Quantitative macroinvertebrate bioassessment in seasonally astatic aquatic habitats, Part I. Quantitative method.

Seasonally astatic aquatic habitats are important ecologically, municipally, and agriculturally. Regulatory agencies and conservation organizations have developed various plans for protecting or constructing temporary wetlands, resulting in habitat monitoring requirements, particularly as relates to restoration and constructed habitats. Unfortunately, there has been no effort to develop a unified, consistent method for wetland biological monitoring. This is particularly true for habitats important in a regulatory sense. We conducted macroinvertebrate bioassessment in constructed vernal pools in California, USA, to assess habitat functionality. This tool is modified from aquatic bioassessment; a primary tool of regulatory agencies in measuring habitat health and water quality and should be equally applicable to seasonally astatic wetlands globally.

Quantitative macroinvertebrate bioassessment in seasonally astatic aquatic habitats, Part II. Applying the method.

Seasonally astatic aquatic habitats are important ecologically, municipally, and agriculturally. Regulatory agencies and conservation organizations have developed various plans for protecting or constructing temporary wetlands, resulting in habitat monitoring requirements, particularly as relates to restoration and constructed habitats. Unfortunately, there has been no effort to develop a unified, consistent method for wetland biological monitoring. In Part I, we presented a quantifiable, replicable method for assessing seasonally astatic wetlands, which would allow for direct comparison between individual wetlands, wetland sites, and wetland types. Here in Part II, we apply the method and present the results from more than a decade of a data on two disparate sites that support California vernal pool habitats. These habitats include natural, restored, and constructed vernal pools. Our results demonstrate that the method we present yields reliable, statistically useful, and actionable data and provides a better method for assessing astatic wetland ecological health and the persistence of federally listed vernal pool crustaceans than other methods so far employed.

Application of modern coexistence theory to rare plant restoration provides early indication of restoration trajectories.

Restoration ecology commonly seeks to re-establish species of interest in degraded habitats. Despite a rich understanding of how succession influences re-establishment, there are several outstanding questions that remain unaddressed: are short-term abundances sufficient to determine long-term re-establishment success, and what factors contribute to unpredictable restorations outcomes? In other words, when restoration fails, is it because the restored habitat is substandard, because of strong competition with invasive species, or alternatively due to changing environmental conditions that would equally impact established populations? Here, we re-purpose tools developed from modern coexistence theory to address these questions, and apply them to an effort to restore the endangered Contra Costa goldfields (Lasthenia conjugens) in constructed ("restored") California vernal pools. Using 16 years of data, we construct a population model of L. conjugens, a species of conservation concern due primarily to habitat loss and invasion of exotic grasses. We show that initial, short-term appearances of restoration success from population abundances is misleading, as year-to-year fluctuations cause long-term population growth rates to fall below zero. The failure of constructed pools is driven by lower maximum growth rates compared with reference ("natural") pools, coupled with a stronger negative sensitivity to annual fluctuations in abiotic conditions that yield decreased maximum growth rates. Nonetheless, our modeling shows that fluctuations in competition (mainly with exotic grasses) benefit L. conjugens through periods of competitive release, especially in constructed pools of intermediate pool depth. We therefore show how reductions in invasives and seed addition in pools of particular depths could change the outcome of restoration for L. conjugens. By applying a largely theoretical framework to the urgent goal of ecological restoration, our study provides a blueprint for predicting restoration success, and identifies future actions to reverse species loss.

The adaptive potential of plant populations in response to extreme climate events.

The frequency and magnitude of extreme climate events are increasing with global change, yet we lack predictions and empirical evidence for the ability of wild populations to persist and adapt in response to these events. Here, we used Fisher's Fundamental Theorem of Natural Selection to evaluate the adaptive potential of Lasthenia fremontii, a herbaceous winter annual that is endemic to seasonally flooded wetlands in California, to alternative flooding regimes that occur during El Niño Southern Oscillation (ENSO) events. The results indicate that populations may exhibit greater adaptive potential in response to dry years than wet years, and that the relative performance of populations will change across climate scenarios. More generally, our findings show that extreme climate events can substantially change the potential for populations to adapt to climate change by modulating the expression of standing genetic variation and mean fitness.

Bioaccumulation of methylmercury in wood frogs and spotted salamanders in Vermont vernal pools.

Mercury (Hg) has accumulated in forested landscapes in the Northeastern U.S., and hotspots with enhanced deposition have been identified throughout the region. Due to a variety of favorable landscape characteristics, including relatively high dissolved organic carbon (DOC), fluctuating water levels, and low pH and dissolved oxygen, vernal pools provide ideal conditions for the conversion of Hg to its more toxic and bioavailable form, methylmercury (MeHg). Yet little is known about the concentrations, speciation, and bioavailability of Hg in vernal pools, or its bioaccumulation in vernal pool fauna and potential export into terrestrial systems. We investigated the role of forest cover type on the bioaccumulation of MeHg in wood frog (Lithobates sylvatica) and spotted salamander (Ambystoma maculatum) eggs, larvae, and adults, and investigated relationships among MeHg and water chemistry (pH, DOC). Water samples from pools located in coniferous stands had greater concentrations of THg and MeHg compared to deciduous pool water, and showed significant positive correlation to DOC (r = 0.683, P < 0.001) and correlated negatively with pH (r = -0.613, P < 0.001). Methylmercury levels in amphibian embryos were similar between the two species (L. sylvatica mean = 5.4 ng/g dw; A. maculatum mean = 3.5 ng/g dw). Concentrations of MeHg increased substantially in larvae, and were significantly greater in A. maculatum (mean = 237.6 ng/g ± 18.5 SE) than L. sylvatica larvae (62.5 ng/g ± 5.7 SE). Forest cover type did not explain variation in MeHg concentration among amphibian embryos or larvae. Methylmercury levels in adult tissue samples were significantly greater in A. maculatum (mean = 79.9 ng/g ± 8.9 SE) compared to L. sylvatica (mean = 47.7 ng/g ± 9.7 SE). This research demonstrates that vernal pools are important hotspots where amphibians bioaccumulate MeHg, which may then be transferred to terrestrial ecosystems. The abundance of amphibian larvae suggests they could be important bioindicators for monitoring MeHg loading and bioavailability.

A new approach for hydrologic performance standards in wetland mitigation.

Wetland restoration performed as a requirement of compensatory mitigation does not always replace lost acreage or functions. Most new projects are required to identify performance standards to evaluate restoration outcomes. Current performance standards are primarily related to vegetation with little to no evaluation of wetland hydrologic regimes. Because of the agreement in the scientific literature about the role of hydrology in creating and maintaining wetland structure and function, hydrologic performance standards may be an ecologically meaningful way to evaluate restoration outcomes. This research tests the use of water level data from project specific reference sites to evaluate restored water levels for three distinct wetland types across the United States. We analyzed existing datasets from past and ongoing wetland mitigation projects to identify the number of years it took water levels in restored wetlands to match reference sites, and to test whether similar water levels between restored and reference sites leads to increased vegetation success. Wetland types differed in the number of years it took for water levels to match reference sites. Vernal pools in California took nine years to match reference sites, fens and wet meadows in Colorado took four years, and forested wetlands in the southeastern US were hydrologically similar to reference sites the first year following restoration. Plant species cover in all three restored wetland types was related to the water level similarity to reference sites. Native cover was higher when water levels were more similar to reference sites, and was lower in areas where water levels were different. Exotic species cover showed the opposite relationship in fens and wet meadows, where hydrologic similarity led to low cover of exotic species. Along with the general agreement of the importance of hydrology for wetland form and function, this research shows that hydrologic performance standards may also lead to increased vegetation success in some wetland types.

Spatiotemporal heterogeneity in precipitation patterns explain population-level germination strategies in an edaphic specialist.

BACKGROUND AND AIMS: Many locally endemic species in biodiversity hotspots are restricted to edaphic conditions that are fixed in the landscape, limiting their potential to track climate change through dispersal. Instead, such species experience strong selection for germination strategies that can track suitable conditions through time. Germination strategies were compared among populations across the geographic range of a California vernal pool annual, Lasthenia fremontii Local germination strategies were tested to determine the associations with geographic variation in precipitation patterns. METHODS: This study evaluated patterns of seed germination, dormancy and mortality in response to simulated variation in the timing, amount and duration of the first autumn precipitation event using seeds from six populations that span a geographic gradient in precipitation. Next, it was tested whether the germination strategies of different populations can be predicted by historical precipitation patterns that characterize each site. KEY RESULTS: A significant positive relationship was observed between the historical variability in autumn precipitation and the extent of dormancy in a population. Marginal populations, with histories of the most extreme but constant autumn precipitation levels, expressed the lowest dormancy levels. Populations from sites with historically higher levels of autumn precipitation tended to germinate faster, but this tendency was not statistically significant. CONCLUSIONS: Germination in L. fremontii is cued by the onset of the first rains that characterize the beginning of winter in California's Great Central Valley. However, populations differ in how fast they germinate and the fraction of seeds that remain dormant when germination cues occur. The results suggest that seed dormancy may be a key trait for populations to track increasingly drier climates predicted by climate change models. However, the low dormancy and high mortality levels observed among seeds of the southernmost, driest populations make them most vulnerable to local extinction.

Community disassembly in ephemeral ecosystems.

Community disassembly is the non-random process of progressive species declines and losses. This process is usually studied to determine how various forces extirpate species, such as catastrophic disturbance, species invasions, habitat fragmentation, or unnatural/anthropogenic stressors. However, in ephemeral ecosystems, community disassembly is a natural and repeatable process. While many ephemeral ecosystems are aquatic (vernal pools, playa lakes, rock pools, saline lakes, phytotelmata, etc.), some disassembly patterns are applicable to other ecosystem types, including terrestrial ecosystems. As ephemeral waterbodies near the end of their hydroperiod, certain aspects fundamentally change. These fundamental changes or mechanisms cause visible patterns of community disassembly. Decreasing habitat size eliminates microhabitats and increases encounter rates between organisms, possibly increasing predation and competition. A harshening habitat eliminates low-tolerance species, changes the proportions of specialists/generalists, and forces organisms to acclimate, emigrate, or die. Additionally, ultraviolet light affects more of the water column, eliminating unprotected species. Furthermore, the entire metacommunity is often in similar stages of disassembly and collapses. Many of these mechanisms drive disassembly of terrestrial ephemeral habitats, such as animal carcasses, dung pads, or fungal fruiting bodies. Organisms obligate to ephemeral habitats have evolved to optimize their life history for a rapid life cycle with specific adaptations for themselves or their offspring to survive through the inactive period of the ecosystem. While some disassembly may occur too fast for biotic interactions or compensatory dynamics to be important, organisms undergoing natural disassembly should "expect" it. Thus, predictions of disassembly based on internal or biotic patterns may be more common in natural disassembly scenarios than in human-induced disassembly of permanent ecosystems. Additionally, natural community disassembly should be more predictable and understandable than a permanent community's reaction to a never-before-seen anthropogenic disturbance. Community disassembly is an important ecological component of ephemeral ecosystems. The processes that occur during disassembly shape assemblages over ecologically and evolutionary relevant timescales. Understanding how natural disassembly can feed back to ultimately drive ecosystem structure and function increases our knowledge of fundamental ecology and provides for a new frontier of study.

The joint evolution of traits and habitat: ontogenetic shifts in leaf morphology and wetland specialization in Lasthenia.

The interplay between functional traits and habitat associations drives species' evolutionary responses to environmental heterogeneity, including processes such as adaptation, ecological speciation, and niche evolution. Seasonal variation is an aspect of the environment that varies across habitats, and could result in adaptive shifts in trait values across the life cycle of a plant. Here, we use phylogenetic comparative methods to evaluate the joint evolution of plant traits and habitat associations in Lasthenia (Asteraceae), a small clade of predominantly annual plants that have differentiated into an ecologically diverse range of habitats, including seasonal ephemeral wetlands known as vernal pools. Our results support the hypothesis that there is a link between the evolution of leaf morphology and the ecohydrological niche in Lasthenia, and, in the formation of aerenchyma (air space), differentiation between vernal pool and terrestrial taxa is fine-tuned to specific stages of plant ontogeny that reflects the evolution of heterophylly. Our findings demonstrate how the relationships between traits and habitat type can vary across the development of an organism, while highlighting a carefully considered comparative approach for examining correlated trait and niche evolution in a recently diversified and ecologically diverse plant clade.

Ecological release exposes genetically based niche variation.

The evolutionary trajectories of ecological niches have profound impacts on community, population and speciation dynamics, yet the underlying causes of niche lability vs. stasis are poorly understood. Here, we conducted a field experiment to quantify the effects of competition and, conversely, competitive release on the microevolutionary processes driving microhabitat niche evolution in an annual plant population restricted to California vernal pool wetlands. Removing competitors generated a strong increase in mean fitness, the exposure of genetically based niche variation and directional selection for niche evolution in the experimental population. In contrast, genetic variation in the microhabitat niche and directional selection for niche evolution were not detected in individuals growing with competitors. These results indicate that ecological opportunity (here, the removal of competitors) can trigger the immediate expression of latent, heritable niche variation that is necessary for rapid evolutionary responses; conversely, competitors may restrict niche evolution, contributing to niche conservatism in saturated communities.

Consequences of above-ground invasion by non-native plants into restored vernal pools do not prompt same changes in below-ground processes.

Given the frequent overlap between biological plant invasion and ecological restoration efforts it is important to investigate their interactions to sustain desirable plant communities and modify long-term legacies both above- and below-ground. To address this relationship, we used natural reference, invaded and created vernal pools in the Central Valley of California to examine potential changes in direct and indirect plant effects on soils associated with biological invasion and active restoration ecosystem disturbances. Our results showed that through a shift in vegetation composition and changes in the plant community tissue chemistry, invasion by non-native plant species has the potential to transform plant inputs to soils in vernal pool systems. In particular, we found that while invasive plant litter decomposition was driven by seasonal and interannual variability, associated with changes in precipitation, the overall decomposition rates for invasive litter was drastically lower than native species. This shift has important implications for long-term alterations in plant-based inputs to soils in an amplifying feedback to nutrient cycling. Moreover, these results were independent of historic active restoration efforts. Despite the consistent shift in plant litter decomposition rates and community composition, we did not detect associated shifts in below-ground function associated with invasion by non-native plants. Instead, soil C:N ratios and microbial biomass did not differ between invaded and naturally occurring reference pools but were reduced in the manipulated created pools independent of invasion levels. Our results suggest that while there is an observed invasive amplifying feedback above-ground this trajectory is not represented below-ground, and restoration legacies dominated 10 years after practices were applied. Restoration practices that limit invasive plant feedbacks and account for soil legacy recovery, therefore offer the best solution for disturbed ephemeral ecosystems.

A sensitivity analysis of pesticide concentrations in California Central Valley vernal pools.

Vernal pools are ephemeral wetlands that provide critical habitat to many listed species. Pesticide fate in vernal pools is poorly understood because of uncertainties in the amount of pesticide entering these ecosystems and their bioavailability throughout cycles of wet and dry periods. The Pesticide Water Calculator (PWC), a model used for the regulation of pesticides in the US, was used to predict surface water and sediment pore water pesticide concentrations in vernal pool habitats. The PWC model (version 1.59) was implemented with deterministic and probabilistic approaches and parameterized for three agricultural vernal pool watersheds located in the San Joaquin River basin in the Central Valley of California. Exposure concentrations for chlorpyrifos, diazinon and malathion were simulated. The deterministic approach used default values and professional judgment to calculate point values of estimated concentrations. In the probabilistic approach, Monte Carlo (MC) simulations were conducted across the full input parameter space with a sensitivity analysis that quantified the parameter contribution to model prediction uncertainty. Partial correlation coefficients were used as the primary sensitivity metric for analyzing model outputs. Conditioned daily sensitivity analysis indicates curve number (CN) and the universal soil loss equation (USLE) parameters as the most important environmental parameters. Therefore, exposure estimation can be improved efficiently by focusing parameterization efforts on these driving processes, and agricultural pesticide inputs in these critical habitats can be reduced by best management practices focused on runoff and sediment reductions.

Vernal pool amphibian breeding ecology monitoring from 1931 to present: A harmonised historical and ongoing observational ecology dataset.

BACKGROUND: For 88 years (1931-present), the Mohonk Preserve's Daniel Smiley Research Center has been collecting data on occupancy and reproductive success of amphibian species, as well as associated water quality of 11 vernal pools each spring (February to May). Though sampling effort has varied over the dataset range, the size of the dataset is unprecedented within the field of amphibian ecology. With more than 2,480 individual species sampling dates and more than 151,701 recorded individual occurrences of the nine amphibian species, the described dataset represents the longest and largest time-series of herpetological sampling with paired water quality data. NEW INFORMATION: We describe the novel publication of a paired dataset of amphibian occurrence with environmental indicators spanning nearly 90 years of data collection. As of February 2020, the dataset includes 2,480 sampling dates across eleven vernal pools and 151,701 unique occurrences of egg masses or individuals recorded across nine species of amphibian. The dataset also includes environmental conditions associated with the species occurrences with complete coverage for air temperature and precipitation records and partial coverage for a variety of other weather and water quality measures. Data collection has included species, egg mass and tadpole counts; weather conditions including precipitation, sky and wind codes; water quality measurements including water temperature and pH; and vernal pool assessment including depth and surface vegetation coverage. Collection of data was sporadic from 1931-1991, but data have been collected consistently from 1991 to present. We also began monitoring dissolved oxygen, nitrate concentrations and conductivity of the vernal pools using a YSI Sonde Professional Plus Instrument and turbidity using a turbidity tube in February 2018. The dataset (and periodic updates), as well as metadata in the EML format, are available in the Environmental Data Initiative Repository under package edi.398.

Environmental Drivers of Ranavirus in Free-Living Amphibians in Constructed Ponds.

Amphibian ranaviruses occur globally, but we are only beginning to understand mechanisms for emergence. Ranaviruses are aquatic pathogens which can cause > 90% mortality in larvae of many aquatic-breeding amphibians, making them important focal host taxa. Host susceptibilities and virulence of ranaviruses have been studied extensively in controlled laboratory settings, but research is needed to identify drivers of infection in natural environments. Constructed ponds, essential components of wetland restoration, have been associated with higher ranavirus prevalence than natural ponds, posing a conundrum for conservation efforts, and emphasizing the need to understand potential drivers. In this study, we analyzed 4 years of Frog virus 3 prevalence and associated environmental parameters in populations of wood frogs (Lithobates sylvaticus) and green frogs (Lithobates clamitans) in a constructed pond system. High prevalence was best predicted by low temperature, high host density, low zooplankton concentrations, and Gosner stages approaching metamorphosis. This study identified important variables to measure in assessments of ranaviral infection risk in newly constructed ponds, including effects of zooplankton, which have not been previously quantified in natural settings. Examining factors mediating diseases in natural environments, particularly in managed conservation settings, is important to both validate laboratory findings in situ, and to inform future conservation planning, particularly in the context of adaptive management.