Aquatic plants (macrophytes) are important components of freshwater ecosystems and serve numerous functions, both physical and biological, that help to structure aquatic communities. However, invasive macrophytes may negatively alter ecosystem properties. Non-native invasive species have been identified as a major cause of biodiversity loss and the increasing prevalence of invasive species has prompted studies to help understand their impacts and to conserve biodiversity. Studying mechanisms of invasion also gives ecological insight into how communities are structured and assembled. This study examined a set of potential factors influencing invasion including biotic resistance, exposure, and water depth using mixed-effects models on macrophyte survey data collected from twenty-nine lakes across the United States. The results of this study indicated that biotic resistance measured from native species richness, exposure due to fetch, and water depth interact, often in non-linear ways to influence probability of invasive species occurrence at a given location; however, models explained a relatively low percentage of variation in probabilities. It is likely that strong predictive principles governing macrophyte invasions do not exist, at least among comparisons across a range of ecosystem types and environmental conditions. However, ecologists should continue to search for general patterns within definable ecosystem units to increase understanding about factors contributing to invasibility.

To test the hitherto generally-accepted hypothesis that most aquatic macrophytes have broad world distributions, we investigated the global distribution, diversity and endemism patterns of 3457 macrophyte species that occur in permanent, temporary or ephemeral inland freshwater and brackish waterbodies worldwide. At a resolution of 10 x 10 degrees latitude x longitude, most macrophyte species were found to have narrow global distributions: 78% have ranges (measured using an approach broadly following the IUCN-defined concept "extent of occurrence") that individually occupy <10% of the world area present within the six global ecozones which primarily provide habitat for macrophytes. We found evidence of non-linear relationships between latitude and macrophyte alpha- and gamma-diversity, with diversity highest in sub-tropical to low tropical latitudes, declining slightly towards the Equator, and also declining strongly towards higher latitudes. Landscape aridity and, to a lesser extent, altitude and land area present per gridcell also influence macrophyte diversity and species assemblage worldwide. The Neotropics and Orient have the richest ecozone species-pools for macrophytes, depending on gamma-diversity metric used. The region around Brasilia/Goias (Brazil: gridcell 10-20 degrees S; 40-50 degrees W) is the richest global hotspot for macrophyte a-diversity (total species alpha-diversity, S-T: 625 species/gridcell, 350 of them Neotropical endemics). In contrast, the Sahara/Arabian Deserts, and some Arctic areas, have the lowest macrophyte alpha-diversity (S-T <20 species/gridcell). At ecozone scale, macrophyte species endemism is pronounced, though with a > 5-fold difference between the most species-rich (Neotropics) and species-poor (Palaearctic) ecozones. Our findings strongly support the assertion that small-ranged species constitute most of Earth's species diversity.

Introduction Many species of fish rely on aquatic plants at some point during their lives and often move to different habitats based on their growth stage. Young fish use the cover provided by aquatic vegetation to hide from predators and their diets may be dependent on algae and the microfauna (e.g., zooplankton, insects and larvae) that live on aquatic plants. Mature fish of some species move to more open waters to reduce foraging competition and also include other fish in their diets. Also, different fish prefer different types of habitats and will move to a new area if foraging conditions in their preferred location decline due to excessive growth of aquatic weeds.

Animal habitat selection, among other ecological phenomena, is spatially scale dependent. Habitat selection by American beavers Castor canadensis (hereafter, beaver) has been studied at singular spatial scales, but to date no research addresses multi-scale selection. Our objectives were to determine if beaver habitat selection was specialized to semiaquatic habitats and if variables explaining habitat selection are consistent between landscape and fine spatial scales. We built maximum entropy (MaxEnt) models to relate landscape-scale presence-only data to landscape variables, and used generalized linear mixed models to evaluate fine spatial scale habitat selection using global positioning system (GPS) relocation data. Explanatory variables between the landscape and fine spatial scale were compared for consistency. Our findings suggested that beaver habitat selection at coarse (study area) and fine (within home range) scales was congruent, and was influenced by increasing amounts of woody wetland edge density and shrub edge density, and decreasing amounts of open water edge density. Habitat suitability at the landscape scale also increased with decreasing amounts of grass frequency. As territorial, central-place foragers, beavers likely trade-off open water edge density (i.e., smaller non-forested wetlands or lodges closer to banks) for defense and shorter distances to forage and obtain construction material. Woody plants along edges and expanses of open water for predator avoidance may limit beaver fitness and subsequently determine beaver habitat selection.

Invasive aquatic plants in U.S. lakes and reservoirs frequently require managers to implement plant control, yet little is known about how these management efforts alter habitat available to adult fish. We used a before-after, control-impact (BACI) design to study four Minnesota lakes (two treated lakes and two untreated control lakes) to evaluate the influence of plant management using herbicides (i.e., endothall/2,4-D) on diets of adult bluegill (Lepomis macrochirus Rafinesque) over the course of 4 yr. We hypothesized that removing plants would result in an immediate increase of prey items available to bluegill reflected in an increase in total items in the bluegill diet, and that an increase in prey items would affect diet breadth. Invasive Eurasian watermilfoil, Myriophyllum spicatum L., was eliminated following herbicide treatment; however, native plants immediately expanded and plant overall abundance in the littoral zone was not reduced. We found no significant treatment effects on number of prey items per stomach, stomach content mass, diet composition, or abundance of major diet groups. However, we found that diet breadth increased posttreatment in the fall season, as evidenced by a more even distribution of bluegill diet items in stomach contents. Bluegill diet composition varied across years and lakes (primarily due to changes in Cladocera), but not due to treatment. We concluded that early seasonal application of herbicides resulted in an immediate shift from invasive aquatic plants to a diverse native community, which had minor effects on diets of bluegill.

Samuel Keith Riffell was born on 30 June 1970 in Springfield, Ohio, and passed away on 11 August 2014 in Starkville, Mississippi. He is survived by his wife Angie and their two daughters, Abigail and Hannah. Sam contributed greatly to the discipline of landscape ecology through his work as a scientist and university professor, and by serving the U.S. Regional Chapter of the International Association for Landscape Ecology (US-IALE) in several important capacities for many years. Here we honor and celebrate Sam’s enthusiasm for landscape ecological research and its application, his role in training and inspiring future landscape ecologists, and his professional service to US-IALE. Samwas raised in Frankfort, Ohio, and attended the Frankfort public school system from grade school through high school. When not in school, Sam spent much of his youth exploring the small stream that ran near the south side of Frankfort, turning over rocks in search of different invertebrates. His fascination with small living things stuck with him as he matured and began courting Angie; she recalls that one of their first dates was spent wading a stream together overturning rocks in search of dragonfly larvae. He graduated in 1988 from Adena High School as valedictorian. After high school he pursued his passion for biology and ecology, obtaining a B.A in biology (Asbury College, 1992), an M.S. in environmental studies (Baylor University, 1994), and a Ph.D. in zoology (Michigan State University, 2000). Sam then worked as a visiting Samuel K. Riffell (Photo courtesy of Mississippi State University)

Although native macrophytes are beneficial in aquatic ecosystems, invasive macrophytes can cause significant ecological and economic harm. Numerous studies have attributed invasiveness to species’ characteristics, whereas others attribute invasion to biotic and abiotic characteristics of the invaded community. It has been suggested that studying the link between invader and invaded community is key to understanding invasiveness, and that invasions can be understood through the framework of community ecology theory. Charles Darwin hypothesized that introduced species would be less likely to naturalize in areas containing closely related species [Darwin’s naturalization hypothesis (DNH)], suggesting competition between closely related species could limit naturalization potential (phylogenetic repulsion). The goal of this research was to test DNH using two species of highly invasive aquatic plants, Myriophyllum spicatum L. and Potamogeton crispus L., and assess whether results were consistent at small and large scales. Twenty-nine lakes containing invasive macrophytes were surveyed between 1997 and 2011. Invasive P. crispus occurred in 15 lakes and M. spicatum occurred in 19 lakes. There were 15 native Potamogeton species and 4 Myriophyllum. We used generalized linear mixed models with congeneric species richness data to estimate probability of invasive P. crispus or M. spicatum occupying a given sampling location. Contrary to predictions of DNH, the relationship between congeneric richness and presence of P. crispus at point and lake scales was positive. Unlike models for P. crispus, native Myriophyllum genera richness was not a significant model parameter. These results do not support DNH (the expectation of a negative relationship); furthermore, models had relatively low determination coefficients indicating very little explained variation. Although this study found no evidence for DNH, there is still a need to investigate how community assembly processes influence species invasions.

Aquatic plants (macrophytes) are important components of freshwater ecosystems and serve numerous purposes that structure aquatic communities. Although macrophytes represent an essential component of stable aquatic communities, invasive macrophytes negatively alter ecosystem properties. Non-native, invasive species have been identified as a major cause of biodiversity loss and the increasing prevalence of invasive species has prompted studies to help understand their impacts and to conserve biodiversity. Studying mechanisms of invasion also give insight into how communities are structured and assembled. This paper examined mechanisms that contribute to macrophyte invasion through a literature review. Mechanisms identified with this review included competition, enemy release, evolution of increased competitive ability, mutualisms, invasional meltdown, novel weapons, allelopathy, phenotypic plasticity, naturalization of related species, empty niche, fluctuating resources, opportunity windows, and propagule pressure; and were then placed within the context of the invasion process. Results of this review indicated that many invasion mechanisms have been tested with fully aquatic macrophytes with varied levels of support (i.e., some mechanisms are not supported by evidence in the context of macrophyte invasions). Future research should continue the search for evidence of invasion mechanisms that allow introduced species to establish. It is likely that general principles governing these invasions do not exist, at least among comparisons across ecosystem types. However, ecologists should continue to search for general patterns within definable ecosystem units to increase understanding about factors contributing to invasibility.

Limited data from terrestrial ecosystems suggest that invasive species can affect energy flow and nutrient cycling in invaded systems. This is likely also true for aquatic ecosystems, yet little information is available on food web effects of invasive macrophytes. This study examined the effects of dominant invasive Eurasian watermilfoil on lake trophic structure and energy flow. Stable isotopes of carbon and nitrogen were used to compare trophic structure in invaded and uninvaded lakes and macrophyte stands. Contribution of native and invasive macrophytes, their epiphyton and detritus to the upper trophic level of lacustrine food webs was partitioned using mixing models. Carbon isotope values of macroinvertebrate consumers were similar to macrophyte-associated production in stands from which they were collected. However, contribution of Eurasian watermilfoil and its epiphyton to higher trophic level was negligible, and littoral fish derived most of their energy from sources associated with native macrophytes, despite their lower abundance. This means that littoral fish may depend on the remaining patches of native macrophytes in lakes invaded by non-native plants. Considering previous findings, these results show that the assessment of ecosystem-level processes is needed to understand the entire range of impacts of invasive species.

Diverse native aquatic macrophytes serve a number of physical and biological functions in the aquatic environment and provide essential habitat for several fish species. In systems that lack submersed macrophytes, native macrophyte re-establishment can be used to revitalize the aquatic community. Planning re-establishment projects requires knowledge of the system along with the growth requirements of macrophytes. Prior studies have identified factors that are important for macrophyte colonization, persistence, and dispersal. However, deductive approaches to identify macrophyte habitat that is suitable for management application have not been developed. A potential solution to this problem is the incorporation of waterscape-wide variables into a Geographic Information System (GIS) and the use of spatial modeling techniques to identify suitable macrophyte habitat. This provides a scientifically based approach to macrophyte re-establishment planning to make efforts more efficient and to recognize potential coverage. The flexibility, scalability, and topological advantages of using a GIS to identify and visualize habitat allow integration with other spatial ecological variables to improve the management of aquatic resources from plants to fish, including invasive species mitigation. Using Little Bear Creek Reservoir, Alabama, as an example system, we illustrate a GIS modeling process that can be applied to any system where the identification of macrophyte habitat is relevant to aquatic resource management goals.

Water turbidity has the capacity to influence fish foraging success and behavior. The largemouth bass Micropterus salmoides is a popular sport fish in the southeastern United States that is primarily a visual predator. The high turbidity in many systems can be attributed to sediment loading from agricultural lands, and it can reduce the availability of light in the water column and have direct impacts on largemouth bass foraging success. We investigated the effect of different turbidity levels (0, 10, 25, 50, 100, and 250 nephelometric turbidity units [NTU]) on largemouth bass foraging in aquaria by testing the hypothesis that turbidity has no effect on the time required to locate tethered prey (fathead minnow Pimephales promelas and golden shiner Notemigonus crysoleucas) or ultimate capture success. The percentages of prey captured that were derived from aggregated data in multiple trials at the different treatment levels differed significantly. One-hundred percent of the largemouth bass in the 0-NTU treatments captured the prey. Conversely, only 15% of the largemouth bass in the 250-NTU treatments captured the prey throughout all trials. The average time taken to capture the prey also was significantly different between treatment combinations, with time to interaction increasing as turbidity increased. The results from this study suggest that greater turbidity levels reduce the ability of largemouth bass to capture prey and increase the time taken to locate and interact with prey. Thus, turbidity may impact individual fitness and management strategies.

Biological invasions of aquatic plants (i.e., macrophytes) are a worldwide phenomenon, and within the last 15 years researchers have started to focus on the influence of these species on aquatic communities and ecosystem dynamics. We reviewed current literature to identify how invasive macrophyte species impact fishes and macroinvertebrates, explore how these mechanisms deviate (or not) from the accepted model of plant–fish interactions, and assess how traits that enable macrophytes to invade are linked to effects on fish and macroinvertebrate communities. We found that in certain instances, invasive macrophytes increased habitat complexity, hypoxia, allelopathic chemicals, facilitation of other exotic species, and inferior food quality leading to a decrease in abundance of native fish and macroinvertebrate species. However, mechanisms underlying invasive macrophyte impacts on fish and macroinvertebrate communities (i.e., biomass production, photosynthesis, decomposition, and substrate stabilization) were not fundamentally different than those of native macrophytes. We identified three invasive traits largely responsible for negative effects on fish and macroinvertebrate communities: increased growth rate, allelopathic chemical production, and phenotypic plasticity allowing for greater adaptation to environmental conditions than native species. We suggest that information on invasive macrophytes (including invasive traits) along with environmental data could be used to create models to better predict impacts of macrophyte invasion. However, effects of invasive macrophytes on trophic dynamics are less well-known and more research is essential to define system level processes.

ABSTRACTThe Wolf–Broad oxbow lake (417 ha) was evaluated by the Mississippi Department of Environmental Quality and included on the Mississippi 303(d) list of impaired waterbodies for total suspended solids (TSS). A study was undertaken for 2 years to evaluate and document changes to TSS (mg L−1) and overall lake turbidity (NTU) through best management practice implementation. These two objectives were analysed with routine monthly surface sampling events of turbidity (Eureka Manta 2, automated data sonde) as well as 20 random samples per sampling trip for TSS from June 2008 to June 2010. Results from a non‐parametric Kruskal–Wallis analysis indicated a significant month‐by‐year effect on turbidity and TSS (chi‐squared = 76.08, p = 0.001), but reach (chi‐squared = 2.45, p = 0.784) and depth by reach (chi‐squared = 2.44, p = 0.784) did not show significant effects on turbidity. There were no significant correlations between TSS concentrations and turbidity and 2 days and 7 days summed or mean rainfall for the duration of the evaluation. Spearman correlation analysis for TSS indicated significant correlations between TSS and mean two‐day (r2 = 0.62, p = 0.002) and seven‐day (r2 = 0.51, p = 0.014) wind speeds. All other variables used in the analysis did not show significant correlation with TSS ( p > 0.05). This suggests that wind conditions, rather than rainfall, predict the greatest variability in TSS and turbidity in Wolf Lake. These documented correlations between lake water column TSS, turbidity and wind highlight the difficulties of demonstrating success of management practices in the short temporal period between project initiation and completion. Unmanageable environmental conditions (wind speed and direction) and limited temporal monitoring scales (1 1/2 years post‐BMP implementation) limit the possibility of demonstrating successful water‐quality improvement within a 303(d) listed waterbody such as Wolf Lake. Copyright © 2011 John Wiley & Sons, Ltd.

Re-establishment of native aquatic macrophytes may be used to enhance habitat for fish and other organisms, with additional positive effects on water quality. Species selection and planting depth for re-vegetation efforts may be of great importance due to lake-specific ecological factors that may affect survival. The objective of this research was to test whether water depth or species selection contributed to the overall survival of macrophytes planted inside protective exclosures. We planted three species along a water depth gradient (0.30, 0.60, and 1.0 m) - Stuckenia pectinata, Vallisneria americana, and Potamogeton nodosus. Our results indicated that the depth in which species were initially planted rarely had an effect on survival of P. nodosus or V. americana (p < 0.05), but species did have an effect (p < 0.05). Stuckenia pectinata did not survive during the experiment.

Invasive species are one of the widespread stressors of aquatic ecosystems. Several studies document food web effects of invasive fish, but little information is available on the effects of invasive macrophytes. We studied differences in food chain length as well as trophic position and trophic diversity of fish and odonates in lakes dominated by native plants or invasive Eurasian watermilfoil. Trophic position and food chain length were determined using baseline-adjusted δ15N isotope signatures. Trophic diversity, or isotope niche width, was estimated from convex hull area analysis. Results show that trophic position of secondary consumers was not affected by the invasive macrophyte, whereas trophic diversity was greater in watermilfoil-dominated lakes. The direction of isotopic niche expansion was different in fish and odonates, suggesting potential decoupling in predator–prey interactions. This study shows that dominant non-native macrophytes may cause significant changes in food web structure of invaded ecosystems. Trophic diversity may be a more sensitive indicator of environmental stress than trophic position and has the potential to be used for assessment of invasive species impacts and restoration success.

P>1. The control of invasive species has become a widespread management practice, yet information on the community effects of such efforts is very limited, there is no unified framework for monitoring their success and no guidelines exist to help minimize potential adverse impacts.2. This study was conducted to determine how long-term efforts to control a widespread invasive macrophyte, Eurasian watermilfoil, affect native macrophytes, fish and macroinvertebrates. In addition, we examined how members of the aquatic fauna respond to changes in invasive macrophyte abundance and habitat complexity to understand the mechanisms underlying any potential community response.3. Selective control of the invasive macrophyte had minor effects on habitat complexity due to timely recolonization by native macrophytes and it did not affect littoral fish richness and abundance. Macroinvertebrate communities were highly variable and some of that variation could be attributed to characteristics of the macrophyte community. Fish and macroinvertebrates were more affected by habitat complexity than by other attributes of the macrophyte assemblage.4.Synthesis and applications. Management plans to control invasive species need to prioritize selective removal and timely restoration of the native assemblage. In this study, the invasive macrophyte was used by aquatic fauna, which emphasizes the need for immediate restoration of the native macrophyte community to mitigate for the lost habitat after invasive plant control efforts. As both fish and macroinvertebrates were more affected by complexity than other attributes of the macrophyte assemblage, re-establishment of habitat complexity appears to be a promising restoration strategy. On a more general note, we highlight the importance of assessing community response to the habitat provided by the invader and invader's function in the community when evaluating strategies to control invasive species.

The non-native peacock bass (Cichla kelberi) is causing freshwater fish extinctions in the tropical regions around the world, but there are very few studies on its interaction with native species. This study, based on a mesocosm experiment, examined direct and indirect effects of a non-native peacock bass on the native prey in Paraná River, Brazil, and tested whether these effects were mitigated by aquatic vegetation. Feeding activity of most prey was unaffected by the presence of peacock bass. All prey were consumed in the absence of vegetation; whereas a marginally significant decrease in mortality was observed in the vegetated habitats. Overall, peacock bass had minor indirect effects on prey foraging, but very significant direct effects on prey survival. As aquatic plants provide very limited protection to native prey, vegetated habitats are unlikely to slow down the decline in biodiversity resulting from this invasive species and conservation measures may need to consider other ways to ensure survival of the source populations.

We explored patterns of habitat use and movement of three declining fish species intolerant to eutrophication in a north-temperate (Minnesota, USA) glacial lake: the blackchin shiner Notropis heterodon , blacknose shiner Notropis heterolepis , and banded killifish Fundulus diaphanus . We marked individuals with elastomer tags and estimated movement distances of recaptured individuals. Estimated home ranges for all species ranged from 3,264 to 19,525 m 2 , which covered 0.8 and 5.0% of our study lake’s total littoral area. Individuals of all species traveled to opposite ends of the lake over periods of time as short as 24 h. Using Geographic Information System (GIS) overlays and generalized additive models, we found fish species occurrences to be positively associated with macrophyte biovolume greater than 20% and with a high probability of occurrence of Chara. The magnitude of main and interaction effects varied among years and species. Overall, blackchin shiner occurrence was most strongly associated with biovolume. In other species by year combinations, biovolume and Chara explained varying degrees of variance in fish probability of occurrence. Our results suggest that controlling lake eutrophication and protecting of refuge areas of dense macrophytes and Chara may be needed to conserve these species.