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Detection of environmental DNA (eDNA) has become a commonly used surveillance method for threatened or invasive vertebrates in both aquatic and terrestrial environments. However, most studies in this field favor vertebrate target species. Environmental DNA protocols can be especially useful for endangered invertebrates such as the Hine’s emerald dragonfly ( Somatochlora hineana ) where conservation efforts have been greatly hindered by training, time, overall costs, and environmental impacts associated with conducting surveys in the calcareous fens occupied by this species. An essential step in developing such a protocol is to evaluate the dynamics of eDNA concentration under controlled conditions. We used the quantitative polymerase chain reaction (qPCR) to examine seasonal shifts in the persistence and net-accumulation of eDNA from captive S. hineana larvae in experimental mesocosms at temperatures corresponding with their overwintering (5.0 °C) and active (16.0 °C) seasons. Environmental DNA persisted longer at 5.0 °C but accumulated more readily at 16.0 °C. Differences in the accumulation and persistence of eDNA reflect differences in the longevity of eDNA at different temperatures and seasonal differences in larval S. hineana behavior. This study highlights the importance of considering how seasonal changes in temperature influence not only the speed of eDNA degradation but also the target species’ eDNA shedding rates.

Structural habitat complexity ( SHC ) and functional habitat connectivity ( FHC ) have important effects on predator–prey interactions and exert a strong influence on community structure/dynamics in terrestrial and aquatic ecosystems. Although these factors vary simultaneously in most systems, their interactive effects are poorly understood. Using artificial pond mesocosms and multiple prey types, we manipulated plant density ( SHC : low, high) and inter‐patch distance ( FHC : short, long) in a full factorial design to test for potential interactive effects of these factors on competition and predation by a dragonfly larva ( Anax junius ) and fish predator ( Lepomis cyanallus ). When inter‐patch distances ( FHC ) were short, A. junius consumed more amphipods (36% ± 4.6%) compared with long treatments (19% ± 4.8%). We detected no significant effects of plant density ( SHC ) on prey consumption by A. junius . There were significant interactive effects of FHC and SHC on Lepomis cyanellus consumption of amphipods and damselflies. The most counterintuitive of these effects was that sunfish consumed more larval damselflies at high plant density (64% ± 6.0%) than at low plant density (38% ± 8.6%) but only in short connection treatments. This interactive effect of SHC and FHC on damselfly predation by L. cyanellus was likely because damselflies exhibited riskier behavior at higher SHC . Prey consumption with both predators present was additive, but no significant effect of either SHC or FHC on interspecific predation was detected, suggesting compensatory foraging responses. Structural habitat complexity and FHC interactively influence predator foraging behavior in complex, non‐intuitive ways that are highly dependent on the predator/prey combination in question. Structural habitat complexity and FHC are currently being influenced by anthropogenic factors in multiple ways (e.g., habitat loss, global climate change), and being able to predict the responses of biotic communities to these changes should be an important consideration in restoration and conservation efforts.

Investigating how prey density influences a prey's combined predation risk from multiple predator species is critical for understanding the widespread importance of multiple predator effects. We conducted experiments that crossed six treatments consisting of zero, one, or two predator species (hellgrammites, greenside darters, and creek chubs) with three treatments in which we varied the density of mayfly prey. None of the multiple predator effects in our system were independent, and instead, the presence of multiple predator species resulted in risk reduction for the prey across both multiple predator combinations and all three levels of prey density. Risk reduction is likely to have population-level consequences for the prey, resulting in larger prey populations than would be predicted if the effects of multiple predator species were independent. For one of the two multiple predator combinations, the magnitude of risk reduction marginally increased with prey density. As a result, models predicting the combined risk from multiple predator species in this system will sometimes need to account for prey density as a factor influencing per-capita prey death rates.

The floodplains of large rivers have been heavily modified due to riparian development and channel modifications, both of which can eliminate shallow off-channel habitats. The importance of these habitats for aquatic organisms like fishes is well studied. However, loss of off-channel habitat also eliminates habitats for the production of emerging aquatic insects, which subsidize riparian consumers in terrestrial food webs. We used field collections of insect emergence, historical mapping, and statistical modeling to estimate the loss of insect emergence due to channel modifications along eight segments of the Missouri River (USA), encompassing 1566 river km, between 1890 and 2012. We estimate annual production of emerging aquatic insects declined by a median of 36,000 kgC (95% CrI: 3000 to 450,000) between 1890 and 2012 (a 34% loss), due to the loss of surface area in backwaters and related off-channel habitats. Under a conservative assumption that riparian birds obtain 24% of their annual energy budget from adult aquatic insects, this amount of insect loss would be enough to subsidize approximately 790,000 riparian woodland birds during the breeding and nesting period (May to August; 95% CrI: 57,000 to 10,000,000). Most of the loss is concentrated in the lower reaches of the Missouri River, which historically had a wide floodplain, a meandering channel, and a high density of off-channel habitats, but which were substantially reduced due to channelization and bank stabilization. Our results indicate that the loss of off-channel habitats in large river floodplains has the potential to substantially affect energy availability for riparian insectivores, further demonstrating the importance of maintaining and restoring these habitats for linked aquatic-terrestrial ecosystems.

The effects of different types of predators may combine in complex ways to impact prey populations. In a series of microcosm experiments I empirically derived the functional response curves for two common types of stream predators, sculpins (Cottus bairdi) and stonefly larvae (Agnetina capitata), on two behaviorally and morphologically distinct types of mayfly prey (Baetis tricaudatus and Ephemerella subvaria). Data from these separate trials were combined using simple additive models to generate predicted combined functional responses for both types of predator. For both types of prey, actual combined functional response curves (both types of predators together in a treatment) differed significantly from predicted combined functional response for some ranges of prey densities. When Baetis was used as prey, significant departures from the predicted values occurred at moderate and high prey densities and were in a negative direction (interference between predators). When Ephemerella was the prey, significant departures occurred at low and moderate densities and were in a positive direction (facilitation between predators). Additive models for predicting combined predator effects cannot account for non—linearities in combined functional response introduced by non—trophic (behavioral) interactions that occur between fish and stoneflies, and between these predators and their prey. Other aquatic and terrestrial food webs contain similar linkages between vertebrate and invertebrate predators and their prey. Inclusion of behavioral interaction terms seems likely to be a necessary part of any general predicting combined effects of predators on prey populations in these systems.

Carbon and nitrogen stable isotopes (δ 13 C and δ 15 N, respectively) were measured for locally abundant primary producers, detritus, aquatic invertebrates, and fish in backwater lakes of two large floodplain rivers in an effort to understand patterns of energy dependence and trophic structure within these habitats. We observed trophic enrichment values for 15 N that were within the ranges observed for other aquatic systems but were often considerably lower than the 3.4‰ typically assumed in stable isotope studies. Production based on benthic and terrestrial material, combined with planktonic production for larval fish, appears to be an important energy source supporting consumers in backwater lakes of large floodplain rivers. Our isotopic data challenge the conventional wisdom that macrophytes are centrally involved in supplying carbon to aquatic consumers in shallow lakes and that food webs in most lakes are sustained almost exclusively by carbon fixed by phytoplankton.

Despite the importance of dispersal to ecology, accurate estimates of dispersal rates are often difficult to obtain, especially for organisms that rely on passive dispersal of propagules to colonize new sites. To investigate potential dispersal vectors and relative colonization rates of zooplankton, we conducted a field experiment in which we restricted potential dispersal vectors (insects, birds, amphibians) from transporting zooplankton to mesocosms. Twenty-six non-insect invertebrate taxa invaded our array during 2 years. Colonization rates of organisms varied considerably, with some species appearing several weeks after the experiment began and others appearing after a year. We observed no difference in colonization rates among treatments, suggesting that species were transported to our experiment primarily by wind or rain, rather than by animal vectors. The absence of an additional 13 zooplankton species common in ponds immediately adjacent to the array either occurred because of dispersal limitation or an inability to invade the existing communities. Ecologists generally assume that all zooplankton are rapidly dispersed hence the potential for dispersal limitation is generally ignored. Our results suggest that zooplankton vary in their dispersal and colonization ability. Hence, increased attention should be focused on the potential role of dispersal limitation and its importance for understanding the structure and function of aquatic communities.

Structural habitat complexity (SHC) and functional habitat connectivity (FHC) are the basic components that make up the physical architecture of an ecosystem, and can have substantial impacts on predator–prey interactions. These structural components influence animal behaviors such as inter‐patch movement, foraging, and competition, and can impact community structure/dynamics in terrestrial and aquatic ecosystems. The effects of SHC and FHC on predator–prey dynamics within an ecosystem may also have important cascading effects on neighboring ecosystems by altering the movement of individuals across ecosystem boundaries. For example, when aquatic insects emerge as adults, they enter terrestrial ecosystems where they become an important food resource for terrestrial predators. Using a multiple patch, predator enclosure design in ponds, we tested whether altering intra‐patch plant stem densities (SHC) and inter‐patch distances (FHC) would influence the impact a predatory fish has on the biomass, quality, and trophic composition of emergent insects. As expected, fish significantly reduced emergent insect biomass (33% ± 7.6, mean ± SE). Intra‐patch stem densities (SHC) did not significantly alter fish effects; however, inter‐patch distance (FHC) did significantly alter the impact of fish on the size of some emergent insects. Damselflies that emerged in treatments with fish present and shorter inter‐patch distances were significantly larger, 4.1 ± 0.1 mg/m2 compared to 3.3 mg/m2 ± 0.1 in the long/fish treatments. In fish treatments, this effect on damselfly size resulted in greater reductions in total emergent insect biomass in long inter‐patch distance treatments (47.3% ± 6.9) compared to short inter‐patch distance treatments (20.5% ± 12.4). Our results suggest that physical components of a habitat, such as inter‐patch distances, have important impacts on predator–prey dynamics within habitats. These altered predator–prey dynamics can then have cascading effects on adjacent habitats by influencing the abundance, trophic composition, and quality of exported trophic subsidies.

Most freshwater food web models assume that fish occupy the top trophic level. Yet many diet studies and a few caging and artificial stream experiments suggest that birds may be top predators in many freshwater systems. We conducted a large-scale field experiment to test whether avian predators affect the size distribution and abundance of fish in two midwestern streams. We used a combination of netting and perches to manipulate predation by Great Blue Herons (Ardea herodias) and Belted Kingfishers (Ceryle alcyon), and measured the response in the fish assemblage. Bird exclusions caused significant increases in medium size classes of two common prey, striped shiners (Luxilus chrysocephalus) and central stonerollers (Campostoma anomalum). We show that these species of piscivorous birds can alter the abundance of common prey and thus need to be considered more fully when attempting to explain the structure of aquatic food webs.

Roadways near wetlands and ponds inflict high roadkill rates on a wide variety of taxa. For threatened or endangered species that typically do not have large adult populations, fast reproduction rates, and/or rapid recolonization rates, such mortality is likely to have significant population consequences. Thus, exploring ways to reduce roadkill rates will have considerable conservation benefits. In this study, we evaluate whether a diversion structure can be used to modify flight behavior of the endangered Hine’s emerald dragonfly (Somatochlora hineana) in ways that would reduce roadway mortality. Flight behavior of adult S. hineana was observed with and without two 3 m high nets spaced at 6 and 12 m to simulate a small and a larger roadway. The netting significantly deterred (p < 0.0001) S. hineana adults from crossing the simulated roadway. Flight height was also influenced significantly (p = 0.0025) with flight heights over the 6 m net spacing being higher than those over the 12 m spacing. This study suggests that the use of diversion netting in areas where sensitive dragonfly species interact with motor vehicles might aid in reducing roadway mortality and might help reduce the overall impact of roadways on wetland ecosystems.