Michael T. Bogan

Scientific Evidence Supports a Ban on Microbeads

Chelsea M. Rochman,*,†,‡ Sara M. Kross,†,§ Jonathan B. Armstrong,†,∥,@ Michael T. Bogan,†,⊥,@ Emily S. Darling,†,#,@ Stephanie J. Green,†,¶,@ Ashley R. Smyth,†,▲,@ and Diogo Verissimo†,▼,@ †David H. Smith Conservation Research Program, Society for Conservation Biology, Washington, DC 20001, United States ‡School of Veterinary Medicine, Aquatic Health Program, University of California Davis, Davis, California 95616, United States Department of Wildlife, Fish and Conservation Biology, University of California Davis, Davis, California 95616-8627, United States USGS Cooperative Fish and Wildlife Research Unit, University of Wyoming, Laramie, Wyoming 82071, United States Department of Environmental Science, Management and Policy, University of California Berkeley, Berkeley, California 94720-3114, United States Marine Program, Wildlife Conservation Society, New York 10460-1099, United States Department of Integrative Biology, Oregon State University, Corvallis, Oregon 97331, United States Virginia Institute of Marine Science, College of William and Mary, Gloucester Point, Virginia 23062, United States Andrew Young School of Policy Studies, Department of Economics, Georgia State University, 33 Gilmer Street SE, Atlanta, Georgia 30303, United States

Evolution of aquatic insect behaviours across a gradient of disturbance predictability

Natural disturbance regimes—cycles of fire, flood, drought or other events—range from highly predictable (disturbances occur regularly in time or in concert with a proximate cue) to highly unpredictable. While theory predicts how populations should evolve under different degrees of disturbance predictability, there is little empirical evidence of how this occurs in nature. Here, we demonstrate local adaptation in populations of an aquatic insect occupying sites along a natural gradient of disturbance predictability, where predictability was defined as the ability of a proximate cue (rainfall) to signal a disturbance (flash flood). In controlled behavioural experiments, populations from predictable environments responded to rainfall events by quickly exiting the water and moving sufficiently far from the stream to escape flash floods. By contrast, populations from less predictable environments had longer response times and lower response rates, reflecting the uncertainty inherent to these environments. Analysis with signal detection theory showed that for 13 out of 15 populations, observed response times were an optimal compromise between the competing risks of abandoning versus remaining in the stream, mediated by the rainfall–flood correlation of the local environment. Our study provides the first demonstration that populations can evolve in response to differences in disturbance predictability, and provides evidence that populations can adapt to among-stream differences in flow regime.

Hydrology shapes taxonomic and functional structure of desert stream invertebrate communities

Hydrology is a fundamental factor influencing ecosystem dynamics, life-history strategies, and diversity patterns in running-water habitats. However, it remains unclear how hydrology may structure the taxonomic and functional composition of communities, especially in systems with high spatiotemporal variability in flow. We examined invertebrate diversity from 7 desert streams in the Huachuca Mountains of southeastern Arizona, USA, that span a flow permanence continuum from highly intermittent to perennial. We examined the relative roles of flow permanence, habitat size, season, and microhabitat in determining taxonomic and functional structure (according to 7 species traits compiled for 234 taxa) of these communities. We predicted that both functional and taxonomic diversity would be positively related to flow permanence and negatively related to the duration and number of stream drying events. As predicted, increased flow permanence was associated with increased functional richness, functional evenness, and taxonomic richness. Conversely, drying events reduced functional diversity across all measured indices. We found a saturating relationship between functional richness and taxonomic richness, indicating functional redundancy in species-rich communities, which may promote resilience of ecosystem function to environmental variation. Our study adds further evidence that hydrology is a key determinant of aquatic invertebrate diversity, and that stream hydroperiod strongly influences both functional and taxonomic diversity in arid-land streams.

Aerial dispersal of aquatic invertebrates along and away from arid-land streams

Abstract.  Dispersal is an essential process in metapopulation and metacommunity dynamics. Most studies of aquatic invertebrate dispersal in streams have focused on in-stream drift of larvae. However, understanding aerial dispersal is important for predicting community assembly in isolated habitats after disturbance or stream restoration. We used artificial pools placed at 3 distances (5, 75, and 250 m) from 1 perennial and 1 ephemeral arid-land stream to examine aerial-dispersal dynamics of aquatic invertebrates over a 6-wk period in summer 2009. We also conducted a 2-wk experiment to examine the relationship between daily rainfall and disperser abundance at the perennial site. Sixty-six aquatic invertebrate taxa (including many Coleoptera and Diptera and fewer Hemiptera, Ephemeroptera, Trichoptera, and noninsect taxa) colonized the artificial pools. They represented ⅓ of taxa documented from neighboring perennial streams. Abundance and species richness declined with distance away from both streams. This result suggests that ephemeral stream channels may serve as important aerial dispersal corridors for aquatic invertebrates even when no surface water is present. Mean species richness tripled after 58 mm of rain during the 4th wk of the experiment. Data from the 2-wk experiment highlighted the role of rainfall as a dispersal cue in this system. Amount of daily rainfall explained 48 to 77% of the variation in disperser abundance at 5, 75, and 250 m from the perennial site. We used spatiotemporal dispersal patterns observed in our study to identify 5 modes of aerial dispersal among 56 taxa: 1) widespread common, 2) widespread haphazard, 3) range-restricted, 4) cue-limited, and 5) infrequent. Classification of specific aerial-dispersal modes provides a conceptual framework for modeling spatially explicit community responses to disturbance, stream restoration, and climate-change-induced habitat contraction or expansion.

Dispersal ability and habitat requirements determine landscape-level genetic patterns in desert aquatic insects

Species occupying the same geographic range can exhibit remarkably different population structures across the landscape, ranging from highly diversified to panmictic. Given limitations on collecting population‐level data for large numbers of species, ecologists seek to identify proximate organismal traits—such as dispersal ability, habitat preference and life history—that are strong predictors of realized population structure. We examined how dispersal ability and habitat structure affect the regional balance of gene flow and genetic drift within three aquatic insects that represent the range of dispersal abilities and habitat requirements observed in desert stream insect communities. For each species, we tested for linear relationships between genetic distances and geographic distances using Euclidean and landscape‐based metrics of resistance. We found that the moderate‐disperser Mesocapnia arizonensis (Plecoptera: Capniidae) has a strong isolation‐by‐distance pattern, suggesting migration–drift equilibrium. By contrast, population structure in the flightless Abedus herberti (Hemiptera: Belostomatidae) is influenced by genetic drift, while gene flow is the dominant force in the strong‐flying Boreonectes aequinoctialis (Coleoptera: Dytiscidae). The best‐fitting landscape model for M. arizonensis was based on Euclidean distance. Analyses also identified a strong spatial scale‐dependence, where landscape genetic methods only performed well for species that were intermediate in dispersal ability. Our results highlight the fact that when either gene flow or genetic drift dominates in shaping population structure, no detectable relationship between genetic and geographic distances is expected at certain spatial scales. This study provides insight into how gene flow and drift interact at the regional scale for these insects as well as the organisms that share similar habitats and dispersal abilities.

LOW SPECIFIC CONDUCTIVITY LIMITS GROWTH AND SURVIVAL OF THE NEW ZEALAND MUD SNAIL FROM THE UPPER OWENS RIVER, CALIFORNIA

Abstract The New Zealand mud snail (NZMS), Potamopyrgus antipodarum (Gray), is an invasive species of aquatic snail that is becoming widespread in inland and coastal waters of the western United States. The New Zealand mud snail can have significant impacts on stream ecosystems, as they may consume a large fraction of available algae production and compete with and displace native invertebrates. Even though the distribution of this species is expanding, the habitat conditions conducive to invasion are incompletely understood. Surveys following the NZMS invasion in the Upper Owens River, California, indicated that the snail may be excluded from waters where dissolved solute content is low, so experimental studies were undertaken to evaluate survival and growth as a function of varied specific conductivity (SC) and calcium availability. Juvenile snails were collected from the Upper Owens River and reared in dilutions of natural river water adjusted to 10, 50, 100, 200 and 300 μS · cm−1 SC. Experiments were also conducted with newborn clones raised in river water dilutions ranging from 25 to 200 μS · cm−1 to examine mortality and growth at this sensitive stage of development. In addition, calcium-free artificial river water was prepared at 200 μS · cm−1 to test for the independent effect of limitation of this mineral ion required for shell-building. Significant reductions in survival and growth occurred among treatments diluting river water from 300 to 50 μS · cm−1. No growth was found at or below 25 μS · cm−1. Growth was also inhibited in calcium-free artificial water compared to natural river water with the same SC, showing that lack of this mineral impedes development. These results suggest that many streams in the range of 25–200 μS · cm−1 cannot support productive NZMS populations and that nuisance invasions may be most prevalent in waters above 200 μS · cm−1 where sufficient dissolved mineral content is present for growth.

High Aquatic Biodiversity in an Intermittent Coastal Headwater Stream at Golden Gate National Recreation Area, California

Abstract Headwater and intermittent streams have traditionally been considered less biologically diverse than downstream perennial reaches. However, recent studies have highlighted the significant role that headwaters play in supporting regional aquatic biodiversity. Additionally, intermittent streams in the Pacific Northwest may be more diverse than similar streams in other regions. Here, we present a four-year biodiversity study of the John West Fork, an intermittent coastal headwater stream in northern California. It only flows for 5–7 months each year, but supports residual perennial pools during the summer dry season. Our goals are to describe the physical and biological settings of the John West Fork, document its aquatic biodiversity, and promote the use of it and similar streams as study systems. From 2009 to 2012, we sampled fish and invertebrates in riffles and pools during early summer (June) and in residual pools during late summer (late September/early October). We documented four vertebrate species (steelhead trout, coho salmon, California giant salamander, and Pacific chorus frog) and 159 aquatic invertebrate taxa. Steelhead trout were common each year, but coho salmon were present only in 2010 and 2011. Most invertebrate taxa were tolerant of stagnant pool conditions; only nine taxa were exclusive to flowing riffle habitats. Intermittent headwater streams similar to John West Fork are numerous along the west coast of North America. This great number of replicate systems and their tractability make them ideal for ecological studies, and their high biodiversity makes them deserving of consideration in local and regional conservation planning.

Summer die-off of western pond turtle (Actinemys marmorata) along an intermittent coast range stream in central California

Abstract During late summer and fall 2014, we documented western pond turtle (Actinemys marmorata) mortality, as indicated by the presence of turtle shells, along a 3.7-km reach of Coyote Creek in the Diablo Range of central California. In total, we observed 39 western pond turtle shells scattered irregularly along our study reach. Shells were found in dry reaches adjacent to or close to pools containing live turtles, as well as in or adjacent to dry pools in isolated dry reaches. Ninety percent of shells observed contained no carcass, and several shells showed evidence of predation. Though the cause of mortality is unclear, our observations confirm that western pond turtles may experience high mortality during droughts, which could result in significant population decline. The presence of live turtles in refugial pools emphasizes the importance of protecting and managing permanent pools in the face of intensified drought conditions.

Links between two interacting factors, novel habitats and non-native predators, and aquatic invertebrate communities in a dryland environment

In dryland regions, increased demand for water has led to the reduction of natural aquatic habitats and threatens persisting aquatic habitats. In the Madrean Sky Islands (MSI), water demands have also resulted in the creation of novel aquatic habitats, including stock ponds. Stock ponds are important surrogate habitat for native species, yet little is known about the aquatic invertebrates utilizing these habitats. Additionally, stock ponds support non-native vertebrate predators including American bullfrogs (Lithobates catesbeiana) and Western mosquitofish (Gambusia affinis), and the effects of these predators on invertebrate communities in stock ponds are unknown. We explored similarities in invertebrate communities in stream pools and stock ponds and compared aquatic invertebrate community composition, abundance, and richness in stock ponds with and without non-native predators. We found that despite considerable functional (trait-based) overlap in aquatic invertebrate communities, a large majority (81%) of taxa were exclusive to either stock ponds or stream pools. Additionally, we observed few differences in aquatic invertebrate community composition, abundance, and richness in stock ponds with and without non-native predators. We discuss ecological implications of our observations, limitations of our approach, and the importance of future work in determining the role of stock ponds in conservation of the region’s aquatic invertebrates.

Environment shapes invertebrate assemblage structure differences between volcanic spring-fed and runoff rivers in northern California

Flow variability plays an important role in structuring lotic communities, yet comparatively little is known about processes governing assemblage dynamics in stream ecosystems with stable environmental conditions, such as spring-fed rivers. Volcanic spring-fed rivers (hereafter spring-fed rivers) occur in geologically active landscapes of the western USA and around the globe. We sampled invertebrate assemblages and quantified primary productivity and habitat characteristics of spring-fed and runoff rivers in northern California over 4 seasons. We predicted that abiotic factors would be more stable and nutrient availability greater and that invertebrate density would be greater and diversity lower in spring-fed than in runoff rivers. Runoff rivers exhibited high variability in discharge and temperature, whereas spring-fed rivers were relatively stable with high naturally occurring nutrient levels. On average, NO3− and PO43− concentrations were 40× greater in spring-fed than in runoff rivers. Spring-fed rivers supported nearly 7 to 16× greater densities of invertebrates than runoff systems, depending on season. However, invertebrate species richness was greater in runoff rivers in all seasons. Spring-fed river invertebrate assemblages were strongly correlated with elevated nutrient concentrations and basal C sources, whereas runoff assemblages were associated with discharge variability and median substrate size. We suggest that strong differences in abiotic variability between spring-fed and runoff rivers play an important role in determining invertebrate assemblage structure. Because spring-fed rivers exhibit more stable temperatures throughout the year and lower temperatures during the summer than runoff rivers, they may provide essential refugia for coldwater taxa in a warming climate.