Collecting environmental DNA (eDNA) as a nonlethal sampling approach has been valuable in detecting the presence/absence of many imperiled taxa; however, its application to indicate species abundance poses many challenges. A deeper understanding of eDNA dynamics in aquatic systems is required to better interpret the substantial variability often associated with eDNA samples. Our sampling design took advantage of natural variation in juvenile Atlantic salmon (
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Abstract Salmo salar ) distribution and abundance along 9 km of a single river in the Province of New Brunswick (Canada), covering different spatial and temporal scales to address the unknown seasonal impacts of environmental variables on the quantitative relationship between eDNA concentration and species abundance. First, we asked whether accounting for environmental variables strengthened the relationship between eDNA and salmon abundance by sampling eDNA during their spring seaward migration. Second, we asked how environmental variables affected eDNA dynamics during the summer as the parr abundance remained relatively constant. Spring eDNA samples were collected over a 6‐week period (12 times) near a rotary screw trap that captured approximately 18.6% of migrating smolts, whereas summer sampling occurred (i) at three distinct salmon habitats (9 times) and (ii) along the full 9 km (3 times). We modeled eDNA concentration as a product of fish abundance and environmental variables, demonstrating that (1) with inclusion of abundance and environmental covariates, eDNA was highly correlated with spring smolt abundance and (2) the relationships among environmental covariates and eDNA were affected by seasonal variation with relatively constant parr abundance in summer. Our findings underscore that with appropriate study design that accounts for seasonal environmental variation and life history phenology, eDNA salmon population assessments may have the potential to evaluate abundance fluctuations in spring and summer.Free, publicly-accessible full text available September 1, 2024 -
Growth–survival tradeoffs may be a generalizable mechanism influencing trajectories of prey evolution. Here, we investigate evolutionary contributions to growth and survival in western mosquitofish ( Gambusia affinis ) from 10 populations from high- and low-predation ancestral environments. We assess (i) the degree to which evolutionary components of growth and survival are consistent or inconsistent across populations within ancestral predation environments, and (ii) whether growth and survival trade off at the population level. We measure growth and survival on groups of common-reared mosquitofish in pond mesocosms. We find that evolution of growth is consistent, with fish from low-predation ancestral environments showing higher growth, while the evolution of survival is inconsistent, with significant population-level divergence unrelated to ancestral predation environment. Such inconsistency prevents a growth–survival tradeoff across populations. Thus, the generalizability of contemporary evolution probably depends on local context of evolutionary tradeoffs, and a continued focus on singular selective agents (e.g. predators) without such local context will impede insights into generalizable evolutionary patterns.more » « less
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Abstract Humans are dominant global drivers of ecological and evolutionary change, rearranging ecosystems and natural selection. In the present article, we show increasing evidence that human activity also plays a disproportionate role in shaping the eco-evolutionary potential of systems—the likelihood of ecological change generating evolutionary change and vice versa. We suggest that the net outcome of human influences on trait change, ecology, and the feedback loops that link them will often (but not always) be to increase eco-evolutionary potential, with important consequences for stability and resilience of populations, communities, and ecosystems. We also integrate existing ecological and evolutionary metrics to predict and manage the eco-evolutionary dynamics of human-affected systems. To support this framework, we use a simple eco–evo feedback model to show that factors affecting eco-evolutionary potential are major determinants of eco-evolutionary dynamics. Our framework suggests that proper management of anthropogenic effects requires a science of human effects on eco-evolutionary potential.more » « less
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The integration of environmental DNA (eDNA) within management strategies for lotic organisms requires translating eDNA detection and quantification data into inferences of the locations and abundances of target species. Understanding how eDNA is distributed in space and time within the complex environments of rivers and streams is a major factor in achieving this translation. Here we study bidimensional eDNA signals in streams to predict the position and abundance of Atlantic salmon ( Salmo salar ) juveniles. We use data from sentinel cages with a range of abundances (3–63 juveniles) that were deployed in three coastal streams in New Brunswick, Canada. We evaluate the spatial patterns of eDNA dispersal and determine the effect of discharge on the dilution rate of eDNA. Our results show that eDNA exhibits predictable plume dynamics downstream from sources, with eDNA being initially concentrated and transported in the midstream, but eventually accumulating in stream margins with time and distance. From these findings we developed a fish detection and distribution prediction model based on the eDNA ratio in midstream versus bankside sites for a variety of fish distribution scenarios. Finally, we advise that sampling midstream at every 400 m is sufficient to detect a single fish at low velocity, but sampling efforts need to be increased at higher water velocity (every 100 m in the systems surveyed in this study). Studying salmon eDNA spatio-temporal patterns in lotic environments is essential to developing strong quantitative population assessment models that successfully leverage eDNA as a tool to protect salmon populations.more » « less
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Abstract While many species distributions are shifting poleward or up in elevation in response to a changing climate, others are shifting their habitats along localized gradients in environmental conditions as abiotic conditions become more stressful. Whether species are moving across regional or local environmental gradients in response to climate change, range‐shifting species become embedded in established communities of competitors and predators. The consequences of these shifts for both resident and shifting species are often unknown, as it can be difficult to isolate the effects of multiple species interactions.
Using a model system of insects in high‐elevation ponds in the Rocky Mountains of Colorado, we sought to disentangle the effects of predation and intraguild interactions on the survival and development of a semi‐permanent pond resident caddisfly
Limnephilus externus and the habitat‐shifting caddisAsynarchus nigriculus that is being forced into semi‐permanent ponds as temporary ponds dry too quickly to complete development.We conducted a manipulative in‐situ pond cage experiment in which
L. externus andA. nigriculus caddisfly larvae in single‐species treatments and together were exposed to the presence/absence of predatoryDytiscus diving beetle larvae. This approach allowed us to isolate the effects of intraguild interactions and predation on the survival and development of both the resident and habitat‐shifting species.We found that intraguild interactions had strong negative effects on the resident and habitat‐shifting species. Intraguild interactions reduced the survival of the resident
L. externus and increased the variation in survival of the shiftingA. nigriculus . However,Dytiscus predators reduced these negative effects, stabilizing the community by increasingL. externus survival and reducing variation inA. nigriculus survival. We also found that intraguild interactions reducedL. externus biomass but resulted in increasedA. nigriculus development.A. nigriculus development was also increased by predation.Our results show that strong intraguild interactions between resident and shifting species are likely to have negative consequences for both species. However, the presence of predators reduces these negative consequences of the habitat shift on both the resident and the shifting.
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Abstract Captive propagation can lead to phenotypic change in fish populations, but the broader community‐level consequences of captive phenotypes remain largely unknown.
We investigate the degree to which captive propagation alters the phenotypes and ecological roles of fish stocked into wild communities. We focus on captive propagation of western mosquitofish (
Gambusia affinis ) for biocontrol, which represents one of the largest scale production efforts for any fish released into the wild.Captive propagation in mosquitofish consistently generated novel mixtures of morphological and behavioural traits that deviate from those of wild populations.
A mesocosm experiment showed that mosquitofish from captive propagation facilities differ from wild fish in their effects on aquatic community structure by shifting their consumption to less‐mobile, benthic prey.
Synthesis and applications . Captive‐propagated and translocated wild fish stocks not only differ in phenotype, but can have substantially different ecological effects on the communities into which they are introduced. Therefore, captive propagation programmes involving continual release should expand their concerns beyond altered phenotypes and fitness to include whether propagated fish actually provide the intended ecological roles and services associated with their wild counterparts. Infusions of wild alleles and captive environments that mimic wild conditions are recommended strategies to retain the desired ecological role of captive‐propagated fish.
