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1. Fine‐scale habitat heterogeneity and vole runways influence seed dispersal in Plagiobothrys nothofulvus

   https://doi.org/10.1002/ajb2.1433  

   Grasty, Monica R. ; Thompson, Pamela G. ; Hendrickson, Elizabeth C. ; Pheil, Avery E. ; Cruzan, Mitchell B. ( February 2020 , American Journal of Botany)

   Seed dispersal allows plants to colonize new sites and contributes to gene flow among populations. Despite its fundamental importance to ecological and evolutionary processes, our understanding of seed dispersal is limited due to the difficulty of directly observing dispersal events. This is particularly true for the majority of plant species that are considered to have gravity as their primary dispersal mechanism. The potential for long‐distance movement of gravity‐dispersed seeds by secondary dispersal vectors is rarely evaluated.

   We employ whole‐genome assays of maternally inherited cpDNAinPlagiobothrys nothofulvusto resolve patterns of genetic variation due to effective (realized) seed dispersal within a 16 hectare prairie that is characterized by a mosaic of habitat types. We evaluate the effects of microgeographic landscape features extracted from micro‐UAVaerial surveys on patterns of seed dispersal using landscape genetics methods.

   We found evidence of high resistance to seed‐mediated gene flow (effective dispersal) within patches ofPlagiobothrys nothofulvus, and strong genetic structure over distances of less than 20 m. Geographic distance was a poor predictor of dispersal distance, while landscape features had stronger influences on patterns of dispersal (distance and direction of seed movement). Patterns of dispersal were best predicted by the combined distribution of flower patches, habitat type, and the network of vole runways, with the latter explaining the largest proportion of variation in the model.

   Our results suggest that primary dispersal occurs mostly within microhabitats and infrequent secondary dispersal may occur over longer distances due to the activity of small mammals and other vertebrates.

    

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2. Bridging the gap between movement data and connectivity analysis using the Time-Explicit Habitat Selection (TEHS) model

   https://doi.org/10.1186/s40462-024-00461-1  

   Valle, Denis ; Attias, Nina ; Cullen, Joshua A. ; Hooten, Mevin B. ; Giroux, Aline ; Oliveira-Santos, Luiz Gustavo R. ; Desbiez, Arnaud L. J. ; Fletcher, Jr., Robert J. ( March 2024 , Movement Ecology)

   Understanding how to connect habitat remnants to facilitate the movement of species is a critical task in an increasingly fragmented world impacted by human activities. The identification of dispersal routes and corridors through connectivity analysis requires measures of landscape resistance but there has been no consensus on how to calculate resistance from habitat characteristics, potentially leading to very different connectivity outcomes.

   We propose a new model, called the Time-Explicit Habitat Selection (TEHS) model, that can be directly used for connectivity analysis. The TEHS model decomposes the movement process in a principled approach into a time and a selection component, providing complementary information regarding space use by separately assessing the drivers of time to traverse the landscape and the drivers of habitat selection. These models are illustrated using GPS-tracking data from giant anteaters (Myrmecophaga tridactyla) in the Pantanal wetlands of Brazil.

   The time model revealed that the fastest movements tended to occur between 8 p.m. and 5 a.m., suggesting a crepuscular/nocturnal behavior. Giant anteaters moved faster over wetlands while moving much slower over forests and savannas, in comparison to grasslands. We also found that wetlands were consistently avoided whereas forest and savannas tended to be selected. Importantly, this model revealed that selection for forest increased with temperature, suggesting that forests may act as important thermal shelters when temperatures are high. Finally, using the spatial absorbing Markov chain framework, we show that the TEHS model results can be used to simulate movement and connectivity within a fragmented landscape, revealing that giant anteaters will often not use the shortest-distance path to the destination patch due to avoidance of certain habitats.

   The proposed approach can be used to characterize how landscape features are perceived by individuals through the decomposition of movement patterns into a time and a habitat selection component. Additionally, this framework can help bridge the gap between movement-based models and connectivity analysis, enabling the generation of time-explicit connectivity results.

    

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3. Population connectivity of aquatic insects in a dam‐regulated, desert river

   https://doi.org/10.1002/rra.3972  

   Abernethy, Erin F. ; Muehlbauer, Jeffrey D. ; Kennedy, Theodore A. ; Dziedzic, Katherine E. ; Elder, Holland ; Burke, Molly K. ; Lytle, David A. ( April 2022 , River Research and Applications)

   Humans have exaggerated natural habitat fragmentation, negatively impacting species dispersal and reducing population connectivity. Habitat fragmentation can be especially detrimental in freshwater populations, whose dispersal is already constrained by the river network structure. Aquatic insects, for instance, are generally limited to two primary modes of dispersal: downstream drift in the aquatic juvenile life stages and flight during the terrestrial winged adult stage. Yet the impacts of large hydropower dams can make rivers uninhabitable for incoming (drifting) juvenile insects, with remaining refugia found only in tributaries. The ability of adult aquatic insects to traverse such river stretches in search of suitable tributary habitat likely depends on factors such as species‐specific dispersal ability and distance between tributaries. To explore the intersection of natural and human‐induced habitat fragmentation on aquatic insect dispersal ability, we quantified population genetics of three taxa with varying dispersal abilities, a caddisfly (Hydropsychidae,Hydropsyche oslari), a mayfly (Baetidae:Fallceon quilleri), and a water strider (Veliidae:Rhagovelia distincta), throughout tributaries of the Colorado River in the Grand Canyon, Arizona, USA. Using 2bRAD reduced genome sequencing and landscape genetics analyses, we revealed a strong pattern of isolation by distance among mayfly populations. This contrasts with caddisfly and water strider populations, which were largely panmictic. Analysis of thousands of informative single nucleotide polymorphisms showed that realized dispersal ability may not be accurately predicted by species traits for these widespread species. Principal components analysis revealed a strong division between caddisfly populations upstream and downstream of Havasu Creek (279 km through the 390 km study reach), suggesting that the geography of the Grand Canyon imposes a dispersal barrier for this species. Our use of genetic tools in the Grand Canyon to understand population structure has enabled us to elucidate dispersal barriers for aquatic insects. Ultimately, these data may be useful in informing effective conservation management plans for understudied organisms of conservation interest.

    

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4. Inferring population connectivity in eastern m assasauga rattlesnakes ( S istrurus c atenatus ) using landscape genetics

   https://doi.org/10.1002/eap.2793  

   Martin, Scott A. ; Peterman, William E. ; Lipps, Jr., Gregory J. ; Gibbs, H. Lisle ( January 2023 , Ecological Applications)

   Assessing the environmental factors that influence the ability of a threatened species to move through a landscape can be used to identify conservation actions that connect isolated populations. However, direct observations of species' movement are often limited, making the development of alternate approaches necessary. Here we use landscape genetic analyses to assess the impact of landscape features on the movement of individuals between local populations of a threatened snake, the eastern massasauga rattlesnake (Sistrurus catenatus). We linked connectivity data with habitat information from two landscapes of similar size: a large region of unfragmented habitat and a previously studied fragmented landscape consisting of isolated patches of habitat. We used this analysis to identify features of the landscape where modification or acquisition would enhance population connectivity in the fragmented region. We found evidence that current connectivity was impacted by both contemporary land‐cover features, especially roads, and inherent landscape features such as elevation. Next, we derived estimates of expected movement ability using a recently developed pedigree‐based approach and least‐cost paths through the unfragmented landscape. We then used our pedigree and resistance map to estimate resistance polygons of the potential extent forS. catenatusmovement in the fragmented landscape. These polygons identify possible sites for future corridors connecting currently isolated populations in this landscape by linking the impact of future habitat modification or land acquisition to dispersal ability in this species. Overall, our study shows how modeling landscape resistance across differently fragmented landscapes can identify habitat features that affect contemporary movement in threatened species in fragmented landscapes and how this information can be used to guide mitigation actions whose goal is to connect isolated populations.

    

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5. The influence of history, geography and environment on patterns of diversification in the western terrestrial garter snake

   https://doi.org/10.1111/jbi.14146  

   Hallas, Joshua M. ; Parchman, Thomas L. ; Feldman, Chris R. ( June 2021 , Journal of Biogeography)

   A central aim of biogeography is to understand how biodiversity is generated and maintained across landscapes. Here, we establish phylogenetic and population genetic patterns in a widespread reptile to quantify the influence of historical biogeography and current environmental variation on patterns of genetic diversity.

   Western North America.

   Western terrestrial garter snake,Thamnophis elegans.

   We used double‐digest RADseq to estimate phylogenetic relationships and characterize population genetic structure across the three widespread subspecies ofT. elegans:T. e. vagrans(wandering garter snake),T. e. elegans(mountain garter snake) andT. e. terrestris(coast garter snake). We assessed patterns of dispersal and vicariance across biogeographic regions using ancestral area reconstruction (AAR) and deviations from isolation‐by‐distance across the landscape using estimated effective migration surfaces (EEMS). We identified environmental variables potentially shaping local adaptation in regional lineages using genetic‐environment association (GEA) analyses.

   We recovered three well‐differentiated genetic groups that correspond to the three subspecies. AAR analyses inferred the eastern Cascade Range as the ancestral area, with dispersal to both the east and west across western North America. Populations ofT. e. elegansdisplayed a latitudinal gradient in genetic variation across the Sierra Nevada and northern California, while populations ofT. e. terrestrisshow discrete genetic breaks consistent with well‐known biogeographic barriers. Lastly, GEA analyses identified allele frequency shifts at loci associated with a common set of environmental variables in bothT. e. elegansandT. e. terrestris.

   T. elegansis composed of distinct evolutionary lineages, each with its own geographic range and history of diversification.T. e. elegansandT. e. terrestrisshow unique patterns of diversification as populations dispersed from east to west and while adapting to the new environments they colonized. Historical events, landscape features and environmental variation have all contributed to patterns of differentiation inT. elegans.

    

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