Wetland plant community variation across replicate urban to rural gradients: non-native species as both drivers and passengers in systems impacted by anthropogenic land-use

Christian M. King & Stephen M. Hovick. 2020. Urban Ecosystems. https://doi.org/10.1007/s11252-020-01012-3

Abstract

Anthropogenic land-use change impacts ecological communities in urban and rural landscapes, and wetlands are particularly vulnerable despite the valuable ecosystem services they provide. Urbanized non-wetland systems are often enriched in non-native plant species, and similar patterns in wetlands would have implications for ecosystem function and biodiversity. We evaluated landscape-scale patterns of plant community diversity across gradients of rural to urban land-use, testing whether diversity was related to environmental conditions indicative of surrounding land-use. We surveyed vegetation and collected soil samples from 45 wetlands throughout Ohio, USA. Sites were categorized based on surrounding land-use as intense urban, moderate urban, or rural, representing 15 replicate urban to rural gradients. Non-native richness was 56% greater and non-native relative abundance 74% greater in intense urban sites compared to rural sites. Structural equation modeling indicated that high non-native relative abundance caused reductions in native plant richness but not native Shannon diversity, which was instead related to high concentrations of urban-associated soil contaminants such as cadmium and sodium. Our results support both versions of the driver-passenger model of invasion impacts, depending on the response: native richness is directly limited by competition with non-native species (the driver model), while native diversity is limited more by urban-associated stressors that also affect non-natives (the passenger model). The few wetlands remaining in highly urban areas thus experience a range of constraints affecting multiple dimensions of wetland health. We argue it is in these sites specifically where the benefits of restoring wetland ecosystems will be maximized.

Projecting future habitat quality of three midwestern reservoir fishes under warming conditions

Richard R. Budnik, Joseph D. Conroy, Richard D. Zweifel, Stuart A. Ludsin, Elizabeth A. Marschall. 2020. https://doi.org/10.1111/eff.12561

Abstract

Rising temperatures caused by climate change are likely to affect cool‐water and warm‐water fishes differently. Yet, forecasts of anticipated temperature effects on fishes of different thermal guilds are lacking, especially in freshwater ecosystems. Towards this end, we used spatially explicit, growth rate potential (GRP) models to project changes in seasonal habitat quality for a warm‐water piscivore (largemouth bass Micropterus salmoides ), a cool‐water piscivore (walleye Sander vitreus ) and a hybrid piscivore (saugeye S. vitreus  × S. canadensis ) in two Midwestern reservoirs. We assessed habitat quality for two periods (early and middle 21st century) under two realistic greenhouse gas emission scenarios (a mid‐century emissions peak and a rapid continuous increase in emissions). Largemouth bass were projected to experience enhanced or slightly reduced habitat during all seasons, and throughout the mid‐21st century. By contrast, walleye habitat was projected to decline with anticipated warming, except during the spring in the smaller of our two study reservoirs and during the fall in the larger of our two study reservoirs. Saugeye habitat was projected to either increase modestly or decline slightly during the spring and fall and declines in habitat quality and quantity that were smaller than those for walleye were identified during summer. Collectively, our findings indicate that climate warming will differentially alter habitat suitability for reservoir piscivores, favouring warm‐water species over cool‐water species. We expect these changes in habitat quality to impact the dynamics of reservoir fish populations to varying degrees necessitating the consideration of climate when making future management decisions.

Little genetic distinction between varieties of Pinto Beardtongue (Penstemon bicolor, Plantaginaceae), a rare plant native to the Mojave Desert

Benjamin W. Stone; Jonathan T. Hauck; Andrea D. Wolfe. 2020. The Journal of the Torrey Botanical Society. https://doi.org/10.3159/TORREY-D-19-00036.1

Abstract

Penstemon bicolor is a relatively rare, short-lived perennial herb of conservation concern and is found in the Mojave Desert and surrounding areas of southern Nevada, southeastern California, and northwestern Arizona. Two varieties of P. bicolor are named according to the color of their corolla: variety bicolor, the yellow or pink-colored form, and variety roseus, the magenta-colored form. The rarity of P. bicolor var. bicolor, coupled with its limited distribution, raises concerns about the genetic diversity present in the species, which is critical for the survival of species in the face of environmental stressors, such as habitat loss. Conservation management strategies for P. bicolor rely partially on the taxonomic status of variety bicolor and variety roseus; if these varieties are in fact distinct genetic lineages more appropriately defined as different species, then the implementation and urgency of management strategies would require updating accordingly. We analyzed amplified fragment length polymorphisms and inter-simple sequence repeats for 13 populations of P. bicolor from southern Nevada and northwestern Arizona to assess genetic diversity within the species and to identify the genetic distinctiveness, if any, between varieties. Our findings reveal surprisingly high levels of genetic diversity, in contrast to expectations for rare, perennial, outcrossing plants. Penstemon bicolor does, however, face ongoing threats of habitat destruction and potential local extirpation due to urbanization of the greater Las Vegas area, and we recommend that the current protective status of the species be maintained. Additionally, our analyses of differentiation failed to reveal genetic distinctiveness between varieties; we thus do not recommend that varieties of P. bicolor be elevated to species level.

The family Opilioacaridae (Acari: Parasitiformes) in Argentina, with description of two new species

Maria Magdalena Vázquez, Leopoldo Ferreira de Oliveira Bernardi, Hans
Klompen. 2020. Acarologia, 60 (3), pp.505-519. https://hal.archives-ouvertes.fr/hal-02870110

Abstract

Two new species of Neocarus, N. entrerios n.sp. and N. misiones n.sp., are described for both adult instars, with locality data for a few additional records of unidentified specimens. Most Argentinean records are from the Northern and Eastern border regions. Even so, current results suggest that opilioacarid diversity in Argentina, while modest, is likely to include several more species.

Population genetic structure and demographic history of the lone star tick, Amblyomma americanum (Ixodida: Ixodidae): new evidence supporting old records

Paula Lado, Megan L. Smith, Bryan C. Carstens, Hans Klompen. 2020. https://doi.org/10.1111/mec.15524

Abstract

Range expansions are a potential outcome of changes in habitat suitability, which commonly result as a consequence of climate change. Hypotheses on such changes in the geographic distribution of a certain species can be evaluated using population genetic structure and demography. In this study we explore the population genetic structure, genetic variability, demographic history of, and habitat suitability for Amblyomma americanum , a North American tick species that is a known vector of several pathogenic microorganisms. We used a double digestion restriction site‐associated DNAsequencing technique (dd‐RAD seq) and discovered 8,181 independent single nucleotide polymorphisms (SNPs) in 189 ticks from across the geographic range of the species. Genetic diversity was low, particularly when considering the broad geographic range of this species. The edge populations were less diverse than populations belonging to the historic range, possibly indicative of a range expansion, but this hypothesis was not statistically supported by a test based on genetic data. Nonetheless, moderate levels of population structure and substructure were detected between geographic regions. For New England, demographic and species distribution models support a scenario where A. americanum was present in more northern locations in the past, underwent a bottleneck, and subsequently recovered. These results are consistent with a hypothesis that this species is re‐establishing in this area, rather than one focused on range expansion from the south. This hypothesis is consistent with old records describing the presence of A. americanum in the northeastern US in the early colonial period.

Towards more robust hydroacoustic estimates of fish abundance in the presence of pelagic macroinvertebrates

Rebecca A.Dillon, Joseph D.Conroy, Lars G. Rudstam, Peter F.Craigmile, Doran M.Mason, Stuart A. Ludsin. 2020. Fisheries Research. https://doi.org/10.1016/j.fishres.2020.105667

Abstract

The inclusion of unwanted targets in hydroacoustic surveys biases estimates of fish abundance. Thus, knowledge of frequency-dependent responses of unwanted targets (e.g., pelagic macroinvertebrates) can help ensure that transducer frequencies are used that minimize this bias. We determined how fish density estimates varied across multiple frequencies when the larval stage of a midge, Chaoborus, was present in the water column. We hypothesized that fish density estimates would increase with increasing transducer frequency, owing to greater backscattering by Chaoborus at higher frequencies than lower ones, which allows it to be included with the backscattering caused by fish. We found that fish density estimates were always greater at higher frequencies (e.g., 120 and 200 kHz) compared to a lower one (70 kHz) in several productive north-temperate reservoirs. Furthermore, pairwise comparisons of total (i.e., fish plus Chaoborus) backscattering showed that significantly more backscattering occurred at higher rather than lower frequencies. We also found that fish density estimates varied between spring and summer, partially owing to inter-seasonal size variation in Chaoborus that influenced its backscattering. Beyond demonstrating why the presence of pelagic macroinvertebrates needs to be considered when estimating fish abundance with hydroacoustics, we provide methods to identify and reduce this bias.

Spatial patterning of walleye recreational harvest in Lake Erie: Role of demographic and environmental factors

David A. Dippold, Grant D. Adams, Stuart A.Ludsin. 2020. https://doi.org/10.1016/j.fishres.2020.105676

Abstract

Demographic and environmental factors can influence the spatial distribution of fish populations, potentially affecting the timing, location, and magnitude of harvest. Quantifying these relationships can be complicated, if their effects vary spatially over a population’s range or are non-additive (i.e., interactive), where one factor mediates the effect of another. Toward understanding the relative influence of demographic and environmental factors on fishery harvest in large freshwater lakes, we used varying-coefficient generalized additive models to explore the existence of non-additive, spatially-dependent effects of adult population size and thermal conditions on recreational harvest patterns of Lake Erie walleye (Sander vitreus) during 2006-2015. We identified nonlinear, additive, and generally positive effects of thermal conditions and adult population size on harvest rates. Their effects were, however, spatially-dependent, the accounting of which can help explain inter-annual and intra-annual variation in lake-wide harvest rates. Specifically, harvest rates increased more with increasing cumulative degree days in the eastern portion of the central basin, especially offshore, relative to the rest of the study area. Harvest rates also increased more with increasing walleye population size in the southwest portion of the west basin and the middle of the central basin compared to other study areas. As in marine ecosystems, our findings demonstrate the benefit of using modeling approaches that consider the spatial dependency of harvest rate on demographic and environmental factors to understanding broader harvest dynamics in large lakes. Their use could help managers and policy-makers ensure the sustained use of valued freshwater fish populations amidst demographic and environmental change.