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Article
Peer Reviewed

Selective predation on cladocerans by common pond insects

Cooper, Scott D

UC Santa Barbara Previously Published Works (1983)

A variety of common pond insects was presented with a mixture of different size classes of Daphnia magna or different sizes of Daphia pulex, Moina affinis, and Ceriodaphnia sp. in predation trials. Juvenile Belostoma flumineum and most instars of Notonecta undulata and Anax Junius fed at the highest rates on the largest available cladoceran prey, and late-instar Buenoa corfusa fed at the highest rates on prey between 0.8 and 2.0 mm in length. Predation rates of instar IV Chaoborus americanus larvae were highest on Daphnia < 1 mm in length, and lowest on Daphnia > 2 mm in length. First-instar Chaoborus larvae did not eat cladocerans in these trials. The size-selective feeding patterns exhibited by Notonecta adults and late-instar Anax were similar in the light and dark, although overall feeding rates were depressed in the dark. Buenoa, on the other hand, only exhibited size-selective feeding in the light. The results indicate, however, that all of these insect predators can feed in the dark. Predation rates for late-instar Chaoborus larvae were unaffected by light conditions or the presence of filamentous algae. Chaoborus larvae were readily eaten by late-instar Notonecta and Anax.

Cover page: Selective predation on cladocerans by common pond insects

Creative Commons 'BY' version 4.0 license

Article
Peer Reviewed

Complex impacts of an invasive omnivore and native consumers on stream communities in California and Hawaii

UC Santa Barbara Previously Published Works (2013)

The effects of invasive species on native communities often depend on the characteristics of the recipient community and on the food habits of the invasive species, becoming complicated when the invader is omnivorous. In field enclosure experiments, we assessed the direct and interactive effects of an invasive omnivorous crayfish (Procambarus clarkii) and either native herbivorous snails (Physella gyrina) or shrimp (Atyoida bisulcata) on stream communities in California and Hawaii, respectively. Based on literature data and the characteristics of each study site, we predicted that crayfish would affect primarily algal-based trophic linkages in an open California stream but detritus-based trophic linkages in a shaded Hawaiian stream, with trophic cascades mediated through crayfish effects on primary consumers being observed in both systems. As predicted, crayfish in California directly reduced periphyton, filamentous algae, sediment, and snail levels, but generated a cascade by decreasing snail densities and increasing periphyton biomass. Contrary to prediction, crayfish did not reduce total invertebrate biomass. As predicted, crayfish in Hawaii reduced leaf litter, filamentous algae, and benthic invertebrate biomass. Contrary to our predictions, however, a trophic cascade was not observed because shrimp did not affect periphyton levels, crayfish did not reduce shrimp abundance, and crayfish had greater negative impacts on filamentous algae than did shrimp. Our findings highlight that the same invasive species can generate different effects on disparate systems, probably as mediated through the availability of different food types, flexibility in the invasive species' food habits, and complex pathways of trophic interaction.

Cover page: Complex impacts of an invasive omnivore and native consumers on stream communities in California and Hawaii

Article
Peer Reviewed

Contrasting effects of an invasive crayfish (Procambarus clarkii) on two temperate stream communities

UC Santa Barbara Previously Published Works (2012)

The effects of omnivorous exotic species on native communities are often difficult to predict because of the broad diets and behavioural flexibility of the omnivore, and the diverse abiotic and biotic characteristics of invaded systems. We investigated experimentally the effects of a gradient of density of the introduced, omnivorous red swamp crayfish Procambarus clarkii (Decapoda: Cambaridae) on two stream communities in southern California, U.S.A. The Ventura River is a clear, flowing stream with a cobble substratum, with abundant algae but low densities of large invertebrates, small herbivores and snails. The Santa Ynez River at the time of the study consisted of a series of drying pools underlain by sand, with abundant charophytes, large predatory invertebrates and herbivores, including snails. In the Ventura River, periphyton biomass and inorganic sediment decreased with increasing crayfish abundance, but in the Santa Ynez River, periphyton and sediment were unrelated to crayfish densities. In the Ventura River, the biomass and density of all benthic invertebrates combined, chironomids, micropredators, the meiofauna (chydorid cladocerans, copepods and ostracods), and specific predatory and herbivorous taxa, as well as taxon richness, were negatively related to crayfish density. In the Santa Ynez River, the biomass and average body size of benthic invertebrates, predatory invertebrates, herbivores and chironomids, but not total invertebrate density or taxon richness, were negatively related to crayfish density. Fewer large predatory invertebrates and snails (Physella gyrina) in both streams, and baetid mayflies in the Ventura River, were visible at night in channels where crayfish were abundant. Snails responded to crayfish by moving above the water line in the Santa Ynez River, but not in the Ventura River. We suggest that the same omnivore had different effects on these neighbouring streams because of crayfish predation on large invertebrates in the Santa Ynez River and the scarcity of such prey in the Ventura River, leading to increased crayfish grazing on periphyton, and reductions in periphyton-associated invertebrates, in the Ventura River. © 2011 Blackwell Publishing Ltd.

Cover page: Contrasting effects of an invasive crayfish (Procambarus clarkii) on two temperate stream communities

Article
Peer Reviewed

Scale effects and extrapolation in ecological experiments

UC Santa Barbara Previously Published Works (2003)

Article
Peer Reviewed

Before and after the deluge: rain-on-snow flooding effects on aquatic invertebrate communities of small streams in the Sierra Nevada, California

UC Santa Barbara Previously Published Works (2010)

Cover page: Before and after the deluge: rain-on-snow flooding effects on aquatic invertebrate communities of small streams in the Sierra Nevada, California

Article
Peer Reviewed

The Interpretation of "Controlled" vs "Natural" Experiments in Streams

UC Santa Barbara Previously Published Works (1988)

Article
Peer Reviewed

Opossum Shrimp (Mysis relicta) Predation on Zooplankton

UC Santa Barbara Previously Published Works (1980)

Mysis relicta clearance rates were not affected by changes in prey and predator density in single-prey systems where Epischura nevadensis late instars were used as food. A comparison of the results obtained from single-, two-prey, and multiple-prey systems revealed that Mysis clearance rates of E. nevadensis late instars and Diaptomus tyrrelli males were significantly affected by the presence and abundance of alternative prey.When offered natural prey assemblages, the smallest Mysis preyed preferentially on the smallest available prey (Bosmina, Ceriodaphnia, Diaptomus nauplii) while larger Mysis showed an increased preference for larger prey (Epischura, Daphnia). In general, Mysis preferred Daphnia over copepods; Epischura, Ceriodaphnia, Bosmina, and cyclopoid copepods over Diaptomus copepodites and adults; and Diaptomus males over Diaptomus females. Total consumption rates increased with increasing predator size and starvation duration. Food selectivity patterns exhibited by Mysis were attributed to the mechanical efficiency with which the predators captured and handled food particles of different sizes, to the vigor of prey escape responses, and to predator–prey encounter frequencies.Key words: Mysis relicta, predation, zooplankton, feeding preferences, opossum shrimp

Cover page: Opossum Shrimp (Mysis relicta) Predation on Zooplankton

Article
Peer Reviewed

Competition, predation and the relative abundances of two species of Daphnia

UC Santa Barbara Previously Published Works (1982)

Article

The influence of introduced trout on native aquatic invertebrate communities in a paired watershed study of High Sierran streams

Technical Completion Reports (2003)

Resource management agencies are often confronted with conflicts between natural resource protection and public recreation in wildland areas. An example of such a conflict is the stocking of non-native trout for recreational fisheries versus the protection of unaltered freshwater habitat for native wildlife. Declines and losses of over half the species of native amphibians and fish found in the Sierra Nevada have been attributed to the introduction of exotic species, especially trout. Although the effects of non-native trout on native biodiversity have been documented for many Sierran lakes, there is practically no information on their impact on Sierran stream ecosystems and communities, which evolved in the absence of fish. These mountain streams harbor high proportions of endemic species in insect groups such as stoneflies and caddisflies, and these insects potentially are vulnerable to direct and indirect effects of fish predation. Inadequate data on the distribution and diversity of stream invertebrates is a major obstacle to evaluating and monitoring the health of native aquatic species and habitats in the High Sierra.

The objective of this research has been to compare the composition of invertebrate communities in streams lacking introduced trout with paired nearby streams containing trout. The studies involved surveys of aquatic invertebrate diversity in riffle and pool habitats of first and second order streams in Yosemite National Park, at elevations from 1350 to over 3000 meters. Invertebrate samples were collected along with an inventory of their food resources, water chemistry and physical habitat. Analyses of the data emphasizes contrasts of the impacts of trout on the organization and diversity of stream communities.

Fish stocking and its impacts on high elevation aquatic ecosystems is a controversial topic currently under review in California by a variety of public and private organizations. The research results presented here provide essential scientific input to policy development through (1) the evaluation of the impact of non-native trout on the biodiversity and ecological integrity of Sierran streams, (2) the development of criteria for identifying aquatic diversity management areas for conserving native species, and (3) the establishment of baseline biological indicators for the monitoring of programs designed to restore stream biodiversity.

The introduction of non-native trout into the Sierra Nevada mountains of California, USA, has caused important changes in the densities of many invertebrate and vertebrate species inhabiting lakes of this region. Researchers, however, know little about the effects of trout introductions on invertebrates in streams of the Sierra Nevada. In this report, we present the results from surveys of 21 fishless streams and 21 paired streams containing introduced trout in Yosemite National Park.

Results show that environmental conditions did not differ between the fishless and trout streams, but that algal biomass and macroalgal cover were significantly higher in the streams containing trout. The majority of taxa were unaffected by trout presence in Yosemite streams but enough were affected that we conclude trout have caused changes in benthic stream community structure and function in many but not all streams to which trout have been introduced. Moderate effects of trout on the structure of the invertebrate community were evident in significant and/or consistent changes in the density of 26 different taxa (20 decreasing and 6 increasing in the presence of fish). Among common taxa, trends were statistically significant for 10 taxa and qualitatively consistent for 8 taxa (statistical power insufficient). This represents 18 of 43 common taxa groups (over 40%). Another 8 uncommon taxa also showed distinct patterns of association with fishless or trout streams but were not abundant enough for statistical tests. The strongest effects of trout appeared to be on endemic taxa (such as the caddisfly Neothremma spp., the mayfly Edmundsius agilis, Triclad flatworms, and others), which may be vulnerable because of the absence of evolved selection for mechanisms of coexistence with fish predators.

The effects of trout on the function of benthic communities were also evident in increased (1) algal density and cover, (2) abundance of midges (which play dominant roles in the consumption of organic matter and algae and as prey to invertebrate predators), and (3) reduced density of the most common large predator (Doroneuria baumanni, likely the dominant aquatic predator prior to trout introductions). These changes suggest that trout alter the resource production and transformation in high Sierra streams.

Because the strongest effects from trout fell primarily on endemic species, we recommend that managers first focus on endemic invertebrates by conducting taxonomic verifications, detailed surveys of species-specific distributions and, when necessary, eradicating trout to increase and recover populations of threatened invertebrates. In addition, experimental removals of trout from stream segments should be combined with benthic invertebrate community monitoring before and after treatments to evaluate the potential for recovery.

1 supplemental file

Cover page: The influence of introduced trout on native aquatic invertebrate communities in a paired watershed study of High Sierran streams

Article
Peer Reviewed

Effects of wildfire on stream algal abundance, community structure, and nutrient limitation

UC Santa Barbara Previously Published Works (2015)

We studied the effects of wildfires in southern California on stream algal communities and their responses to nutrient enrichment. The intensity of scouring floods, concentrations of nutrients during ensuing rains (4-13× increases depending on nutrient), and postflood sediment deposition were greater at sites in burned than in unburned basins (UN sites). Postfire storms reduced algal biomass >10× more at sites in burned than in unburned basins. After the fire and subsequent floods, algal biomass, particularly of Cladophora, was up to 5 (chlorophyll a) to 20 (macroalgal mass) times higher at sites in burned basins with burned riparian vegetation (BRB sites) than at sites in unburned basins (UN sites), but algal abundance at sites in burned basins with intact riparian vegetation (BRI sites) was as low as 10 to 30% of that recorded at UN sites. Two to 3 mo after the wet season, nutrient and algal levels were similar among sites in UN, BRI, and BRB basins. We used summer nutrient diffusing substrata (NDS) experiments where N, P, N+P, or neither were added and found that algal density, chl a, and chl a/algal unit increased by ∼1.5 to 4.5× with N additions at sites in BRB and UN basins but did not change at sites in BRI basins. In contrast, algal biovolume increased 2 to 9× with N additions at all sites and with P addition at sites in BRI basins. General depressions in chl a by 40 to 50% with P addition were related to decreased chl a/algal unit. Diatoms increased with N and N+P additions at sites in UN and BRI basins and with P addition at sites in BRI basins but declined with P or N+P additions at sites in BRB basins, with cyanobacteria and green algae generally showing the opposite pattern. Algal responses to nutrient augmentation across sites were related to fire effects on riparian canopy cover, temperature, and ambient nutrient concentrations. Fire effects on algal communities and nutrient limitation appeared to be mediated through fire effects on flood disturbance and light regimes.

Cover page: Effects of wildfire on stream algal abundance, community structure, and nutrient limitation