Urban development modifies lake food webs in the Pacific Northwest

Thesis (Master's)--University of Washington, 2015Residential shoreline and watershed development by humans are leading drivers of biodiversity loss in lake ecosystems that reduce abundances and diversity littoral invertebrates. Invertebrate biological and life history traits provide good indicators of environmental quality and ecosystem functioning, yet surprisingly few studies have utilized trait-based approaches to assess impacts of human development to lake littoral communities. My thesis addresses how human development modifies lake food webs by restructuring littoral macroinvertebrate communities and altering the flow of energy to lake consumers. In Ch. III, I used a traits-based approach to assess the impacts of development to littoral macroinvertebrate community structure, and I discuss environmental mechanisms and implications to ecosystem functioning. Multiple linear regressions revealed that functional diversity declined with increasing watershed development, concentrations of total phosphorus, and littoral macrophyte cover. Results from multivariate constrained ordination and fourth corner analysis indicated that high phosphorus concentrations and macrophyte cover filtered taxa with semivoltine life cycles and filter feeders from lake communities, and that both regional and local characteristics of watershed development were important determinants of invertebrate community structure. Urban development had particularly pronounced effects on invertebrate communities in deep littoral zones, for which overall community abundances declined as a result of removals of woody debris and increased phosphorus concentrations. My study indicates that lake shoreline development and nutrient loading favor assemblages of short-lived organisms and herbivores and act as environmental filters of other functional feeding groups. These changes to invertebrate community structure may have important implications for energy flow between terrestrial, littoral, and pelagic food webs. In Ch. II, I examined whether a non-native species provides a prey resource to consumers in lakes across gradients of urban development and native prey availability. I used stable isotopes of carbon, nitrogen, and hydrogen to assess resource use by consumers in undeveloped and developed lakes and determine whether non-native Chinese Mystery snail maintains the integration of benthic resources in food webs of developed lakes by providing an abundant prey resource. I found that consumers in undeveloped lakes were supported primarily by benthic resources, and lakeshore development dramatically reduced consumer reliance on these resources. This was at least partly due to a reduction in the availability of native snails, a high quality prey item, to the dominant littoral consumer, molluscivorous pumpkinseed sunfish (Lepomis gibbosus). In developed lakes with non-native Bellamya, generalist yellow perch (Perca flavescens) and piscivorous largemouth bass (Micropterus salmoides) consumed benthic resources in proportions similar to undeveloped lakes, and pumpkinseed sunfish consumed Bellamya in higher proportions than in undeveloped lakes

Amazing Graze: Shifts in Jellyfish and Clam Distributions During Dry Years in the San Francisco Estuary

Aquatic invasive species have drastically changed how the San Francisco Estuary functions. During the past 2 decades, the effects of invasive species in the estuary may have increased in response to frequent and severe drought conditions. The invasive overbite clam (Potamocorbula amurensis), and the Asian clam (Corbicula fluminea) have well documented consequences on the estuarine food web, but their responses to drought are not well understood. Another invasive species, the jellyfish Maeotias marginata, can further affect the food web, but these effects have not been studied. We investigated the population responses of these invasive species to dry years and their potential effects on the pelagic food web using data from the Interagency Ecological Program’s monitoring surveys. We found M. marginata rapidly moves upstream with changing salinities during dry years, though it sees its highest abundance during high-outflow years in Suisun Bay and Suisun Marsh. Grazing rates of M. marginata in the estuary have not been quantified but are potentially high during localized blooms. The two invasive clams overlap in distribution, but have opposite population responses to drought conditions, with increases in P. amurensis densities and decreases in C. fluminea densities in dry years. With increasing P. amurensis densities, the clams’ combined annual filtration rates increase during drier years in the confluence and Suisun Marsh. Like M. marginata, P. amurensis also shifts upstream during droughts, but because adults cannot move immediately with a change in salinity, the population center of distribution shifts upstream the year after a dry year as a result of juvenile recruitment. If multiple dry years occur in a row, and both P. amurensis and M. marginata move upstream together, their effects on the food web could be compounded, and phytoplankton and zooplankton biomass could steeply decline in the confluence, affecting higher trophic levels in the estuary

Supporting Datasets for Life History Responses to Temperature and Seasonality Mediate Ectotherm Consumer-Resource Dynamics Under Climate Warming

  We surveyed populations of the damselfly E. annexum, and their prey zooplankton, to characterize seasonal changes in population abundances and biomass. We sampled three ponds of Lux Arbor Reserve, southwestern Michigan, USA, twice per month from May 2016 to November 2016, and again from April to May 2017. We recorded surface water temperatures at hourly intervals using HOBO pendant temperature loggers (UA-001-64, Onset Corporation, Bourne, MA, USA). We collected E. annexum at three locations within each pond by sweeping a D-frame aquatic dip net (500 mm mesh, Wildco Wildlife Supply Co., Yulee, FL, USA) through macrophyte beds along a 1-m transect parallel to shore at depths of 0.25-0.75 m. We sampled zooplankton using vertical zooplankton net tows (153 mm mesh, 20.32 cm diameter opening, Wildco Wildlife Supply Co.) at water depths of 0.25 to 1.0 m and froze samples for estimation of biomass. We monitored adult emergence of E. annexum from May to June 2017 using floating insect emergence traps. We collected and counted all damselflies every other day and identified males to species.  We identified E. annexum under a dissecting microscope (Stemi 508, Zeiss, USA) using published and online taxonomic guides. We tracked growth in body size of E. annexum by measuring the head capsule width of the first 20 individuals in each sample with an ocular micrometer (± 0.1 mm) and drying and weighing (± 0.01 mg) at least ten individuals of each probable instar. We estimated zooplankton biomass by sorting individuals of the Orders Diptera, Cladocera, Copepoda, and Rotifera from each sample under a dissecting microscope, drying them for 24 hours at 60°C, and weighing them (± 0.01 mg). We then calculated zooplankton biomass per liter sampled as: (dry weight)/(volume filtered by the plankton net). We estimated the volume filtered as: pi * net radius2 * sample depth * filtering efficiency, assuming filtering efficiency of 0.5. The datasets presented here represent unprocessed data with measurements from three ponds, including hourly temperature, damselfy counts and head capsule widths, and zooplankton weights from biweekly pond sampling. These data also include counts of emerging adult damselflies. The included R script ("Insect_abundances_1_30_23.R") processes these data files to characterize seasonal changes in damselfly body sizes, abundances, zooplankton biomass, abundances of emerging adult damselflies, and pond temperature seasonality. The R script produces Figure S1, and the estimates of K, Smin, Smax, Tav, Tamp, and the phase shift of the temperature function for Table S1, of the manuscript supplementary materials.  </p

Appendix A. Table of size-specific fecundities for NZMS.

Table of size-specific fecundities for NZMS

Size-dependent foraging niches of European Perch Perca fluviatilis (Linnaeus, 1758) and North American Yellow Perch Perca flavescens (Mitchill, 1814)

Body size of consumer species is a fundamental trait that influences the trophic ecology of individuals and their contribution to the functioning of freshwater ecosystems. However, the relationship between body size and trophic ecology can be highly variable both within and between closely-related and similarly-sized species. In this study we compared the intra- and interspecific relationship between body size and trophic position for North American Yellow Perch Perca flavescens and European Perch Perca fluviatilis, which share similarities in morphology, life history traits and trophic requirements. We used stable isotope ratios (δ15N and δ13C) to characterize differences in size-dependency of trophic position and to trace consumer foraging history of Yellow Perch in lakes in the Northwestern United States and European Perch in lakes in Germany. The trophic position and stable isotope ratios of Yellow Perch and European Perch steadily increased with total body length, but European Perch were consistently feeding at higher trophic positions than Yellow Perch at a given length. European Perch occupied considerably higher trophic positions (mean trophic position = 3.9) than Yellow Perch (mean trophic position = 2.8). Large European Perch were increasingly piscivorous, whereas large Yellow Perch were more opportunistic and omnivorous predators of invertebrate prey. Overall, the trophic position among individual Yellow Perch varied more strongly than in European Perch. We conclude that both species similarly increase in trophic position with size, but the specific size-dependency of both trophic position and resource use varies with taxonomy and local ecological conditions. Thus, body size as a sole measure of trophic position should be considered cautiously when generalizing across populations and species

Appendix B. Table of observed size distribution of NZMS.

Table of observed size distribution of NZMS

Trophic tangles through time? Opposing direct and indirect effects of an invasive omnivore on stream ecosystem processes.

Omnivores can impact ecosystems via opposing direct or indirect effects. For example, omnivores that feed on herbivores and plants could either increase plant biomass due to the removal of herbivores or decrease plant biomass due to direct consumption. Thus, empirical quantification of the relative importance of direct and indirect impacts of omnivores is needed, especially the impacts of invasive omnivores. Here we investigated how an invasive omnivore (signal crayfish, Pacifastacus leniusculus) impacts stream ecosystems. First, we performed a large-scale experiment to examine the short-term (three month) direct and indirect impacts of crayfish on a stream food web. Second, we performed a comparative study of un-invaded areas and areas invaded 90 years ago to examine whether patterns from the experiment scaled up to longer time frames. In the experiment, crayfish increased leaf litter breakdown rate, decreased the abundance and biomass of other benthic invertebrates, and increased algal production. Thus, crayfish controlled detritus via direct consumption and likely drove a trophic cascade through predation on grazers. Consistent with the experiment, the comparative study also found that benthic invertebrate biomass decreased with crayfish. However, contrary to the experiment, crayfish presence was not significantly associated with higher leaf litter breakdown in the comparative study. We posit that during invasion, generalist crayfish replace the more specialized native detritivores (caddisflies), thereby leading to little long-term change in net detrital breakdown. A feeding experiment revealed that these native detritivores and the crayfish were both effective consumers of detritus. Thus, the impacts of omnivores represent a temporally-shifting interplay between direct and indirect effects that can control basal resources

Invertebrate communities and the comparative study of crayfish.

<p>Each point represents the average for a study pool. (a) Invertebrate biomass (average biomass for coarse mesh leaf litter bags) as a function of crayfish density. Shown is the best fit exponential decay relationship (invertebrate biomass = 42.7 * exp (crayfish * −3.2)). (b). Average individual invertebrate mass as a function of crayfish density. White symbols with the solid line are caddisflies (Tricoptera), corresponding to the left y-axis and gray symbols with the dashed line correspond to stoneflies (Plecoptera), corresponding to the right y-axis. If pools did not contain any individuals, these points are not shown.</p

Results from the experimental manipulation of crayfish densities.

<p>Each point represents a study pool. Total non-crayfish benthic invertebrate abundance corresponds to open white symbols and gray confidence interval while total non-crayfish biomass corresponds to the gray symbols and darker gray confidence intervals. Benthic invertebrates were negatively associated with crayfish for both non-crayfish benthic invertebrate numerical density (log (invertebrates m⁻²) = −0.087 * crayfish +3.38, <i>R²</i> = 0.59, <i>P</i><0.001) and biomass density (log (invertebrates m⁻²) = −0.046 * crayfish +2.82; <i>R²</i> = 0.33, <i>P</i> = 0.02). The solid lines denote these best fit linear model and the polygons indicate 95% confidence intervals. Note data are log-transformed.</p