Joseph R. Holomuzki

Taxon-specific responses to high-flow disturbance in streams:implications for population persistence

This study examined how the leptophlebiid mayfly Deleatidium spp., the mudsnail Potamopyrgus antipodarum, and stony-cased caddisflies Pycnocentrodes aeris and Hudsonema amabilis, each with different flow habitat preferences and motilities, respond to elevated flows. Our aim was to learn more about how refuge-seeking behavior and life-history traits affect species persistence along the flow disturbance gradient. All taxa responded to incrementally increased flows in a recirculating laboratory flume with layered substrata by moving to deeper, more stable layers. However, snails made the most pronounced shift to protected sublayers. Caddisflies that remained on epibenthic surfaces during high flows laid draglines on surface rocks to effectively resist dislodgment. Very few individuals of any taxon were washed from epibenthic habitats by high flows alone. Simulated flash floods in artificial stream channels revealed that dislodgment was linked to substrate stability and that likelihood to be dislodged varied among taxa. Dislodgment was relatively low for mayflies and snails (∼8%) compared to caddisflies (20.7%) in stabilized patches of gravel. However, in unstable patches, dislodgment rates of both mayflies and caddisflies (both ∼30%) were significantly higher than those of snails. The relatively high dislodgment rate of caddisflies in both stable and unstable substrate patches was related to their propensity to occupy epibenthic surfaces. Mortality rates of mayflies (∼25%) were about 3× higher than those of the other 2 taxa in both patch types. Our results suggest that high dispersal capabilities seem particularly important for Deleatidium to persist in flood-prone streams, whereas short-term behavioral modifications play a key role in allowing the snails and caddisflies to persist in flow-variable habitats.

Habitat use and fish avoidance behaviors by the stream-dwelling isopod Lirceus fontinalis

We examined patterns of habitat use of an isopod, Lirceus fontinalis, that coexists with predatory fish in second and third order permanent streams in central Kentucky, USA. Isopods were significantly more dense in Cladophora, a filamentous green alga, than on bare substrates of silt, sand, and gravel, and in submerged leaf litter when predatory fish were present. The dense, entangled filaments of the algae precluded most fish from entering Cladophora mats and eating isopods. Nonetheless, fish predation significantly reduced total isopod densities in these habitats. In laboratory manipulations, emergences from and entrances into Cladophora along with overall movements by isopods in open sandy areas were significantly reduced when green sunfish (Lepomis cyanellus) were present. Lirceus responded similarly to only water conditioned with green sunfish, indicating isopods use chemical cues, in part, to detect predatory fish. Isopods predominantly ate decaying leaf tissue (i.e., coarse particulate organic matter [CPOM] > 0.5 mm in diameter), but amounts of CPOM were significantly lower in Cladophora than in sediments of bare substrates. Lirceus did not eat the algae. Over 80% of the organic particulates in algal mats were < 0.5 mm (fine POM). Isopods reared on FPOM grew significantly slower than those on CPOM. Long-term use of algal mats poor in forage by isopods may adversely affect relative fitness since egg production by females is dependent on body size.

Distributional responses to flow disturbance by a stream-dwelling snail

This study examines how flow disturbance influences distributions of the snail Potamopyrgus antipodarum, a common grazer in New Zealand streams, at the drainage basin, substratum, and rock face scales. We analyzed survey data from 48 streams across New Zealand to relate snail densities to hydrological patterns and conducted experiments in a laboratory flow tank and in artificial streams in field conditions to evaluate refugium effects of different substrate types in high flows. The survey showed that local densities were significantly inversely related to flood frequency, suggesting flow disturbance influenced regional distributions of P. antipodarum. The survey also revealed that lake-fed streams and low-gradient streams in foothill regions tended to have fewer, less severe floods and higher snail densities than high-gradient (>1%) streams in mountain and foothill regions. Results from both the flow tank and artificial stream experiments showed that finer-grained substrates provided better refugium from dislodgment conditions than larger substrates (i.e., cobbles) when bed sediments were artificially stabilized. In the flow tank where velocities were incrementally increased, dislodgment rates of snails were significantly lower on artificial gravels than on artificial cobbles or bedrock. Snails moved to low-velocity patches (i.e., crevices) on all substrates as current velocities increased. However, more snails accumulated in crevices between gravels and pebbles than between cobbles; the relatively high turbulence between cobbles, in part, contributed to high dislodgment rates from this substrate. Similar differences in dislodgment vulnerability and flow refugium effects were observed in experiments using real substrates in artificial streams in field conditions. A substrate size-flood duration experiment showed that significantly more snails were dislodged from cobbles and pebbles than from gravels and that more were dislodged in longer-lasting high discharge events (30 min) than in brief ones (1 min). Another experiment in which snails were transported downstream (1, 3, 6 or 9 m) from non-stabilized substrate patches similarly showed that snail dislodgment and mortality rates were generally higher from cobbles than from gravels and pebbles. Like other studies, we found that larger substrate particles were less likely to move than smaller ones (gravels) under similar hydraulic conditions. However, we discovered that the best refugium conditions for resisting dislodgment are not necessarily linked to larger substrate size. Our findings also suggest that flooding may alter local densities of snails by moving and relocating snails rather than by killing them. The observed patterns of distributions of these snails appear to result from complex interactions between hydrological. hydraulic features and substrate architecture.

Trophic control of fishless ponds by tiger salamander larvae

We examined the extent to which predation by larval tiger salamanders (Ambystoma tigrinum nebulosum) affected lower trophic levels in fishless ponds in montane eastcentral Arizona. An enclosure experiment manipulating salamander densities showed that effects associated with larval presence can cascade downward through three trophic levels in environments of low complexity. Enclosures with larvae contained comparatively lower herbivorous zooplankton biomasses and densities, higher chlorophyll a concentrations, and lower orthophosphate levels than those without larvae. Relative frequency of zooplankton species also varied significantly among enclosure treatments. Cyclopoid copepod frequencies were higher in treatments with salamanders than without, while ostracods were found only in treatments without salamanders. Salamander presence negatively affected cladoceran abundance and influenced cladoceran species composition. Proportions of both Ceriodaphnia quadrangula and Simocephalus vetulus were significantly greater in treatments without salamanders than in treatments with salamanders. Although Daphnia pulex frequencies were similar in enclosures with cladocerans across treatments, individuals were on average larger and biomasses were greater in enclosures without salamanders than they were in enclosures with salamanders. Trophic interactions analyzed from our survey of 14 ponds, however, were most often uncorrelated, and the few top-down effects exerted by salamanders were limited to contiguous trophic links below them. Densities of only one zooplankter, ostracods, and two taxa of macroinvertebrates, Baetis spp. mayflies and odonate larvae, were negatively related to salamander density. In contrast, benthic chironomid densities correlated positively with salamander density. However, in the two salamander-free ponds surveyed, we observed a distinct pattern of alternating responses of trophic levels that paralleled those in enclosure treatments without salamanders. Although modulating factors operate in ponds to complicate salamander impacts, salamanders have discernible direct and indirect effects on pond trophic webs.

OVIPOSITION SITES AND FISH-DETERRENT MECHANISMS OF TWO STREAM ANURANS

VIELKIND,J. R. 1992. Progression from pigment cell patterns to melanomas in platyfish-swordtail hybrids-multiple genetic changes and a theme for tumorigenesis, p. 285-301. In: Transformation of human epithelial cells, G. Milo, B. Casto and C. Shuler (eds.). CRC Press, Ann Arbor, MI. , K. D. KALLMAN, AND D. C. MORIZOT. 1989. Genetics of melanomas in Xiphophorus fishes. Journal of Aquatic Animal Health 1:69-77. WHITE, G. 1971. The Texas golden green: a color mutation of the green sunfish. Prog. Fish Cult. 33: 155. DEPARTMENT OF BIOLOGY, DUKE UNIVERSITY, DURHAM, NORTH CAROLINA 27706. PRESENT ADDRESS: DEPARTMENT OF BIOLOGY, SAN DIEGO STATE UNIVERSITY, SAN DIEGO, CALIFORNIA 92182-0057. Submitted: 25 April 1994. Accepted: 4 Jan. 1995. Section editor: R. Winterbottom.

Trophic Dynamics of a Top Predator, Ambystoma tigrinum nebulosum (Caudata: Ambystomatidae), in a Lentic Community

. 1973. Six new species of Eleutherodactylus (Anura, Leptodactylidae) from Hispaniola. J. Herpetol. 7(3):249-273. 1980. The herpetogeography of Hispaniola, West Indies. Stud. Fauna Curacao Carib. Ids. 189: 86-127. WILLIAMS, E. E. 1961. Notes on Hispaniolan herpetology. 3. The evolution and relationships of the Anolis semilineatus group. Breviora 136:1-8. 1969. The Antillean Eleutherodactylus of the riculatus group. Stud. Fauna Curacao Carib. Ids. (SBH) DEPARTMENT OF ZOOLOGY, UNIVERSITY OF MARYLAND, COLLEGE PARK, MARYLAND 20742; (RT) DEPARTMENT OF BIOLOGY, UNIVERSITY OF PUERTO RICO, RIO PIEDRAS, PUERTO RICO 00931; AND (RF) DEPARTMENT OF NATURAL SCIENCES, THE FLORIDA STATE MUSEUM, UNIVERSITY OF FLORIDA, GAINESVILLE, FLORIDA 32611. Accepted 20 March 1987. ) DEPARTMENT OF ZOOLOGY, UNIVERSITY ARYLAND, COLLEG PARK, MARYLAND 42; (RT) DEPARTMENT OF BIOLOGY,

Spatial variability and assemblage structure of stream hydropsychid caddisflies

We sampled 8 sites (riffles) in a parent stream and its major upstream tributary in northern Michigan to quantify environmental heterogeneity or gradients to identify spatial determinants of 5 species of larval hydropsychid caddisflies. Abundance patterns of species varied at both small (microhabitats) and intermediate (sites) spatial scales, as did key determinants of abundance. Substrate size and type were important in affecting species microdistributions. A selectivity index (L) showed that Hydropsyche betteni and Ceratopsyche sparna, the 2 most abundant species, were disproportionately more abundant on boulders and logs, respectively, than occurrence of these substrates at sites. Cheumatopsyche spp. also exhibited a propensity to use logs but avoided boulders. Microdistributions of Ceratopsyche morosa and C. slossonae were more variable than these other species. Nonetheless, all 5 species occupied gravels in disproportionately lower frequencies than occurrence of this substrate at sites. Current velocity explained a small but significant amount of variation (4−18%) of densities on microhabitats for all species but C. morosa. The presence of the macroalga Cladophora glomerata significantly increased larval densities on substrates but had no significant effect on overall site densities. Stepwise regression analyses revealed that amount of habitable substrate, seston quantity, and temperature were key predictors of site assemblages along the upstream–downstream gradient. The finding that amount of habitable substrate was significantly related to site densities of all species, except C. morosa, emphasizes the large impact suitable habitat has on larval hydropsychid densities in these sandy streams. Site densities of C. morosa were negatively associated with seston quantity, whereas those of C. sparna were positively associated with seston amount and kind. Ceratopsyche sparna were predominant in downstream reaches, where detrital (leaf) seston loads were relatively high. Site densities of H. betteni and C. slossonae were positively correlated with algal seston and temperature. These 2 factors were affected by proximity to lake outlets and beaver dams. Our study shows that multiple factors operate synergistically over several spatial scales to influence hydropsychid species distributions.

Sediment texture mediates high-flow effects on lotic macroinvertebrates

We conducted 2 experiments to examine how sorting, shape, and size of sediment grains affected drift and mortality of the mayfly Deleatidium spp., the snail Potamopyrgus antipodarum, and the stone-cased caddisfly Pycnocentrodes aeris in ramped flows in a large, outdoor, recirculating flume. These macroinvertebrates are common to many New Zealand streams and have different flow habitat preferences, body morphologies, and motilities. In the 1st experiment, we quantified taxon drift and mortality and sediment erosion in well-sorted gravel (i.e., high grain-size homogeneity), moderately sorted cobble, and a poorly sorted mixture of gravel and cobble. In the 2nd experiment, we examined the same response variables in angular (rough), oblate (flat, elliptical), and spherical gravel or cobble. Grain sorting significantly affected drift, and this effect was taxon-specific. Drift was highest from moderately sorted cobble, largely because of the relatively high number of dislodged snails. Overall, caddisflies had the highest propensity to drift, regardless of sorting treatment, whereas mayflies had the lowest. Caddisflies generally remained on tops of rocks in ramped flows, and their dislodgment was linked to velocity increases rather than sediment erosion. In contrast, dorsoventrally flattened Deleatidium clung to rock undersides. The result of clinging to sediment undersides to reduce dislodgment was significantly higher mortality compared to the other 2 taxa, particularly in well-sorted gravel with relatively low transport thresholds. The addition of cobble to gravel (i.e., poorly sorted sediments) decreased sediment erosion and significantly reduced mayfly mortality. Grain shape also significantly affected sediment transport thresholds and hence taxon responses. Erosion of angular gravel equaled that of spherical cobble, and no angular cobble eroded in ramped flows. Drift by dislodgment was relatively low in angular gravel and cobble, even for caddisflies. Mortality was again greater for mayflies than for snails and caddisflies, particularly in spherical and oblate gravel that tended to erode. Our results suggest that the interplay between sediment textural properties that affect transport thresholds, and species behaviors and morphologies, influence the overall effectiveness of sedimentary flow-refugia.

Snail-tadpole Interactions in Streamside Pools

We studied competitive interactions and grazing effects of the snail Physella integra and the American toad Bufo americanus in ephemeral streamside pools in W-central Kentucky. Snails and tadpoles reared alone and combined at ambient densities in artificial pools revealed that costs of coexisting differed between taxa. Snails invested resources into growth and survival at the expense of reproduction when with anuran competitors, whereas tadpoles exhibited slowed development and decreased biomass per pool in combined-species treatments. These negative effects were likely a result of food limitation, considering that herbivory by both taxa significantly reduced algal abundance relative to ungrazed controls. Herbivory by both species also affected the assemblage of benthic algae. Diatoms, particularly Nitzschia spp. were the predominant algae in both single-species treatments, whereas the green algae Eudorina and Oedogonium comprised most of the community biovolume in com- bined-species treatments. The filamentous green algae Cladophora was dominant in ungrazed controls. A survey of 16 isolated pools along three third-order streams revealed patterns of snail egg production and benthic algal assemblage similar to treatment effects in the artificial pool experiment. The survey also indicated that snails and tadpoles seldom co-occur in these pools; thus competition between them may be infrequent. Linkages between phosphate avail- ability, predation and habitat persistence seem particularly important in mediating compet- itive interactions between these taxa.

Homing Behavior of Desmognathus ochrophaeus along a Stream

Homing behavior has been demonstrated in several species of the Plethodontidae (Barthalmus and Bellis, 1969, 1972; Madison, 1969; Madison and Shoop, 1970; Huheey and Brandon, 1973; Kleeberger and Werner, in press). Brandon and Huheey (1973) reported many Desmognathus ochrophaeus from a rockface population exhibit homing behavior when displaced 1.3 to 4.0 m. However, evidence of homing in the species from a long distance relative to mean size of the home range is lacking. The present study examined homing performance of D. ochrophaeus from 30 m displacements within a stream-margin habitat. Home range was estimated to determine whether these displacements were significantly beyond an animals typical movements. The study was conducted from May-September, 1980, along a portion of stream about 4.0 km W of Garretsville, Ohio. The stream flows northerly through a shallow ravine and is shaded by a dense beech-maple canopy. Mean width of the stream is 1.2 m and its margins, from the stream edge to the embankment, are about 1.3 m. A grid system along both stream-margins was used to determine location of points of capture. Grid schematics were a modification of Barthal-