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At least 505 records · Page 28Linked to original sources
USGS2025

Satellite assessment of winter cover crop and conservation tillage outcomes to support adaptive management in working landscapes

The use of winter cover crops and conservation tillage are agricultural practices promoted to reduce nutrient and sediment loss from cropland, improve soil health, increase infiltration, and support farm nutrient cycling and ecosystem services. However, environmental performance of these practices is variable in the working farm landscape. The Lower Chesapeake Bay research project within the USDA Long-Term Agroecosystem Research (LTAR) network has collaboratively developed satellite remote sensing algorithms to measure the performance and phenology of winter cover crops (aboveground biomass, nitrogen content, fractional cover, and emergence and termination dates) using no-cost Harmonized Landsat and Sentinel-2 multispectral satellite imagery. This research supports annual operational assessment of >28,000 fields per year in four states. Results document the impacts of agronomic management on conservation outcomes, support adaptive management of incentive payment structures, and can reduce the workload for conservation district staff by remotely verifying cover crop management. Additionally, super-spectral satellite applications have been developed to accurately map crop residue cover by measuring lignocellulose absorption in shortwave infrared wavelengths, producing a 7-year time series of tillage intensity maps for the Delmarva Peninsula. These remote sensing products can be used in decision support and modeling to estimate changes in nutrient, sediment, and carbon cycling resulting from conservation practice implementation in the working farm landscape. This manuscript provides an overview of remote sensing research findings and applications associated with the USDA LTAR and Conservation Effects Assessment Projects (CEAP), documenting a variety of previously published outcomes with update and expansion of techniques using additional unpublished data and analyses as appropriate.

Maryland↗
USGS2017

Landscape capability predicts upland game bird abundance and occurrence

Landscape capability (LC) models are a spatial tool with potential applications in conservation planning. We used survey data to validate LC models as predictors of occurrence and abundance at broad and fine scales for American woodcock ( Scolopax minor ) and ruffed grouse ( Bonasa umbellus ). Landscape capability models were reliable predictors of occurrence but were less indicative of relative abundance at route (11.5–14.6 km) and point scales (0.5–1 km). As predictors of occurrence, LC models had high sensitivity (0.71–0.93) and were accurate (0.71–0.88) and precise (0.88 and 0.92 for woodcock and grouse, respectively). Models did not predict point-scale abundance independent of the ability to predict occurrence of either species. The LC models are useful predictors of patterns of occurrences in the northeastern United States, but they have limited utility as predictors of fine-scale or route-specific abundances.

Journal of Wildlife Management↗
USGS2019

Landscape-scale greater prairie-chicken–habitat relations and the Conservation Reserve Program

Both the abundance of greater prairie-chickens ( Tympanuchus cupido pinnatus ) and the area of grassland enrolled in the Conservation Reserve Program (CRP) in northwestern Minnesota, USA, have recently declined. Although wildlife conservation is a stated objective of the CRP, the impact of the CRP on greater prairie-chicken populations has not been quantified. To address that information need, we evaluated the association between greater-prairie chicken lek density (leks/km 2 ), the number of males at leks (males/lek), and CRP enrollments in the context of landscape structure and composition in northwestern Minnesota. Using data from standardized prairie-chicken surveys and land cover in 17 41-km 2 survey blocks during 2004–2016, we used a mixed-effect model and a layered approach in an information-theoretic framework at multiple spatial scales to identify covariates related to prairie-chicken abundance. At the landscape scale, lek density was best explained by the amount of CRP grassland and wetland, grassland and wetland with long-term conservation goals (state, federal, and The Nature Conservancy owned); other wetlands managed with variable or no continuity in conservation goals; the contiguity of grasslands; and the number of patches of grasslands and wetlands in each survey block each year. Increasing the amount of CRP grassland in 41-km 2 survey blocks by 1 km 2 (2.4%) resulted in a corresponding increase of 6% in lek density. At the lek scale, the number of males per lek was best explained by the amount of CRP grassland and other grassland, CRP wetland and other wetland, forests, developed areas, shrubland, and the contiguity of CRP grassland. Increasing the amount of CRP grassland in the 2-km breeding-cycle habitat radius around a lek by 25% (3 km 2 ) corresponded to a 5% increase in males per lek. Our results suggest that both increasing the quantity of grassland CRP and wetland CRP enrollments and aggregating CRP grassland enrollments may increase greater prairie-chicken abundance.

Minnesota↗
USGS2014

Modelling landscape-scale erosion potential related to vehicle disturbances along the U.S.-Mexico border

Decades of intensive off-road vehicle use for border security, immigration, smuggling, recreation, and military training along the USA–Mexico border have prompted concerns about long-term human impacts on sensitive desert ecosystems. To help managers identify areas susceptible to soil erosion from anthropogenic activities, we developed a series of erosion potential models based on factors from the Universal Soil Loss Equation (USLE). To better express the vulnerability of soils to human disturbances, we refined two factors whose categorical and spatial representations limit the application of the USLE for non-agricultural landscapes: the C -factor (vegetation cover) and the P -factor (support practice/management). A soil compaction index ( P -factor) was calculated as the difference in saturated hydrologic conductivity ( K s ) between disturbed and undisturbed soils, which was then scaled up to maps of vehicle disturbances digitized from aerial photography. The C -factor was improved using a satellite-based vegetation index, which was better correlated with estimated ground cover ( r 2  = 0·77) than data derived from land cover ( r 2  = 0·06). We identified 9,780 km of unauthorized off-road tracks in the 2,800-km 2 study area. Maps of these disturbances, when integrated with soil compaction data using the USLE, provided landscape-scale information on areas vulnerable to erosion from both natural processes and human activities and are detailed enough for adaptive management and restoration planning. The models revealed erosion potential hotspots adjacent to the border and within areas managed as critical habitat for the threatened flat-tailed horned lizard and endangered Sonoran pronghorn.

Land Degradation and Development↗
USGS2011

Groundwater influences on the distribution and abundance of riverine smallmouth bass, Micropterus dolomieu , in pasture landscapes of the midwestern USA

This study examined how spring-flow (SF) contributions to streams related to the distribution and abundance of smallmouth bass Micropterus dolomieu in a predominately pasture landscape in Missouri, USA. Stream segments (N=13) with similar landscape characters were classified by SF volume into high SF (HSF) or low SF (LSF) groups. The densities of smallmouth bass, channel unit (CU) use and temperature-selection patterns were assessed for several life stages and frequency distributions for age 0 fish. More smallmouth bass were present in stream segments with HSF influence. Age 0 fish were twice as likely to be present in HSF stream segments. Older age classes were present in stream reaches independent of SF contribution. For all age classes, the use of particular CUs did not depend on SF influence. All age classes were more likely to be present in pools than other CUs. Microhabitat temperature selection differed among age classes. Age 0 fish selected warmer temperatures with a gradual shift towards cooler temperatures for older age classes. The length frequency of age 0 fish was skewed towards larger individuals in streams with limited SF influence, whereas the length frequency in HSF stream segments was skewed towards smaller individuals. The benefits of significant groundwater via SF influence seem to be related to increased hatch or survival of age 0 fish and the availability of optimal temperatures for adult smallmouth bass growth. Thermal refugia and stable flows provided by springs should be recognised for their biological potential to provide suitable habitat as climate change and other land-use alterations increase temperature regimes and alter flow patterns.

River Research and Applications↗
USGS2013

Hydrologic connectivity of floodplains, northern Missouri: implications for management and restoration of floodplain forest communities in disturbed landscapes

Hydrologic connectivity between the channel and floodplain is thought to be a dominant factor determining floodplain processes and characteristics of floodplain forests. We explored the role of hydrologic connectivity in explaining floodplain forest community composition along streams in northern Missouri, USA. Hydrologic analyses at 20 streamgages (207–5827 km 2 area) document that magnitudes of 2-year return floods increase systematically with increasing drainage area whereas the average annual number and durations of floodplain-connecting events decrease. Flow durations above the active-channel shelf vary little with increasing drainage area, indicating that the active-channel shelf is in quasi-equilibrium with prevailing conditions. The downstream decrease in connectivity is associated with downstream increase in channel incision. These relations at streamflow gaging stations are consistent with regional channel disturbance patterns: channel incision increases downstream, whereas upstream reaches have either not incised or adjusted to incision by forming new equilibrium floodplains. These results provide a framework to explain landscape-scale variations in composition of floodplain forest communities in northern Missouri. Faust ( 2006 ) had tentatively explained increases of flood-dependent tree species, and decreases of species diversity, with a downstream increase in flood magnitude and duration. Because frequency and duration of floodplain-connecting events do not increase downstream, we hypothesize instead that increases in relative abundance of flood-dependent trees at larger drainage area result from increasing size of disturbance patches. Bank-overtopping floods at larger drainage area create large, open, depositional landforms that promoted the regeneration of shade-intolerant species. Higher tree species diversity in floodplains with small drainage areas is associated with non-incised floodplains that are frequently connected to their channels and therefore subject to greater effective hydrologic variability compared with downstream floodplains. Understanding the landscape-scale geomorphic and hydrologic controls on floodplain connectivity provides a basis for more effective management and restoration of floodplain forest communities.

Missouri↗
USGS2021

White-nose Syndrome and environmental correlates to landscape-scale bat presence

Over the past 13 years, White-nose Syndrome (WNS) has caused North American bat population declines and shifted community structure towards species less or unaffected by the disease. Mist-netting, acoustic surveys, and cave count data have been used to document changes in bat presence and activity through site-specific, pre- and post-WNS studies. Management and survey guidance often must be applied at a combined landscape and site-specific scale. Our objective was to explore the relationships among WNS impact, influence of available hibernacula, and environmental factors for the nightly presence of 3 WNS-affected bats: the Indiana bat ( Myotis sodalis ), northern long-eared bat ( M. septentrionalis ), and big brown bat ( Eptesicus fuscus ). We used recordings from 10 acoustic monitoring study areas, each with 3 survey locations across the states of Virginia, West Virginia, Ohio and Kentucky to assess changes in nightly bat presence during the summer of 2017. There were significant positive and negative correlates of broad land-cover categories for presence of all 3 bat species. Our findings also corroborated trends in abundance and distribution patterns found in prior, smaller-scale studies, supporting the relevance of land cover categories in a large-scale acoustic monitoring framework. We observed a negative association between WNS impact-years and nightly northern long-eared bat presence, but low occurrence and patchy distribution reduced our ability to infer strong relationships. Big brown bat presence showed a significant positive relationship with WNS occurrence on the landscape, providing evidence that big brown bats are maintaining populations after years of exposure. Indiana bats were the least-documented species, limiting the strength of our conclusions, but we did observe significant temporal patterns in nightly presence, with higher probabilities of presence earlier in the summer. Our results show the potential efficacy of using a WNS impact metric to predict summer bat presence, inform current U.S. Fish and Wildlife Service acoustic monitoring guidelines, and highlight which environmental variables are relevant for large-scale acoustic monitoring.

Wildlife Society Bulletin↗
USGS2018

Nest tree use by Southern flying squirrels in fragmented midwestern landscapes

Southern flying squirrels ( Glaucomys volans ; SFS) nest in naturally formed cavities in snags and hardwoods found in mature, oak ( Quercus spp.)–hickory ( Carya spp.) forests. Intensive forest fragmentation of the Midwest United States limits the number of available nesting trees. We quantified annual nest‐site selection patterns by southern flying squirrels across fragmented landscapes of west‐central Illinois, USA. We used radiotelemetry to measure nest‐tree use by 55 SFS (30 males, 25 females) captured during 2014–2016. Of 105 nest trees used by SFS, live trees and snags comprised 75% and 25%, respectively. Probability of diurnal nest‐tree use increased 1.08/1.00‐cm increase in diameter‐breast‐height and by 1.50/1‐unit increase in the number of overstory mast trees between random and nest‐tree habitat areas (i.e., 300‐m 2 circular plots). Similarly, probability of diurnal nest‐tree use increased 1.29/1‐unit increase in the number of snags between random and nest‐tree habitat areas. Our results revealed no intersexual differences in patterns of nest‐site selection, which may reflect the tendency for SFS to compensate for reduced availability of key structural attributes (i.e., snags, overstory trees) across fragmented forests by exhibiting similar intersexual patterns of nest‐tree use. Use of natural cavities for denning is encouraging, but also underscores the importance of unharvested oak–hickory forests in contributing essential habitat to SFS populations in fragmented Midwestern landscapes.

Wildlife Society Bulletin↗
USGS1991

Landscape analysis: Theoretical considerations and practical needs

Numerous systems of land classification have been proposed. Most have led directly to or have been driven by an author's philosophy of earth-forming processes. However, the practical need of classifying land for planning and management purposes requires that a system lead to predictions of the results of management activities. We propose a landscape classification system composed of 11 units, from realm (a continental mass) to feature (a splash impression). The classification concerns physical aspects rather than economic or social factors; and aims to merge land inventory with dynamic processes. Landscape units are organized using a hierarchical system so that information may be assembled and communicated at different levels of scale and abstraction. Our classification uses a geomorphic systems approach that emphasizes the geologic-geomorphic attributes of the units. Realm, major division, province, and section are formulated by subdividing large units into smaller ones. For the larger units we have followed Fenneman's delineations, which are well established in the North American literature. Areas and districts are aggregated into regions and regions into sections. Units smaller than areas have, in practice, been subdivided into zones and smaller units if required. We developed the theoretical framework embodied in this classification from practical applications aimed at land use planning and land management in Maryland (eastern Piedmont Province near Baltimore) and Utah (eastern Uinta Mountains). ?? 1991 Springer-Verlag New York Inc.

Environmental Geology and Water Sciences↗
USGS2003

Use of radar remote sensing (RADARSAT) to map winter wetland habitat for shorebirds in an agricultural landscape

Many of today's agricultural landscapes once held vast amounts of wetland habitat for waterbirds and other wildlife. Successful restoration of these landscapes relies on access to accurate maps of the wetlands that remain. We used C-band (5.6-cm-wavelength), HH-polarized radar remote sensing (RADARSAT) at a 38?? incidence angle (8-m resolution) to map the distribution of winter shorebird (Charadriiformes) habitat on agricultural lands in the Willamette Valley of western Oregon. We acquired imagery on three dates (10 December 1999, 27 January 2000, and 15 March 2000) and simultaneously collected ground reference data to classify radar signatures and evaluate map accuracy of four habitat classes: (1) wet with ??? 50% vegetation (considered optimal shorebird habitat), (2) wet with > 50% vegetation, (3) dry with ??? 50% vegetation, and (4) dry with > 50% vegetation. Overall accuracy varied from 45 to 60% among the three images, but the accuracy of focal class 1 was greater, ranging from 72 to 80%. Class 4 coverage was stable and dominated maps (40% of mapped study area) for all three dates, while class 3 coverage decreased slightly throughout the study period. Among wet classes, class 1 was most abundant (30% coverage) in December and January, decreasing in March by 15%. Conversely, class 2 increased dramatically from January to March, likely due to transition from class 1 as vegetation grew. This approach was successful in detecting optimal habitat for shorebirds on agricultural lands. For modest classification schemes, radar remote sensing is a valuable option for wetland mapping in areas where cloud cover is persistent. ?? 2003 Springer-Verlag New York Inc.

Environmental Management↗
USGS2011

Estimating the Cumulative Ecological Effect of Local Scale Landscape Changes in South Florida

Ecosystem restoration in south Florida is a state and national priority centered on the Everglades wetlands. However, urban development pressures affect the restoration potential and remaining habitat functions of the natural undeveloped areas. Land use (LU) planning often focuses at the local level, but a better understanding of the cumulative effects of small projects at the landscape level is needed to support ecosystem restoration and preservation. The South Florida Ecosystem Portfolio Model (SFL EPM) is a regional LU planning tool developed to help stakeholders visualize LU scenario evaluation and improve communication about regional effects of LU decisions. One component of the SFL EPM is ecological value (EV), which is evaluated through modeled ecological criteria related to ecosystem services using metrics for (1) biodiversity potential, (2) threatened and endangered species, (3) rare and unique habitats, (4) landscape pattern and fragmentation, (5) water quality buffer potential, and (6) ecological restoration potential. In this article, we demonstrate the calculation of EV using two case studies: (1) assessing altered EV in the Biscayne Gateway area by comparing 2004 LU to potential LU in 2025 and 2050, and (2) the cumulative impact of adding limestone mines south of Miami. Our analyses spatially convey changing regional EV resulting from conversion of local natural and agricultural areas to urban, industrial, or extractive use. Different simulated local LU scenarios may result in different alterations in calculated regional EV. These case studies demonstrate methods that may facilitate evaluation of potential future LU patterns and incorporate EV into decision making.

Florida↗
USGS2022

Climate and landscape controls on old-growth western juniper demography in the northern Great Basin, USA

Western juniper ( Juniperus occidentalis Hook.) woodlands have persisted for millennia in semiarid parts of the northern Great Basin, USA, providing critical habitat for plant and animal species. Historical records suggest that the establishment of western juniper is strongly associated with regional climatic variability. For example, the abundance of western juniper pollen and macrofossils measured in lake sediment cores increased rapidly in the mid-1500s, concurrent with a regional increase in winter precipitation. However, little is known about how climatic factors interact with landscape structure to control the spatial distribution of western juniper at fine scales and at lower treelines. We used tree rings to reconstruct a spatially distributed history of establishment for 421 western juniper trees across 130 ha on Horse Ridge in central Oregon. Establishment occurred between 845 and 1961 CE, but most trees established after the mid-1550s. The pronounced sixteenth century pulse of establishment represents a transition from more open wooded shrublands to persistent woodlands and coincides with an increase in cool-season moisture and generally cool summer temperatures. Ancient trees that established before this were limited to certain microsites, suggesting that local topoedaphic conditions influenced juniper woodland demography and distributions, although we could not identify consistent environmental drivers. In the future, warmer and drier growing season conditions and a potential increase in wildfire activity may broadly limit western juniper recruitment and its distribution across the region, but at finer scales landscape features that buffer climate change impacts or provide fire safe niches may serve as refugia.

Oregon↗
USGS2015

Repeated landscape-scale treatments following fire suppress a non-native annual grass and promote recovery of native perennial vegetation

Invasive non-native species pose a large threat to restoration efforts following large-scale disturbances. Bromus tectorum (cheatgrass) is a non-native annual grass in the western U.S. that both spreads quickly following fire and accelerates the fire cycle. Herbicide and seeding applications are common restoration practices to break the positive fire-invasion feedback loop and recover native perennial species, but their interactive effects have infrequently been tested at the landscape-scale and repeated in time to encourage long-lasting effects. We determined the efficacy of repeated post-fire application of the herbicide imazapic and seeding treatments to suppress Bromus abundance and promote perennial vegetation recovery. We found that the selective herbicide reduced Bromus cover by ~30 % and density by >50 % across our study sites, but had a strong initial negative effect on seeded species. The most effective treatment to promote perennial seeded species cover was seeding them alone followed by herbicide application 3 years later when the seeded species had established. The efficacy of the treatments was strongly influenced by water availability, as precipitation positively affected the density and cover of Bromus ; soil texture and aspect secondarily influenced Bromus abundance and seeded species cover by modifying water retention in this semi-arid region. Warmer temperatures positively affected the non-native annual grass in the cool-season, but negatively affected seeded perennial species in the warm-season, suggesting an important role of seasonality in a region projected to experience large increases in warming in the future. Our results highlight the importance of environmental interactions and repeated treatments in influencing restoration outcomes at the landscape-scale.

Utah↗
USGS2014

Opposing resonses to ecological gradients structure amphibian and reptile communities across a temperate grassland-savanna-forest landscape

Temperate savannas are threatened across the globe. If we prioritize savanna restoration, we should ask how savanna animal communities differ from communities in related open habitats and forests. We documented distribution of amphibian and reptile species across an open-savanna–forest gradient in the Midwest U.S. to determine how fire history and habitat structure affected herpetofaunal community composition. The transition from open habitats to forests was a transition from higher reptile abundance to higher amphibian abundance and the intermediate savanna landscape supported the most species overall. These differences warn against assuming that amphibian and reptile communities will have similar ecological responses to habitat structure. Richness and abundance also often responded in opposite directions to some habitat characteristics, such as cover of bare ground or litter. Herpetofaunal community species composition changed along a fire gradient from infrequent and recent fires to frequent but less recent fires. Nearby (200-m) wetland cover was relatively unimportant in predicting overall herpetofaunal community composition while fire history and fire-related canopy and ground cover were more important predictors of composition, diversity, and abundance. Increased developed cover was negatively related to richness and abundance. This indicates the importance of fire history and fire related landscape characteristics, and the negative effects of development, in shaping the upland herpetofaunal community along the native grassland–forest continuum.

Indiana↗
USGS2023

Landscape-scale drivers of tayra abundance in the Ecuadorian Andes

Habitat conversion to agriculture and overexploitation of wildlife are the two largest drivers of biodiversity loss globally. Biodiversity loss is especially prevalent in areas undergoing rapid economic development at the expense of natural land cover as is the case across much of South America. Despite expected declines in wildlife populations associated with ongoing large-scale land conversions, for many species we lack sufficient data on key threats and drivers of abundance in order to inform appropriate management and conservation. Collecting data to estimate critical state variables such as abundance can be expensive, logistically challenging, and even implausible on spatial scales relevant to species management, especially for carnivores which are elusive and difficult to monitor. Here, we use detection-non-detection data collected using a structured camera trap survey repeated over two years in the Ecuadorian Andes to produce insights into the habitat associations and potential threats faced by the tayra, a medium-sized carnivore that despite being perceived to be relatively common in South America, remains largely understudied. We use hierarchical modelling to estimate an index of abundance for the tayra while accounting for imperfect detection. We demonstrate the tayra to be a lowland habitat generalist, with conversion of land to agriculture potentially benefitting this species in the short term, with increasing proportion of core agricultural land being associated with higher indices of abundance. However, we highlight that this state could potentially serve as an ecological trap in the long term. We provide evidence for negative impacts of human population density on tayra abundance. We hypothesize this relationship could be underpinned by conflict and subsequent persecution by humans, which is likely to be exacerbated in agricultural landscapes. These findings suggest that like many carnivores, the tayra may be able to adapt and even thrive in human modified landscapes given societal acceptance, thus, conservation strategies for the tayra that focus on fostering co-existence between humans and this medium-sized carnivore may contribute to its future.

Biodiversity and Conservation↗
USGS2015

Landscape genomics of Sphaeralcea ambigua in the Mojave Desert: a multivariate, spatially-explicit approach to guide ecological restoration

Local adaptation influences plant species’ responses to climate change and their performance in ecological restoration. Fine-scale physiological or phenological adaptations that direct demographic processes may drive intraspecific variability when baseline environmental conditions change. Landscape genomics characterize adaptive differentiation by identifying environmental drivers of adaptive genetic variability and mapping the associated landscape patterns. We applied such an approach to Sphaeralcea ambigua , an important restoration plant in the arid southwestern United States, by analyzing variation at 153 amplified fragment length polymorphism loci in the context of environmental gradients separating 47 Mojave Desert populations. We identified 37 potentially adaptive loci through a combination of genome scan approaches. We then used a generalized dissimilarity model (GDM) to relate variability in potentially adaptive loci with spatial gradients in temperature, precipitation, and topography. We identified non-linear thresholds in loci frequencies driven by summer maximum temperature and water stress, along with continuous variation corresponding to temperature seasonality. Two GDM-based approaches for mapping predicted patterns of local adaptation are compared. Additionally, we assess uncertainty in spatial interpolations through a novel spatial bootstrapping approach. Our study presents robust, accessible methods for deriving spatially-explicit models of adaptive genetic variability in non-model species that will inform climate change modelling and ecological restoration.

California, Nevada↗
USGS2017

Small-scale genetic structure in an endangered wetland specialist: possible effects of landscape change and population recovery

The effects of anthropogenic landscape change on genetic population structure are well studied, but the temporal and spatial scales at which genetic structure can develop, especially in taxa with high dispersal capabilities like birds, are less well understood. We investigated population structure in the Hawaiian gallinule ( Gallinula galeata sandvicensis ), an endangered wetland specialist bird on the island of O`ahu (Hawai`i, USA). Hawaiian gallinules have experienced a gradual population recovery from near extinction in the 1950s, and have recolonized wetlands on O`ahu in the context of a rapidly urbanizing landscape. We genotyped 152 Hawaiian gallinules at 12 microsatellite loci and sequenced a 520 base-pair fragment of the ND2 region of mitochondrial DNA (mtDNA) from individuals captured at 13 wetland locations on O`ahu in 2014–2016. We observed moderate to high genetic structuring (overall microsatellite F ST = 0.098, mtDNA F ST = 0.248) among populations of Hawaiian gallinules occupying wetlands at very close geographic proximity (e.g., 1.5–55 km). Asymmetry in gene flow estimates suggests that Hawaiian gallinules may have persisted in 2–3 strongholds which served as source populations that recolonized more recently restored habitats currently supporting large numbers of birds. Our results highlight that genetic structure can develop in taxa that are expanding their range after severe population decline, and that biologically significant structuring can occur over small geographic distances, even in avian taxa.

Hawai'i↗
USGS2020

Genes in space: What Mojave desert tortoise genetics can tell us about landscape connectivity

Habitat loss and fragmentation in the Mojave Desert have been increasing, which can create barriers to movement and gene flow leading to decreased populations of native species. Disturbance and degradation of Mojave desert tortoise habitat includes linear features (e.g. highways, railways, and a network of dirt roads), urbanized areas, and their associated infrastructure, mining activities, energy distribution systems, and most recently, utility-scale solar facilities. To evaluate the spatial genetic structure of tortoises in an area experiencing rapid habitat loss, we conducted field surveys from 2015-2017 and genotyped 299 tortoises at 20 microsatellite loci within and around Ivanpah Valley along the California/Nevada border. We used a Bayesian clustering analysis to examine population genetic structure across valley and mountain pass habitat. Spatial principal components analysis was included to further investigate population genetic structure with isolation-by-distance. To explicitly incorporate landscape features (e.g. habitat and anthropogenic linear barriers) we used maximum likelihood population effects. We assessed recent gene flow on the landscape through maximum likelihood pedigree analyses of relatedness. We detected three to four genetic clusters with high levels of admixture that generally corresponded to three valleys separated by mountain ranges, and a genetically distinguishable population in one mountain pass. Pedigree analyses showed second order relationships up to 60 km apart suggesting a greater range of interactions and inter-relatedness between individuals than previously suspected. Our results support historical gene flow with isolation-by-resistance, and reveal a genetic signal indicative of reduction in genetic connectivity across two parallel linear features (a railway and a highway). This work demonstrates the value of protecting connected tracts of functional habitat and the importance of connectivity research in conservation.

California, Nevada↗