveillance of sentinel households from July 2017 to December 2018. The intervention took place from August to December of both years. Multilevel models (generalized linear and additive mixed models) were used to analyse the changes in population abundance of female A. aegypti.We observed that female populations were being suppressed 77% (2018) and four times lower outdoor female abundance when AGO coverage (number of intervention AGO traps that surrounded a sentinel home) was high (2.7 AGOs/house). However, we also observed that areas with low intervention AGO coverage resulted in no difference (2017) or slightly higher abundance compared to the control. These results suggest that coverage rate might play a critical role on how populations of female A. aegypti are being modulated in the field. The lack of larval source habitat reduction and the short duration of the intervention period might have limited the A. aegypti population suppression observed in this study. Synthesis and applications. The mosquito, A. aegypti, is a public health concern in most tropical and subtropical regions. With the rise of insecticide resistance, the evaluation of non‐chemical tools has become pivotal in the fight against arboviral disease transmission. Our study shows that the AGO intervention, as a stand‐alone control tool, is limited by its coverage in human settlements. Vector control programmes should consider, that if the target coverage rate is not achieved, measures will be ineffective unless coupled with other control approaches. Although our multilevel modelling was focused on A. aegypti and the AGO, the approach can be applied to other mosquito vector species.

Anthropogenic Resources Contribute to Settlement of Mud-Nesting Barn Swallows (Hirundo rustica) in an Arid Environment

Globally, bird populations are declining. This may be caused by human alterations of habitats formerly used by birds. Migratory birds show flexibility in resource use, however, a distinct move to a different habitat type demands investigation. The objective of this study is to understand the resources available to Barn swallows (Hirundo rustica) in White Sands National Park, New Mexico (WSNP) and how this species is utilizing this arid landscape. Results show that Barn swallows are aided by resources provided by the WSNP Visitor Center. Water and mud sources, perching and foraging sites, and protection from weather extremes and predators are all present and are exploited by Barn swallows in WSNP. Future research of this population could help determine if the Visitor Center is functioning as a sink or source habitat and how the establishment of a generalist species (with certain advantages) is competing with specialist species in this area. Understanding shifts in habitat types for migratory birds is important as conservation and management modeling continue to forecast suitable and available habitats for protected birds.

Selection favors adaptive plasticity in a long-term reciprocal transplant experiment.

Spatial and temporal environmental variation can favor the evolution of adaptive phenotypic plasticity, such that genotypes alter their phenotypes in response to local conditions to maintain fitness across heterogeneous landscapes. When individuals show greater fitness in one habitat than another, asymmetric migration can restrict adaptation to the lower quality environment. In these cases, selection is predicted to favor traits that enhance fitness in the higher-quality (source) habitat at the expense of fitness in the marginal (sink) habitat.Here, we test whether plasticity is adaptive in a system regulated by demographic source-sink dynamics.Vaccinium elliottii (Ericaceae) occurs in dry upland and flood-prone bottomland forests throughout the southeastern United States, but has larger populations and higher average individual fitness in upland sites. We conducted a multi-year field experiment to evaluate whether plasticity in foliar morphology increases survival and lifespan. Both across and within habitats, selection favored plasticity in specific leaf area, stomatal density, and leaf size. Stabilizing selection acted on plasticity in stomatal density within habitats, suggesting that extreme levels of plasticity are disadvantageous. Thus, even in systems driven by source-sink dynamics, temporal and spatial variation in conditions across the landscape and within habitat types can favor the evolution of plasticity.