An approximation approach to spatial connectivity for a data-limited endangered species with implications for habitat restoration

Among numerous concerns, restoration ecologists are routinely plagued with the problem of where to implement conservation efforts to best maintain spatial connectivity and population structure. Knowledge about connectivity within a metapopulation could offer valuable insight to address this issue and could help with the allocation of limited resources more effectively. However, direct estimation of dispersal is challenging because species can disperse widely within a landscape. Here, we developed a novel hierarchical Bayesian model to estimate spatial connectivity from occurrence data of an endangered stream fish, Topeka shiner (Notropis topeka). Our goal was to identify dispersal corridors that are centrally connected to the metapopulation that could be beneficial in decision making about future habitat restorations aimed at maintaining population structure. Connectivity modeling is data intensive and resource managers may not have the necessary data requirements; thus, we also examined the usefulness of graph theory (i.e. network centrality) as a proxy for connectivity. Model selection identified an upstream biased asymmetric dispersal pattern for the species. We were able to quantify and map connectivity and identified over 68 km of stream reaches as highly connected to the metapopulation. Probability of occurrence in dispersal corridors (i.e. streams) increased with connectivity and decreased with drainage area, highlighting the importance of conserving dispersal corridors and preferred habitat patches. Restorations in connected locations would provide critical habitat near important dispersal corridors. Betweenness centrality was positively correlated with connectivity and occurrence in restored habitat. Modeling of metapopulation connectivity and its correlation with graph theory demonstrated the usefulness of these techniques to guide conservation actions, especially in countries where data collection efforts are not common and conservation funding is limited.This article is published as Wahl, Charles F., Nika Galic, Richard Brain, Maxime Vaugeois, Michael Weber, Kevin J. Roe, Timothy Stewart et al. "An approximation approach to spatial connectivity for a data-limited endangered species with implications for habitat restoration." Biological Conservation 291 (2024): 110470. doi:10.1016/j.biocon.2024.110470. Works produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted

Floods, drying, habitat connectivity, and fish occupancy dynamics in restored and unrestored oxbows of West Central Iowa, USA

1. In the agricultural landscape of the Midwestern USA, waterways are highly altered. Oxbows are among the few remaining off‐channel habitats associated with streams, supporting fish assemblages that include the endangered Topeka shiners Notropis topeka in portions of their remaining range. Oxbow restorations seek to increase the number and quality of oxbows for Topeka shiners. For oxbows to provide optimal habitat, periods of isolation from streams and connection with streams during floods are necessary. 2. Water levels and patterns of drying and hydrological connectivity between 12 oxbows and their neighboring streams in West Central Iowa were continuously monitored from May to October 2011, and fish assemblages were assessed for responses to the differing hydrodynamics using dynamic occupancy modelling. 3. The 12 oxbows exhibited varied hydrodynamics and connectivity with streams. Two oxbows never contained fish; these oxbows never flooded and were among the three oxbows that were dry for the longest periods. 4. Occupancy modelling suggested that connection with the stream via floods significantly increased the probability of colonization, and low water level increased the probability of local extinction from oxbows. Thirteen of the 16 fish species encountered had detection probabilities over 60%, and eight had detection probabilities over 90%, including Topeka shiners. 5. None of the five previously restored oxbows flooded; all five contained fish, but only one contained Topeka shiners. Three of the four oxbows containing Topeka shiners flooded and all four dried at least once. 6. These results suggest that planning for future oxbow restorations should consider: (i) sites that flood frequently; and (ii) construction methods promoting alternating periods of isolation from and connection with streams

Effects of Commercial Harvest on Shovelnose Sturgeon Populations in the Upper Mississippi River

Shovelnose sturgeon Scaphirhynchus platorynchus have become an increasingly important commercial species in the upper Mississippi River (UMR) because of the collapse of foreign sturgeon (family Acipenseridae) populations and bans on imported caviar. In response to concerns about the sustainability of the commercial shovelnose sturgeon fishery in the UMR, we undertook this study to describe the demographics of the shovelnose sturgeon population and evaluate the influence of commercial harvest on shovelnose sturgeon populations in the UMR. A total of 1,682 shovelnose sturgeon were collected from eight study pools in 2006 and 2007 (Pools 4, 7, 9, 11, 13, 14, 16, and 18). Shovelnose sturgeon from upstream pools generally had greater lengths, weights, and ages than those from downstream pools. Additionally, mortality estimates were lower in upstream pools (Pools 4, 7, 9, and 11) than in downstream pools (Pools 13, 14, 16, and 18). Linear regression suggested that the slower growth of shovelnose sturgeon is a consequence of commercial harvest in the UMR. Modeling of potential management scenarios suggested that a 685-mm minimum length limit is necessary to prevent growth and recruitment overfishing of shovelnose sturgeon in the UMR

Phagosomal Rupture by Mycobacterium tuberculosis Results in Toxicity and Host Cell Death

Survival within macrophages is a central feature of Mycobacterium tuberculosis pathogenesis. Despite significant advances in identifying new immunological parameters associated with mycobacterial disease, some basic questions on the intracellular fate of the causative agent of human tuberculosis in antigen-presenting cells are still under debate. To get novel insights into this matter, we used a single-cell fluorescence resonance energy transfer (FRET)-based method to investigate the potential cytosolic access of M. tuberculosis and the resulting cellular consequences in an unbiased, quantitative way. Analysis of thousands of THP-1 macrophages infected with selected wild-type or mutant strains of the M. tuberculosis complex unambiguously showed that M. tuberculosis induced a change in the FRET signal after 3 to 4 days of infection, indicating phagolysosomal rupture and cytosolic access. These effects were not seen for the strains M. tuberculosisΔRD1 or BCG, both lacking the ESX-1 secreted protein ESAT-6, which reportedly shows membrane-lysing properties. Complementation of these strains with the ESX-1 secretion system of M. tuberculosis restored the ability to cause phagolysosomal rupture. In addition, control experiments with the fish pathogen Mycobacterium marinum showed phagolysosomal translocation only for ESX-1 intact strains, further validating our experimental approach. Most importantly, for M. tuberculosis as well as for M. marinum we observed that phagolysosomal rupture was followed by necrotic cell death of the infected macrophages, whereas ESX-1 deletion- or truncation-mutants that remained enclosed within phagolysosomal compartments did not induce such cytotoxicity. Hence, we provide a novel mechanism how ESX-1 competent, virulent M. tuberculosis and M. marinum strains induce host cell death and thereby escape innate host defenses and favor their spread to new cells. In this respect, our results also open new research directions in relation with the extracellular localization of M. tuberculosis inside necrotic lesions that can now be tackled from a completely new perspective

Grassland Birds in Restored Grassland of the Rainwater Basin Region in Nebraska

Conservationists and managers mention grassland restorations as a conservation strategy to reverse the decline of grassland bird populations in the Great Plains. In the Rainwater Basin Region of southcentral Nebraska, state and federal resource agencies have used grassland restorations to protect wetlands from sedimentation and agrichemical runoff. These grassland restorations may also provide important habitat for breeding grassland birds. In this paper, we describe the abundance, composition, nesting success, and habitat requirements of breeding birds in grassland restorations in the Rainwater Basin Region. We observed 14 grassland bird species in 12 grassland restorations. The most abundant species were dickcissels (Spiza americana), grasshopper sparrows (Ammodramus savannarum), and bobolinks (Dolichonyx oryzivorus). We found a total of 84 nests composed of II species in restorations. Dickcissels and grasshopper sparrows accounted for 77% of all nests found. Nest success was 31% (26 nests), and the major cause of nest loss was predation, which accounted for 66% (38 nests) of all nest failures. The occurrence of 10 of the species in grassland restorations was influenced by a variety of vegetation variables. Grassland bird species have benefited from grassland restorations in the Rainwater Basin Region. Conservation strategies for grassland birds in the Rainwater Basin Region should continue to focus on restoring marginal croplands back to grasslands