Daniel J. Larkin

Ecology of native vs. introduced Phragmites australis (common reed) in Chicago-area wetlands.

Rapid spread of Phragmites australis (common reed) in North American wetlands is widely attributed to cryptic invasion by an introduced lineage. However, in the Midwestern U.S., the native subspecies (subsp. americanus) may also exhibit rapid expansion. Where both lineages occur, wetland managers are sometimes unsure whether they should limit management activities to the introduced lineage or control both. We conducted field studies to contrast the ecology of native and introduced Phragmites by pairing patches of each with native reference vegetation. We measured each lineage’s association with environmental conditions, their growth metrics (stem heights, stem densities, and plant cover), and their invasiveness as indicated by the diversity and composition of associated plant communities. Introduced Phragmites exhibited more robust growth than the native, and its growth was more positively correlated with increases in soil nutrient availability and salinity. Areas with introduced Phragmites had lower plant diversity and altered species composition relative to reference vegetation. We did not observe similar evidence of invasiveness in native Phragmites. We encourage wetland managers to differentiate populations by lineage and, unless there is compelling evidence to do otherwise, restrict control efforts to the introduced lineage.

Phylogenetic measures of plant communities show long‐term change and impacts of fire management in tallgrass prairie remnants

Summary Phylogenies are increasingly incorporated into ecological studies on the basis that evolutionary relatedness broadly correlates with trait similarity. However, phylogenetic approaches have rarely been applied to monitoring long-term community change or guiding management. We analysed a 25-year resampling data set (1976–2001) of 41 tallgrass prairie remnants (Illinois, USA) to test for phylogenetic signals of plant community structure, change, environmental associations, fire management and functional traits. A community phylogeny was constructed using GenBank sequences, and trait data were acquired from the TRY consortium. Phylogenetic measures of alpha and beta diversity were compared with taxonomic and functional measures. From 1976 to 2001, communities became more phylogenetically clustered relative to null model expectations, that is increasingly restricted to subsets of species more closely related than expected by chance. Phylogeny was a sensitive indicator of environmental gradients and fire management. There were strong relationships between phylogeny and traits: key traits were phylogenetically non-random and phylogenetic diversity was a necessary complement to species richness for explaining variation in trait diversity. Phylogeny revealed a shift in community structure over time, with sites having been phylogenetically random in 1976 but becoming differentiated from each other by 2001. In contrast, measures of taxonomic and functional diversity showed differentiation at both time points. Phylogenetic patterns likely reflected changes in species’ abundances mediated by the influence of environmental conditions and fire frequency. Synthesis and applications. Phylogenetic analyses can elucidate factors central to sound monitoring and management of plant communities. In this system, phylogeny was not a proxy for other indicators, but provided information complementing taxonomic-based and trait-based approaches for understanding vegetation structure, change and response to fire management. Phylogenetic approaches to ecological analysis are increasingly accessible, but fuller understanding of phylogeny–trait relationships and further development of user-friendly analytical tools are needed for phylogenetics to widely inform restoration and management. In some systems, targeting phylogenetic diversity may be an effective means for restoring functionally diverse plant communities.

Realized niche shift associated with the Eurasian charophyte Nitellopsis obtusa becoming invasive in North America

Nitellopsis obtusa (starry stonewort) is a dioecious green alga native to Europe and Asia that has emerged as an aquatic invasive species in North America. Nitellopsis obtusa is rare across large portions of its native range, but has spread rapidly in northern-tier lakes in the United States, where it can interfere with recreation and may displace native species. Little is known about the invasion ecology of N. obtusa, making it difficult to forecast future expansion. Using ecological niche modeling we investigated environmental variables associated with invasion risk. We used species records, climate data, and remotely sensed environmental variables to characterize the species’ multidimensional distribution. We found that N. obtusa is exploiting novel ecological niche space in its introduced range, which may help explain its invasiveness. While the fundamental niche of N. obtusa may be stable, there appears to have been a shift in its realized niche associated with invasion in North America. Large portions of the United States are predicted to constitute highly suitable habitat for N. obtusa. Our results can inform early detection and rapid response efforts targeting N. obtusa and provide testable estimates of the physiological tolerances of this species as a baseline for future empirical research.

Taking the long view: Integrating recorded, archeological, paleoecological, and evolutionary data into ecological restoration

Historical information spanning different temporal scales (from tens to millions of years) can influence restoration practice by providing ecological context for better understanding of contemporary ecosystems. Ecological history provides clues about the assembly, structure, and dynamic nature of ecosystems, and this information can improve forecasting of how restored systems will respond to changes in climate, disturbance regimes, and other factors. History recorded by humans can be used to generate baselines for assessing changes in ecosystems, communities, and populations over time. Paleoecology pushes these baselines back hundreds, thousands, or even millions of years, offering insights into how past species assemblages have responded to changing disturbance regimes and climate. Furthermore, archeology can be used to reconstruct interactions between humans and their environment for which no documentary records exist. Going back further, phylogenies reveal patterns that emerged from coupled evolutionary-ecological processes over very long timescales. Increasingly, this information can be used to predict the stability, resilience, and functioning of assemblages into the future. We review examples in which recorded, archeological, paleoecological, and evolutionary information has been or could be used to inform goal setting, management, and monitoring for restoration. While we argue that long-view historical ecology has much to offer restoration, there are few examples of restoration projects explicitly incorporating such information or of research that has evaluated the utility of such perspectives in applied management contexts. For these ideas to move from theory into practice, tests performed through research-management partnerships are needed to determine to what degree taking the long view can support achievement of restoration objectives.

Assessing Potential Seed Transfer Zones for Five Forb Species from the Great Basin Floristic Region, USA

ABSTRACT: For plant species important in ecological restoration, seed transfer zones have been developed to maximize the probability that sown seed will germinate, establish, persist, and reproduce without negatively impacting the genetic composition of remnant plant populations. However, empirically based seed transfer zones have not been developed for most species. In their absence, maps based on ecological or climatic variables have been suggested as proxies. In the United States, these maps typically include the Environmental Protection Agencys Levels III and IV Ecoregion maps and the US Forest Services Provisional Seed Zones. Maps of different spatial scales represent a compromise between economic and ecological considerations; those that delineate larger seed transfer zones are less costly to implement but impose more risk of poor adaptation to local conditions. To test the relative suitability of each map in delineating seed transfer zones, we conducted common garden experiments using five forb species found throughout the Great Basin and measured variation in traits thought to influence plant performance. We distinguished between environmentally and genetically controlled variation in measured traits and assessed how well this variation was explained by different candidate seed transfer zones. We found significant, population-level variation in all species for most measured traits. All tested seed transfer zones significantly explained some of this variation, but the proportion explained generally decreased with increasing zone size. Results suggest the intersection of Provisional Seed Zones and Level III Ecoregions was the best proxy for formal seed transfer zones developed based on common garden studies. This spatial scale captured 80% of the variation among source populations on average, and represents a viable compromise between ecological and economic considerations.

Restored tallgrass prairies have reduced phylogenetic diversity compared with remnants

Summary Ecological restoration is critical for mitigating habitat loss and providing ecosystem services. However, restorations often have lower diversity than remnant, reference sites. Phylogenetic diversity is an important component of biodiversity and ecosystem function that has only recently been used to evaluate restoration outcomes. To move towards prediction in the restoration of biodiversity, it is necessary to understand how phylogenetic diversity of restorations compares with that of reference sites, and where deficits are found, to evaluate factors constraining phylogenetic diversity. We quantified plant taxonomic and phylogenetic diversity in eastern tallgrass prairie, one of the most endangered ecosystems on earth. We measured diversity at large (site) and small (plot) scales in 19 restored prairies and compared patterns with those from 41 remnant prairies. To evaluate how environmental conditions and management actions influence outcomes, we tested the effects of soil properties and seed mix composition on diversity of restorations. Restored prairies were less phylogenetically diverse than remnants at both spatial scales. On the other hand, the total species richness of remnant and restored prairies did not significantly differ, but remnants had higher native richness. Restored communities were taxonomically and phylogenetically distinct from remnants. Soil properties (moisture and pH) influenced phylogenetic diversity and composition. There were positive relationships between the taxonomic and phylogenetic diversity of seed mixes and resulting diversity of planted assemblages (excluding volunteer species). Species in seed mixes were more closely related than expected by chance, and several clades found in remnant prairies were missing from seed mixes. Synthesis and applications. Restored tallgrass prairies had lower phylogenetic diversity than remnant prairies, which may contribute to the widely observed phenomenon of restorations not being functionally equivalent to reference sites. It is encouraging for restoration efforts that seed mix phylogenetic diversity predicted phylogenetic diversity of planted assemblages. This indicates that designing phylogenetically diverse seed mixes for restoration is beneficial. In addition, clades found in reference sites that are missing from restoration seed mixes could be added to new or existing restorations to reduce gaps in phylogenetic diversity. Further work on the effects of management on phylogenetic diversity is needed to advance restoration of biodiversity.

Forecasting distributions of an aquatic invasive species (Nitellopsis obtusa) under future climate scenarios

Starry stonewort (Nitellopsis obtusa) is an alga that has emerged as an aquatic invasive species of concern in the United States. Where established, starry stonewort can interfere with recreational uses of water bodies and potentially have ecological impacts. Incipient invasion of starry stonewort in Minnesota provides an opportunity to predict future expansion in order to target early detection and strategic management. We used ecological niche models to identify suitable areas for starry stonewort in Minnesota based on global occurrence records and present-day and future climate conditions. We assessed sensitivity of forecasts to different parameters, using four emission scenarios (i.e., RCP 2.6, RCP 4.5, RCP 6, and RCP 8.5) from five future climate models (i.e., CCSM, GISS, IPSL, MIROC, and MRI). From our niche model analyses, we found that (i) occurrences from the entire range, instead of occurrences restricted to the invaded range, provide more informed models; (ii) default settings in Maxent did not provide the best model; (iii) the model calibration area and its background samples impact model performance; (iv) model projections to future climate conditions should be restricted to analogous environments; and (v) forecasts in future climate conditions should include different future climate models and model calibration areas to better capture uncertainty in forecasts. Under present climate, the most suitable areas for starry stonewort are predicted to be found in central and southeastern Minnesota. In the future, suitable areas for starry stonewort are predicted to shift in geographic range under some future climate models and to shrink under others, with most permutations indicating a net decrease of the species’ suitable range. Our suitability maps can serve to design short-term plans for surveillance and education, while future climate models suggest a plausible reduction of starry stonewort spread in the long-term if the trends in climate warming remain.

Keeping all the PIECES: Phylogenetically Informed Ex Situ Conservation of Endangered Species

Ex situ conservation in germplasm and living collections is a major focus of global plant conservation strategies. Prioritizing species for ex situ collection is a necessary component of this effort for which sound strategies are needed. Phylogenetic considerations can play an important role in prioritization. Collections that are more phylogenetically diverse are likely to encompass more ecological and trait variation, and thus provide stronger conservation insurance and richer resources for future restoration efforts. However, phylogenetic criteria need to be weighed against other, potentially competing objectives. We used ex situ collection and threat rank data for North American angiosperms to investigate gaps in ex situ coverage and phylogenetic diversity of collections and to develop a flexible framework for prioritizing species across multiple objectives. We found that ex situ coverage of 18,766 North American angiosperm taxa was low with respect to the most vulnerable taxa: just 43% of vulnerable to critically imperiled taxa were in ex situ collections, far short of a year-2020 goal of 75%. In addition, species held in ex situ collections were phylogenetically clustered (P < 0.001), i.e., collections comprised less phylogenetic diversity than would be expected had species been drawn at random. These patterns support incorporating phylogenetic considerations into ex situ prioritization in a manner balanced with other criteria, such as vulnerability. To meet this need, we present the ‘PIECES’ index (Phylogenetically Informed Ex situ Conservation of Endangered Species). PIECES integrates phylogenetic considerations into a flexible framework for prioritizing species across competing objectives using multi-criteria decision analysis. Applying PIECES to prioritizing ex situ conservation of North American angiosperms, we show strong return on investment across multiple objectives, some of which are negatively correlated with each other. A spreadsheet-based decision support tool for North American angiosperms is provided; this tool can be customized to align with different conservation objectives.

Heterogeneity theory and ecological restoration

Natural ecosystems are heterogeneous; their physical, chemical, and biological characteristics display variability in space and time. In trying to understand vegetation heterogeneity, early ecologists found that species sorted among habitats according to environmental conditions, such as along lakeshore dunes of different size and age (Cowles 1899; Gleason 1926). Later, ecologists recognized that some species act as “engineers,” creating heterogeneity and affecting other species and ecosystem processes (Jones et al. 1994). Examples are sedge tussocks (Watt 1947), ant mounds (Vestergaard 1998; Nkem et al. 2000), and bison and alligator wallows (Collins and Barber 1985; Gunderson 1997). With the emergence of landscape ecology, spatial heterogeneity drew interest across spatial scales—no longer a “troublesome source of error,” but a key variable for explaining ecosystem structure and function (Pickett and Cadenasso 1995).

Response of the invasive alga starry stonewort (Nitellopsis obtusa) to control efforts in a Minnesota lake

ABSTRACT Glisson WJ, Wagner CK, McComas SR, Farnum K, Verhoeven MR, Muthukrishnan R, Larkin DJ. 2018. Response of the invasive alga starry stonewort (Nitellopsis obtusa) to control efforts in a Minnesota lake. Lake Reserv Manage. 00:00–00. Starry stonewort (Nitellopsis obtusa), an invasive green macroalga in the family Characeae, has recently been found for the first time in several Midwestern states. This aquatic invasive species is of increasing concern to management agencies, lakeshore property owners, and other stakeholders. Starry stonewort has proven difficult to control, partly due to its ability to reproduce via bulbils (asexual reproductive structures). There has also been a lack of applied research addressing the efficacy of current management practices for controlling starry stonewort. We examined the effects of mechanical and algaecide treatments on starry stonewort biomass, bulbil density, and bulbil viability by monitoring treated areas and untreated reference locations concurrent with management implemented on Lake Koronis in Minnesota. Chelated copper algaecide applications alone and in combination with mechanical harvesting significantly reduced starry stonewort biomass, but algaecide treatment alone failed to reduce the capacity of starry stonewort to regenerate via bulbils. A second, granular algaecide application following an initial treatment with liquid algaecide did not further reduce biomass in any treated area and was associated with a substantial increase in bulbil density in an area treated with algaecide alone. Bulbil viability was greatest in the area treated only with algaecide (86%) and an untreated reference area (84%) and was lowest in an area treated with both mechanical harvest and algaecide (70%). The ability of starry stonewort to regenerate and persist following algaecide treatment is concerning. Multi-pronged management incorporating both chemical and mechanical approaches may improve outcomes of starry stonewort control efforts.