Lerminiaux J, Norton B, Wilson RJ, Rimas R, Lavender TM, Finlay K. 2024. Effects of aeration on water quality in agricultural reservoirs in the northern Great Plains. Lake Reserv Manage. XX:XXX-XX. Aeration of agricultural reservoirs is an encouraged practice in the northern Great Plains of Canada as it can improve water quality by reducing pathogenic bacteria and algal abundance. Cattle also prefer aerated water, resulting in greater weight gain. Despite its known benefits, agricultural reservoir aeration is still not uniformly adopted, largely given its cost of installation and maintenance. Wind powered aeration has been shown to be an eco-friendly and sustainable way to increase oxygen levels in agricultural reservoirs, but the mechanisms by which this aeration can improve water quality are not well documented. By comparing 5 aerated agricultural reservoirs to 5 unaerated agricultural reservoirs, we evaluated whether wind-powered aeration improves water quality. We measured dissolved oxygen, nitrogen, and phosphorus, algal biomass (as chlorophyll a), cyanobacteria abundance, and algal toxins (microcystin, anatoxin-a, and beta-N-methylamino-L-alanine) in the aerated and unaerated agricultural reservoirs on a weekly basis over a 12-week period from mid June through August 2022. We found that the aerators were able to mix the water column and add oxygen to deeper regions of the agricultural reservoir, but this did not result in consistent improvements to any measured water quality parameter. The observed lack of a strong response to aeration suggests that this practice may provide only minimal water quality benefits, but aeration may still prove beneficial for deep (>2 m) and sheltered agricultural reservoirs that do not regularly mix from wind effects alone.

Experimental evidence suggests that larger plant species generally have a competitive advantage and thus should dominate communities where competition for limiting resources (i.e. water, soil nutrients, light, space and/or mutualists) is intense. Additionally, researchers have postulated that competition can generate negative co-occurrence patterns. However, neither expectation is strongly supported by empirical evidence. In a relatively undisturbed old-field plant community, we explored the interdependency of these expectations by examining pairwise species co-occurrences, and pairwise species maximum height differences (measured here as the maximum potential height of the species), and by estimating competition intensity for sample plots using field transplants grown with and without neighbours. Specifically, we tested whether maximum species height differences were greater for negatively co-occurring species pairs than for positively co-occurring pairs found growing together. We also tested whether the maximum species height differences and co-occurrence status of species pairs were associated with the average competitive environment they tended to be found growing in. Negatively co-occurring species pairs found growing together differed more in maximum height than in positively co-occurring species pairs that were more similar in maximum height. Additionally, species maximum height differences between negatively co-occurring species pairs where higher in less competitively intense plots, whereas species maximum heights were more similar between positively co-occurring species pairs found growing together in less competitively intense plots. Synthesis. Our results suggest an association between estimates of competition intensity generated using transplant experiments and co-occurrence patterns. These findings contribute to our understanding of the association between size-mediated competition and spatial organization in plant communities and provide a framework for future research in this area. These results suggest an association between estimates of competition intensity generated using transplant experiments and co-occurrence patterns. These findings contribute to our understanding of the association between size-mediated competition and spatial organization in plant communities and provide a framework for future research in this area.image

The rockpool cluster offers unique characteristics making it a model system for general questions in ecology: (1) all rockpools share biotic history (any species can reach any rockpool); (2) they form a strong gradient of conditions from benign to harsh; (3) 1-day sampling across all rockpools ensures census consistency; (4) rockpools respond to changing conditions within a short (days) time frame; (5) they are easy to manipulate (note: the data are from an unmanipulated rockpool subset), and (6) they may act as a single metacommunity that exhibits consistent species distribution patterns on a broader scale (unpublished). Consequently, the rockpools continue generating insights, with the first publications in 1996. The data represent an intensive rockpool metacommunity monitoring project, making them of considerable value to our understanding of tropical coastal metacommunity dynamics and general ecological processes. The dataset covers surveys of invertebrate fauna in 49, primarily supratidal, rockpools on a fossil coral reef over 25 years. All rockpools occur within a 73 × 47 m array of rocks at a distance of less than 2 m from the nearest neighbor. About 200 other rockpools occur on the same area. They are in a sheltered bay (Discovery Bay, Jamaica) between 0 and 5 m from the ocean. Typically, rockpools are 5-30 cm deep and 40 cm across on average, with elevation from a few centimeters to 300 cm above sea level. Rockpools may drain excess water from precipitation or waves into other rockpools, which allows organisms to disperse passively downstream. Of the 49 rockpools in the survey, 35 are subject to occasional drying up, while the others appear permanent. Most collections (1989-2004) were annual censuses of invertebrate populations, exceeding a total of 475,000 invertebrates counted, with only minor record gaps. In all cases, species level taxonomic information consists of detailed photographs. In some cases, notes are included with the taxonomic data where species identification could not be matched to information available in the literature. Samples from 2005 to 2019 still require organism identification. Abiotic parameters were measured the day before biotic sampling took place as the process of biotic sampling can impact abiotic parameters through stirring, oxygenation and filtering (temperature, pH, turbidity, dissolved oxygen, light intensity, salinity, alkalinity, and nutrients). The cumulative richness in the metacommunity consist of 78 freshwater, marine, and brackish water taxa, with a mean richness per rockpool of 5.5 distinct species. Regarding taxonomic makeup, ostracods dominated in both diversity and number, followed by copepods, and insects. There are no copyright restrictions on the data set; please cite this data paper when using these data in publications.

Researchers have long viewed patterns of species association as key to understanding the processes that structure communities. Community-level tests of species association have received the most attention; however, pairwise species associations may offer greater opportunity for linking patterns to specific mechanisms. Although several tests of pairwise association have been developed, there remain gaps in our understanding of their performance. Consequently, it is unclear whether these methods reliably detect patterns of association, or if any one method is superior. We maximized association patterns for single species pairs in synthetic community matrices and examined how accurately five pairwise association tests found that pair, while not finding others (i.e., type I and II error rates). All tests are more likely to miss patterns of association than to falsely detect them. When we maximized association for a species pair that included one or more rare or common species, tests were frequently unable to identify that pair as significantly associated. Consequently, these tests are best suited for identifying significant associations between pairs of species that occur in an intermediate number of samples; for such pairs, three of the five tests considered here detected 100% of the pairs for which we maximized associations.

Inherent differences between naturally-formed lakes and human-made reservoirs may play an important role in shaping zooplankton community structure. For example, because many reservoirs are created by impounding and managing lotic systems for specific human purposes, zooplankton communities may be affected by factors that are unique to reservoirs, such as shorter water residence times and a reservoir’s management regime, compared to natural lakes. However, the environmental factors that structure zooplankton communities in natural lakes vs. reservoirs may vary at the continental scale and remain largely unknown. We analyzed data from the 2007 U.S. Environmental Protection Agency’s National Lakes Assessment and the U.S. Army Corps of Engineers’ National Inventory of Dams to compare large-bodied crustacean zooplankton communities (defined here as individuals retained by 0.243 mm mesh size) in natural lakes and reservoirs across the continental U.S. using multiple linear regressions and regression tree analyses. We found that large-bodied crustacean zooplankton density was overall higher in natural lakes compared to reservoirs when the effect of latitude was controlled. The difference between waterbody types was driven by calanoid copepods, which were also more likely to be dominant in the >0.243 mm zooplankton community in natural lakes than in reservoirs. Regression tree analyses revealed that water residence time was not a major driver of calanoid copepod density in natural lakes but was one of the most important drivers of calanoid copepod density in reservoirs, which had on average 0.5-year shorter water residence times than natural lakes. Reservoirs managed for purposes that resulted in shorter residence times (e.g., hydroelectric power) had lower zooplankton densities than reservoirs managed for purposes that resulted in longer residence times (e.g., irrigation). Consequently, our results indicate that water residence time may be an important characteristic driving differing large-bodied zooplankton dynamics between reservoirs and natural lakes.

Simple hydrological models, such as the Seasonal Water Yield Model developed by the Natural Capital Project (InVEST SWYM), are attractive as data requirements are relatively easy to satisfy. However, simple models may produce unrealistic results when the underlying hydrological processes are inadequately described. We used the variation in performance of the InVEST SWYM across watersheds to identify correlates of poorly modeled outcomes of InVEST SWYM. We grouped 749 watersheds from across North America into five bioclimatic regions using nine environmental variables. For each region, we compared the predicted flow patterns to actual flow conditions over a 15-year period. The correlation between the modeled and actual flows was highly dispersed and relatively poor, with 92% of r(2) values less than 0.5 and 42% less than 0.1. We linked cryospheric variables to model performance in the bioclimatic region with the poorest model performance (the Low elevation Boreal Sub-humid region-LeBSh). After incorporating cryospheric conditions into the InVEST SWYM, predictions improved significantly in 30% of the LeBSh watersheds. We provide a relatively straightforward approach for identifying processes that simple hydrological models may not consider or which need further attention or refinement.

Null models exploring species co-occurrence and trait-based limiting similarity are increasingly used to explore the influence of competition on community assembly; however, assessments of common models have not thoroughly explored the influence of variation in matrix size on error rates, in spite of the fact that studies have explored community matrices that vary considerably in size. To determine how smaller matrices, which are of greatest concern, perform statistically, we generated biologically realistic presence-absence matrices ranging in size from 3-50 species and sites, as well as associated trait matrices. We examined co-occurrence tests using the C-Score statistic and independent swap algorithm. For trait-based limiting similarity null models, we used the mean nearest neighbour trait distance (NN) and the standard deviation of nearest neighbour distances (SDNN) as test statistics, and considered two common randomization algorithms: abundance independent trait shuffling (AITS), and abundance weighted trait shuffling (AWTS). Matrices as small as three × three resulted in acceptable type I error rates (p < 0.05) for both the co-occurrence and trait-based limiting similarity null models when exclusive p-values were used. The commonly used inclusive p-value (≤ or ≥, as opposed to exclusive p-values; < or >) was associated with increased type I error rates, particularly for matrices with fewer than eight species. Type I error rates increased for limiting similarity tests using the AWTS randomization scheme when community matrices contained more than 35 sites; a similar randomization used in null models of phylogenetic dispersion has previously been viewed as robust. Notwithstanding other potential deficiencies related to the use of small matrices to represent communities, the application of both classes of null model should be restricted to matrices with 10 or more species to avoid the possibility of type II errors. Additionally, researchers should restrict the use of the AWTS randomization to matrices with fewer than 35 sites to avoid type I errors when testing for trait-based limiting similarity. The AITS randomization scheme performed better in terms of type I error rates, and therefore may be more appropriate when considering systems for which traits are not clustered by abundance.

Strains of insect-pathogenic fungi with high virulence toward certain pest insects have great potential for commercial biological control applications. Identifying such strains has been a central theme in using fungi for biological control. This theme is supported by a persistent paradigm in insect pathology which suggests that the host insect is the predominant influence on the population genetics of insect-pathogenic fungi. In this study, a population genetics analysis of the insect-pathogenic fungus Metarhizium anisopliae from forested and agricultural habitats in Ontario, Canada, showed a nonrandom association of alleles between two distinct, reproductively isolated groups (index of multilocus association = 1.2). Analyses of the mitochondrial DNA showed no differences between the groups. The two groups were associated with different habitat types, and associations with insect hosts were not found. The group from forested areas showed an ability for cold-active growth (i.e., 8 degrees C), while the group from the agricultural area showed an ability for growth at high temperatures (i.e., 37 degrees C) and resilience to UV exposure. These results represent a significant paradigm shift; habitat selection, not host insect selection, drives the population structure of these insect-pathogenic deuteromycetous fungi. With each group we observed recombining population structures as well as clonally reproducing lineages. We discuss whether these groups may represent cryptic species. Worldwide, M. anisopliae may be an assembly of cryptic species, each adapted to certain environmental conditions. The association of fungal genotypes with habitat but not with host insects has implications on the criteria for utility of this, and perhaps other, fungal biocontrol agents.

Several isolates of the entomopathogenic Metarhizium anisopliae that harboured dsRNA viruses of similar electrophoretic band sizes (1.8 and 2.0 kbp) were assessed for homologies of the dsRNA by Northern analysis. The isolates were also characterised genetically by RAPD and VCG. Similarly sized dsRNA, as visualised by electrophoresis, were not always homologous, suggesting that the comparison of dsRNA based solely on electrophoretic banding patterns is an unreliable method of dsRNA characterisation. Several isolates, but not all, harbouring multiple dsRNA patterns, including a 1.8 and 2.0 kbp doubler, also showed homologies to strains harbouring only the dsRNA banding doubler. This suggests that mixed infections of different dsRNA elements are found in M. anisopliae. Genetically similar fungi, based on RAPD banding patterns and vegetative compatibility, were more likely to harbour genetically related dsRNA. The findings suggested that dsRNA elements in M. anisopliae are horizontally transferred to genetically related isolates or are maintained through clonal lineages.

Disturbance gradients are particularly useful for understanding the relative influences of competition and dispersal. Shortly after disturbance, plant composition should be influenced more strongly by dispersal than competition; over time, this should reverse, with competition becoming more important. As such, we predicted that plant functional traits associated with high dispersal ability would be over-represented shortly after a disturbance event occurs, while those associated with high competitive ability would have increased representation as time progresses. Additionally, it has been suggested that competitive interactions may contribute to negative co-occurrence patterns; if this is the case, negative co-occurrence patterns should also increase as time-since-disturbance increases. Here, we examine how functional trait and co-occurrence patterns change over time following a herbicide-based disturbance, compared to undisturbed vegetation, in a temperate, old-field grassland dominated by herbaceous perennials. In our study system, negative co-occurrence patterns were most pronounced in disturbed plots one year after herbicide application, consistent with several lines of evidence that dispersal can strongly impact both composition and co-occurrence patterns. Over three years post-disturbance, co-occurrence patterns in disturbed plots decreased, becoming more similar to control plots. This pattern is inconsistent with the expectation that competition contributes to negative co-occurrence patterns, at least over three growing seasons. More pronounced negative co-occurrence patterns were associated with higher species evenness among plots. Functional traits related to increased dispersal (mean seed mass, and proportion of stoloniferous/rhizomatous species) and competitive ability (mean species height, and mean specific leaf area) did not differ significantly across treatments, with the exception of mean height in the third-year post-disturbance; however, the overall trajectory of this trait was inconsistent with theoretical expectations. Overall, co-occurrence patterns changed across the gradient of time-since disturbance, but not as expected; functional trait patterns (trait means, functional diversity measures) were not responsive to our experimental disturbance gradient.