Backcasting the decline of a vulnerable Great Plains reproductive ecotype: identifying threats and conservation priorities

Conservation efforts for threatened or endangered species are challenging because the multi‐scale factors that relate to their decline or inhibit their recovery are often unknown. To further exacerbate matters, the perceptions associated with the mechanisms of species decline are often viewed myopically rather than across the entire species range. We used over 80 years of fish presence data collected from the Great Plains and associated ecoregions of the United States, to investigate the relative influence of changing environmental factors on the historic and current truncated distributions of the Arkansas River shiner Notropis girardi. Arkansas River shiner represent a threatened reproductive ecotype considered especially well adapted to the harsh environmental extremes of the Great Plains. Historic (n = 163 records) and current (n = 47 records) species distribution models were constructed using a vector‐based approach in MaxEnt by splitting the available data at a time when Arkansas River shiner dramatically declined. Discharge and stream order were significant predictors in both models; however, the shape of the relationship between the predictors and species presence varied between time periods. Drift distance (river fragment length available for ichthyoplankton downstream drift before meeting a barrier) was a more important predictor in the current model and indicated river segments 375–780 km had the highest probability of species presence. Performance for the historic and current models was high (area under the curve; AUC > 0.95); however, forecasting and backcasting to alternative time periods suggested less predictive power. Our results identify fragments that could be considered refuges for endemic plains fish species and we highlight significant environmental factors (e.g., discharge) that could be manipulated to aid recovery.     

Riffles as barriers to interpool movement by three cyprinids (Notropis boops,Campostoma anomalum and Cyprinella venusta)

1. The effects of riffles as barriers to movement of stream fish was investigated in a set of eight large outdoor artificial streams. Pools were 183 cm in diameter and 45 cm deep; riffles were 183 cm long and 43 cm wide. Rates of movement of three species of minnows (Cyprinidae) (Campostoma anomalum, Cyprinella venusta and Notropis boops) among pools were measured at four riffle current velocities (0, 15, 30 and 45 cm s^–1), three thalweg depths (10, 50 and 100 mm), two riffle lengths (183 and 549 cm), and with and without the threat of predation. Visual observation and video cameras were used to quantify movement rate. 2. Mean movement rate (percentage of fish crossing a riffle each 30 min) was 18.1% at 0 cm s^–1 and only 1.8 at 45 cm s^–1. Movement rate was 7.2% with no predators present and 20.2% with caged predators in pools. Notropis boops had a lower rate of movement than C. venusta or C. anomalum across all trials. The mean group size (number of individuals crossing a riffle together) was 1.2 fish overall, indicating most movement was by individuals and not groups. Group size was significantly greater only with shallow riffles or under the threat of predation. 3. Overall biotic and abiotic factors in these artificial streams do influence movement rates and may affect movement among pools in natural streams.     

Absence of population subdivision in the common shiner,Notropis cornutus (Cyprinidae)

Synopsis Starch gel electrophoresis of the common shiner, Notropis cornutus, was used to determine if this species exhibits genotypic structuring. Specimens were collected from seven widespread localities representing three branches of a single river drainage. χ² tests revealed no significant heterogeneity of Est-A electromorphs within or between localities except where physical barriers prevent contact. Therefore, schooling behavior of N. cornutus is not associated with significant genotypic structuring of this species.     

Comparison of sleds versus plankton nets for sampling fish larvae and eggs

Fish larvae and fish eggs were sampled from the inshore waters of eastern Lake Michigan from 1978 through 1980, using a benthic sled and a plankton net towed within 0.5 m of the lake bottom. Differences between estimates of ichthyoplankton abundance based on the benthic sled and those based on the plankton net towed near bottom were examined along with interactions between gear, bottom depth, and time of day. Time of day was determined to be an important factor in comparing these two gear, but data were inconclusive as to the effect of depth on gear differences. Abundance of fish eggs calculated using sled tow data was significantly higher than that for the plankton net. For nighttime collections, density of alewife Alosa pseudoharengus larvae sampled in the plankton net significantly exceeded that for the sled, whereas density of spottail shiner Notropis hudsonius larvae based on sled data was significantly higher than that based on the plankton net for day sampling. Overall, the plankton net appeared to be adequate for sampling abundance of alewife larvae, while the sled was preferred for sampling fish eggs, spottail shiner larvae, and the following less common, but apparently demersal larvae: trout-perch Percopsis omiscomaycus, johnny darter Etheostoma nigrum, ninespine stickleback Pungitius pungitius, and slimy sculpin Cottus cognatus.     

Resilience of Alternative Stable States during the Recovery of Shallow Lakes from Eutrophication: Lake Veluwe as a Case Study

In this paper we analyze a long-term dataset on the recovery from eutrophication of Lake Veluwe (The Netherlands). Clear hysteresis was observed in a number of ecosystem variables: the route to recovery differed significantly from the route that led to loss of clear water. The macrophyte dominated state disappeared in the late 1960s at TP above 0.20 mg l⁻¹, whereas its return occurred at less than 0.10 mg TP l⁻¹. Several regime shifts resulting in the occurrence of three alternative stable states were observed over a period of 30 years. The turbid state showed resistance to change, despite a strong and prompt reduction in Chl-a following reduction of external P-loading. The most important component that determined hysteresis in the return to clear water was not internal P-loading, but a high level of nonalgal light attenuation (through sediment resuspension) maintained by the interaction between wind and benthivorous fish. Although Chara was able to re-colonize the most shallow parts of the lake, recovery stalled and for a number of years clear (above charophyte beds) and turbid (deeper parts of the lake) water co-existed, as a separate alternative state on route to full recovery. Lake-wide clear water was re-established after bream density had been reduced substantially. This allowed a return of zebra mussels to the lake, whose high filtration capacity helped in maintaining clear water. In this study, we were able to identify the main drivers of hysteresis and regime shifts, although formal demonstration of cause and effect was not possible on the basis of field data alone. We argue that resilience of the present clear water state of Lake Veluwe very much depends on sizable populations of a few keystone species, especially Chara (stoneworts) and Dreissena (zebra mussels), and that careful management of these species is equally important as control of nutrients. Lake management should strive to maintain and strengthen resilience of the ecosystem, and this should offer protection against a renewed collapse of the clear state.     

Comparative Morphology and Taxonomic Status of the Ghost Shiner, Notropis Buchanani, In Canada

The origins of the ghost shiner, Notropis buchanani, in Ontario, Canada is not known. It has been assumed that the species was recently introduced because of the discontinuous geographic distribution between populations in Ontario and other more southern locales. To evaluate this assumption, we completed a systematic morphological study of ghost shiner collected from Ontario, Illinois, Missouri, and Oklahoma. Morphological similarity among specimens along this northeast–southwest gradient supports the assumption that the Ontario populations are not the result of a recent introduction. Dissimilarity along this axis would support the hypothesis that the species has been isolated in Ontario. Based on the pattern of morphological differentiation among populations and locales considered in our analysis, the Ontario populations appear to represent a species native to Canada. These fish were likely overlooked during earlier biotic surveys. The degree of morphological differentiation, characterised particularly in the head morphology, suggests that the ghost shiner in Canada is at the racial level of segregation, and does not warrant further subspecific designation.     

Ecological sensitivity of marl lakes to nutrient enrichment: evidence from Hawes Water,UK

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The effects of species immigrations and changing conditions on isoetid communities

Historical data from the 1930s were compared with new data gathered during the 2000s to evaluate the effects of increased numbers of larger stature submersed species (both elodeids and characeans) on resident isoetid communities. The cover and species richness of submersed species were assessed in 23 seepage lakes in northwestern Wisconsin, USA, using randomly located 1 m × 1 m plots. Water clarity, conductivity and residential land use were determined on a whole-lake basis and the sediment type and water depth were recorded at each plot. The probability of elodeids or characeans occurring in isoetid plots increased with the number of elodeids and characeans gained by a lake since the 1930s, with additions ranging from two to 15 species per lake. However, not all species were equally likely to co-occur with isoetids. Six elodeid species (Najas flexilis, Najas gracillima, Potamogeton gramineus, Potamogeton pusillus, Potamogeton spirillus and Vallisneria americana) along with Chara spp. were the most frequent isoetid associates, while other species that were common in the lakes, such as Elodea canadensis and Potamogeton robbinsii, were less frequent in isoetid plots. The lake-wide proportion of isoetid plots colonized by elodeids or characeans ranged from 5% to 100%, with increasing conductivity and total elodeids (plus Chara spp. and Nitella spp.) the strongest predictors of this colonization. Approximately half (49.6%) of all isoetid plots sampled had elodeids or characeans present (39.2% elodeids, 7.4% elodeids and characeans, 3.0% characeans), and isoetid cover and species richness were lower when these larger stature species were present. The risks this colonization poses for the long-term viability of isoetid species appeared to depend on multiple factors, including whole-lake characteristics, opportunities for refuge, and connections among regional isoetid populations. There was evidence of a time lag between the introduction of elodeid or characean species to a lake and invasion of isoetid plots within the lake, a process that deserves further study.     

Indirect food web interactions increase growth of an algivorous stream fish

1. We tested the hypothesis that indirect food web interactions between some common, invertivorous fishes and their prey would positively affect growth of an algivorous fish species. Specifically, we predicted that orangethroat darter (Etheostoma spectabile) would increase periphyton biomass via a top‐down pathway, indirectly enhancing growth of the algivorous central stoneroller minnow (Campostoma anomalum). Moreover, we predicted that sand shiner (Notropis stramineus) would increase periphyton biomass via a bottom‐up pathway and indirectly enhance growth of the stoneroller minnow. 2. In an 83‐day experiment in large, outdoor, stream mesocosms, we stocked two fish species per mesocosm (stoneroller and either darter or shiner), estimated the effects of the invertivorous and grazing fishes on periphyton biomass and estimated growth of the algivorous fish. 3. The darter consumed grazing invertebrates, indirectly increasing periphyton biomass. The shiner consumed terrestrial insects as predicted, but it did not affect periphyton biomass. 4. In support of our hypothesis, the darter indirectly enhanced stoneroller growth. As predicted, stonerollers consumed the increased periphyton in streams with darters, resulting in greater growth, condition and gut fullness compared to streams without darters. No indirect interaction was observed between stonerollers and shiners. 5. Our study suggests that some invertivorous fish species can positively affect growth of algivorous fishes through indirect food web interactions. Thus, in stream communities, it is possible that the loss of a single, invertivorous fish taxon could have negative consequences on algivorous fish populations via the removal of positive indirect food web interactions.     

Salvelinus namaycush spawning substratum attracts egg predators and opportunists through chemosensory cues

Two separate field experiments were conducted in a series of small boreal lakes to test for the attraction of egg predators to lake trout Salvelinus namaycush spawning shoals and subsequently to determine whether chemosensory cues attract egg predators to these sites. In the first experiment, minnow traps set on spawning sites captured significantly more egg predators than those set on structurally similar non‐spawning sites. Captures of slimy sculpin Cottus cognatus, common shiner Luxilus cornutus, blacknose shiner Notropis heterolepis and virile crayfish Orconectes virilis were more than double on spawning sites relative to non‐spawning sites for the two study lakes. To test whether chemosensory cues could attract egg predators to S. namaycush spawning sites, paired minnow traps were placed on eight to 10 sites in each of the three study lakes; one trap contained visually concealed S. namaycush spawning substratum and the other with visually concealed non‐spawning substratum. Traps containing spawning substratum consistently captured more fish and had higher mean daily catches than those that contained non‐spawning substratum. The combined results demonstrate a greater prevalence of egg predators on S. namaycush spawning shoals that appears to be the result of chemosensory attraction to spawning substratum.     

The influence of large water level fluctuations and hurricanes on periphyton and associated nutrient storage in subtropical Lake Okeechobee,USA

The abundance, community structure and nutrient content of periphyton, and the host plant taxa Chara, Hydrilla, Potamogeton, Vallisneria and Scirpus were studied in Lake Okeechobee, USA. Water levels were generally high during the study period (August 2002–January 2006), but substantial fluctuations occurred. All host plant biomass was seasonally variable but only Vallisneria biomass was spatially variable. All submerged plant beds disappeared after the passage of two hurricanes in September 2004, and a third hurricane passed over the lake in October 2005. Periphyton assemblages were statistically separated most by substrate and then by season. Prior to the hurricanes, annual maxima of periphyton biovolumes and those of summer submerged plant coverage coincided. During all study years, the diatom taxa dominated periphyton total biovolumes. Periphyton biomass was generally highest during the summer or prior to the hurricanes (in the case of epiphytes) and was spatially variable in the case of both Scirpus and Vallisneria. Epiphytic nutrient contents within each host plant group seasonally varied except for nitrogen and carbon in the Vallisneria epiphytes. Epipelic nutrient contents were spatially variable and seasonally variable for carbon. Nutrient contents in epipelon were significantly higher than that in Scirpus epiphytes and were similar but lower among all epiphytic communities. The total annual areal potential epiphytic phosphorus storage extrapolated during this study (2.0 × 10⁻⁴ metric tons ha⁻¹ year⁻¹) was underestimated because storage estimates for epipelon, Chara and Hydrilla-associated epiphytes were omitted. The Chara and Hydrilla-associated epiphytic nutrient storage values were omitted because of limited data, whereas the epipelic data may have not been spatially representative. For periphyton biovolume, host substrate type, water level fluctuation and hurricane impacts on host substrates appear to be more important than seasonal variation in such factors as temperature and nutrients. Epiphytic nutrient storage appears to be influenced most by water level fluctuation and hurricane-related impacts, while the host substrate type appears to be a less important factor than it is for periphyton biovolume. Maximum periphyton biomass and high nutrient storage in shallow subtropical and tropical eutrophic lakes may only occur at consistently lower water levels and during infrequent periods of disturbance, which enhance host substrate colonizable area.     

Effect of macrophyte community composition and nutrient enrichment on plant biomass and algal blooms

Submerged freshwater macrophytes decline with increasing eutrophication. This has consequences for ecosystem processes in shallow lakes and ponds as macrophytes can reduce algal blooms under eutrophic conditions. We hypothesize that the productivity of submerged vegetation, biomass change under eutrophication and the suppression of algal blooms may be affected by macrophyte community composition. To test our hypothesis, we established three macrophyte community types in 36 fishless experimental ponds: one dominated by the oligotrophic species Chara globularis, one dominated by the eutrophic species Potamogeton pectinatus and a diverse vegetation which became co-dominated by Elodea nuttallii and C. globularis, and we fertilized half of the ponds.The macrophyte communities produced different amounts of biomass and they responded differently to fertilization. The community dominated by Potamogeton produced the lowest overall biomass, but was not affected by nutrient addition. The communities dominated by Chara and co-dominated by Elodea and Chara produced more than four-fold the amount of biomass produced in Potamogeton communities under oligotrophic conditions, but were strongly negatively affected by nutrient addition.Phytoplankton abundance did not differ significantly among the plant community types, but showed large variation within community types. There was a significant negative relationship between spring macrophyte biomass and the probability of summer algal blooms. The occurrence of algal blooms coincided with low daphnid densities and high pH (>10).We conclude that the macrophyte community composition, characterized by the dominant species, strongly affected the amount of biomass production as well as the short-term response of the vegetation to nutrient enrichment. Macrophyte community composition had no direct effect on algal blooms, but can affect the occurrence of algal blooms indirectly as these occurred only in ponds with low (<100 g/m² DW) spring macrophyte biomass.     

Trophic consequences of non‐native species for commercial fish in a backwater bay of the Three Gorges Reservoir,Southwest China

Trophic niche overlap in native and alien fish species can lead to competitive interactions whereby non‐native fishes outcompete indigenous individuals and eventually affect the viability of natural populations. The species Erythroculter mongolicus and Erythroculter ilishaeformis (belonging to the Culterinae), which are two commercially important fish species in the backwater bay of the Pengxi River in the Three Gorges Reservoir (TGR), were threatened by competition from the non‐native Coilia ectenes (lake anchovy). The latter is an alien species introduced into the lower reaches of the Yangtze River in China and now widespread in the TGR. The trophic consequences of non‐native lake anchovy invasion for E. mongolicus and E. ilishaeformis were assessed using stable isotope analysis (δ¹³C and δ¹⁵N) and associated metrics including the isotopic niche, measured as the standard ellipse area. The trophic niche of native E. mongolicus had little overlap (<15%) with the alien fish species and was significantly reduced in size after invasion by lake anchovy. This suggests that E. mongolicus shifted to a more specialized diet after invasion by lake anchovy. In contrast, the trophic niche overlap of native fish E. ilishaeformis with the alien fish species was larger (>50%) and the niche was obviously increased, implying that fish in this species exploited a wider dietary base to maintain their energetic requirements. Thus, marked changes for the native E. mongolicus and E. ilishaeformis were detected as the trophic consequences of invasion of non‐native lake anchovy.     

Mutualism or parasitism: Partner abundance affects host fitness in a fish reproductive interaction

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Seasonal dynamics of zooplankton in a shallow eutrophic,man-made hyposaline lake in Delhi (India): role of environmental factors

Old Fort Lake, a small (1.6 ha), shallow, and recreational water body in Delhi (India) was studied through monthly surveys in two consecutive years (January, 2000–December, 2001). Precipitation is the major source of water for this closed basin lake. In addition, ground water is used for replenishing the lake regularly. This alkaline, hyposaline hard water lake contains very high ionic concentration, especially of nitrates. Based on overall ionic composition, this lake can be categorized as chloride–sulfate alkaline waters with the anion sequence dominated by SO₄ ²⁻ > Cl⁻ > HCO₃ ⁻, and the cations by Mg⁺⁺ > Ca⁺⁺. The overall seasonal variability in physicochemical profile was largely regulated by the annual cycle of evaporation and precipitation, whereas the ground water largely influences its water quality. The lake exhibited phytoplankton-dominated turbid state due to dominance of the blue green alga, Microcystis aeruginosa. The persistent cyanobacterial blooms and the elevated nutrient levels are indicative of the cultural eutrophication of the lake. This study focuses on the relative importance of eutrophic vis-à-vis hyposaline conditions in determining the structure and seasonal dynamics of zooplankton species assemblages. A total of 52 zooplankton species were recorded and rotifers dominated the community structure qualitatively as well as quantitatively. The genus Brachionus comprised a significant component of zooplankton community with B. plicatilis as the most dominant species. The other common taxa were B. quadridentatus, B. angularis, Lecane grandis, L. thalera, L. punctata, Mesocyclops sp., and Alona rectangula. Multivariate data analysis techniques, Canonical Correspondence Analysis (CCA) along with Monte Carlo Permutation Tests were used to determine the minimum number of environmental factors that could explain statistically significant (P < 0.05) proportions of variation in the species data. The significant variables selected by CCA were NH₃–N followed by percent saturation of DO, COD, SS, BOD, NO₂–N, rainfall, silicates, and PO₄–P. The results indicate that the seasonal succession patterns of the zooplankton species were largely controlled by physicochemical factors related directly or indirectly to the process of eutrophication, whereas hyposaline conditions in the lake determined the characteristic species composition. Guest Editors: J. John & B. Timms Salt Lake Research: Biodiversity and Conservation—Selected papers from the 9th Conference of the International Society for Salt Lake Research     

Shape analysis of the jaws between two minnow species over ontogeny

This study compares sand shiner (Notropis stramineus ) and silverjaw (Ericymba buccata ) minnows, in terms of the morphological shape changes of the upper, lower, and pharyngeal jaws over ontogeny. These two species of minnows initially feed on midge larvae and undergo an ontogenic prey shift. The traditional morphometrics measured—total length, snout‐to‐vent length, eye diameter, premaxilla length, lower jaw length, gape—were regressed onto total length to test for allometry. Digital pictures were processed with tpsDig and further analyzed with MorphoJ utilizing a regular geometric morphometrics procedure using principle component analyses. We examined gut contents for 16 fish of each species. For the silverjaw minnows, we found all jaw variables to exhibit positive allometric growth with increasing total length, while most of the jaw variables for the sand shiner exhibited negative allometric growth with increasing total length. This correlates with an ontogenic prey shift for both species. Sand shiner minnows have been found to be more omnivorous, feeding on algae later in life, while silverjaw minnows undergo a prey shift to larger invertebrates. These species lack oral dentition causing an increased reliance on the pharyngeal apparatus. Principle component analyses revealed elongation of pharyngeal jaw elements in the silverjaw minnows and a relative shortening and bulking of pharyngeal jaws in the sand shiner minnows. The ontogenic dietary shifts observed in these two species provide possible explanation for the morphological changes over ontogeny in jaw elements, which are likely enabling these species to occupy the same habitat with little niche overlap.     

DNA barcoding the genus Chara: molecular evidence recovers fewer taxa than the classical morphological approach

Charophytes (Charales) are benthic algae with a complex morphology. They are vulnerable to ecosystem changes, such as eutrophication, and are red‐listed in many countries. Accurate identification of Chara species is critical for understanding their diversity and for documenting changes in species distribution. Species delineation is, however, complicated, because of high phenotypic plasticity. We used barcodes of the ITS2, matK and rbcL regions to test if the distribution of barcode haplotypes among individuals is consistent with species boundaries as they are currently understood. The study included freshly collected and herbarium material of 91 specimens from 10 European countries, Canada and Argentina. Results showed that herbarium specimens are useful as a source of material for genetic analyses for aquatic plants like Chara. rbcL and matK had highest sequence recoverability, but rbcL had a somewhat lower discriminatory power than ITS2 and matK. The tree resulting from the concatenated data matrix grouped the samples into six main groups contrary to a traditional morphological approach that consisted of 14 different taxa. A large unresolved group consisted of C. intermedia, C. hispida, C. horrida, C. baltica, C. polyacantha, C. rudis, C. aculeolata, and C. corfuensis. A second unresolved group consisted of C. virgata and C. strigosa. The taxa within each of the unresolved groups shared identical barcode sequences on the 977 positions of the concatenated data matrix. The morphological differences of taxa within both unresolved groups include the number and length of spine cells, stipulodes, and bract cells. We suggest that these morphological traits have less taxonomic relevance than hitherto assumed.     

Utilization of the exotic cladoceran Daphnia lumholtzi by juvenile fishes in an Illinois River floodplain lake

Daphnia lumholtzi comprises a substantial component of the zooplankton community during mid‐ to late‐summer in Lake Chautauqua, a floodplain lake along the Illinois River near Havana, Illinois. In order to quantify the utilization of D. lumholtzi by juvenile fishes, diet analyses were conducted for seven juvenile fish species collected from Lake Chautauqua during the 2001 annual drawdown period. Freshwater drum Aplodinotus grunniens and emerald shiner Notropis atherinoides demonstrated negative selectivity for D. lumholtzi relative to native zooplankton species whereas four species of fish (bluegill Lepomis macrochirus, white bass Morone chrysops, white crappie Pomoxis annularis and black crappie Pomoxis nigromaculatus) consumed substantial amounts of D. lumholtzi. Although selectivity values for D. lumholtzi varied among these fish species, positive selection for D. lumholtzi increased similarly among larger size classes of each fish species, and corresponded with ontogenetic shifts in diet. Mean body length of D. lumholtzi consumed by 20–69 mm L_T juvenile fishes ranged from 0·75 to 0·99 mm with a calculated total length range of 2·0–2·6 mm. Results from this study provide evidence that high abundances of D. lumholtzi in mid‐ to late‐summer provide an additional food source for several juvenile fish species during a time when abundances of large native cladoceran species (i.e. Daphnia) are low, and juvenile fishes are searching for larger prey associated with ontogenetic shifts from zooplankton to macroinvertebrates and fishes. Because zooplankton production is typically lower in rivers than in lakes, survivorship of juvenile fishes produced in floodplain lakes may be higher in riverine systems if they are not reliant on zooplankton as a primary food resource. Therefore, high abundances of D. lumholtzi may benefit juvenile fishes in managed floodplain lakes, such as Lake Chautauqua, by increasing growth and facilitating the transition from zooplanktivory to insectivory or piscivory.